Stent Coating Adhesion and Delamination Analysis Using Nano Scratch Testing

Application Note | Stent Coating Adhesion Testing

Stent Coating Adhesion and Delamination Analysis Using Nano Scratch Testing

Quantifying Coating Failure and Adhesion Performance on Drug-Eluting Stents

Research & Experimental Testing

Duanjie Li, PhD

Visual Design & Editorial

Andrew Shore

Introduction

Blood is carried through arteries from the heart to the rest of the body. Any weakening or blockage of these vessels can pose significant health risks and may become life-threatening. A stent is a small mesh tube inserted into the lumen of a blood vessel to treat narrowed or weakened arteries. Stent implantation is now a widely used procedure to support the arterial wall and restore blood flowᶦ.

Metal stent mesh geometry illustrating the structural complexity of vascular implant design.

Why coating adhesion matters in drug-eluting stents

Drug-eluting stents represent a major advancement in stent technology. They incorporate a biodegradable, biocompatible polymer coating that enables controlled drug release at the arterial site, helping to inhibit intimal thickening and reduce the risk of restenosisᶦᶦ.

A critical concern in these systems is the delamination of the polymer coating from the metallic stent substrate. This coating carries the drug-eluting layer, and its adhesion directly impacts device performance and reliability.

To improve coating adhesion, stents are often designed with complex geometries. In this study, the polymer coating is located at the bottom of grooves within the stent mesh. This configuration presents a significant challenge for adhesion measurement.

A reliable method is required to quantitatively evaluate the interfacial strength between the polymer coating and the metal substrate. The small diameter of the stent mesh, comparable to a human hair, combined with its three-dimensional geometry, requires:

ultrafine X-Y positioning accuracy
precise control of applied load
accurate depth measurement during testing

ℹ️ Learn more about nanoindentation and scratch testing lab services for coating adhesion and failure analysis.

Measurement Method

Nano scratch testing is performed using the NANOVEA PB1000 Mechanical Tester, in Nano Scratch Mode, to evaluate the cohesive and adhesive strength of the polymer coating on the metal mesh of stent samples.

Controlled scratch measurements are carried out on stent geometries with dimensions comparable to a human hair, enabling precise evaluation of coating adhesion on complex stent structures.

NANOVEA PB1000 Advanced

Mechanical Tester

Test Conditions

1. Regular Stent Samples

The stent is fixed on the sample stage, with a support wire inserted inside the stent tube to ensure stability during nano scratch testing. The NANOVEA Mechanical Tester is used to perform nano scratch measurements using the parameters summarized in Table 1, to evaluate the cohesive and adhesive strength of the polymer coating on the metal substrate.

Parameter	Value
Load type	Progressive
Initial load	0.05 mN
Final load	300 and 100 mN
Sliding speed	0.5 mm/min
Sliding distance	0.5 mm
Indenter geometry	Conical
Indenter material (tip)	Diamond
Indenter tip radius	20 µm
Temperature	24°C (room)

Table 1: Test parameters for nano scratch measurements on regular stent samples

2. Grooved Stent Samples

The SEM image in Fig. 1 shows the cross-section of the stent sample. The stent features a groove with a depth of approximately 30 µm. The polymer coating, with a thickness of 10.8 µm, is located at the bottom of the groove.

Standard 60° conical diamond tips are not sharp enough to reach the bottom of the groove without contacting the sidewalls. Therefore, a sharper 40° conical diamond tip is used in this study (Fig. 2).

Nano scratch measurements are performed using the parameters summarized in Table 2.

Parameter	Value
Load type	Progressive
Initial load	0.1 mN
Final load	300 mN
Loading rate	300 mN/min
Scratch length	0.25 mm
Scratch speed	0.25 mm/min
Indenter geometry	40° cone
Indenter material (tip)	Diamond
Indenter tip radius	5 µm

Table 2: Test parameters for nano scratch measurements on grooved stent samples

Fig. 1: SEM cross-section of a grooved stent showing polymer coating located at the bottom of the groove, highlighting the challenge of coating adhesion measurement in recessed geometries.

Fig. 2: Schematic of a 40° conical diamond tip designed for nano scratch testing inside stent grooves, enabling accurate adhesion measurement without sidewall interference.

Results and Discussion

The stent mesh has a diameter of approximately 100 μm, comparable to a human hair. Precise positioning is therefore critical to ensure the scratch test is performed at the center of the stent mesh. The NANOVEA Mechanical Tester provides X–Y positioning accuracy down to 0.25 μm, enabling accurate test placement under the integrated optical microscope.

1. Regular Stent Samples

Nano scratch testing is performed with a progressively increasing load up to 300 mN. The full scratch track on the stent is shown in Fig. 3a, while failure behavior at different stages is presented in Fig. 3b and 3c.

Two critical loads are identified:

Lc1: the load at which the first visible damage appears on the coating
Lc2: the load at which the coating is fully removed and the substrate is exposed

The evolution of coefficient of friction (COF) and penetration depth is shown in Fig. 4, providing insight into the progression of coating failure during the test.

The first signs of coating damage appear at Lc1 ≈ 14.5 mN. As the applied load increases, the diamond tip progressively penetrates the polymer coating, resulting in a wider and deeper scratch track. During this phase, the COF increases from approximately 0.05 to 0.7.

At Lc2 ≈ 78.1 mN, the coating is fully delaminated from the metal substrate. Beyond this point, as the load continues to increase, both COF and penetration depth remain relatively stable due to the mechanical support of the underlying metal substrate.

(a) Full Scratch Track

(b) Lc1 ≈ 14.5 mN

Fig. 3: Nano scratch track on a stent coating under progressively increasing load, showing (a) full scratch path, (b) initial coating failure at Lc1 ≈ 14.5 mN, and (c) complete coating delamination at Lc2 ≈ 78.1 mN.

Fig. 4: Evolution of coefficient of friction (COF) and penetration depth during nano scratch testing of a stent coating under progressively increasing load, showing the progression of coating failure and transition to substrate support.

Failures during nano scratch testing up to a maximum load of 300 mN occur at critical loads below 100 mN. To enable a more quantitative comparison of coating performance, additional tests are performed with a maximum load of 100 mN on two stent samples, referred to as Sample 1 and Sample 2.

Fig. 5 compares the scratch tracks of Sample 1 and Sample 2 after nano scratch testing. Sample 1 exhibits the first sign of coating damage at a critical load of Lc1 ≈ 13.2 mN, while Sample 2 shows initial failure at a higher load of Lc1 ≈ 21.1 mN.

Coating delamination occurs at 62.5 mN for Sample 1. In contrast, the coating on Sample 2 remains intact throughout the test, continuing to protect the metal substrate under the same loading conditions.

This behavior is further reflected in the evolution of coefficient of friction (COF) and penetration depth, as shown in Fig. 6. When the diamond tip penetrates through the coating and contacts the metal substrate in Sample 1, the COF reaches a peak while the penetration depth decreases due to the increased stiffness of the underlying substrate.

(a) Sample 1 – Early Coating Failure

(b) Sample 2 – Improved Coating Integrity

Fig. 5: Comparison of nano scratch tracks for two stent coatings, showing (a) early coating failure and delamination in Sample 1, and (b) improved coating integrity in Sample 2 under the same loading conditions.

Fig. 6: Comparison of coefficient of friction (COF) and penetration depth for Sample 1 and Sample 2 during nano scratch testing, showing earlier substrate contact and higher friction response in Sample 1, indicating weaker coating adhesion.

2. Grooved Stent Samples

As shown in Fig. 1 and Fig. 7, the grooved stent mesh has a diameter of approximately 90 μm, comparable to a human hair. The groove has a width of ~50 μm and a depth of 30 μm. This geometry presents a significant challenge for nano scratch testing, particularly for evaluating coating adhesion at the bottom of the groove.

Precise positioning is critical to locate the scratch test within the groove. The nano scratch test is performed with a progressively increasing load up to 300 mN. The full scratch tracks of grooved stent Samples 3 and 4 are compared in Fig. 7.

The critical load Lc is defined as the load at which the coating fails and the substrate becomes exposed. The evolution of normal load and penetration depth, shown in Fig. 8, provides further insight into the progression of coating failure during testing.

As the applied load increases, the diamond tip progressively penetrates the polymer coating, resulting in a deeper scratch track. When the critical load Lc is reached, the coating delaminates from the metal substrate.

Sample 3 exhibits coating failure at Lc ≈ 126 mN, while Sample 4 fails at a higher load of Lc ≈ 173 mN. This difference indicates stronger adhesion of the coating in Sample 4.

The measured critical loads enable quantitative comparison of coating adhesion performance. Under the same testing conditions, the coating on Sample 4 demonstrates higher resistance to delamination, making it the better-performing candidate in this study.

(d) Sample 4 – Higher Adhesion in Groove (Lc ≈ 173 mN)

Fig. 7: Nano scratch tracks inside stent grooves for Samples 3 and 4, showing (c) coating failure at Lc ≈ 126 mN in Sample 3 and (d) higher adhesion with delayed failure at Lc ≈ 173 mN in Sample 4.

(a) Sample 3 – Earlier Coating Failure (Lc ≈ 126 mN)

(b) Sample 4 – Delayed Failure and Higher Adhesion (Lc ≈ 173 mN)

Fig. 8: Evolution of normal load and penetration depth during nano scratch testing inside stent grooves for Samples 3 and 4, showing earlier coating failure in Sample 3 and delayed failure at higher load in Sample 4. The vertical green line indicates the critical load (Lc) where coating delamination occurs.

Conclusion

This study demonstrates the ability of the NANOVEA Mechanical Tester to quantitatively evaluate the cohesive and adhesive strength of polymer coatings on both regular and grooved stent geometries using nano scratch testing.

The recessed geometry of the stent grooves, approximately 50 μm wide and 30 μm deep, presents a significant challenge for coating adhesion measurement. The high X–Y positioning accuracy of 0.25 μm enables precise placement of the scratch test within these confined regions, allowing direct evaluation of coating performance where failure is most critical.

By applying a controlled, progressively increasing load, critical loads associated with coating failure can be identified and compared across samples. This approach enables reliable differentiation of coating adhesion performance and interfacial integrity, even on small, complex stent structures.

References

[I] http://www.nhlbi.nih.gov/health/health-topics/topics/stents
[II] http://www.scielo.org.mx/scielo.php?script=sci_arttext&pid=S1405-99402006000300008

Frequently Asked Questions About Stent Coating Adhesion Testing

What is stent coating adhesion testing?

Stent coating adhesion testing evaluates how strongly a polymer coating is bonded to the metal substrate of a stent. Techniques such as nano scratch testing quantify the load at which coating damage and delamination occur, providing measurable indicators of adhesion strength.

What is critical load (Lc) in nano scratch testing?

Critical load (Lc) is the applied load at which a coating fails during a scratch test.

Lc1 corresponds to the first visible damage in the coating
Lc2 indicates complete coating removal and exposure of the substrate

These values are used to quantify and compare coating adhesion performance.

Why is coating adhesion important in drug-eluting stents?

Coating adhesion directly affects the reliability of drug-eluting stents. Poor adhesion can lead to coating delamination, which may compromise controlled drug release and increase the risk of device failure.

How do you measure coating adhesion inside stent grooves?

Measuring adhesion inside stent grooves requires high positioning accuracy and appropriate indenter geometry. Nano scratch testing with sharp diamond tips allows access to recessed coating regions, enabling direct evaluation of adhesion within complex stent geometries.

What does coefficient of friction (COF) indicate in scratch testing?

The coefficient of friction (COF) reflects changes in surface interaction during the scratch test. A sudden increase in COF often indicates coating failure and contact between the indenter and the underlying metal substrate.

How can nano scratch testing compare different coating formulations?

Nano scratch testing enables direct comparison of coatings by measuring critical loads under controlled conditions. Higher critical loads indicate stronger adhesion and improved resistance to delamination, allowing selection of better-performing coating systems.

Need Reliable Stent Coating Adhesion Testing?

Dental Surface Roughness Measurement & 3D Tooth Topography

Application Note | Dental Surface Characterization

Dental Surface Roughness Measurement and Full 3D Tooth Topography

Surface Roughness Analysis Using Non-Contact Optical Profilometry

Prepared by

Walter Alabiso, PhD; Davide Morrone, MPhys; Andrew Shore, MA

Introduction

The ability to accurately characterize tooth surfaces, including micro-roughness and 3D surface topography at the nanometer scale, enables advanced research and applications in orthodontics and dental materials science. Non-contact optical profilometry provides a precise method for measuring dental surface roughness and analyzing tooth surface morphology without damaging delicate structures. These measurements support the development of composite dental materials that replicate the natural surface roughness of enamel, as well as the design and fabrication of patient-specific dental casts and restorative components.

Low surface roughness plays a primary role in limiting bacterial adhesion and plaque formation, thereby reducing the risk of cavities. An increase in average roughness (Ra) above 2 µm leads to a steep increase in biofilm formation in vivo.¹ An Ra of 0.2 µm is considered the threshold value below which no further reduction in bacterial adhesion can be expected.²

Reconstruction of the tooth’s 3D surface topography enables the fabrication of dental casts, which are essential for accurate diagnosis, treatment planning, and the fabrication of dental appliances.

Non-Contact Optical Profilometry for Dental Surface Analysis

The present study illustrates the potential of NANOVEA’s high-precision non-contact optical profilometers for dental surface roughness measurement and 3D tooth topography analysis. Chromatic Light technology offers significant advantages over classical touch probe techniques. It acquires data points from deep crevices and complex geometries without introducing measurement errors or artifacts caused by local plastic deformation and without requiring extensive data manipulation.

Compared to focus variation systems, single-point optical sensing provides superior lateral and height accuracy, with X/Y resolution below 0.5 µm, maximum vertical resolution of 1.9 nm, and the ability to measure surface angles up to 87°. The technique is effective on transparent, opaque, specular, diffusive, polished, and rough dental surfaces, making it well suited for comprehensive dental surface characterization.

ℹ️ Learn more about non-contact optical profilometry and surface roughness measurement services.

Measurement Method

In this application, the NANOVEA JR25 Non-Contact Optical Profiler was used to analyze the surface roughness and 3D surface topography of an adult human molar previously affected by tooth decay. The side of the tooth was scanned using a PS2–MG140 single-point optical sensor to measure surface roughness parameters over a defined region of interest and along multiple line profiles.

The crown of the tooth was then scanned and reconstructed using a PS5–MG35 single-point optical sensor, which is suited for larger-area acquisition and full 3D tooth topography measurement.

NANOVEA JR25 Portable
Optical Profilometer

Surface Measurement Using NANOVEA Optical Profilometer

Surface roughness measurements were performed on the lateral side of the molar crown, followed by full 3D reconstruction of the crown surface. Separate single-point optical sensors were used to optimize measurement accuracy for both localized roughness analysis and large-area surface topography acquisition.

PS2 – MG140

Surface roughness analysis by area and parallel line profiles on the side of the tooth’s crown.

PS5 – MG35

Full 3D surface reconstruction of the tooth’s crown.

Measurement Parameters

The following measurement parameters were used for localized surface roughness analysis and full 3D surface reconstruction of the molar crown using NANOVEA single-point optical sensors.

Parameter	Roughness Analysis (Area)	Roughness Analysis (Profiles)	Full 3D Reconstruction
Optical Pen	PS2-MG140	PS2-MG140	PS5-MG35
Z-Range [µm]	300	300	10000
X-Distance [mm]	2.00	3.00	7.50
X-Step Size [µm]	1.70	1.70	10.00
Y-Distance [mm]	2.00	1.00	7.00
Y-Step Size [µm]	1.70	100.00	10.00
Average (Avg)	1	1	1
Measurement Type	Direct	Direct	Direct
Acquisition Mode	Single Frequency	Single Frequency	Double Frequency
Acquisition Rate [Hz]	200	200	100–400
Light Intensity [%]	100	100	100

Optical Profilometry Results

Surface Roughness Analysis (Area)

The PS2 single-point optical sensor was used to investigate fine surface features on the side of the tooth. The image below shows a false-color 2D surface map of the scanned region obtained by non-contact optical profilometry.

A least-squares degree-8 polynomial form removal was applied to isolate the surface roughness component. The roughness filters S-Gaussian 2.5 µm and L-Gaussian 0.8 mm were then applied according to ISO 25178. The resulting filtered surface and corresponding roughness parameters are presented below.

ISO 25178 – Roughness (S-L)
S-filter (λs): Gaussian, 2.5 µm
F: [Workflow] Form removed (LS-poly 8)
L-filter (λc): Gaussian, 0.8 mm
Height Parameters
Sq	2.433	µm	Root-mean-square height
Ssk	-0.102		Skewness
Sku	3.715		Kurtosis
Sp	18.861	µm	Maximum peak height
Sv	16.553	µm	Maximum pit depth
Sz	35.414	µm	Maximum height
Sa	1.888	µm	Arithmetic mean height

The average surface roughness Sa is 1.888 µm, while the peak-to-valley height Sz reaches 35.414 µm.

A 3D surface rendering of the filtered area is shown below for visualization.

Roughness Analysis (Profiles)

Surface roughness profiles were measured using a series of 11 parallel line scans along the X direction on the side of the tooth. The false-color 2D surface map of the raw scan is shown below.

The surface form was removed using a least-squares 8-degree polynomial prior to applying the metrological filters, leaving the residual surface shown below.

A statistical analysis of the measured surface roughness profiles reveals the following line roughness parameters.

		Description	Mean	Std dev	Min	Max
ISO 4287 – Roughness (S-L)
F: None
S-filter (λs): Gaussian, 2.5 µm
L-filter (λc): Gaussian, 0.8 mm
Evaluation length: All λc (3)
Amplitude Parameters – Roughness Profile
Rp	µm	Maximum peak height of the roughness profile	5.683	0.761	4.315	6.610
Rv	µm	Maximum valley depth of the roughness profile	6.242	1.009	4.701	8.438
Rz	µm	Maximum height of roughness profile	11.925	1.676	9.123	15.048
Ra	µm	Arithmetic mean deviation of the roughness profile	2.063	0.297	1.710	2.629
Rq	µm	Root-mean-square (RMS) deviation of the roughness profile	2.523	0.361	2.057	3.175

F: None

S-filter (λs): Gaussian, 2.5 µm

L-filter (λc): Gaussian, 0.8 mm

Evaluation length: All λc (3)

The value of Ra is consistent with the Sa value extracted from the surface area measurement.

Different metrological filters can be applied to distinguish between macroscopic waviness and microscopic surface roughness. For example, a coarser filter cut-off, such as the 8 mm cut-off used with the Robust Gaussian order-2 filter, produces a smoother waviness profile (red) that is less sensitive to sharp local variations and follows the original surface profile more loosely.

Alternatively, a finer cut-off (e.g., 0.08 mm) enables the analysis of micro-roughness by removing the waviness component that follows the original profile at a larger scale, leaving the finer surface roughness features of the tooth visible.

The microroughness analysis obtained using a 0.08 mm L-Gaussian filter is presented below.

		Description	Mean	Std dev	Min	Max
ISO 4287 – Roughness (S-L)
F: None
S-filter (λs): Gaussian, 2.5 µm
L-filter (λc): Gaussian, 0.08 mm
Evaluation length: All λc (37)
Amplitude Parameters – Roughness Profile
Rp	µm	Maximum peak height of the roughness profile	1.582	0.122	1.342	1.748
Rv	µm	Maximum valley depth of the roughness profile	1.466	0.119	1.254	1.661
Rz	µm	Maximum height of roughness profile	3.049	0.196	2.820	3.409
Ra	µm	Arithmetic mean deviation of the roughness profile	0.495	0.047	0.423	0.597
Rq	µm	Root-mean-square (RMS) deviation of the roughness profile	0.643	0.056	0.562	0.762

F: None

S-filter (λs): Gaussian, 2.5 µm

L-filter (λc): Gaussian, 0.8 mm

Evaluation length: All λc (3)

Full 3D Tooth Surface Topography Reconstruction

The extended Z-scan range of the PS5 optical sensor enables high-fidelity scanning of the entire tooth crown surface. The resulting 3D surface topography is shown below.

2D VIEW: 2D surface map of the tooth crown measured with optical profilometry

3D VIEW: High-fidelity 3D rendering of the molar crown surface obtained with optical profilometry

Conclusion

In this application, the NANOVEA JR25 Non-Contact Optical Profiler was used to measure the surface roughness and 3D surface topography of an adult human molar.

Both the area scan and the line profile analysis revealed a roughness Rq of approximately 2.5 µm and an Ra of about 1.9–2.0 µm. These values are consistent with results reported in the literature.³ The use of a narrower L-Gaussian filter with an 80 µm cut-off enabled further investigation of micro-roughness, revealing an Rq of 0.643 µm and an Ra of 0.495 µm.

The full 3D surface topography of the molar crown was reconstructed with high fidelity. The high measurement resolution allows detection of fine surface features and crevices. The resulting surface data can be easily processed and exported as STL files, enabling the design and fabrication of customized dental devices and restorative components.

References

[1] Shin, B.W., et al. Surface Roughness of Prefabricated Pediatric Zirconia Crowns Following Simulated Toothbrushing. Pediatric Dentistry 44.5 (2022): 363–367.
[2] Bollen, C.M.L., Paul Lambrechts, and Marc Quirynen. Comparison of surface roughness of oral hard materials to the threshold surface roughness for bacterial plaque retention: A review of the literature. Dental Materials 13.4 (1997): 258–269.
[3] Suputtamongkol, K., et al. Surface roughness resulting from wear of lithia-disilicate-based posterior crowns. Wear 269.3–4 (2010): 317–322.

Frequently Asked Questions About Dental Surface Roughness Measurement

What is dental surface roughness measurement?

Dental surface roughness measurement quantifies the microscopic texture of tooth surfaces using parameters such as Ra, Rq, and Sa. Optical profilometers measure these features without contacting the surface, allowing accurate analysis of enamel, restorative materials, and dental crowns.

Why use optical profilometry to measure tooth roughness?

Optical profilometry provides non-contact surface measurement with nanometer-scale vertical resolution. It captures 2D surface maps and full 3D surface topography of dental structures without damaging soft or polished surfaces.

What roughness parameters are used for dental surface analysis?

Common roughness parameters include Ra (arithmetic mean roughness), Rq (root mean square roughness), Sa (areal roughness), and Sz (maximum surface height). These parameters help evaluate enamel wear, plaque adhesion risk, and the performance of restorative materials.

Why is surface roughness important in dentistry?

Surface roughness affects plaque retention, wear resistance, and the long-term performance of dental restorations. Controlling micro-roughness can reduce bacterial adhesion and improve the durability of dental materials.

Need Reliable Surface Roughness Measurement for Dental Materials?

Scratch Resistance Testing of Phone Screen Protectors

Prepared by

Stacey Pereira, Jocelyn Esparza, and Pierre Leroux

Understanding Scratch Resistance in Phone Screen Protectors

Protective coatings on phone screens play a critical role in scratch resistance, adhesion strength, and long-term durability. Over time, scratches, micro-cracks, and coating delamination can reduce optical clarity and reliability — especially in high-use environments. To evaluate how different screen protectors resist mechanical damage, instrumented scratch testing provides quantifiable insight into coating failure mechanisms, including adhesion, cohesion, and fracture behavior.

In this study, NANOVEA PB1000 Mechanical Tester is used to compare TPU vs. tempered-glass screen protectors under controlled progressive loading. Using precise acoustic emission detection, we identify critical failure loads and characterize how each material responds to increasing mechanical stress.

Why Scratch Resistance Testing Matters for Screen Protectors

Many users assume that thicker or harder protectors automatically perform better, but real durability depends on how the material behaves under progressive load, surface deformation, and localized stress. Instrumented scratch testing allows engineers to measure coating adhesion, cohesive strength, surface wear resistance, and the exact loads at which failures initiate or propagate.

By analyzing crack initiation points, delamination behavior, and failure modes, manufacturers can validate screen-protector performance for R&D, quality control, or comparative benchmarking. Nano- and micro-scratch testing offer repeatable, data-driven insight into real-world durability far beyond traditional hardness ratings.

ℹ️ Learn more about scratch and adhesion testing services for coatings and screen protectors.

Scratch Testing Objective:
Measuring Failure Loads in Screen Protectors

The objective of this study is to demonstrate how the NANOVEA PB1000 Mechanical Tester performs repeatable, standardized scratch resistance testing on both polymeric and glass screen protectors. By progressively increasing the applied load, the system detects critical loads for cohesive and adhesive failure, captures acoustic emission signals, and correlates these events with scratch depth, friction force, and surface deformation.

This methodology provides a complete mechanical profile of each protective coating, allowing manufacturers and R&D teams to evaluate material formulations, coating adhesion strength, surface durability, and optimal coating thickness for improved product performance. These scratch evaluations are part of NANOVEA’s broader suite of mechanical testing solutions used to characterize coatings, films, and substrates across R&D, quality control, and production environments.

NANOVEA PB1000 Large-Platform
Mechanical Tester

Scratch Test Parameters and Instrument Setup

The scratch resistance evaluation of TPU and tempered-glass screen protectors was conducted under controlled conditions to ensure repeatability and accurate failure-load detection. The following parameters define the progressive-load scratch testing setup used on the NANOVEA PB1000 Mechanical Tester.

LOAD TYPE	PROGRESSIVE
INITIAL LOAD	0.1 N
FINAL LOAD	12 N
SLIDING SPEED	3.025 mm/min
SLIDING DISTANCE	3 mm
INDENTER GEOMETRY	ROCKWELL (120° CONE)
INDENTER MATERIAL (TIP)	DIAMOND
INDENTER TIP RADIUS	50 µm
ATMOSPHERE	AIR
TEMPERATURE	24 °C (ROOM TEMP)

TABLE 1: Test parameters used for scratch testing

Screen protector sample mounted on the NANOVEA PB1000 Mechanical Tester during progressive-load scratch measurement.

Screen Protector Samples Used for Scratch Resistance Testing

Two commercially available screen protector materials were selected to compare differences in scratch resistance, failure behavior, and mechanical durability. Both samples were mounted securely on the NANOVEA PB1000 Mechanical Tester and evaluated under identical progressive-load conditions to ensure a consistent and unbiased comparison.

The TPU screen protector represents a flexible polymeric film with high elasticity but lower abrasion resistance, while the tempered-glass protector represents a rigid, brittle material designed for high hardness and enhanced impact protection. Testing both materials under the same load profile allows a clear assessment of how material composition, elasticity, and hardness influence scratch failure modes.

TPU Screen Protector

Tempered Glass

FIGURE 1: TPU and tempered-glass screen protectors prepared for scratch resistance testing.

Scratch Test Results: Failure Modes in TPU vs. Tempered Glass Screen Protectors

TYPE OF SCREEN PROTECTOR	CRITICAL LOAD #1 (N)	CRITICAL LOAD #2 (N)
TPU	n/a	2.004 ± 0.063
TEMPERED GLASS	3.608 ± 0.281	7.44 ± 0.995

TABLE 2: Summary of critical loads for each screen protector sample.

Because TPU and tempered-glass screen protectors have fundamentally different mechanical properties, each sample exhibited distinct failure modes and critical load thresholds during progressive-load scratch testing. Table 2 summarizes the measured critical loads for each material.

Critical Load #1 represents the first observable point of cohesive failure under optical microscopy, such as crack initiation or radial fracture.

Critical Load #2 corresponds to the first major event detected through acoustic emission (AE) monitoring, typically representing a larger structural failure or penetration event.

TPU Screen Protector — Flexible Polymer Behavior

The TPU screen protector exhibited only one significant critical event (Critical Load #2). This load corresponds to the point along the scratch track where the film began to lift, peel, or delaminate from the phone screen surface.

Once Critical Load #2 (≈2.00 N) was exceeded, the indenter penetrated sufficiently to cause a visible scratch directly on the phone screen for the remainder of the test. No separate Critical Load #1 event was detectable, consistent with the material’s high elasticity and lower cohesive strength.

Tempered Glass Screen Protector — Brittle Failure Behavior

The tempered-glass screen protector showed two distinct critical loads, characteristic of brittle materials:

Critical Load #1 (≈3.61 N): Radial fractures and crack initiation were observed under the microscope, indicating early cohesive failure of the glass layer.
Critical Load #2 (≈7.44 N): A large AE spike and a sharp increase in scratch depth indicated protector penetration at higher loads.

Although the AE magnitude was higher than TPU, no damage was transferred to the phone screen, demonstrating the tempered-glass protector’s ability to absorb and distribute load before catastrophic failure.

In both materials, Critical Load #2 corresponded to the moment when the indenter broke through the screen protector, confirming the protective limit of each sample.

TPU Screen Protector: Scratch Test Data and Failure Analysis

SCRATCH	CRITICAL LOAD #2 (N)
1	2.033
2	2.047
3	1.931
AVERAGE	2.003
STANDARD DEVIATION	0.052

TABLE 3: Critical loads measured during TPU screen protector scratch testing.

FIGURE 2: Friction force, normal load, acoustic emission (AE), and scratch depth vs. scratch length for the TPU screen protector. (B) Critical Load #2

FIGURE 3: Optical microscopy image of the TPU screen protector at Critical Load #2 (5× magnification; image width 0.8934 mm).

FIGURE 4: Full-length post-scratch image of the TPU screen protector showing the complete scratch track following progressive-load testing.

Tempered Glass Screen Protector: Critical Load Data and Fracture Behavior

SCRATCH	CRITICAL LOAD #1 (N)	CRITICAL LOAD #2 (N)
1	3.923	7.366
2	3.382	6.483
3	3.519	8.468
AVERAGE	3.653	6.925
STANDARD DEVIATION	0.383	0.624

TABLE 4: Critical loads measured during tempered-glass screen protector scratch testing.

ℹ️ For comparison with non-silicate polymer coatings, see our study on PTFE coating wear testing, which highlights failure behavior in low-friction polymer films under similar progressive-load conditions.

FIGURE 5: Friction force, normal load, acoustic emission (AE), and scratch depth vs. scratch length for the tempered-glass screen protector. (A) Critical Load #1 (B) Critical Load #2

FIGURE 6: Optical microscopy images showing the failure locations for Critical Load #1 (left) and Critical Load #2 (right) at 5× magnification (image width: 0.8934 mm).

FIGURE 7: Post-test optical microscopy image of the tempered-glass scratch track, highlighting fracture initiation (CL#1) and the final penetration zone (CL#2) following progressive-load testing.

Conclusion: Scratch Performance Comparison of TPU vs. Tempered Glass Screen Protectors

This study demonstrates how the NANOVEA PB1000 Mechanical Tester delivers controlled, repeatable, and highly sensitive scratch resistance measurements using progressive loading and acoustic emission (AE) detection. By precisely capturing both cohesive and adhesive failure events, the system enables a clear comparison of how TPU and tempered-glass screen protectors behave under increasing mechanical stress.

The experimental results confirm that tempered glass exhibits significantly higher critical loads than TPU, providing superior scratch resistance, delayed fracture initiation, and reliable protection against indenter penetration. TPU’s lower cohesive strength and earlier delamination highlight its limitations in high-stress environments.

After identifying failure loads, the resulting scratch tracks can also be analyzed using a non-contact 3D optical profilometer to measure groove depth, residual deformation, and post-scratch topography. This helps complete the mechanical profile of each material.

The NANOVEA Mechanical Tester is engineered for accurate and repeatable indentation, scratch, and wear testing, and supports ISO- and ASTM-compliant nano and micro modules. Its versatility makes it an ideal solution for evaluating the full mechanical profile of thin films, coatings, polymers, glasses, and substrates across R&D, production, and quality control.

Frequently Asked Questions
About Scratch Resistance Testing

What is scratch resistance testing?

Scratch resistance testing evaluates how a material or coating responds when a diamond stylus applies a progressively increasing load. The test identifies the critical loads where cohesive or adhesive failures occur, providing a quantifiable measure of durability, adhesion strength, and resistance to surface damage.

What’s the difference between cohesive and adhesive failure?

Cohesive failure occurs within the coating or material, such as cracking, tearing, or internal fracture.
Adhesive failure happens when the coating detaches from the substrate, indicating insufficient bonding strength.

The NANOVEA PB1000 detects both using synchronized acoustic emission monitoring, scratch depth tracking, and friction analysis.

Why use a mechanical tester instead of manual methods?

A mechanical tester like the NANOVEA PB1000 provides precise, repeatable, and standardized measurements, ensuring reliable data for R&D, production validation, and quality control. It also offers advanced features, such as acoustic emission detection and real-time depth monitoring, that manual methods cannot deliver.

Need Reliable Scratch Testing for Your Materials?

In Situ Wear Measurement at High Temperature

IN SITU WEAR MEASUREMENT AT HIGH TEMPERATURE

USING TRIBOMETER

Prepared by

Duanjie Li, PhD

INTRODUCTION

The Linear Variable Differential Transformer (LVDT) is a type of robust electrical transformer used to measure linear displacement. It has been widely used in a variety of industrial applications, including power turbines, hydraulics, automation, aircraft, satellites, nuclear reactors, and many others.

In this study, we feature the add-ons of LVDT and high temperature modules of the NANOVEA Tribometer which allow the change of wear track depth of the tested sample to be measured during the wear process at elevated temperatures. This enables users to correlate different stages of wear process with the evolution of COF, which is critical in improving fundamental understanding of the wear mechanism and tribological characteristics of the materials for high temperature applications.

MEASUREMENT OBJECTIVE

In this study. we would like to showcase the capacity of NANOVEA T50 Tribometer for in situ monitoring the evolution of the wear process of materials at elevated temperatures.

The wear process of the alumina silicate ceramic at different temperatures is simulated in a controlled and monitored manner.

NANOVEA

T50

TEST PROCEDURE

The tribological behavior, e. g. coefficient of friction, COF, and wear resistance of alumina silicate ceramic plates was evaluated by the NANOVEA Tribometer. The alumina silicate ceramic plate was heated up by a furnace from room temperature, RT, to elevated temperatures (400°C and 800°C), followed by the wear tests at such temperatures.

For comparison, the wear tests were carried out when the sample cooled down from 800°C to 400°C and then to room temperature. An AI2O3 ball tip (6mm dia., Grade 100) was applied against the tested samples. The COF, wear depth and temperature were monitored in situ.

TEST PARAMETERS

of the pin-on-disk measurement

The wear rate, K, was evaluated using the formula K=V/(Fxs)=A/(Fxn), where V is the worn volume, F is the normal load, s is the sliding distance, A is the cross-sectional area of the wear track, and n is the number of revolution. Surface roughness and wear track profiles were evaluated by the NANOVEA Optical Profiler, and the wear track morphology was examined using an optical microscope.

RESULTS & DISCUSSION

The COF and wear track depth recorded in situ are shown in FIGURE 1 and FIGURE 2, respectively. In FIGURE 1, “-I” indicates the test performed when the temperature was increased from RT to an elevated temperature. “-D” represents the temperature decreased from a higher temperature of 800°C.

As shown in FIGURE 1, the samples tested at different temperatures exhibit a comparable COF of ~0.6 throughout the measurements. Such a high COF leads to an accelerated wear process which creates a substantial amount of debris. The wear track depth was monitored during the wear tests by LVDT as shown in FIGURE 2. The tests performed at room temperature before sample heating up and after sample cooling down show that the alumina silicate ceramic plate exhibits a progressive wear process at RT, the wear track depth gradually increases throughout the wear test to ~170 and ~150 μm, respectively.

In comparison, the wear tests at elevated temperatures (400°C and 800°C) exhibit a different wear behavior – the wear track depth increases promptly at the beginning of the wear process, and it slows down as the test continues. The wear track depths for tests performed at temperatures 400°C-I, 800°C and 400°C-D are ~140, ~350 and ~210 μm, respectively.

FIGURE 1. Coefficient of Friction during pin-on-disk tests at different temperatures

FIGURE 2. Evolution of wear track depth of the alumina silicate ceramic plate at different temperatures

The average wear rate and wear track depth of the alumina silicate ceramic plates at different temperatures were measured using NANOVEA Optical Profiler as summarized in FIGURE 3. The wear track depth is in agreement with that recorded using LVDT. The alumina silicate ceramic plate shows a substantially increased wear rate of ~0.5 mm3/Nm at 800°C, compared to the wear rates below 0.2mm3/N at temperatures below 400°C. The alumina silicate ceramic plate does not exhibit significantly enhanced mechanical/tribological properties after the short heating process, possessing a comparable wear rate before and after the heat treatment.

Alumina silicate ceramic, also knows as lava and wonderstone, is soft and machinable before heating treatment. A long process of firing at elevated temperatures up to 1093°C can substantially enhance its hardness and strength, after which diamond machining is required. Such a unique characteristic makes alumina silicate ceramic an ideal material for sculpture.

In this study, we show that heat treatment at a lower temperature that the one required for firing (800°C vs 1093°C) in a short time does not improve the mechanical and tribological characteristics of alumina silicate ceramic, making proper firing an essential process for this material before its usage in the real applications.

FIGURE 3. Wear rate and wear track depth of the sample at different temperatures

CONCLUSION

Based on the comprehensive tribological analysis in this study, we show that the alumina silicate ceramic plate exhibits comparable coefficient of friction at different temperatures from room temperature to 800°C. However, it shows a substantially increased wear rate of ~0.5 mm3/Nm at 800°C, demonstrating the importance of proper heat treatment of this ceramic.

NANOVEA Tribometers are capable of evaluating the tribological properties of materials for applications at high temperatures up to 1000°C. The function of in situ COF and wear track depth measurements allows users to correlate different stages of wear process with the evolution of COF, which is critical in improving fundamental understanding of the wear mechanism and tribological characteristics of the materials used at elevated temperatures.

NANOVEA Tribometers offer precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. NANOVEA’s unmatched range is an ideal solution for determining the full range of tribological properties of thin or thick, soft or hard coatings, films and substrates.

Optional 3D Non-Contact Profilers are available for high resolution 3D imaging of wear tracks in addition to other surface measurements such as roughness.

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Fish Scale Surface Analysis Using 3D Optical Profiler

Learn more

FISH SCALE SURFACE ANALYSIS

using 3D OPTICAL PROFILER

Prepared by

Andrea Novitsky

INTRODUCTION

The morphology, patterns, and other features of a fish scale are studied using the NANOVEA 3D Non-Contact Optical Profiler. The delicate nature of this biological sample along with its very small and high angled grooves also highlights the importance of the profiler’s non-contact technique. The grooves on the scale are called circuli, and can be studied to estimate the age of the fish, and even distinguish periods of different rates of growth, similar to the rings of a tree. This is very important information for the management of wild fish populations in order to prevent overfishing.

Importance of 3D Non-Contact Profilometry FOR BIOLOGICAL STUDIES

Unlike other techniques such as touch probes or interferometry, the 3D Non-Contact Optical Profiler, using axial chromatism, can measure nearly any surface. Sample sizes can vary widely due to open staging and there is no sample preparation needed. Nano through macro range features are obtained during a surface profile measurement with zero influence from sample reflectivity or absorption. The instrument provides an advanced ability to measure high surface angles with no software manipulation of the results. Any material can be easily measured, whether it’s transparent, opaque, specular, diffusive, polished or rough. The technique provides an ideal, broad and user friendly capability to maximize surface studies along with the benefits of combined 2D & 3D capabilities.

MEASUREMENT OBJECTIVE

In this application, we showcase NANOVEA ST400, a 3D Non-Contact Profiler with a high-speed sensor, providing comprehensive analysis of the surface of a scale.

The instrument has been used to scan the entire sample, along with a higher resolution scan of the center area. The outer and inner side surface roughness of the scale was measured for comparison as well.

NANOVEA

ST400

3D & 2D Surface Characterization of Outer Scale

The 3D View and False Color View of the outer scale show a complex structure similar to a finger print or the rings of a tree. This provides users a straightforward tool to directly observe the surface characterization of the scale from different angles. Various other measurements of the outer scale are shown along with the comparison of the outer and inner side of the scale.

SURFACE ROUGHNESS COMPARISON

CONCLUSION

In this application, we have shown how the NANOVEA 3D Non-Contact Optical Profiler can characterize a fish scale in a variety of ways.

The outer and inner surfaces of the scale can be easily distinguished by surface roughness alone, with roughness values of 15.92μm and 1.56μm respectively. Additionally, precise and accurate information can be learned about a fish scale by analyzing the grooves, or circuli, on the outer surface of the scale. The distance of bands of circuli from the center focus were measured, and the height of the circuli were also found to be approximately 58μm high on average.

The data shown here represents only a portion of the calculations available in the analysis software.

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Dynamic Mechanical Analysis (DMA) Frequency Sweep on Polymer

DMA FREQUENCY SWEEP

ON POLYMER USING NANOINDENTATION

Prepared by

Duanjie Li, PhD

INTRODUCTION

IMPORTANCE OF DYNAMIC MECHANICAL ANALYSIS FREQUENCY SWEEP TEST

The changing frequency of the stress often leads to variations in the complex modulus, which is a critical mechanical property of polymers. For example, tires are subjected to cyclical high deformations when vehicles are running on the road. The frequency of the pressure and deformation changes as the car accelerates to higher speeds. Such a change can result in variation in the viscoelastic properties of the tire, which are important factors in the car performance. A reliable and repeatable test of the viscoelastic behavior of polymers at different frequencies is in need. The Nano module of the NANOVEA Mechanical Tester generates sinusoidal load by a high precision piezo actuator and directly measures the evolution of force and displacement using ultrasensitive load cell and capacitor. The combination of easy setup and high accuracy makes it an ideal tool for Dynamic Mechanical Analysis frequency sweep.

Viscoelastic materials exhibit both viscous and elastic characteristics when undergoing deformation. Long molecular chains in polymer materials contribute to their unique viscoelastic properties, i.e. a combination of the characteristics of both elastic solids and Newtonian fluids. Stress, temperature, frequency and other factors all play roles in the viscoelastic properties. Dynamic Mechanical Analysis, also known as DMA, studies the viscoelastic behavior and complex modulus of the material by applying a sinusoidal stress and measuring the change of strain.

MEASUREMENT OBJECTIVE

In this application, we study viscoelastic properties of a polished tire sample at different DMA frequencies using the Most Powerful Mechanical Tester, NANOVEA PB1000, in Nanoindentation mode.

NANOVEA

PB1000

TEST CONDITIONS

FREQUENCIES (Hz):

0.1, 1.5, 10, 20

CREEP TIME AT EACH FREQ.

50 sec

OSCILLATION VOLTAGE

0.1 V

LOADING VOLTAGE

1 V

indenter type

Spherical

Diamond | 100 μm

RESULTS & DISCUSSION

The Dynamic Mechanical Analysis frequency sweep at the maximum load allows a fast and simple measurement on the viscoelastic characteristics of the sample at different loading frequencies in one test. The phase shift and the amplitudes of the load and displacement waves at different frequencies can be used to calculate a variety of fundamental material viscoelastic properties, including Storage Modulus, Loss Modulus and Tan (δ) as summarized in the following graphs.

Frequencies of 1, 5, 10 and 20 Hz in this study, correspond to speeds of about 7, 33, 67 and 134 km per hour. As the test frequency increases from 0.1 to 20 Hz, it can be observed that both Storage Modulus and Loss Modulus progressively increase. Tan (δ) decreases from ~0.27 to 0.18 as the frequency increases from 0.1 to 1 Hz, and then it gradually increases to ~0.55 when the frequency of 20 Hz is reached. DMA frequency sweep allows measuring the trends of Storage Modulus, Loss Modulus and Tan (δ), which provide information on the movement of the monomers and cross-linking as well as the glass transition of polymers. By raising the temperature using a heating plate during the frequency sweep, a more complete picture of the nature of the molecular motion under different test conditions can be obtained.

EVOLUTION OF LOAD & DEPTH

OF THE FULL DMA FREQUENCY SWEEP

LOAD & DEPTH vs TIME AT DIFFERENT FREQUENCIES

STORAGE MODULUS

AT DIFFERENT FREQUENCIES

LOSS MODULUS

AT DIFFERENT FREQUENCIES

TAN (δ)

AT DIFFERENT FREQUENCIES

CONCLUSION

In this study, we showcased the capacity of the NANOVEA Mechanical Tester in performing the Dynamic Mechanical Analysis frequency sweep test on a tire sample. This test measures the viscoelastic properties of the tire at different frequencies of stress. The tire shows increased storage and loss modulus as the loading frequency increases from 0.1 to 20 Hz. It provides useful information on the viscoelastic behaviors of the tire running at different speeds, which is essential in improving the performance of tires for smoother and safer rides. The DMA frequency sweep test can be performed at various temperatures to mimic the realistic working environment of the tire under different weather.

In the Nano Module of the NANOVEA Mechanical Tester, the load application with the fast piezo is independent from the load measurement done by a separate high sensitivity strain gage. This gives a distinct advantage during Dynamic Mechanical Analysis since the phase between depth and load is measured directly from the data collected from the sensor. The calculation of phase is direct and does not need mathematical modeling that adds inaccuracy to the resulting loss and storage modulus. This is not the case for a coil-based system.

In conclusion, DMA measures loss and storage modulus, complex modulus and Tan (δ) as a function of contact depth, time and frequency. Optional heating stage allows determination of materials phase transition temperature during DMA. The NANOVEA Mechanical Testers provide unmatched multi-function Nano and Micro modules on a single platform. Both the Nano and Micro modules include scratch tester, hardness tester and wear tester modes, providing the widest and most user friendly range of testing available on a single module.

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Fresnel Lens Topography

FRESNEL LENS TOPOGRAPHYUSING 3D NON-CONTACT OPTICAL PROFILOMETER

Prepared by

Duanjie Li & Benjamin Mell

INTRODUCTION

A lens is an optical device of axial symmetry that transmits and refracts light. A simple lens consists of a single optical component for converging or diverging the light. Even though spherical surfaces are not ideal shape for making a lens, they are often used as the simplest shape which glass can be ground and polished to.

A Fresnel lens consists of a series of concentric rings, which are thin parts of a simple lens with a width as small as a few thousandths of an inch. Fresnel lenses contain a large aperture and short focal length, with a compact design reducing the weight and volume of material required, compared to conventional lenses with the same optical properties. A very small amount of light is lost by absorption due to the thin geometry of the Fresnel lens.

IMPORTANCE OF 3D NON-CONTACT PROFILOMETRY FOR FRESNEL LENS INSPECTION

Fresnel lenses are extensively employed in the automotive industry, lighthouses, solar energy and optical landing systems for aircraft carriers. Molding or stamping the lenses out of transparent plastics can make their production cost-effective. Service quality of Fresnel lenses mostly depends on the precision and surface quality of their concentric ring. Unlike a touch probe technique, NANOVEA Optical Profilers perform 3D surface measurements without touching the surface, avoiding the risk of making new scratches. The Chromatic Light technique is ideal for precise scanning of complex shapes, such as lenses of different geometries.

FRESNEL LENS SCHEMATIC

Transparent plastic Fresnel lenses can be manufactured by molding or stamping. Accurate and efficient quality control is critical to reveal defective production molds or stamps. By measuring the height and pitch of the concentric rings, production variations can be detected by comparing the measured values against the specification values given by the manufacturer of the lens.

Precise measurement of the lens profile ensures that the molds or stamps are properly machined to fit manufacturer specifications. Moreover, the stamp could progressively wear out over time, causing it to lose its initial shape. Consistent deviation from the lens manufacturer specification is a positive indication that the mold needs to be replaced.

MEASUREMENT OBJECTIVE

In this application, we showcase NANOVEA ST400, a 3D Non-Contact Profiler with a high-speed sensor, providing comprehensive 3D profile analysis of an optical component of a complex shape. To demonstrate the remarkable capabilities of our Chromatic Light technology, the contour analysis is performed on a Fresnel lens.

NANOVEA ST400 Large Area
Optical 3D Profilometer

The 2.3” x 2.3” acrylic Fresnel lens used for this study consists of

a series of concentric rings and a complex serrated cross-section profile.

It has a 1.5” focal length, 2.0” effective size diameter,

125 grooves per inch, and an index of refraction of 1.49.

The NANOVEA ST400 scan of the Fresnel lens shows a noticeable increase in height of the concentric rings, moving outward from the center.

2D FALSE COLOR

Height Representation

3D VIEW

EXTRACTED PROFILE

PEAK & VALLEY

Dimensional Analysis of the Profile

CONCLUSION

In this application, we have showcased that the NANOVEA ST400 non-contact Optical Profiler accurately measures the surface topography of Fresnel lenses.

The dimension of the height and pitch can be accurately determined from the complex serrated profile using NANOVEA analysis software. Users can effectively inspect the quality of the production molds or stamps by comparing the ring height and pitch dimensions of manufactured lenses against the ideal ring specification.

The data shown here represents only a portion of the calculations available in the analysis software.

NANOVEA Optical Profilers measure virtually any surface in fields including Semiconductors, Microelectronics, Solar, Fiber Optics, Automotive, Aerospace, Metallurgy, Machining, Coatings, Pharmaceutical, Biomedical, Environmental and many others.

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Machined Parts Inspection

MACHINED PARTS

inspection from CAD model using 3D profilometry

Author:

Duanjie Li, PhD

Revised by

Jocelyn Esparza

INTRODUCTION

The demand for precision machining able to create complex geometries has been on the rise across a spectrum of industries. From aerospace, medical and automobile, to tech gears, machinery and musical instruments, the continuous innovation and evolution push expectations and accuracy standards to new heights. Consequently, we see the rise of the demand for rigorous inspection techniques and instruments to ensure the highest quality of the products.

Importance of 3D Non-Contact Profilometry for Parts Inspection

Comparing properties of machined parts to their CAD models is essential to verify tolerances and adherence to production standards. Inspection during the service time is also crucial as wear and tear of the parts may call for their replacement. Identification of any deviations from the required specifications in a timely manner will help avoid costly repairs, production halts and tarnished reputation.

Unlike a touch probe technique, the NANOVEA Optical Profilers perform 3D surface scans with zero contact, allowing for quick, precise and non-destructive measurements of complex shapes with the highest accuracy.

MEASUREMENT OBJECTIVE

In this application, we showcase NANOVEA HS2000, a 3D Non-Contact Profiler with a high-speed sensor, performing a comprehensive surface inspection of dimension, radius, and roughness.

All in under 40 seconds.

NANOVEA

HS2000

CAD MODEL

A precise measurement of the dimension and surface roughness of the machined part is critical to make sure it meets the desired specifications, tolerances and surface finishes. The 3D model and the engineering drawing of the part to be inspected are presented below.

FALSE COLOR VIEW

The false color view of the CAD model and the scanned machined part surface are compared in FIGURE 3. The height variation on the sample surface can be observed by the change in color.

Three 2D profiles are extracted from the 3D surface scan as indicated in FIGURE 2 to further verify the dimensional tolerance of the machined part.

PROFILES COMPARISON & RESULTS

Profile 1 through 3 are shown in FIGURE 3 through 5. Quantitative tolerance inspection is carried out by comparing the measured profile with the CAD model to uphold rigorous manufacturing standards. Profile 1 and Profile 2 measure the radius of different areas on the curved machined part. The height variation of Profile 2 is 30 µm over a length of 156 mm which meets the desired ±125 µm tolerance requirement.

By setting up a tolerance limit value, the analysis software can automatically determine pass or fail of the machined part.

The roughness and uniformity of the machined part’s surface play an important role in ensuring its quality and functionality. FIGURE 6 is an extracted surface area from the parent scan of the machined part which was used to quantify the surface finish. The average surface roughness (Sa) was calculated to be 2.31 µm.

CONCLUSION

In this study, we have showcased how the NANOVEA HS2000 Non-Contact Profiler equipped with a high speed sensor performs comprehensive surface inspection of dimensions and roughness.

High-resolution scans enable users to measure detailed morphology and surface features of machined parts and to quantitatively compare them with their CAD models. The instrument is also capable of detecting any defects including scratches and cracks.

The advanced contour analysis serves as an unparalleled tool not only to determine whether the machined parts satisfy the set specifications, but also to evaluate the failure mechanisms of the worn components.

The data shown here represents only a portion of the calculations possible with the advanced analysis software that comes equipped with every NANOVEA Optical Profiler.

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Fretting Wear Evaluation

FRETTING WEAR EVALUATION

Author:

Duanjie Li, PhD

Revised by

Jocelyn Esparza

INTRODUCTION

Fretting is “a special wear process that occurs at the contact area between two materials under load and subject to minute relative motion by vibration or some other force.” When machines are in operation, vibrations inevitably occur in joints that are bolted or pinned, between components that are not intended to move, and in oscillating couplings and bearings. The amplitude of such relative sliding motion is often in the order of micrometers to millimeters. Such repetitive low-amplitude motion causes serious localized mechanical wear and material transfer at the surface, which may lead to reduced production efficiency, machine performance or even damage to the machine.

Importance of Quantitative
Fretting Wear Evaluation

Fretting wear often involves several complex wear mechanisms taking place at the contact surface, including two-body abrasion, adhesion and/or fretting fatigue wear. In order to understand the fretting wear mechanism and select the best material for fretting wear protection, reliable and quantitative fretting wear evaluation is needed. The fretting wear behavior is significantly influenced by the work environment, such as displacement amplitude, normal loading, corrosion, temperature, humidity and lubrication. A versatile tribometer that can simulate the different realistic work conditions will be ideal for fretting wear evaluation.

Steven R. Lampman, ASM Handbook: Volume 19: Fatigue and Fracture
http://www.machinerylubrication.com/Read/693/fretting-wear

MEASUREMENT OBJECTIVE

In this study, we evaluated the fretting wear behaviors of a stainless steel SS304 sample at different oscillation speeds and temperatures to showcase the capacity of NANOVEA T50 Tribometer in simulating the fretting wear process of metal in a well-controlled and monitored manner.

NANOVEA

T50

TEST CONDITIONS

The fretting wear resistance of a stainless steel SS304 sample was evaluated by NANOVEA Tribometer using Linear Reciprocating Wear Module. A WC (6 mm diameter) ball was used as the counter material. The wear track was examined using a NANOVEA 3D non-contact profiler.

The fretting test was performed at room temperature (RT) and 200 °C to study the effect of high temperature on the fretting wear resistance of the SS304 sample. A heating plate on the sample stage heated up the sample during the fretting test at 200 °C. The wear rate, K, was evaluated using the formula K=V/(F×s), where V is the worn volume, F is the normal load, and s is the sliding distance.

Please note that a WC ball as a counter material was used as an example in this study. Any solid material with different shapes and surface finish can be applied using a custom fixture to simulate the actual application situation.

TEST PARAMETERS

of the wear measurements

RESULTS & DISCUSSION

The 3D wear track profile allows direct and accurate determination of the wear track volume loss calculated by the NANOVEA Mountains analysis software.

The reciprocating wear test at a low speed of 100 rpm and room temperature exhibits a small wear track of 0.014 mm³. In comparison, the fretting wear test carried out at a high speed of 1000 rpm creates a substantially larger wear track with a volume of 0.12 mm³. Such an accelerated wear process may be attributed to the high heat and intense vibration generated during the fretting wear test, which promotes oxidation of the metallic debris and results in severe three-body abrasion. The fretting wear test at an elevated temperature of 200 °C forms a larger wear track of 0.27 mm³.

The fretting wear test at 1000 rpm has a wear rate of 1.5×10^-4 mm³/Nm, which is nearly nine times compared to that in a reciprocating wear test at 100 rpm. The fretting wear test at an elevated temperature further accelerates the wear rate to 3.4×10^-4 mm³/Nm. Such a significant difference in wear resistance measured at different speeds and temperatures shows the importance of proper simulations of fretting wear for realistic applications.

Wear behavior can change drastically when small changes in testing conditions are introduced into the tribosystem. The versatility of the NANOVEA Tribometer allows measuring wear under various conditions, including high temperature, lubrication, corrosion and others. The accurate speed and position control by the advanced motor enables users to perform the wear test at speeds ranging from 0.001 to 5000 rpm, making it an ideal tool for research/testing labs to investigate the fretting wear in different tribological conditions.

Fretting wear tracks at various conditions

under the optical microscope

3D WEAR TRACKs PROFILES

provide more insight in fundamental understanding
of the fretting wear mechanism

RESULT SUMMARY OF WEAR TRACKS

measured using different test parameters

CONCLUSION

In this study, we showcased the capacity of the NANOVEA Tribometer in evaluating the fretting wear behavior of a stainless steel SS304 sample in a well-controlled and quantitative manner.

The test speed and temperature play critical roles in the fretting wear resistance of the materials. The high heat and intense vibration during the fretting resulted in substantially accelerated wear of the SS304 sample by close to nine times. The elevated temperature of 200 °C further increased the wear rate to 3.4×10^-4 mm³/Nm.

The versatility of the NANOVEA Tribometer makes it an ideal tool for measuring fretting wear under various conditions, including high temperature, lubrication, corrosion and others.

NANOVEA Tribometers offer precise and repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear, lubrication and tribo-corrosion modules available in one pre-integrated system. Our unmatched range is an ideal solution for determining the full scope of tribological properties of thin or thick, soft or hard coatings, films and substrates.

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Ball Bearings: High Force Wear Resistance Study

INTRODUCTION

A ball bearing uses balls to reduce rotational friction and support radial and axial loads. The rolling balls between the bearing races produce much lower coefficient of friction (COF) compared to two flat surfaces sliding against each other. Ball bearings are often exposed to high contact stress levels, wear and extreme environmental conditions such as high temperatures. Therefore, wear resistance of the balls under high loads and extreme environmental conditions is critical for extending the lifetime of the ball bearing to cut down cost and time on repairs and replacements.
Ball bearings can be found in nearly all applications that involve moving parts. They are commonly used in transportation industries such as aerospace and automobile as well as the toy industry that manufactures items such as fidget spinner and skateboards.

BALL BEARING WEAR EVALUATION AT HIGH LOADS

Ball bearings can be made from an extensive list of materials. Commonly used materials range between metals like stainless steel and chrome steel or ceramics such as tungsten carbide (WC) and silicon nitride (Si3n4). To ensure that the manufactured ball bearings possess the required wear resistance ideal for the given application’s conditions, reliable tribological evaluations under high loads are necessary. Tribological testing aids in quantifying and contrasting the wear behaviors of different ball bearings in a controlled and monitored manner to select the best candidate for the targeted application.

MEASUREMENT OBJECTIVE

In this study, we showcase a Nanovea Tribometer as the ideal tool for comparing the wear resistance of different ball bearings under high loads.

Figure 1: Setup of the bearing test.

TESTING PROCEDURE

The coefficient of friction, COF, and the wear resistance of the ball bearings made of different materials were evaluated by a Nanovea Tribometer. P100 grit sandpaper was used as the counter material. The wear scars of the ball bearings were examined using a Nanovea 3D Non-Contact Profiler after the wear tests concluded. The test parameters are summarized in Table 1. The wear rate, K, was evaluated using the formula K=V/(F×s), where V is the worn volume, F is the normal load and s is the sliding distance. Ball wear scars were evaluated by a Nanovea 3D Non-Contact Profiler to ensure precise wear volume measurement.
The automated motorized radial positioning feature allows the tribometer to decrease the radius of the wear track for the duration of a test. This test mode is called a spiral test and it ensures that the ball bearing always slides on a new surface of the sandpaper (Figure 2). It significantly improves the repeatability of the wear resistance test on the ball. The advanced 20bit encoder for internal speed control and 16bit encoder for external position control provide precise real-time speed and position information, allowing for a continuous adjustment of rotational speed to achieve constant linear sliding speed at the contact.
Please note that P100 Grit sandpaper was used to simplify the wear behavior between various ball materials in this study and can be substituted with any other material surface. Any solid material can be substituted to simulate the performance of a wide range of material couplings under actual application conditions, such as in liquid or lubricant.

Figure 2: Illustration of the spiral passes for the ball bearing on the sandpaper.

Table 1: Test parameters of the wear measurements.

RESULTS & DISCUSSION

Wear rate is a vital factor for determining the service lifetime of the ball bearing, while a low COF is desirable to improve the bearing performance and efficiency. Figure 3 compares the evolution of COF for different ball bearings against the sandpaper during the tests. The Cr Steel ball shows an increased COF of ~0.4 during the wear test, compared to ~0.32 and ~0.28 for SS440 and Al2O3 ball bearings. On the other hand, the WC ball exhibits a constant COF of ~0.2 throughout the wear test. Observable COF variation can be seen throughout each test which is attributed to vibrations caused by the sliding movement of the ball bearings against the rough sandpaper surface.

Figure 3: Evolution of COF during the wear tests.

Figure 4 and Figure 5 compare the wear scars of the ball bearings after they were measured by an optical microscope and Nanovea Non-Contact optical profiler, respectively, and Table 2 summarizes the results of the wear track analysis. The Nanovea 3D profiler precisely determines the wear volume of the ball bearings, making it possible to calculate and compare the wear rates of different ball bearings. It can be observed that the Cr Steel and SS440 balls exhibit much larger flattened wear scars compared to the ceramic balls, i.e. Al2O3 and WC after the wear tests. The Cr Steel and SS440 balls have comparable wear rates of 3.7×10-3 and 3.2×10-3 m3/N m, respectively. In comparison, the Al2O3 ball shows an enhanced wear resistance with a wear rate of 7.2×10-4 m3/N m. The WC ball barely exhibits minor scratches on the shallow wear track area, resulting in a significantly reduced wear rate of 3.3×10-6 mm3/N m.

Figure 4: Wear scars of the ball bearings after the tests.

Figure 5: 3D morphology of the wear scars on the ball bearings.

Table 2: Wear scar analysis of the ball bearings.

Figure 6 shows microscope images of the wear tracks produced on the sand paper by the four ball bearings. It is evident that the WC ball produced the most severe wear track (removing almost all sand particle in its path) and possesses the best wear resistance. In comparison, the Cr Steel and SS440 balls left a large amount of metal debris on the wear track of the sand paper.
These observations further demonstrate the importance of the benefit of a spiral test. It ensures that the ball bearing always slides on a new surface of the sandpaper, which significantly improves the repeatability of a wear resistance test.

Figure 6: Wear tracks on the sand paper against different ball bearings.

CONCLUSION

The wear resistance of the ball bearings under a high pressure plays a vital role in their service performance. The ceramic ball bearings possess significantly enhanced wear resistance under high stress conditions and reduce the time and cost due to bearing repairing or replacement. In this study, the WC ball bearing exhibits a substantially higher wear resistance compared to the steel bearings, making it an ideal candidate for bearing applications where severe wear takes place.
A Nanovea Tribometer is designed with high torque capabilities for loads up to 2000 N and precise and controlled motor for rotational speeds from 0.01 to 15,000 rpm. It offers repeatable wear and friction testing using ISO and ASTM compliant rotative and linear modes, with optional high temperature wear and lubrication modules available in one pre-integrated system. This unmatched range allows users to simulate different severe work environments of the ball bearings including high stress, wear and high temperature, etc. It also acts as an ideal tool to quantitatively assess the tribological behaviors of superior wear resistant materials under high loads.
A Nanovea 3D Non-Contact Profiler provides precise wear volume measurements and acts as a tool to analyze the detailed morphology of the wear tracks, providing additional insights in the fundamental understanding of wear mechanisms.

Prepared by
Duanjie Li, PhD, Jonathan Thomas, and Pierre Leroux

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