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AR Monthly Archives: January 2020
Dimensional and Surface Finish of Polymeric Tubes
Importance of Dimensional and Surface Analysis of Polymeric Tubes
Tubes made from polymeric material are commonly used in many industries ranging from automotive, medical, electrical, and many other categories. In this study, medical catheters made of different polymeric materials were studied using the Nanovea 3D Non-Contact Profilometer to measure surface roughness, morphology, and dimensions. Surface roughness is crucial for catheters as many problems with catheters, including infection, physical trauma, and inflammation can be linked with the catheter surface. Mechanical properties, such as coefficient of friction, can also be studied by observing surface properties. These quantifiable data can be obtained to ensure the catheter can be used for medical applications.
Compared to optical microscopy and electron microscopy, 3D Non-Contact Profilometry using axial chromatism is highly preferable for characterizing catheter surfaces due to its ability to measure angles/curvature, ability to measure material surfaces despite transparency or reflectivity, minimal sample preparation, and non-invasive nature. Unlike conventional optical microscopy, the height of the surface can be obtained and used for computational analysis; e.g. finding dimensions and removing form to find surface roughness. Having little sample preparation, in contrast to electron microscopy, and non-contact nature also allows for quick data collection without fearing contamination and error from sample preparation.
Measurement Objective
In this application, the Nanovea 3D Non-Contact Profilometer is used to scan the surface of two catheters: one made of TPE (Thermoplastic Elastomer) and the other made of PVC (Polyvinyl Chloride). The morphology, radial dimension, and height parameters of the two catheters will be obtained and compared.
Results and Discussion
3D Surface
Despite the curvature on polymeric tubes, the Nanovea 3D Non-contact profilometer can scan the surface of the catheters. From the scan done, a 3D image can be obtained for quick, direct visual inspection of the surface.
2D Dimensional Analysis
The outer radial dimension was obtained by extracting a profile from the original scan and fitting an arc to the profile. This shows the ability of the 3D Non-contact profilometer in conducting quick dimensional analysis for quality control applications. Multiple profiles can easily be obtained along the catheter’s length as well.
Surface Analysis Roughness
The outer radial dimension was obtained by extracting a profile from the original scan and fitting an arc to the profile. This shows the ability of the 3D Non-contact profilometer in conducting quick dimensional analysis for quality control applications. Multiple profiles can easily be obtained along the catheter’s length as well.
Conclusion
In this application, we have shown how the Nanovea 3D Non-contact profilometer can be used to characterize polymeric tubes. Specifically, surface metrology, radial dimensions, and surface roughness were obtained for medical catheters. The outer radius of the TPE catheter was found to be 2.40mm while the PVC catheter was 1.27mm. The surface of the TPE catheter was found to be rougher than the PVC catheter. The Sa of TPE was 0.9740µm compared to 0.1791µm of PVC. While medical catheters were used for this application, 3D Non-Contact Profilometry can be applied to a large variety of surfaces as well. Obtainable data and calculations are not limited to what is shown.
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Tooth Hardness Evaluation using Nanoindentation
Importance of Nanoindentation for Bio Materials
With many traditional mechanical tests (Hardness, Adhesion, Compression, Puncture, Yield Strength, etc.), today’s quality control environments with advanced sensitive materials, from gels to brittle materials, now require greater precision and reliability control. Traditional mechanical instrumentation fails to provide the sensitive load control and resolution required; designed to be used for bulk materials. As the size of material being tested became of greater interest, the development of Nanoindentation provided a reliable method to obtain essential mechanical information on smaller surfaces such as the research being done with biomaterials. The challenges specifically associated with biomaterials have required the development of mechanical testing capable of accurate load control on extremely soft to brittle materials. Also, multiple instruments are needed to perform various mechanical tests which can now be performed on a single system. Nanoindentation provides a wide range of measurement with precise resolution at nano controlled loads for sensitive applications.
Measurement Objective
In this application, the Nanovea Mechanical Tester, in Nanoindentation mode, is used to study the hardness and elastic modulus of the dentin, decay, and pulp of a tooth. The most critical aspect with Nanoindentation testing is securing the sample, here we took a sliced tooth and epoxy mounted leaving all three areas of interest exposed for testing.
Results and Discussion
This section includes a summary table that compares the main numerical results for the different samples, followed by the full result listings, including each indentation performed, accompanied by micrographs of the indentation, when available. These full results present the measured values of Hardness and Young’s modulus as the penetration depth with their averages and standard deviations. It should be considered that large variation in the results can occur in the case that the surface roughness is in the same size range as the indentation.
Summary table of main numerical results:
Conclusion
In conclusion, we have shown how the Nanovea Mechanical Tester, in Nanoindentation mode, provides precise measurement of the mechanical properties of a tooth. The data can be used in the development of fillings that will better match the mechanical characteristics of a real tooth. The positioning capability of the Nanovea Mechanical Tester allows full mapping of the hardness of the teeth across the various zones.
Using the same system, it is possible to test teeth material fracture toughness at higher loads up to 200N. A multi-cycle loading test can be used on more porous materials to evaluate the remaining level of elasticity. Using a flat cylindrical diamond tip can give yield strength information in each zone. In addition, with DMA “Dynamic Mechanical Analysis”, the viscoelastic properties including loss and storage moduli can be evaluated.
The Nanovea nano module is ideal for these tests because it uses a unique feedback response to control precisely the load applied. Because of this, the nano module can also be used to do accurate nano scratch testing. The study of scratch and wear resistance of tooth material and filling materials adds to the overall usefulness of the Mechanical tester. Using a sharp 2-micron tip to quantitatively compare marring on filling materials will allow better prediction of the behavior in real applications. Multi-pass wear or direct rotative wear testing are also common tests providing important information on the long term viability.
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Friction Evaluation at Extreme Low Speeds
Importance of Friction Evaluation at Low Speeds
Friction is the force that resists the relative motion of solid surfaces sliding against each other. When the relative motion of these two contact surfaces takes place, the friction at the interface converts the kinetic energy into heat. Such a process can also lead to wear of the material and thus performance degradation of the parts in use.
With a large stretch ratio, high resilience, as well as great waterproof properties and wear resistance, rubber is extensively applied in a variety of applications and products in which friction plays an important role, such as automobile tires, windshield wiper blades. shoe soles and many others. Depending on the nature and requirement of these applications, either high or low friction against different material is desired. As a consequence, a controlled and reliable measurement of friction of rubber against various surfaces becomes critical.
Measurement Objective
The coefficient of friction (COF) of rubber against different materials is measured in a controlled and monitored manner using the Nanovea Tribometer. In this study, we would like to showcase the capacity of Nanovea Tribometer for measuring the COF of different materials at extremely low speeds.
Results and Discussion
The coefficient of friction (COF) of rubber balls (6 mm dia., RubberMill) on three materials (Stainless steel SS 316, Cu 110 and optional Acrylic) was evaluated by Nanovea Tribometer. The tested metal samples were mechanically polished to a mirror-like surface finish before the measurement. The slight deformation of the rubber ball under the applied normal load created an area contact, which also helps to reduce the impact of asperities or inhomogeneity of sample surface finish to the COF measurements. The test parameters are summarized in Table 1.
The COF of a rubber ball against different materials at four different speeds is shown in Figure. 2, and the average COFs calculated automatically by the software are summarized and compared in Figure 3. It is interesting that the metal samples (SS 316 and Cu 110) exhibit significantly increased COFs as the rotational speed increases from a very low value of 0.01 rpm to 5 rpm -the COF value of the rubber/SS 316 couple increases from 0.29 to 0.8, and from 0.65 to 1.1 for the rubber/Cu 110 couple. This finding is in agreement with the results reported from several laboratories. As proposed by Grosch4 the friction of rubber is mainly determined by two mechanisms: (1) the adhesion between rubber and the other material, and (2) the energy losses due to the deformation of the rubber caused by surface asperities. Schallamach5 observed waves of detachment of rubber from the counter material across the interface between soft rubber spheres and a hard surface. The force for rubber to peel from the substrate surface and rate of waves of detachment can explain the different friction at different speeds during the test.
In comparison, the rubber/acrylic material couple exhibits high COF at different rotational speeds. The COF value slightly increases from ~ 1.02 to ~ 1.09 as the rotational speed increases from 0.01 rpm to 5 rpm. Such high COF is possibly attributed to stronger local chemical bonding at the contact face formed during the tests.
Conclusion
In this study, we show that at extremely low speeds, the rubber exhibits a peculiar frictional behavior – its friction against a hard surface increases with the increased speed of the relative movement. Rubber shows different friction when it slides on different materials. Nanovea Tribometer can evaluate the frictional properties of materials in a controlled and monitored manner at different speeds, allowing users to improve fundamental understanding of the friction mechanism of the materials and select the best material couple for targeted tribological engineering applications.
Nanovea Tribometer offers 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. It is capable of controlling the rotational stage at extremely low speeds down to 0.01 rpm and monitor the evolution of friction in situ. 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.
