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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.
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
Dental Tools: Dimensional and Surface Roughness Analysis
INTRODUCTION
Having precise dimensions and optimal surface roughness are vital to the functionality of dental screws. Many dental screw dimensions require high precision such as radii, angles, distances, and step heights. Understanding local surface roughness is also highly important for any medical tool or part being inserted inside the human body to minimize sliding friction.
NON-CONTACT PROFILOMETRY FOR DIMENSIONAL STUDY
Nanovea 3D Non-Contact Profilers use a chromatic light-based technology to measure any material surface: transparent, opaque, specular, diffusive, polished or rough. Unlike a touch probe technique, the non-contact technique can measure inside tight areas and will not add any intrinsic errors due to deformation caused by the tip pressing on a softer plastic material. Chromatic light-based technology also offers superior lateral and height accuracies compared to focus variation technology. Nanovea Profilers can scan large surfaces directly without stitching and profile the length of a part in a few seconds. Nano through macro range surface features and high surface angles can be measured due to the profiler’s ability to measure surfaces without any complex algorithms manipulating the results.
MEASUREMENT OBJECTIVE
In this application, the Nanovea ST400 Optical Profiler was used to measure a dental screw along flat and thread features in a single measurement. The surface roughness was calculated from the flat area, and various dimensions of the threaded features were determined.
Sample of dental screw analyzed by NANOVEA Optical Profiler.
Dental screw sample analyzed.
RESULTS
3D Surface
The 3D View and False Color View of the dental screw shows a flat area with threading starting on either side. It provides users a straightforward tool to directly observe the morphology of the screw from different angles. The flat area was extracted from the full scan to measure its surface roughness.
2D Surface Analysis
Line profiles can also be extracted from the surface to show a cross-sectional view of the screw. The Contour Analysis and step height studies were used to measure precise dimensions at a certain location on the screw.
CONCLUSION
In this application, we have showcase the Nanovea 3D Non-Contact Profiler’s ability to precisely calculate local surface roughness and measure large dimensional features in a single scan.
The data shows a local surface roughness of 0.9637 μm. The radius of the screw between threads was found to be 1.729 mm, and the threads had an average height of 0.413 mm. The average angle between the threads was determined to be 61.3°.
The data shown here represents only a portion of the calculations available in the analysis software.
Prepared by
Duanjie Li, PhD., Jonathan Thomas, and Pierre Leroux
Ceramics: Nanoindentation Fast Mapping for Grain Detection
INTRODUCTION
Nanoindentation has become a widely applied technique for measuring mechanical behaviors of materials at small scalesi ii. The high-resolution load-displacement curves from a nanoindentation measurement can provide a variety of physicomechanical properties, including hardness, Young’s modulus, creeping, fracture toughness and many others.
Importance of Fast Mapping Indentation
One significant bottleneck for further popularization of the nanoindentation technique is time consumption. A mechanical property mapping by conventional nanoindentation procedure can easily take hours which hinders the application of the technique in mass production industries, such as semiconductor, aerospace, MEMS, consumer products such as ceramic tiles and many others.
Fast mapping can prove to be essential in the ceramic tile manufacturing industry, Hardness and Young’s modulus mappings across a single ceramic tile can present a distribution of data that indicates how homogeneous the surface is. Softer regions on a tile can be outlined in this mapping and show locations more prone to failure from physical impacts that happen on a day to day basis in someone’s residence. Mappings can be made on different types of tiles for comparative studies and on a batch of similar tiles to measure tile consistency in a quality control processes. The combination of measurements setups can be extensive as well as accurate and efficient with the fast mapping method.
MEASUREMENT OBJECTIVE
In this study, the Nanovea Mechanical Tester, in FastMap mode is used to map the mechanical property of a floor tile at high speeds. We showcase the capacity of the Nanovea Mechanical Tester in performing two fast nanoindentation mappings with high precision and reproducibility.
Test Conditions
The Nanovea Mechanical Tester was used to perform a series of nanoindentations with the FastMap Mode on a floor tile using a Berkovich indenter. The test parameters are summarized below for the two indent matrices created.
Table 1: Test parameter summary.
RESULTS & DISCUSSION
Figure 1: 2D and 3D view of 625-indent hardness mapping.
Figure 2: Micrograph of 625-indent matrix showcasing grain.
A 625-indent matrix was conducted on a 0.20mm2 area with a large visible grain present. This grain (Figure 2) had an average hardness lower than the overall surface of the tile. The Nanovea Mechanical Software allows the user to see the hardness distribution map in 2D and 3D mode which are depicted in Figure 1. Using the high-precision position control of the sample stage, the software allows users to target areas such as these for in depth mechanical properties mapping.
Figure 3: 2D and 3D view of 1600-indent hardness mapping.
Figure 4: Micrograph of 1600-indent matrix.
A 1600-indent matrix was also created on the same tile to measure the homogeneity of the surface. Here again the user has the ability to see the hardness distribution in 3D or 2D mode (Figure 3) as well as the microscope image of the indented surface. Based on the hardness distribution presented, it can be concluded that the material is porous due to the even scattering of high and low hardness data points.
Compared to conventional nanoindentation procedures, FastMap mode in this study is substantially less time-consuming and more cost-effective. It enables speedy quantitative mapping of mechanical properties including Hardness and Young’s Modulus and provides a solution for grain detection and material consistency which is critical for quality control of a variety of materials in mass production.
CONCLUSION
In this study, we showcased the capacity of the Nanovea Mechanical Tester in performing speedy and precise nanoindentation mapping using FastMap mode. The mechanical property maps on the ceramic tile utilize the position control (with 0.2µm accuracy) of the stages and force module sensitivity to detect surface grains and measure homogeneity of a surface at high speed.
The test parameters used in this study were determined based on the size of the matrix and sample material. A variety of test parameters can be chosen to optimize the total indentation cycle time to 3 seconds per indent (or 30 seconds for every 10 indentations).
The Nano and Micro modules of the Nanovea Mechanical Tester all include ISO and ASTM compliant indentation, scratch and wear tester modes, providing the widest and most user-friendly range of testing available in a single system. Nanovea’s unmatched range is an ideal solution for determining the full range of mechanical properties of thin or thick, soft or hard coatings, films and substrates, including hardness, Young’s Modulus, fracture toughness, adhesion, wear resistance and many others.
In addition, optional 3D non-contact profiler and AFM Module are available for high resolution 3D imaging of indentation, scratch and wear track in addition to other surface measurements such as roughness.
Author: Duanjie Li, PhD Revised by Pierre Leroux & Jocelyn Esparza
