Measuring and Understanding Vibrational Wear on Components at the Nano Scale using Nano-Fretting

Topics Covered

Introduction to Nano-Fretting
Nano-Fretting Experiments Using NanoTest Vantage
Advantages of NanoTest Fretting Module
Nano-Fretting Tests on Biomedical Materials
Friction Measurements During Fretting

Introduction to Nano-Fretting

A wide variety of components experience vibrational wear whilst in operation. Fretting tests are performed at regular intervals on the macro-scale, in order to test the performance of a material under vibrational stress.

The nano-fretting module (Figure 1) is designed to handle examination of fretting and reciprocating wear at the micro/nano scale, providing a much needed solution to the previous metrology gap.

Figure 1. Nano-fretting stage design

This capability allows evaluation of the effect of small oscillatory micro-motion on the durability of complex systems such as hip prostheses. In hip prostheses the contacting surfaces can be gradually damaged due to the trapping of small particles between the socket and ball components.

Nano-Fretting Experiments Using NanoTest Vantage

NanoTest Vantage experiments have:

  • Range of indenter materials - Micro Materials Ltd offers several indenters for fretting tests ranging from diamond and sapphire to steel balls
  • Fully programmable experimental conditions - The nano-fretting hardware allows experiments to be ran at specific amplitudes and oscillation frequecies. This enables the simulation of different wear behaviors.
  • High cycle wear – With a superior stability, the NanoTest Vantage nano-fretting module enables high cycle wear behaviour to be reliably measured with up to 1 million cycles within a few hours of testing (Figure 2).
  • Friction measurements – Friction measurements are included in the Nano-fretting module meaning frictional forces are accurately measured allowing subtle changes in wear behaviour to be observed.
  • Flexible indenter geometry - The NanoTest Vantage is compatible with both traditional nanoindentation probes or large diameter probes allowing a greater range of contact pressures with which to simulate real world conditions.

Figure 2. Data from a million cycle nano-fretting experiment on a DLC coating on a silicon substrate. The coating fails after around 450,000 cycles.

Advantages of NanoTest Fretting Module

The key advantages of the NanoTest fretting module are:

  • True fretting behaviour on the nano-scale
  • High cycle wear behaviour
  • Reciprocating sliding wear
  • Friction sensing is incorporated for enhanced data interpretation
  • Versatility to simulate in-service conditions

Nano-Fretting Tests on Biomedical Materials

The nano-fretting module has been established as a practical tool for the evaluation of new materials to be used in biomedical implants (Figure 3). Due to flexibility in the applied load and contact geometry, the module can be used to simulate a wide variety of load conditions.

Figure 3. Fretting scars from experiments on uncoated silicon. An increased wear rate is seen in experiments above 120 mN fretting load

large probes and low forces can be used to simulate high cycle low pressure contacts whilst a small probe at high forces can be used to simulate high pressure contacts from particles or single asperities or particles trapped in the implanted joint. Figure 4 illustrates the load dependence of fretting wear on three frequently used alloys in biomedical applications. The SEM images reveal how surface deformation increases with increasing load as well as the limitation of 316L steel to this particular wear.

Figure 4. Load dependence of fretting tests on alloys for biomedical applications.

Friction Measurements During Fretting

The fretting module allows the collection of friction data during wear experiments. The data can then be used to analyze the development of friction in the contacting surfaces as the material begins to wear. Figure 5 displays a typical depth and friction graph from a fretting analysis performed on a thin DLC coating. The graph shows the significant increase in friction following coating failure which corresponds to a change in the wear rate and is observed in the depth signal.

Figure 5. Typical depth and friction data for a fretting test on a thin DLC coating.

This information has been sourced, reviewed and adapted from materials provided by Micro Materials.

For more information on this source, please visit Micro Materials.

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