To recreate wear in a laboratory setting, a complicated combination of interrelated properties need to be determined. The objective is that the test provides predictive performance under a specified set of criteria and correlate with end-use performance. However it is both difficult and complicated to develop the test methodology.
Steps to Follow
The steps that need to followed are:
Step 1 – Identify the Purpose of the Test
Before conducting any laboratory test, the first step is to establish the purpose of the test. By formally stating the objectives, one needs to define why one is undergoing the tests. Laboratory tests can offer considerable insight into a number of factors that contribute to the materials performance, and it is easy to become distracted.
Step 2 – Identify the Dominant Wear Mechanism
Careful consideration needs to be given to the wear mode and the wear system in order to generate useful data. The wear system includes the materials that experience the relative movement. The wear mode or modes is established by how the system wears. The identification of the dominant wear mechanism at the start of the test will help ensure meaningful results.
How are the conditions that a product needs to be exposed are determined? In case field failure is studied the surface wear appearance is studied from an actual component. It is possible to match the operating conditions. It is important to remember that there may be several wear modes at the same time and matching conditions in a lab is not perfect normally.
Before moving to the next step it is important to decide which wear mode is highly important. Also be aware of the system output and the wear process products. Simple guidelines are detailed below:
- Input to the wear system
- Mechanical action
- Type of motion
- Contact geometry
- Presence of lubricant or abrasive
- Relative sliding velocity (speed)
- Normal force (load)
- Sliding distance
- Materials that are interacting
- Output of the system
- Heat and/or Friction
- Material removal and/or Wear Debris
The International Standard ISO 6601 (Plastics – Friction and wear by sliding – Identification of test parameters) performs an excellent job determining parameters related to sliding wear on plastics. The parameters are classified into three groups:
- Intrinsic parameters related to the involved materials such as their surface condition, nature and finish. These include bulk properties such as physical characteristics, chemical composition, hardness, mechanical properties and surface properties such as physico-chemical characteristics and roughness.
- External parameters relating to the sliding conditions, such as applied load, sliding velocity, characteristics of the motion, mode of contact, ambient conditions (temperature, humidity), and interstitial substances (lubricant, wear debris).
- Parameters that are based on both the nature of the materials involved and the sliding conditions, particularly surface temperature of the rubbing surfaces.
Step 3 – Select/Establish Testing Methodology
The next step is to select a testing methodology and select a tester. Several industries have established test procedures and recommend instruments that might be used.
It is possible to obtain this data by contacting an industry association, testing lab or an organization such as ASTM International. If a method does not exist or you decide not to follow the industry standard, it is essential to select a test that models the system that needs to be studied. There are a number of widely used instruments to meet this goal and it may be essential to perform initial trials and match the wear mechanism.
A fundamental principal of establishing new abrasion tests is to use the simplest technique first and to stop once the required information is available. Mostly, the additional information that is obtained by studying additional factors does not justify the additional time and cost.
The general methodology for conducting abrasion tests should include some common reporting items in order to generate meaningful results. These include:
- Material documentation
- Statistical significance
- Surface conditions
- Role of time / distance
- Test environment
- Wear Measurement
It is also important to note that by developing a correlation between laboratory test results and field data is difficult and time consuming and may not be necessary in all cases. While it is important to establish a predictive wear model for design and component life estimation, no model is universally satisfactory owing to the many potential factors that could affect wear.
This information has been sourced, reviewed and adapted from materials provided by Taber Industries.
For more information on this source, please visit Taber Industries.