Much depends on the application. Some applications require low friction (such as bearing materials), while others require high friction (such as braking systems). For most applications, minimal wear of the material is the primary objective. For many applications, the defined advantages between low friction levels and good wear properties are often targeted.
When designing experiments to describe friction and wear, tribological tests can be placed in one of six main categories, ranging from field tests in one category to laboratory model tests in the sixth category.
Category I: Field tested under normal operating conditions, which may include extended operating conditions. This results in poor repeatability but is close to the realistic requirements that tribological systems will face.
Category II: Experiment with complete equipment in a factory environment. These experiments can achieve results close to normal operating conditions and can be performed over some time to replicate extended operating conditions while reducing environmental impact.
Category III: Components, subsystems, or assemblies are tested in the laboratory near-normal extended operating conditions with moderate repeatability.
Category IV: Laboratory testing using scaled-down test equipment.
Category V: Experiments are performed on samples with test equipment to provide near-normal operating conditions with excellent repeatability.
Category VI: Bench testing using simple laboratory test equipment.
Importantly, in the first to third categories, the system structure of the original friction body needs to be consistent, only the collective pressure is simplified. Categories II and III provide more repeatable collective pressure than Category I. In contrast, in categories IV to VI, the system structure is simplified, with the disadvantage of reducing the transferability of test results to the predictability of comparable real tribotechnical systems. Categories IV to VI offer better sub-friction contact metrology, lower cost, and more stringent test times;1 Therefore, with ascending test categories, test times, as well as test costs, increase significantly, but test results are transferable Sex has also increased.