The use of equivalent estimation designs in tribological studies

Abstract

Tribological experiments in which friction is examined as a function of multiple factors often involve some factors whose levels are harder to change than others. For example, changing the temperature in a test setup usually is more time consuming than changing the sliding speed or the contact pressure. In such cases, it is preferable to rearrange the runs in the experiment in a way that minimizes the number of changes of the factor levels that are hard to change. This restricts the randomisation of the experiment and leads to a split-plot structure. A new class of split-plot designs called equivalent estimation designs has properties which seem to be well suited for use in tribological studies. This paper compares the performance of these designs to two commonly used designs (a completely randomised three level factorial design and a one-factor-at-a-time experiment) in a tribological example study. The results show that using equivalent estimation designs in tribology can deliver results that are similar to those of conventional designs while requiring just a fraction of their effort.