Application of plain fretting test to extract fatigue properties of materials

Abstract

Most structures subjected to fretting fatigue loading are computed using conventional fatigue data. This strategy involves different limitations. Indeed, it requires a large quantity of material to machine the fatigue specimens, the bulk material properties are usually different from the surface ones and above all it does not reproduce the stress gradient generated by contact like fretting fatigue. In this work we consider an original strategy which consists of analysis of the crack nucleation threshold and the crack arrest condition observed on plain fretting test. By computing the test loading state related to these threshold conditions and considering a reverse identification strategy, crack nucleation and crack arrest fatigue properties related to the contact stress configuration can then be extracted.The following methodology has been applied: fretting tests were performed under partial slip condition using a cylinder on plane contact configuration. By plotting the evolution of the maximum crack length as a function of the tangential force amplitude, both crack nucleation condition related to a crack length equal to zero and crack arrest condition related to the maximum crack length observed at the sliding transition have been identified. An analytical contact stress analysis, with plain strain hypothesis, is then performed for both crack nucleation and crack arrest conditions. Afterward, the principal stress for crack nucleation and a fretting stress intensity factor threshold are calculated. Hence fatigue properties representative of the contact stressing condition can be extracted using a very small quantity of material. This strategy is applied to compare three different titanium based composites and discussed regarding conventional fatigue properties.