Investigation on fretting fatigue crack initiation of IN718 alloy in very high cycle regime

Abstract

The objective is to investigate the characteristic of crack initiation in Inconel 718 alloy (IN718) under very high cycle fretting fatigue (VHCFF) conditions. Experimental data and microscopic analysis were used to examine the fatigue performance and microstructure of IN718 at room temperature (RT) and 650 °C. Additionally, a crystal plastic finite element model (CPFEM) was developed to simulate fretting contact, and a multiaxial fatigue damage parameter was established by considering parameters such as the total dislocation density, grain elastic modulus, and equivalent grain size. The findings indicate that the depth of fretting wear increases with the number of fatigue cycles for the same level of cyclic loads. However, when different orders of magnitude of fatigue cyclic loads are applied, the axial load becomes the determining factor in fretting wear. The crack initiation is primarily attributed to the cleavage fracture of relatively large facets. Crack initiation is likely to take place in grains exhibiting a higher Schmid factor in the activated slip system, a larger equivalent grain size, and a reduced elastic modulus.