Microstructure sensitivity of fretting crack nucleation for ferretic-pearlitic steel

Ferrite-pearlite steels are used in many fretting applications, including railway tracks and flexible marine risers. Fretting-induced relative slip and contact width is typically at the same length-scale as key microstructural features in these materials. Previous work has shown the statistical significance of average grain size in fretting crack initiation for a CoCr alloy [1]. The material investigated here contains two distinct phases. The distribution of these phases in the contact zone may be crucial in the fatigue behavior of the material, along with other potentially important microstructural attributes, such as crystallographic texture. A crystal plasticity (CP) computational framework is developed to assess the microstructure sensitivity of ferrite-pearlite steel in fretting fatigue. The microstructure of the material is characterized using optical microscope and SEM techniques to facilitate the generation of realistic micromechanical finite element geometries with respect to grain size, grain shape, and phase volume fractions via a weighted Voronoi tessellation approach. A physically based material model [2] is implemented to describe the micromechanical behavior of the material. Mechanical cyclic test data is employed to calibrate and validate a representative volume element model to identify CP parameters for the material. A 3D fretting contact model, which incorporates the calibrated CP material model and microstructure geometry in the contact zone, is then employed to investigate microstructure sensitivity in fretting fatigue. Fretting wear tests are conducted to identify coefficient of friction for this model set-up. A study is performed to assess the significance of phase distribution and texture in crack initiation. A scale-consistent fatigue indicator parameter strain energy dissipation W is implemented to predict number of cycles to crack initiation. The capability of this parameter to predict crack location and wear scars is also investigated, following previous micromechanical fretting work [3].