Shape-instability life scatter prediction of 40Cr steel: Damage-coupled crystal plastic probabilistic finite element method

Disposable mechanical elements, which are widely used in spacecrafts, undergo fracture primarily via shape-instability failure. A cyclic crystal plasticity model based on the probabilistic finite element method is developed with the aim of predicting the shape-instability lifespan. In the model, a two-dimensional (2D) finite element model is established, based on the Voronoi tessellation, to simulate the morphology of the microstructure measured during electron backscatter diffraction of 40Cr steel. A damage-coupled cyclic crystal plasticity model is used to describe the mechanical behavior and material degradation. In addition, the material properties described by a stochastic distribution are randomly generated and then assigned to the elements in the 2D model in order to simulate the heterogeneity of the material. The validity of the prediction model is revealed through a comparison of the simulation and experimental results. Furthermore, the sensitivities of the control parameters, such as the element size, variance of the stochastic distribution, and morphology of the microstructure, are determined. The presented model allows the determination of the shape-instability lifespan of disposable mechanical elements. This model accurately predicts, and hence negates the need for many measurements of, the lifespan and therefore has significant potential for use in an appropriate field.