Thermomechanical Fatigue Life Prediction of Lamellar Graphite Cast Iron Brake Disks Using Advanced Material Models and Elastic-Plastic Fracture Mechanics

A comprehensive thermomechanical fatigue (TMF) life prediction methodology is developed for cast iron brake disks. The approach employs transient temperature fields as thermal loads in a nonlinear structural finite-element analysis (FEA). To obtain reliable stress and strain histories for cast iron, a time- and temperature-dependent plasticity model is required that captures viscous effects, nonlinear kinematic hardening, and tension–compression asymmetry. For this purpose, a unified elasto-viscoplastic Chaboche constitutive model coupled with damage is developed and implemented as a user material subroutine (UMAT) in the general-purpose FEA software Abaqus by Dassault Systèmes. In addition, a mechanism-based short-crack TMF model is extended to three-dimensional stress states under transient non-proportional loading conditions for TMF life prediction. The material parameters of the constitutive and the damage models are identified for lamellar graphite cast iron using isothermal and non-isothermal uniaxial test data. The proposed methodology is applied to two cast iron brake disks to predict TMF life. Results show that life predictions based on the developed methodology, combined with the short-crack growth model, correlate well with experimentally observed test results from two bench tests in terms of both crack location and cycles to observed short-cracks. Finally, the methodology is further extended using elastic–plastic fracture mechanics to perform crack-growth simulations, enabling prediction of crack paths and cycles to through-thickness failure.