Strain-controlled thermomechanical fatigue testing of EN-GJL-250 for automotive brake disc application

Abstract

In an automobile braking system, the heating and cooling cycles that take place on the brake disc surface during braking action lead to thermomechanical fatigue (TMF). TMF, a type of non-isothermal fatigue, occurs when a material experiences simultaneous mechanical and thermal loads. Based on a material’s elastic and plastic deformation, the strain-life technique of fatigue analysis calculates how many TMF cycles a material will withstand before failing. However, it is challenging to effectively recreate the TMF process using conventional testing methods due to the cyclical changes in temperature, stress, and strain. So, in the current situation, all TMF life projections are based mostly on isothermal condition because low-cycle fatigue (LCF) data, which is normally used for design purposes, has been created isothermally. In the present work, a reliable test procedure is adopted to measure the TMF behavior of cast iron grade EN-GJL-250. The novel testing procedure closely resembles the field’s cyclical patterns of temperature and mechanical strain, in addition to online monitoring of the TMF cycles. The testing procedure complies with ISO 12111, ASTM E2368, and the European Code of Practice (CoP). The TMF behavior of EN-GJL-250 was characterized by hysteresis loops and cyclic stress-strain responses. Designers can use test data to help them simulate component behavior and validate current designs through numerical simulations.