A Systematic Study for Fatigue Life Prediction of Grey Cast Iron Disc Brakes

摘要

Disc brakes are mainly manufactured in grey cast iron because of its good thermal conductivity, low thermal expansion, and last but not least low costs. The materials used in this study were the lamellar grey cast irons GG-15 and GG-25. Tensile/compression tests, resonance frequency measurements, expansion tests at temperatures up to 900℃ were conducted at first. The results of these tests gave a closed picture of relevant material properties over a wide temperature range. The failure/damage mechanism under isothermal and thermal fatigue loadings was studied by strain controlled LCF and temperature controlled TF tests. Quantitative life predictions were made by applying Neuber's notch analysis i.e. grey cast iron was considered as an internally notched steel and compared to wrought steels of comparable structure. Even at temperatures up to 500℃ life prediction is in very good accordance with reversals to failure ascertained by our LCF tests and those of other investigators. Finite element (FE) analyses was applied to the problem of thermal fatigue. Commercial FE codes cannot accurately simulate the ratcheting (defined as the accumulation of deformation with cycles) response recorded in TF tests. To overcome this deficiency, an improved cyclic plasticity model must be incorporated into FE material model subroutines.