Fatigue tests on notched specimens of G20Mn5QT cast steel and life prediction by a new strain-based method

Abstract

Fatigue performance of notched specimens of G20Mn5QT cast steel was investigated experimentally and analytically. Fatigue tests on a total number of 22 semi-circular notched specimens were conducted with the load ratios of − 1 and 0.1. Nominal stress-fatigue life relationship was obtained, and mean stress correction rules were verified for the notched specimens based on the test results. A new strain-based approach, strain field intensity (SNFI) method, was proposed, in which fatigue life of materials is predicted based on the weighted average strain in the fatigue damage region. The fatigue lives of the test specimens were predicted using three strain-based approaches, modified Neuber's rule, equivalent strain energy density (ESED) method and the proposed SNFI method. The fatigue life prediction by the SNFI method was in very good agreement with the test results, which verified the rationality and applicability of the proposed SNFI method and also the adopted fatigue properties of G20Mn5QT cast steel. Both the modified Neuber's rule and the ESED method gave conservative prediction of the fatigue life of the notched specimens. The necessity of the 3-dimensional fatigue damage region was also discussed for the proposed SNFI method. Keywords Fatigue life prediction • Strain field intensity method • G20Mn5QT cast steel • Fatigue tests • Notched specimens List of symbols b Fatigue strength exponent c Fatigue plastic exponent E Elastic modulus K ′ Cyclic hardening coefficient K f Fatigue notch factor K t Theoretical stress concentration coefficient n ′ Cyclic hardening exponent N in f