Avaliação da resistência à fadiga de aços avançados de alta resistência para aplicação em componentes de segurança veicular

Abstract

This work evaluated the fatigue behavior of advanced high-strength steels (AHSS) aimed at the manufacture of vehicle safety components, with a focus on low-cycle fatigue behavior under axial strain control. For this purpose, three Dual Phase steels (DP780P, DP780M, and DP780S) and two Transformation Induced Plasticity steels (TRIP780 and TRIP1000) were evaluated through: i) determining the fatigue strength coefficient and exponent (σf′ and b), the fatigue ductility coefficient and exponent (εf′ and c), and the cyclic strength coefficient (H′) and cyclic strain-hardening exponent (n′); ii) verifying the occurrence of cyclic hardening or softening; and iii) conducting fractographic analyses of the fracture surfaces after the fatigue tests. The methodology included manufacturing the specimens (CPs), performing fatigue tests under axial strain control, in a fully reversed regime, with strain amplitudes ranging between 0,2 % and 1 %, in accordance with ISO 12106 (ISO, 2017), followed by processing the experimental data and conducting fractographic analyses by scanning electron microscopy on the fracture surfaces of the CPs. The results obtained showed that: i) DP780S presented low-cycle fatigue performance slightly superior to DP780M and TRIP780, followed by DP780P and, lastly, TRIP1000; ii) DP780P exhibited cyclic hardening for strains above 0.4 %, DP780M showed cyclic hardening over the entire strain range analyzed, and DP780S exhibited mixed behavior, whereas TRIP780 presented cyclic softening in the range between 0.2 % and 0.4 % and cyclic hardening for strains above 0.4 %, and TRIP1000 exhibited cyclic softening over the entire strain range analyzed; and iii) fractographic analyses revealed the recurrent presence of secondary microcracks in all steels, with more difficulty in identifying fatigue striations in the TRIP steels than in the DP steels.