Study Of Damage Evolution For 304 Stainless Steel And 42CrMo Steel Under Ratchetting-fatigue Interaction

The damage of material or component during cycling is one hot problem that always be concerned by engineers and researchers.For the study of damage,the primary problem is to select a proper damage variable to describe the damage state of material.Recent years,many research results of damage-revolution about monotonic tension,strain-controlling low-cycle fatigue and stress-controlling high-cycle fatigue have been obtained.But it is still rare for the study of ratchetting-fatigue interaction damage under asymmetric stress-controlling cycling.In this paper,the ratchetting-fatigue damage revolution during asymmetric stress-controlling cycling has been studied for three kinds of materials,which are cyclic hardening 304 stainless steel,cyclic stability annealed 42CrMo steel and cyclic softening tempered 42CrMo steel.This paper mainly contains following parts:1.The damage variable was defined by the decline of elastic modulus.Then,the features of damage evolution were researched for various cyclic characteristics materials(cyclic hardening,cyclic stability and cyclic softening).It was revealed that the influence of mean stress and stress amplitude on damage.2.According to elastic modulus,the damage evolution characteristics of 304 stainless steel,annealed 42CrMo steel and tempered 42CrMo steel under multi-axial ratchetting-fatigue interaction were discussed respectively.The influence of loading path,stress amplitude and mean stress on the damage were analyzed different material under multi-axial non-proportional loading.3.According to the characteristics of three kinds of materials under uniaxial asymmetric loading condition,a new damage evolution model considering ratchetting-fatigue interaction was established based on the superposition of ratchetting damage and fatigue damage.This model can correctly reflect the influence of mean stress on the damage.It can embody the difference of critical damage between ratchetting failure and fatigue failure too.In most traditional fatigue damage models,the accurate fatigue life is necessary,which is hard to know without a completed fatigue experiment.In this model,this flaw is avoided and the fatigue life in fatigue damage is estimated from strain-life relationship.Furthermore,the damage model is easy to apply in engineering for its simple form and easy-measured variables.