Q235's Fracture Properties Study Under Extra-low Cycle

Under the subsidy of the talents project fund of Gansu Province and academic step & characteristic study of Lanzhou University of Technology, more useful theoretic foundation in order to prevent or utilize fatigue break more effectively was obtained by fatigue break analyzing to common metallic material Q235, especially finite element simulating to its crack growth direction and studying of multiple regression to calculate the parameters of crack growth.Firstly, on the basis of the mechanical analysis, analytical expression to the stress and displacement field of plain crack and V-notch were analyzed, and the stress intensity factor (SIF) and fracture criterion of the crack and V-notch were discussed. Secondly finite element analysis (FEA) method to solve fatigue break was introduced.FEA to Q235's axial fatigue break properties was studied. It was found by the stress nephogram analysis that the maximal stress of V-notch column sample only exist at tip where the V-notch lies and this will do good to Q235's regular fracture. Then appropriate notched parameters to tensile-pressural regular fracture of Q235's V-notch sample was obtained by fatigue break analysis making use of ANSYS software andthey are: notch angle a=60°, tip radius of notch r=0.2mm, notch depth t=0.12D.Crack growth path was simulated by element death-birth module of ANSYS software under extra-low cycle (N_f ≤100). First all element in the module was set to be alive (active element), then element is alive or killed was decided by stress nephogram analysis of ANSYS, the element which crack growth pass through was translated into killed element (inactive element). Crack growth direction of V-notch column sample under tensile-pressural loading was found by means of simulating the crack growth path side by side analyzing the distribution of Von Minses equivalent stress of the V-notch sample, the result shows crack growth direction of the sample under tensile-pressural loading is diametral direction of circle where the V-notch lies.Statistical analysis to fatigue breaking law was studied. The multiple regression method to calculate the parameters of crack growth was set up by using empirical formula of crack growth as regression function. The fatigue crack growth formula of Q235's box-shape section girder sample which under simulative loading was obtained by using this method and it is .