FATIGUE-CRACK GROWTH-RATE OF METAL BY PLASTIC ENERGY DAMAGE ACCUMULATION THEORY

The fatigue crack growth phenomenon is analyzed by means of postulated damage accumulation theory herein. By considering the plastic compone nt of J integral as a damage factor, the proposed damage accumulation theory successfully leads to a simple formula for the fatigue crack gr owth rate. This formula covers all three regions of the fatigue crack growth rate and shows a high potential in future application to differ ent groups of materials. This research yields the following results: ( 1) The crack growth rate is not simply a function of DELTAK, but a fun ction of average local yielding strength, fracture toughness, and ampl itude of the applied effective stress intensity factor in regions II a nd III; (2) the behavior of the fatigue crack growth rate (FCGR) near the threshold value is found to be dominated by maximum value of appli ed effective stress intensity factor instead of its amplitude; (3) the onset instability value of DELTAK(c) is a specimen geometrical-depend ent parameter; and (4) the average yielding local strength has a signi ficant influence on the threshold value, K(th) that cannot be ignored when one studies the problem of the crack growth properties in region II. Test data reported were compared with the proposed formula and wer e found to be in reasonably good agreement.