A Computer Simulation of Fatigue Crack Propagation Based on Elber's Equation

Abstract

A simpler model than the one which we reported in the previous paper has been proposed to economize the computer time. It is essentially based on the following three assumptions:
(1) When the applied stress range is held constant, the effective stress range ratio U follows Elber's equation, i. e., U=0.5+0.4R, where R is the stress ratio.
(2) When the applied stress varies, there appears a transition period during which the crack opening stress is affected by the previous load. This transition period continues until the cyclic plastic zone formed by the present stress range will pass over the cyclic plastic zone formed by the previous large stress range.
(3) The rate of crack propagation is given by the equation da/dN=C(ΔK_eff)^m, where ΔK_eff is the effective range of the stress intensity factor and C and m are the material constants.
Based on this model, a computer simulation of fatigue crack propagation has been carried out. The summary of the results is as follows:
(1) The model can express the retarding and accelerating effects which appear in the variable amplitude block loading tests. A series of simulation results are in good agreement with the experimental results.
(2) The model can be applied directly to the simulation of the random loading tests.
(3) The model can be applied to the practical problems from the viewpoint of the computer time.