Study On the Crack Plastic Zone of Bridge Structure Steel and Its Application

In order to study the influence of crack plasticity on crack growth, the shape and size of crack tip plastic zone of bridge steel were calculated by using engineering simplification algorithm, the stress function method and extended finite element method respectively. As a result of the cyclic plasticity of wake field under plane stress and plane strain being different, cyclic plasticity and plastic accumulation of crack tip and wakes were simulated and analyzed by using the discontinuous extended finite element method. The formation of crack tip plastic zone, cyclic plastic zone and the mechanism of compressive stress of wake field were studied. The results showed that the appearances and sizes of plastic zone at the crack tip were proportional to the square of the stress level (the ratio of nominal stress to the yield limit). When the stress level was greater than 0.4, the size of the crack tip plastic zone had to be taken into account the effect of the stress level. The butterfly-shaped crack tip plastic zone symmetrically extended forward, shielding the tensile force of the crack tip high stress field on the wake field, which was beneficial to crack closure. There exists reverse flow of material in plastic zone of crack tip. The compressive stress effect induced by the plastic accumulation on the crack surface was beneficial to the crack closure in advance. Crack closure produced by plasticity had an important influence on the retardation of crack extension in the case of variation load and overload.