Due to the importance of small fatigue cracks, many researchers at home and abroad have carried out extensive research on the fatigue cracks of various important components.
Huang believes that structural integrity assessment based on probabilistic fracture mechanics should accurately characterize the dispersion of fatigue crack growth behavior of materials. In his research work, ten groups of crack propagation tests of superalloys were carried out under the same conditions. According to the statistical results of experimental data, the fatigue crack growth behavior of gh420li is dispersed to a considerable extent. In the same Δ The crack growth rate (DA / DN) at k follows a lognormal distribution. According to the random number generation principle of lognormal distribution variables, a random crack propagation model based on mean value and coefficient of variation (COV) is derived. Since the average value of in (DA / DN) and cov can be expressed as a function of M, the random crack growth rate is determined by and standard normal distribution random variables. Finally, the random model is used to calculate the fatigue crack growth of compact tensile specimens. The comparison between the prediction results and the experimental results proves the effectiveness of the proposed model.
Corts. R evaluated the fatigue and crack growth behavior of incone and AL6XN alloys combined with ernifecr-2 filler by gas tungsten arc welding. The whler curves of monolithic IN718 and AL6XN alloy dissimilar welded joints were compared. Although the Vickers microhardness curve shows that there is a soft zone in the heat affected zone of 1n718 matrix material, the fatigue crack nucleates in the fusion zone near AL6XN and propagates on the weld. Although there is no mixing at the AL6XN / weld metal interface, the welded joint and AL6XN base material still have similar high cycle fatigue behavior. The fatigue crack growth test results show that the weld metal has the highest growth rate due to the existence of brittle second phases (such as Laves and NBC). The measured results of the fatigue crack growth rate obtained from the experimental data and the distance between the stripes on the crack surface are compared, and they are very close.
In the research work of Li and Jian, considering the plastic deformation degree at the crack tip, the fatigue crack growth behavior of commercial pure titanium (cp Ti) under different load levels was studied. The results show that there are great differences in the stages of stable crack propagation under different loading conditions. At the same crack growth rate, when the crack growth rate is low, the strain energy and plastic zone under high load ratio are higher than those under low load ratio. However, when the crack growth rate is high, the difference between the strain energy and plastic zone between the two loading conditions is much smaller. Under high load amplitude, more plastic strain energy will be consumed, and greater plastic deformation at the crack tip is required. it seems that Δ K and Δ J can not describe these phenomena, but proposed Δ J α C (it may be more suitable to describe these phenomena on the fracture surface. Under different loading conditions, the fracture morphology is pit in the later stage of crack propagation. The data under all conditions follow the Paris law and use parameters in the rapid growth stage Δ J α C has the same coefficients and indices.