Analysis of Influencing Factors of Fatigue Crack Propagation of Q960D High Strength Steel
In order to study the fatigue crack growth behavior of Q960D high-performance steel(HPS),the effect of several key parameters on the fatigue crack growth was numerically analyzed by using CT compact tensile specimens.The fatigue crack growth length,cycle numbers and stress intensity factor based on the numerical simulation were compared with the experimental data,and it was found that the established finite element model had a good agreement.The relationship between the number of cycles and the crack propagation length,and the corresponding stress intensity factors were obtained by combining the fracture mechanics theory and contour integral.The effects of loading,stress ratio,sample thickness,crack depth ratio,initial crack angle,and corrosion pits on the stress intensity factors during the crack growth process of the HPS were revealed.The results show that the crack growth rate become greater as the load is higher.With the increase of stress ratio and thickness,the crack growth rate decreases,but the fatigue life increases.It is easier to fracture when the rack depth ratio is higher.More attention should be paid to the effective crack length in engineering practice.The initial crack angle of 46° is a critical angle of the crack stress intensity factor mutation.When the initial crack angle is 0°,the crack tip stress is the largest and fracture is most likely to occur.In the case of corrosion pit,the K value around the corrosion pit gradually decreases along the thickness direction,and the crack tip around the corrosion pit will first reach the yield state,accelerating the fatigue fracture of the test piece,and finally leading to the reduction of life.
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