Numerical Simulation Of Fatigue Crack Closure Behavior Under Constant Amplitude And Overload

Large mechanical structures and components such as aerospace,ships,rail vehicles and pressure vessels are often subjected to complex alternating loads,and micro-cracks will appear in the places of stress concentration and structural weakness.Under the action of alternating load,the microcracks begin to extend and propagate continuously,thus forming macroscopic cracks.Macroscopic cracks are a great threat to the safety and life of structures,and are prone to catastrophic accidents of low stress brittle fracture,resulting in heavy casualties and property losses.The phenomenon of fatigue crack closure occurs in the crack propagation process,and is one of the important factors affecting the fatigue crack growth law under constant amplitude and variable amplitude loading.The premature closure of the crack will have a great impact on the stress-strain field near the crack tip,reducing the amplitude of the stress intensity factor at the crack tip,and reducing the rate of fatigue crack growth.However,In the field of actual engineering,when predicting the remaining life of cracked parts and judging the state of crack growth,it is often easy to ignore the existence of the crack closure effect.Therefore,studying the influence of the crack closure effect on the growth of fatigue cracks is of great engineering practical significance and economic value for accurately assessing the remaining fatigue life of equipment and ensuring the safe operation of large mechanical equipment within the expected design life.The main contents of this paper are as follows:(1)This article systematically discusses the current research status of fatigue crack growth and crack closure in constant amplitude loading and analyzes related theories to lay a solid foundation for subsequent research.(2)Using large-scale finite element software ABAQUS to perform twodimensional elastoplastic analysis of compact tensile specimens of Q345 R material,through the joint debonding technology,simulate dynamic fatigue crack growth under constant amplitude loading,and explore the effects of crack length,stress ratio,and maximum loading load on the fatigue crack closure/opening load.The results show that the maximum loading load and crack length have little effect on crack closure.As the stress ratio increases,the crack opening load increases,but the closing effect weakens.(3)The finite element method simulates the fatigue crack growth behavior under a variety of variable amplitude loads,explains the hysteresis behavior of fatigue cracks after overload based on the plastic-induced crack closure theory,explores the influence of overload ratio and stress ratio on the crack hysteresis effect,and finally studies the double overload peak and the influence of the interaction between tensile overload and compressive load on crack growth.The results show that with a single overload,the overload hysteresis effect increases as the overload ratio increases,while the stress ratio increases,the overload hysteresis effect weakens.The double-peak overload can effectively strengthen the crack closure effect,and the compression load has the inhibitory effect on the overload hysteresis effect.