Research On Fracture Prediction Model Of Ductile Metal Considering The Dispersibility Of Material Mechanical Properties

Ductile metals have the characteristics of low density,high strength,good processing performance and excellent welding performance,and are widely used in high-end equipment such as aviation equipment and high-speed trains.With the rapid development of China's high-end equipment,people have put higher and higher requirements on the accuracy and reliability of the performance parameters of ductile metal materials.This thesis takes Q235 B steel,5005 aluminum alloy and 7075-T6 aluminum alloy as the research objects,and conducts research on the physical mechanism and prediction model of ductile fracture.The main research contents are as follows:(1)An analytical model for predicting the yield strength and fracture toughness of ductile metallic materials is proposed.Based on the experimental data of the fracture test of 5005 aluminum alloy and Q235 B steel,by analyzing the plastic zone of the crack tip during the ductile fracture of the metal,a formula for calculating the fracture strength with the size of the plastic zone was established;combined with the normal distribution theory,a reliable fracture was established The prediction model can predict the distribution range of material tensile strength and fracture toughness.The model can be used to predict the yield strength and fracture toughness of metallic materials using small-sized tensile specimens,effectively solving the large size of the test specimen and the harshness of the sample surface roughness in the linear elastic fracture theory(LEFM)claim.(2)A finite element model with different initial cracks was established through ANSYS simulation analysis.A simulation study was carried out on the size of the crack tip plastic zone and the stress distribution of the 7075-T6 tensile specimens with different slit width ratios at break,and the effects of the initial crack size and the size of the crack tip plastic zone on the fracture of ductile metal were studied.Through the finite element model,the size of the crack tip plastic zone can be preliminarily determined,which provides a basis for further experiments to verify the fracture prediction model proposed in this paper.(3)The rationality and adaptability of the metal ductile fracture prediction model proposed in this paper are verified by analyzing the test data of 7075-T6 tensile specimens with different slit width ratios.Under different machine limit factors,the comparative analysis of the test data of the three materials Q235 B steel,5005 aluminum alloy and 7075-T6 aluminum alloy shows that the test machine has a relatively large limit on the sample.The appropriate machine limit factor will directly determine the fracture prediction Reliability and accuracy.Based on the large area of plastic deformation of the crack tip during ductile fracture of the metal,the size of the plastic zone of the crack tip has a great influence on the fracture prediction results.Through experimental analysis,it is found that the yield strength and fracture toughness values obtained by considering the larger plastic zone at the crack tip are more accurate than those obtained by considering the smaller plastic zone.