Study On The Influence Of The Strain Rate On The Stress And Strain Concentration Of The Metal Orifice Plate

Metal perforated plate structures are widely used in engineering fields.Under the action of the far-end load,the stress and strain concentration will occur at the root of the hole,which will lead to the generation of cracks and reduce the bearing capacity and fatigue life of the metal orifice plate.Therefore,the research on the stress and strain concentration of perforated plates has always been a key topic in the field of structural safety assessment.For the stress and strain concentration of linear elastic perforated plates subjected to quasi-static loads,the existing researches have given more comprehensive and accurate results and have been widely applied.However,a large number of structures in engineering need to bear dynamic loads.For metal perforated plate structures,the material strain rate effect caused by dynamic load often has a significant influence on the numerical result and spatial distribution of stress and strain concentration at the root of the orifice,resulting in the results based on quasi-static linear elasticity no longer being applicable.Therefore,in order to solve this problem,two typical steels,45 steel and LYP225 steel,are selected as research objects in this paper.The strain rate effect of stress and strain concentration in metal perforated plates is studied by means of experiments and numerical simulation analysis.The main research contents and results are summarized as follows:(1)For LYP225 steel,the quasi-static and dynamic tensile tests of LYP225 steel are carried out by using a 20-ton microcomputer-controlled electronic universal testing machine and INSTRON VHS 80/20 high-speed testing machine of British Instron Company.The stress-strain curves of LYP225 steel at different tensile speeds were obtained,and the material parameters in Johnson-Cook model were fitted according to the experimental data.(2)The JC damage model was used to study the effect of different speeds on the fracture properties of LYP225 steel.The reliability of JC model of LYP225 steel established in this paper is verified.(3)Using ABAQUS simulation software,the strain rate effect of stress and strain concentration in perforated plate is numerically analyzed.Under the strain rate range of 0.01~100/s,the effects of elliptical shape factor,thickness and distal loading strain on the stress and strain concentration distribution of 45 steel and LYP225 steel were studied.With the increase of strain rate,the stress and strain concentration coefficients of 45 steel increase and decrease sharply respectively.When the strain rate reaches 20/s,the stress and strain concentration coefficients increase at a constant speed and tend to stabilize respectively.The stress and strain concentration coefficients of LYP225 steel first decrease and increase sharply respectively.When the strain rate reaches 5/s,the stress and strain concentration coefficients remain unchanged.When the strain rate continues to increase to 80/s,the two increase at a uniform speed respectively.Based on the above research,the Johnson-Cook constitutive model of LYP225 steel in the strain rate range of 0.01~100/s is established.The reliability of the JC model of LYP225 steel is verified.The effect of strain rate on stress and strain concentration of 45 steel and LYP225 steel perforated plate is revealed.The results obtained in this paper provide theoretical and technical support for future research on dynamic stress and strain concentration under plastic stage.