| The extractor is an important component of breech extraction mechanism,and work under large stress in the extraction process.The fatigue crack is found in the extractor.The crack will extend in continuous operation,even the extractor will be broken.The study on the fatigue crack propagation life of the extractor is very important to ensure the reliability of the shell pulling mechanism and the combat effectiveness of the naval gun.In this paper,a gun breech mechanism is taken as the research object.This extraction forceforce is analyzed in theory.The fracture toughness and crack propagation rate of gun steel were studied by experiment.The extractor crack propagation rules and the fracture formula of extractor material was obtained,combined with XFEM.Influence factors of crack extension extractor were studied.Firstly,the fracture mechanism of extractor were analyzed.Based on the analytical expressions of fatigue crack propagation equation and the growth rate equation,the factors affecting fatigue crack growth rate are analyzed.The factors is from the ability of the material to resist crack propagation and the load applied to the specimen or structure.The relation curves of stress ratio,fracture toughness,parameter C and parameter m,crack growth rate and stress intensity factor are obtained.The experimental research and engineering application of fatigue crack propagation rate was also proposed.Secondly,fracture toughness KIC test was done in this paper.By using three point bending specimens,fracture toughness of 45 CrNiMoVA materials were studied.The fracture mechanical properties of the material were obtained.The results show that the fracture toughness of45 CrNi MoVA material is 73.2155MPa·m1/2.The fatigue crack growth rate test for 45 CrNiMoVA material was done at room temperature.This test used CT samples and obtained the relationship between the fatigue crack growth rate and the number of repeated loading.The relationship between the crack growth rate and the stress intensity factor is determined.The Paris formula for calculating the crack propagation life of 45 CrNi MoVA material is established.Based on the elastic-plastic mechanics,the extraction force between the bore and the cartridge case are calculated.Combined with flexible body dynamics method,the extractor are analyzed in the ABAQUS;The dangerous part of the extractor and the stress value were found out.The extractor was simplified as plate structure with edge crack,crack tip stress intensity factor was calculated by XFEM.Compared with the theoretical calculation,the feasibility of the method is verified,and the relationship between the stress intensity factor range and the crack length is plotted.At last,the evaluation method of the crack propagation life of the extractor is established.Bas-ed on the Paris fracture formula,the crack propagation life of the extrator is estimated.Based on XFEM method,the crack propagation simulation of the extrator was done;The effects of loading conditions and crack characteristics on crack propagation life were studied. |
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