Strength Analysis Of Large Caliber Autofretted Barrel Based On The Finite Element Method

Barrels’ fatigue invalidation occasionally occurred in modern guns with large calibre,high power, extended firing range and high chamber pressure and may even cause seriousaccidents in service. So it is very important to study the thermo-mechanical couplinganalysis, the distribution of the autofrettage residual stress and invalidation mechanism ofa large calibre gun. Thus, we select a155mm autofretted barrel as the object of the research.The main contents of this paper are as follows:①Do research on the residual stresscontribution of Autofretted barrel, mainly focusing on the point of the impact on residualstress derived from the gun steel’s Bauschinger effect by ABAQUS.②Calculate thetemperature field and thermal stress distribution of the gun barrel under thecircumstance of continuous shots by using ABAQUS.③Illustrate the application offracture mechanics when designing gun barrel, apply finite element simulationmethod and weight function method to calculate the stress intensify factors of thegun barrel, and exert ALOF(Analyses Laboratory of Fracture) to stimulate theexpanding pattern of the cracks on the gun chamber and comprehensively analysesthe fracture strength of the gun barrel. The major innovative points and main results ofthis paper are as follows.（1）The gun steel’s Bauschinger effect（σ_Ε=1.4338σ_s）is more obvious thanmodel of the linear kinematic hardening（σ_Ε=2σ_s）. Material models given in theABAQUS can not express the impact on residual stress derived from the gun steel’sBauschinger effect. In this paper the loading model and unloading model, which truthfullydepicted the linear hardening and Bauschinger effect during unloading process byredefining the plastic parametric of material, have been established. Computationalresults are well coincided with the theoretical value and the related documents.（2）The results of autofrettage residual stress are regarded as the pre-stress field ofthe thermo-mechanical coupling analysis model. The transient temperature field andthermal stress distribution of the gun barrel, which considered the residual stress and heatshock, were obtained by ABAQUS during continuous shots. The numerical results showedthat the further radial gaps depart from the inner wall, the lower and more smoothtemperatures increase. Moreover, the temperature field and thermal stress distributionof the gun barrel present periodical pulse changes during continuous shots.Temperature, mises stress and temperature gradient of determining position increase with the addition of firing rounding numbers. But it tends to be very gentlewhen reaching to certain shots. The peaks of transient temperature and thermal misesstress can reach to1100.0K and1041.0MPa respectively within1.0mm of the barrel bore.（3）The stress intensity factors of the cracks on the gun chamber’s inner surface arecalculated by using finite element analysis method. To investigate the crack propagationprocess, ALOF has been introduced to simulate the propagation of the cracks. The resultsbased on the simulation show that the stress intensity factors increase with the elongation ofthe size of cracks. The mainly characteristic is that longitudinal cracks propagate frominterior to exterior along the radial of the barrel. The barrel will break and lose efficacywhen the size of the crack reach to the critical value. Simultaneously, the stress intensityfactors caused by the autofrettage residual stress is negative, and it combines the stressintensity factors caused by the chamber pressure, the fatigue life of the barrel will beeffectively improved.The results of all the studies provide significant scientific supports for thereinforcement of the gun barrel’s strength and reliability, also for precisely definingits fatigue life.