Damage Tolerance Design And Crack Propagation Analysis For Autofrettaged Gun Barrel

With the large caliber gun barrel for research object, the gun barrel heatstructure coupling field and influence of Bauschinger effect on residual stress ofautofrettaged gun barrel was simulated and analyzed by ABAQUS and ALOFsoftware based on fatigue fracture theory. Studied the stress intensity factor’schange rule of thick wall cylinder which under static loading and the influence ofthermal stress on different initial shape crack’s propagation. Estimated the criticalcrack size and residual fatigue life of the gun barrel which under cyclic loadingaccording to damage tolerance design theory. The primary work and remarks of thepaper are as follows:(1) The heat conduction process of a large-caliber artillery firing is simulatedusing the one-dimensional two-phase flow interior ballistic model and theone-dimensional tube transient heat transfer model, by which the transienttemperature field and thermal stress distribution of the barrel champer of a155mmgun are calculated by ABAQUS after twenty shots. The results show that: Thermalshock of bore has the obviously thin layer effect, during continuous shooting thebore instantaneous temperature can up to1350K. Gun tube wall generate hightemperature gradient along the radial and form high pulse heat stress.(2) Based on ABAQUS, this paper analyzed the gun barrel residual stress fielddistribution under several conditions. Compared the difference of the barrelresidual stress field between ideal elastic-plastic model and linear strengthen andBauschinger effect model. Study of the influence of loading strengthen coefficientm and unloading strengthen coefficient m’ on residual stress field of theautofrettaged gun barrel. Research shows that: The strain hardening of the material,especially the Bauschinger effect has great influence on the gun barrel residualstress. The influence of loading strengthen coefficient on the residual stress field ofthe autofrettaged gun barrel is far less than unloading strengthen coefficient whenother parameters are the same. The more m’ is smaller, the more modulus of thebarrel tangential residual stress is smaller. The best autofrettage force of the barrelis obtained since the maximum equivalent stress take the minimum value, and the modulus of the maximum tangential stress take minimum value. Take the bestautofrettage force for620Mpa after integrating.(3) Based on ABAQUS and ALOF software, calculated the stress intensityfactors of the barrel under internal pressure. The calculation results quite well withliterature data. Using ABAQUS analyzed the influence of different crack size anddifferent initial barrel temperature on stress intensity factors under the action ofthermal stress. To research the crack propagation rule of different initial shapecrack, analyzed the crack stress intensity factors of the bore. Results show that:Surface crack tip in radial direction generate negative stress intensity factor underthermal stress, and as the crack size increases, the modulus of stress intensity factorfirst increases and then decreases, however, as the barrel temperature increases, themodulus of stress intensity factor decreases. With different shapes of the initialcrack, the shape ratio trend to a_certain range in propagation process.(4) Based on damage tolerance design theory, considering linear strengthenand Bauschinger effect, calculated critical crack size is7.92mm and residualfatigue life is936shoots of the autofrettaged gun barrel using literature data. Theresults show that: Fatigue life of the autofrettaged gun barrel is far more thanordinary gun barrel.This research is significant to secure gun barrel safety and avoid disastrousaccident.