【作者】 刘力力；

【导师】 徐诚； 樊黎霞；

【作者基本信息】 南京理工大学 ， 武器系统与运用工程， 2013， 博士

【摘要】 以某自动步枪身管的径向锻造成形过程为研究对象,针对身管成形过程中涉及的材料性能、工艺过程及成形性能等内容,通过理论分析、数值模拟及试验研究相结合的方法,对身管径向锻造成形工艺过程及成形后的身管材料性能和使用性能进行研究。根据身管冷热径向锻造成形特点,将身管的变形区域分为下沉段、锻造段和整形段三个部分,在考虑应变、应变率及温度对身管毛坯材料流动应力的影响及多角度入口角锤头对成形的影响的基础上,应用主应力法推导出身管冷热径向锻造成形过程中应力分布及锻压力的解析解公式；通过身管冷热径向锻造成形实例中锤头锻压力的解析解计算值与实际测定值的对比,验证了应用主应力法推导出的解析解公式的准确性。应用数值模拟技术建立了某口径自动步枪身管冷径向锻造成形过程的轴对称模型,通过锤头锻压力的数值预测值与实测值的对比,验证了轴对称模型的准确性；根据此轴对称模型,应用正交试验设计法安排模拟过程,通过对模拟结果的方差分析得到了锤头入口角度、断面缩减率、锤头整形段长度、工件轴向进给速度、工件尾端夹持压强5个工艺参数及锤头角度与断面缩减率之间、锤头角度与整形段长度之间、断面缩减率与整形段长度之间3个参数间的交互作用对锤头锻压力、身管与芯棒间压力及身管变形的非均匀性3个成形过程评价指标参数的相对影响程度；并由方差分析结果预测了最小的锤头锻压力、身管与芯棒间压力值及相应的工艺参数组合。基于对受内压产生弹塑性变形的身管进行受力分析,设计了测定径向锻造成形前后身管材料横向力学性能的试验,得到了径向锻造成形前后身管材料的横向力学性能；并根据国家标准GB228-2002《金属材料室温拉伸试验方法》测定了径向锻造成形前后身管材料的纵向力学性能；通过分别对比锻前身管材料横向与纵向力学性能、锻前身管材料横向与锻后身管材料横向力学性能、锻前身管材料纵向与锻后身管材料纵向力学性能,验证了测定身管材料横向力学性能的试验的准确性,得到了冷径向锻造工艺使锻后身管材料强度性能增加、塑性性能降低的影响规律。在身管径向锻造成形过程的轴对称模型的基础上,建立了预测锻后身管内残余应力分布的轴对称模型,得到了锻后身管内沿径向上的径向、轴向和周向残余应力的分布状态；分析了身管的轴向进给速度、摩擦系数、断面缩减率及锤头的形状等成形过程中的全套工艺参数对残余应力分布的影响；应用拟合回归模型法建立了锻后身管内外表面及身管内部残余应力分布拐点处各向残余应力值与其主要工艺参数的拟合回归方程,由拟合回归方程预测了各残余应力的最大值和最小值及相应的工艺参数取值；并通过与相应工艺参数下有限元模拟值的对比,验证了拟合回归方程预测残余应力值的有效性。将盲孔法测定平板表面残余应力的理论应用到径向锻造身管表面残余应力的试验测量中,应用数值方法标定盲孔法的应变释放系数A、B值,通过对比在相同条件下径向锻造身管表面与平板表面的应变释放系数值,得到了当身管外径与钻孔直径的比值D/a≥16时,可应用盲孔法测定径向锻造身管表面残余应力的结论；在此适用范围内,应用盲孔法试验测定了某锻后身管表面的残余应力,并通过直接修正释放系数的方法修正了由钻孔偏心所引起的误差；由试验结果验证了预测残余应力分布的数值模型的准确性。分别建立了计算身管在火药气体压力作用下动态应力及身管内表面轴向和周向裂纹应力强度因子的数值模型,得到了身管按动态应力计算时各向应力的分布状态及身管内表面半椭圆形轴向裂纹的应力强度因子与裂纹形状的关系；在数值模型的基础上,结合对径向锻造成形身管内各向残余应力极值分布状态的预测结果,定量的计算了当身管内由第三强度理论计算的残余应力在极值分布状态时身管的动态应力、身管内周向残余应力在极值分布状态时轴向裂纹应力强度因子的大小及轴向残余应力在极值分布状态时周向裂纹应力强度因子的大小；从而得到了锻后身管内部残余应力分布拐点处及外表面上残余应力的存在不利于身管的动态应力、身管内残余压应力不利于裂纹扩展及残余拉应力有利于裂纹扩展的定性影响规律。更多还原

【Abstract】 The radial forging process of an automatic rifle barrel is the research object of this dissertation.In allusion to the material properties, manufacturing process and formability involved in the forming process of barrel, the radial forging process of barrel, the material properties and the service performance of forged barrel are studied by theoretical analysis, numerical simulation and experimental research.Based on the characters of cold and hot radial forging process of barrel, the deformation region of barrel is divided into the sinking zone, the forging zone and the sizing zone. On the basis of considering the effects of strain, strain rate and temperature on flow stress of barrel blank and the effect of multi-inlet angle die on the forming, the analytical formulae of stress distribution and forging load in the cold and hot radial forging process of barrel are derived by using the slab method; then the accuracy of the analytical formulae is verified by comparing the die forging load calculated by the analytical formulae with the die forging load measured by the test.The axisymmetric model for cold radial forging process of an automatic rifle barrel is established by numerical simulation technology, the accuracy of the axisymmetric model is verified by comparing the die forging load predicted by the model with the die forging load measured by the test; based on the axisymmetric model, the simulations are arranged by the orthogonal experiment method, the relative effects of5process parameters, which are die inlet angle, reduction rate, die land length, axial feed velocity of barrel, champing pressure on the end of barrel, and3interactions between process parameters, which are the interaction between die inlet angle and reduction rate, interaction between die inlet angle and die land length, interaction between reduction rate and die land length, on the3forming indicators, which are die forging load, the load between barrel and mandrel, the deformation in-homogeneity of barrel, are obtained by performing analysis of variance on simulation results; the minimum die forging load, minimum load between barrel and mandrel and the corresponding process parameters values are predicted by the variance analysis results.Based on stress analysis on the barrel which deformed plastically under internal pressure, the test used to determine the tangential mechanical properties of barrel blank material and forged barrel material is designed, the tangential mechanical properties of barrel blank material and forged barrel material are obtained; then the axial mechanical properties of barrel blank material and forged barrel material are measured according to the national standard GB228-2002<Metallic materials——Tensile testing at ambient temperature>:The accuracy of the test used to determine the tangential mechanical properties is verified by comparing the tangential and axial mechanical properties of barrel blank material:by comparing the mechanical properties of barrel blank material and forged barrel material, the influence laws that increasing in strength, decreasing in plastic for forged barrel material by cold radial forging process are obtained, and the anisotropic of forged barrel material is verified.The axisymmetric model for predicting residual stresses distributions in forged barrel is established on the basis of the axisymmetric model for simulating the radial forging process of barrel, the distributions of the radial, axial and circumferential residual stresses along radial direction in forged barrel are obtained; the effects of the axial feed velocity of barrel, friction factors, reduction rate and die shape on residual stresses distributions are analyzed; the regression equations between residual stresses on inner, outer surface of forged barrel, in the middle of forged barrel and the main process parameters are built by the regression model method, then the maximum and minimum residual stresses and the corresponding process parameters values are derived through the regression equations; the validity of the regression equations are proved by comparing the predicted residual stresses with the FE simulated values.The theory of the blind-hole method used to measure surface residual stresses in plate is applied to measure surface residual stresses in forged barrel. The numerical method is used to calibrate the relaxation coefficients A, B values of the blind-hole, by comparing the relaxation coefficients of the blind-hole in the forged barrel and in the plate under the same material, the same force and the same drilling condition, the conclusion that when the ratio of barrel diameter to hold diameter D/a≥16, the blind-hole method can be used to measure the surface residual stresses in forged barrel is obtained; in this applicable range, the surface residual stresses on a forged barrel are determined by using the blind-hole method, and the off-center error is minimized by a method of modifying the relaxation coefficients directly; the accuracy of the numerical model predicted residual stresses distribution is confirmed by the test results.The numerical models used to calculate the dynamic strength of barrel and the axial and circumferential crack stress intensity factor on the inner surface of barrel under the explosive gas pressure are established respectively, the stresses distributions in the barrel calculated in dynamic strength and the relationship between the semi-elliptical crack stress intensity factor and the crack shape on the inner surface of barrel are received; based on the numerical models and combined with the prediction results of residual stresses in forged barrel, when the residual stresses values in forged barrel are extreme, the dynamic strength of barrel, axial crack stress intensity factor and circumferential crack stress intensity factor in the barrel are calculated respectively; so the qualitative influence laws of residual stresses in forged barrel on dynamic strength of barrel and crack stress intensity factor are obtained.更多还原