Development of multi-physics numerical simulation model to investigate thermo-mechanical fatigue crack propagation in an autofrettaged gun barrel

In this research,a detailed multi-physics study has been carried out by numerically simulating a solid fractured gun barrel for 20 thermo-mechanical cycles.The numerical model is based on thermal effects,mechanical stress fields and fatigue crack mechanics.Elastic-plastic material data of modified AISI 4340 at temperatures ranging from 25 to 1200℃and at strain rates of 4,16,32 and 48 s^(-1) was acquired from high-temperature compression tests.This was used as material property data in the simulation model.The boundary conditions applied are kept similar to the working gun barrel during continuous firing.A methodology has been provided to define thermo-mechanically active surface-to-surface type interface between the crack faces for a better approximation of stresses at the crack tip.Comparison of results from non-autofrettaged and autofrettaged simulation models provide useful information about the evolution of strains and stresses in the barrel at different points under combined thermo-mechanical loading cycles in both cases.The effect of thermal fatigue under already induced compressive yield due to autofrettage and the progressive degradation of the accumulated stresses due to thermo-mechanical cyclic loads on the internal surface of the gun barrel(mimicking the continuous firing scenario)has been analyzed.Comparison between energy release rate at tips of varying crack lengths due to cyclic thermo-mechanical loading in the non-autofrettaged and autofrettaged gun has been carried out.

The detrimental effect of autofrettage on externally cracked modern tank gun barrels

Overstraining gun tubes has a twofold advantage. First, it enables the increase of the Safe Maximum Pressure(SMP) in the tube, resulting in a higher muzzle velocity which extends the gun's range and its projectile kinetic energy. Second, it reduces the tube's susceptibility to internal cracking which prolongs its fatigue life. Unfortunately, autofrettage also bears an inherent detrimental effect as it considerably increases the tensile hoop stress at the outer portion of the barrel's wall, which enhances external cracking of the tube by increasing the prevailing Stress Intensity Factor(SIF). In order to quantify this disadvantageous effect, 3-D Mode I SIFs distributions along the front of a single external radial semielliptical crack initiating from the outer surface of an autofrettaged modern gun barrel, overstrained by either the Swage or the Hydraulic autofrettage processes, are evaluated. The analysis is performed by the finite element(FE) method, using singular elements along the crack front. Innovative residual stress fields(RSFs), incorporating the Bauschinger effect for both types of autofrettage are applied to the barrel.Hill's [1] RSF is also applied to the tube for comparison reasons. All three RSFs are incorporated in the FE analysis, using equivalent temperature fields, Values for K_(IA)-the SIF resulting from the tensile residual stresses induced by autofrettage are evaluated for: a typical barrel of radii ratio R_o/R_i = 2, crack depth to wall-thickness ratios(a/t = 0.005-0.1),crack ellipticities(a/c = 0.2-1.0),and five levels of Swage,Hydraulic and Hill's autofrettage(e = 40%,60%,70%,80%,and 100%). In total,375 different 3-D cases are analyzed. The analysis demonstrates undoubtedly the detrimental effect of all types of autofrettage in increasing the prevailing effective stress intensity factor of external cracks, resulting in crack initiation enhancement and crack growth rate acceleration which considerably shortens the total fatigue life of the barrel. Nonetheless, the detrimental effect is autofrettage-type dependent. Swage and Hydraulic autofrettage RSFs differ substantially from each other. The disadvantageous effect of Swage autofrettage is much greater than that resulting from Hydraulic autofrettage. The results also emphasize the significance of the Bauschinger effect and the importance of the 3-D analysis.

Thermo-Mechanical Analysis of Water-Cooled Gun Barrel During Burst Firing

The thermo-mechanical stress and deformation of water-cooled gun barrel during burst firing are studied by finite element analysis (FEA). The problem is modeled in two steps: 1) A transient heat transfer analysis is first carried out in order to determine temperature evolution and to predict the residual temperatures during the burst firing event; 2) The thermo-mecha- nical stresses and deformation caused by both the residual temperature field and the gas pressure are then calculated. The results show that the residual temperature field tends to a steady state with the increasing of rounds. The residual temperature field has much effect on the gun barrel stress and deformation, especially on the assembly area between barrel and water jacket. The gage between the barrel and water jacket is the critical factor to the thermo- mechanical stress and deformation. The results of this analysis will be very useful to develop the new strength design theory of the liquid-cooled gun barrel.

Analysis of Heat Transfer in Actively Cooled Compound Gun Barrel

when a gun fires, a large amount of heat is brought in the barrel. Erosion/wear and security problems(self ignition of the propellant) associated with this high thermal energy have to be solved owing to the use of higher combustion gas temperature for improved cannon performance and firing at the sustained high rates. Barrel cooling technologies are the effective measures for addressing this issue. In view of the importance of having knowledge of the heat flux, an approach to calculate heat flux based on measurements was presented and validated. The calculated heat flux is used as the inner boundary condition for modeling heat transfer in a 155 mm mid-wall cooled compound gun barrel. Theoretical analysis and simulated results show that natural air cooling is dramatically slower than the forced liquid mid-wall cooling, accordingly wear life of actively cooled barrel is increased and barrel overheating is prevented.

Quantitative Testing of Defect for Gun Barrels

The magnetic flux leakage (MFL) method is commonly used in the nondestructive evaluation (NDE) of gun barrels. The key point of MFL testing is to estimate the crack geometry parameters based on the measured signal. The analysis of magnetic leakage fields can be obtained by solving Maxwell’s equations using finite element method (FEM). The radial component of magnetic flux density is measured in MFL testing. The peak-peak value, the separation distance between positive and negative peaks of signal and the lift-off value of Hall-sensor are used as the main features of every sample. This paper establishes the multi-regression equations related to the width (the depth) of crack and the main characteristic values. The regression model is tested by use of the magnetic leakage data. The experimental results indicate that the regression equations can accurately predict the 2-D defect geometry parameters and the MFL quantitative testing can be achieved.

Tribology of rotating band and gun barrel during engraving process under quasi-static and dynamic loading

The engraving process of a projectile rotating band is one of the most basic research aspects in interior ballistics,which has not been thoroughly understood thus far.An understanding of this process is of great importance from the viewpoints of optimal design,manufacturing,use,and maintenance of gun and projectile.In this paper,the interaction of copper and nylon rotating bands with a CrNiMo gun barrel during engraving was studied under quasi‐static and dynamic loading conditions.The quasi‐static engraving tests were performed on a CSS‐88500 electronic universal testing machine(EUTM)and a special gas‐gun‐based test rig was designed for dynamic impact engraving of the rotating bands.The mechanical behaviors of copper and nylon were investigated under strain rates of 10^(−3) s^(−1) and 2×10^(3) s^(−1) using an MTS 810 and a split Hopkinson pressure bar(SHPB),respectively.Morphologies of the worn surfaces and cross‐sectional microstructures were observed with scanning electron microscope(SEM)and optical microscope(OM).It was found that large deformation and severe friction occur during engraving.The surface layer is condensed and correlated with a hardness gradient along the depth from the top worn surface.The structure of the rotating band and gun bore,band material,and loading rate have great effects on band engraving.The flow stress‐strain of the copper strongly depends on the applied strain rate.It is suggested that strain rate and temperature play significant roles in the deformation mechanism of rotating bands.

Vibration characteristics analysis of tank gun barrel with nonuniform cross-section

The firing accuracy of a tank gun is affected significantly by the flexural motion of the barrel.For the purpose of satisfying the requirement of efficiently and accurately dynamic analysis and optimization of the tank gun barrel to ensure it has good dynamic characteristics and firing accuracy,the high-fidelity dynamic model of a tank gun barrel is developed according to the transfer matrix method for multibody system which has features of high degree of stylization and high computational speed.The transfer matrix of the non-uniform Euler-Bernoulli beam(NU-EB beam)is deduced from governing differential equations of motion utilizing the differential transform method.The orthogonality of augmented eigenvectors for the NU-EB beam is proven which can be used for its exact dynamics response analysis using the modal method.In allusion to the tank gun barrel with non-uniform cross-section,the barrel is modeled as a combination of several uniform and non-uniform transverse vibrating Euler-Bernoulli beams.The overall transfer equation and matrix of the tank gun barrel are established according to the automatic deduction theorem of the overall transfer equation of multibody system.The present method is proven to be effective by comparing the computational results to those in published literatures.The vibration characteristics of a tank gun barrel with a non-uniform cross-section are analyzed accurately and are verified by the modal test.

基于射击时机的坦克射击门分析及改进

针对坦克的射击门控制逻辑,分析现有射击门在坦克高速行进条件下在射击时机判断上的不足,提出基于预测机制的射击门改进方法,该射击门在考虑射击时延和炮口切向速度影响的情况下,去除了身管必须满足进入简单射击门的角度约束,可更大限度地把握有效射击时机,数字仿真结果验证了改进射击门的优越性。

主成分分析和灰色模型组合的身管多点烧蚀磨损量预测

身管是火炮类武器的关键零件,对其烧蚀磨损量进行预测,有助于保持火炮作战效能。针对火炮身管沿轴向各点烧蚀磨损量需分别建立数学模型进行预测问题,提出一种组合烧蚀磨损量预测方法。采用主成分分析(principal component analysis,PCA)方法对身管多点烧蚀磨损量进行数据空间降维,提取反映烧蚀磨损量变化的主成分,利用灰色模型对主成分进行多步预测,通过PCA逆运算获得身管内膛多点烧蚀磨损量预测值。结果表明,在历史数据较少的条件下,通过选择合适的预测步数可获得较为准确的预测值,为身管内膛多点烧蚀磨损量的预测提供了一种新的有效途径。

枪管用环保镀层摩擦行为研究

传统枪管内膛表面采用的六价铬镀层,高温耐磨性好,但对环境污染严重。为开发环保镀层,采用超景深三维显微镜、扫描电子显微镜表征了室温和高温(400℃)摩擦磨损试样,对比分析了六价铬、三价铬、钴-镍和镍-钨四种电镀层的磨损特征。研究结果表明:在500℃定性回火后,三价铬、镍-钨、六价铬和钴-镍镀层硬度依次递减,与六价铬层相比,三价铬层脆性大,镍-钨和钴-镍镀层韧性高;室温下与H62黄铜对摩后,六价铬和三价铬镀层摩擦程度较轻,钴-镍和镍-钨镀层呈现明显粘着特征,二者摩擦系数高于两种铬层;400℃下与08Al钢对摩后,六价铬呈粘着磨损特征,摩擦程度较大;三价铬层摩擦系数相对较高;镍-钨镀层呈磨粒磨损特征,摩擦系数与六价铬接近,摩擦程度相对较轻。

基于身管应变的小口径火炮弹丸速度测试方法

针对传统火炮弹丸速度测试方法中存在难以获取整条速度曲线、易受环境影响、体积庞大、成本较高、操作复杂等问题,提出了一种基于身管应变的小口径火炮弹丸速度测试方法。基于30 mm口径火炮设计了应变测试仪,实现身管外壁应变测试。根据厚壁圆筒理论计算得出火炮膛压曲线,通过弹底压力解算模型得出弹底压力曲线,与弹载存储测试方法得到的弹底压力曲线进行对比。结合弹丸运动方程得出弹丸速度曲线,采用四阶龙格库塔算法建立弹丸速度仿真模型,将应变测试、弹载存储测试得到的弹丸速度曲线与仿真曲线进行对比。结果表明:应变测试、弹载存储测试与仿真弹丸速度曲线趋势基本吻合,最大速度误差分别为1.1%和0.5%,验证了应变测试方法的可行性,为小口径火炮弹丸测速开辟了新途径。

发射不同被甲材料弹头各向异性身管膛内应力状态

为研究某小口径步枪发射过程中身管膛内的应力场与温度场,建立弹头膛内运动时期弹头/身管相互作用的精细热力耦合有限元模型,其中考虑了温度对身管与被甲材料力学性能的影响以及枪管钢力学性能的各向异性。仿真获得覆铜钢被甲弹头和铜被甲弹头挤进运动规律与身管膛内应力状态变化。研究结果表明:被甲材料的不同对挤进过程有很大影响,钢被甲弹头挤进阻力大于铜被甲,相应地前者膛内应力也大于后者;身管不同轴向位置处应力分布规律不同,坡膛处内膛应力最大值在阳线导转侧,膛口处内膛应力最大值在阴线上。研究结果为优化弹头/枪管匹配提供了支持。

基于PSD的火炮身管膛线精度测量数据补偿方法

针对火炮身管内部膛线测量技术及自动检测问题,提出一种精度测量数据补偿方法。搭建火炮内膛检测机器人测量系统。采用激光测距仪对火炮身管阴阳线内径进行测量,使用PSD激光位置传感器对火炮身管轴线与测量系统轴线的偏心距离进行测量,分析检测误差产生的原因,推导基于矢量三角法的测量数据精度补偿算法和误差补偿计算公式,通过补偿前后数据的对比分析,结果表明:该测量补偿方法是有效的,能够解决火炮内膛轴线与机器人旋转中心不重合产生误差的问题。

模块装药短管炮实验及数值模拟研究

大口径加榴炮主要以模块装药结构为主,炮管内部流场复杂。基于模块装药结构,对短管炮内部燃烧场分区域建立二维轴对称两相流内弹道数理模型,采用MUSCL格式对该模型进行离散求解,编制程序对短管炮膛内流场进行了数值模拟,研究两模块装药结构在燃烧过程中的膛内流场特性以及不同破膜压力对两模块装药结构膛内燃烧的影响。仿真结果表明:与实验值相比,计算获得的膛内压力全局平均误差约为7.42%,峰值误差仅0.72%,说明所建立的内弹道数学模型与编制的程序能够较好地对两模块装药火炮发射过程进行数值模拟。模块药盒对火焰波的传递有阻碍作用,在模块药盒破裂之前,火焰波与压力波主要在模块内部流动,与外界物质交换较少。模块药盒破碎后,火药颗粒才随着压力波向膛内自由空间运动,火焰波和压力波开始在膛内传递。随着模块药盒破裂压力的增大,模块装药膛内发射药燃烧越充分,压力上升时间减少。点火药燃气从传火孔处向周围区域扩散,膛内温度也从传火孔处开始升高,逐渐向四周传导,从而点燃发射药。

不同环境温度下身管钢的摩擦机理研究

轻武器、火炮身管在服役过程中受到火药燃气和弹丸的高温摩擦作用而产生磨损,导致内膛形貌发生变化和身管寿命的降低。为揭示身管材料的高温摩擦磨损机理,采用PCrNi3MoV身管钢与H90黄铜球配副,在200、400、600℃的环境温度下,使用UMT-3型摩擦磨损试验机进行了摩擦磨损试验并开展了机理分析。采用三维白光干涉表面形貌仪、XRD、SEM、EDS等设备对磨痕表面及断面的形貌、结构和成分进行了分析。研究结果表明:由于温度的增加会导致黄铜球塑性变形加重从而增加摩擦接触面积,磨损过程中压入身管钢表面深度加深,导致摩擦力增大,氧化物层下的基体发生剧烈的塑性变形,摩擦系数会随着温度的升高而增大。但是身管钢的磨损率呈现出随着温度升高先增大再降低的规律,这与在不同温度下身管钢和黄铜的强度变化以及氧化物层的厚度有关。

基于YOLOv5算法的炮管内壁污渍识别与定位技术

为准确评估炮管内壁的清理情况,采用YOLOv5人工神经网络结合机器视觉对清理后的155mm口径炮管内壁的污渍进行实时检测。考虑到污渍主要分为油污与残留的铜渍2种,在检测任务中通过图像识别技术分别对污渍进行种类识别、定位以及对污渍面积判定;利用图像像素信息与外部环境信息,基于单目摄像头采集的视频图像,采用改进并训练后的YOLOv5人工神经网络模型作为识别工具对炮管内壁进行实时图像识别。实验结果表明:该检测系统能较好地完成目标检测任务,对目标定位误差控制在5 cm内,满足炮管内壁自动清理中的内壁污渍定位要求。

火炮身管疲劳断裂试验和数值模拟研究

烧蚀磨损和疲劳是影响火炮身管寿命的主要因素,前者使内膛表面产生了随机的烧蚀坑或微裂纹,形成了大量的应力集中区,在疲劳作用下,微裂纹沿身管径向由内向外扩展形成宏观裂纹,一旦其深度达到临界值,继续发射则可能导致身管断裂。针对身管疲劳断裂问题,根据火炮发射过程中载荷作用特点,自主设计了液压冲击疲劳试验装置,在实验室条件下再现了身管服役条件下的疲劳断裂现象。试验结果表明:冲击载荷作用下,身管疲劳断口包括裂纹源、扩展区和瞬断区3个部分,扩展区呈现典型的“海滩条纹”特征;身管外壁面周向应变的演化规律与裂纹的扩展速率变化规律之间存在内在的映射关系,从而可为身管健康监测、发射安全性评估提供新的技术手段。数值模拟采用J-C方程描述炮钢材料的动态本构关系,将材料的应变率效应纳入仿真计算过程中,模拟结果与试验结果之间具有较好的一致性。

基于应变的火炮身管健康监测和剩余寿命评估的可行性研究

火炮发射过程中产生的烧蚀磨损和疲劳使身管性能逐渐衰退直至不能使用,更为严重的是,时而发生的膛炸事故对人员生命和武器装备安全构成威胁,身管发射安全隐患始终存在。传统的身管寿命评估方法,包括基于尺寸、图像、温度和初速变化来预测身管剩余使用寿命的方法,尚不能科学、准确地评估身管健康状态和剩余使用寿命。针对该问题,在深入分析身管内膛损伤物理机制的基础上,提出以发射时身管外壁面应变为损伤特征参数的身管健康监测方法,揭示了应变与弹丸-身管-发射药系统之间的内在映射关系,阐释了该方法的基本原理以及如何用于评估身管剩余使用寿命。火炮实弹射击数据和数值模拟结果均证实了该方法的科学性、可靠性和实用性。

基于激光圆周扫描和定心修正的火炮身管内膛检测方法研究

火炮身管内膛的状态直接影响着火炮的射击精度和安全性,针对目前激光圆周扫描检测方法存在的定心不准、激光束与管壁垂直度差等现状所导致的检测精度不高的问题,提出一种基于激光圆周扫描的通用口径火炮身管内膛检测定心修正算法。通过校正管道和装置上的姿态传感器完成检测装置轴线与校正管道轴线的平行。修正装置根据定心修正算法完成激光位移传感器旋转轴线与校正管道轴线的重合以及激光束与管壁的精确垂直,完成身管内膛深度特征的精确测量。该修正算法及装置对于提高火炮身管检测精度和效率,研究身管剩余寿命和健康监测有着重要的理论意义和实用价值。

射击过程中火炮身管发热的简便计算及其影响分析

针对火炮身管设计中精确计算身管温度变化的问题,提出一种身管吸收热量的简便算法。对身管射击中的能量转换作了简要分析,以某科研产品身管数据进行验证,分析身管发热的影响,介绍身管烧蚀寿命以及烧蚀寿命终止标准,冷却措施以及提高身管寿命措施。实验结果表明:该算法切实可行,可为身管设计提供参考。