爆炸焊接界面波物质点法三维数值模拟

基于冲击动力学和爆炸焊接理论,采用物质点法对爆炸焊接界面波的形成进行三维数值模拟。通过数值模拟结果与爆炸焊接实验结果的对比,对复合界面材料的塑性流动变形以及界面波形成的机理进行探讨。结果表明:界面波是因为在碰撞点处的金属材料发生熔化并产生涡旋流动形成的;同时也说明采用物质点法模拟爆炸焊接界面波的形成是可行的。     

合金工具钢的水下爆炸焊接

针对水下爆炸焊接法对超薄、高硬度脆性材料的独特应用特点,开展合金工具钢与铜箔的焊接复合实验。采用高爆速炸药倾斜装药方式,开展实验研究。利用有限元软件ANASYS/LS-DYNA对水下爆炸冲击波驱动飞板的飞行过程进行数值模拟,验证焊接参数合理性。模拟结果显示,飞板与基本碰撞速度沿焊接方向逐渐减小。微观组织观察显示,界面整体表现为爆炸焊接波状形态,呈沿焊接方向逐渐减弱的趋势,与模拟预计结果一致。对焊接实验样品界面处进行显微硬度测试,显示近界面处硬度稍有增加。     

材料强度对爆炸焊接结合界面的影响

为了研究爆炸焊接结合界面机理及材料强度对爆炸焊接的影响，采用相同的爆炸焊接参数对不同强度的基板进行了爆炸焊接。通过光学显微镜、扫描电子显微镜以及数值模拟技术对焊接试样的形貌、缺陷以及焊接机理进行了分析。结果表明:当材料强度较低时，碰撞点动压与基板材料强度的比值较高，界面出现较大的塑性应变并生热，此时界面熔化区较大，在焊接过程中可以将界面等效为不可压缩流体；当材料强度较高而碰撞点动压与基板强度的比值较低时，试样界面形貌受材料强度的影响较大。随着材料强度的上升，周期性的波状界面逐渐趋于平直。界面熔化现象减弱但温升速率较高，并受碰撞点附近高压出现热失稳现象形成剪切带及裂缝。此时材料强度的影响不可忽略，界面不能等效为不可压缩流体。     

爆炸焊接界面波的数值模拟

借助动力学分析软件ANSYS/LS-DYNA 11.0,运用光滑粒子流体动力学方法(SPH方法),建立以Johnson-Cook材料模型和Grüneisen状态方程为基础的热塑性流体力学模型,对同种钢板爆炸焊接界面波进行了数值模拟.结果表明,运用SPH方法可以得到清晰的爆炸焊接界面波形貌.与实验结果的比较表明:模拟误...     

钛/钢复合板爆炸焊接实验

以3mm 厚的TA2钛板和26mm 厚的正火态Q345R为材料,通过爆炸焊接实验,对钛/钢复合板 爆炸焊接的动态参数进行了研究。结合复合板结合界面特征、复合板结合强度(剪切强度)以及界面波的金相 组织,讨论了钛/钢爆炸焊接时获得高强度结合和规则的界面结合波状形态的条件。对于3mm 厚TA2与 26mm厚正火态Q345R,该条件是动态碰撞角17,动态碰撞速度vp760m/s。根据界面波及基板轧制 金相组织形态,分析了形成界面波的机理,认为射流阻碍复板连续碰撞基板是形成界面波的一个主要原因。     

铝-铝爆炸焊接界面的实验研究

对铝-铝同质金属爆炸焊接进行系列实验,研究不同装药比条件下焊接界面的变化特征。所得试件的金相照片表明,焊接界面均具有宏观波状,但其细观形貌又不同于文献报导的连续性波状界面。本次实验得到的三种界面随装药不同而分别呈正弦曲线型、点线型及纯点型,且后两者不再连续。最后利用爆轰波与金属壳表面相互作用理论进行分析,认为焊接界面细观形貌由射流厚度及堆积特征决定,其中界面连续性类似于水流连续性对流量的依赖,当射流厚度不足时难以形成连续界面。     

爆炸焊接驻点近区应变率分布规律计算

为了认识爆炸焊接驻点近区材料的力学和热学行为 ,分析波状界面和绝热剪切带生成 ,采用理想流体对称碰撞模型沿流线研究了驻点近区的应变率分布规律 ,并推导出了驻点应变率的理论计算公式。通过数值与理论计算对爆炸焊接碰撞角、界面距离等因素对应变率的影响进行了讨论。计算结果表明 ,爆炸焊接中强烈变形集中在驻点附近区域 ,其应变率高达 10 6～ 10 7s-1,拉压应变率的绝对值在驻点处达到最大 ;而剪应变在焊接界面上为零 ,其最大值出现在驻点的前方 ,为拉压应变率的约二倍。     

304L/Q235B大面积金属板爆炸焊接物质点法模拟分析

大面积金属板材304L/Q235B的爆炸焊接过程涉及炸药爆轰、金属板材的高速碰撞和塑性变形等。采用有限元法计算模拟这个问题时,网格单元会发生扭曲畸变现象,导致计算精度下降,甚至出现单元负体积而使计算终止,并且炸药爆轰形成气体产物飞散过程也很难模拟。为了能模拟大面积金属板材的爆炸焊接整个过程并获得合理的技术工艺参数,采用物质点法进行三维数值模拟分析。物质点法作为一种无网格法,在模拟冲击动力学问题中主要采用显式积分算法。通过将拉格朗日质点单元与固定的欧拉背景网格相结合,可以实现爆炸焊接的复板与基板的高速碰撞、炸药滑移爆轰、金属板面的塑性变形过程的数值模拟,并给出爆炸复合板材的形变、有效塑性应变和复板与基板的碰撞速度的计算结果。采用物质点法模拟的复合板材变形与爆炸焊接实验结果基本一致。计算复板与基板的碰撞速度这个重要的物理参数时,物质点法与Richter理论公式的相对误差不超过13%。数值计算和实验结果表明,物质点法在数值精度和计算效率方面具有优势,物质点法是研究金属焊接爆炸问题的一种有效数值方法。     

水下爆炸焊接和压实

回顾了水下爆炸在军事海战和经济建设方面的应用,并且探索了水下爆炸在工业方面的发展。结合水下冲击波独特的性能,提出了水下爆炸焊接和水下冲击波压实粉末混合物2种加工方法。焊接试样显微组织中典型的波状界面表明水下冲击波对于脆性和薄片材料具有很好的焊接效果。粉末混合物在水下冲击波加载作用下能形成致密体。利用水下冲击波,在纯铜表面制备出了性能优良的弥散强化涂层。涂层内部弥散颗粒分布均匀,高硬度显示了优良的机械性能。     

表面涂层对非晶薄带爆炸焊接温度影响探讨

针对在非晶薄带爆炸复合制备块体非晶复合材料过程中涂层对温度的影响,提出对非晶薄带实施涂层后再进行爆炸复合。利用放缩法将涂层后的薄带简化为均匀材料,并对30 m厚的Fe78B13Si9非晶涂层前、后爆炸焊接层内温度场进行系列分析计算,表明:(1) 高速撞击产生的热量主要集中在涂铜层上,涂层处理能够显著减小界面撞击引起的热影响区域;(2) 相对于非涂层的非晶爆炸复合,文中方案平均温升降低约280 K;(3) 铜涂层后,碰撞界面冷却速率高达107 K/s。研究表明,具有表面涂层的非晶薄带在爆炸复合制备层合块体非晶复合材料过程中,能够更好地保持非晶材料的非晶结构,并有效扩大爆炸焊接窗口。     

爆炸焊接基复板间隙中的气体冲击波

通过分析研究爆炸焊接基复板间隙中的气体运动,建立了冲击波传播的理论模型,通过理论分析和计算说明了基复板间存在气体冲击波管道效应。管道效应使复合板尾部在爆炸焊接形成前发生上翘,造成板尾部焊接能量偏大,或使尾部炸药压死,是工程中长大复合板尾部焊接质量降低或失效的主要原因。还通过建立简化模型,分析了复合板宽度、各种保护性气体和粗真空对管道效应的影响,说明了选择爆炸焊接保护气体的原则,进而使用氦气保护进行了钛钢、铝镁爆炸焊接实验验证,为气体保护爆炸焊接、真空爆炸焊接技术的进一步开发研究奠定了理论基础。     

Numerical simulation of wave formation in an oblique impact of plates by the method of molecular dynamics

Results of numerical simulations of wave formation in an oblique symmetric impact of metal plates by the method of molecular dynamics are presented. In this case, the impacting plates experience the same loading conditions as in explosive welding. It is demonstrated that the evolution of waves on the interface between the welded plates is caused by self-induced oscillations in the vicinity of the contact point. A mechanism of building-up and sustaining of self-induced oscillations is proposed on the basis of numerical calculations performed.     

过渡层对锆/钢爆炸复合板剪切强度的影响

为了考察钛作为过渡层提高锆/钢复合板结合强度的有效性,同时给出合理的爆炸焊接碰撞参数,对双层锆/钢和三层锆/钛/钢进行了小倾角法爆炸焊接实验研究。借助金相显微技术测量了复合板结合界面的波形参数,采用光滑粒子动力学法模拟得到了不同位置的碰撞速度和碰撞角,并按照国家标准(GB/T 6396-2008)测量了复合板结合界面的爆炸态及退火态的剪切强度。结果表明:钛作为过渡层能够显著提高锆/钢界面的剪切强度;退火消除加工应力后,锆/钢及钛/钢结合面的剪切强度会有所降低;当锆/钛界面的碰撞速度为734~805 m/s,碰撞角为19.8°~20.8°,钛/钢界面的碰撞速度为803~904m/s,碰撞角为19.5°~20.5°时,锆/钛/钢三层复合板的锆/钛和钛/钢界面的剪切强度都能高于140 MPa。     

爆炸法消除焊接接头残余应力的数值模拟

利用非线性动力有限元法对爆炸处理消除焊接接头残余应力的全过程进行了数值模拟。首先，采用温度场与位移场的间接耦合方法计算了钢板对接焊的焊后冷却及残余应力的生成过程，求得焊接接头处由高温冷却到室温由于变形受到阻碍而产生的不均匀的残余塑性变形和应力。然后，在焊缝区引入移动的爆炸载荷，计算了爆炸波作用下该钢板焊接接头附近应力的变化。计算结果表明，爆炸处理可引起板内应力的重新分布，从而有效地释放超过塑性极限的残余应力。利用炸药爆炸消除大型焊接结构残余应力是一种经济有效的方法，本文的数值模拟为研究炸药爆炸消除焊接结构残余应力的机理提供了有力的工具。     

Deformation of liquid line with the collision of jets

With the study of the collision of metallic plates accelerated by an explosion, investigation of plastic deformations in the collision zone is of great importance. In [1] a method is expounded for investigations of deformation with explosion welding under conditions of wave formation; the method consists of the pressing of a thin wire into the metallic plate. With collision of the plates, the flowing metal carries the wire with it; the change in the form of the latter makes it possible to evaluate the character of the plastic deformation in the collision zone. From an investigation of the deformation of the wires, such important characteristics as the viscosity of the metals can be found. The method set forth in [1] is one of the few means of investigating the deformation of metals with high-speed collisions. The difficulties in the investigation are bound up with the small times of the process and with the high pressures, developing with an explosion and demolishing the experimental unit. In [1], from an analysis of viscous flow during the collision of plates, a dependence of the shift on the distance to the interface between the materials, described by a parabola, is derived. It is noted that, near the interface, the theoretical and experimental results differ considerably. It is important to make an attempt at a theoretical analysis of the wire deformation if, with the collision of metallic plates, a jet is formed and the interface between the materials is even. In this case, the flow differs strongly from the flow under conditions of wave formation [2], and near the interface the flow cannot be described by a parabolic dependence; this dependence will probably be exponential. To describe flow with the formation of a jet, in [3] a model of an ideal liquid is employed. Since the analysis of a collision between viscous jets with a free boundary is bound up with serious difficulties, in the first approximation it is advisable to consider the deformation of the liquid line with the deformation of ideal jets.Translated from Zhurnal Prikladnoi Mekhaniki i Tekhnicheskoi Fiziki, No. 6, pp. 65–71, November–December, 1977.The author wishes to express his thanks to N. S. Kozin and V. V. Efremov for a number of valuable observations with an evaluation of the work, and N. M. Maksimova for her aid in making the numerical calculation.     

Shear instability of plastically-deforming metals in high-velocity impact welding

High-speed oblique impact of two metal plates results in the development of an intense shear region at their interface leading to interfacial profile distortion and interatomic bonding. If the relative velocity is sufficient, a distinct wavy morphology with a well-defined amplitude and wavelength is observed. Emergence of this morphology below the melting point of the metal plates is usually taken as evidence of a successful weld. Amongvarious proposed mechanisms, instability owing to large tangential velocity variations near the interface has received significant attention. With one exception, the few quantitative stability analyses of this proposed mechanism have treated an anti-symmetric/shear-layer base profile (i.e., a Kelvin-Helmholtz configuration) and employed an inviscid or Newtonian viscous fluid constitutive relation. The former stipulation implies the energy source for the instability is the presumed relative shearing motion of the two plates, while the latter is appropriate only if melting occurs locally near the interface. In this study, these restrictions, which are at odds with the conditions realized in high-velocity impact welding, are relaxed. A quantitative temporal linear stability analysis is performed to investigate whether the interfacial wave morphology could be the signature of a shear-driven high strain-rate instability of a perfectly plastic material undergoing a jet-like deformation near the interface. The resulting partial differential eigenvalue problem is solved numerically using a spectral collocation method in which customized boundary conditions near the interface are implemented to properly treat the singularity arising from the vanishing of the base flow strain-rate at the symmetry plane of the jet. The solution of the eigenvalue problem yields the wavelength and growth rate of the dominant wave-like disturbances along the interface and confirms that a shear instability of a plastically-deforming material is compatible with the emergent wavy interfacial morphology.