强激光辐照下纯铝动力学响应和层裂的数值模拟

采用改进的损伤度函数模型,该模型将材料损伤断裂看作为一种典型的逾渗过程,根据逾渗临界准则,采用应力松弛函数来描述损伤后期微损伤之间的连通效应,考虑了损伤对材料本构的影响,对纯铝在强激光辐照下的动态力学响应和层裂破实验进行了数值模拟。通过高斯分布激光脉冲压力加载,计算分析了激光与样品相互作用。计算结果表明：损伤演化明显地改变了材料力学响应以及样品中波传播特性,计算较精确地再现了实测自由面速度随时间的变化过程。根据计算结果分析了损伤演化过程,485 μm厚样品中损伤的分布主要集中在距离样品后界面100 μm 范围内,具有明显的损伤局部化特征,最大损伤值为11.2%。     

强激光辐照下纯铝的力学响应和层裂的实验测量与分析

采用速度干涉（VISAR）测试技术,对强激光辐照下纯铝的动态力学响应和层裂特性进行了实验测量和分析。样品厚度分别为200 μm 和485 μm,激光脉冲的半高宽约为10 ns,功率密度变化范围为1010~1011 W·cm-2。实测了样品自由面速度波形,反映了强激光加载作用下材料损伤演化过程以及损伤对材料动态响应的影响。计算得到了冲击波强度(2.0~13.4 GPa) 和不同拉伸应变率下铝的层裂强度(1.6~2.3 GPa)。在所采用的实验条件和1维近似下,激光辐照产生的冲击波强度与激光功率密度之间成线性关系。最后讨论了层裂强度与拉伸应变率之间的关系,显示层裂强度随着拉伸应变率的增加而增大。     

冲击加载下LY12铝合金的动态屈服强度和层裂强度与温度的相关性

采用可测量任意反射表面的速度干涉仪对LY12铝合金在不同初始温度条件下的动态屈服与层裂行为进行了实验研究，温度范围从室温到接近熔化温度.实验结果显示：LY12铝合金的动态屈服强度随着温度升高而快速下降，当初始温度为847K (比熔化温度低86K) 时，其屈服强度仅为室温下的15％，层裂强度也随着温度升高而减小，在296—847K的实验温度范围内，层裂强度损失80%.通过实验结果与模型估算值的比较，发现Zerilli-Armstrong (ZA) 模型可以对LY12铝合金的动态屈服强度与温度的相关性进行较好 关键词： 温度相关性 LY12铝合金 动态屈服强度 层裂强度     

强激光辐照下纯铝动力学响应和层裂的数值模拟

 采用改进的损伤度函数模型,该模型将材料损伤断裂看作为一种典型的逾渗过程,根据逾渗临界准则,采用应力松弛函数来描述损伤后期微损伤之间的连通效应,考虑了损伤对材料本构的影响,对纯铝在强激光辐照下的动态力学响应和层裂破实验进行了数值模拟。通过高斯分布激光脉冲压力加载,计算分析了激光与样品相互作用。计算结果表明：损伤演化明显地改变了材料力学响应以及样品中波传播特性,计算较精确地再现了实测自由面速度随时间的变化过程。根据计算结果分析了损伤演化过程,485 μm厚样品中损伤的分布主要集中在距离样品后界面100 μm 范围内,具有明显的损伤局部化特征,最大损伤值为11.2%。     

Construction of homogeneous loading functions for elastoplastic damage models for concrete

Over the past 2 decades, tight restriction has been imposed on strength criteria of concrete by the combination of plasticity and damage in one theory. The present study aims at constructing plastic/damage loading functions for elastoplastic damage models for concrete that can perform more satisfactorily in 3D stress states. Numerous strength criteria of concrete are reorganized according to their simplest representations as Cartesian, cylindrical, mixed cylindrical-Cartesian, and other forms, and the homogeneity of loading functions discussed. It is found that under certain supplementary conditions from physical meanings, an unambiguous definition of the cohesion in a strength criterion, which is demanded in an elastoplastic damage model, is usually available in an explicit or implicit form, and in each case the loading function is still homogeneous. To apply and validate the presented theory, we construct the respective homogeneous damage and plastic loading functions and implant them into some widely used elastoplastic damage models for concrete, and their performances in triaxial compression prove to have improved significantly.     

Interfacial debonding and slipping of carbon fiber-reinforced ceramic-matrix composites under two-stage cyclic loading

In this paper, the interface debonding and frictional slipping of carbon fiber-reinforced ceramic-matrix composites (CMCs) under two-stage cyclic fatigue loading have been investigated using micromechanics approach. Under cyclic fatigue loading, the fiber/matrix interface shear stress degrades with increasing cycle number due to interface wear. The synergistic effect of interface wear and fatigue loading sequence on interface debonding and frictional slipping has been analyzed. Based on the fatigue damage mechanism of fiber slipping relative to matrix, in the interface debonded region, upon unloading and subsequent reloading, the interface debonded length and interface slip lengths, i.e. interface counter-slip length and interface new-slip length, are determined using the fracture mechanics approach. The relationships between interface debonding, interface slipping, interface wear, cycle number, and different loading sequences are determined. There are two types of fatigue loading sequences considered, i.e. (1) cyclic loading under low peak stress for N₁ cycles, and then high peak stress; and (2) cyclic loading under high peak stress for N₁ cycles, and then low peak stress. The effects of peak stress level, interface wear, cycle number, and loading sequence on interface debonding and frictional slipping of fiber-reinforced CMCs have been analyzed. The fatigue hysteresis loops of cross-ply carbon fiber-reinforced silicon carbide composite corresponding to different cycle number under two-stage cyclic fatigue loading have been predicted.     

强激光辐照下纯铝的力学响应和层裂的实验测量与分析

 采用速度干涉（VISAR）测试技术,对强激光辐照下纯铝的动态力学响应和层裂特性进行了实验测量和分析。样品厚度分别为200 μm 和485 μm,激光脉冲的半高宽约为10 ns,功率密度变化范围为10¹⁰~10¹¹ W·cm^-2。实测了样品自由面速度波形,反映了强激光加载作用下材料损伤演化过程以及损伤对材料动态响应的影响。计算得到了冲击波强度(2.0~13.4 GPa) 和不同拉伸应变率下铝的层裂强度(1.6~2.3 GPa)。在所采用的实验条件和1维近似下,激光辐照产生的冲击波强度与激光功率密度之间成线性关系。最后讨论了层裂强度与拉伸应变率之间的关系,显示层裂强度随着拉伸应变率的增加而增大。     

Influence of boundary structure and near neighbor crystallographic orientation on the dynamic damage evolution during shock loading

The role of crystallographic orientation on damage evolution in ductile metals during shock loading has been investigated. By utilizing large-grained copper specimens, it has been shown that the development of intragranular damage, in the form of void growth and coalescence, is influenced by the grain orientation with respect to the applied load. Additionally, strain incompatibility and the inability to promote transmission or activation of secondary dislocation slip across a grain boundary, are proposed as the likely cause for intergranular failure. Finally, the free surface velocity profiles of each grain, specifically the decay of the oscillations after the pull-back, correlated well with the amount of damage measured within the respective grain.     

Fatigue damage behavior of a surface-mount electronic package under different cyclic applied loads

This paper studies and compares the effects of pull-pull and 3-point bending cyclic loadings on the mechanical fa- tigue damage behaviors of a solder joint in a surface-mount electronic package. The comparisons are based on experimental investigations using scanning electron microscopy （SEM） in-situ technology and nonlinear finite element modeling, respec- tively. The compared results indicate that there are different threshold levels of plastic strain for the initial damage of solder joints under two cyclic applied loads; meanwhile, fatigue crack initiation occurs at different locations, and the accumulation of equivalent plastic strain determines the trend and direction of fatigue crack propagation. In addition, simulation results of the fatigue damage process of solder joints considering a constitutive model of damage initiation criteria for ductile materials and damage evolution based on accumulating inelastic hysteresis energy are identical to the experimental results. The actual fatigue life of the solder joint is almost the same and demonstrates that the FE modeling used in this study can provide an accurate prediction of solder joint fatigue failure.     

激光辐照超音速气流下TA15钛合金和LY12铝合金的热响应

利用超音速气流环境模拟装置,开展了自然对流和马赫数为3切向气流下,1064nm连续激光辐照TA15钛合金和LY12铝合金热响应实验研究,得到了材料在两种条件下的温升曲线及熔穿时间。结果表明:在激光辐照材料未使得其表面发生熔化前,气流对材料激光辐照过程中的冷却效应较为明显,在表面发生熔化时,熔化的液态物质在气流切向力剥蚀作用下被吹离材料表面,使得激光继续作用在材料上,熔化→剥离→熔化→剥离如此反复,可加速熔穿过程;此外,切向气流将影响钛合金这类热扩散系数较低材料的温度场分布,使得气流下游处的温度高于上游,而对铝合金这类热扩散系数较高的材料而言,影响不明显。     

激光辐照超音速气流下TA15钛合金和LY12铝合金的热响应

利用超音速气流环境模拟装置,开展了自然对流和马赫数为3切向气流下, 1064 nm连续激光辐照TA15钛合金和LY12铝合金热响应实验研究,得到了材料在两种条件下的温升曲线及熔穿时间。结果表明：在激光辐照材料未使得其表面发生熔化前,气流对材料激光辐照过程中的冷却效应较为明显,在表面发生熔化时,熔化的液态物质在气流切向力剥蚀作用下被吹离材料表面,使得激光继续作用在材料上,熔化剥离熔化剥离如此反复,可加速熔穿过程;此外,切向气流将影响钛合金这类热扩散系数较低材料的温度场分布,使得气流下游处的温度高于上游,而对铝合金这类热扩散系数较高的材料而言,影响不明显。     

An improved model of damage depth of shock-melted metal in microspall under triangular wave loading

Damage depth is an important dynamic parameter for describing the degree of material damage and is also a key fundamental issue in the field of impact compression technology. The present work is dedicated to the damage depth of shock-melted metal in microspall under triangular wave loading, and an improved model of damage depth considering the material's compressibility and relative movement is proposed. The damage depth obtained from the proposed model is in good agreement with the laser-driven shock loading experiment. Compared with the previous model, the proposed model can predict the damage depth of shock-melted metal in microspall more accurately. Furthermore, two-groups of the smoothed particle hydrodynamics(SPH) simulations are carried out to investigate the effects of peak stress and decay length of the incident triangular wave on the damage depth, respectively. As the decay length increases, the damage depth increases linearly. As the peak stress increases, the damage depth increases nonlinearly, and the increase in damage depth gradually slows down. The results of the SPH simulations adequately reproduce the results of the proposed model in terms of the damage depth. Finally, it is found that the threshold stress criterion can reflect the macroscopic characteristics of microspall of melted metal.     

Initial damage induced by thermal residual stress and microscopic failure analysis of carbon-fiber reinforced composite under shear loading

In order to study the mechanical properties and the progressive failure process of composite under shear loading, a representative volume element (RVE) of fiber random distribution was established, with two dominant damage mechanisms – matrix plastic deformation and interfacial debonding – included in the simulation by the extended Drucker–Prager model and cohesive zone model, respectively. Also, a temperature-dependent RVE has been set up to analyze the influence of thermal residual stress. The simulation results clearly reveal the damage process of the composites and the interactions of different damage mechanisms. It can be concluded that the in-plane shear fracture initiates as interfacial debonding and evolves as a result of interactions between interfacial debonding and matrix plastic deformation. The progressive damage process and final failure mode of in-plane shear model which are based on constitute are very consistent with the observed result under scanning electron microscopy of V-notched rail shear test. Also, a transverse shear model was established as contrast in order to comprehensively understand the mechanical properties of composite materials under shear loading, and the progressive damage process and final failure mode of composite under transverse shear loading were researched. Thermal residual stress changes the damage initiation locations and damage evolution path and causes significant decreases in the strength and fracture strain.