无氧铜层裂的实验与数值研究

利用一级气体炮对国产的无氧铜（OFHC）进行了平板撞击致层裂实验,3 mm厚的OFHC飞片撞击6 mm厚的OFHC靶,采用锰铜应力计记录试样/有机玻璃（PMMA）界面附近的应力历史,获得试样发生层裂的信息。软回收试样,观测回收试样的层裂片。采用基于空穴聚集的层裂模型,数值模拟这些平板撞击致层裂实验。数值模拟的应力剖面以及试样层裂片厚度与实验结果基本一致。此外,对于国外相关的OFHC层裂实验,采用基于空穴聚集的层裂模型也作了相应的数值模拟,并进行了比较。     

纯铁材料的冲击相变与"反常"层裂

采用VISAR、X射线衍射和金相处理联合测试分析技术,开展等厚对称碰撞实验,研究了纯铁材料的冲击相变与层裂行为特征。结果发现,冲击加载压力大于纯铁材料相变阈值(13 GPa)时,等厚对称碰撞样品发生反常2次层裂。结合相关文献的实验结果,从应力波相互作用的角度分析了反常层裂形成的原因,指出纯铁材料的冲击相变和卸载逆转变及引发的稀疏冲击波是导致反常2次层裂的物理机制。     

冲击相变对FeMnNi合金层裂行为影响研究

通过逆向加载和等厚对称碰撞实验相结合的方法,确定了FeMnNi合金完整的加卸载物理过程和相变层裂特征。采用修正的Boettger模型与非平衡两相相变理论模型,成功模拟再现了实验过程,解释了冲击相变、卸载逆相变及稀疏冲击波形成的物理机理。实验和数值模拟相结合,从应力波相互作用的角度定量分析了层裂发生的原因,指出层裂发生的机制正是由于受载样品发生了冲击相变和卸载逆相变。      

Influence of Phase Transition on Spalling Behavior in FeMnNi alloy

通过逆向加载和等厚对称碰撞实验相结合的方法,确定了FeMnNi合金完整的加卸载物理过程和相变层裂特征。采用修正的Boettger模型与非平衡两相相变理论模型,成功模拟再现了实验过程,解释了冲击相变、卸载逆相变及稀疏冲击波形成的物理机理。实验和数值模拟相结合,从应力波相互作用的角度定量分析了层裂发生的原因,指出层裂发生的机制正是由于受载样品发生了冲击相变和卸载逆相变。     

一种基于空穴聚集的层裂模型

基于如下假设，给出了层裂过程中的应力松弛方程，并建立了一种基于空穴聚集的延性层裂模型:在层裂早期，微空穴的主要效应是减小应力作用面积；在层裂后期，应力按空穴聚集时的应力-空隙度依赖关系减小。把P.F.Thomason、D.L.Tonks等及S.Cochran等给出的依赖于应力（压力）的层裂空隙度方程分别耦合于守恒方程、计及损伤的状态方程及本构方程，建立了求解所有变量包括损伤的封闭方程组。这种基于空穴聚集的层裂模型已被应用于一维层裂试验的数值模拟。模型中的层裂强度及临界损伤度初始可以估计，最终的确定将使数值模拟结果与实测的速度（或应力）剖面以及观测的层裂面上的损伤基本一致。分别基于D.L.Tonk等及S.Cochran等给出的依赖于压力的层裂空隙度方程所作的一维层裂试验数值模拟结果基本一致，而与基于P.F.Thomason给出的依赖于应力的层裂空隙度方程所作的相应数值模拟结果有明显差异。     

低相变阈值金属高压加载下的相变层裂特性

采用激光速度干涉仪（VISAR）和X光联合测试技术,在冲击压力远高于相变应力加载下,实验研究低相变阈值金属FeMnNi合金的相变层裂特性,结果发现等厚对称碰撞加载下FeMnNi合金出现反常的层裂行为。针对该反常的层裂行为,利用塑性波、相变波、稀疏波和逆相变引发的稀疏冲击波的相互作用过程进行分析,结果表明,该实验状态下FeMnNi合金样品存在相变和逆相变行为,逆相变引发的稀疏冲击波是导致反常层裂行为的主要因素。     

延性材料平面冲击波基本实验数值模拟的若干问题

假设屈服强度正比于剪切模量,分别构建了四种强度模型,并用于数值模拟Ly12铝的平面冲击波试验的质点速度剖面以及钨合金的平面冲击波试验的锰铜计应力记录.研究发现,基于Steinberg等的屈服强度模型比较符合实验.还对平面冲击波试验的层裂现象进行了简化的数值模拟,其中,采用了该文作者所提出的一种基于空穴聚集的层裂模型,该模型的特点是分别引入了层裂过程的早期及后期应力松弛方程.     

45钢层裂研究

对４５钢进行了层裂实验，对软回收试件进行了显微金相观测，观察了材料中微损伤的形核、增和聚合机制。将文献［３］中的动态损伤模型编入一维Ｌａｇｒａｎｇｅ有限差分动力学程序，对层裂实验进行了数值模拟，计算结果与实验吻合较好。     

强角闪石化橄榄二辉岩的动态拉伸强度实验研究

对强角闪石化橄榄二辉岩的动态拉伸断裂强度进行了实验研究。设计了能在样品中产生持续时间大约为1.5 s拉伸应力脉冲的平板冲击回收实验。通过对回收样品的宏观和微观观察,确定了样品出现拉伸破坏开始阶段以及破坏裂纹的扩展阶段,进而确定了该岩石样品的动态拉伸强度约为265.6~315.3 MPa。同时,基于线弹性近似,导出了在一维应变条件下样品内拉伸应力和作用时间的估算公式。     

高导无氧铜圆柱-平板冲击实验及不同本构模型效果比较

利用一级气炮对高导无氧铜(OFHC)进行了圆柱以205 m/s速度冲击平板实验,并进行了数值模拟。用锰铜应力计测试了靶中应力随时间的变化,并进行了回收观测。采用Johnson-Cook(J-C)、Zerilli-Armstrong(Z-A)、Steinberg-Cochran-Guinan(S-C-G)3种本构模型对实验进行了数值模拟。实验结果与数值模拟结果比较表明:就峰值应力而言,采用J-C、Z-A及S-C-G本构模型的计算结果都比较接近实验;就圆柱变形而言,Z-A及S-C-G模型的计算较J-C模型结果更符合实验。然而,速度为500 m/s冲击实验的数值模拟结果表明:3种本构模型的计算结果差异明显。     

Spall Characterization in Epoxy Via Laser Spallation

Background: The strength of materials under extreme dynamic loading conditions, such as in the case of shock wave loading, is assessed from their spallation characteristics. Under laboratory conditions, flyer plate impact, or sometimes laser-induced stress waves, is employed to instigate spall in a material. These methods are often combined with velocity interferometer system for any reflector (VISAR) technique for performing transient measurements. Although the VISAR can record the velocity of extremely fast-moving surfaces, it requires a complex optical setup and a specialized data reduction technique. Objective: In this study, a simpler approach is adopted by extending laser spallation method to determine the spall strength of epoxy, while performing in situ interferometric measurements, directly on top of thick epoxy films. Methods: The glass/epoxy test samples are prepared by transferring an aluminum coating on top of epoxy layers with different thicknesses. Laser-induced stress waves transmit across the substrate/film interface and induce subsurface failure in the epoxy at sufficiently high incident laser energy. The nature and magnitude of the waves are deciphered from the out-of-plane displacement histories of the top reflective sample surfaces, which are recorded by using a Michelson interferometer. Results: The interferometric data reveal the development of two (temporally) well-separated stress waves: an ablation-induced high-amplitude short-duration longitudinal pulse, which is referred to as the primary wave, and a secondary wave, which travels at a comparatively slower speed. The complex constructive interaction of the two waves develops a high-magnitude tensile stress region in the epoxy layer. The spall strength is quantified by superimposing the two stress wave histories associated with the critical energy fluence. Conclusions: The spall depths predicted from spatiotemporal wave travel analyses are in excellent agreement with the experimental observations. The newly adopted methodology estimates the spall strength of epoxy as 260?±?20 MPa.

     

三角波强加载下延性金属多次层裂破坏问题

基于应力瞬时断裂判据和Tuler-Butcher损伤累积判据，分析了没有升压的简单三角波强加载下延性金属的多次层裂破坏问题。分析结果显示:层裂片的厚度随着冲击波宽度与强度的比值的增大而增大，材料的破坏深度小于冲击波宽度的一半；在强冲击加载下，材料的破坏深度约为冲击波宽度的一半。     

PROGRESSIVE FRACTURE MODELING OF THE FAILURE WAVE IN IMPACTED GLASS

The failure wave has been observed propagating in glass under impact loading since 1991. It is a continuous fracture zone which may be associated with the damage accumulation process during the propagation of shock waves. A progressive fracture model was proposed to describe the failure wave formation and propagation in shocked glass considering its heterogeneous meso-structures. The original and nucleated microcracks will expand along the pores and other defects with concomitant dilation when shock loading is below the Hugoniot Elastic Limit. The governing equation of the failure wave is characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from the collapse of the original pores. Numerical simulation of the free surface velocity was performed and found in good agreement with planar impact experiments on K9 glass at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.     

冲击压缩下玻璃样品后自由表面速度的过冲现象

实验发现当飞片碰撞玻璃样品产生的冲击载荷超过一定值后 ,玻璃样品后自由表面速度时程曲线上有过冲现象 ,即速度上升到最大值后 ,立即开始下降 ,其时间的开始部分类似于三角波。通过高速摄影和VISAR等测试手段对这一现象进行了较系统的研究 ,发现其与玻璃样品后自由表面附近的破碎有关 ,建立了描述这一破坏现象的损伤演化方程 ,并进行了数值模拟。计算结果和实验结果吻合 ,表明对这个现象的解释是合理的。     

对激光干涉测速中信号丢失现象的分析

分析了当应用任意反射面速度干涉仪(VISAR)测量强冲击波作用下样品自由面速度时丢失部分测量信号的问题。除了普遍的光电系统有限频率响应以及数字示波器采样率的影响,主要考虑了干涉仪延迟时间、多模光纤的多模色散对测量信号的影响。干涉仪延迟时间导致速度历史与一个宽度为延迟时间的矩形函数进行卷积,使速度历史的高频细节丢失;多模色散导致干涉信号与某一梳状函数进行卷积,使高频干涉条纹丢失。对丢条纹的整数性进行了分析。     

PROGRESSIVE FRAGMENT MODELING OF FAILURE WAVE IN CERAMICS UNDER PLANAR IMPACT LOADING

Polycrystalline ceramics have heterogeneous meso-structures which result in high singularity in stress distribution. Based on this, a progressive fragment model was proposed which describes the failure wave formation and propagation in shocked ceramics. The governing equation of the failure wave was characterized by inelastic bulk strain with material damage and fracture. And the inelastic bulk strain consists of dilatant strain from nucleation and expansion of microcracks and condensed strain from collapse of original pores. Numerical simulation of the free surface velocity was performed in good agreement with planar impact experiments on 92.93％ aluminas at China Academy of Engineering Physics. And the longitudinal, lateral and shear stress histories upon the arrival of the failure wave were predicted, which present the diminished shear strength and lost spall strength in the failed layer.     

Mechanical behaviors and damage constitutive model of ceramics under shock compression

One-stage light gas gun was utilized to study the dynamic mechanical properties of AD90 alumina subjected to the shock loading. Manganin gauges were adopted to obtain the stress-time histories. The velocity interferometer system for any reflector （VISAR） was used to obtain the free surface velocity profile and determine the Hugoniot elastic limit. The Hugoniot curves were fitted with the experimental data. From Hugoniot curves the compressive behaviors of AD90 alumina were found to change typically from elastic to ＂plastic＂. The dynamic mechanical behaviors for alumina under impact loadings were analyzed by using the path line principle of Lagrange analysis, including the nonlinear characteristics, the strain rate dependence, the dispersion and declination of shock wave in the material. A damage model applicable to ceramics subjected to dynamic compressive loading has been developed. The model was based on the damage micromechanics and wing crack nucleation and growth. The effects of parameters of both the micro-cracks nucleation and the initial crack size on the dynamic fracture strength were discussed. The results of the dynamic damage evolution model were compared with the experimental results and a good agreement was found.     

冲击压缩下氧化铝陶瓷中破坏阵面的传播

进行了平面冲击波压缩下氧化铝陶瓷中破坏阵面的实验测试和理论探索. 通过氧 化铝陶瓷的平板碰撞实验，借助VISAR测试系统测量了试件自由面的质点速度历程，并对回 收试件进行了电镜扫描观察. 质点自由面速度历程曲线表明，氧化铝陶瓷材料中存在破坏阵 面的传播. 考察了破坏阵面的传播特性，给出了陶瓷材料的动态破坏模型，并对破坏阵面的 传播进行了数值分析.     

Formation mechanism of cavitating spalls

The dynamics of formation of cavitation zones in a liquid upon reflection of a shock pulse from the free surface is studied numerically in a one-dimensional formulation using the Iordanskii-Kogarko-van Wijngaarden two-phase model. It is shown that the formation of a system of cavitation zones (clusters) with a dynamically increasing volume concentration of the gas phase near the free surface is due to oscillations of the structure of the rarefaction wave profile. The fast relaxation of tensile stresses in the cavitation zone ends in the formation of a quasistationary mass-velocity field, which provides for almost unbounded growth of cavitation bubbles in subsurface clusters and explains the occurrence of the spall layers observed in experiments. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 49, No. 2, pp. 65–73, March–April, 2008.     

多次激光冲击导致的Ti17合金层裂

为研究激光冲击Ti17合金中厚样品的层裂特性和层裂阈值,对样品（厚5 mm）表面进行单点连续1~8次激光冲击,激光工艺参数为:频率1 Hz,脉宽15 ns,激光能量30 J,方形光斑4 mm×4 mm。采用白光干涉仪、超声波无损检测技术和扫描电镜,分析和检测中厚样品冲击区域的表面形貌、内部损伤以及层裂形貌。实验结果表明,连续从4次到5次激光冲击中厚样品的表面凹坑深度增加值最大为64.5%。连续5次激光冲击为中厚样品层裂阈值,层裂面积随冲击次数增加而增加。连续5~8次激光冲击中厚样品层裂厚度的实验值为280~310 μm。层裂机理为韧性微孔洞的形核、增长和汇合,形成晶界失效和晶内失效。研究结果可为激光冲击强化整体叶盘改性提供工艺参考。