冲击压缩下非均质脆性固体的弛豫破坏

与韧性金属材料相比，脆性材料在冲击压缩下表现出许多异常的力学响应特性，尤其是损伤破坏特性，经常在应变不到1％时就发生破坏。因此对脆性固体的动态压缩特性研究不仅是一个工程问题，也是一个非常有意义的科学问题。     

可控爆轰平面加载样品回收装置

介绍了一种可控爆轰平面加载样品回收装置，该装置包括一个近似平面波发生器和一个“动量陷阱”式样品腔体。工作原理是由近似平面波发生器加速一块飞片，经适当长空腔飞行后与样品腔体碰撞，产生高压冲击波对样品实现冲击波压缩，并由“动量陷阱”式腔体回收样品，飞片材料为４５钢。此装置可在１．５￣３．５ｋｍ／ｓ范围内实现飞片击靶速度的连续调节，并且具有较理想的飞片击靶平面性，经测定在直径３０ｍｍ的范围内飞片弯曲的时     

不同应变率下45钢的层裂研究

本文在利用轻气炮加载技术，确定击靶速度为500m／s左右的非对称碰撞情况下，利用VISAR测试技术，测得样品后表面的的自由面速度历史，并通过在靶前加不同阻抗的铝和有机玻璃(PMMA)来改变材料的加载应变率，其应变率范围在10^4-10^5／s情况下，测得45钢的层裂强度受应变率的影响．     

Manipulating metal-insulator transitions of VO2 films via embedding Ag nanonet arrays

Manipulating metal-insulator transitions in strongly correlated materials is of great importance in condensed matter physics, with implications for both fundamental science and technology. Vanadium dioxide (VO₂), as an ideal model system, is metallic at high temperatures and shown a typical metal-insulator structural phase transition at 341 K from rutile structure to monoclinic structure. This behavior has been absorbed tons of attention for years. However, how to control this phase transition is still challenging and little studied. Here we demonstrated that to control the Ag nanonet arrays (NAs) in monoclinic VO₂(M) could be effective to adjust this metal-insulator transition. With the increase of Ag NAs volume fraction by reducing the template spheres size, the transition temperature (T_c) decreased from 68° to 51°. The mechanism of T_c decrease was revealed as:the carrier density increases through the increase of Ag NAs volume fraction, and more free electrons injected into the VO₂ films induced greater absorption energy at the internal nanometal-semiconductor junction. These results supply a new strategy to control the metal-insulator transitions in VO₂, which must be instructive for the other strongly correlated materials and important for applications.     

高压下SiC增强Al基纳米复合材料

 采用高压技术合成了纳米尺寸SiC颗粒增强Al基复合材料,针对合成中增强相与基体的化学反应行为、增强相与基体界面结合等问题进行了研究。X射线衍射、高分辨率、正电子湮没以及显微硬度结果表明：高压技术在合成SiC_p/Al纳米复合材料中,具有抑制界面反应、提高致密度、改善界面结合等优点。     

单晶铜中冲击波阵面结构的数值模拟研究

 用分子动力学方法模拟计算了在初始温度为0 K时单晶铜中的冲击波结构,相互作用势采用铜的嵌入原子势（EAM）,模拟计算结果表明即使是在初始温度为0 K的FCC晶体中,冲击波波阵面后的区域也会向平衡态演化。局域分析表明冲击波阵面后区域的压力、粒子速度、应变和温度随时间逐步变化到稳定态,在所研究的冲击波强度（约262 GPa）下,波后区域的平均压力、粒子速度、应变均在约1 ps内逐渐上升并达到稳定值。动能温度在波阵面处始终为最大值,随着冲击波的传播,波后非零温度区域逐渐扩大,不同时刻的粒子速度分布函数说明波后区域逐渐向热力学平衡态演化,并最终达到热力学平衡,进一步的分析说明局域平衡是系统向平衡态演化的基本过程。     

沿〈111〉晶向冲击加载下铜中纳米孔洞增长的塑性机制研究

 用分子动力学方法计算模拟了沿〈111〉晶向冲击加载过程中，单晶铜中纳米孔洞（直径约1.3 nm）的演化及其周围区域发生塑性变形的过程。模拟结果表明，在沿〈111〉晶向冲击加载后，在面心立方（fcc）结构中的4族{111}晶面中有3族发生了滑移。伴随孔洞的增长，在所激活的3族{111}晶面上，观察到位错在孔洞表面附近区域成核，然后向外滑移，其中在剪切应力最大的〈112〉方向上，其位错速度超过横波声速，其它〈112〉方向的位错速度低于横波声速。模拟得到的位错阻尼系数范围与实验值基本符合。由于孔洞周围产生的滑移在空间比较对称，孔洞增长形貌接近球形。在恒定的冲击强度下，孔洞半径增长速率近似保持恒定，其速率随着冲击强度的增加而增大。     

Effect of grain size and arrangement on dynamic damage evolution of ductile metal

Plate-impact experiments have been carried out to examine the effect of grain size and grain arrangement on the damage evolution of ultrapure aluminum. Two groups of samples, "cross-cut" and "longitudinal-cut," are obtained from the rolled aluminum rod along different directions. The peak compressive stress is approximately 1.25 GPa-1.61 GPa, which can cause incipient spall damage that is correlated to the material microstructure. The metallographic analyses of all recovered samples show that nearly all damage nucleates at the grain boundaries, especially those with larger curvature. Moreover, under lower shock stress, the spall strength of the "longitudinal-cut" sample is smaller than that of the "crosscut" sample, because the different grain sizes and arrangement of the two samples cause different nucleation, growth, and coalescence processes. In this study, the difference in the damage distribution between "longitudinal-cut" and "cross-cut" samples and the causes for this difference under lower shock-loading conditions are also analyzed by both qualitative and semi-quantitative methods. It is very important for these conclusions to establish a reasonable and perfect equation of damage evolution for ductile metals.     

基于微孔洞长大惯性机制的动态拉伸断裂模型构建

 采用圆柱体胞模型分析方法,对球形微孔洞在不同加载应变率条件下的动力学响应行为进行了有限元分析,计算结果表明：在微孔洞稳定增长阶段,惯性对微孔洞的快速增长起着关键性作用,其它因素的影响基本可以忽略,微孔洞半径增长率与平均应力的平方根成正比。提出了一个微孔洞增长惯性机制的损伤度演化方程,结合逾渗软化函数描述微孔洞聚集行为,从而构建了一个新的动态拉伸断裂模型,并通过自定义材料模型子程序,把断裂模型嵌入LS-DYNA程序中,对无氧铜平板撞击层裂实验进行了数值模拟研究,计算结果与实验结果的比较令人满意,初步检验了新模型的实用性。     

低冲击应力下脆性介质电阻率的实时测量

 冲击波压缩下材料宏观性质的变化与微观结构演化有着密切联系。通过改进对称差分电路测量方法,测量K9玻璃在失效破坏过程中的电阻率变化,研究了脆性介质在低冲击波应力下的损伤破坏机制。结果表明,随着冲击波在K9玻璃中传播,K9玻璃的电阻率逐渐下降;在7.6 GPa冲击压缩下,K9玻璃由最初的绝缘体状态逐渐转变为电阻率约420 Ω·m的稳定状态。