Influence of pre-stress on elastic precursor of LY12 aluminum
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摘要: 通过过盈配合的热装配方法对LY12铝合金平面样品施加了径向预应力,采用平面飞片撞击方法获得了预应力对弹性前驱波的影响。结果表明:当飞片均以500 m/s的速度撞击样品时,压缩预应变为0(无预应变)、964.5×10-6和1 886.0×10-6时,弹性前驱波幅值分别为87.56、95.24、121.03 m/s,压缩预应力(变)提高了LY12铝弹性前驱波幅值。结合实验的特点,探讨了对样品施加静态径向预应力的数值模拟方法,结果表明,上升沿(100 μs)较为缓慢的加载可以达到与准静态加载应力分布一样的结果。采用该数值模拟方法给出和验证了弹性前驱波随压缩预应力增加而上升的计算结果,与实验结果较为吻合。Abstract: The effect of pre-stress on elastic precursor of disk-shaped LY12 aluminum samples was studied, and the radial pre-stress (or pre-strain) state was achieved by using an excessively-conjugated heat assembly device. In the experiment, the LY12 samples were impacted by flyer plates driven by a one-stage light-gas gun, and elastic precursor signals of the samples in several pre-strain states were measured by VISAR. The experimental results show that the elastic precursors are 87.56, 95.24 and 121.03 m/s respectively corresponding to the pre-strains of 0, 964.5×10-6 and 1 886.0×10-6 when the samples are impacted by the flyer plates with almost the same velocity. This clearly indicates that the pre-stress (pre-strain) increases the elastic precursor of LY12 aluminum. According to these experiments, we discussed how to apply static loading on the sample in the radial direction. The result shows that the loading with rising edge time 100 μs can produce the same stress distribution as that of static loading. Using this technology, the simulation results show that by increasing pre-stress we can enhance the elastic precursor velocity on the free surface of the samples. The simulated results are in good agreement with those from the experiments.
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Key words:
- mechanics of explosion /
- pre-stress /
- impact /
- elastic precursor
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1. 加州大学研究人员在螳螂虾指节中发现一种高刚度大阻尼抗冲击涂层
自然界利用现有资源,在有限的环境条件下组建了轻质、坚固、坚韧的材料。例如,螳螂虾指关节的迎撞面就是这类典型的复合材料,此类虾具有在摄食过程中避免高速碰撞造成巨大伤害的能力。美国加州大学研究人员发现螳螂虾的指节包含一层由纳米颗粒紧密堆积的抗冲击涂层,这些纳米颗粒由排列整齐的小纳米晶体组成。在高应变率冲击下(约104 s−1),粒子旋转和平移,而纳米晶网络在低角度晶界处发生断裂,形成位错并发生非晶化。此外,这种材料在保持高刚度(弹性模量约为58.9 GPa)的情况下还具有较大的阻尼(损耗系数约为0.02),相互渗透的有机网状结构提供了额外的增韧和阻尼,这种罕见的刚度和阻尼组合在工程材料中并不常见,其性能也优于许多工程材料。这些新发现可为结构的高速冲击和破坏失效提供新的研究思路。
源自:HUANG W, MEHDI S, NICOLAS G Z, et al. A natural impact-resistant bicontinuous composite nanoparticle coating [J]. Nature Materials, 2020, 19: 1236−1243.
2. 迈阿密大学等研究人员首次定量描述了铜箔材料在高应变率下的失效过程
理解高速碰撞以及随后的高应变率材料变形和潜在的灾难性破坏,对于包括天体物理学、材料科学和航空航天工程在内的系列科学和工程学科至关重要。由于在极短时间尺度下,用实验来量化材料的演变面临着巨大挑战,相关变形和破坏机制还很不明确。美国迈阿密大学等研究人员将铜箔通过皮秒激光烧蚀实现快速变形(0.5×109 s−1),并利用30-fs超快X射线自由电子(XFEL)脉冲进行原位探测,首次定量描述了材料在高应变率条件下的失效过程。结果发现最终破坏是通过空洞成核、增长和聚合发生的,与分子动力学模拟的结果吻合较好。发展和应用具有飞秒分辨率的原位超快小角度X射线散射(SAXS)对高应变率层裂破坏进行定量表征,是对广角X射线散射(WAXS)的补充,具有重要的应用价值。
源自:JAMES C, ANDREW H, DAVID M, et al. Femtosecond quantification of void evolution during rapid material failure [J]. Science Advances, 2020, 6(51): eabb4434.
3. 韩国浦项科技大学等研究人员发现了高熵合金纳米材料在应变率5×10−2 s−1下的超塑性
超塑性描述的是材料以拉伸延伸的形式将大塑性变形维持到其原始长度400%以上的能力,但通常只能在低应变率(约10−4 s−1)下观察到,这使得加工时间大大增加,由于经济原因导致不适合大规模生产。而超过10−2 s−1应变率下的超塑性,通常只能在低强度的镁和铝合金中才能出现。韩国浦项科技大学等研究人员通过高压扭转试验,发现了Al9(CoCrFeMnNi)91高熵合金纳米材料在应变率5×10−2 s−1下的超塑性,其伸长率达到了原始长度的2000%。多相合金中的高压扭转诱导晶粒细化与热塑性变形过程中的有限晶粒增长相结合,通过位错活动调节晶界滑移,实现了高应变率下的超塑性。
源自:NGUYEN N T C, ASGHARI-RAD P, SATHIYAMOORTHI P, et al. Ultrahigh high-strain-rate superplasticity in a nanostructured high-entropy alloy [J]. Nature Communications, 2020, 11: 2736.
4. 佛罗里达大学等研究人员开发了一种用于描述含能材料激波-爆炸转换的多尺度方法
佛罗里达大学、佛罗里达理工学院以及洛斯阿拉莫斯国家实验室等科学家合作开发了一种耦合微观尺度空洞坍塌动力学到介观尺度模拟中的多尺度方法,可以描述微观结构在起爆中发挥的重要作用。第一步,作者进行空隙塌陷模拟,并收集点火时间和总输出功率与冲击压力和空隙直径的关系;第二步,通过将功率沉积项添加到能量方程,将第一步的信息反馈给介观尺度模拟。该研究通过使用单独的反应物和产物状态方程,并在反应区中定义了混合规则,可以获得与实验数据更好的一致性。由于没有HMX单晶数据,因此用PBX9501替代(即含95%HMX),优势是PBX9501数据比较全面。另一个改进是介观尺度上的动力学建模。作者采用了基于压力的幂定律,针对实验的Pop-plot数据和CJ点附近爆轰曲线斜率进行了校准。以前的校准过程是在连续范围内进行的,没有考虑微观结构的细节;该论文是研究空洞塌陷而引起的起爆,因此包括了微观结构的细节。
源自:THOMAS J L, ZHANG J, SHORT M. Multiscale approach to shock to detonation transition in energetic materials [J]. Propellants, Explosives, Pyrotechnics, 2020, 45: 316−329.
5. 中物院化工材料研究所等研究人员制备出具有类石墨烯结构的稠环单质炸药
中物院化工材料研究所与美国爱达荷大学研究人员近期利用分子间氢键和偶极-偶极协同相互作用,联合研究制备出一种新的含能材料NAPTO。该物质不仅含有稠环母体结构,还具有超平的二维层状堆积结构,分子中所有原子处于同一平面内,二面角均为0°或180°。其平面性优于常见的二维层状单质炸药如TATB、FOX-7等,成为首个具有类石墨烯结构的稠环单质炸药,且层间距仅为2.855×10−10 m。该新型化合物能量高(爆速为9.12 km/s,爆压为35.1 GPa)、外部刺激敏感度优异(撞击感度为18 J,摩擦感度为325 N,静电放电感度为0.32 J)、热分解温度高(203.2 ℃),因此具有高能量和低机械感度双重优点。
源自:FENG Y A, DENG M C, SONG S W,et al. Construction of an unusual two-dimensional layered structure for fused-ring energetic materials with high energy and good stability [J]. Engineering, 2020, 6(9): 1006−1012.
(敬霖 编译)
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表 1 不同径向预应力下实验结果
Table 1. Experimental results of samples under different pre-strains
ε0, r/10-6 σ0, r/MPa v/(m·s-1) ue*/(m·s-1) 0 0 497.82 87.56 964.5 99.2 497.06 95.24 1 886.0 194.0 499.60 121.03 -
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