Dynamics of Energetic Events in Condensed Phase Media

当能量释放的速率超过能量沉积到其中的材料的强度时，高能事件发生。在这些条件下，随后的动态介质是由可压缩（非线性）波，如冲击波。虽然这些现象远远超出日常经验，但它们在许多自然过程和技术应用中发挥着重要作用。这个拟议的实验和理论研究计划将集中在三个主题，涉及的问题和应用的动力学充满活力的事件，重点是问题的非线性波方面。离散爆炸：爆炸波通过高能材料的传播，在传播时释放储存的能量，是具有重要技术应用的高能事件的一个例子，因为炸药广泛用于采矿和土方工程。作者、他的同事和其他地方的研究人员最近的实验结果已经确定了非均匀凝聚相材料中的爆轰波行为，这些材料不能用纯粹经典的、基于连续介质的爆轰波传播模型来解释。这些结果表明，在中尺度发生的现象（例如，颗粒、空隙等）可能对波的传播有显著影响。这项研究计划将进一步研究这种效应的实验，以及开发一种方法来模拟介质中的爆炸传播占主导地位的离散，充满活力的事件。内爆动力学：暴露于高动态事件的材料的响应也相当感兴趣。我和我的学生最近进行了一项研究，研究圆柱体在脉冲内爆时的动力学。这项工作最初是由下文所述的超高速发射器的开发所激发的，但与利用热核聚变发电的方法直接相关（即，惯性约束和磁化靶聚变）。我们将在拟议的计划下继续这些研究，重点是固体和液体中动态加载收敛几何形状（内爆圆柱形空腔）的稳定性，以确定可以实现的对称压缩的极限以及材料特性和流体动力学不稳定性的作用。超高速发射器和撞击：高能事件的另一个例子是轨道碎片或微流星体对航天器的超高速撞击。这一日益严重的问题现已得到广泛承认，因为失控的碰撞级联在地球轨道上产生新的碎片。这类撞击的速度为7至70公里/秒（对于自然形成的微流星体），目前在实验室中无法获得这种情况。当撞击速度超过10 km/s时，撞击产生的压力足以克服外层电子层之间的排斥势垒，从而产生新的结构相变，并且在压力释放时，许多工程材料进入混合液体和蒸汽状态的区域。这些现象以前没有被研究过，因为它们在实验室中无法进行实验。我在麦吉尔的小组最近开发了一种独特的超高速发射器，它使用炸药动态内爆发射器推进剂气体，现在已经证明它有能力超过常规发射器的弹丸速度。这一研究方案将继续发展超高速发射器，并将其应用于撞击物理学的基本问题以及对航天器屏蔽材料的研究。

Highly energetic events occur when the rate of energy release exceeds the strength of the material into which the energy is deposited. Under these conditions, the ensuing dynamics of the media is governed by compressible (nonlinear) waves such as shock waves. While these phenomena are far outside everyday experience, they play an important role in a number of natural processes and technological applications. This proposed experimental and theoretical research program will focus on three topics involving the problems and applications of the dynamics of energetic events, with an emphasis on the nonlinear wave aspects of the problems.**Discrete Detonation: The propagation of detonation waves through energetic material, releasing stored energy as it propagates, is an example of a highly energetic event with important technological applications, since explosives are extensively used in mining and earth moving. Recent experimental results by the author, his colleagues, and researchers elsewhere have identified behavior of detonation waves in heterogeneous, condensed phase materials that cannot be explained by purely classical, continuum-based models of detonation wave propagation. These results suggest that phenomena occurring at the mesoscale (e.g., grains, voids, etc.) may have significant influence on the propagation of the wave. This research program will further investigate this effect experimentally as well as develop a methodology for modeling detonation propagation in media dominated by discrete, energetic events.**Implosion Dynamics: The response of materials exposed to highly dynamic events is also of considerable interest. My students and I have recently undertaken a study of the dynamics of cylinders that are impulsively imploded. This work was originally motivated by the development of the hypervelocity launcher described below, but has direct relevance to approaches to harness thermonuclear fusion for power generation (i.e., inertial confinement and magnetized target fusion). We will be continuing these studies under the proposed program, focusing upon the stability of dynamically loaded converging geometries (imploding cylindrical cavities) in both solids and liquids in order to determine the limits to symmetric compression that can be achieved and the role of material properties and hydrodynamic instabilities.**Hypervelocity Launcher and Impact: Another example of an energetic event is the hypervelocity impact of orbital debris or micrometeoroids on spacecraft. This mounting problem is now widely recognized due to the runaway cascade of collisions generating new debris in Earth orbit. These types of impacts occur at speeds of 7 to 70 km/s (for naturally occurring micrometeoroids), a regime that is not presently accessible in the laboratory. At impacts exceeding 10 km/s, the impact-generated pressures are sufficient to overcome the repulsion barrier between outer electron shells, giving rise to novel structural phase transitions, and upon pressure release, many engineering materials enter a region of mixed liquid and vapor states. These phenomena have not been previously studied due to their experimental inaccessibility in the laboratory. A unique hypervelocity launcher that uses explosives to dynamically implode the launcher propellant gas has recently been developed by my group at McGill, and has now demonstrated the ability to exceed the projectile velocity of conventional launchers. This research program will continue the development of the hypervelocity launcher and apply it to both fundamental problems in impact physics as well as examination of materials of interest for spacecraft shielding.