Foreword to the Special Issue on Ejecta

Abstract

A Brief History of Ejecta Physics 1950s and 1960sThere exists anecdotal evidence that ejecta research began in the 1950s, but little of this early research was documented publicly. In Russia, the ejecta phenomenon was first observed in plate impact experiments, and shown to be dependent on the initial surface roughness [1]. The Los Alamos PHERMEX radiographic facility was used to study the production and interaction of jets from shocked surfaces, starting from its very first shot in 1963 [2]. By 1969, Bristow and Hyde [3] describe the results of a mature program in the UK using photographic imaging of ejecta processes to infer whether melt had occurred at the surface of shocked materials. They showed that drive nonuniformity and subsurface fragmentation (spall/scabbing) were also contributory factors in determining the nature of ejecta produced. 1970sThe earliest published ejecta research was done by James Asay [4]. Asay went on to develop a non-radiographic ejecta diagnostic, the eponymous Asay foil [5]. Later, he developed a prescriptive model of ejecta, where he associated the amount of mass ejected from a shocked surface to the volume of surface defects, the rise time of the shock impulse, the yield strength of the material, and the phase of the material on release, i.e., liquid or solid [6]; interestingly he also observed that ejecta production was independent over broad ranges to the peak loading stress P S . Los Alamos National Laboratory (LANL) also became active in the development of ejecta diagnostics, as released by Hopson and Olinger [7].Ejecta physics is a young field, having developed over the last 60 years or so. Essentially, ejecta forms as a spray of dense particles generated from the free surface of metals subjected to strong shocks, but the detailed mechanisms controlling the properties of this particulate ejecta are only now being fully elucidated. The field is dynamic and rapidly growing, with military and industrial applications, and applications to areas such as fusion research.This Special Issue on Ejecta reports the current state of the art in ejecta physics, describing experimental, theoretical and computational work by research groups around the world. While much remains to be done, the dramatic recent progress in the field, some of it first reported here, means that this volume provides a particularly timely review.In this foreword, we provide a brief historical overview of the development of ejecta physics, to define the context for the work in the rest of this Special Issue.

Dynamics behavior of porous tin under strong shockwave impact

“…强冲击作用下的金属材料动态破碎过程, 既包含 简单的单次加载微喷、层裂/微层裂破碎 [1][2][3][4][5][6][7][8][9][10][11][12][13] , 也有复 杂多次加载产生的表面微射流、主体区域反复冲击再 破碎、主体区域对微射流颗粒回收等一系列复杂过 程 [14][15][16] , 是耦合材料特性、加载状态、样品初始状态 等多因素的复杂多尺度问题, 在惯性约束核聚变、冲 击防护等领域有重要的工程价值和科学意义, 最近几 十年被广泛研究 [17][18][19] .…”

The Role of Helium on Ejecta Production in Copper

“…It is well known that when a shock wave in a material reaches a free surface, it can lead to ejection of particles from the surface [1][2][3]; this process and the launched material is referred to as ejecta. Over the last few decades there has been a body of research to understand the relationship between the total ejected mass and parameters associated with the free surface itself.…”

Velocity and mass density of the ejecta produced from sinusoidal grooves in laser shock-loaded tin

“…One of the processes governing such ejection is the interaction of a shock wave with a free surface presenting geometrical defects such as pits, scratches, grooves, or machining-inherited roughness. This process, usually referred to as "material ejection" or "microjetting" (because ejecta often consist of "jets" breaking up into micrometer-scale particles), has been the subject of extensive research work for about six decades [5], and it still motivates both theoretical and experimental investigations worldwide [6][7][8][9][10][11][12][13][14]. For a few years, we have explored how laser-driven shocks can provide some valuable, complementary insights into ejecta physics under pulsed pressure loads of high amplitude (some tens of GPa) and very short duration (a few ns).…”

“…Ref. 5 and references therein) that material ejection upon shock breakout can be considered as a limiting case of the Richtmyer-Meshkov Instability (RMI) theory [24], especially after partial or full melting of the shocked specimen. Still, isolated (non-periodic) grooves do not fully fit this picture because of inadequate boundary conditions at the groove edges [25].…”