激光加载下金属锡材料微喷颗粒与低密度泡沫混合实验研究

金属材料的微喷是冲击加载下金属表面发生的一种动态破碎现象,微喷研究在很多领域都具有重要意义,包括惯性约束聚变(ICF)和烟火制造等.由于激光实验特有的优势,近几年国内外开展了很多利用强激光驱动冲击加载研究材料微喷过程的实验.利用泡沫材料对微喷颗粒进行静态软回收虽然可以获得颗粒的形态分布、颗粒尺寸及颗粒质量等定量结果,但并不能反演微喷颗粒从进入泡沫到停滞过程中的动态混合过程.为此,在神光Ⅱ升级装置上利用皮秒脉冲激光照射金丝产生高能X射线,实现了对锡微喷颗粒与低密度泡沫混合过程的高时间分辨和高空间分辨背光照相.背光图像面密度结果证实微喷颗粒在泡沫中并没有发生二次破碎.静态回收结果表明,在锡材料与泡沫紧贴放置的情况下,微喷颗粒在泡沫中的穿透深度随着加载压强升高呈现先增大后减小的规律,与非紧贴放置的实验结果有明显的差别.

Observation of ejecta tin particles into polymer foam through high-energy X-ray radiograpy using high-intensity short-pulse laser

Micron-scale fragment ejection of metal is a kind of surface dynamic fragmentation phenomenon upon shock loading. The study of ejecta is crucial in many fields, such as inertial confinement fusion and pyrotechnics. Due to the particular advantages of laser experiments, a lot of studies of ejecta by strong laser-induced shock loading have been conducted in recent years. The shapes, size and mass of particle can be obtained via static soft recovery technique with foam. However, the stagnation and succedent mixing of the ejecta in the foam could not be deduced by this technique. To study the mixing between the ejecta and foam, a radiography experiment is performed by using the X-ray generated through the irradiation of picosecond laser on the golden wire. This radiography technique has not only high spatial resolution but also high temporal resolution. Two kind of experiments are designed and performed. In the first one, the tin sample and the foam are close to each other while a vacuum gap is arranged between them in the other one. The mixing process is analyzed with the determined areal density and volume density, as well as the results of recovery. The areal density of the front mixing area is similar to the scenario in the case with a vacuum gap, suggesting that the ejecta have not underwent a secondary fragmentation due to the collision with foam. Furthermore, the static recovery results show a different characteristic of penetration depth for the ejecta in the foam. When the tin sample is not close to the foam, the penetration depth in the foam increases with the loading pressure increasing. However, the penetration depth begins to decrease at a critical pressure after a brief increase, which is attributed to the interaction between the shock and the foam before the ejecta coming, and also to the ejecta size and composition. The shock pressure is high enough to change the foam performance, thus enhancing the stagnation ability for ejecta penetration. Moreover, the size and composition vary with loading pressure, thereby leading to the momentum change of the ejecta related to the penetration depth. In the future work, we will improve the field of view of the X-ray radiography to achieve a direct comparison between the dynamic results and the recovery results. Moreover, we will arrange perturbations at the interface to study the mixing between the micro-jetting and the foam and the interface instability.