Studying dynamic fragmentation in shock-loaded metals and evaluating the geometrical and kinematical properties of the resulting fragments are of significant importance in shock physics, material science as well as microstructural modeling. In this paper, we performed the laser-driven shock-loaded experiment on the Shenguang-Ш (SGШ) prototype laser facility, and employed X-ray micro-tomography technique to give a whole insight into the actual fragmentation process. To investigate the size distribution of the soft recovered fragments from Poly 4-methyl-1-pentene (PMP) foam sample, we further developed an automatic analysis approach based on the improved watershed segmentation. Comparison results of segmenting fragments in slices with different methods demonstrated that our proposed segmentation method can overcome the drawbacks of under-segmentation and over-segmentation, and has the best performance in both segmentation accuracy and robustness. With the proposed automatic analysis approach, other parameters such as the position distribution and penetration depth are also obtained, which are very helpful for understanding the dynamic failure mechanisms.

The dynamic fragmentation of shock-loaded high-Z metal is of considerable importance for both basic and applied science. The areal density and mass-velocity distribution of dynamic fragmentation are crucial factors in understanding this issue. Experimental methods, such as pulsed X-ray radiography and proton radiography, have been utilized to obtain information on such factors; however, they are restricted to a complex device, and the spatial resolution is in the order of 100 μm. In this work, we present the high-quality radiography of the dynamic fragmentation of laser shock-loaded tin, with good two-dimensional (2D) spatial resolution. Dynamic fragmentation is generated via high-intensity ns-laser shock-loaded tin. A high-energy X-ray source in the 50–200 keV range is realized by the interaction of a high-intensity ps-pulse with an Au microwire target, attached to a low-Z substrate material. A high 2D resolution of 12 μm is achieved by point-projection radiography. The dynamic-fragmentation radiography is clear, and the signal-to-noise ratio is sufficiently high for a single-shot experiment. This unique technique has potential application in high-energy density experiments.

<a></a><a></a><a></a><a>U</a><a></a><a></a><a></a><a></a><a></a><a>nderstanding the structural, geometrical and chemical changes that occur after electronic excitation is essential to unraveling the inherent mechanism of nitro explosives. In this work, relaxed structures of typical nitro explosives in the excited state are investigated by time-dependent density functional theory. During the excitation process, nitro group becomes activated and then relaxes, leading to a relaxed structure. </a><a></a><a>All five nitro explosives exhibit a similar behavior, and impact sensitivity is related to excitation energy of relaxed structure.</a> <a></a><a>H</a>igh sensitivity d-HMX has a lower excitation energy for relaxed structure than b-HMX. This work offers a novel insight into energetic material.<a></a>

This work investigates the geometric statistics method to characterize the size distribution of tin fragments produced in the laser shock-loaded dynamic fragmentation process. In the shock experiments, the ejection of the tin sample with etched V-shape groove in the free surface are collected by the soft recovery technique. Subsequently, the produced fragments are automatically detected with the fine post-shot analysis techniques including the X-ray micro-tomography and the improved watershed method. To characterize the size distributions of the fragments, a theoretical random geometric statistics model based on Poisson mixtures is derived for dynamic heterogeneous fragmentation problem, which reveals linear combinational exponential distribution. The experimental data related to fragment size distributions of the laser shock-loaded tin sample are examined with the proposed theoretical model, and its fitting performance is compared with that of other state-of-the-art fragment size distribution models. The comparison results prove that our proposed model can provide far more reasonable fitting result for the laser shock-loaded tin. © 2017 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license

When a triangular shock wave reflects from the free surface of a solid sample, microjetting may emit from the grooved surface, leading to high velocity approximately micrometer-size fragments. Microjetting is an important issue for material dynamic response under shock loading in both fundamental science and practical applications. In this paper, the dynamic process of microjetting is investigated in the laser-driven shock loading conditions, the experiments were performed at the ShenguangII-U (SGII-U) laser facility. Microjetting from the triangular grooves in the free surface of a tin sample is diagnosed with x-ray radiography, where the 40–200 keV high energy x-ray is created with the picosecond laser beam focused on a Au µ-wire target. The density distribution along the microjetting and cumulated mass can be inferred from the images radiographied by such ultrashot high energy x-ray. The density distribution shows two representative regions including the head region of microjetting with low density and high speed, and the root region with high density and low speed. The microjets from three continuous parallel grooves with 60° angle are significantly different from that of 120° angle, the effect of the groove angle was verified by numerical simulation and experimental results.