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Stress Waves
Published in Paul J. Hazell, Armour, 2023
When the target material is strong enough to withstand the generated tensile stress, no spall will occur. This results in a further release of the shock state within the target and so the free surface velocity value will continue to diminish (see time 4’ in Figure 5.26b). Theoretically, this would be expected to reach zero providing a shock trace similar to Figure 5.11. However, this is rarely the case and the arrival of release waves from the periphery of the sample interferes with this process resulting in non-zero values of free surface velocities (see also Figure 5.27). Ringing of the wave backwards and forwards through the thickness of the specimen would also be expected, as shown in Figure 5.27.
Ballistic Properties of Hybrid Kenaf Composites
Published in S.M. Sapuan, J. Sahari, M.R. Ishak, M.L. Sanyang, Kenaf Fibers and Composites, 2018
R. Yahaya, S.M. Sapuan, M.R. Ishak, Z. Leman, M. Jawaid
Spall liners work as protective layers next to an armor panel, which is usually composed of steel or ceramics. Spall liners work by preventing the intrusion of fragments or splinters from hard armored panels, and by decreasing the risk and the effect of the threat to a crew of armored vehicles (Erbil et al. 2011). The cause of this spall is an impact-generated compressive stress wave that passes through the armor at the speed of sound (in the struck material). When this wave strikes the rear face of the material, it is reflected as a tensile stress wave. This tensile wave can exceed the tensile strength of the material, causing a disc-shaped fracture that results in a large “scab” of material being separated from the back of the armor. Spall liners are constructed of plies of ballistic protective material such as Kevlar in the form of panels tailored to match the interior side of a protected vehicle. Figure 9.7 illustrates the spall debris cone that occurs in the vehicle’s hull with and without a spall liner.
The characteristics of void distribution in spalled high purity copper cylinder under sweeping detonation
Published in Philosophical Magazine, 2018
Yang Yang, Zhi Jiang, Jixinog Chen, Zhaoliang Guo, Tiegang Tang, Haibo Hu
Meanwhile, the shock wave propagated in cylinder sample with obliquity during the sweeping detonation process, which may evoke a stress state of radial tension and axial shear stress (the direction of shear stress is in parallel with the direction of sweeping detonation) when the shock wave reflect from the inner free surface. Gray et al. [9] also discovered the spall strength of Ta decreased during sliding impact of Ta plate, namely, the spall strength of Ta plate which subjected to sweeping detonation is lower than that under 1-D shock loading. This phenomenon is probably resulted from the change of damage mechanism in materials when spallation occurred. The shock-wave shape also has a strong influence on the spallation response, which is reflected in both the real-time rear surface wave profiles and the micro-mechanisms of damage evolution [24]. During sweeping detonation, the spall damage process transformed from pure tensile failure to a coactions of dynamic tension damage and shear damage processes, which reduces the critical shock stress for spallation, ultimately results in lower spall strength.