| The dynamic damage characteristics of materials is a concern of great significance in many fields such as aerospace, high speed collision of automobile, the new material synthesis and weapon designs etc. Spall is a typical dynamic fracture that takes place inside a solid body as a result of tensile stresses that develop due to the interaction of rarefaction waves and it proceeds through the nucleation, growth, and coalescence of micro-cracks or micro-voids.In this work, High-power laser induced shocks has been used to study spall fracture of polycrystalline aluminum at strain rates more than 106s-1 at "ShenGuang Ⅱ" laser facility. The free surface velocity histories of shock-loaded samples have been recorded using velocity interferometer system for any reflector (VISAR). From the free surface velocity profile,spall strength and yield stress have been calculated and we have analyzed the results to study the effects of samples’ thickness and initial temperature on the dynamic damage characteristics of materials.Both of the unloaded but preheated and loaded by laser shocks samples have been recovered to do metallographic analysis through Laser Scanning Confocal Microscopy. It is found that the grain size increases with temperature slowly except the sharply change at 873K(near melting point). And there are more micro-voids and more opportunity to appear bigger voids near the spall plane than places away from it. Meanwhile, the fracture mechanisms change from mainly intergranular fracture to transgranular fracture with initial temperature increasing. |
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