Abstract
High-power laser induced shocks generated by “ShenGuang II” laser facility has been used to study spall fracture of polycrystalline aluminum at strain rates more than 106/s. The free surface velocity histories of shock-loaded samples, 150 μm thick and with initial temperature from 293 K to 873 K, have been recorded using velocity interferometer system for any reflector (VISAR). From the free surface velocity profile, spall strength and yield stress are calculated, it demonstrates that spall strength will decline and yield strength increase with initial temperature. The loaded samples are recovered to obtain samples' section and free surface metallographic pictures through Laser Scanning Confocal Microscopy. It is found that there are more micro-voids and more opportunity to appear bigger voids near the spall plane and the grain size increases with temperature slowly but smoothly except the sharply change at 893 K (near melting point). Besides, the fracture mechanisms change from mainly intergranular fracture to transgranular fracture with the increase of initial temperature.
Highlights
Experimental techniqueCharacteristics of the optical system (Lens+LA) were such that the focal spot had a ∼1 mm diameter flat region
Using the acoustic approximation formula (1), (2), (3), spall strength and yield stress of different initial temperature aluminum samples can be calculated through the HEL velocity and pullback velocity
Under the same initial temperature, materials loading by high-power laser should have higher yield stress and spall strength, and this have been proved by lots of researches
Summary
Characteristics of the optical system (Lens+LA) were such that the focal spot had a ∼1 mm diameter flat region. Foils of polycrystalline aluminum of 99.99% purity with 150 μm thickness and different initial temperature were used in the experiment. The metallography examination of the foils shows that the foils contain. The shock-loaded samples were 10 mm × 10 mm squares of different thicknesses. The heating system could heat up the sample to 973 K with temperature controlling accuracy of 2 K. Make metallographic analysis using fracture surface and section pictures got by LSCM(laser scanning confocal microscope)
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