Static and dynamic failure behavior of transparent polycrystalline spinel (MgAl2O4) under compression/shear loading experiments

Abstract

Compression tests were conducted on transparent polycrystalline spinel (MgAl2O4) at strain rates from 10−4 s−1 to 103 s−1. Besides normal cubic samples that only bear compression along the loading direction, leaning cubic samples with different leaning angles (10° and 20°) were also employed in order to induce higher shear stress during compression. Results show that cracks were initiated from the loading end and inside of the cubic sample, but they preferred to initiate in stress-concentrated regions in leaning cubic samples. After initiation, cracks mainly propagated along the loading direction in the cubic sample, whereas they propagated parallel with the leaning side in the leaning cubic sample. The failure strength of leaning cubic MgAl2O4 is lower than cubic ones due to the introduced shear stress, but it is in direct proportional to the strain rate in samples of both geometrical shapes. For leaning cubic samples, this strain-rate strengthening behavior is not affected by the leaning angles. Sizes of MgAl2O4 fragments increase when larger shear stress is introduced, but they decrease with the increase of strain rate.