Bullet-resistant performance of spruce in a sandwich structure

Abstract

Spruce is generally used as cushion material. The structure composed of two thin steel plates and spruce core inside is one typical sandwich structure for shock mitigation. The bullet-resistant performance of the sandwich structure is experimentally studied in the present paper. Four types of configurations of the sandwich structure are shot by three types of bullets in active service. Specifically, the spruce is laid out with different fibre directions in the sandwich structure. The depth of penetration in the target or the residual velocity of the bullet is obtained in tests. The observation of the failure pattern of the spruce after shot reveals that the fibre direction dominates the bullet-resistant performance of the spruce. The ballistic performance of the transverse spruce is better than that of the longitudinal spruce. The opening of cleavage surfaces in spruce is mainly caused by the limited lateral confinement of the tested specimen, which would discount the bullet-resistant performance of spruce. Moreover, the ballistic trajectory of bullet is inclined to deflect in spruce, which would slightly enhance the bullet-resistant performance of the sandwich structure. Furthermore, the velocity-range model is derived to represent the bullet-resistant performance of the sandwich structure. Based on this model, the stopped-location of bullet after penetrating the sandwich structure could be predicted, if the initial impact velocity of the bullet is known. The model prediction is consistent to the experimental results. The limitations of the model are also further discussed.