Abstract: The mechanical properties of 30 kg/m³, 45 kg/m³ and 60 kg/m³ foamed polypropylene foams with different densities were obtained through material compression experiments, and the cranial response of a dummy under the protection of a functional gradient foam lining subjected to high velocity impact of gunshot was tested and simulated to analyze the cranial biomechanical response under the combination of homogeneous foam, positive and negative gradients, and concave and convex gradients. Based on this, a new type of bulletproof helmet capable of resisting rifle bullets was developed, and the protective effect of functionally graded foam lining in bulletproof helmet was studied. The local and overall energy absorption of the foam was analyzed. The results show that the energy absorption of the layered foam is mainly concentrated in the support layer near the head, accounting for 62.33% of the total energy absorption of the foam; the gradient structure has more significant protection effect than the homogeneous structure when the average density is the same, and the negative gradient is better than the positive gradient in protection; the convex gradient structure increases the energy absorption by at least 19.57% compared with other gradient structures while reducing the overall weight.

Key words: bulletproofhelmet, bullet, functionallygradedfoam, high-speedimpact, protectiveproperty, energyabsorption