Protective performance of gradient encapsulating materials for printed circuit boards in fuze system during impact process

When the projectile penetrates a hard target at a high speed, the fuze system inside the projectile will inevitably withstand high impact load, and thus encapsulating protection is necessary to prevent the internal electronic components to fail. However, currently encapsulating materials are usually homogeneous and lack sufficient flexibility to resist complex impact loads. Carbon nanotubes (CNTs) reinforced gradient materials exhibit excellent toughness and buffer effect while it has not been applied in encapsulating protection of fuze system. Therefore, this article establishes a simplified projectile body system with different CNT gradient types in the fuze encapsulation and investigates the protective performance of the gradient encapsulating materials for printed circuit boards (PCBs) in fuze system during impact process. Firstly, homogeneous CNT reinforced epoxy matrix composite materials with different concentrations are prepared and 0.7 wt% CNT content is found to have highest quasi-static strength and dynamic strength. Next, a finite element model for a gradient encapsulating composite plate with a PCB is established, and its material model and relevant settings are verified by dropweight impact experiments. Finally, a simplified projectile model with gradient encapsulated fuze system impacting concrete panel is established and the protective effects of different axial and radial gradient types on the internal circuit system of the fuze are studied. The research results show that the protective performance of gradient materials is superior to that of homogeneous materials. Specifically, the failure speed and overload acceleration of the PCB in axial gradient material "V-L" (the CNT content gradually decreases from the head to the tail of the projectile) have increased from 400 m/s to 500 m/s and 42500 g-65000 g compared to homogeneous materials, respectively. The failure speed and overload acceleration of the PCB in radial gradient material "O-R" (the CNT content gradually increases from the exterior to the interior of the projectile) have increased from 400 m/s to 460 m/s and 42500 g-50000 g compared to homogeneous materials, respectively. This gradient encapsulating structure proposed in this article serves for the design of encapsulating protection of fuze systems.