Investigation on in-situ dynamic impregnation forming mechanism of fiber metal superhybrid laminates

Abstract

Fiber Metal Laminates (FMLs) are considered ultra-hybrid composites due to their exceptional fatigue resistance and high damage tolerance. These characteristics make them ideal for critical thin-walled components in large aircraft. However, the forming and manufacturing of heterogeneous components is challenging due to the significant differences in their properties, the complexity of interfaces, and various defects like delamination and fracture. Focusing on the interface/interlaminar deformation-impregnation issue, this study proposed an in-situ dynamic impregnation forming method to transform the traditional static resin injection composite molding into a synchronized dynamic injection coupled with deep drawing. A specialized experimental setup was established to investigate the influence of injection flow rate on in-situ forming, the correlation of the injection starting point and the deep drawing depth, and the coupling mechanism between deep drawing speed and injection flow rate. The results revealed that an excessively high injection flow rate causes a bulging effect, causing laminate failure due to expansion and rupturing. Simultaneously, the injection flow rate critically affects the formation and location of pores. The injection starting point affects the resin flow direction and distribution between layers, and some defects may occur, such as resin overflow, wrinkling, misalignment, and dry spots. When the injection starting point is set at 0 % of the punch stroke, the resin injection begins at the start of deep drawing, improving the forming process quality. However, a mismatch between the deep drawing speed and the injection speed can affect the friction state and fiber deformation at the small intricate features, leading to defects such as pores, wrinkling, delamination, and interface debonding, which affect the interfacial bonding effect. This study provides a theoretical foundation for the in-depth analysis of the in-situ dynamic impregnation forming of Al/GFRP laminates, thereby promoting the applications of laminates.