Identifying the contributions of constituents to the fracture performance and failure mechanism of fiber metal laminate

Fiber metal laminate (FML) is a damage-tolerant material that has gained special attention in the aircraft industry. To clarify the confusing contributions of constituents to the quasi-static fracture performance and failure mechanism, six kinds of glass fiber reinforced aluminum laminates (Glare) were designed. Quasi-static fracture tests were carried out to examine their crack resistance, stable crack extension, and residual strength. Moreover, postmortem characterizations were performed to reveal the macro and micro failure morphologies. It was found that the glass fiber reinforced polymer (GFRP) layers can positively contribute to Glare's quasi-static fracture performance due to its in-situ quasi-brittle but not completely brittle fracture characteristics, which was shown by the special plateau formed on P-Delta a curve of Glare, and by the improved crack resistance, longer critical crack length, and higher residual strength in Glare with higher content of GFRP. However, the enhancement achieved by increasing the volume fraction of GFRP was not as effective as by increasing the aluminum thickness, since thickening aluminum in a limited range could increase the fracture toughness and promote the delamination and fiber pull-outs in Glare. To further identify the effect of the properties of the metal layer, a titanium-reinforced Glare was designed and tested. It was found to transform the fracture process to be titanium dominant, which delayed the fracture of GFRP and meandered the fracture path, then resulted in superior quasi-static fracture performance than the basic Glare.

Automated summary

Fiber metal laminate (FML) is a damage-tolerant material that is widely used in the aircraft industry. This study designed and tested different types of glass fiber reinforced aluminum laminates (Glare) to understand their fracture performance and failure mechanism. It was found that increasing the content of glass fiber reinforced polymer (GFRP) positively contributes to the quasi-static fracture performance of Glare. However, increasing the thickness of aluminum is more effective in enhancing the fracture toughness and promoting delamination and fiber pull-outs. Additionally, a titanium-reinforced Glare exhibited superior fracture performance compared to basic Glare, as it transformed the fracture process to be titanium dominant.