Study on static load performance of FMLs based on ultra-thin stainless-steel foils and cross-ply thin CFRP

Abstract

The ultra-thin stainless steel/CFRP laminates overcome the limitations in application due to the weight drawbacks of conventional thick cold-rolled stainless steel. By laminating these two high-performance materials, it allows enhanced design flexibility and exceptional formability, rendering them highly promising in various industries such as automotive structures, shipbuilding, and electronics. The existing research on steel/CFRP laminates primarily revolves around locally reinforcing CFRP with cold-rolled plates of typical thickness (≥1 mm). Nonetheless, there remains a dearth of investigations examining the mechanical properties of laminates with varying metal thicknesses under the same volume fraction, particularly for ultra-thin stainless steel below 0.1 mm in thickness. In this study, to investigate the influence of micron-scale thickness ultra-thin stainless-steel foils on the performance of fiber metal laminates (FMLs), the laminates were manufactured and characterized using stainless-steel foils with thicknesses of either 0.05 mm or 0.025 mm. The tension and bearing properties of cross-ply thin CFRP (30 g/m2) laminates were examined both with and without the incorporation of ultra-thin stainless-steel foils. The findings confirmed that a substantial improvement in tensile strength of up to 35 % when ultra-thin stainless-steel foils were incorporated, accompanied by a remarkable increase in modulus by 65 %. Furthermore, the addition of stainless-steel foils to CFRP composites shifted their failure mode from brittle failure to progressive damage during three-point bending tests. Notably, utilizing 0.025 mm thick stainless-steel foils not only enhanced the strength and modulus but also mitigated post-yield stiffness loss compared to FMLs incorporating 0.05 mm thick stainless-steel foils for cross-ply thin CFRP laminates. Further researches revealed that ultra-thin stainless-steel foils with a thickness of 0.025 mm exhibited improved compatibility for deformation with cross-ply thin CFRP as evidenced by both tensile and bending damage behavior.