Adopting the functionally graded materials concept and different manufacturing procedures to enhance the efficiency of the pin joints in fiber metal laminates sandwich panels

Fiber metal laminates (FMLs) sandwich panels are typically installed using mechanical joints. This investigation aims to enhance the bearing behavior of pin joints made of aluminum 1050–E glass FMLs. A novel core modification was achieved using a functionally graded material (FGM) technique. The impact of inserting aluminum layers at the mid-thickness of the specimens and stacking sequences of the composite core ([Al/(0o/90o/0o)s/Al] and [Al/(90o/0o/90o)s/Al]) on joint performance was also examined across different ratios of joint geometries. Furthermore, composite-like and sandwich-like layups were also compared. All tests were conducted in accordance with ASTM D5931/5961 M-17. The results indicated that the sandwich-like layup slightly enhanced the bearing strength of these joints, ranging from 1.37% to 6.16% depending on the joint geometry. Notably, inserting the mid-aluminum layer increased joint bearing strength by 11.18% by constraining delamination within the composite core. Using an FGM technique can increase the bearing strength of pin joints in FMLs by up to 27%. Furthermore, visual examination indicated that the [0°] layers exhibited shear-out, while the [90°] layers failed in net tension. The SEM images show fiber breakage, fiber-matrix debonding, matrix crack, delamination between the [0°] and [90°] composite layers, and delamination between the composite and metal layers.