Optimization of interlaminar shear strength behavior of anodized and unanodized ARALL composites fabricated through VARTM process

Aramid Aluminum laminates (ARALLs), which belong to the family of fiber metal laminates (FML’s) are prone to interlaminar shearing because of weak bonding between Aluminium and Kevlar layers. Moreover standard fabrication procedure of these composites is to use unidirectional fiber prepregs with Aluminium alloy sheets. The fabrication thus involves expensive semi prepared materials (prepregs) followed by autoclaving. Over the recent years VARTM (Vacuum assisted resin transfer molding) has emerged as a viable and low cost technique for composites fabrication. In this paper an alternative fabrication procedure for ARALL composites using VARTM has been presented. For this purpose Aluminium 2024 T3 alloy and plain woven Para-Aramid (Kevlar 49 from DuPont) fibrous tow sheets were used to make ARALL composites. ARALL comprises of one sheet of Kevlar in the center and two layers of Aluminum on its two sides. Two types of Aluminium sheets were prepared i.e., anodized and unanodized. Specimens were prepared using VARTM technology. Two types of post curing treatments were chosen. One group of specimens was post cured at 100 °C while the other group was left to cure at room temperature. T-peel tests were then conducted using ASTM D1876 standard on ARALL specimens thus prepared. This research study entails anodization and curing/post curing for enhancement of interfacial bonding so as to suppress interfacial debonding. Various parameters in this respect have been varied and their effect on the interfacial bond strength and thus on the Mode-I fracture toughness has been quantized. Experimental results, electrochemical characterization and optical/SEM observations of delaminated surfaces have established that anodization coupled with post curing results in an optimized interface between Aluminium alloy and Para-Aramid sheets. The optimization scheme described in this paper can be used to manufacture ARALL composites through low cost VARTM technology.