Roll bonding of metal-polymer-metal sandwich composites

Abstract

<p>Metal-polymer sandwich composites have been rapidly replacing metallic materials in the aerospace and automobile industries. Their desirable mechanical properties, including excellent fatigue and impact strength, as well as damage tolerance, are accomplished without sacrificing the benefit of lightweight. Manufacturing metal-polymer sandwich composites via roll bonding can offer great advantages over other techniques such as overmolding and injection molding, which are more complex and costly. Roll bonding of multilayer composites, however, is challenging because of the significant differences in the mechanical properties and the adhesion characteristics of polymeric and metallic materials. In this study, a three-layer metal-polymer-metal sandwich composite, which consisted of aluminum (AL1100) and polyurethane (PU), was successfully fabricated using a direct adhesion warm roll bonding (WRB) technique without the use of an adhesive agent. In the first part of this work, the effects of WRB process parameters, which include surface roughness, preheat temperature, rolling speed, and total thickness reduction, on the adhesion strength have been investigated using the peel test. Mechanical interlocking was the primary adhesion mechanism in direct bonding of the aluminum and polyurethane. The failure mode transitioned from adhesive to cohesive as the surface roughness increased. The optimum rolling speed and preheat temperature of the WRB process were identified. In the second part of this work, the small punch test (SPT) was employed to characterize the mechanical properties of the sandwich composites, including ultimate load, specific load, average stiffness, and specific fracture energy, at various thickness reductions. The results showed significant improvements in the specific fracture energy of the sandwich composites compared with monolithic material by 26%, 20%, and 36% at thickness reductions of 50%, 60%, and 75%, respectively. The presence of the soft layer in the sandwich composite helps to arrest cracking propagation. In the third part, glass fiber introduced at the interface of metal-polymer-metal laminated composites using the WRB process. The reinforcing effects of the glass fiber on the adhesion strength and shear resistance were analyzed. A single lap shear test, SPT, and T-peel test were used to evaluate the mechanical and bonding properties, and electron microscopy was employed to analyze the fracture behavior of the fiber-reinforced laminate composites. The shear strength of the glass fiber reinforced sandwich composite improved nearly 40% compared with the unreinforced samples. The SPT results showed increase in the ultimate load, specific load, and specific fracture energy for the samples with glass fibers incorporated between the roll-bonded layers.</p>