Formability and Springback Analysis of Aluminum/Polypropylene/Aluminum Sandwich Laminates
Kella, Caroline K.
2022-12-17
Abstract
The advancement in vehicle fuel efficiency brings about an increasing need to develop lightweight materials of equal or better mechanical properties compared to those of traditionally used materials. To meet this need, hybrid materials are being developed in which two or more different materials are combined to produce better structural performance than the original material themselves. One such hybrid material is a sandwich laminate, which is made of two thin skins of a high modulus material, such as a steel or an aluminum alloy, and a low density core of a lower modulus material, such as a polymer. The application of metal/polymer/metal sandwich laminates results in increased flexural stiffness per unit weight, higher flexural strength, and in some cases, vibration and noise abatement. Because of these advantages, they are being considered for many automotive body panel and structure applications to achieve significant weight reduction. Although a few studies have been published on the mechanical properties and formability of metal/polymer/metal sandwich laminates, continued growth in usage of such materials requires additional knowledge of their formability, springback characteristics, and failure modes during press forming operations. The objective of this research is to address the challenges of formability and springback of sandwich laminates made of aluminum skins and a polypropylene core with various thickness combinations. The effect of the polypropylene core on the formability of sandwich laminates is studied and compared to the formability of aluminum-aluminum laminates and monolithic aluminum sheets. The predicted forming limit curves are validated by comparing them to published experimental forming limit curves. The springback behavior of aluminum/polypropylene/aluminum laminates after draw bending of a U-channel is studied. Various process parameters such as die and punch radius, friction and blank holder force are studied to understand their effect on springback behavior of sandwich laminates. For accurate prediction of springback by finite element method, simulation parameters such as model type, material models and number integration points are studied. The springback results predicted by simulation are validated by comparing them to experimental springback values. The residual stress distribution through the thickness of the sandwich laminate of different thickness combinations is also studied and compared with the stress distribution in a single aluminum sheet of equal thickness. The various combinations of Al/PP/Al laminates studied in this research have lower weight than single aluminum sheets of equivalent bending stiffness. Their formability and springback are either equivalent or slightly lower than single aluminum sheets of equivalent thickness. For better formability and springback of the sandwich laminate, its core to skin thickness ratio can be adjusted, albeit with some sacrifice in weight savings.Deep Blue DOI
Subjects
Formability Springback Sandwich laminates Aluminum/Polypropylene/Aluminum Metal-Polymer-Metal laminates Residual stresses
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