Characterization of Deformation and Failure Modes of Ordinary and Auxetic Foams at Different Length Scales
Sandwich panels with foam core have gained substantial importance in marine structures for the past several decades. However, designers of ships still lack the confidence in composites when compared to traditional structural materials such as aluminum or steel. As a result, composite structures tend to be overdesigned to provide added safety. While there have been numerous studies, most investigators treat the foam cores as made of homogeneous and isotropic materials. But at the length scale of the order of millimeter or smaller, foam is neither homogeneous nor isotropic. In this paper, we present some results of the characteristics of deformation and failure mechanism of polymer foam composites at different length scales. Central to this investigation is a multiscale digital speckle photography technique whereby we can measure detailed full deformation with spatial resolution ranging from centimeters to micrometers. We first investigate the size effect on the mechanical properties of polyurethane foams with and without nanoparticles, crack tip deformation field at different length scales, and the crack propagation characteristics in a foam. Then we present results for a newly created auxetic PVC foam composite. Auxetic materials have a negative Poisson's ratio rendering them to be more resistant to shear failure, indentation, and impact damages. We describe the manufacturing process of this material and demonstrate its advantageous properties as compared to the original foam.
KeywordsPolyurethane Foam Speckle Pattern Sandwich Panel Deformation Pattern Foam Core
The author gratefully acknowledges the support provide by the Office of Naval Research's Solid Mechanical Program under the leadership of Dr. Yapa D.S. Rajapakse. The development of the speckle technique was supported by earlier grants from ONR. The foam composite work was supported by the grant # N000140410357. The encouragement of Dr. Rajapakse is in-dispensible for the success of the work.
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