The Effect of Functionally‐Graded Voids and GNPs on the Damage Tolerance of Polyurethane Foam Core

Abstract

AbstractThe weight of sandwich composite structures with foam cores mainly depends on the volume fraction and the distribution of air voids in its porous structure. A considerable reduction of the weight can be achieved at the expense of mechanical and strength properties by increasing the fraction of air voids in the sandwich composite's core. Therefore, high stiffness nano‐fillers such as graphene nano‐platelets (GNPs) are frequently used to improve the specific stiffness and mechanical strength of sandwich composites without sacrificing from the lightweight requirements. In this contribution, the effect of the square‐ and circle‐shaped distributions of air‐voids and GNPs on damage tolerance properties of thermoplastic polyurethane (TPU) resin is investigated. TPU foams with randomly oriented air voids and GNPs are used as a baseline to evaluate the improvement of the properties mentioned above. For that purpose, finite element based micro‐mechanical models for representative volume elements (RVEs) are used to homogenize the properties of multi‐scale models of TPU foam. The analysis results show that the air pores increase the ductility of brittle TPU resin significantly when the pores are non‐linearly distributed in circular functionally graded (FG) shape. Besides, it is concluded that Young's modulus degradation associated with the use of linearly distributed air‐voids composed of the square‐shaped FG foam can be compensated by using GNPs. The results of the study suggest that the functional grading design of TPU foam has excellent potential for applications, which require meeting the challenging weight, strength, stiffness and toughness requirements at the same time.