Theoretical and experimental study of punched laminate composites protected by outer paper layer

Lightweight laminate composite sandwich-like materials are one of the most used composite materials. When a laminate composite is punched normally to the surface, the outer skin layer plays a protective role, which is studied in the present work by elucidating the corresponding stress distribution in the core. First, a theoretical framework is developed to predict the stress distribution in the core corresponding to different mechanical properties of the skin. Thus, the location of the highest stress is predicted and a potential failure domain in the core of the laminate composite is established. The theory is verified by novel photoelastic experiments developed and conducted in this work. In addition, a micromechanical model of behavior of paper filaments under compression is proposed and verified experimentally. Based on this model, a novel method of measuring Young's modulus and Poisson's ratio of compressed paper is proposed and demonstrated.