Tensile and compressive properties of polymer laminates containing internal sensor cavities

This research paper presents an experimental study into the effect of introducing long, narrow interlaminar galleries on the tensile and compressive properties of aerospace carbon/epoxy laminates. Galleries are thin and long holes used for the installation of small measuring devices, such as structural health monitoring (SHM) sensors. The galleries considered in this study are similar to those used in a novel SHM system known as comparative vacuum monitoring (CVM), developed for damage detection in aircraft structures. The effects of the shape, size and orientation of open-hole galleries on the in-plane tensile and compressive properties of a carbon/epoxy laminate were experimentally determined. The modulus and strength properties decrease with increasing gallery diameter (above a critical size) due to ply waviness around the galleries, reduced load-bearing area, and reduced fibre volume content caused by swelling. The mechanical properties of the laminate are generally higher when the galleries are aligned in the longitudinal (0°) direction to the applied load compared to the transverse (90°) direction. This is because a higher percentage of load-bearing plies are distorted by galleries in the transverse direction. An analytical model is presented for calculating the elastic modulus of laminates containing galleries. A simplified model is also presented for determining the strength of laminates with galleries aligned longitudinal to the load direction. The models and data presented in the paper can be used in the design of aerospace composite structures containing interlaminar sensor cavities for comparative vacuum monitoring.