Polymer matrix composites (PMC’s) are becoming increasingly common in structural applications. This trend is especially noticeable in the aerospace industry. The increased use of composite components is due to their higher specific strength and stiffness, better fatigue and corrosion resistance, and lighter weight compared to their metal counterparts. PMC’s are typically multi-layer materials, consisting of continuous fiber reinforcement embedded in a rigid polymer matrix. A major disadvantage of this laminate structure is a high susceptibility to defects and damage in the form of interlaminar fracture, or delamination, which can greatly compromise the structural integrity of the material. To reduce the maintenance costs on aircraft with extensive composite based airframe components, qualified repair processes are needed as these parts are expensive to replace.
In this project we are developing innovative injection repair processes that can improve the mechanical performance of repaired aerospace composite panels. The novelty of this method lies in adopting bisphenol E cyanate ester (BECy) resin which has a very low viscosity yet cures into a high glass transition temperature thermoset with excellent adhesive and mechanical properties. The repair process involves injecting the low viscosity BECy resin directly into the damaged area with the support of vacuum pressure.
Ultrasonic C-scan images of repaired specimens illustrate that the infiltration of BECy into the damage zone can be successfully achieved. The interlaminar shear strength restored after repair was evaluated by comparing the load bearing capacity of pristine, delaminated, and repaired specimens using a hole plate shear (HPS) testing procedure. The repair efficiency was estimated to be 155 %, demonstrating that the repaired samples were even stronger than the undamaged pristine sample. This project has also included significant research into the cure kinetics of the BECy resin, as well as the effect of cure state on the resin’s mechanical and adhesive properties.
Mahendra Thunga, Amy Bauer, Mufit Akinc, Michael Kessler