Hybrid composites using out-of-autoclave process for aerospace sub-structures

Carbon/epoxy composite parts are replacing traditional aluminum aerospace components. However, replacing aluminum parts with composites will require bonding/riveting of the composite parts to the aluminum structure. The coefficient of thermal expansion of carbon/epoxy composites is significantly lower than aluminum and directly bonding carbon/epoxy composites to aluminum will result is large residual thermal stresses which can lead to failure. To overcome this issue, glass/epoxy composite laminates are introduced in between the aluminum and carbon/epoxy to bridge the mismatch in thermal expansion. In the present study, hybrid carbon-glass/epoxy composite laminates have been fabricated using the Out-of-Autoclave (OOA) manufacturing process. OOA is a oven/vacuum bagging process in which prepregs are laid-up and vacuum bagged. The prepregs are then cured in an oven. The OOA process does not require external pressure which is typical to the traditional autoclave molding process and produces high quality composite parts. The hybrid panels are bonded to an aluminum substrate. The response of these panels to mechanical and thermal loads is studied. The test results obtained are compared with finite element simulation. The input material properties for the simulation are determined experimentally. The simulation results are in good agreement with experimental values. Results indicate that hybrid composites exhibit significant increase in failure strains and have lower thermal strains as compared to the carbon/epoxy composites.