Measurement and prediction of embedded copper foil fatigue crack growth in multifunctional composite structure

Copper strips embedded in glass/epoxy composite compose a discrete-path multifunctional load-bearing configuration which can conduct electricity. This combination of materials permits efficient packaging of increasingly large numbers of electrical systems being installed in aircraft and vehicle systems. It also allows systems such as large aperture antennas to be embedded within an aircraft’s load-bearing structural skin. The fatigue fracture of the embedded metal foil is of interest since composite materials tend to be more fatigue resistant. Copper embedded glass/epoxy coupons were manufactured and fatigue tested at 35% and 50% of the composite ultimate tensile strength. Nondestructive evaluation was used to measure copper crack growth and debonding at the copper-to-composite interface. The debonding plays a key role controlling the crack growth. A combined experimental–analytical methodology is defined for establishing relationships between crack tip opening angle (CTOA), crack size, and crack growth rate of the embedded copper via a combined experimental-analysis approach.