Effects of thermo-oxidative aging on progressive bending damages and electromechanical behaviors of carbon fiber/epoxy 3D woven composites

The effect of thermo-oxidative aging on mechanical properties is important to designing carbon fiber-reinforced composites serviced in long-term atmospheric environments. Here, we report the progressive bending damage behaviors of carbon fiber/epoxy 3D angle-interlock woven composites (3DAWCs) after thermo-oxidative aging. Three-point bending tests were conducted to characterize bending damage behaviors after different aging days. The electrical resistance change of 3DAWCs was also simultaneously measured with the two-probe method during three-point bending tests. Combining side image and digital image correlation (DIC) technology, we found that the bending strength and modulus deteriorated rapidly during thermo-oxidative aging. The strain distribution and progressive bending damage modes also changed significantly, i.e., a symmetrical strain distribution for the unaged specimens, while the existing interface cracks of the aged specimen changed this symmetry. The electrical resistance method (ERM) effectively identified the early-stage damages, and the first derivative of the rate of resistance change (FDC) revealed differences in the progressive damage modes of aged and unaged specimens.