Damage in CFRP composites subjected to simulated lighting strikes - Assessment of thermal and mechanical responses

Abstract

Damage is inflicted upon Carbon Fiber Reinforced Polymer (CFRP) composite laminates using simulated lightning strikes to investigate the resulting residual mechanical properties. Seven different CFRP laminate specimens were exposed to simulated lightning strikes using three different electric waveforms. The three waveforms imposed were the 10/350 μs waveform, which simulates the first return stroke during a direct strike according to IEC 61400–24 Ed1.0. The second was a unipolar long stroke component, and the third was a combination of the first return stroke and the long stroke. After exposure to lightning, coupon specimens were prepared for mechanical testing. The test specimens were subsequently subjected to compression and shear loading to determine the post-strike mechanical properties. The compression tests were conducted using uniaxial coupons in accordance with ASTM standard D6641. The shear tests were conducted using V-notch specimens utilizing an Iosipescu test rig in accordance with ASTM standard D5379. Digital Image Correlation was used to capture the strain fields on the surface of the specimens. The results of the material coupon tests are compared with test results from pristine CFRP coupon samples that were not exposed to any electrical current. The shear and compression strengths, compressive and shear stress-strain curves, compressive and shear moduli, and the maximum temperature on the CFRP specimens during lightning tests are presented and discussed. Key results include that the largest reduction of strength occurred in the specimens that were subjected to the largest current and specific energy. The specific energy correlated more closely to the observed reduction of residual strength than the charge, and the damaged specimens displayed a higher degree of nonlinear stress-strain behavior than the pristine specimens.