Improvement of low-temperature impact value of sandwich-structural (CFRP/ABS/CFRP) laminate plies by Homogeneous Low-Energy Electron Beam Irradiation (HLEBI)

Abstract

Experimental results show applying homogeneous low-energy electron beam irradiation (HLEBI) treatment of 0.30MGy to both sides of sandwich structural CFRP/ABS/CFRP composite constructed of an ABS core between two thin plies of carbon cross textile fiber/epoxy CFRP apparently increased Charpy impact values, auc at all fracture probabilities, Pf at temperatures of 77, 200 and 300 K, within the low temperature range of aircraft operation and below the minimum of reusable launch vehicle operation in space reported as 116K. At median-Pf = 0.50 auc was increased 98% from 11.4 to 22.5 kJm-2 at low temperature of 77 K, while the HLEBI increased auc at Pf = 0.50 221% and 25% at 200 and 300 K, respectively. Although the lowest statistical impact value calculated by the 3-parameter Weibull equation, as at Pf = 0 (as) was reduced in the 200K samples, as was improved for the 77 and 300K samples. The lower as for the 200K samples is probably the result of high scatter in the data although the auc was remarkably improved at all experimental Pf. In general, the auc increased with test temperature. Optical observation shows the HLEBI appears to increase the auc by preventing brittle shattering of the ABS core in the 77 and 200K samples, and increasing core ductility in the 300K samples. Within the outer single CFRP plies the HLEBI strengthens by generating dangling bonds in the epoxy matrix as micro-compressive forces increasing adhesion to the fibers by terminated atoms by Coulomb attractive force. Since calculated HLEBI penetration depth, Dth into the sample was less (119 μm) than the 265μm CFRP ply thickness, it is possible the strengthened plies carried the load protecting the ABS core. It is also possible the highly conductive carbon fibers transferred charge to the ABS core, generating dangling bonds and/or polarizing the ABS polymer strengthening the ABS itself preventing shattering.