Tensile Shear Strength Improvement of 18-8 Stainless Steel/CFRP Joint Irradiated by Electron Beam Prior to Lamination Assembly and Hot-Pressing

摘要

Adhesive 2-layer lamination joints of 18 mass%Cr-8mass%Ni austenite stainless steel and carbon fiber reinforced polymer (18-8/CFRP joint) were prepared using a new adhesion method consisting of applying low dose of 0.13 MGy of homogeneous low energy electron beam irradiation (HLEBI) to connecting surfaces of the 18-8 and CFRP prior to lamination assembly and hot-pressing in vacuum below 1 Pa for 2 h at 401 +/- 0.5 K. Although untreated 18-8/CFRP joint exhibited decent adhesion by hot-pressing, application of 0.13 MGy HLEBI dose apparently improved the tensile shear strength tau(B) of the 18-8/CFRP joint 58% at median accumulative probability (P-B = 0.50) from 4.0 to 6.3 MPa. In addition, applying HLEBI from 0.13 and 0.30 MGy was found to enhance the tau(B) at all P-B. Based on the 3-parameter Weibull equation, the statistically lowest tau(B) value at P-B = 0 (tau(s)) was increased from zero to 4.39 MPa by the 0.13 MGy HLEBI. XPS (X-ray photoelectron spectrometry) measurements detected carbon on the shear-fractured 18-8 interface indicating the residual epoxy adhered well to the 18-8 by the HLEBI. This is probably a result of adhesion force of 18-8/CFRP being made stronger than the cohesive force of epoxy polymer in the CFRP itself. Since HLEBI cuts the chemical bonds and generates active terminated atoms with dangling bonds in epoxy polymer and passive film on 18-8, the increased adhesion force in the 18-8/CFRP joint can be explained by the chemical bonding and coulomb attractive forces thus induced at the interface. Since the experimental data shows the optimum HLEBI dose is about 0.13 MGy, above which at 0.30 MGy the tau(B) begins to drop off; carefulness in optimization is highly recommended when applying in industry to insure safety.