EFFECTS OF THE CURE PRESSURE ON INTERLAMINAR SHEAR STRENGTH OF CFRP-STEEL HYBRID LAMINATE CURED BY HOT PRESSING FOR A SHORT TIME

摘要

In recent years, researches on the application of carbon fiber reinforced plastic (CFRP) of high specific stiffness and strength to various transportation vehicles have attracted much attention with the increasing requirements of energy saving vehicles and clean air environment. As a great progress, CFRP has been successfully applied to primary structures of airplanes, such as Airbus A380 and Boeing 787. In addition to CFRP, a kind of fiber metal laminate (FML) named Glare composed by glass fiber reinforced plastic (GFRP) layers and Aluminum alloy layers (GFRP-Al hybrid laminate) has been successfully applied to the upper fuselage of A380 and CFRP-Al hybrid laminates has been developed for the application of primary structural elements[1,2]. Now, more and more researchers and automotive manufacturers are concerned with the application of CFRP to the mass-produced automobiles to reduce the weight of cars due to the rapid increase of the fuel prices and the increasing word-wide requirements of clean air environment [3,4]. On the other hand, the application of CFRP to automobiles must consider different requirements compared to aircraft applications. One of the requirements is about the fabrication cost. Much lower fabrication cost of structural elements than that of aircraft is very important for the application of CFRP to the automotive structure. It is difficult to apply the technologies of autoclave or even vacuum assisted resin transfer molding (VaRTM) to the automotive structures due to the long cure time and the high energy consumption. Therefore, in order to explore a new cure method within very short time and with low energy consumption, the prepreg-based hot pressing for a short time comes into the front stage and several composite manufacturers have developed CFRP prepregs which can be cured by hot pressing for only several minutes[3,4]. Another requirement is relative to the adhesive strength between CFRP and metal. A proper adhesive strength to the CFRP-metal interface is required to effectively transfer the load between CFRP and metal for CFRP-metal joints or CFRP-metal hybrid structures. Many researches have been conducted to explore effective adhesive technologies[5,6]. In the new hot pressing cure technology for a short time, different cure pressures are recommended by different manufacturers. Thus, how to choose a proper cure pressure for the CFRP-steel hybrid laminates is not clarified. In this paper, CFRP-steel hybrid laminate is focused on for the fabrication of lightweight automotive elements. The effects of the cure pressure on the interlaminar shear strength of CFRP-steel hybrid laminate cured by hot pressing for a short time are investigated by short beam test of three-point bend. Three cure pressures of 5MPa, 8MPa, 13MPa are investigated. Furthermore, repeated thermal shock tests (-40°C to 150°C) of 500 cycles are conducted for the hybrid laminates cured at different cure pressures. The interlaminar shear strength of the hybrid laminates after thermal shock test is investigated. Experimental results shows that cure pressure has significant effects on the interlaminar shear strength of hybrid laminates and, the thermal shock also significantly affect the interlaminar shear strength of the hybrid laminates. The hybrid laminates cured at 8MPa gives relatively higher interlaminar shear strength.