Investigating the Composite/Metal Interface and its Influence on the Electrical Resistance Measurement

The advantages introduced by carbon fiber reinforced polymer (CFRP) composites has made them an appropriate choice in many applications and an ideal replacement for conventional materials. The benefits using CFRP composites are due to their lightweight, high stiffness, as well as corrosion resistance. For this reason, there is a fast growing trend in using CFRP composites for aircraft and wind turbine structural applications. The replacement of the conventional aerospace-grade metal alloys (aluminum, titanium, magnesium, etc.) with CFRP composites results in new challenges. For example, an aircraft during flight is prone to be struck by lightning. To withstand the injection of such massive amount of energy, adequate electrical properties, mainly electrical conductivity, is required. In fact, electrical conductance (or its reciprocal, resistance) is a critical parameter representing any material change and it can be considered an index for health monitoring. In this paper, AS4/8552 carbon/epoxy laminated composites were injected with two types of electrical currents, impulse current and direct current. The change in measured electrical resistance was recorded. A significant resistance drop occurred after electrical current injections. Furthermore, four-point flexural tests were performed on these composites to correlate an electrical resistance change with a potential flexural property change. There was no clear trend between a resistance change and flexural strength/modulus change of the test coupons, regardless of current injection. However, it was observed that the injection of the current affects the contact resistance such that its resistance decreases.