Metal fiber incorporation in carbon fiber reinforced polymers (CFRP) for improved electrical conductivity

Compared to aluminum alloys, contemporary carbon fiber reinforced polymers (CFRP) structures offer poor electrical conductivity. Additional metal elements are necessary to fulfill important electrical functions like lightning strike protection, electromagnetical shielding, electrical bonding and grounding, compromising carbon fiber reinforced polymers' lightweight potential. Past research attempts tried to overcome this drawback by modifying the resin system, but could not demonstrate sufficient improvements. A different approach is the incorporation of highly conductive endless metal fibers into the carbon fiber reinforced polymers. The increased density of the composite is compensated by eliminating the need for additional electrical system installation items. The present paper covers the feasibility of this novel hybrid material concept. For this purpose, electrical conductivity tests are realized on unidirectional coupons with different steel fiber volume fractions and compared with analytical values. Stainless chrome-nickel steel fibers as well as copper cladded low carbon steel fibers are investigated. First, the specific conductance of the steel fibers is determined. These values are used to calculate the potential conductivity of unidirectional reinforced hybrid laminates based on the rule of mixture. Subsequently, unidirectional reinforced hybrid laminates with different steel fiber fractions are manufactured. The specific conductance of these composites is measured, using an in-house developed conductivity testing facility. The test results show that by incorporating steel fibers the electrical conductance of the composite can be increased by a factor of 29.8, compared to conventional carbon fiber reinforced polymers.