Damage to Composites from Electrochemical Processes

Damage to a carbon fiber vinyl ester matrix composite material has been evaluated with different test techniques. Surface examination after long-term galvanic coupling in seawater indicated removal of the polymer matrix above carbon fibers in addition to previously found blisters. Therefore, two types of damage, blistering and dissolution, occurred due to galvanic interactions and seawater exposure. In a laboratory simulation of the process, after 90 h exposure in 3.5% NaCl with the composite at a potential of –0.65 V_SCE, regions of polymer surface dissolution were found. After 720 h, blistering was found accompanying dissolution. Imposing a potential of –1.2 V_SCE resulted in exposing carbon fibers after the covering polymer layer was rapidly removed. Laboratory testing techniques were found to simulate accurately long-term surface damage from galvanic marine exposure in seawater. Electrochemical mechanisms for the polymer dissolution process are discussed.