The ultrasonically induced cavitation erosion of fiber glass reinforced epoxy and nodular cast iron (NCI) in seawater

An investigation was carried out to study and compare the cavitation erosion behavior of a non-metallic fiber glass reinforced epoxy system and a metallic nodular cast iron (UNS F32800) alloy utilizing an ultrasonically induced cavitation facility in seawater. The cavitation tests were made at a frequency of 20 KHz as per ASTM-G30-90 and at a temperature of 25⁰C. the cavitation action increased the rate of mass loss of both the fiber glass reinforced epoxy and that of the UNS F32800 by several orders of magnitude with respect to stagnant conditions. Cavitation also made the surfaces of the fiber glass reinforced epoxy and UNS F32800 very rough, exhibiting large cavity pit in the region of the attacked area as revealed by the scanning electron microscope (SEM). The main mechanisms of failure for the fiber glass epoxy system was due to loss of adhesion of the matrix / fiber glass interface and subsequent removal of the resin as well as glass fibers by the mechanical action of cavitation. However, the failure of UNS F32800 was due to severe plastic deformation and the fragmentation of the graphite nodules . Mechanical factors and surface defects were determined to be the leading cause of resin and glass fiber loss for the epoxy system and micro-galvanic activities between the ferrite matrix and graphite nodules for the UNS F32800.