Fatigue crack growth characterization of layered composite materials using acoustic emission

Natural Gas (NG) is mainly used for the generation of electricity. It is transported in liquefied form at -160 °C in vessels with specially insulated storage tanks. An advanced insulation material is used to protect the internal surface of the structure from both cryogenic conditions and fire; however, when damaged, fatigue cracking occurs under low frequency wave-induced vibrations experienced by the vessel. Mechanical tests were performed under cyclic loading, along with online fatigue crack monitoring using acoustic emission (AE) and resistive crack gauges to characterise growth behaviour. It was found that there is a general reduction in crack growth rate da/dN with increasing stress intensity factor range ΔK as crack growth approaches the layered interfaces, which is also independent of the stress range. Furthermore, estimates of da/dN and crack length obtained from AE signals are in close agreement with measurements from resistive crack gauges.