Environmentally induced changes in fatigue life and durability of marine structures and vessels

Abstract

Failure and fatigue life prediction becomes more important for design of composite marine vessels and structures as their application as constructive material increases. Harsh environmental operational conditions have a great impact on such structures. Realistic environmental input parameters for structural modeling of marine structures are crucial and can be obtained by conducting tests in real sea environment for prolonged periods, as opposed to usual accelerated laboratory experiments. The needed changes in the approach to the modelling of S-N curves for composite materials prescribed by the Classification societies, considering the material properties degradation due to the effects of water absorption, fouling marine organisms and prolonged exposure to the marine environment are discussed here. Regression analysis results for experimental data collected during a 2-year period are presented and a procedure for the decrease estimation of expected fatigue life is given for glass/polyester composite material for three different fiber layout configurations. All the submerged coupons with different fiber layout configuration exhibited a significant loss of ultimate tensile strength (UTS) which consequently shortened their fatigue life and decreased durability.