Foam core sandwich composites were subjected to creep to failure and cyclic (loading/unloading) creep in seawater in order to mimic an actual ship hull service lifetime scenario. In spite of minute water absorption observed in the creep to failure tests, about 15% higher deflection and over 50% reduction in the overall lifetime were observed in specimens subjected to seawater as compared with tests performed in air; which is explained in terms of various possible paths to interface cell wall collapse. In the cyclic creep testing performed in seawater, the specimens were loaded for 24 h while the unloading (relaxation) times were varied from 24 to 6 h. Significantly reduced life and extensive damage were observed under cyclic creep as compared with creep to failure specimens. Curiously, lifetime and number of cycles to failure were found to decrease as a function of increasing relaxation periods. Modes of failure were predominantly indentation and core compression.
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