Currently, the life time of rubber marine fender (hereafter “fender”) hasbeen evaluated by the external damage but many of large size fendersare not visually deteriorated even after over 30 years of use. But, thereis a concern that material and performance maybe changed even thoughthey show no problems. Authors studied what kind of aging ishappening to the material and the performance of used fenders whichwere picked up from the floating oil storage tanks in the NOSB and theberths of VLCC terminals and found that the reaction force increaseswith a year. The rubber blocks were cut off from the used fenders andsliced into the test pieces for physical properties. The remarkable dropof strength and elongation showed only in the vicinity of surface andflat and modest increase of elasticity was seen in the main body. TheFinite Element Analysis with these material properties suggested thatthis change of material properties to be the reason of the increase ofreaction force. This tendency of aging was also obtained from theaccelerated aging of rubber material and scale models. The models afteraging broke earlier than the less aged models in the fatiguecompression cycle tests. The ultimate aging limit was assumed about60 to 70 years due to the fact that the models were broken at the firstcompression.
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