STRESS CONSENTRATION ANALISIS OF ANCHOR CHAINS SUBJECTED TO ABRASION OR CORROSION

Recently a floating structure tends to be in-placed offshore as long as twenty years. As anchor chains for mooring system, not only conventional ones having a stud but also new type ones without a stud are used. In such a case, durability of chains, especially fatigue strength is required. Fatigue strength depends on stress concentration factor (Kt). Besides this, erosion or abrasion concentrated in a contact area of chain links is taken into considerations for the evaluation of fatigue strength. Therefor, we conducted two dimensional stress analyses for the intact chain and the chains subjected to erosion or abrasion by linear Boundary Element Method (BEM). As a result, the following conclusions are obtained: Firstly the Kt of new type chains is greater than that of the conventional ones but the Kt induced in outer edge of link is almost equal to that in inner edge. Meanwhile the Kt induced in outer edge of conventional chains is larger than that in inner edge. The Kt of both new type chains and conventional ones having erosion or abrasion are greater than the ones of the undamaged chain by 14%.