The Fatigue Strength Research Of A Typical Form Of Hull Longitudinals Of Bulk Carriers Structure

Fatigue failure is one of the principal failure modes of ship structures.In order to ensure the maximum safety of the ship operations,the fatigue strength of the region which is prone to fatigue failure should be checked. Hull Longitudinals'connections are the most vulnerable regions of fatigue damage because of the great stress peak caused by their geometric discontinuity.Therefore,the fatigue strength of the region has a very important influence on the entire operational life of the hull structure.Based on the theory of specification, the fatigue strength of Hull Longitudinals'connections are checked.Results show that longitudinals within the outer bottom are more vulnerable to fatigue failure than longitudinals within the inner bottom,and the more close to the hull bilge,the higher degree of longitudinals'cumulative damage will accumulate.Meanwhile,four different methods have been used in this paper to check the fatigue strength of the same longitudinal. Results show that hot spot stress method is more accurate than the simplified method of nominal stress.Based on the method of hot spot stress, a large number of local finite element models of a typical form of hull longitudinals is analyzed in this paper by using MSC.Patran /Nastran software . The influence of four different size factors, the thickness of outer plate and the magnitude of lateral load on stress concentration factor(SCF)for hot spots of ship watertight and non-watertight connections are considered.Finally, based on the method of hot spot stress , the hull structure is analyzed under lateral loads and wave bending moments in the finite element model of three cargo holds. Then the SCF(Kf and Kg)which is obtained by the above analysis is applied to a new combination of hot spot stress range. Data results show that the conclusion obtained by local finite element analysis have some value,and can be used in actual engineering.