Fatigue Strength Analysis Of Aluminum Alloy Partiton Bulkhead Structure Of Long Superstructure

Fatigue damage of ship structure under the action of cyclic wave load is common.Fatigue strength is an important factor affecting the life of ship structure,and classification societies around the world pay particular attention to the fatigue assessment of ship structure.With years of research work,there are corresponding assessment methods for many types of ships.For large ships with long superstructure such as cruise ships,passenger ships and navy vessels,with the development of lightweight design of ship structures,aluminum alloy materials are more widely used in superstructure.Then,the long superstructure of navy ship has a high degree of participation in the longitudinal strength,so the stress level of each superstructure component is high.In the design work,it is considered that the light bulkhead structure is not involved in the longitudinal strength,so people has not paid enough attention to the strength of light bulkhead.However,the light bulkhead is connected with the main structure of superstructure,and deforms with the main structure of superstructure,and also participates in the longitudinal bending.However,the aluminum light bulkhead structure has thin thickness,weak material and anti-fatigue capacity.Especially,the stress concentration positions which are located in the opening corner of the door frame mounted on light bulkheads are easier to cause the shortage of fatigue resistance.In this thesis,the aluminum alloy superstructure of a navy ship was taken as an example to study on the fatigue assessment method,numerical simulation prediction and structural optimization of the light bulkhead structure in superstructure.The main research contents are as follows :(1)The fatigue load response calculation of the light bulkhead structure in the first floor of superstructure was carried out through the whole ship structure model.The stress concentration positions of the aluminum alloy light bulkhead structure were selected according to calculation results.According to the geometric shape and stress state of joints,three typical evaluation joints were obtained.(2)Aiming at the fatigue joints selected from the fatigue load response calculation results of aluminum alloy light bulkhead structure,the nominal stress method,hot-spot stress method and linear cumulative damage model based on Palmgren-Miner rule were used to calculate the fatigue life of typical joints of aluminum alloy light bulkhead structure,and the position of joints that do not meet the life requirements was determined.(3)The structural optimization design of joints that do not meet the life requirements was carried out.The structural types of rectangular opening corner joints of aluminum alloy light bulkhead were discussed by three optimization directions,and the structural design types that meet the evaluation requirements in different optimization directions were obtained.