Study On Residual Strength Of Structure With Double Crack Damage

Structural strength is one of the important indicators of the safety performance of marine structures.It is of crucial importance to estimate the ultimate strength of structures during the design and service of ships.During long-term use of ship and offshore structures,multi-crack damage will occur in its key parts under the action of fatigue loads.It will cause the residual strength of the structure to decrease sharply,which cannot guarantee the safety and service life of the structure.Therefore,it is particularly important to do research on prediction of residual strength of structures with multiple cracks.In this paper,based on the study of the residual strength of structures with two collinear cracks and two parallel cracks,finite element calculation was conducted to quantify the influences of crack inclination angle,and the change law and calculation model of residual strength of structures with double cracks are established.First,a new method was proposed to determine the crack-tip plastic zone for the inclined center-cracked plate.On the basis of the obtained relationship between the crack-tip plastic zone and the MCOD,finite element calculation were employed.It is verified that the plastic zone estimation method of straight crack is also applicable to the inclined crack model.Next,the plate models with two collinear cracks and two parallel cracks were established respectively,a numerical study was conducted to determine the size of the plastic zone inside the crack tip.And the residual strength for different crack models are presented basing on the plastic zone linkup criterion and finite element calculation was conducted to quantify the influences of plate sizes,elastic modulus,yield stress,length ratio on the calculation model.The calculation model of residual strength for crack damage structures with two collinear cracks and two parallel cracks were established respectively.Finally,on the basis of the above calculation models,the residual strength of the structure with double cracks was considered,and the effects of crack length ratio,crack inclination angle,crack vertical spacing ratio and crack lateral spacing ratio are obtained.And then,basing on the previous calculation model of residual strength for parallel cracks,a calculation model was proposed to determine the residual strength for double crack structures.The proposed method to determine residual strength for double crack structures is suitable for engineering application.