Limit Load And J-integral Of Embedded Elliptical Cracks In Plates Under Combined Tension And Bending

When performing a structure integrity assessment,the limit load is used to define L_r,a parameter that measures the proxitmity to plastic collapse.Because the R6 method is based on the reference stress J-estimation approach,the limit load is a parameter against fracture.Therefore,a good limit load solution should be able to predict plastic collapse of the cracked structure and J values using the reference stress approach.The limit load,stress intensity factor and elastic-plastic J values of the plates with embedded elliptical cracks under combined tension and bending are obtained in the present work.The results of J are compared with the prediction using the reference stress method.(1) A limit load solution is derived for plates with embedded elliptical cracks under combined tension and bending based on net-section collapse principle.The limit load solution is compared with the results of elastic-plastic finit element analysis for the plates with different crack shapes(φ=0.2,0.4,1.0),different crack depths(α=0.1, 0.15,0.2,0.3),different crack offsets(κ=0,0.1,0.2) and different load ratios (λ=0,0.2,∞),the results show that the analytical solution of the limit load are conservative and the maximum difference between the analytical solution and the FEA results is less than 15%.(2) The stress intensity factor is obtained for the plates under pure tension and pure bending with different crack shapes(φ= 0.2,0.4,1.0),different crack depths(α=0.1, 0.15,0.2,0.3),different crack offsets(κ=0,0.1,0.2),the stress intensity factor for the plates under combined tension and bending can be obtained easily using Superposition Principle.(3) Fully plastic J solution is obtained for the plates with different crack shapes (φ= 0.2,0.4,1.0),different crack depths(α=0.1,0.15,0.2,0.3),different crack offsets (κ=0,0.1,0.2) and different load ratios(λ=0,0.2,oo) for two Ramberg-Osgood materials with n=5 and n=10 respectively.(4) Comparision of J values between FE and the prediction using the reference stress method shows that the prediction using the reference stress method is accurate for pure tension when using global limit load of plates with embedded elliptical cracks. However,it may significantly underestmate the FE J values for the cases under pure bending.Therefore,for a plate with an embedded elliptical defect under combined tension and bending,it is reasonable to use global limit load in a structure integrity assessment when the tension stress is dominant.However,it may lead to nonconservative result when bending stress is dominant.