An Analytical Method of Determining Damage Initiation for Potential Use in Establishing Strain-Based Failure Criteria

This paper proposes a methodology for analytically determining the initiation of ductile fracture due to the nucleation, growth, and coalescence of voids. Since structural damages in the shipping packages of radioactive materials are judged to be mainly caused by ductile fracture rather than shear fracture due to shear band localization, the proposed methodology has potential use in establishing strain-based failure criteria. The proposed methodology is based on the concept that, to ensure its structural integrity, a package should be designed within the maximum load-carrying capability. The load-carrying capabilities for various states of stress can be determined from the load-displacement relationships obtained from the numerical simulations of various specimen tests. As a result, the maximum equivalent plastic strain corresponding to the maximum load-carrying capability can be expressed in terms of stress triaxiality. This paper demonstrates that it is possible to analytically determine the effective plastic strains at the damage initiation in the state of multiple stresses where the load-carrying capacity is at maximum. By considering both material and geometrical nonlinearity in the mathematical representations of structures, the maximum load-carrying capabilities can be calculated as long as the stress-strain data is given.