Modeling the Tension-Compression Asymmetric Yield Behavior of -Treated Zircaloy-4

Zirconium alloys such as Zircaloy-4 are used in nuclear applications due to adequate strength, ductility and resistance to radiation damage. Recent modeling efforts have focused on improvements to the predicted elastic–plastic response, complicated by the strong strength-differential (S-D) effects in HCP materials. This study develops a pressure-insensitive, continuum plasticity model, dependent on the second and third invariants of the stress deviator (J2 and J3), with an internal variable related to the plastic strain to describe the tension–compression asymmetry of a β-treated Zircaloy-4. Plastic deformation drives isotropic and distortional hardening of the non-Mises yield surface. The proposed plasticity model has been calibrated and validated using measured results from an experimental test program. Results show that the proposed model captures the complex elastic–plastic response observed in measured load–displacement and torque–rotation curves over a range of triaxiality and Lode parameter values

On the Extension of the Gurson-Type Porous Plasticity Models for Prediction of Ductile Fracture under Shear-Dominated Conditions

One of the major drawbacks of the Gurson-type of porous plasticity models is the inability of these models to predict material failure under low stress triaxiality, shear dominated conditions. This study addresses this issue by combining the damage mechanics concept with the porous plasticity model that accounts for void nucleation, growth and coalescence. In particular, the widely adopted Gurson–Tvergaard–Needleman (GTN) model is extended by coupling two damage parameters, representing the volumetric damage (void volume fraction) and the shear damage, respectively, into the yield function and flow potential. The effectiveness of the new model is illustrated through a series of numerical tests comparing its performance with existing models. The current model not only is capable of predicting damage and fracture under low (even negative) triaxiality conditions but also suppresses spurious damage that has been shown to develop in earlier modifications of the GTN model for moderate to high triaxiality regimes. Finally the modified GTN model is applied to predict the ductile fracture behavior of a beta-treated Zircaloy-4 by coupling the proposed damage modeling framework with a recently developed J2–J3 plasticity model for the matrix material. Model parameters are calibrated using experimental data, and the calibrated model predicts failure initiation and propagation in various specimens experiencing a wide range of triaxiality and Lode parameter combinations

Application of the Plasticity Models That Involve Three Stress Invariants

Increasing experimental evidence shows that the classical J2 plasticity theory may not fully describe the plastic response of many materials, including some metallic alloys. In this paper, the effect of stress state on plasticity and the general forms of the yield function and flow potential for isotropic materials are assumed to be functions of the first invariant of the stress tensor (I1) and the second and third invariants of the deviatoric stress tensor (J2 and J3). A 5083 aluminum alloy, Nitronic 40 (a stainless steel), and Zircaloy-4 (a zirconium alloy) were tested under tension, compression, torsion, combined torsion–tension and combined torsion–compression at room temperature to demonstrate the applicability of a proposed I1-J2-J3 dependent model. The I1-J2-J3 dependent plasticity model was implemented in ABAQUS via a user defined subroutine. The model parameters were determined and validated by comparing the numerically predicted and experimentally measured load versus displacement and/or torque versus twist angle curves. The results showed that the proposed model incorporating the I1-J2-J3 dependence produced output that matched experimental data more closely than the classical J2 plasticity theory for the loading conditions and materials tested. Read More: http://www.worldscientific.com/doi/abs/10.1142/S175882511250021