An Isotropic Model for Cyclic Plasticity Calibrated on the Whole Shape of Hardening/Softening Evolution Curve

Abstract

This work presents a new isotropic model to describe the cyclic hardening/softening plasticity behavior of metals. The model requires three parameters to be evaluated experimentally. The physical behavior of each parameter is explained by sensitivity analysis. Compared to the Voce model, the proposed isotropic model has one more parameter, which may provide a better fit to the experimental data. For the new model, the incremental plasticity equation is also derived; this allows the model to be implemented in finite element codes, and in combination with kinematic models (Armstrong and Frederick, Chaboche), if the material cyclic hardening/softening evolution needs to be described numerically. As an example, the proposed model is applied to the case of a cyclically loaded copper alloy. An error analysis confirms a significant improvement with respect to the usual Voce formulation. Finally, a numerical algorithm is developed to implement the proposed isotropic model, currently not available in finite element codes, and to make a comparison with other cyclic plasticity models in the case of uniaxial stress and strain-controlled loading.

Benchmarks for Accelerated Cyclic Plasticity Models with Finite Elements

“…The material stabilizes when R reaches R ∞ , which (according to [4]) occurs approximately when the exponent bp = 5. Obviously, as is also pointed out in [4], a more precise way to determine the material stabilization is to plot the normalized maxima (Equation ( 4)) as a function of the accumulated plastic strain for several low-cycle fatigue tests; see [23]. For the CuAg alloy presented in [23], the material stabilizes when the exponent is approximately in the range 4 ÷ 12.…”

“…Obviously, as is also pointed out in [4], a more precise way to determine the material stabilization is to plot the normalized maxima (Equation ( 4)) as a function of the accumulated plastic strain for several low-cycle fatigue tests; see [23]. For the CuAg alloy presented in [23], the material stabilizes when the exponent is approximately in the range 4 ÷ 12. In case of strain-controlled loading, the plastic strain range per cycle ∆ε pl is approximately constant and the plastic strain accumulated after N cycles becomes [1,4]:…”

Metal Plasticity and Fatigue at High Temperature

“…As a part of this Special Issue, researchers were invited to submit their innovative research papers aimed at providing a state-of-the-art knowledge on the topic of metal plasticity, creep deformation and fatigue strength of metals operating at high temperatures, with emphasis on both experimental characterization and numerical modeling of material behavior. A total of eleven research papers were published [1][2][3][4][5][6][7][8][9][10][11].…”

“…The paper by Testa et al [10] describes a model to estimate the yield stress at different strain rates and temperatures for metals with body-centered-cubic (bcc) structure. Srnec Novak et al [11] develop a new isotropic model to describe the cyclic hardening/softening plasticity behavior of metals. The proposed model is described with three parameters which were calibrated based on LCF experimental data of CuAg alloy.…”

“…Papers in this Special Issue addressed different types of material, from stainless steel studied by [1,2,4,10], to aluminum alloys investigated by [3,6,9], Ni-based supper alloy in [8], spheroidal graphite iron by [7], and copper alloy discussed in [11].…”