Didier Marquis

Ratchetting under tension-torsion loadings: experiments and modelling

Abstract This paper is concerned with the mechanical behaviour of 316 austenitic stainless steel under multiaxial loadings and particular attention is paid to ratchetting under tension–torsion non-proportional loadings. First, a series of uniaxial tests and biaxial tests has been carried out in order to calibrate five different cyclic plasticity models based on an isotropic hardening rule and a non-linear kinematic hardening rule. It is shown that this class of models gives quite good agreement between the experimental and numerical results. Second, another series of ratchetting tests has been carried out under tension–torsion loadings in order to test the prediction capacities of the previous models. It is shown that whereas the models have been calibrated with similar loading paths, four of the five selected models give poor predictions.

Triaxial tension-compression tests for multiaxial cyclic plasticity

Abstract The aim of this paper is to present triaxial tension–compression tests and a new triaxial specimen devoted to the study of cyclic plasticity under non-proportional loadings. Because the stress state in the central part of the specimen is not homogeneous, the analysis of the tests need a 3D finite element computation. The constitutive equations used in the simulations have been deduced from complex tension–torsion tests. The comparison between the structural analysis and the experimental results allows to determine the accuracy of the set of constitutive equations and if needed to optimize this set by modifying some hardening rules.

An Improvement of Multiaxial Ratchetting Modeling Via Yield Surface Distortion

Many theoretical studies have been made to describe multiaxial ratchetting and most of them have been concentrated on the location of the yield domain, not on its shape. In this paper; we introduce nonlinear kinematic constitutive equations consistent with ratchetting modeling into the distortional model of subsequent yield surfaces proposed by Kurtyka, T., and Zyczkowski, M. We use an efficient polycrystalline model to simulate complex tests including yield surface detections in order to get some reference predictions to use in the development of the constitutive laws introduced into the distoritional model. The distortional model is thus qualitatively identified with the polycrystalline model and then quantitatively identified with the experimental results on a type 316L stainless steel. It gives promising results.

Additional Hardening Due to Tension-Torsion Nonproportional Loadings: Influence of the Loading Path Shape

This paper is concerned with the mechanical behavior of Type 316 austenitic stainless steel under cyclic multiaxial loadings and particular attention is paid to the additional hardening due to the loading path shape. A 90° out-of-phase tension-torsion loading is usually considered in most of phenomenological models as the highest hardening cyclic path. An experimental investigation has been carried out in order to check this hypothesis, and it is shown that other loading paths lead to a higher hardening.

Analysis of the Failure of Ceramics Due to Subcritical Crack Growth

Failure conditions are assessed when ceramics exhibit Subcritical Crack Growth from preexisting flaws. In the framework of the weakest link theory and independent events hypothesis, a reliability analysis is carried out by modeling flaw distributions and crack growth laws. Experimental data obtained on a spinel Mn Zn ferrite subjected to five different load rates are analyzed by using an expression for the failure probability accounting for Subcritical Crack Growth.

Lifetime prediction of structures in anisothermal viscoplasticity coupled to damage

Abstract The anisothermal conditions are introduced in the constitutive equations of elastoviscoplasticity through the state kinetic coupling theory. This allows us to consider elasticity, isotropic and kinematic hardenings and damage as coupled phenomena that can be used to predict the crack initiation on structures by finite-element calculations. The identification of material parameters is performed in the range of temperature 20–650°C for the nickel-based alloy Inconel 718. Several levels of couplings in the structural calculations may be performed: uncoupled, locally coupled, and fully coupled. Two applications are given: the first one is devoted to the damage analysis of a hollow sphere by the fully coupled method whereas the second simulates the crack initiation in a notched plate subjected to a cyclic thermomechanical loading by the uncoupled approach.

Modeling of plasticity and aging as coupled phenomena

Abstract This paper concerns the study of the interaction between aging and plasticity in a 2024 aluminum-copper alloy. The framework of thermodynamics of irreversible processes is used to introduce the effect of aging in the constitutive equations by means of an internal variable. These constitutive equations are checked by comparing the prediction of uniaxial tests with the experimental responses. They are also introduced into a finite element code, and the evolution of notched structures shows that the coupling between aging and plasticity can strongly modify the distribution of the stresses.

Thermodynamics and phenomenology

The general way to derive constitutive equations for different phenomena, coupled or not, is briefly described with an emphasis on the choice of state variables and analytical expressions for the state potential and the (pseudo) potential of dissipation by qualitative experiments. Quantitative experiments are used to determine the numerical values of the materials dependent parameters. Applications are given for anisotropic damage coupled to stress-strain behaviour of materials, for aging coupled to plasticity and for magneto-mechanical couplings. A brief «state of the art» on localisation phenomena is given as a conclusion.

The Role of Mean Strain on the Stress Response in Nonproportional Cyclic Plasticity

ABSTRACT From nonproportional cyclic tension-torsion tests on metallic materials with different mean strains, it is shown that the mean strain has no effect on the stress response. Some conclusions about the modelling are deduced.

Additional Cyclic Hardening of metals under Tension-Torsion and Triaxial Tension-Compression Loadings

The additional cyclic hardening due to the nonproportionality of the loading has been shown for the first time by H. Lamba and O. Sidebottom, [1]. These first experimental results have clearly shown that the constitutive models developed from uniaxial experiments were not able to predict the behavior of metals under complex loadings. Since, a great number of experiments have been made in order to understand the hardening and the softening of metals under multiaxial loadings, [2], [3], [4], [5]. Now, a lot of phenomenological models of elasto-plasticity have been proposed for the description of the additional cyclic hardening under complex paths. In all cases, the authors consider that out of phase tension-torsion test leads to the maximum hardening, [6], [7], [8]. This hypothesis is now controversial. On one hand, some experimental data obtained, on a Nickel-Base alloy (waspaloy), with “butterfly” loading path, [9], exhibit a higher hardening than the one corresponding to a 90 deg. out-of-phase path. On the other hand, some simulations made with a micromechanical model due to G. Cailletaud lead for some very complex loading paths to a very high cyclic hardening, again higher than the one corresponding to an out-of-phase path.