Multiaxial Proportional Loading Research Articles

Mechanical Behavior of a Cu-Al-Be Shape Memory Alloy Under Multiaxial Proportional and Nonproportional Loadings

Abstract This paper is concerned with the mechanical behavior of a Cu-Al-Be Shape Memory Alloy (SMA). A large experimental database, made of tension-internal pressure tests and biaxial compressive tests, is reported. Particular attention is paid to the behavior of the material under multiaxial proportional and nonproportional loadings. Moreover, these two types of complementary tests allow for the determination, on the one hand, of the shape of the initial surface of transformation onset and, on the other hand, of the initial direction of the transformation strain rate. A generalized macroscopic J2-J3 criterion to describe the transformation onset is proposed and identified.

Long life fatigue under multiaxial loading

A life prediction model in the field of high-cycle (i.e. long-life) fatigue is presented in this paper. The proposed model applies in the case of constant amplitude multiaxial proportional and non-proportional loading. The problems of the fatigue limit criterion and of the fatigue life prediction are both addressed and comparisons with experimental data are shown. Some limited discussion of the stress gradient effect is also offered. Although the particular model developed here is better suited for ferritic steels, it is explained in the paper that the methodology used to obtain this model can be adequately adapted to derive mathematically consistent models for other classes of metallic materials.

Engineering Components under Multiaxial Loading

This paper deals with some of the most important theoretical approaches to calculate the fatigue life of engineering components under multiaxial-proportional loading. The calculation procedures which are to be followed are demonstrated using as an example, a notched shaft made from two different materials under uniaxial and multiaxial loading with constant and variable amplitudes. Particular attention is paid to the characterisation of the damaging mechanisms resulting from the sequence of the variable amplitude load cycles. The calculation accuracy is checked using appropriate experimental fatigue life results, and discussed in relation to the experimental effort necessary to determine the input data. In addition, the feasibility and limitations of the theoretical approaches are discussed.

Life of constructional materials in multiaxial proportional low-cycle

A method has been developed for calculation of the low-cycle life of constructional materials in multiaxial proportional loading. Thin-walled cylindrical tubular specimens of 08KH18N1OT stainless steel and VT3-1 titanium alloy were loaded by a torsional moment and by an axial force both in hard and in soft loading. It is shown that the form of the stressed and strained condition influences the fatigue life of constructional materials. On the basis of an analysis of the structure of the regression equations obtained the Coffin-Manson criterion was modified for the case of proportional loading by an axial force and a torsional moment. The calculation results obtained using the proposed method agree well with experimental data.

Multiaxial Creep of 2618 Aluminum Under Proportional Loading Steps

Creep data of 2618-T61 aluminum alloy under multistep multiaxial proportional loadings at 200°C (392°F) are reported. Two viscoplastic flow rules were developed using constant stress creep and creep recovery data. One was based on the accumulated strain (isotropic strain hardening), and the other on a tensorial state varible (kinematic hardening). Data were represented by two models: a nonrecoverable viscoplastic model, and a viscous-viscoelastic model in which the time-dependent strain was resolved into recoverable (viscoelastic) and nonrecoverable components. The modified superposition principle was used to predict the viscoelastic strain component under variable stress states. The experiments showed that the viscous-viscoelastic model with either isotropic strain hardening or kinematic hardening gave very good predictions of the material responses. Isotropic strain hardening was best in some step-down stress states. The viscoelastic component accounted for not only the recovery strain but also the transient creep strain upon reloadings and step-up loadings.