Sharif Digital Repository

Most engineering components are subjected to multiaxial rather than uniaxial cyclic loading, which causes multiaxial fatigue. The pre-requisite to predict the fatigue life of such components is to determine the multiaxial stressstrain relationship. In this paper the multiaxial cyclic stress-strain model under proportional loading is derived using the modified power law stress-strain relationship. The equivalent strain amplitude consisted of the normal strain excursion and maximum shear strain amplitude is used in the proportional model to include the additional hardening effect due to nonproportional loading. Therefore a new multiaxial cyclic stress-strain relationship is devised for out of... 

Knowledge of the complete multiaxial residual stress distribution in engineering components is essential for assessing their integrity. Often, however, only limited measurements are made. Here, an analysis is presented for determining the multiaxial distribution from a limited set of measurements. These measurements are used with an assumed plastic strain distribution. Residual stress measurements were made on hot forged and shot blasted steel bars using X-ray and neutron diffraction techniques. The residual stresses were measured on the surface and at selected interior points of the specimens. The predicted multiaxial distributions were compared with experimental measurements obtained using... 

In the present paper, a steering knuckle of a passenger car that serves as a highly critical component from the safety point of view, is considered to evaluate accuracy some of categories of the multiaxial fatigue criteria, through comparing their predictions with the experimental results. This component is subjected to the highest road- and steering-induced random and non-proportional loads that are exerted on several points of the component. The mechanical properties and fatigue strengths are determined experimentally and the fatigue life assessment tests are performed by the authors. Quantometric analyses and scanning electron microscope (SEM) have been employed to detect the failure... 

This paper presents a new phenomenological constitutive model for shape memory alloys, developed within the framework of irreversible thermodynamics and based on a scalar and a tensorial internal variable. In particular, the model uses a measure of the amount of stress-induced martensite as scalar internal variable and the preferred direction of variants as independent tensorial internal variable. Using this approach, it is possible to account for variant reorientation and for the effects of multiaxial non-proportional loadings in a more accurate form than previously done. In particular, we propose a model that has the property of completely decoupling the pure reorientation mechanism from... 

In composites, the stress intensity factors (SIFs) of a lamellar inhomogeneity near a multiphase reinforcement are of interest. Based on extension of Eshelby's equivalent inclusion method, a unified approach is presented to study the effect of a multiphase inhomogeneity on the SIF at the tip points of two- and threedimensional lamellar inhomogeneities under nonuniform far-field loadings. Alteration of the SIF due to the presence of a coating layer around the inhomogeneity is addressed. Furthermore, the effect of geometry and stiffness of each phase of a multiphase reinforcement on the mixed mode SIFs of a lamellar inhomogeneity is investigated. In contrast to cracks whose SIFs are the same... 

In this paper seven different multiaxial fatigue criteria based on stress, strain and energy were employed to estimate the fatigue lives of double shear lap joint specimens of aluminum 2024-T3 with bolt clamped and interference fitted-bolt clamped fastener holes. Detailed finite element (FE) simulations were conducted to obtain the stress and strain distributions in the joint to be used to as basic data in estimating the fatigue lives using multiaxial fatigue criteria. The estimated lives were compared with available experimental fatigue test results to investigate the capability of the criteria in predicting the fatigue lives. The results showed that the accuracy of life estimation for any... 

The ever increasing applications of shape memory polymers have motivated the development of appropriate constitutive models for these materials. In this work, we present a 3 D constitutive model for shape memory polymers under time-dependent multiaxial thermomechanical loadings in the small strain regime. The derivation is based on an additive decomposition of the strain into six parts and satisfying the second law of thermodynamics in Clausius-Duhem inequality form. In the constitutive model, the evolution laws for internal variables are derived during both cooling and heating thermomechanical loadings. The viscous effects are also fully accounted for in the proposed model. Further, we... 

Porous shape memory alloys (SMAs) exhibit the interesting characteristics of porous metals together with shape memory effect and pseudo-elasticity of SMAs that make them appropriate for biomedical applications. In this paper, a 3-D phenomenological constitutive model for the pseudo-elastic behavior and shape memory effect of porous SMAs is developed within the framework of irreversible thermodynamics. Comparing to micromechanical and computational models, the proposed model is computationally cost effective and predicts the behavior of porous SMAs under proportional and non-proportional multiaxial loadings. Considering the pressure dependency of phase transformation in porous SMAs, proper... 

Porous shape memory alloys are a class of very interesting materials exhibiting features typical of porous metals and of shape memory alloys. In contrast to dense shape memory alloys, considerable plastic strain accumulates in porous shape memory alloys even during phase transformation. Moreover, due to the microstructure of porous materials, phase transformation and plasticity phenomena are significantly pressure-dependent. In this article, we propose a three-dimensional phenomenological constitutive model for the thermomechanical behavior of porous shape memory alloys able to predict shape memory effect, pseudo-elastic behavior and plastic behavior under proportional as well as...