Journal of Stress Analysis
Volume:2 Issue: 2, Autumn-Winter 2017-18

Investigation of residual stresses is of crucial importance due to their effect on the performance of engineering components. Recently, inverse methods have been developed for determination of the residual stresses. Inverse eigenstrain method is one of the mentioned inverse methods. The inverse eigenstrain method, which is based on the eigenstrain theory, uses limited measurements of residual elastic strains obtained from the experimental tests. In this study, effective parameters on result accuracy obtained from the 2D inverse eigenstrain method in residual stresses measurement were investigated using numerical experiment. The results indicated that in the inverse eigenstrain method the accuracy of the results increases with increasing the basis functions order and the number of the points where displacement is measured. Additionally, the result accuracy increases selecting the appropriate basis functions. Moreover, in this paper the inverse eigenstrain method was applied for an actual part. The results showed that in the real conditions too, accurate results can be obtained by selecting the appropriate parameters of the inverse eigenstrain method.

In this study, crankshaft failure of four-cylinder light-duty truck diesel engine was examined. The failure occurred by fatigue crack growth which was initiated from a surface defect after about 95000 km on the second crankpin from the crankpin-web fillet where the stress concentration was at the highest level. To evaluate the mechanical properties, some hardness and tensile tests were conducted and spectrometry analysis was used for studying the chemical composition of the crankshaft material. Additionally, for considering and evaluating the microstructure, microcracks, fracture surface, and the cause of failure, optical microscopy (OM) and scanning electron microscopy (SEM) equipped with energy dispersive spectrometry (EDS) were used. The morphology of the fracture surface showed a smooth and flat crack initiation with the beach marks and ratchet marks and second crack propagation zone with beach marks and fast final fracture zone near the end. The results of EDS observations indicated that inclusions of non-metallic aren’t distributed throughout on the steel and in some places leads to the formation of the microcrack clusters.

In this study, a nonlinear superelastic bending of shape memory alloy (SMA) beam with consideration of the material and geometric nonlinearity effects which are coupled with each other, has been investigated. By using the Timoshenko beam theory and applying the principle of virtual work, the governing equations were extracted. In this regard, Von Karman strains were applied to take the large deflections into account. Via Boyd-Lagoudas 3D constitutive model, SMA was simulated, which was properly reduced to two dimensions. With the development of an iterative nonlinear finite element model, and for the purpose of obtaining characteristic of finite element beam, the Galerkin weighted-residual method was applied. In this study, by considering the different force and support conditions for the SMA beam, their effects on the distribution of martensitic volume fraction (MVF) and stress distribution were investigated. The obtained results indicate that the magnitude of MVF and consequently the level of hysteresis increases, which leads to the reduction of the modulus of elasticity and the strength of the material and therefore the deflection of SMA beam increases consequently. To validate the proposed formulation, the results were compared with other experimental and numerical results and a good agreement was achieved between outcomes.

Recent studies on the mechanics of materials have shown that the ductile fracture is significantly affected by the stress invariants among progressive plastic deformation. In this paper the micro-mechanical Gurson-TvergaardNeedleman (GTN) model is utilized to investigate the fracture behavior of high-strength steel AISI 4340 under various stress triaxialities. Experimental tensile tests were conducted on the smooth and notched round-bar specimens to evaluate the effect of the stress triaxiality on the fracture initiation. Subsequently, finite element (FE) simulations were implemented using Abaqus/Explicit via the user subroutine VUMAT. The comparison between the simulations and experimental results indicate the best accuracy of the GTN micromechanical model to appraise the ductile fracture initiation. Furthermore, the results demonstrate the significant effect of the stress triaxiality value on the start of the ductile rupture.

Under cyclic loading, the plastic zone becomes complicated during unloading. The energy-absorbing cyclic plastic zone is a stimulant for crack growth and can be a criterion for determining the damage around the fatigue crack tip. Presenting analytical models for determining the shape and size of the plastic zone often makes restrictive assumptions such as elastic-perfectly plastic response. In this research, the effects of non-linear kinematic hardening behavior of pure copper on the cyclic plastic reaction of the crack tip in different conditions were investigated. Chaboche nonlinear material model was used to determine the hardening parameters. According to the numerical results, the cyclic plastic zone around the crack tip was constant in the same load range but load ratio had a slight effect on this zone. Moreover, presence of the kinematic hardening in the cyclic loading caused reverse plastic zone to be predicted smaller than analytical model. According to the results, for materials such as pure copper with kinematic hardening behavior, the cyclic plastic zone increases with increase in the crack length. Therefore, the cyclic plastic zone, as well as other parameters in the fracture mechanics can be a proper criterion for fatigue crack growth studies.

This paper is concerned with the theoretical treatment of thermoelastic problem in multilayer elliptical composite plate and the generation of heat in the body as well as at the interfaces with imperfect thermal contact under arbitrary initial temperature distribution. In order to obtain a closed-form solution of transient heat conduction problem, an alternative approach using a new Sturm-Liouville integral transform is presented that considers the series expansion using the eigenfunction expansion method for Sturm-Liouville boundary value problem. Any particular case of special interest can be
derived from assigning suitable values to the parameters and functions of the temperature field and its associated stresses. As a particular case, the quandary on the heat conduction and its stresses on a two-layered elliptical plate were solved.