Key Engineering Materials Vols. 348-349

Abstract: Parametrical elastic-plastic finite element analyses of a circumferentially notched shaft subjected to multiaxial synchronous fatigue loading are performed considering two load combinations: (1) constant tension with cyclic torsion and (2) constant torsion with cyclic tensioncompression. The load amplitudes and the mean loads are varied to investigate their influences on the local stress-strain responses. The Multilayer Plasticity Model of Besseling in conjunction with the von Mises yield criterion is applied to describe the elastic-plastic material behavior. Coarse and fine meshes as well as three different types of multilinear approximations (twenty-, five- and threesegments) of the material stress-strain curve are used. Numerical results are presented to reveal the mutual interactions between the applied normal and torsional loads and the stress-strain response at the notch-root.

Abstract: The fatigue damage behavior of three two-phase steels in the very high cycle fatigue regime (VHCF >108cycles) has been studied by both fatigue testing and microstructural investigation using SEM and TEM. The results show that the S-N curves can vary from a single to multi S-N curves, and there is also a transition of fatigue crack initiation from surface defect, subsurface defect such as inclusion to subsurface non defect area or matrix depending on the steel grades and its conditions. The surface crack initiation is caused by formation of irreversible slip bands at the free surface or around surface defect. Subsurface inclusion crack initiation is mainly caused by strain localization (slip bands) emanating at subsurface inclusion. Crack initiation in the subsurface non defect area occurs in the areas that are physically weak. It is also a fatigue damage process caused by micro cyclic plastic deformation. Formation of subsurface non defect fatigue crack origin is a crack initiation and propagation process.

Abstract: Light armors are used to protect people against light weapons for military and nonmilitary purposes such as protecting police and civilians against criminals or protecting people even in hunting. Today, they are usually manufactured from polymer matrix composites due to their high stiffness/weight ratio. The good ballistic property means the measure of absorbability of the kinetic energy of a bullet or projectile without any major injury on the person. Designing the armor for only penetration is not enough for protection. The backside deformation of the armor must be also investigated because the projectile can produce not only bruises and lacerations of the surface of the skin, but can also damage internal organs. In this study, the backside deformation is determined experimentally and analytically for Kevlar 29/Polivnyl Butyral and Polyethylene fiber composites.

Abstract: In this research, fatigue tests were carried out to investigate the fatigue behavior of corroded structural members in boundary with concrete. Specimens were corroded by accelerated exposure tests and then used in the fatigue tests. FEM analyses were also performed on the models of the corroded surfaces of the specimens and the simulated corrosion surfaces to investigate the stress concentration at the corrosion pit in the boundary. The experimental and analytical results clarified the fatigue behaviors of corroded steel plates in boundary with concrete. The method for evaluating and predicting the fatigue life of corroded steel members were also proposed.

Abstract: A procedure that makes use of a conventional stress value (ERS) is applied to spot welded joints. The ERS can be evaluated for every spot weld of the structural model. Through the use of ERS-N curves, fatigue data performed on different joint geometries can be successfully mixed together. One of the main aspects is that progressive damage deeply influences fatigue behaviour, so that a simple numerical solution neglecting accumulated damage is unable to foresee the whole fatigue life. In the present paper the method has been applied to many experimental results: it is shown that a unique criterion is able to deal with several different structures and materials.

Abstract: The paper presents a simplified version of the Notch Stress Intensity Factor (NSIF) approach useful for fatigue strength assessments of welded joints. The evaluation of the NSIF from a numerical analysis of the local stress field usually needs very refined meshes and then large computational effort. A relationship is proposed here to estimate the Notch Stress Intensity Factor from finite element analyses carried out by using a mesh pattern with a constant element size. The main advantage of the presented relationship is that only the elastic peak stress numerically evaluated at the V-notch tip is necessary to estimate the NSIF instead of the whole stress-distance set of data (that is why the method has been called Peak Stress Method, i.e. PSM). An application of the PSM to fatigue strength assessment of fillet welded joints made of structural steels and aluminium alloys under tensile or bending loads is presented. In those joints, only mode I stress distribution is singular at the weld toe due to the presence of a V-notch angle equal to 135 degrees.

Abstract: This paper proposes a method for evaluation of the Stress Intensity Factors (SIFs) of embedded cracks lying along the bisector of the welded toe angle. The SIFs are calculated on the basis of the JV parameter (extension of the J-integral to a sharp V-notch) for a path radius equal to the crack extension without modelling the crack. The numerical calculations in the paper show the stability of the proposed method also with course meshes.

Abstract: In this work the fatigue crack growth properties of friction stir welded butt joints are evaluated. Fatigue Crack Growth (FCG) tests have been carried out on two particle-reinforced aluminium alloys (AA6061/Al2O3/20p and AA7005/Al2O3/10p). FCG properties have been evaluated at the centre and at the side of the weld, respectively. The results are compared with FCG properties of base materials. The role of alumina in particles inside the matrix is evident in the threshold region: this can be explained in terms of Roughness Induced Crack Closure.

Abstract: A new interest has been increasingly directed in recent years to study the behaviour of joints provided with various kinds of fasteners and the mechanism of load transfer; profiting of the present capabilities of computing systems and analysis codes, which appear such as to deal with models built with more than one million elements, thanks to new numerical techniques which can solve huge systems of equations. However, the main interest has been limited to the case of bolted joints, for which several models are now available, while a few results are known for the case of riveted joints, where more complex mechanisms are involved. In the present paper a full set of analyses has been reported, with reference to both normal and blind rivets, where the manufacturing operation has been simulated through Ls-Dyna to evaluate the stress and strain states induced into the jointed sheets, varying the dimensional and riveting load characteristics of the joint. A subsequent investigation is presented, which aims to evaluate the effects of the compressed zone over the behaviour of an approaching crack.

Abstract: Some preliminary experiments are conducted to investigate the responses of granite， marble and red stone in the states of natural，water-saturation and oil-saturated under the shock of short pulse laser. The 3D contour of ablation pit and the preliminary relations of the ablation contour to the number of laser pulses are obtained. The results show that some cracks generate at local places for the shock of laser，and the degree of ablation of the oil-saturated rocks is more severe than that of the natural and water saturated rocks. However，further work should be conducted to control the direction，sizes and number of cracks generated under the shock of laser.