Papers by Keyword: Stress Intensity Factor (SIF)

Abstract: Under the continuing action of temperature stress and load vehicle, the crack in cement stabilized aggregate base can easily reflect up into the asphalt surface layer, affecting driving condition and then affecting the fatigue life of pavement. On the basis of fracture mechanics, taking center crack loaded with uniform tensile stress as study state, methods were derived to calculate the stress intensity factor (abbreviated in the following “SIF”) of the crack at the bottom of asphalt layer using weight function theory and method of Petroski and Achenbach. Through the comparison of different SIFs under different conditions, factors affecting the SIFs such as crack length, load conditions, modulus ratio between base and surface layer and different jointed conditions were studied. To facilitate comparison, taking completely smooth and completely continuous as study boundary conditions. According to calculation results, factors mentioned above all influence the SIF values of the crack at the bottom of asphalt layer greatly, among which jointed condition between base and surface layer has the most important influence. The SIF values of the completely smooth interface is several times that of the completely continuous interface. We can take measures to improve the jointed condition between the asphalt surface layer and the cement stabilized aggregate base thus can reduce reflection crack effectively.

Abstract: In this paper the fatigue characterization of an austempered ductile iron (ADI) is presented. The aim of the work is to provide design engineers involved in fatigue assessments with an engineering tool suitable to deal with notches of different severity. Classically, U-notches are divided into blunt notches and sharp notches. The former are characterized by large notch tip radii such that the high cycle fatigue strength is controlled by the elastic peak stress, i.e. by the elastic stress concentration factor. The latter are characterized by reduced notch tip radii such that the effective stress which controls the high cycle fatigue strength is significantly lower than the elastic peak stress and their behaviour become similar to that of a crack having the same length. Blunt notches are assessed according to the classical Notch Mechanics principles, while sharp notches are treated with the Linear Elastic Fracture Mechanics approach. After presenting the classical Frost diagram which highlights the different fatigue behaviour of sharp and blunt notches, fatigue test results generated from notches of different severity are presented as well as a synthesis in a diagram able to account for short cracks/notches, long cracks, sharp notches and blunt notches.

Abstract: In this article, the thermo-mechanical responses of ceramic/metal functionally graded thermal barrier coating(TBC) in work environment are analyzed by a finite element method. Both the crack-tip field and the stress intensity factor of functionally graded TBC are analyzed and calculated. It is discussed that the effect of crack length on mechanical properties of functionally graded TBC in the condition creep and no creep of pure metal. The numerical results indicate that the effect of crack length(a/t) is negligible to temperature distributions and the maximum displacements of whole model but remarkable to the 1st principal stress and stress intensity factor of crack region. Moreover, creep phenomenon of pure metal can relax the value of displacement, stress and stress intensity factor but do not alter their distribution.

Abstract: The distributions of stress intensity factor KI and KII in notched beam specimens have been obtained in this paper by researching on internal force distributions, photoelastic experiments and statistics from numerical results. Two approximate formulae of KI and KII have been constructed. A simple and correct way to calculate KI and KII of beam is provided.

Abstract: In this work the time-domain boundary element method (BEM) is applied to simulate dynamic fracture experiments. The fast fracture is modelled by adding new boundary elements at the crack tip. The direction of crack growth is perpendicular to the direction of maximum circumferencial stress. The time dependent loading of specimens and velocities of crack growth are taken from experiments as input data for computer simulations. The method is used to analyze: a short beam specimen, a special mixed-mode specimen and a three-point bend specimen subjected to impact loads. The dynamic stress intensity factors (DSIF) and the crack paths are compared with the results obtained by other authors who used the finite element method (FEM) and experimental methods.

Abstract: . In this paper a variational technique is developed to calculate stress intensity factors with high accuracy using the element free Glerkin method. The stiffness and mass matrices are evaluated by regular domain integrals and the shape functions to determine displacements in the domain are calculated with radial basis function interpolation. Stress intensity factors were obtained by a boundary integral with a variation of crack length along the crack front. Based on a static reference solution, the transformed stress intensity factors in the Laplace space are obtained and Durbin inversion method is utilised in order to determine the physical values in time domain. The applications of proposed technique to two and three dimensional fracture mechanics are presented. Comparisons are made with benchmark solutions and indirect boundary element method.

Abstract: From the perspective of Fracture Mechanics, concrete/rebar bonding failure process in reinforced concrete (RC) structures means the decreasing of the crack closure force imposed by rebar in RC beams, which will result in crack propagation, and eventually structural damage. In this paper the crack-arresting mechanism of the concrete/rebar bonding stress in RC beams was analyzed, which was employed to reveal the degradation mechanism of RC beams induced by concrete/rebar bonding failure; and bending tests of RC beams were presented where effects of concrete/rebar bonding failure on bending performance of RC beams had been investigated. The concrete/rebar bonding failure was obtained by wrapping the rebar with different length of plastic film during casting. The results shows effective concrete/rebar bonding is the key to provide crack closure force, which can prevent functional degradation of RC beams.

Abstract: In this study, the photoelastic experiment hybrid method was introduced and applied to the fracture problems of the isotropic polycarbonate plate with a central crack under the uniaxial and equibiaxial tensile load. The influences of equibiaxial tensile load on the isochromatic fringes and stress fields, stress intensity factors near the mixed mode crack-tip were investigated. As the results, without relation to the inclined angle of crack, the asymmetric isochromatic fringes around the crack propagation line under uniaxial tensile load has become symmetric and the slope of isochromatic fringe loop has inclined toward crack surface when an equal lateral tensile load was added. Furthermore, the distribution of all stress components have changed from asymmetric shape to symmetric shape, and only the range of compressive stress of σχ/σ0 have changed as compared with the mode I condition under unaxial load with β = 0°. When an equal lateral tensile load was added to uniaxial load, the value of stress intensity factors are little changed when β = 0° but the values of KI /K0 are increased and KII /K0 are become zero, that is, mode I situation when β = 15°~45°.

Abstract: Experiments and numerical simulations were conducted to investigate the propagation patterns of pre-existing 3-D elliptical crack in rock-like material under uniaxial tension. Research results demonstrated that as the load was increased, the wrapping wing cracks initiated near the front of long axis of crack, with the lateral growth of initial crack close to the front of short axis. A distortion surface formed from the growth of initial crack leaded to the macro fracture of samples. The distribution laws of mixed-mode stress intensity factor (SIF) along crack contour were derived with FRANC3D, and propagation process of 3-D crack under tension was simulated. It was concluded that propagation patterns of 3-D crack under tension were quite different from compressive cases, mainly in aspects of growth orientation and velocity.

Abstract: Some authors proposed to combine a torsional loading of cylindrical specimens with surface semi-elliptical cracks (the principal axes along the axial direction) with superimposed static axial compression in order to eliminate kinking or branching of shear cracks from the shear plane. To authors’ knowledge, however, no precise numerical analysis of such a loading configuration is currently available. The aim of this article is to calculate stress intensity factors KI, KII and KIII along the semi-elliptical crack front using the ANSYS code. The problem is solved for a semi-circular crack front and various crack inclination angles. The results reveal that the compressive loading cannot eliminate the branching process. The inclination of the crack plane induces a rather high opening mode which means that the microscopically tortuous fatigue cracks observed in experiments grew under mixed-mode I+II+III.