Showing papers on "Crack closure published in 1970"
TL;DR: In this article, an analysis of the stress distribution acting on the fracture surfaces shows that the local compressive stress maxima may exceed the yield stress of the material and that crack closure may influence the shape of the striation pattern.
1,876 citations
TL;DR: In this article, the authors used fracture mechanics techniques to measure the crack velocities in water as a function of applied stress intensity factor and temperature, and apparent activation energies for crack motion were obtained.
Abstract: Stress corrosion cracking of six glasses was studied using fracture mechanics techniques. Crack velocities in water were measured as a function of applied stress intensity factor and temperature, and apparent activation energies for crack motion were obtained. Data were consistent with the universal fatigue curve for static fatigue of glass, which depended on glass composition. Of the glasses tested, silica glass was most resistant to static fatigue, followed by the low-alkali aluminosilicate and borosilicate glasses. Sodium was detrimental to stress corrosion resistance. The crack velocity data could be explained by the Charles and Hillig theory of stress corrosion. It is probable that stress corrosion of glass is normally caused and controlled by a chemical reaction between the glass and water.
920 citations
01 Jan 1970
676 citations
224 citations
TL;DR: In this article, a comparison of the slip line flow field at the tip of a sharp crack and of a blunted crack is made, and it is shown that fatigue crack propagation is the result of repeated cyclic crack extension by alternating shear.
204 citations
TL;DR: In this paper, the authors examined the fracture and fatigue in elastic cylindrical shells with circumferential crack under axial tension and noted precracked specimens with precariness.
Abstract: Fatigue and fracture in elastic cylindrical shells with circumferential crack under axial tension, noting precracked specimens
146 citations
TL;DR: In this article, the influence of the stress ratio on the crack growth was predicted by the equation in agreement with the test results but that the effects of the environment and the load frequency could not be coped with by changes in the constants of the equation.
142 citations
01 Jun 1970
TL;DR: In this paper, both wedge force loading and remote loading techniques were employed to achieve the desired ΔK levels, and preliminary experiments were designed to test their compatibility, and the observed crack growth rates compared with those in desiccated air.
Abstract: Environmental fatigue crack propagation in 2024-T3, 7075-T6, and 7178-T6 has been studied at low levels of cyclic amplitude of stress intensity, ΔK. Both wedge force loading and remote loading techniques were employed to achieve the desired ΔK levels, and preliminary experiments were designed to test their compatibility. Testing was carried out in humid air, distilled water, and 3.5 pct sodium chloride solution, and the observed crack growth rates compared with those in desiccated air. Later studies were also conducted in an inert reference environment with a total water content of less than 2 ppm. When the data are plotted as log ΔK vs log d2a /dN, alloy 2024-T3 exhibits a marked slope transition, alloy 7075-T6 a slight slope transition, and alloy 7178-T6 a rectilinear behavior throughout the whole range of ΔK studied. The basic shape of these curves is discussed in terms of state-of-stress conditions at the crack tip, frequency effects, environmental effects, strain rate sensitivity, and metallurgical structure. An attempt is also made to correlate the rate of fatigue crack propagation in a particular environment and at a particular ΔK level with the fracture topography.
138 citations
TL;DR: In this paper, the unstable growth of a crack in a large viscoelastic plate is considered, within the framework of continuum mechanics, and a non-linear, first order differential equation is found to describe the time history of the crack size if the stress applied far from the crack is constant.
Abstract: The unstable growth of a crack in a large viscoelastic plate is considered, within the framework of continuum mechanics. Starting from the local stress and deformation fields at the tip of the crack, a non-linear, first order differential equation is found to describe the time history of the crack size if the stress applied far from the crack is constant. The differential equation contains the creep compliance and the intrinsic surface energy of the material. The surface energy concept for viscoelastic materials is clarified. Inertial effects are not considered, but the influence of temperature is included for thermorheologically simple materials.
Initial crack velocities are given as a function of applied load in closed form, as well as a comparison of calculated crack growth history with experiments. Above a certain high stress, crack propagation ensues at high speeds controlled by material inertia while at a lower limit infinite time is required to produce crack growth. Thus an upper and lower limit criterion of the Griffith type exists. For rate insensitive (elastic) materials the two limits coalesce and only the brittle fracture criterion of Griffith exists. The implications of these results for creep fracture in metals and inorganic glasses are examined.
138 citations
TL;DR: In this article, a general procedure for evaluating the stiffness matrix of a cracked element is developed, and numerical results obtained by the simplest elements are compared with those provided by other methods.
Abstract: The calculation of stress intensity factors for complicated crack configurations in finite plates usually presents substantial difficulty. A version of the finite element method solves such problems approximately by means of special cracked elements. A general procedure for evaluating the stiffness matrix of a cracked element is developed, and numerical results obtained by the simplest elements are compared with those provided by other methods.
126 citations
TL;DR: In this paper, it was shown experimentally that in the absence of plasticity crack propagation in anti-plane shear occurs by the opening of semi-penny-shaped cracks which straddle the crack front at an angle of 45 degrees.
Abstract: It is shown experimentally that in the absence of plasticity crack propagation in anti-plane shear occurs by the opening of semi-penny-shaped cracks which straddle the crack front at an angle of 45 degrees. It follows that if crack instability calculations are based on the assumption that a planar crack propagates in its own plane they are valid only if all shear stresses vanish along the crack periphery, i.e., if KIII is zero along that boundary.
01 Jan 1970
TL;DR: In this article, the authors considered a growing crack growing in anti-plane strain with the slip-planes making an almost zero angle with the plane of the crack and showed that the plastic zone size in front of a crack is the same as for a stationary crack.
Abstract: For a growing crack the residual stresses caused by plastic flow at previous positions of the crack-tip affect the current plastic zone. This effect is calculated by an extension of the BCS model which replaces the plastic zone by two planar arrays of dislocations emanating from the crack-tips. For a growing crack a succession of such axrays is formed. We consider a crack growing in anti-plane strain with the slip-planes making an almost zero angle with the plane of the crack. The plastic zone size in front of the crack turns out to be the same as for a stationary crack, while the relative displacement of the crack faces is less concentrated in the vicinity of the crack-tip. The rate of plastic dissipation of energy is calculated, and turns out to be identical with the elastic energy release rate. The earliest solution for the elastic-plastic field near the tip of a crack was obtained by Hult & McClintock (I 956). These authors considered a crack in an infinite medium deformed in anti-plane strain (mode III) and -showed that for perfectly plastic material the plastic zone at low stresses was a circle with circumference passing through the crack-tip. This analysis holds for a crack of fixed length, whereas many situations involve growing cracks, for which the residual stresses in regions which suffered plastic deformation at earlier positions of the crack-tip will affect the nature of the current plastic zone. Thus, for example, the criteria for the initial instability of monotonically loaded crack and for the continued growth of an already growing crack will in general not be identical. The need for consideration of the growing crack problem has led Chitaley & McClintock (I968) to look at the case of steady growth im mode III under constant stress intensity factor. They show that the length of the zone in the forward direction is almost the same as for the static case, but the whole forward zone is included within an angle of roughly 400 from the crack-tip. Furthermore, there are small zones of reversed plastic flow along the flanks of the crack, although their thickness is only 1/40 of the thickness of the forward zone, and neglecting to include them makes an insignificant difference in the resulting properties of the forward zone. The plastic displacement at the crack-tip is reduced to 7 % of its value for an identically loaded stationary crack. An alternative approach to calculating crack-tip plasticity has been given by Bilby, Cottrell & Swinden (i963) (referred to as B.C.S.) who represent the plastic zone by a continuous array of dislocations, coplanar with the crack. In terms of the
TL;DR: In this article, an analytical and experimental program was conducted to determine if a biaxial stress field produces a significant effect on the fatigue and fracture behavior of thin plates, and it was shown that the effect of nonsingular stresses on the behavior of a crack is examined from both a linear elastic and an elastic-plastic viewpoint.
Abstract: The results are presented of an analytical and experimental program which was conducted to determine if a biaxial stress field produces a significant effect on the fatigue and fracture behavior of thin plates. The materials tested were 6061-T4 and 6061-T6 aluminum sheets and plexiglas sheets. The experimental program included fracture tests with various magnitudes of biaxial load at fracture and fatigue tests with sinusoidal loading normal to the crack and either constant or sinusoidal stresses applied parallel to the crack. The effect of nonsingular stresses on the behavior of a crack is examined from both a linear elastic and an elastic-plastic viewpoint. The experimental study indicates that a biaxial stress field does affect the behavior of a crack in a thin sheet. An increase in the apparent fracture toughness with increasing biaxial load was observed experimentally but as yet cannot be adequately explained using linear fracture mechanics theory. Biaxial stresses were found to produce a shift in the fatigue crack growth rate data, and it is shown that this shift can be predicted using several empirical fatigue crack propagation models.
TL;DR: In this paper, the authors present theoretical analyses of the crack tip stress intensity factors for some typical basic models of sheet structures, which are based on Laurent's expansions of complex stress potentials where the expansion coefficients are determined from the boundary conditions.
TL;DR: An exact solution for an elastic half-plane containing a crack perpendicular to the free surface, when the faces of the crack are subjected to a particular, but rather general, distribution of pressure is given in this paper.
TL;DR: In this article, a series of fatigue tests were performed on several different polymer materials representing different classes of mechanical response and a strong correlation was found between the fatigue crack propagation rate and the stress intensity factor range prevailing at the advancing crack tip.
Abstract: In order to gain a better understanding of matrix-controlled fatigue failure processes in non-metallic materials a series of fatigue tests were performed on several different polymer materials representing different classes of mechanical response Fatigue crack propagation rates between 5×10−6 in cycle−1 (127 nm cycle−1) and 4×10−4 in cycle−1 (10 300 nm cycle−1) were measured in nylon, polycarbonate, ABS resin, low-density polyethylene and polymethyl methacrylate A strong correlation was found between the fatigue crack propagation rate and the stress intensity factor range prevailing at the advancing crack tip Whereas metals exhibit comparable fatigue growth rates for a given stress intensity range when normalised with respect to their static elastic modulus, the polymer materials exhibited a 1300-fold difference in crack growth rate for a given normalised stress intensity range This observation dramatically illustrates the importance of understanding molecular motion and energy dissipation processes in polymer materials as related to their chemistry and architecture The relative behaviour of the different polymer materials could be generally correlated with their reported damping characteristics
TL;DR: The theory of the motion of a cleavage crack created by wedging open the ends of a double cantilevered crystal at a constant rate has been investigated in this article, and the results are presented for use in analysis of experimental studies of fracture dynamics in lithium fluoride reported in Part II of this series.
Abstract: The theory of the motion of a cleavage crack created by wedging open the ends of a double cantilevered crystal at a constant rate has been investigated. The results are presented for use in analysis of experimental studies of fracture dynamics in lithium fluoride reported in Part II of this series. A solution of the quasistatic equations of motion of the crack including kinetic energy effects has been found from which the dynamic fracture surface energies may be deduced for a propagating crack of this geometry by observations of either the time dependence of the crack length or the profile of the fracture opening near its tip. The detailed configurations of dislocations accompanying the tip of a moving crack in alkali halides have been calculated using dislocation dynamics and continuum elasticity theory. The plastic deformation contribution to the effective fracture surface energy has been determined and some of its consequences worked out.
TL;DR: In components which operate at elevated temperatures there is a need to develop methods which describe the growth of crack-like defects in creed conditions, particularly relevant to welded joints where defects can be evident after stress relief and assessments are required of fitness for use.
Abstract: IN recent years there has been a growing awareness that the techniques of linear elastic fracture mechanics provide a powerful method for quantifying the behaviour of engineering components containing crack-like defects. In the fast fracture of high strength, low toughness materials1 and in fatigue crack growth2, it is now established that data from laboratory tests can be confidently applied to predict the integrity of a structure or crack extension in service using sharp crack stress intensity factors. More recently, a study of fatigue crack initiation from sharp notches in mild steel3 has shown that the number of cycles to initiate a crack can also be calculated using stress intensity factors. In components which operate at elevated temperatures there is a need to develop methods which describe the growth of crack-like defects in creed conditions. This is particularly relevant to welded joints where defects can be evident after stress relief and assessments are required of fitness for use.
TL;DR: In this article, a crack growth study in viscoelastic solids by linear continuum mechanics is presented, discussing cyclic loads, composite solids mechanical behavior and thermodynamics.
TL;DR: In this article, the effect of biaxiality of stress on the fatigue-crack-propagation rate in 2024-T351 aluminum alloy in completely reversed bending is investigated.
Abstract: The effect of biaxiality of stress on the fatigue-crack-propagation rate in 2024-T351 aluminum alloy in completely reversed bending is investigated. Round and elliptical plates, simply supported at the edge, are subjected to bulge bending. The plate dimensions are such that nominal stress-biaxiality ratios of 1∶1, 1∶0.86 and 1∶0.75 are obtained in the plane of the specimen in the region of its geometric center. It is postulated that, in strain-hardening materials, crack-growth rate is a function of nominal biaxial-stress condition in the crack-tip region. Experimental data for different biaxiality ratios fall in a straight line when a modified stress-intensity factor is plotted against the rate of crack propagation.
TL;DR: In this paper, the plane strain problem of a crack terminating perpendicular to a planar interface between two isotropic half spaces with different elastic constants is solved to obtain the distribution of stress in the vicinity of the crack tip.
Abstract: The plane strain problem of a crack terminating perpendicular to a planar interface between two isotropic half spaces with different elastic constants is solved to obtain the distribution of stress in the vicinity of the crack tip. The relative elastic constants are shown to strongly affect the relative magnitudes of the various stress components as well as their radial drop off with distance from the crack tip. The implications of the results with regard to failure modes in composite materials are discussed.
01 Jun 1970
TL;DR: The hot fracture of Inconel 600 has been studied over the temperature range from 800° to 2000°F using a hot torsion tester that is capable of superimposing either axial tensile or compressive stresses on the torsional shearing stresses as discussed by the authors.
Abstract: The hot fracture of Inconel 600 has been studied over the temperature range from 800° to 2000°F using a hot torsion tester that is capable of superimposing either axial tensile or compressive stresses on the torsional shearing stresses. Microscopic studies of fracture initiation have been made over the entire temperature region. From 800° to 1200°F fracture initiates at inclusions and propagates by transgranular shear. In the temperature region of minimum ductility, 1300° to 1500°F, fracture initiates at grain boundaries and propagates readily in an intergranular manner. At 1600°F and above, fracture initiates easily at grain boundaries, but because recrys-tallization intervenes crack propagation is difficult and strain to fracture is high. Microcracks initiate at the peak in the torque-twist curve. The higher the temperature the smaller is the strain at which fracture initiates. Correlations have been found between the stress state and the shearing strain at crack initiation and total fracture strain. These correlations show the strong influence of a compressive normal stress on retarding crack initiation and resisting crack propagation.
TL;DR: In this paper, two sets of photoelastic experiments employing stress freezing were performed in order to evaluate closure and precatastrophic extension of cracks in plates under cylindrical bending.
Abstract: Two sets of photoelastic experiments employing stress freezing were performed in order to evaluate closure and precatastrophic extension of cracks in plates under cylindrical bending. Data were compared with the Hartranft-Sih theory in order to obtain quantitative results. It was found that crack closure on the compressive side of the plate produced somewhat larger local elastic stresses on the tensile side of the plate for straight through cracks than predicted by the mathematical model. When precatastrophic extension was allowed on the tension side of the plate, accompanying stress relaxation neutralized the stress intensification effect of closure. For short, nearly square cracks, three-dimensional effects appeared to reduce the stress intensification effects due to closure.
TL;DR: In this paper, the authors investigated the growth characteristics of a forging-grade Ni-Mo-V alloy steel with Wedge-Opening-Loading type crack-notch fracture toughness specimens and the results expressed in terms of the stress intensity factor fracture mechanics parameter.
TL;DR: In this article, notched polycrystalline specimens of an Al 1 2% Mg alloy were fatigue-cracked at four different stress levels to a crack length of approximately 1 mm.
TL;DR: In this article, a semi-infinite crack traveling with constant velocity in an infinitely long strip of finite width is considered and the effect of strip width on the dynamic stresses is examined.
Abstract: This paper is concerned with the anti-plane stress distribution around a semi-infinite crack traveling with constant velocity in an infinitely long strip of finite width. The problem is reduced to the solution of the Riemann-Hilbert problem by application of the Schwarz-Christoffel transformation and the theory of complex functions. Closed-form solutions are obtained for two cases of practical interest: (1) the boundaries of the strip are clamped and displaced in equal and opposite directions causing a tearing motion along the leading edge of the crack and (2) the crack is sheared longitudinally by a pair of concentrated forces moving with the crack while the strip boundaries are free of tractions. In both cases, the effect of strip width on the dynamic stresses is examined. A dynamic crack extension force is defined by a line integral the value of which is independent of the path of integration and requires only a knowledge of the local stress and displacement fields. The information gained in this study is useful in that it can assist interpretation of results from dynamic experiments on moving cracks.
TL;DR: In this article, the authors analyzed the stress distribution caused by twisting an infinite plate containing a finite crack in terms of Reissner's theory for the bending of thin plates and determined the singular character and detailed structure of the stresses near the ends of the crack in closed form.
Abstract: The stress distribution caused by twisting an infinite plate containing a finite crack is analyzed in terms of Reissner's theory for the bending of thin plates. The singular character and the detailed structure of the stresses near the ends of the crack are determined in closed form. Numerical results are given for the magnitudes of the stress couples and stress resultants for a range of plate thicknesses.
TL;DR: In this article, a correlation between plastic deformation at crack tips in sodium chloride and the measured value of the fracture surface energy is presented, and the specific surface free energy of sodium chloride, 100 plane, is estimated to be less than 0.37 J/m2.
Abstract: A correlation between plastic deformation at crack tips in sodium chloride and the measured value of the fracture surface energy is presented. Plastic deformation can either aid or hinder crack growth, depending on the mode of deformation at the crack tip. If plane-stress deformation occurs, crack motion is hindered by step formation, dislocation generation, and plastic blunting of the crack tip. If plane-strain deformation occurs, crack motion is aided by stress fields that arise from the deformation. The specific surface free energy of sodium chloride, {100} plane, is estimated to be less than 0.37 J/m2.
TL;DR: The relationship between stress corrosion crack velocity and crack tip stress intensity is discussed in this article, where methods of estimating this velocity are described and their implications with regard to testing procedure, crack morphology, and service performance are outlined.
Abstract: The relationship between stress corrosion crack velocity and crack-tip stress intensity is discussed. In most high strength steels, there is a wide range of stress intensity over which crack velocity is essentially constant. Methods of estimating this velocity are described. Values for a variety of high strength steels are presented and the effects of metallurgical variables are indicated. Implications with regard to testing procedure, crack morphology, and service performance are outlined.
TL;DR: In this paper, the effects of geometry on the propagation of cracks in finite rectangular plates were investigated, and the results for the strain energy and the moment stress intensity factor were derived for three cases: (1) crack at opposite edges, (2) crack in center and (3) crack on one side only.