Showing papers on "Stress concentration published in 1978"
400 citations
TL;DR: In this paper, the authors used the acoustic emission technique to monitor fatigue crack growth, and attributed the peak load emissions to both crack extension and deformation and fracture events occurring within the crack tip plastic zone, and these emissions have been correlated with the energy released during crack growth.
240 citations
Book•
01 Jan 1978
TL;DR: Theories of stress and strain have been studied in this article, where linear stress-strain-temperature relations have been used to describe the behavior of various materials. But they do not consider the effects of bending of straight beams.
Abstract: Introduction. Theories of Stress and Strain. Linear Stress-Strain-Temperature Relations. Inelastic Material Behavior. Applications of Energy Methods. Torsion. Bending of Straight Beams. Shear Center for Thin-Wall Beam Cross Sections. Curved Beams. Beams of Elastic Foundations. The Thick-Wall Cylinder. Elastic and Inelastic Stability of Columns. Flat Plates. Stress Concentrations. Fracture Mechanics. Fatigue: Progressive Fracture. Contact Stresses. Creep: Time-Dependent Deformation. Appendix A: Average Mechanical Properties of Selected Materials. Appendix B: Second Moment (Moment of Inertia) of a Plane Area. Appendix C: Properties of Steel Cross Sections. Author Index. Subject Index.
231 citations
TL;DR: In this article, an analytical investigation on the influence of bond thickness upon the stress distribution in single-lap adhesive joints is presented. But the results of this study were not included in any of the numerous analytical investigations reviewed.
Abstract: Results of an analytical investigation on the influence of bond thickness upon the stress distribution in singlelap adhesive joints are presented. The present work extends the basic approach for bonded joints, orginally introduced by Goland and Reissner, through use of a more complete shear-strain/displacement equation for the adhesive layer. This refinement was not found to be included in any of the numerous analytical investigations reviewed. As a result of the approach employed, the present work uncovers several interesting phenomena without adding any significant complication to the analysis. Besides modifying some coefficients in the shear stress equations, completely new terms in the differential equation and boundary conditions for bond peel stress are obtained. Sn addition, a variation of shear stress through the bond thickness, no matter how thin it may be, is analytically predicted only by the present theory. This through-the-bond-thickness variation of shear stress identifies two antisymmetrical adherend-bond interface points at which the shear stresses are highest. The growth of joint failures originating from these points agrees with results obtained from actual experiments.
195 citations
TL;DR: In this paper, field equations of nonlocal elasticity are solved to determine the state of stress in the neighborhood of a line crack in an elastic plate subject to a uniform shear at the surface of the crack tip.
Abstract: Field equations of nonlocal elasticity are solved to determine the state of stress in the neighborhood of a line crack in an elastic plate subject to a uniform shear at the surface of the crack tip. A fracture criterion based on the maximum shear stress gives the critical value of the applied shear for which the crack becomes unstable. Cohesive stress necessary to break the atomic bonds is calculated for brittle materials.
148 citations
TL;DR: In this article, the details of crack nucleation phenomena in the high strain fatigue of OFHC copper have been studied by optical microscopy and two-beam interferometry, and the plastic instability mechanism of cracks has been ruled out in polycrystalline metals in favor of one which takes into account the detailed crystallographic aspects of slip in adjoining grains.
135 citations
TL;DR: In this article, a unified picture of fracture mechanics is proposed for small scale yielding conditions (a small plastic zone at a crack tip) for two-dimensional cracks, where the stress singularity at the crack tip can break the solid apart and create surfaces of energy.
133 citations
TL;DR: In this article, a cracked adhesive-bonded DCB-type fracture was analyzed using a hybrid stress model finite element analysis which incorporated an advanced crack tip element, and the results were compared to monolithic systems with regard to the stress intensity factor and the localization of the singular stress domain associated with the crack tip.
Abstract: The problem of a cracked adhesive bonded DCB-type fracture specimen has been analyzed using a hybrid stress model finite element analysis which incorporates an advanced crack tip element. Stresses in the near and far fields have been studied as a function of adherend/adhesive modulus ratio and adhesive thickness. The results are compared to monolithic systems with regard to the stress intensity factor and the localization of the singular stress domain associated with the crack tip.
131 citations
TL;DR: In this paper, the authors examined the hypothesis that concentrations of regional stress in or near mafic intrusions in the felsic continental plate may cause nearby seismicity and found that if the intrusions are stiffer than the plate, stress concentrations of only 20 or 30 percent above regional values are likely, but intrusions which have been weakened (as by serpentinization) may concentrate stresses more than 200 percent above the regional values.
Abstract: The hypothesis is examined that concentrations of regional stress in or near mafic intrusions in the felsic continental plate may cause nearby seismicity. If the intrusions are stiffer than the plate, stress concentrations of only 20 or 30 percent above regional values are likely, but intrusions which have been weakened (as by serpentinization) may concentrate stresses more than 200 percent above the regional values. Pockets of seismicity may then occur in the continental plate near the intrusive.
131 citations
TL;DR: In this article, a technique has been developed to evaluate numerically the anisotropic point load soultions, and used to generate data bases for various materials, and an intrpolation technique is used to evaluate the point load solutions efficiently within a higher order boundary-integral equation code.
Abstract: The boundary-integral equation medthod is particularly well suited for solution of stress concentration and elastic fracture mechanics problems. The method was not previously applicable to anisotropic three dimensional problems because no efficient technique existed for calculation of the required point load solution for an infinite body. A technique has been developed to evaluate numerically the anisotropic point load soultions, and used to generate data bases for various materials. An intrpolation technique is used to evaluate the point load solutions efficiently within a higher order boundary-intgral equation code. The effectiveness of the technique is verified by solution of problems involving both uniaxial stress states and stress concentrations.
128 citations
TL;DR: In this article, the relation between the stress concentration factor and the fatigue notch factor was derived theoretically, taking into account both the effect of the cyclic plasticity at the notch root and the influence of the notch stress field on the nucleated cracks.
TL;DR: In this article, field equations of nonlocal elasticity are solved to determine the state of stress in a plate with a line crack subject to a constant anti-plane shear, and it is found that no stress singularity is present at the crack tip.
TL;DR: In this article, an automated test system utilizing computer control was developed to obtain crack growth rate data down to the fatigue crack growth threshold with a decreasing stress intensity technique and compact type specimens.
Abstract: An automated test system utilizing computer control was developed to obtain crack growth rate data down to the fatigue crack growth threshold with a decreasing stress intensity technique and compact type specimens. The starting stress intensity range ΔK0 was chosen to yield crack growth rates in the range of 2.54 × 10−8 m/cycle (10−6 in./cycle) and subsequent values of ΔK are controlled to the equation ΔK = ΔK0 exp [C(a − a0)] (a0 and a are the initial and instantaneous crack lengths and C is a test variable). Crack length is continuously monitored by using the elastic compliance technique, thereby enabling ΔK to be decreased continuously. Comparison crack growth data were also obtained by the more conventional constant load amplitude or K-increasing method. Excellent agreement was observed between data obtained from the two procedures for a Society of Automotive Engineers 1045 steel at load ratios R of 0.1 and 0.5, an A356-T6 sand-cast aluminum alloy at load ratios of 0.1 and 0.8, and a 2219-T851 aluminum alloy at a load ratio of 0.1.
TL;DR: In this article, the authors have calculated the strain-rate and temperature field in which ductility would be enhanced by diffusion at elevated temperature diffusion can relax these stress-concentrations and enhance ductility.
TL;DR: In this paper, the authors used computer simulation methods to estimate the fatigue crack initiation life of butt welds using strain-controlled fatigue concepts, and found that the initiation life was very sensitive to changes in Kf, but rather insensitive to strength level.
Abstract: The fatigue crack initiation life (cycles to obtain a 0.25-mm fatigue crack) was estimated for butt welds using strain-controlled fatigue concepts. Key developments which facilitated these estimates were the assumption of(K f ) m a x conditions (the largest value of Kf possible for a given weld shape), the use of computer simulation methods which modeled cyclic hardening and softening as well as mean stress relaxation effects, and the use of the fatigue properties of the actual weld zone in which the initial notch was located. The initiation life was found to be very sensitive to changes in Kf, but rather insensitive to strength level. The importance of residual stresses and mean stress varied with material as did the fraction of total life devoted to crack initiation. Mild steel (ASTM Specification for Structural Steel (A 36)) high strength, low alloy (ASTM Specification for High-Yield Strength, Quenched and Tempered Alloy Steel Plate, Suitable for Welding (A 514)) steel and aluminum alloy welds were considered.
TL;DR: In this article, the authors investigated the effect of load biaxiality on the crack-tip region and showed that the impact of load applied parallel to the plane of the crack appears entirely in the second terms of the series representations for local stress and displacement.
TL;DR: In this article, a finite element analysis has been used to examine the effect of non-rigid adherends and a spew fillet in solid and annular butt joints for a range of geometries and adhesive properties.
Abstract: Axisymmetric butt joints are widely used as specimens for testing the response of adhesives to shear and tensile stresses. When analysing the results from these tests, the stress distributions must be accurately known. A finite-element analysis has been used to examine the effect of non-rigid adherends and a spew fillet in solid and annular butt joints for a range of geometries and adhesive properties. It has been shown that stress concentrations occur in butt joints loaded in tension; in the latter case, the stress concentration is directly due to the presence of the spew fillet.
TL;DR: In this paper, a critical review of available information and models for crack propagation at elevated temperatures is provided, where the authors divide the behavior of crack propagation into brittle, ductile and plane stress conditions.
Abstract: The prediction of crack propagation rates at elevated temperatures is important and this paper provides a critical review of available information and models for behaviour. For simplicity, behaviour is divided into three situations. At one extreme, a brittle situation may exist in which the material is brittle and the degree of constraint high, so that substantially plane strain conditions exist and stress redistribution at the crack tip is small; in this situation, the fracture is a local crack tip event and the stress intensity may be of use in correlaiting creep crack propagation data. At the other extreme, ductile behaviour may result if the material is ductile and the constraint is low with plane stress conditions prevailing; in this case, stresses at and near the crack tip will redistribute quickly down to more even values and conventional creep analysis techniques using, say, the reference stress will be most useful, particularly for estimating times to rupture. It is postulated that there ...
TL;DR: In this article, a theory of intergranular creep crack growth in brittle materials has been developed, which is analogous to those developed previously for the growth of r-type voids in grain boundaries.
TL;DR: In this paper, the authors investigated the closure phenomena of fatigue cracks with a 1 mm gage length extensometer over the range of stress ratio, R, from −1 to 0.8.
Abstract: The closure phenomena of fatigue cracks were investigated with a 1 mm gage length extensometer over the range of stress ratio, R, from −1 to 0.8. Plate specimens with a center slot of HT80 steel and SUS304 stainless steel were fatigued under push-pull loading, and the crack propagation rate, da/dn, was measured. The stress ratio, R, was found to influence da/dn in both materials. The crack opening stress intensity factor, K
op, was determined from the relationship between the crack tip extensometer displacement and the load. The effective stress intensity range ratio, U(=ΔKeff/ΔK), decreases with the decrease of the stress intensity amplitude, ΔK/2. As for the data which show the crack closure phenomena (R≦0.4), the relationship between log(da/dn) and log(ΔK
eff/2) falls on a straight line near the stress intensity threshold level. For R=0.8 where the crack tip is fully open over the whole range of loading, the data show a discrepancy from the same line. The strain at the crack tip was also measured with the Moire fringe multiplication method. A large amount of plastic strain at the crack tip was observed even below the crack opening load for R=−1 in HT80 steel. These phenomena show that fatigue damage still exists when the crack is closed. These also show that the crack closure cannot fully account for the effect of R on da/dn.
TL;DR: In this article, the fracture is related to a shear mechanism across the colonies from the initiation stage through the overload fracture, and the density of the shear bands increased with increasing stress intensity.
Abstract: In order to better understand the large scatter in the fatigue results associated with β-annealed microstructures of α+ β titanium alloys, the fatigue crack initiation and propagation behavior of thin center notched Ti-11 specimens with a large colony α platelet microstructure was investigated. Colonies with a mean intercept diam of greater than 1 mm were grown in 2 mm thick specimens by means of a vacuum β-annealing process. This enabled crack path morphologies and crack propagation rates to be determined within single colonies by means of optical microscopy on the polished and etched surfaces. The results showed that the fracture is related to a shear mechanism across the colonies from the initiation stage through the overload fracture. Intense shear bands were observed ahead of and in the same direction as the propagating cracks. The density of the shear bands increased with increasing stress intensity. Since the colonies are randomly oriented, the fatigue cracks propagated at various angles with respect to the tensile axis. The crack propagation rate across a single colony is no faster than the propagation rate in the equiaxed α+ β microstructure of the same material. However, cracks were halted at the colony boundaries and forced to reinitiate through a cycle consuming process into the next colony. It is mainly this reinitiation process and microstructurally dependent growth which are responsible for the slower crack growth rates and large scatter band obtained for the β-annealed microstructures when compared to the α+ β microstructures. It is suggested that by reducing the colony size the crack growth rates will be reduced and the fatigue scatter band will be narrowed.
TL;DR: In this article, the authors explained the influence of external stress on the manner of extension of linepipe linepipe fracture by stress analysis around a hydrogen gas pressurized crack-like cavity under stress.
Abstract: Hydrogen induced fracture in linepipe steels is characterized by the formation of internal blisters caused by hydrogen precipitation at an inclusion-matrix interface, followed by the formation of blister-crack array by cracking the region connecting the blisters through the action of internal hydrogen pressure and external stress. The manner of extension of the hydrogen induced fracture of this type is considerably influenced by the presence of external stress: in the absence of the external stress fracture develops by linking the blisters which are formed in stacked arrays out of a plane approximately perpendicular to the external stress axis. Shear stress distribution induced around the blister is sensi-tively influenced by the external stress applied parallel to the blister plane; therefore, it is expected that the manner of extension of the blister-crack array should be influenced by the external stress. In the present paper the above mentioned influence of the external stress on the manner of extension of the hydrogen induced fracture is explained based on stress analysis around a hydrogen gas pressurized crack-like cavity under stress.
TL;DR: In this article, the contribution of oxidation to crack growth during high strain fatigue of a Cr-Mo-V steel at 550°C from three separate oxidation studies was assessed, and it was shown that internal stresses, as in bainitic material, promote enhanced oxidation.
Abstract: This paper attempts to assess the contribution of oxidation to crack growth during high strain fatigue of a Cr-Mo-V steel at 550°C from three separate oxidation studies. Stress-free data are clearly inapplicable to the highly strained crack tip and so it is first shown that internal stresses, as in bainitic material, promote enhanced oxidation. Weight gain experiments on oxide-free fracture surfaces are next described. It is shown that the stored energy of fatigue fracture likewise causes an increase in oxidation rate but that it is difficult to simulate the process at the tip of an advancing crack. Similarly, metallography of oxide in fatigue cracks does not reveal propagation. history. Finally, a dynamically worked surface, provided. by high-strain fatigue specimens deforming at 550°C, causes increasing oxidation with increasing total strain above a threshold value of oxide strain. It is shown that this is due to layering producing at least a tenfold increase compared with stress-free specimens....
TL;DR: In this article, the authors investigated the fatigue behavior of local structural assemblies under loadings that differ from the fatigue test loading in magnitude or in statistical distribution, or after a local change in structural sizes or design, stress concentrations m critically loaded assemblies are considered.
TL;DR: In this article, the effects of microstructure on the fatigue and creep crack growth of Waspaloy and P/M Astroloy were evaluated at 650°C.
Abstract: The effects of microstructure on the fatigue and creep crack growth of Waspaloy and P/M Astroloy were evaluated at 650°C. In Waspaloy, changes in γ′ size and distribution did not markedly affect fatigue crack growth. An increase in fatigue crack growth rate occurred at low test frequencies and was associated with a transition to intergranular crack propagation. In P/M Astroloy, a coarser grain size lowered the fatigue crack growth rate. Serrated grain boundaries, though beneficial under creep loading, have no effect in fatigue.
TL;DR: In this article, smaller holes are introduced on either side of the original hole to help smooth the flow of the tensile principal-stress trajectories past the hole, and the maximum stress was reduced to 84 percent of that due to a single hole.
Abstract: The problem of determining stress distributions and reducing stress concentrations around holes in plates occurs in numerous design situations. One method for reducing the stress concentration around a central circular hole in a uniaxially loaded plate was demonstrated by Heywood. With this approach, smaller holes are introduced on either side of the original hole to help smooth the flow of the tensile principal-stress trajectories past the original hole. For the one case reported by Heywood (which did not produce the greatest reduction possible), the maximum stress was reduced to 84 percent of that due to a single hole.
TL;DR: In this article, a method for obtaining viscoelastic stresses and displacements from elastic solutions is described, and the traction boundary condition for the crack faces is not in general satisfied by these results; however, it is shown by modifying the failure zone in the elastic problem this condition can be met, and an integral equation for the stress in the modified failure zone is derived.
Abstract: Equations are developed for predicting crack growth in the opening mode for quite general situations, including many quasi-static and dynamic problems involving moisture and temperature gradients in monolithic and composite materials. Except for the small zone of failing material at the crack tip, the body is assumed to be linearly viscoelastic. A method for obtaining viscoelastic stresses and displacements from elastic solutions is first described. The traction boundary condition for the crack faces is not in general satisfied by these results. However, it is shown by modifying the failure zone in the elastic problem this condition can be met, and an integral equation for the stress in the modified failure zone is derived. Approximate analysis similar to that used previously by the author in stress analysis is then employed to solve the integral equation and develop relatively simple equations for predicting crack speed; these equations relate crack speed in the viscoelastic material to stress intensity factors in a suitably defined elastic body.
IBM1
TL;DR: The strength and extensibility of an elastomer depend on its overall viscoelastic properties, as reflected in the time and temperature dependence of stress-strain curves, and also on those discrete processes, including crack formation and growth, that culminate in high-speed crack propagation as discussed by the authors.
Abstract: The strength and extensibility of an elastomer depend on its overall viscoelastic properties, as reflected in the time and temperature dependence of stress-strain curves, and also on those discrete processes, including crack formation and growth, that culminate in high-speed crack propagation. The discrete processes determine the lifetime of a specimen; the viscoelastic characteristics affect the dependence of stress on deformation. The interplay between these effects causes strength and extensibility to depend strongly on test conditions. An elastomeric network composed solely of highly mobile chains is very weak indeed and fractures at a low elongation. This characteristic differs diametrically from that expected of an idealized network of mobile chains. If such a network were stretched, stress concentrations and unbalanced forces at the molecular level, which can result from short chains, entanglements, and network imperfections, would be vitiated rapidly by stress-biased segmental diffusion, ...
TL;DR: In this paper, a model of fatigue crack growth is proposed that utilizes the recent developments in notch analysis of fracture and a concept of size effect that results from the changes in the critically stressed volume ahead of a crack tip.
Abstract: A model of fatigue crack growth is proposed that utilizes the recent developments in notch analysis of fracture and a concept of size effect that results from the changes in the critically stressed volume ahead of a crack tip. Accordingly, the fatigue crack growth mechanism involves local stresses reaching the theoretical cohesive strength and causing brittle fracture of atomic bonds at nominal stresses near the threshold, whereas slip-plane decohesion and plastic blunting and resharpening of the crack tip process may occur at stresses above the threshold range. The model contains three material parameters σFF nF, and ρF, that conveniently extend continuum analysis to situations where inhomogeneity of the material structure can influence the behavior appreciably. The analytical expression from the model was found to correlate fatigue crack growth data reasonably well in the low and intermediate stress ranges in Al 2024-T3, Al 7075-T6 and 250 grade maraging steel. The fracture modes observed are in agreement with the predictions from the model. The same fatigue crack growth model can be extended to estimating the threshold stress intensity factor range, ΔKo and fatigue notch sensitivity of different materials.
TL;DR: In this article, a study of the behavior of notched plexiglas specimens under stress pulses created from an air-gun was undertaken, and it was concluded that the initial notch is propagated by steps under the action only of tensile stress pulses, while the compressive stress pulses do not have any influence on crack propagation.