scispace - formally typeset
Search or ask a question

Showing papers on "Stress concentration published in 1982"


Journal ArticleDOI
TL;DR: In this article, a geometric model is presented for crack closure induced by fracture surface roughness, specifically addressing the contribution from both Mode I and Mode II crack tip displacements in addition to considering the nature of the fracture surface morphology.
Abstract: Mechanisms for fatigue crack closure under plane strain conditions have recently been identified at very low (near-threshold) stress intensities in terms of effects of excess corrosion deposits or fracture surface roughness in promoting premature closure of the crack. In the present paper, a geometric model is presented for crack closure induced by fracture surface roughness. This model specifically addresses the contribution from both Mode I and Mode II crack tip displacements in addition to considering the nature of the fracture surface morphology. The implications of this model are briefly discussed in light of the roles of grain size, yield strength, microstructure, and crack size in influencing near-threshold fatigue behavior in engineering alloys.

379 citations


Journal ArticleDOI
TL;DR: The problem associated with short crack growth, defined as situations in which the intensity of the crack tip field is underestimated by linear elastic fracture mechanics analyses, is briefly reviewed in this paper.
Abstract: — The problem associated with short crack growth, defined as situations in which the intensity of the crack tip field is underestimated by linear elastic fracture mechanics analyses, is briefly reviewed. Two cases are identified, cracks growing in plastically strained materials, such as occurs in high strain fatigue studies and at notch roots, and small cracks growing in single grains as occurs close to the fatigue limit in plain specimens. Important mechanical and metallurgical features of short cracks are discussed with particular reference to the upper and lower bound definition of a short crack.

333 citations


Journal ArticleDOI
TL;DR: In this paper, the authors proposed that the grain-size dependence of the yield stress of metals is due to the elastic incompatibility stresses at the grain boundaries, and the generation and motion of these "geometrically necessary" dislocations attenuated the stress concentrations; a work-hardened grain-boundary layer is formed.
Abstract: It is proposed that the grain-size dependence of the yield stress of metals is due to the elastic incompatibility stresses at the grain boundaries. For clarity, the process of yielding is divided into three stages. In the first stage (prior to microyielding), the differences in elastic properties arising from the elastic anisotropy of adjacent grains establish localized stress concentrations at the grain boundaries. In the second stage, the stress concentrations at the grain boundaries result in localized plastic flow; this is the microyield region. The generation and motion of these 'geometrically necessary' dislocations attenuates the stress concentrations; a work-hardened grain-boundary layer is formed. As the stress is increased, the polycrystalline metal acts as a composite material consisting of a continuous network of a work-hardened grain-boundary material and discontinuous bulk material. The bulk is prevented from flowing plastically because the continuous network of work-hardened grain-...

269 citations


Journal ArticleDOI
TL;DR: In this paper, the authors extended the dislocation dipole accumulation model for fatigue crack initiation to an analysis of the fatigue strength reduction due to inclusions in high strength alloys.
Abstract: The dislocation dipole accumulation model for fatigue crack initiation previously proposed by the authors is extended to an analysis of the fatigue strength reduction due to inclusions in high strength alloys. The initiation of a fatigue crack is determined by an energy criterion under the assumption that the crack initiation takes place when the self strain energy of dislocation dipoles accumulated at the damaged part in the material reaches a critical value. Explicit formulae for the crack initiation criterion in several cases are derived as functions of the applied stress, the inclusion size, the slip band shape, and the shear moduli of the inclusion and matrix. The following three types of fatigue crack initiation at inclusions are considered: the slip-band crack emanating from a debonded inclusion, the inclusion cracking due to impinging of slip bands, and the slip-band crack emanating from an uncracked inclusion. The first mechanism was reported to be operative in high strength steels, while the last two mechanisms were reported in high strength aluminum alloys. The present theoretical results are in good agreement with the experimental data published for each case of fatigue crack initiation at inclusions.

259 citations



Journal ArticleDOI
TL;DR: In this article, a finite difference method was developed for dynamic shear cracks with a focus on the modeling of the stress field, and the authors compared their numerical results for semi-infinite and self-similar cracks with the few exact solutions available in the literature.
Abstract: We have developed a finite difference method that is especially adapted to the study of dynamic shear cracks. We studied a number of simple earthquake source models in two and three dimensions with special emphasis on the modeling of the stress field. We compared our numerical results for semi-infinite and self-similar shear cracks with the few exact solutions that are available in the literature. We then studied spontaneous rupture propagation with the help of a maximum stress criterion. From dimensional arguments and a few simple examples, we showed that the maximum stress criterion depended on the physical dimensions of the fault. For a given maximum stress intensity, the finer the numerical mesh, the higher the maximum stress that had to be adopted. A study of in-plane cracks showed that at high rupture velocities, the numerical results did not resolve the stress concentration due to the rupture front from the stress peak associated with the shear wave propagating in front of the crack. We suggest that this is the reason why transonic rupture velocities are found in the numerical solutions of in-plane faulting when the rupture resistance is rather low. Finally, we studied the spontaneous propagation of an initially circular rupture. Two distinct modes of nucleation of the rupture were studied. In the first, a plane circular shear crack was formed instantaneously in a uniformly prestressed medium. After a while, once stress concentrations had developed around the crack edge, the rupture started to grow. In the second type of nucleation, a preexisting circular crack became unstable at time t = 0 and started to grow. The latter model appeared to us as a more realistic simulation of earthquake triggering. In this case, the initial stress was nonuniform and was the static field of the preexisting fault.

139 citations


Journal ArticleDOI
TL;DR: In this paper, the low cycle fatigue and fatigue crack propagation of Inconel 718 alloy and Waspaloy were investigated at 25, 550 and 650 °C and the qualitative observations indicate that there exists a close correspondence between the near-threshold regime and stage I crack initiation in low-cycle fatigue.

124 citations


Book ChapterDOI
TL;DR: In this article, a linear elastic fracture mechanics approach to crack growth rate prediction implies the need to calculate accurate, effective stress intensity (K) factors, and hence effective R-values, (K m i n /K m a x ), for components containing residual stress.
Abstract: A linear elastic fracture mechanics approach to crack growth rate prediction implies the need to calculate accurate, effective stress intensity (K) factors, and hence effective R-values, (K m i n /K m a x ), for components containing residual stress. To this end the weight function and associated superposition techniques are described, with emphasis on stress intensity and crack shape prediction for residual stress problems. Stress intensity factors are presented for various geometries with residual stress fields. The nonlinear, crack surface 'overlapping' effect is noted, and the case of cracks emanating from notches in residual stress fields is shown to be an associated problem. The application of such results in crack growth rate prediction is addressed. The characteristic crack growth rate features of several different loading systems are predicted, and shown to agree with available experimental data. Finally, the qualitative changes in the form of standard S-N curves for welded details are predicted, and shown to conform with limited available S-N curve experimental data.

110 citations


Book
01 Jan 1982
TL;DR: In this paper, a conceptual review of the fundamental relations and concepts of forces and force systems is presented, including simple stress and strain, simple shear stress, simple strain, and simple strain.
Abstract: Fundamental Relations and Concepts Forces and Force Systems Simple Stress and Strain: Simple Shear Stress and Strain Hooke's Law and Material Strength Stress in Two and Three Dimensions Strain in Two and Three Dimensions Curvilinear Coordinates Hooke's Law in Two and Three Dimensions Straight and Long Structural Components: Beams, Rods, and Bars Beams: Bending Stresses (Flexure) Beams: Displacement from Bending Beam Analysis Using Singularity Functions Beam Bending Formulas for Common Configurations Torsion and Twisting of Rods Thick Beams: Shear Stress in Beams Curved Beams Stability: Buckling of Beams, Rods, Columns, and Panels Shear Center Plates, Panels, Flanges, and Brackets Plates: Bending Theory Plates: Fundamental Bending Configurations and Applications. Panels and Annular Plate Closures Flanges Brackets Special Plate Problems and Applications Dynamic Loadings, Fatigue, and Fracture Dynamic Behavior of Structures: A Conceptual Review Elements of Seismic Design Impact Stress Propagation Fatigue Fracture Mechanics: Design Considerations Fracture Control Piping and Pressure Vessels Vessels with Internal Pressure Externally Pressured Cylindrical Vessels and Structures Buckling of Spherical Shell Axial and Bending Response Advanced and Specialized Problems Special Cylinder Problems Stress Concentration Thermal Considerations Axial Response of Straight and Tapered Bars Thin Rings and Arches Links and Eyebars Springs Irregular Shape Springs

93 citations


Book ChapterDOI
DV Nelson1
TL;DR: In this article, the effects of compressive and tensile residual stresses on Mode I fatigue crack growth are reviewed and current limitations of the methods and their relative advantages and drawbacks for use in design analysis are discussed.
Abstract: Experimental results on the effects of compressive and tensile residual stresses on Mode I fatigue crack growth are briefly reviewed. Prediction methods that attempt to account for the observed effects are compared. Current limitations of the methods and their relative advantages and drawbacks for use in design analysis are discussed. The possible role of residual stress re-equilibration on growth behavior, caused by crack extension itself, is also discussed.

89 citations


Journal ArticleDOI
01 Jan 1982
TL;DR: In this paper, the problem of minimum stress concentration is highly nonlinear and must be solved iteratively, and each iteration (redesign) involves three steps: an analysis of the stresses for a design, a sensitivity analysis corresponding to possible changes in this design, and the decision of redesign.
Abstract: The problem of design for minimum stress concentration is highly nonlinear and must be solved iteratively. Each iteration (redesign) involves three steps: an analysis of the stresses for a design, a sensitivity analysis corresponding to possible changes in this design, and the decision of redesign. For stress analysis, the FEM is a unified approach which is applied in the present paper to axisymmetric solids that are also subjected to nonaxisymmetric loads. The decision of redesign is a linear programming problem and can thus be solved with the Simplex algorithm. The introduction of move-limits to the formulation is of major importance. The optimization approach is described in general, but most of the paper concentrates on a specific example and shows optimum shapes of a shoulder fillet in a stepped bar. Loads are bending, tension, or torsion, and the stress concentrations are considerably reduced.

Journal ArticleDOI
TL;DR: In this article, the authors extended the dislocation-free zone (DFZ) model of fracture to study the relationship between the stress intensity factor, extent of plastic deformation, and crack tip geometry of an elasticplastic crack as a function of applied stress.
Abstract: The dislocation‐free zone (DFZ) model of fracture has been extended to study the relationship between the stress intensity factor, extent of plastic deformation, and crack tip geometry of an elastic‐plastic crack as a function of applied stress. The results show that the stress intensity factor K decreases from the elastic value at first slowly, then goes rapidly to zero as the number of dislocations in the plastic zone increases. The crack with a zero stress intensity factor has its crack tip stress field completely relaxed by plastic deformation and hence is called a plastic crack. Between the elastic and plastic cracks, a wide range of elastic‐plastic cracks having both a stress singularity and a plastic zone are possible. These elastic‐plastic cracks with a DFZ are predicted if there is a critical stress intensity factor Kg required for the generation of dislocations at the crack tip. The expression for Kg is obtained from the crack tip dislocation nucleation model of Rice and Thomson. In most metals,...

Journal ArticleDOI
TL;DR: Torsional resonance experiments performed on wet human compact bone disclose effects due to couple stress and the characteristic length is of the order of the size of osteons and appears to be smaller at high frequencies than at low frequencies.
Abstract: Torsional resonance experiments performed on wet human compact bone disclose effects due to couple stress. The characteristic length, which is an additional material coefficient which appears in couple-stress theory, is of the order of the size of osteons and appears to be smaller at high frequencies than at low frequencies. The presence of couple-stress effects implies a reduction in the stress concentration factor around holes, particularly small holes.

Journal ArticleDOI
TL;DR: In this paper, a model of fatigue crack growth based on an analysis of elastic/plastic stress and strain at the crack tip is presented and the number of cycles required for material failure inside the highly strained zone is calculated.

Journal ArticleDOI
TL;DR: In this paper, structural constitutive equations were applied to the calculation of stress waves in snow and recorded acoustic emissions, indicating intergranular bond fractures, can also be used for the construction of constitutive equation.
Abstract: : The investigation of the mechanical properties of seasonal snow cover aims mostly at applications in avalanche release and avalanche control but also at no less important problems such as vehicle mobility in snow, snow removal, or construction on snow. Primary needs are (1) constitutive equations, that is, relations between the stress tensor and the motion, and (2) fracture criteria which limit the region of validity of constitutive equations., Both can be tackled from the aspect of continiuum theories and structure theories. With modern continiuum theories the characteristic nonlinear behavior of snow can be taken into account and also the strong dependence on stress and strain history. When thermodynamics is introduced, more insight into the deformation and fracture processes can be gained. High initial deformation rates cause low dissipation, elastic behavior, and brittle fracture, whereas when dissipative mechanisms can develop, ductile fracture occurs. The advantage of structural theories lies in the immediate physical insight into deformation mechanisms, but the disadvantage is that only simple states of stresses acting macroscopically on a snow sample can be considered. Different approaches have been elaborated: for low-density snow the concept of chains (a series of stress-bearing grains) or the neck growth model (consideration of stress concentrations in bonds between grains) and for high-density snow the pore collapse model (snow idealized as a material containing air voids). Structural constitutive equations were applied to the calculation of stress waves in snow. Recorded acoustic emissions, indicating intergranular bond fractures, can also be used for the construction of constitutive equations.

Journal ArticleDOI
TL;DR: In this article, a new technique for recording stress patterns called thermoelastic stress analysis (TSA) is described, which measures the distribution of stress on the surface of a structure under load, and the connection between stress concentration, mechanical design and safety.
Abstract: After discussions on the need to measure the distribution of stress on the surface of a structure under load, and the connection between stress concentration, mechanical design and safety, a new technique for recording stress patterns called thermoelastic stress analysis (TSA) is described. For given material constants, the change in temperature on the surface of a structure, subject to dynamic loading, is directly proportional to the change in stress at that point. A specially designed, high-sensitivity I.R. camera is described which can present a colour display of the distribution of stress which could arise from temperature variations as small as 0·001 K resulting from a few units of microstrain in metals. A selection of typical results obtained by recording the stress concentration on the surface of a model pedestal structure are given to illustrate how TSA could be used as an aid to design. The likely useful areas of application of TSA can be identified with the help of a list of the principal charac...

Journal ArticleDOI
TL;DR: In this article, a study of fatigue crack propagation in Mode III (antiplane shear) for a mill-annealed AISI 4140 steel (RB88, 590 MN/m2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens.
Abstract: Turbo-generator and automotive shafts are often subjected to complex histories of high torques. To provide a basis for fatigue life estimation in such components, a study of fatigue crack propagation in Mode III (anti-plane shear) for a mill-annealed AISI 4140 steel (RB88, 590 MN/m2 tensile strength) has been undertaken, using torsionally-loaded, circumferentially-notched cylindrical specimens. As demonstrated previously for higher strength AISI 4340 steel, Mode III cyclic crack growth rates(dc/dN) IIIcan be related to the alternating stress intensity factor ΔKIII for conditions of small-scale yielding. However, to describe crack propagation behavior over an extended range of crack growth rates (∼10-6 to 10-2 mm per cycle), where crack growth proceeds under elastic-plastic and full plastic conditions, no correlation between(dc/dN) III and ΔKIII is possible. Accordingly, a new parameter for torsional crack growth, termed theplastic strain intensity Γ III, is introduced and is shown to provide a unique description of Mode III crack growth behavior for a wide range of testing conditions, provided a mean load reduces friction, abrasion, and interlocking between mating fracture surfaces. The latter effect is found to be dependent upon the mode of applied loading(i.e., the presence of superimposed axial loads) and the crack length and torque level. Mechanistically, high-torque surfaces were transverse, macroscopically flat, and smeared. Lower torques showed additional axial cracks (longitudinal shear cracking) perpendicular to the main transverse surface. A micro-mechanical model for the main radi l Mode III growth, based on the premise that crack advance results from Mode II coalescence of microcracks initiated at inclusions ahead of the main crack front, is extended to high nominal stress levels, and predicts that Mode III fatigue crack propagation rates should be proportional to the range of plastic strain intensity (ΔΓIII if local Mode II growth rates are proportional to the displacements. Such predictions are shown to be in agreement with measured growth rates in AISI {dy4140} steel from 10-6 to 10-2 mm per cycle.

Journal ArticleDOI
TL;DR: In this paper, the effect of R -ratio ( σ min / σ max ) on the threshold stress intensity range, ΔK th, can be correlated with the development of oxide thickness at the crack tip during near-threshold testing.

Journal ArticleDOI
TL;DR: In this paper, the authors deal with the stress concentration factors for a general fiber breakage model and use the knowledge of stress redistribution at fiber fracture for a Monte Carlo simulation of composite strength.
Abstract: This paper first deals with the stress concentration factors for a general fiber breakage model. The knowledge of stress redistribution at fiber fracture is then used for a Monte Carlo simulation of composite strength. The theoretical analysis has predicted the multiple fracture pattern of the low elongation fibers and the progressive nature of failure of hybrid composites. The enhanced ultimate failure strain of the hybrid as compared with that of the low elongation fiber composites signifies a hybrid effect. The major fin dings of this theoretical analysis coincide well with experimental observa tions.

Journal ArticleDOI
TL;DR: In this paper, the effect of ion implantation on the friction and wear behavior of metals was investigated, and it was shown that a hard surface layer formed during the implantation process minimizes plowing and subsurface deformation and reduces the delamination wear process.
Abstract: : The effect of ion implantation on the friction and wear behavior of metals was investigated. Experiments were conducted with iron, titanium, and copper implanted with nitrogen ions, iron implanted with aluminum ions, and copper implanted with zinc ions. The significant reduction in friction and wear of the iron and titanium systems is attributed to a hard layer formed during the ion implantation process. This hard layer minimizes plowing and subsurface deformation and hence reduces the delamination wear process, i.e. crack nucleation, crack propagation, and the formation of delamination wear sheets. A finite element model of an elastic semi-infinite solid under the contact of a stationary rigid asperity showed that the hard layer does not change the subsurface stress distribution by supporting the load, but rather that this thin layer decreases the plowing component of friction. The model predicts that this decrease in the friction coefficient in turn, substantially reduces subsurface deformation and thus wear. The implanted copper specimens which did not appear to have a hard surface layer showed little improvement in their tribological behavior over the unimplanted copper.

Journal ArticleDOI
TL;DR: In this paper, the influence of hydrogen environment on near-threshold fatigue crack propagation rates was examined in a 779 MPa yield strength NiCrMoV steel at 93 °C, and an automatically decreasing and increasing stress intensity technique was employed to generate crack growth rates at three load ratios (R = 0.1, 0.5, and 0.8).
Abstract: The influence of hydrogen environment (448 kPa) on near-threshold fatigue crack propagation rates was examined in a 779 MPa yield strength NiCrMoV steel at 93 °C. An automatically decreasing and increasing stress intensity technique was employed to generate crack growth rates at three load ratios(R = 0.1, 0.5, and 0.8). Results show that the crack propagation rates in hydrogen are slower than those in air for levels of stress intensity range, ΔK, below about 12 MPa√m. The crack closure concept does not explain the slower crack growth rates in hydrogen than in air. Near-threshold growth rates appear to be controlled by the levels of residual moisture in the environments. In argon and air, the fracture morphology is transgranular, while in H2 the amount of intergranularity varies with ΔK and achieves a maximum when the cyclic plastic zone is approximately equal to the prior austenite grain size.

Journal ArticleDOI
TL;DR: From a solution for the stress distribution in the skin, the severity of the stress concentration and the location and form of initial cuticular failure have been deduced, the latter two being in broad agreement with observed crack initiation in the cuticle of grapes.
Abstract: The skin around a lenticel on a soft fruit has been modelled as a thin elastic plate with a rigid circular inclusion and applied tensile loads at the edges. A solution for the stress distribution in the skin has then been found using the linear theory of elasticity. From that solution the severity of the stress concentration and the location and form of initial cuticular failure have been deduced, the latter two being in broad agreement with observed crack initiation in the cuticle of grapes.

Journal ArticleDOI
TL;DR: In this paper, a modified maximum tension stress theory is developed, in which the fracture theories of the crack and the notch can be roughly unified, and it is shown that the classical strength theories belong to the unconditional extremum criteria while the S criterion, etc.

Journal ArticleDOI
TL;DR: In this paper, a three dimensional finite element analysis was used to calculate interlaminar stresses near the hole boundary of a circular hole in a laminate with a hole as input to a quasi-three dimensional model.
Abstract: Stress distributions were calculated near a circular hole in laminates, using a three dimensional finite element analysis. These stress distributions were presented three ways: through the thickness at the hole boundary, along radial lines at the 0/90 and 90/0 interfaces, and around the hole at these interfaces. The interlaminar normal stress, and the shear stress, distributions had very steep gradients near the hole boundary, suggesting interlaminar stress singularities. The largest compressive stress occurred at about 60 deg from the load axis. A simple procedure was introduced to calculate interlaminar stresses near the hole boundary. It used stresses calculated by an exact two dimensional analysis of a laminate with a hole as input to a quasi three dimensional model. It produced stresses that agreed closely with those from the three dimensional finite element model.

Journal ArticleDOI
TL;DR: In this article, the authors measured the fatigue crack propagation rates and threshold stress intensity factors for welded joints and base metal by using 200 mm wide centre-cracked specimens and revealed that the fatigue cracks were fully open during the whole range of loading, due to the tensile residual stress distribution in the middle part of the welded joint.

Journal ArticleDOI
TL;DR: In this article, a technique for estimating crack opening stress during fatigue crack growth is proposed, which involves electron fractography of fracture surfaces obtained under specially designed load sequences and is experimentally validated on an AlCu alloy.

Book ChapterDOI
TL;DR: In this paper, a model was developed that predicts the influence of residual stress and stress ratio on the total fatigue life of a weld, which was considered to be composed of both crack initiation and crack propagation.
Abstract: A model was developed that predicts the influence of residual stress and stress ratio on the total fatigue life of a weld The total fatigue life of a weld was considered to be composed of both crack initiation and crack propagation Weld toe residual stresses were considered to influence the crack initiation life but not the crack propagation life The crack initiation life was estimated using cumulative damage concepts Actual weld material properties (weld metal and heat-affected zone) were considered in the initiation life estimation Neuber's rule was used to determine the local cyclic stress-strain behavior at the weld toe, and the fatigue notch factor was evaluated by using Peterson's equation Residual stresses were introduced into the analysis as a simulated pre-stressing of the weld Cyclic relaxation of the mean stress established during the set-up cycle was modeled by a power function and allowed relaxation to be considered in the life estimates Fatigue tests of steel weldments and aluminum butt welds having tensile and compressive residual stresses were conducted to verify the analytically predicted total fatigue life predictions Agreement between analytical predictions and experimental results was quite good


Journal ArticleDOI
TL;DR: In this article, the development of "special hole-elements" to enable an efficient and accurate analysis of stress concentration around through-thickness holes in angle-ply laminates is presented.

Journal ArticleDOI
TL;DR: In this paper, the fracture behavior of human hair has been investigated with a view toward delineating fracture mechanisms that lead to different types of fracture under tensile loading, including smooth fracture, step fracture, and fracture involving undefined fibrillated ends.
Abstract: The fracture behavior of human hair has been investigated with a view toward delineating fracture mechanisms that lead to different types of fracture under tensile loading. Principally, three types of fracture are encountered—smooth fractures, step fractures, and fractures involving undefined fibrillated ends. The moisture content of the fiber plays an important role in determining the type of fracture that occurs. Fiber conditioned at either low (∼0%) or high (90%) relative humidity give predominantly smooth fractures, whereas those conditioned at intermediate relative humidities given predominantly step fractures. Surface treatments with polymers or surfactants do not seem to have any effect on the strength or the fracture behavior of fibers. At low moisture contents, fracture initiation occurs more often in the cortex, whereas, at high moisture contents, fracture almost always initiates at the surface of the fiber, suggesting that the swelling pressure of the cortex plays a significant role in fracture initiation. Fibers with larger cross-sectional areas tend to split along the axis because of the higher probability of encountering flaws or medullary cells which direct cracks along the fiber axis. Unlike synthetic polymeric fibers, hair fibers seem to follow the Griffith criterion of brittle fracture. This may be coincidental since electron microscopic evidence suggests that fracture propagation occurs by secondary cracks generated as a result of stress concentrations building up at the periphery of the primary crack. The rate of stress transfer to adjacent cortical cells via intercellular cement probably plays an important role in the fracture mechanism.