Showing papers on "Crack closure published in 1976"
TL;DR: In this article, fracture mechanics is introduced into finite element analysis by means of a model where stresses are assumed to act across a crack as long as it is narrowly opened, which may be regarded as a way of expressing the energy adsorption in the energy balance approach.
5,505 citations
TL;DR: In this paper, an attempt is made to apply the J-integral concept as an elastic-plastic criterion for fatigue crack growth, and the results show correlation with Jintegral values estimated from load versus deflection hysteresis loops.
Abstract: An attempt is made to apply the J-integral concept as an elastic-plastic criterion for fatigue crack growth. Compact tension fracture specimens of A533B steel are subjected to gross cyclic plastic deformations, and fatigue crack growth rates up to 0.01 in./cycle are obtained. The results show correlation with J-integral values estimated from load versus deflection hysteresis loops. Also, agreement is obtained with the extrapolation of linear elastic fatigue crack growth rate data.
395 citations
TL;DR: In this article, a fracture mechanics approach was used to study high-temperature creep crack propagation, and crack growth rates were correlated with the C*-parameter which is an energy rate line integral.
Abstract: A fracture mechanics approach was used to study high-temperature creep crack propagation. Crack growth rates were correlated with the C*-parameter which is an energy rate line integral. For materials conforming to a nonlinear stress and strain rate relationship in the steady-state creep range, specifically, those which can be properly idealized as purely viscous (negligible elastic and transient creep effects), C* characterizes the crack tip stress and strain rate fields. Crack growth rate tests were conducted in the creep range on a discaloy superalloy at 1200°F (920 K). Two specimen geometries were tested, a center cracked panel and a compact geometry, to establish the geometry independence of this approach. The results showed that crack growth rate correlated with the C*-integral, while other parameters (K and nominal stress) failed to adequately characterize crack growth rate.
355 citations
01 Jan 1976
TL;DR: In this paper, a two-dimensional finite-element analysis for predicting crack-closure and crack-opening stresses during cyclic loading has been proposed, which accounts for elastic-plastic material behavior and changing boundary conditions associated with crack extension and intermittent contact of the crack surfaces under cyclic load cycling.
Abstract: Experiments have shown that fatigue cracks close at positive loads during constant-amplitude load cycling. The crack-closure phenomenon is caused by residual plastic deformations remaining in the wake of an advancing crack tip. The present paper is concerned with the application of a two-dimensional, nonlinear, finite-element analysis for predicting crack-closure and crack-opening stresses during cyclic loading. A two-dimensional finite-element computer program, which accounts for both elastic-plastic material behavior and changing boundary conditions associated with crack extension and intermittent contact of the crack surfaces under cyclic loading, has been developed. An efficient technique to account for changing boundary conditions was also incorporated into the nonlinear analysis program. This program was subsequently used to study crack extension and crack closure under constant-amplitude and two-level block loading. The calculated crack-closure and crack-opening stresses were qualitatively consistent with experimental observations.
271 citations
TL;DR: In this paper, a hybrid crack element is constructed to properly account for the crack tip singularity, and the stress intensity factors and energy release rate for cracks in different bi-material continua are then calculated using the finite element method.
Abstract: The stress singularity at the tip of a crack, either lying along or perpendicular to the interface of the two materials, is first investigated by the complex variable method. The order of the singularity is shown to be dependent on both the crack geometry and two parameters α, β which are related to the four elastic constants of the two materials. A hybrid crack element is constructed to properly account for the crack tip singularity. The stress intensity factors and energy release rate for cracks in different bi-material continua are then calculated using the finite element method. The results show that the present finite element analysis makes possible a highly accurate and efficient numerical solution of fracture mechanics problems.
225 citations
TL;DR: In this paper, the stable growth of a crack created by hydraulic pressurizing of a penny-shaped crack in a dry rock mass is investigated, and it is verified on the basis of the equations of fluid dynamics that the fracturing fluid cannot penetrate the entire domain of the crack when the crack is moving.
Abstract: The stable growth of a crack created by the hydraulic pressurizing of a penny-shaped crack in a dry rock mass is investigated. The rock mass is infinitely extended, homogeneous, and isotropic. It is verified on the basis of the equations of fluid dynamics that the fracturing fluid cannot penetrate the entire domain of a crack when the crack is moving. The effects of various terms in the basic equations are also studied. The solution of some typical examples is given, and the significant effect of the stress intensity factor of the rock on the crack propagation is shown. When the crack is expanding under a constant flow rate, the classical solution by Sack is found to be approximately valid for very large cracks, and nevertheless the crack is stable.
204 citations
TL;DR: In this paper, an underaged, aged, and overaged microstructure of an austenitic Fe-36 at.% Ni-12 at.%. Al alloy was investigated for fatigue crack propagation.
175 citations
TL;DR: In this paper, it was shown that grain-boundary voids resemble voids in liquids, or in very viscous adhesives, all of which show a transition from a stable smooth periphery to an unstable, finger-like one as the void growth rate increases.
Abstract: When voids or cracks grow by diffusion on grain boundaries in stressed solids, it is sometimes observed that the void periphery becomes finger-like, the fingers advancing ahead of the main body of the void. In this, grain-boundary voids in solids resemble voids in liquids, or in very viscous adhesives, all of which show a transition from a stable smooth periphery to an unstable, finger-like one as the void (or crack) growth-rate increases. We have analysed these phenomena, adapting and extending results due to Taylor and Zener. This allows us to derive conditions for the instability to occur, and expressions for the finger spacing and for the overall growth-rate of the finger-like crack
127 citations
TL;DR: In this article, a procedure compatible with linear elastic fracture mechanics (LEFM) and crack opening displacement (COD) testing was suggested for finding a three-point bend specimen with COD.
Abstract: Possible methods for evaluating J for a three-point bend specimen are reviewed and the effects of slow crack growth, experimental limit load, and lateral constraint noted. A procedure, compatible with linear elastic fracture mechanics (LEFM) and crack opening displacement (COD) testing, is suggested for finding J c .
123 citations
TL;DR: In this article, the fracture mechanics approach to fatigue crack growth may be extended by the use of the J-integral concept, so that large scale plasticity effects are included.
Abstract: Fatigue crack growth rate data are obtained for center cracked specimens of A533B steel subjected to elastic-plastic cyclic loading. Cyclic J-integral values estimated from load versus deflection hysteresis loops are correlated with these growth rate data. The relationship obtained is in agreement with previous elastic-plastic data on compact specimens and also with linear elastic data on large size compact specimens. These experimental data suggest that the fracture mechanics approach to fatigue crack growth may be extended by the use of the J-integral concept, so that large scale plasticity effects are included.
TL;DR: In this article, a simple analogy between the interfacial continuity conditions for the plane and bending problems is derived and its implications are discussed using the eigenfunctionexpansion method using the crack tip stress singularities for various crack orientations and material combinations.
Abstract: The plane, bending and antiplane strain elastostatic problems for two bonded half planes containing an arbitrarily oriented semi-infinite crack meeting the interface, are examined. A simple analogy between the interfacial continuity conditions for the plane and bending problems is derived and its implications are discussed. Using the eigenfunction-expansion method the crack tip stress singularities for various crack orientations and material combinations are compared for the three problems. It is shown that, under certain conditions, singularities are no longer present in the stress field. In the case of the antiplane strain problem subsequent paths of crack propagation are predicted.
TL;DR: In this paper, twelve different combinations of hot die forging and heat treatment, in the α+β and β phase regions, were investigated, and the resulting heat treated forgings were classified into four distinct categories based on their microstructural appearance.
Abstract: To establish correlations between microstructure and mechanical properties for the Till alloy, twelve different combinations of hot die forging and heat treatment, in the α+β and β phase regions, were investigated. The resulting heat treated forgings were classified into four distinct categories based on their microstructural appearance. The room temperature tensile, post-creep tensile, fracture toughness and fatigue crack propagation properties were measured along with creep and low cycle fatigue at 566°C. The creep, tensile, fatigue crack propagation and fracture toughness properties, grouped in a manner similar to the microstructural categories. The fracture appearance and behavior of the cracks during propagation in fatigue and in fracture toughness tests were examined, and correlations with the microstructure discussed. In the case of the fully transformed acicular microstructure, it was found that the size and the orientation of colonies of similarly aligned α needles are dominant factors in the crack behavior.
Journal Article•
TL;DR: In this article, an incremental theory of plasticity was used to predict crack-closure and crack-opening stresses during the crack-growth process under cyclic loading, and the calculated crackopening stresses were found to be quantitatively consistent with experimental measurements.
Abstract: Experiments have shown that fatigue cracks close at positive loads during constant-amplitude load cycling. The crack-closure phenomenon is caused by residual plastic deformations remaining in the wake of an advancing crack tip. The present paper is concerned with the application of a two-dimensional, nonlinear, finite-element analysis using an incremental theory of plasticity to predict crack-closure and crack-opening stresses during the crack-growth process under cyclic loading. A two-dimensional finite-element computer program, which accounts for both elastic-plastic material behavior and changing boundary conditions associated with crack extension and intermittent contact of the crack surfaces under cyclic loading, has been developed. An efficient technique to account for changing boundary conditions under cyclic loading was also incorporated into the nonlinear analysis program. This program was used subsequently to study crack extension and crack closure behavior in a center-cracked panel under constant-amplitude and two-level block loading. The calculated crack-opening stresses were found to be quantitatively consistent with experimental measurements.
TL;DR: In this article, a survey of variable-amplausitude loading as applied in test programs is given, with an analysis of the consequences for prediction techniques. But the authors focus on the effects of variableamplitude loading on fatigue cracks.
Abstract: The paper starts with a discussion on loads in service, after which a survey is given of various types of variable-amplitude loading as applied in test programs. The various phenomenological aspects of fatigue damage associated with fatigue cracks are indicated. Interaction effects between cycles of different magnitudes are defined. Methods for measuring interaction effects, examples of interaction effects, and possible explanations are reviewed. This includes both tests with simple types of variable-amplitude loading (overloads and step loading) and more complex load-time histories (program loading, random load, and flight-simulation loading). New evidence on crack closure is presented. Various types of prediction methods are discussed. The paper is primarily a survey of the present knowledge, with an analysis of the consequences for prediction techniques.
TL;DR: In this article, a brief treatment of the application of linear elastic fracture mechanics theory to sharp cracks in concrete beams is presented and the effect of beam size is particularly examined, where the same basic technique is applied to reentrant notches.
Abstract: Synopsis At the tip of a sharp crack or re-entrant notch, the stresses calculated by a simple elastic analysis become infinite. Consequently, maximum-stress or -strain failure criteria and stress-concentration factors cannot be used to predict failure at such points. The linear elastic fracture mechanics theory can, however, be applied. In the paper, a brief treatment of the application of this theory to sharp cracks in concrete beams is presented and the effect of beam size is particularly examined. The same basic technique is applied to re-entrant notches. Experimental evidence of the validity of the approach is given. Theoretical results are included which allow these test data to be extended to a wide range of notch conjigurations. It is expected that this work will have considerable importance for the problem of crack initiation at corners of openings in walls etc.
TL;DR: The theory of crack extension in elastic bodies is summarized in this article, and it is recognized that there is still no satisfactory explanation of the phenomenon of crack branching, but it is probable that branching of a main crack is the result of its interaction with micro-cracks generated ahead of it.
Abstract: Some recent and important results of the theory of crack extension in elastic bodies are summarized. The theory can adequately account for most of the features of fast brittle fracture observed experimentally. In particular, the fact that the maximum crack speeds observed in practice are considerably lower than the speed of Rayleigh waves may be attributed to a sharp increase in the effective surface energy with increasing crack speed. This increase in surface energy would make branching more likely, but it is recognized that there is still no satisfactory explanation of the phenomenon of crack branching. It is probable that branching of a “main crack” is the result of its interaction with “microcracks” generated ahead of it. The difficulties involved in a theoretical analysis of this interaction are outlined and certain suggestions for further research are given.
Journal Article•
TL;DR: In this paper, the potential interference of crack surfaces is determined from analyses of elastic displacements during loading and unloading and of the permanent deformation left in the wake of a growing crack.
Abstract: A method for prediction of crack growth behavior has been developed, based on evaluations of stress intensity caused by crack surface contact. The potential interference of the crack surfaces is determined from analyses of elastic displacements during loading and unloading and of the permanent deformation left in the wake of a growing crack. The potential interference is treated as a wedge acting behind the crack tip and the contact stresses created by this wedge are computed through an elastic-plastic analysis. The effective stress intensity range used for crack growth prediction is found by subtracting the stress intensity caused by these contact stresses from the applied stress intensity range. Comparisons of crack growth behavior predicted by this method and that measured in constant amplitude tests, with and without high loads, and in block spectrum tests have shown that the method accounts for load interaction effects in these cases. These effects include delayed retardation following high loads, crack growth acceleration during high loads, and dependence of growth rates on number of high loads.
TL;DR: A strong correlation was found between the experimentally determined crack growth rate and the applied stress intensity and the relationship takes the form of a power law similar to that for other materials.
Abstract: The purpose of this investigation was to apply the techniques of fracture mechanics to a study of fatigue crack propagation in compact bone. Small cracks parallel to the long axis of the bone were initiated in standardized specimens of bovine bone. Crack growth was achieved by cyclically loading these specimens. The rate of crack growth was determined from measurements of crack length versus cycles of loading. The stress intensity factor at the tip of the crack was calculated from knowledge of the applied load, the crack length, and the specimen geometry. A strong correlation was found between the experimentally determined crack growth rate and the applied stress intensity. The relationship takes the form of a power law similar to that for other materials. Visual observation and scanning electron microscopy revealed that crack propagation occurred by initiation of subcritical cracks ahead of the main crack.
TL;DR: In this article, the authors investigated the fatigue crack growth behavior resulting from single and multiple applications of overload for HT80 steel and found that a peak load was found to cause retardation of the crack growth rate, which becomes stronger with increasing the peak/baseline stress ratio or with decreasing baseline stress intensity.
TL;DR: In this article, the plane-strain yielding from a crack in an infinite elastic body is represented by a distribution of edge dislocations on two planes inclined at angles ±ga to the crack plane, and the equilibrium condition is solved numerically.
Abstract: Plane-strain yielding from a crack in an infinite elastic body is represented here by a distribution of edge dislocations on two planes inclined at angles ±ga to the crack plane, and the equilibrium condition is solved numerically. Approximate analytical expressions are obtained for the plastic-zone length, the crack opening displacement, and the J -integral, as functions of the applied stress and α. A comparison with a co-planar model of the plastic zone gives very similar results for α ≈ 65°. It is shown that fracture criteria based either on a critical crack opening displacement (COD) or on a critical value of J are always different, and the use of the former may lead to critical defect-sizes which are twice as large as those given by the latter. Furthermore, COD appears not to be a well-defined material property. The critical J criterion gives a fracture stress which is α-dependent : this may be responsible for deviations towards results of linear elastic fracture mechanics when post-yield fracture mechanics is used to analyse extensive yielding. The changes in the stress field of the crack due to the existence of the plastic zone are also discussed.
TL;DR: In this article, the effects of specimen type (precracked tension or bend) on the relationship between the Jintegral and the crack tip opening displacement (COD) and on crack initiation values of J and COD were investigated.
Abstract: The effects of specimen type (precracked tension or bend) on the relationship between the J-integral and the crack tip opening displacement (COD) and on crack initiation values of J and COD were investigated. The material used was a mild steel. COD was measured by infiltrating the crack with a catalytically hardening silicone rubber. The J-integral was measured both by the compliance technique and using analytical formulae. No significant effect of specimen type was noted. Measurements of J from the analytical formulae used agreed well with compliance measurements. Simultaneous J and COD values were also measured on a low alloy steel. The results indicate that the J/G/COD relationships are material dependent, possibly being controlled by the material's work-hardening rate.
TL;DR: In this article, the authors tested panels of PMMA having edge cracks at an angle to applied load in tension and bending, and the direction of initial crack growth and load to failure were recorded.
Abstract: Panels of PMMA having edge cracks at an angle to applied load were tested in tension and bending. Direction of initial crack growth and load to failure were recorded. Stress analysis of each test configuration was performed, and the maximum hoop stress and minimum strain energy density criteria were used to predict failure data. Reasonable correlation between experiment and theory was realised, but with little basis for discriminating between the two failure criteria.
01 Jan 1976
Abstract: A method for prediction of crack growth behavior has been developed, based on evaluations of stress intensity caused by crack surface contact. The potential interference of the crack surfaces is determined from analyses of elastic displacements during loading and unloading and of the permanent deformation left in the wake of a growing crack. The potential interference is treated as a wedge acting behind the crack tip and the contact stresses created by this wedge are computed through an elastic-plastic analysis. The effective stress intensity range used for crack growth prediction is found by subtracting the stress intensity caused by these contact stresses from the applied stress intensity range. Comparisons of crack growth behavior predicted by this method and that measured in constant amplitude tests, with and without high loads, and in block spectrum tests have shown that the method accounts for load interaction effects in these cases. These effects include delayed retardation following high loads, crack growth acceleration during high loads, and dependence of growth rates on number of high loads.
01 Jun 1976
TL;DR: In this paper, the application of Griffith energy concepts to Elastic-Plastic Fracture Mechanics (EPFM) is investigated and an elastic-plastic finite element program is used to calculate the values of the C...
Abstract: SYNOPSIS The application of Griffith energy concepts to Elastic-Plastic Fracture Mechanics (EPFM) is investigated. An elastic-plastic finite element program is used to calculate the values of the C...
TL;DR: In this article, the authors investigated the effect of relative humidity on crack initiation in Al 2219-T851 for fully reversed loading (R = σ/σmax =−1) parallel to the material rolling direction, and found that there is no significant dependence of fatigue life on relative humidity.
Abstract: Fatigue crack initiation in Al 2219-T851 for fully reversed loading(R = σ/σmax =−1) parallel to the material rolling direction is found to occur at intermetallic inclusions at the specimen surface. The inclusions are not involved in crack initiation for fatigue perpendicular to the rolling direction, and for this orientation crack initiation is at grain boundaries and specimens have an increased fatigue life. Except for fatigue at low peak stress, multiple numbers of microcracks are formed and for selected failed specimens the number of cracks has been determined as a function of crack length. Such crack length distribution measurements show that there is significant retardation of microcracks by interaction with grain boundaries. Furthermore it is found that the coalescence of microcracks provides a mechanism for cracking to “jump“ grain boundaries and reduce fatigue lifetime. The effect of relative humidity on this process is to increase the observed mean crack length, and decrease the number of crack initiations apparently due to weakening of the matrix-intermetallic interface at potential initiation sites. The overall result is that no significant dependence of fatigue life on relative humidity is found.
TL;DR: In this article, the authors measured the fracture toughness of poly(vinyl chloride) sheet and made an analysis made of circular "advance fractures" that occur on the fracture surface, and showed that the craze fracture mechanism is quite different from the monotonic loading failure mechanism.
TL;DR: In this paper, the effect of loading frequency on fatigue crack propagation rate and striation spacing in 2024-T3 aluminium alloy and SM-50 steel was studied at room temperature, and the results showed that dc/dN and s will not coincide except the very narrow region near the intersecting point.
TL;DR: In this paper, the authors present the results of the first phase of an investigation sponsored by the National Cooperative Highway Research Program, Project 12-14, to study subcritical crack growth in steel bridge members.
Abstract: Well-conceived procedures used to study the safety and reliability of structures recognize that the performance of a structure or a structural component is governed not only by material properties but also by the design; fabrication, inspection, erection, and use of the structure. These parameters govern the initiation of subcritical cracks and their propagation to critical dimensions, and therefore, determine the useful fatigue life of structural components subjected to load fluctuations. This paper presents the results of the first phase of an investigation sponsored by the National Cooperative Highway Research Program, Project 12-14, to study "Subcritical Crack Growth in Steel Bridge Members." The paper describes the fatigue-crack-growth behavior of various bridge steels (A36, A588-A, A588-B, A514-B, A514-E, and A514-F) under variable-amplitude random-sequence stress spectra such as occur in actual bridges. The fatigue crack growth-rate data were obtained by using wedge-opening-loading specimens tested under variable-amplitude random-sequence load spectra that are represented by a Rayleigh distribution function. The data obtained for these steels showed that the average fatigue crack growth rates, da/dN, under variable-amplitude random-sequence load fluctuation and under constant-amplitude load fluctuation agreed closely when da/dN was plotted as a function of the root-mean-square stress intensity factor range, ΔK r m s . Thus, within the limits of the present investigation, the average fatigue crack-growth rates, da/dN, of various bridge steels subjected to variable-amplitude random-sequence load fluctuations, such as occur in actual bridges and to constant-amplitude load fluctuations, can be represented by the equation da dN = A (ΔK r m s ) n where ΔK r m s is the root-mean-square stress intensity factor fluctuation, and A and n are material constants.