Showing papers on "Fracture toughness published in 1973"
TL;DR: In this paper, the critical value of tensile stress (a) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions.
Abstract: SUMMARY AN ANALYSIS is presented which relates the critical value of tensile stress (a,) for unstable cleavage fracture to the fracture toughness (K,,) for a high-nitrogen mild steel under plane strain conditions. The correlation is based on (i) the model for cleavage cracking developed by E. Smith and (ii) accurate plastic*lastic solutions for the stress distributions ahead of a sharp crack derived by J. R. Rice and co-workers. Unstable fracture is found to be consistent with the attainment of a stress intensification close to the tip such that the maximum principal stress a,, exceeds a, over a characteristic distance, determined as twice the grain size. The model is seen to predict the experimentally determined variation of K,, with temperature over the range -150 to -75°C from a knowledge of the yield stress and hardening properties. It is further shown that the onset of fibrous fracture ahead of the tip can be deduced from the position of the maximum achievable stress intensiiication. The relationship between the model for fracture ahead of a sharp crack, and that ahead of a rounded notch, is discussed in detail.
1,374 citations
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01 Jan 1973
TL;DR: In this article, the authors introduce the concept of a crack extension force which can be used to rank materials in some order of fracture resistance and determine the largest crack that a material will tolerate without failure.
Abstract: It is weH known that the traditional failure criteria cannot adequately explain failures which occur at a nominal stress level considerably lower than the ultimate strength of the material. The current procedure for predicting the safe loads or safe useful life of a structural member has been evolved around the discipline oflinear fracture mechanics. This approach introduces the concept of a crack extension force which can be used to rank materials in some order of fracture resistance. The idea is to determine the largest crack that a material will tolerate without failure. Laboratory methods for characterizing the fracture toughness of many engineering materials are now available. While these test data are useful for providing some rough guidance in the choice of materials, it is not clear how they could be used in the design of a structure. The understanding of the relationship between laboratory tests and fracture design of structures is, to say the least, deficient. Fracture mechanics is presently at astandstill until the basic problems of scaling from laboratory models to fuH size structures and mixed mode crack propagation are resolved. The answers to these questions require some basic understanding ofthe theory and will not be found by testing more specimens. The current theory of fracture is inadequate for many reasons. First of aH it can only treat idealized problems where the applied load must be directed normal to the crack plane.
629 citations
TL;DR: In this paper, fracture tests of 105 fine-grained quartz arenites were conducted at 25°C, 1.0-kb confining pressure, constant strain rate of 6.5 × 10−5/sec, and pore pressure ranging from 0 to 750 bars.
Abstract: Brittle fracture tests of 105 fine-grained quartz arenites were conducted at 25°C, 1.0-kb confining pressure, a constant strain rate of 6.5 × 10−5/sec, and pore pressure ranging from 0 to 750 bars. Orientation of planar anisotropy (bedding or cross-bedding) with respect to principal stresses has little influence on the fracture strength. The Donath orientation effect depends on rock type. Strong dependence of fracture strength on porosity is of the form y = axb (where y equals stress difference at failure, x equals porosity, and a > 0 > b; in our samples, values for a ranged between 16 and 25 kb, and b between −0.8 and −1.0). Through-going shear fractures result from coalescence of grain boundary cracks, extension fractures within grains, and void space. Rocks with low porosity develop through-going shears only after many grains are extension fractured. The functional relationship between porosity and fracture strength derives from the lower energy required for propagating cracks to use void space rather than forming extension fractures.
249 citations
TL;DR: In this paper, a study has been made of fatigue crack propagation in a low alloy steel which is subject to temper embrittlement and effects of mean stress on the growth rate have been examined and comparisons between temper embrittled and unembrittled conditions have been made.
242 citations
TL;DR: In this paper, a dislocation model was developed compatible with this point of view, which yields a relation between the fracture strain and the volume fraction of the inclusions, which is the critical event in ductile fracture; it is immediately followed by spontaneous growth and coalescence of the voids.
213 citations
TL;DR: In this paper, an analysis was made of cantilever beam specimens used for crack propagation studies, including the effects of a plastic zone at the crack tip, beam rotation, and the viscoelastic response of the material.
Abstract: An analysis was made of cantilever beam specimens used for crack propagation studies, Included in this analysis were the effects of a plastic zone at the crack tip, beam rotation, and the viscoelastic response of the material. This analysis showed that application of a constant bending moment to the specimen rather than a constant load provides a test in which the strain energy release rate,G, is independent of crack length. Other advantages of this test configuration are that corrections for shear or beam rotation effects are not necessary. Results of this test on both glass and ceramics are reported.
185 citations
TL;DR: This deformation and fracture of high polymers is well known book in the world, of course many people will try to own it and this is it the book that you can receive directly after purchasing.
Abstract: Why should wait for some days to get or receive the deformation and fracture of high polymers book that you order? Why should you take it if you can get the faster one? You can find the same book that you order right here. This is it the book that you can receive directly after purchasing. This deformation and fracture of high polymers is well known book in the world, of course many people will try to own it. Why don't you become the first? Still confused with the way?
176 citations
TL;DR: In this article, the shape of the primary craze at the tip of a crack has been studied by optical microscopy for two grades of poly(methyl methacrylate).
136 citations
TL;DR: In this paper, the Neuber stress-concentration relation for notches in an elastic-plastic material subjected to shear loading was generalized for a crack in a finite plate subjected to tensile loading.
116 citations
TL;DR: In this paper, a finite-element method has been extended for the description of growth phenomena at a crack tip in plane stress and the necessary introduction of hereditary properties of elastic-plastic stiffnesses has been carried out as well as the inclusion of routines for relaxation of cohesive crack-tip forces.
Abstract: In this paper, finite-element methods have been extended for the description of growth phenomena at a crack tip in plane stress. The necessary introduction of hereditary properties of the elastic-plastic stiffnesses has been carried out as well as the inclusion of routines for relaxation of cohesive crack-tip forces. Simple macroscopic models of the fracture process are discussed and the crack-tip opening angle is chosen for determination of a fracture criterion in the finite-element model. Under the somewhat arbitrary assumption of a constant crack opening-angle as a fracture criterion, results are obtained that make clear the possibility of simulating stable crack-growth with this method, particularly in connection with fracture toughness tests in the non-linear range. The further extension of the model for the achievement of quantitative results is also discussed.
113 citations
TL;DR: In this paper, a fracture mechanical analysis has been developed to account for the observed dependence of the energy/unit area (w) on the notch size, and a correction factor (φ) has been derived to accommodate notch effects.
Abstract: Previous work on impact testing has shown that the energy/unit area (w) normally measured in notched impact tests is dependent on specimen geometry. A fracture mechanical analysis has now been developed to account for the observed dependence ofw on notch size. A correction factor (φ) has been derived to accommodate notch effects and this allows for the calculation of the strain energy release-rateG directly from the measured fracture energies. Tests on PMMA have shown that “corrected” results are independent of specimen geometry and theG
c for PMMA has been evaluated as 1.04 × 103 J m−2. The experimental results show that there is an additional energy term which must be accounted for and this has been interpreted here as being due to kinetic energy losses in the specimens. A conservation of momentum analysis has allowed a realistic correction term to be calculated to include kinetic energy effects and the normalized experimental results show complete consistency between all the geometries used in the test series. It is concluded that the analysis resolves many of the difficulties associated with notched impact testing and provides for the calculation of realistic fracture toughness parameters.
TL;DR: In this article, a theory of fracture mechanics is proposed in which attention is focused on the intensity of the energy field in the crack tip region and the strength or amplitude of this field is referred to as the energy-density factor, S. The difference between k and S is analogous to the difference between a scalar and vector quantity.
TL;DR: In this article, a notching technique was devised to produce pure cracks and a curve showing the relationship between crack speed and crack toughness was also obtained and a lower bound for crack initiation was extrapolated as being 0.78 MN/m3/2.
Abstract: Fracture mechanics concepts, in terms of stress intensity factors, have been used in a study of the growth of cracks and crazes in Crystal Polystyrene in air at 293°K. Single edge notch tension specimens and tapered cleavage specimens have been tested over a wide range of strain rates and also at constant load. It was initially found that the critical stress intensity factor K
Ic
(evaluated at crack instability) which should be a constant, independent of test method and specimen geometry, could apparently vary over a wide range. This phenomenon was shown to be caused by the presence of craze bunches at the crack tips; the size of these bunches being dependent upon the method of notching employed. A notching technique producing pure cracks was devised and as a result the lower bound value of K
Ic
at instability for the material was shown to be 1.05 MN/m3/2. A curve showing the relationship between crack speed and crack toughness K
c
was also obtained and a lower value of K
c
for crack initiation was extrapolated as being 0.78 MN/m3/2. The role of inherent flaws in the fracture of unnotched tensile specimens and the consequences of crazing are discussed in terms of fracture stresses predicted from the notched tests using a Dugdale model.
TL;DR: In this paper, the effects of porosity, pore distribution, and grain size on fracture energy were evaluated and a grain-size effect dominates in dense material; the fracture energy decreases with increasing grain size.
Abstract: Alumina specimens were fabricated under a wide range of conditions using cold-pressing and sintering techniques. Fracture energies were measured by an analytical technique (notched beam) and by the Tattersall-Tappin method. Problems in using the latter method are discussed. The effects of porosity, pore distribution, and grain size on fracture energy are evaluated. Connected porosity has a deleterious effect on fracture energy. A grain-size effect dominates in dense material; the fracture energy decreases with increasing grain size.
01 Mar 1973
TL;DR: In this article, a theory is developed for predicting the time-dependent size and shape of cracks in linearly viscoelastic, isotropic media, and its validity is demonstrated by applying the theory to crack growth and failure of unfilled and particulate-filled polymers.
Abstract: : A theory is developed for predicting the time-dependent size and shape of cracks in linearly viscoelastic, isotropic media, and its validity is demonstrated by applying the theory to crack growth and failure of unfilled and particulate-filled polymers. Starting with a bounded solution for the stress distribution near a crack tip in an elastic body and the extended correspondence principle for viscoelastic media with moving boundaries, a simple equation is derived for predicting instantaneous crack tip velocity in terms of the opening- mode stress intensity factor; although the undamaged portion of the continuum is assumed linear, no significant restrictions are placed on the nature of the disintegrating material near the crack tip and, therefore, this material may be highly nonlinear, rate- dependent, and even discontinuous. A further analysis is made to predict the time at which a crack starts to grow, and then some explicit solutions are given for this so- called fracture initiation time, the time- dependent crack growth, and the time at which gross failure occurs under time- varying applied forces and environmental parameters. Following a derivation of the linear cumulative damage rule, an examination of its theoretical range of validity, and a discussion of the experimental determination of fracture properties, the theory is applied to monolithic and composite materials under constant and varying loads. Some concluding remarks deal with extensions of the theory to include finite strain effects, crack growth in the two shearing modes and in combined opening and shearing modes, and adhesive fracture.
TL;DR: In this article, normal shear fracture initiation from compressive stress concentration at the periphery of voids and cracks, subjected to compressive loading, is examined experimentally and theoretically.
TL;DR: In this paper, the concept of fracture mechanics is applied to analyze the brittle fracture of unidirectional composites and the analytical prediction based on the newly developed Sc-theory agrees well with the experimental data on Scotchply 1002 where crack propagation occurs along the fiber direction.
Abstract: The concept of fracture mechanics is applied to analyze the brittle fracture of unidirectional composites. The analytical prediction based on the newly developed Sc-theory agrees well with the experimental data on Scotchply 1002 where crack propagation occurs along the fiber direction. The Sc-theory represents a departure from the classical stress-intensity factor Kc concept in that it is designed to treat the mixed mode fracture problem while the Kc-theory is limited to Mode I crack extension.
TL;DR: It was concluded that voids preceding ductile fracture could be initiated without the presence of secured phase particles in pure metals and 'clean' alloys.
TL;DR: The room-temperature fracture behavior of partially stabilized ZrO3 (PSZ) in the system CaO-ZrO2 was investigated in this paper, where fracture energy was measured using standard single-edge crack and work-of-fracture techniques.
Abstract: The room-temperature fracture behavior of partially stabilized ZrO3 (PSZ) in the system CaO-ZrO2 was investigated Fracture energy was measured using standard single-edge-crack and work-of-fracture techniques Attempts were made to relate the fracture toughness parameters to the microstructure of the material Stable crack propagation was always observed; a model is proposed to explain these observations on the basis of the formation of a microcrack zone at the tip of a propagating crack The occurrence of initial stable crack propagation is explained in terms of an increase in microcrack zone size The possibility that crack stability results from testing geometry superimposed on the microcracking stability is also discussed
TL;DR: In this paper, the specific fracture energy, w/A, is derived from linear fracture mechanics by integrating well known functions for the stress field intensity factor to give the compliance and hence the work done.
TL;DR: The effective fracture toughness of a range of cement pastes and mortars have been measured using both a notched beam and a doublt cantilever beam method as discussed by the authors.
01 Feb 1973
TL;DR: In this article, the volume fraction and mean spacing of voids within the cyclic plastic zone have been determined as a function of ΔK by quantitative fractography, and it is concluded that the inclusion content increases the fatigue-crack growth rates only within the plane stress range, that is for values of the stress intensity-factor range ΔK \s> 20 kpsi√in.
Abstract: Fatigue crack growth rates were measured at room temperature in dry air for three 7075-T6 aluminum alloys with different inclusion content. Volume fractions of inclusions were determined for each alloy by the point count method with two different automated systems. Plots of the fatigue crack growth rate (da/dN) vs the stress-intensity-factor range (ΔK) show a well defined change of slope at the transition between plane strain and plane stress fracture. This transition is associated with a marked increase in the amount of fracture by void growth around inclusions. The volume fraction and mean spacing of voids within the cyclic plastic zone have been determined as a function of ΔK by quantitative fractography. Fracture by voids is important when the mean spacing of such voids is approximately equal to the width of the cyclic plastic zone in the plane of the crack. It is concluded that the inclusion content increases the fatigue-crack growth rates only within the plane stress range, that is for values of the stress-intensity-factor range ΔK \s> 20 kpsi√in.
TL;DR: In this article, an elastic-plastic analysis is performed for an infinite plate under plane stress conditions which contains a finite line crack and is subjected to biaxial loading, and the amplitude of the dominant singularity at the crack tip, the plastic stress (or strain) intensity factor, is found to depend on the magnitude of loading parallel to the crack direction.
Abstract: An elastic-plastic analysis is performed for an infinite plate under plane stress conditions which contains a finite line crack and is subjected to biaxial loading. In the large scale yielding range, the amplitude of the dominant singularity at the crack tip, the plastic stress (or strain) intensity factor, is found to depend on the magnitude of loading parallel to the crack direction. The predicted value for the fracture initiation stress which is based on a plastic intensity factor fracture criterion, increases under lateral, tensile loading. Compressive loading parallel to the crack has the opposite effect on the fracture initiation stress.
TL;DR: In this paper, the fracture toughness of low alloy quenched and tempered steels with yield strengths over 200,000 psi can be improved by microstructural control by as much as 70 per cent.
TL;DR: In this article, the authors examined the fatigue-crack propagation characteristics in polyvinyl chloride (PVC) in terms of fracture mechanics concepts where the crack growth rate is related to the applied stress intensity factor range.
Abstract: The fatigue-crack propagation characteristics in poly(vinyl chloride) (PVC) are examined in terms of fracture mechanics concepts where the crack growth rate is related to the applied stress intensity factor range. The microscopic details of fatigue crack extension are examined with the aid of light optical, scanning and transmission electron microscopes. The mechanism of crack advance is found to be that of void coalescence through craze material generated in advance of the crack tip. While the craze is shown to grow continuously with cyclic loading, the crack is found to grow discontinuously in several hundred cycle increments.
TL;DR: In this paper, two thermomechanical treatments have been considered, one a high strength condition equivalent to the conventional T-6 treatment and the other an over-aged condition comparable to the T-73 treatment.