Showing papers on "Fracture toughness published in 1976"
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01 Jan 1976TL;DR: In this article, the authors present an overview of fracture mechanics of engineering materials and examine the role of the transition temperature approach to fracture control in the engineering failure process, as well as various aspects of fracture toughness.
Abstract: DEFORMATION OF ENGINEERING MATERIALS. Tensile Response of Materials. Elements of Dislocation Theory. Slip and Twinning in Crystalline Solids. Strengthening Mechanisms in Metals. High-Temperature Deformation Response of Crystalline Solids. Deformation Response of Engineering Plastics. FRACTURE MECHANICS OF ENGINEERING MATERIALS. Fracture: An Overview. Elements of Fracture Mechanics. Transition Temperature Approach to Fracture Control. Microstructural Aspects of Fracture Toughness. Environment-Assisted Cracking. Cyclic Stress and Strain Fatigue. Fatigue Crack Propagation. Analyses of Engineering Failures. Appendices. Indexes.
3,611 citations
1,926 citations
TL;DR: In this paper, an approximate stress analysis has indicated the importance of both the impression radius and the ratio of the hardness to the fracture toughness in the development of the observed fractures, which has been used to examine several important consequences of indentation fracture.
771 citations
TL;DR: The fracture toughness of Al2O3 is considerably increased by the incorporation of fine monoclinic ZrO2 particles in hot-pressed composites as mentioned in this paper, and the increase results from a high density of small matrix micro cracks absorbing energy by slow propagation.
Abstract: The fracture toughness of Al2O3 is considerably increased by the incorporation of fine monoclinic ZrO2 particles. Hot-pressed composites containing 15 vol % ZrO2 yield Klcvalues of ∼ 10 MN/m3/2, twice that of the A12O3 matrix. It is hypothesized that this increase results from a high density of small matrix microcracks absorbing energy by slow propagation. The microcracks are formed by the expansion of ZrO2during the tetragonal → monoclinic transformation. Since extremely high tensile stresses develop in the matrix, very small ZrO2 particles can act as crack formers, thus limiting the critical flaw size to small values.
577 citations
TL;DR: In this paper, a polynominal expression is given for the stress intensity factor, K, from the applied force, P, and the specimen dimensions, which is explicitly stated that these expressions should not be used outside the range of relative crack length, a/W.
Abstract: For each of the two types of specimens, bend and compact, described previously for plane strain fracture toughness of materials, E 399, a polynominal expression is given for calculation of the stress intensity factor, K, from the applied force, P, and the specimen dimensions. It is explicitly stated, however, that these expressions should not be used outside the range of relative crack length, a/W, from 0.45 to 0.55. While this range is sufficient for the purpose of E 399, the same specimen types are often used for other purposes over a much wider range of a/W; for example, in the study of fatigue crack growth. Expressions are presented which are at least as accurate as those in E 399-74, and which cover much wider ranges of a/W: for the three-point bend specimen from 0 to 1; and for the compact specimen from 0.2 to 1. The range has to be restricted for the compact specimen because of the proximity of the loading pin holes to the crackline, which causes the stress intensity factor to be sensitive to small variations in dimensions when a/W is small. This is a penalty inherently associated with the compactness of the specimen.
484 citations
TL;DR: In this article, a model of dynamic ductile and brittle fracture was developed for wave propagation in one-and two-dimensional geometries, and the model features were taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results where applicable.
Abstract: Computational models of dynamic ductile and brittle fracture are developed for wave propagation in one‐ and two‐dimensional geometries. The model features have been taken mainly from detailed observations of samples partially fractured during impacts, but the functional forms are consistent with theoretical results where applicable. Basic features of the models are the nucleation and growth (hence, the acronym NAG for the models) of voids or cracks, and the stress relaxation resulting from the growing damage. The results of the calculations include number and sizes of cracks, voids, or fragments as a function of position in the material. The NAG analysis presents the nucleation law, determined from experiment, and two growth laws: both growth and nucleation are functions of stress and stress duration. Procedures for treating cracks with a range of sizes and orientation are presented with the method for computing the stress relaxation that accompanies growth of damage. Brittle fracture is essentially aniso...
350 citations
TL;DR: In this article, an approximate analysis of the instability in the well known logarithmic spiral slip line field of a blunted crack in an ideally plastic medium leads to the description of a steady state form of the corrugation front which is capable of predicting the fracture toughness of glassy metals and their characteristic fracture surface features.
272 citations
TL;DR: In this article, it is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness.
Abstract: It has been reported for as-quenched AISI 4340 steel that high temperature austenitizing treatments at 1200°C, instead of conventional heat-treatment at 870°C, result in a two-foldincrease in fracture toughness,KIc, but adecrease in Charpy impact energy. This paper seeks to find an explanation for this discrepancy in Charpy and fracture toughness data in terms of the difference betweenKIc and impact tests. It is shown that the observed behavior is independent of shear lip energy and strain rate effects, but can be rationalized in terms of the differing response of the structure produced by each austenitizing treatment to the influence of notch root radius on toughness. The microstructural factors which affect this behavior are discussed. Based on these and other observations, it is considered that the use of high temperature austenitizing be questioned as a practical heat-treatment procedure for ultrahigh strength, low alloy steels. Finally, it is suggested that evaluation of material toughness should not be based solely onKIc or Charpy impact energy values alone; both sharp crack fracture toughness and rounded notch impact energy tests are required.
256 citations
254 citations
TL;DR: In this article, an experimental program was carried out to clarify the structure-property relationships in fully-pearlitic steels of moderately high strength levels and to identify the critical microstructural features that control the deformation and fracture processes.
Abstract: An experimental program was carried out to clarify the structure-property relationships in fully-pearlitic steels of moderately high strength levels, and to identify the critical microstructural features that control the deformation and fracture processes. Specifically, the yield strength was shown to be controlled primarily by the interlamellar pearlite spacing, which itself was a function of the isothermal transformation temperature and to a limited degree the prior-austenite grain size. Charpy tests on standard and fatigue precracked samples revealed that variations in the impact energy and dynamic fracture toughness were dependent primarily on the prior-austenite grain size, increasing with decreasing grain size, and to a lesser extent with decreasing pearlite colony size. These trends were substantiated by a statistical analysis of the data, that identified the relative contribution of each of the dependent variables on the value of the independent variable of interest. The results were examined in terms of the deformation behavior being controlled by the interaction of slip dislocations with the ferrite- cementite interface, and the fracture behavior being controlled by a structural subunit of constant ferrite orientation. Preliminary data suggests that the size of such units are controlled by, but are not identical to, the prior-austenite grain size. Possible origins of this fracture unit are considered.
242 citations
TL;DR: In this paper, the critical stress intensity factor and related parameters have been measured in three-point bending for 18 different combinations of different volume fractions of cobalt and grain size of tungsten carbide.
Abstract: Critical stress intensity factor, and related parameters have been measured in three-point bending for 18 different combinations of different volume fractions of cobalt (5 to 37%) and grain size of tungsten carbide (0.7, 1.1 and 2.2 μm). In particular, a study was made of the correlations between the strength and mechanical and microstructural parameters, such as ¯LCo,CWC, ¯LCo/¯DWC, ¯LCo2/¯DWC,HV and wear resistance. A hypothesis for the mechanism of fracture has been proposed following an analysis of these results and a study of the mode of fracture.
TL;DR: In this article, the A-KIC relationship was used to predict critical flaw sizes in glass, glass ceramics, and single and polycrystalline ceramic materials, and it was shown that the elastic modulus is proportional to the mirror constant and probably to the critical fracture energy.
Abstract: Flaw size, c, fracture mirror boundaries, r, fracture stress, σ, and critical fracture energy were measured for glasses, glass ceramics, and single and polycrystalline ceramics The relationship σr1/2 = constant was verified for all these materials The mirror constants, A, in these materials were shown to be directly proportional to the average critical stress intensity factor for crack propagation, KIC Based on the A — KIC relationship, the outer mirror to flaw size ratio is shown to scatter about a value of 13∶1 Thus, the mirror constants were used to predict critical flaw sizes in these materials The observed flaw sizes in most cases correlated well with those calculated The cases in which poorer correlation was obtained are those in which flaw sizes were smaller than the grain size, flaws were pores or surrounded by porous regions, or where severe microcracking existed It is shown that the elastic modulus is proportional to the mirror constant and probably to the critical fracture energy, but that the latter is highly dependent on local microstructure The smaller inner to outer mirror ratios for polycrystalline ceramics over glasses is attributed to the difference in available paths for crack propagation
TL;DR: In this article, the ways in which the cleavage-fracture stress and fracture toughness vary with grain size in mild steel have been studied and a statistical argument has been advanced to explain the grain-size dependence of this distance.
Abstract: The ways in which the cleavage-fracture stress and fracture toughness (K IC) vary with grain size in mild steel have been studied. The fracture toughness is related to the cleavage-fracture stress by a microstructural characteristic distance. A statistical argument has been advanced to explain the grain-size dependence of this distance.
TL;DR: In this article, the bulk and adhesive fracture behavior of a diglycidyl ether bisphenol-a epoxy modified with 15% carboxy-terminated butadiene acrylonitrile was determined as a function of temperature.
Abstract: The bulk and adhesive fracture behavior of a diglycidyl ether bisphenol-A epoxy modified with 15% carboxy-terminated butadiene acrylonitrile was determined as a function of temperature. The bulk fracture toughness increased sharply near the resin Tg in a manner similar to unmodified epoxy resins. The adhesive fracture energy exhibited a maximum with respect to bond thickness and this maximum broadened and shifted to larger bond thicknesses with increasing temperature. These results are discussed in terms of the size and stress condition of the crack tip deformation zone.
TL;DR: In this article, the area of the true stress/true strain diagram determined under tensile test conditions is equal to the energy absorbed per unit volume at the point of fracture, where the critical specific fracture energy (W c ) characteristic of the material has been absorbed whereby the proportionality law of notched specimens can then be derived.
TL;DR: In this paper, the authors describe an investigation into the fracture behavior of hardened cement paste and suggest that the concept of fracture toughness is not readily applicable to hardened cement, which would appear to be a relatively notch insensitive material whose strength is not greatly reduced by the presence of flaws.
Abstract: This paper describes an investigation into the fracture behaviour of hardened cement paste. Notched specimens of the material were tested to failure in flexure and tension. In the initial flexural tests on beams of fixed overall depth, the stress intensity factor at failure as calculated from linear-elastic fracture mechanics appeared to be a material constant. However, further investigation showed that this factor varied with specimen size, and suggested that linear-elastic fracture mechanics and the concept of fracture toughness are not readily applicable to hardened cement paste, which would appear to be a relatively notch insensitive material whose strength is not greatly reduced by the presence of flaws. A “tied crack” model explains semi-quantiatively the observed behaviour.
TL;DR: In this article, the authors made fracture-toughness measurements on standard three-point-bend fracture specimens of Indiana limestone and found that typical strain-gage-type clip-in displacement gages were insufficient for measuring the crack-opening displacement.
Abstract: Fracture-toughness measurements were made on standard three-point-bend fracture specimens of Indiana limestone. Specimen dimensions, experimental techniques, and methods of data reduction were chosen to comply as closely as possible to the Tentative Method of Test for Plane Strain Fracture Toughness of Metallic Materials (ASTM Designation: E399-72T). Typical strain-gage-type clip-in displacement gages were found to lack the necessary sensitivity for measuring the crack-opening displacement while an LVDT displacement transducer having a linear range of ±0.25 mm (±0.010 in.) was found to be ideal.
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.
TL;DR: In this article, a criterion for ductile fracture is developed based on the statistical process of shear joining of voids and on the assumption that the voids responsible for fracture have experienced considerable growth prior to this stage of shearing.
Abstract: A criterion for ductile fracture is developed based on the statistical process of shear joining of voids and on the assumption that the voids responsible for fracture have experienced considerable growth prior to this stage of shearing. From the knowledge of uniaxial flow properties and fracture strain measurement, this model is capable of predicting the strain at fracture for other strain states. The predicted data are in good agreement with experiments. Although this model assumes spherical inclusions, some quantitative estimates for elongated inclusions can also be made.
TL;DR: In this article, the effects of prestrained QIN (HY-80) low-alloy steel on crack-opening displacement have been investigated and it was shown that the decrease in toughness with prestrain is accompanied by the development of zigzag fractures.
Abstract: Crack-opening displacement (COD) tests have been performed on prestrained QIN (HY-80) low-alloy steel. In specimens containing fatigue precracks the COD is largely insensitive to prestrains below 0.17, but a significant reduction in COD occurs at higher prestrains. Measurements of the yield-stress variation with tensile strain have enabled the effects of prestrain on fracture toughness to be estimated. Apart from a small initial increase, the general effect of prestrain is to reduce fracture toughness. The decrease in toughness with prestrain is accompanied by the development of zig-zag fractures. Crack growth appears to be intermittent and occurs by a process of shear decohesion along paths corresponding to either the spiral slip-lines emanating from a blunted cracktip, or, at lower displacements, the straight slip-lines emanating from a sharp crack.
TL;DR: A fracture mechanics method was utilised to derive values of the fracture toughness (as defined by the critical stress intensity factor, KIC), the specific surface energy (γ) and the “intrinsic” flaw size (c0).
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, a thermal cycling technique was used to refine the grain size of commercial 9Ni cryogenic steel and the grain refined alloy was then tempered, a treatment which introduced a small admixture of retained austenite.
Abstract: A thermal cycling technique was used to refine the grain size of commercial “9Ni” cryogenic steel. The grain refined alloy was then tempered, a treatment which introduced a small admixture of retained austenite. The reprocessed alloy shows an excellent combination of strength and toughness to temperatures as low as 6 K, and shows little evidence of embrittlement in liquid helium. The microstructure and mechanical properties of the reprocessed alloy are described and compared to those obtained through conventional treatment.
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, a two-parameter fracture criterion has been derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters.
Abstract: A two-parameter fracture criterion has been derived which relates the linear-elastic stress-intensity factor at failure, the elastic nominal failure stress, and two material parameters. The fracture criterion was applied to center-crack tension, compact, and notch-bend fracture specimens made of steel, titanium, or aluminum alloy materials tested at room temperature. The fracture data included a wide range of crack lengths, specimen widths, and thicknesses. The materials analyzed had a wide range of tensile properties. Failure stresses calculated using the criterion agreed well (plus or minus 10 percent) with experimental failure stresses. The criterion was also found to correlate fracture data from different specimen types (such as center-crack tension and compact specimens), within plus or minus 10 percent for the same material, thickness, and test temperature.
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.