Showing papers on "Fracture toughness published in 1984"
TL;DR: In this article, a fracture analysis of indentation-induced delamination of thin films is presented based on a model system in which the section of film above the delaminating crack is treated as a rigidly clamped disc, and the crack extension force is derived from changes in strain energy of the system as the crack extends.
Abstract: A fracture analysis of indentation‐induced delamination of thin films is presented. The analysis is based on a model system in which the section of film above the delaminating crack is treated as a rigidly clamped disc, and the crack extension force is derived from changes in strain energy of the system as the crack extends. Residual deposition stresses influence the cracking response by inducing buckling of the film above the crack and by providing an additional crack driving force once buckling occurs. A relation for the equilibrium crack length is derived in terms of the indenter load and geometry, the film thickness and mechanical properties, the residual stress level, and the fracture toughness of the interface. The analysis provides a basis for using controlled indentation cracking as a quantitative measure of interface toughness and for evaluating contact‐induced damage in thin films.
438 citations
TL;DR: In this article, the second of a series of four papers in which problems of dynamic crack propagation are examined experimentally in large, thin sheets of Homalite 100 simulating crack growth in an unbounded plate.
Abstract: This is the second of a series of four papers in which problems of dynamic crack propagation are examined experimentally in large, thin sheets of Homalite 100 simulating crack growth in an unbounded plate. In the first paper crack initiation resulting from stress wave loading to the crack tip and crack arrest were investigated. It was found that for increasing rates of loading in the micro second range, the stress intensity required for initiation rises markedly. Crack arrest occurs abruptly without any deceleration phase at a stress intensity below that value which causes initiation under quasi-static loading.
365 citations
TL;DR: The development of hot-pressed Sic-whisker-reinforced alumina has resulted in composites with fracture toughness values ∼;8.7 MPa·m112 at 20 vol% SiC as mentioned in this paper.
Abstract: The development of hot-pressed Sic-whisker-reinforced alumina has resulted in composites with fracture toughness values ∼;8.7 MPa·m112 at 20 vol% SiC. Whisker orientation during processing leads to anisotropy in both fracture toughness and fracture strength. Fracture strengths are also limited by the ability to disperse the Sic whiskers; however, use of both fine alumina powders and ultrasonic dispersion techniques yields strengths ∼;800 MPa.
339 citations
TL;DR: In this paper, the effect of particle/matrix adhesion on crack propagation in an epoxy resin reinforced with spherical glass particles was investigated in terms of crack pinning and blunting.
Abstract: The investigation outlined in the preceding paper has been extended to cover the effect of particle/matrix adhesion upon crack propagation in an epoxy resin reinforced with spherical glass particles. The behaviour has again been interpreted in terms of crack pinning and blunting. It has again been shown that in the absence of blunting a critical crack opening displacement criterion can be applied. The strength of the particle/matrix interface is found to affect both the crack propagation behaviour and the appearance of the fracture surface. It is also found to have a profound effect upon the fracture strength of the composites. The best overall mechanical properties are obtained for composites containing particles treated with coupling agent.
336 citations
326 citations
TL;DR: In this paper, a statistical method based on carbide induced cleavage fracture is proposed, by which it is possible to estimate the fracture toughness and study the effect of different variables.
Abstract: Factors affecting the cleavage fracture stress and the fracture toughness K 1C in steel have been examined. A statistical method based on carbide induced cleavage fracture is proposed, by which it is possible to estimate the fracture toughness and study the effect of different variables. The predictions made are in excellent agreement with experimental results for a variety of microstructures.
277 citations
TL;DR: In this paper, the microstructure consists of fine TiC particles in a fine-grained SiC matrix, which increases the critical fracture toughness of SiC and yields high flexure strength.
Abstract: Silicon carbide ceramics containing up to 24.6 vol% dispersed TiC particles yielded fully dense composites by hot-pressing at 2000/sup 0/C with 1 wt% Al and 1 wt% C added. The microstructure consists of fine TiC particles in a fine-grained SiC matrix. Addition of TiC particles increases the critical fracture toughness of SiC (to approx. =6 MPa /SUP ./ m /SUP 1/2/ at 24.6 vol% TiC) and yields high flexure strength (greater than or equal to 680 MPa), with both properties increasing with increasing volume fraction of TiC. The strengths at high temperatures are also improved by the TiC additions. Observations of the fracture path indicate that the improved toughness and strength are a result of crack deflection by the TiC particles.
236 citations
222 citations
220 citations
TL;DR: In this article, a series of four papers dealing with experimental observations of dynamic crack propagation in thin, large sheets of a Homalite 100 plastic material which allow simulation of crack growth in unbounded plates.
Abstract: This is the last in a series of four papers dealing with experimental observations of dynamic crack propagation in thin, large sheets of a Homalite 100 plastic material which allow simulation of crack growth in unbounded plates. In the first paper crack initiation resulting from stress wave loading was examined as well as crack arrest. It was found that for increasing rates of loading in the microsecond range the stress intensity factor required for initiation rises markedly. Crack arrest occurs abruptly without any deceleration phase at a stress intensity lower than that which causes initiation under quasi-static loading.
207 citations
TL;DR: The fracture mechanics parameters of critical stress intensity factor and critical strain energy release rate for longitudinal fracture of bovine tibia cortical bone were determined by the compact tension method and demonstrated that, for a given bone density, Kc and Gc depended on the loading rate, and resultant crack velocity.
TL;DR: The results from the first phase of a 6-university study are presented in this article, which includes specimen size, fiber volume content, fiber type, and the effect of a notch as the primary parameters of investigation.
Abstract: The results from the first phase of a 6-university study are presented in this article. This first phase includes specimen size, fiber volume content, fiber type, and the effect of a notch as the primary parameters of investigation. Results from the tests, including toughness, and other important properties such as stress at first-crack, ultimate strength, and the elastic modulus as influenced by the specified parameters, are presented and discussed. The importance of making accurate deflection measurements and the influence of these measurements on the toughness and other flexural characteristics are disscussed. Conclusions are made with regard to lessons learned from the inter-university testing program, drawbacks of some currently used measures of toughness, observed material property trends, and a possible alternate measure of toughness.
TL;DR: In this article, a change in crack path from the interface to the film, accompanied by an increase in crack radius, is observed and interpreted as a buckling-induced stress intensification.
Abstract: Indentation‐induced delamination between thin films of ZnO and Si substrates is examined. Delamination occurs by the growth of lateral cracks, either along the interface or within the film adjacent to the interface. The crack path is determined by the indenter load and the film thickness, as well as by residual stresses formed during deposition. A change in crack path from the interface to the film, accompanied by an increase in crack radius, is observed and is interpreted as a buckling‐induced stress intensification. The interface fracture toughness is estimated from the relative crack lengths in the buckled and unbuckled films.
TL;DR: In this article, a simple formula was established to estimate the fracture toughness of concrete in terms of specimen dimensions, maximum aggregate size and notch depth, together with the mix compressive strength and modulus of elasticity.
Abstract: Synopsis Tests were performed on cement mortar and concrete beams, in two stages, with a view to studying the influence of several specimen and mix variables upon the fracture behaviour of concrete. On the basis of the results from the first stage of tests, in which a single water/cement ratio and type of coarse aggregate were used, a simple formula was established to estimate the fracture toughness of concrete in terms of specimen dimensions, maximum aggregate size and notch depth, together with the mix compressive strength and modulus of elasticity (determined from separate standard cylinder tests). It was found to predict, with sufficient accuracy, the results from the second stage of tests in which, besides variation of the type of coarse aggregate and water/cement ratio, some of the specimen sizes were outside the range used in the first series.
01 Jul 1984
TL;DR: In this paper, a unified set of composite micromechanics equations of simple form is summarized and described for predicting: (1) ply in-plane uniaxial strength; (2) through-the-thickness strength (interlaminar and flexural); (3) inplane fracture toughness; (4) in-planar impact resistance; and (5) impact resistance.
Abstract: A unified set of composite micromechanics equations of simple form is summarized and described. This unified set includes composite micromechanics equations for predicting: (1) ply in-plane uniaxial strengths; (2) through-the-thickness strength (interlaminar and flexural); (3) in-plane fracture toughness; (4) in-plane impact resistance; and (5) through-the-thickness (interlaminar and flexural) impact resistance. Equations are also included for predicting the hygrothermal effects on strength, fracture toughness and impact resistance. Several numerical examples are worked out to illustrate the ease of use of the various composite micromechanics equations.
TL;DR: In this article, a model is developed for evaluating stresses in the surfaces of brittle materials from changes in indentation crack dimensions, and the underlying basis of the model is a stress intensity formulation incorporating the solution for a penny-like crack system subjected to a constant stress over a relatively thin surface layer.
Abstract: A model is developed for evaluating stresses in the surfaces of brittle materials from changes in indentation crack dimensions. The underlying basis of the model is a stress intensity formulation incorporating the solution for a penny-like crack system subjected to a constant stress over a relatively thin surface layer. Results from a previous study of surface damage in proton-irradiated glass are used to illustrate the scope of the method. The indentation fracture analysis also provides some fresh insight into the susceptibility of brittle surfaces to spontaneous cracking. Implications of the study concerning the potential effect of surface stresses on mechanical properties, such as strength, erosion and wear, are briefly discussed.
TL;DR: In this article, the dynamic crack propagation experiments have been performed using wedge loaded double cantilever beam specimens of an austenitized, quenched and tempered 4340 steel.
Abstract: Dynamic crack propagation experiments have been performed using wedge loaded double cantilever beam specimens of an austenitized, quenched and tempered 4340 steel. Measurements of the dynamic stress intensity factor have been made by means of the optical method of caustics. The interpretation of experimental data, obtained from the shadow spot patterns photographed with a Cranz-Schardin high speed camera, is based on an elastodynamic analysis. The instantaneous value of the dynamic stress intensity factor KdI is obtained as a function of crack tip velocity. Finally, the interaction of reflected shear and Rayleigh waves with the moving crack tip stress field is considered.
TL;DR: A fracture mechanics approach has been used to quantify the failure of tooth coloured restorative materials which are subjected to tensile forces, and the parameter chosen was the plane strain critical stress intensification factor, KIC.
Abstract: Summary
A fracture mechanics approach has been used to quantify the failure of tooth coloured restorative materials which are subjected to tensile forces. The materials examined included silicates, glass ionomers, composites (both chemically and photo-initiated) and bonding resins for composites. The parameter chosen was the plane strain critical stress intensification factor, KIC. Silicate and glass ionomer are both brittle and have values for KIC inferior to those of composites. Composites have fracture toughnesses in a range from marginally higher than that of the bonding resin to almost three times that figure. The reason for this is discussed in terms of the dispersion toughening theories.
TL;DR: In this article, an extensive literature survey of the evolution of the indentation technique is made and the elastic/plastic solution for the spherical cavity expansion is used to obtain a physical explanation for the quantitative measurement of the radial cracks that occur at the impression corners.
TL;DR: In this article, a series of transparent RTPMMA (rubber-toughened poly (methyl methacrylate)) polymers have been studied by measuring volume changes during creep in tension at 20° C. The authors concluded that the dominant mechanism of deformation is shear yielding.
Abstract: Mechanisms of deformation in a series of transparent RTPMMA (rubber-toughened poly (methyl methacrylate)) polymers have been studied by measuring volume changes during creep in tension at 20° C. Volume strains remained small throughout each test, even at total extensions greater than 6%, although the material became heavily stress whitened at strains above about 3%. It was concluded that the dominant mechanism of creep is shear yielding. Rate coefficients, defined by fitting the creep data to the Andrade equation, increase exponentially with applied stress, in accordance with the Eyring equation. Apparent activation volumes increase with rubber content, from 1.55 nm3 for PMMA itself, to 2.89 nm3 for RTPMMA containing 36 vol % of rubber particles. These observations provide an explanation of the toughness and ductility of RTPMMA.
TL;DR: In this paper, the effect of applied pressure was studied by hot pressing and hot-isostatic-pressing exeriments with powder compacts and sintered materials, and the results showed a strong dependence of the densification behavior on powder properties (specific surface area, grain morphology, oxygen and carbon content), amount and composition of sintering aids, and applied pressure.
TL;DR: The micro-roughness of a fracture surface refers to the depth, shape, and aspect ratio of the dimples on the surface which in turn are determined by the mechanism of fracture and by the microstructure as discussed by the authors.
TL;DR: The influence of temperature and frequency on the crack propagation behavior of a single crystal superalloy has been investigated in this article, where failure at all temperatures is associated with the fracture of script carbides ahead of the crack tip.
Abstract: The influence of temperature and frequency on the crack propagation behavior of a single crystal superalloy has been investigated. At applied stress intensities approaching the fracture toughness, failure at all temperatures is associated with the fracture of script carbides ahead of the crack tip. At low and intermediate levels of ΔK the fatigue crack growth behavior is influenced by the temperature and frequency. At room temperature crack growth is found to occur by failure on {111} planes; at 600 °C and 850 °C crack growth is parallel to {100} . It has been shown that this behavior is not attributable to environmental interactions but arises from the morphology and distribution of the strengthening γ’ precipitate. Dislocations within the crack tip plastic zone are contained within the matrix, and crack propagation occurs primarily within the γ matrix by plasticity-controlled failure.
TL;DR: In this paper, a pseudo-elastic damage-accumulation model is developed by application of the strain energy density theory, where the three-point bending specimen is analyzed to illustrate the crack growth characteristics according to a linear elastic softening constitutive law that is typical of concrete materials.
01 Jan 1984
TL;DR: In this article, a unified set of composite micromechanics equations of simple form is summarized and described for predicting composite strength and fracture toughness, impact resistance, and through-the-thickness strength.
Abstract: : A unified set of composite micromechanics equations of simple form is summarized and described This unified set includes composite micromechanics equations for predicting (1) ply in-plane uniaxial strengths; (2) through-the-thickness strength (interlaminar and flexural); (3) in-plane fracture toughness; (4) in-plane impact resistance; and (5) through-the-thickness (interlaminar and flexural) impact resistance Equations are also included for predicting the hygrothermal effects on strength, fracture toughness and impact resistance Several numerical examples are worked out to illustrate the ease of use of the various composite micromechanics equations The numerical examples were selected, in part, to demonstrate the interrelationships of the various constituent properties in composite strength and strength-related behavior, to make comparisons with available experimental data and to provide insight into composite strength behavior
TL;DR: In this article, the applicability of plane-strain fracture toughness testing techniques to several polymers was examined using pre-notched test specimens and was characterized by the linear elastic fracture parameter,Kc.
Abstract: Experimental work is described which examines the applicability of plane-strain fracture toughness testing techniques to several polymers. The fracture behaviour of five polymers was studied using pre-notched test specimens and was characterized by the linear elastic fracture parameter,Kc. Two test geometries and loading modes were used; SEN tension and three-point bending have been investigated by varying both thickness and width. It has been established that the ASTM criterion for plane-strain conditions ofB>2.5 (Kc1/σy)2 is sufficient for SEN bending but not for tension where an extrapolation method is needed. For width effects the BCS model was shown to describe the observations and this with a limiting nominal stress analysis gave quite close agreement with the ASTM criterionW>5 (Kc1/σy)2. This value was shown to be a good estimate of the practical minimum width. There is some evidence that PP, which gives substantial crazing and whitening, can give satisfactory values at sizes about half these limiting values.
TL;DR: In this paper, a three-component glass system was nitrided by adding amorphous and crystalline Si3N4, and their mechanical properties were measured, including density, hardness, Young's elastic modulus, and fracture toughness.
Abstract: A three-component glass system (Mg–Al–Si) was nitrided by adding amorphous and crystalline Si3N4. Glasses with varying amounts of nitrogen were melted, and their mechanical properties were measured. Density, hardness, Young's elastic modulus, and fracture toughness increased with increasing nitrogen content.
TL;DR: In this article, the suitability of interferometric methods in scattered coherent light in the analysis of concrete cracking was evaluated and compared with the application of the interferometry in scattering coherent light to concrete cracking.
Abstract: 1. Mechanics of material damage in concrete.- 1.1 Introduction.- 1.2 Mechanical strength of concrete.- 1.3 Stress and fracture analysis.- 1.4 Damage analysis of concrete beam in bending: effects of softening and loading step.- 1.5 Scaling of specimen size.- 1.6 Long time behavior and failure of concrete.- 1.7 Local and global stationary values of strain energy density function.- 1.8 General discussion.- References.- 2. Evaluation of concrete fracture.- 2.1 Introduction.- 2.2 Mechanism of failure in concrete.- 2.3 Behaviour of concrete under loading related to damage.- 2.4 Mechanical modeling of concrete by means of fracture mechanics.- References.- 3. Fracture toughness testing of cement and concrete.- 3.1 Introduction.- 3.2 Physical phenomena involved in fracture.- 3.3 Rate of loading effects.- 3.4 Notch sensitivity.- 3.5 Historical review of the applications of fracture mechanics to cementitious materials.- 3.6 Fracture toughness parameters and techniques.- 3.7 Valid specimen size.- 3.8 Conclusions.- References.- 4. Dependence of concrete fracture toughness on specimen geometry and on composition.- 4.1 Introduction.- 4.2 Resistance curves.- 4.3 Theoretical model.- 4.4 Uniaxial tensile stress-displacement relationship.- 4.5 Experimental investigation.- 4.6 Comparison with experimental data.- 4.7 Effects of compositions.- References.- 5. Microcracking in concrete.- 5.1 Introduction.- 5.2 Microcracking of concrete.- 5.3 Methods of study of microcracking.- 5.4 Effects of microcracks on the properties of concrete.- 5.5 Cracking of higher-strength versus lower-strength concrete.- 5.6 Summary.- References.- 6. Interferometry in scattered coherent light applied to the analysis of cracking in concrete.- 6.1 Introduction.- 6.2 The suitability of interferometric methods in scattered coherent light in the analysis of concrete cracking.- 6.3 Significance and quality of fringes obtained with interferometry in scattered coherent light.- 6.4 Comparative summary.- 6.5 Application of interferometric methods in scattered coherent light to the analysis of concrete cracking.- 6.6 Conclusion.- References.- Author index.