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Showing papers in "Journal of Materials Science in 1975"


Journal ArticleDOI
TL;DR: The basic principles and practical applications of indentation fracture are reviewed in this article, with a focus on the application of fracture fracture in the field of orthogonal fracture repair and alignment.
Abstract: The basic principles and practical applications of indentation fracture are reviewed.

1,172 citations


Journal ArticleDOI
TL;DR: In this article, the conditions for the retention of a zirconia-rich tetragonal phase at ambient temperature were established and the existence of a miscibility gap, closed below the solidus temperature, in the yttria-rich solid solution region was proposed.
Abstract: Metastable and equilibrium phase relationships in the system ZrO2:YO1.5 have been studied by X-ray diffraction. The conditions for the retention of a zirconia-rich tetragonal phase at ambient temperature are established. The existence of a miscibility gap, closed below the solidus temperature, in the yttria-rich solid solution region is proposed. Some evidence for partially ordered phases is presented.

1,170 citations


Journal ArticleDOI
TL;DR: In this paper, the authors made a study of the mechanics of two basic types of indentation fracture, cone cracks (blunt indenters) and median cracks (sharp indenters).
Abstract: A study is made of the mechanics of two basic types of indentation fracture, cone cracks (“blunt” indenters) and median cracks (“sharp” indenters). The common feature which forms the central theme in this work is that both crack types, in their well-developed stages of growth, may be regarded as essentially “penny-like”. On this basis a universal similarity relation is derived for equilibrium crack dimension as a function of indentation load. Experimental measurements confirm the general form of this relation. A more detailed fracture mechanics analysis is then given, to account for additional, contact variables evident in the data. Notwithstanding certain analytical limitations, the study serves as a useful basis for investigating a wide range of contact-related problems, both fundamental and applied, in brittle solids.

680 citations


Journal ArticleDOI
TL;DR: In this paper, the authors investigated the microfracture patterns observed around point indentations in brittle solids and derived the means for predetermining, in principle, the depth of fracture damage under given point loading conditions.
Abstract: The microfracture patterns observed around point indentations in brittle solids are investigated. A description is first given of the stress field in an elastic half-space loaded normally at a point in its surface. This field is then used as a basis for analysing the crack geometry. A localized zone of irreversible deformation forms about the contact point, thereby removing a singularity in the elasticity solutions and providing nucleation centres for the ensuing microcracks. Generally, two main types of ‘vent’ cracks are observed to propagate from the deformation zone: median vents, formed during indenter loading, spread downward below the point of contact on planes of symmetry, and lateral vents, formed during unloading, spread sideways toward the specimen surface. Of these, the median vent is relatively well-behaved, and is amenable to standard fracture-mechanics analysis. From such an analysis we derive the means for predetermining, in principle, the depth of fracture damage under given point loading conditions. The significance of the results in relation to important practical applications, such as glass cutting and surface fragmentation processes, is discussed.

629 citations


Journal ArticleDOI
Bulent E. Yoldas1
TL;DR: In this paper, the authors discuss the requirements for a porous transparent Al2O3 from aluminium alkoxides to retain its integrity during drying and pyrolysis, and show that there is a critical electrolyte concentration at which the gelling volume goes through a pronounced minimum.
Abstract: Formation of a porous transparent Al2O3 from aluminium alkoxides has been previously reported. During the process, alkoxides are hydrolyzed and the resultant hydroxide is peptized to a clear sol. The sol then must be gelled and pyrolyzed to 500° C to obtain the aluminium oxide. This paper discusses the gel state and the requirements for the system to retain its integrity during the drying and pyrolysis. Influence of electrolytes on the sol-gel transformation shows that there is a critical electrolyte concentration at which the gelling volume goes through a pronounced minimum. Deviation in either direction of this electrolyte concentration causes a sharp increase in the relative gelling volume and detrimentally effects the capability of the gel to retain its integrity. The sols that gel at concentrations less than ∼4 g equivalent oxide per 100 ml do not retain their integrity during pyrolysis.

534 citations


Journal ArticleDOI
TL;DR: In this paper, the flow and fracture properties of amorphous metals synthetized by fast quenching from the liquid state were analyzed in conjunction with recently proposed theoretical models.
Abstract: This paper reviews the flow and fracture properties of amorphous metals synthetized by fast quenching from the liquid state. The data are analysed in conjunction with recently proposed theoretical models.

455 citations


Journal ArticleDOI
TL;DR: In this paper, the pull-out test is used to evaluate the interfacial strength of polyethylene composites, and the results show that the strength of the polyethylenes is mainly due to the unique epitaxial bonding rather than the radial forces from compressive shrinkage.
Abstract: One polymer composite materials have been prepared using a difference in melting points between the components. This depends on the fact that aligned and extended chains provide thermodynamically more stable crystals, which thus will have higher melting points than conventionally crystallized melts. The growth of transcrystalline regions in the melt matrix at the interface plus an observed partial melting between fibre and matrix are indications of a strong and intimate interfacial bond with a gradient in morphologies for the system studied, high-density polyethylene. The pull-out test is a simple and adequate method for evaluating the interfacial shear strength of one polymer composites. The value for the high-density polyethylene composite falls between the strengths for glass-reinforced polyester and epoxy resins. However, the interfacial strength in the polyethylene composites is due mainly to the unique epitaxial bonding rather than the radial forces from compressive shrinkage. The low critical aspect ratio for the filaments in these polyethylene composites suggests possible advantageous uses as short fibrereinforced materials where the interfacial strength is a controlling factor.

279 citations


Journal ArticleDOI
TL;DR: In this article, a general theory of kinetic crack growth in ideally brittle solids is developed from first principles, where emphasis is placed on the essential need to provide for the existence of an energy barrier to activated, non-linear crack motions at the atomic level.
Abstract: A general theory of kinetic crack growth in ideally brittle solids is developed from first principles. In setting up a basic model, emphasis is placed on the essential need to provide for the existence of an energy barrier to activated, non-linear crack motions at the atomic level. The picture is presented of an ideally brittle fracture crack in which sequential bond rupture occurs via the lateral motion of atomic kinks along the crack front. Approximate solutions to the equations of kink motion are then obtained from the discrete, “lattice trapping” theory of Thomson and co-workers. Assuming a classical distribution of kink sites, an expression for the steady-state crack velocity follows. A feature of the present theory is the formulation in terms of the fundamental energy-balance concept of Griffith, with two major advantages: in the first place, standard fracture-mechanics parameters, such as the mechanical-energy-release rate and the fracture-surface energy, enter into the description in a natural manner; in the second, the effect of extrinsic agents on activated kink motion is readily accountable, through a simple modification of the total energy function for the crack system. To illustrate the model, the case of a slowly growing brittle crack in the presence of an interacting ideal gas environment is treated in some detail.

202 citations


Journal ArticleDOI
TL;DR: In this article, tensile, creep, and stress-rupture data for Norton HS-110 and HS-130 hot-pressed Si3N4 are presented, and it is shown that the strength of the material is controlled by the grain-boundary glass phase.
Abstract: Tensile, creep, and stress-rupture data for Norton HS-110 and HS-130 hot-pressed Si3N4 are presented. It is shown that the strength of the material is controlled by the grain-boundary glass phase. At elevated temperatures, >1000‡ C, deformation is controlled by grain-boundary sliding. A model based on the concept of geometrically necessary wedge cracks is then developed which accounts for the observed effects of strain rate, stress, temperature, environment, and impurity content. It is concluded that the currently available hot-pressed Si3N4 is creep strain limited.

186 citations


Journal ArticleDOI
TL;DR: In this article, a review of phase equilibria in glass-forming systems is presented together with a discussion of the thermodynamic behaviour of systems exhibiting liquid-liquid immiscibility.
Abstract: This review is concerned with the process of liquid-phase separation in glass-forming systems. In the first part a general account of phase equilibria is presented together with a discussion of the thermodynamic behaviour of systems exhibiting liquid-liquid immiscibility. The estimation of free energies from phase-boundary data and the location of the spinodal boundary are briefly considered. The origin of immiscibility in silicate solutions is discussed from a thermodynamic approach. The importance of association, particularly in silicate systems, is stressed. In the second part of the review, an outline of the theories of homogeneous nucleation and spinodal decomposition is given and a review of recent theoretical developments. The intersecting growth model is discussed and also the laterstage coarsening of both droplet and interconnected structures. The theories are compared with experimental results (including electron microscope and small-angle X-ray scattering data) for various systems. The effects of phase separation on crystallization processes in glasses and on the physical and chemical properties of glasses are outlined. Although the results considered are for oxide systems where sufficient data are available, much of the discussion is applicable to glass-forming systems in general.

169 citations


Journal ArticleDOI
TL;DR: A survey of the results from a variety of techniques has shown that the substitution behaviour of alloying additions is primarily determined by electronic considerations as discussed by the authors, and that the mechanical properties of γ′ depended on both the substitution behavior of the alloying addition and the degree of non-stoichiometry.
Abstract: A survey of the results from a variety of techniques has shown that the substitution behaviour of alloying additions is primarily determined by electronic considerations. Thus, Si, Ti, V, Mn, Nb, Hf and Ta substitute for aluminium; Co and Cu substitute for nickel and Cr, Fe, W, and Mo substitute for both species. A number of conclusions have been drawn from an analysis of compression test data, the most significant of which was that the mechanical properties of γ′ depended on both the substitution behaviour of the alloying addition and the degree of non-stoichiometry. Considerable strengthening is only obtained when (1) the alloying addition substitutes for aluminium and has a large size misfit parameter, and (2) the alloy is aluminium-rich or stoichiometric.

Journal ArticleDOI
TL;DR: The hot-pressing behavior of different silicon carbide powders (average particle sizes ranging from ∼ 0.5 to 9 μm) with aluminium oxide additions ranging from 0.01 to 0.15 volume fractions was investigated in this paper.
Abstract: The hot-pressing behaviour of different silicon carbide powders (average particle sizes ranging from ∼ 0.5 to 9 μm) with aluminium oxide additions ranging from 0.01 to 0.15 volume fractions was investigated. Using powders with an average particle size < 3 μm, densities ≥ 99% theoretical could be achieved at 1950° C (1 h) with 28 MN m−2 for volume fractions of AI2O3 $$\bar > $$ 0.02. A liquid phase forms at high temperatures which dissolves the silicon carbide particles to promote densification by a solution-reprecipitation mechanism.

Journal ArticleDOI
TL;DR: In this article, a method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth.
Abstract: A method for determining the activation energy for crystal growth was calculated on the basis of the heat balance in the differential thermal analysis (DTA) measurements and the mechanism of nucleation and growth. The theoretical analysis showed that the term ln[C pd(δT)/dt+KδT] should be a linear function of l/T, whereC p is the heat capacity of sample and sample holder,K is the heat transfer coefficient,δT is the temperature difference between the sample and reference substance andt is the time. The energy term,E D, obtained by multiplying the slope of the resulting straight line byR is indicative of the activation energy for crystal growth. It was shown thatE D should be three times the activation energy for crystal growth when bulk nucleation is dominant, and equal to that for crystal growth only when surface nucleation predominates. The result of the analysis was tested by comparing the experimentally determinedE D's with the activation energy for viscous flow, which was known to represent that for crystal growth. TheE D for Li2O·2SiO2 glass with dominant bulk nucleation, approached three times the activation energy for viscous flow, as the heating rate in DTA decreased. TheE D for 33.3Li2O·66.7SiO2·3TiO2 glass with dominant surface nucleation approached the activation energy for viscous flow as the heating rate increased, suggesting the validity of the analysis.

Journal ArticleDOI
TL;DR: In this paper, the authors describe the behavior of a carbon-fibre reinforced epoxy composite when deformed in compression under high hydrostatic confining pressures and show that the failure strength of the composite increased rapidly with increasing confining pressure, though the elastic modulus remained constant.
Abstract: This paper describes the behaviour of a carbon-fibre reinforced epoxy composite when deformed in compression under high hydrostatic confining pressures. The composite consisted of 36% by volume of continuous fibres of Modmur Type II embedded in Epikote 828 epoxy resin. When deformed under pressures of less than 100 MPa the composite failed by longitudinal splitting, but splitting was suppressed at higher pressures (up to 500 MPa) and failure was by kinking. The failure strength of the composite increased rapidly with increasing confining pressure, though the elastic modulus remained constant. This suggests that the pressure effects were introduced by fracture processes. Microscopical examination of the kinked structures showed that the carbon fibres in the kink bands were broken into many fairly uniform short lengths. A model for kinking in the composite is suggested which involves the buckling and fracture of the carbon fibres.

Journal ArticleDOI
TL;DR: In this article, the authors examined the nature of microcracking about small-scale indentations in two highly brittle solids, sapphire and carborundum, and found that cleavage steps comprise the main source of obstruction to lattice restoration across the interfaces.
Abstract: Transmission electron microscopy is used to examine the nature of microcracking about small-scale indentations in two highly brittle solids, sapphire and carborundum. The observed crack geometry is discussed in terms of an earlier model of indentation fracture beneath a point force, in which both loading and unloading half-cycles contribute to the crack growth. The residual interfaces are generally found to exhibit moire fringe contrast, and occasionally to contain dislocation networks. These observations are discussed in relation to spontaneous closure and healing mechanisms, and the associated “lattice mismatch” is estimated at about one part in a thousand. It is suggested that cleavage steps comprise the main source of obstruction to lattice restoration across the interfaces. Mechanical and thermal treatments of the indented specimens are found to influence the extent of the residual cracking. Some practical implications concerning the strength degradation of brittle solids are discussed.

Journal ArticleDOI
TL;DR: In this article, a simple compression test, suitable for quality control measurements on unidirectional carbon fiber composite, is described, where a plane bar, with aluminium end tabs attached, is compressed by applying shear forces over the ends.
Abstract: A simple compression test, suitable for quality control measurements on unidirectional carbon fibre composite, is described. The specimen, a plane bar, with aluminium end tabs attached, is compressed by applying shear forces over the ends. With either type 1 or type 2 treated fibre the failure mode is one of shear over a plane at approximately 45° to the fibre axis. With untreated type 1 material failure is due to delamination. The variation of the compression strength of treated material with fibre volume loading is linear, the values being considerably below those predicted by buckling theory. Increasing void content causes a steady decrease in compression strength, and off-axis strength values are above those given by the maximum work criterion. The present work supports the recently proposed view that the compression strength of unidirectional carbon fibre composites at room temperature is not governed by fibre buckling but is related to the ultimate strength of the fibre.

Journal ArticleDOI
TL;DR: In this article, the thermal polymerization of bis-(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol has been studied by optical and Raman spectroscopy and X-ray diffraction.
Abstract: The thermal polymerization of bis-(p-toluene sulphonate) of 2,4-hexadiyne-1,6-diol has been studied by optical and Raman spectroscopy and X-ray diffraction. Single phase polymerization is revealed by continuous changes in the spectra of polymer chains in polymerizing crystals. Spectroscopic and X-ray measurements on extracted polymer are interpreted in terms of random polymer formation. Polymer formed initially is strained but this anneals to a strain-free conformation in the fully converted polymer or on extraction from the monomer lattice. Possible causes of the variations in polymerization rate are discussed.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the shrinkage by a liquid phase mechanism and bulk decomposition are two countervailing processes in the sintering of Si3N4 powder with the addition of 5 wt % MgO.
Abstract: An investigation of the pressureless sintering of Si3N4 powder with the addition of 5 wt % MgO revealed that shrinkage by a liquid phase mechanism and bulk decomposition are two countervailing processes. Within the temperature range studied, i.e. between 1500 and 1750° C, high densities can be achieved when sintering is performed either for long periods at low temperatures or short periods at higher temperatures. A model is presented showing that pore growth due to decomposition causes a decrease in the driving force for sintering and causes shrinkage to cease.

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the cracks in a silica particle-filled epoxy resin composite system in air as a function of volume fraction of particles for volume fractions ranging from 0 to 0.52.
Abstract: The mechanical properties of a silica particle-filled epoxy resin composite system have been investigated in air as a function of volume fraction of particles for volume fractions ranging from 0 to 0.52. The Young's modulus and the compressive yield stress both increase as the volume fraction of silica particles is increased and various models of particle strengthening have been used to explain this behaviour. Slow crack growth in the various particulate composites has been studied using a fracture mechanics approach. The variation of crack velocity (V) with stress intensity factor (KI) has been measured for each of the compositions investigated. In each case, a unique relationship between V and KI has been found with KI increasing with volume fraction of particles at a given value of V. The failure mechanisms and the variation of other fracture mechanics parameters, for example, crack opening displacement and plastic zone size with increasing particle volume fraction have been discussed.

Journal ArticleDOI
TL;DR: In this paper, a barium titanate ceramic containing 13.5 mol % calcium zirconate was doped with oxides of various metals that were considered likely on the basis of ionic size and valence to enter the small cation lattice with charge less than 4+.
Abstract: A barium titanate ceramic containing 13.5 mol % calcium zirconate was doped with up to 3 mol % of oxides of various metals that were considered likely on the basis of ionic size and valence to enter the small cation lattice with charge less than 4+. It was hoped in this way to compensate electrically for loss of oxygen during sintering in CO-CO2 mixtures, so as to obtain high resistivity dielectrics and allow the use of base metal electrodes in a monolithic capacitor. Doping with approximately 0.5 mol % Mn, Co, or Mg produced the highest resistivities, and dielectrics with nickel electrodes and relative permittivity up to 10 000 were obtained with resistivity in excess of 1012 Ω cm at room temperature. When the doped ceramic sintered in contact with nickel, the grain structure and permittivity-temperature characteristics depended on the oxygen partial pressure of the sintering atmosphere, apparently influenced by dissolution of Ni into the ceramic.

Journal ArticleDOI
TL;DR: In this article, the fracture toughness of polycarbonate was obtained over the temperature range 20 to − 120° C. This change is associated with the β transition and stable crack growth was observed in this region with accompanying instabilities arising from adiabatic heating at the crack tip.
Abstract: The fracture toughness of polycarbonate was obtained over the temperature range 20 to − 120° C. There is a strong thickness dependence which is described in terms of plane stress and plane strain values which are insensitive to temperatures above −40° C but the plane stress value increases below this temperature. This change is associated with theβ transition and stable crack growth was observed in this region with accompanying instabilities arising from adiabatic heating at the crack tip.

Journal ArticleDOI
TL;DR: In this article, the influence of hydrostatic pressure (∼ 6.5 kbar) on the stress for plastic flow in Pd77.5Cu6Si16.5 amorphous metallic alloy in compression and tension was examined.
Abstract: The influence of hydrostatic pressure (∼ 6.5 kbar) on the stress for plastic flow in a Pd77.5Cu6Si16.5 amorphous metallic alloy in compression and tension has been examined. The observed effect (δlnσ/δP ∼- 5×10−6 bar−1) is very close to that exhibited by crystalline metals. The highly inhomogeneous nature of the deformation appears to be unaltered by pressure. As at one atmosphere, failure in tension with high superposed pressure occurs by rupture through a zone of intense plastic shear. The fracture surface topography is strikingly different, however, because cracking inside the shear zone is suppressed in favour of crack initiation at its periphery.

Journal ArticleDOI
B. Tuck1
TL;DR: A review of chemical polishing of semiconductors can be found in this article, where the authors consider the types of reaction which occur when a semiconductor is chemically polished, taking the dissolution of silicon in nitric acid solutions as an example.
Abstract: The review first considers the types of reaction which occur when a semiconductor is chemically polished, taking the dissolution of silicon in nitric acid solutions as an example. Most initial reactions are of the oxidation-reduction type, which can be separated into their anodic and cathodic components. It is shown that electrons and holes can take part in both parts of the reaction, so chemical polishing can interfere with the carrier concentrations close to the surface being polished. In general, the products of the initial reaction are not soluble, so it is necessary to include a component in the polishing solution which will react to give soluble material, which can then be removed from the surface. The factors controlling the dissolution rate are then outlined. It is shown that polishing processes are conveniently divided into two main groups: (1) those for which the rate-limiting process is some aspect of the chemical reaction, and (2) those for which diffusion of atoms to or from the surface controls the rate. Crystallographic effects are discussed. It is shown that different surface orientations are etched at different rates, and possible reasons for this are outlined. The various types of surface features that can be observed under the microscope after polishing are then described, and their origins are discussed. A review of some of the more extensive investigations is then given, followed by an Appendix containing lists of chemical polishes that have been used for semiconductors of groups IV, III–V and II–VI.

Journal ArticleDOI
TL;DR: In this paper, the theory of the evolution of a surface contour under ion etching is recalled and further improvements dealing with angular points of the profile shows that: angular points having straight trajectory may exist; and they can be found either by computation or by graphic method.
Abstract: The previously published theory of our model on the evolution of a surface contour under ion etching is recalled. Further improvements dealing with angular points of the profile shows that: angular points having straight trajectory may exist; and they can be found either by computation or by graphic method.

Journal ArticleDOI
TL;DR: In this paper, fracture mechanics and strength studies performed on two silicon carbides (a hot-pressed material with alumina and a sintered material with boron) have shown that both materials exhibit slow crack growth at room temperature in water.
Abstract: Fracture mechanics and strength studies performed on two silicon carbides — a hot-pressed material (with alumina) and a sintered material (with boron) — have shown that both materials exhibit slow crack growth at room temperature in water, but only the hotpressed material exhibits significant high temperature slow crack growth (1000 to 1400‡ C). A good correlation of the observed fracture behaviour with the crack growth predicted from the fracture mechanics parameters shows that effective failure predictions for this material can be achieved using macro-fracture mechanics data.

Journal ArticleDOI
TL;DR: In this article, an analysis of the effects of varying the coating parameters of concern is presented for toughness and strength in Boron-epoxy composites of volume fraction 0.20 to 0.25, which have fracture toughnesses of over 200 kd m -2, whilst retaining rule of mixtures tensile strengths (~ 650 MN m-2).
Abstract: High strength and high toughness are usually mutually exclusive in brittle filament/brittle matrix composites. The high tensile strength characteristic of strong interfacial filament/matrix bonding can, however, be combined with the high fracture toughness of weak interfacial bonding, when the filaments are arranged to have alternate sections of high and low shear stress (and low and high toughness). Such weak and strong areas can be achieved by appropriate intermittent coating of the fibres. The strong regions ensure that the filament strength is picked up; weak areas randomly in the path of running cracks serve to blunt them by the Cook/Gordon mechanism which, in turn, produces long pull-out lengths with an associated large contribution to toughness. Boron-epoxy composites of volume fraction 0.20 to 0.25 have been made in this way which have fracture toughnesses of over 200 kd m -2, whilst retaining rule of mixtures tensile strengths (~ 650 MN m-2). At the volume fractions used, this apparently represents Kic values greater than 100 MN m -3/2, An analysis is presented for toughness and strength which demonstrates, in broad terms, the effects of varying the coating parameters of concern. Results show that the "toughness" of interfaces is an important parameter, differences in which may not be shown up in terms of interfacial "strength". The choice of coating material is crucial in getting the desired effect. Some observations are made upon methods of measuring the components of toughness in composites.

Journal ArticleDOI
TL;DR: In this paper, the wetting and bonding behavior between diamond plaques and copper alloyed with chromium, titanium or vanadium has been studied using the sessile drop technique.
Abstract: The wetting and bonding behaviour between diamond plaques and copper alloyed with chromium, titanium or vanadium has been studied using the sessile drop technique. Wetting was induced at 1150° C by additions of more than 0.1 at. % of titanium, but additions of vanadium up to and beyond the solubility limit did not cause wetting to occur. The room temperature strengths of the interfaces between the diamond plaques and the solidified sessile drops increased with increasing alloying element concentration, reached a maximum value at a concentration less than that needed to induce wetting, and thereafter decreased. The maximum strengths achieved by alloying with chromium, titanium or vanadium were 35.5, 42.0 and 69.8 kg mm−2 respectively. The reactivity of the alloyed sessile drops was assessed using metallography, EPMA and a surface contour device. A tentative picture of the effects of diamond-metal interactions on wetting and bonding behaviour was developed.

Journal ArticleDOI
TL;DR: In carbon fiber reinforced plastics (CFRP), the initial resistance to crack propagation parallel to fibres is determined largely by the matrix toughness as discussed by the authors, and the suppression of toughness is related to the thickness of resin film through which the crack propagates.
Abstract: In carbon fibre reinforced plastics (CFRP), the initial resistance to crack propagation parallel to fibres is determined largely by the matrix toughness. The fracture toughness (G IC) of an epoxide resin can be increased considerably by the addition of butadieneacrylonitrile co-polymers (CTBN). These cause the precipitation of small spheres of a second phase and, for example, increaseG IC from ∼ 300 to ∼ 3000 J m−2 on the addition of 9 wt% CTBN. The large increases obtained in bulk resins are not obtained in CFRP, instead significant but modest increases are achieved. The suppression of toughness is related to the thickness of resin film through which the crack propagates.

Journal ArticleDOI
TL;DR: In this paper, the fracture strength of soda lime silicate glass is predicted from fracture mechanics data obtained during slow crack growth by identifying and evaluating several key parameters, and the predicted strength characteristics are illustrated using fracture mechanics analysis.
Abstract: An analysis is presented which enables the fracture strength, (under constant stress-rate conditions) to be predicted from fracture mechanics data obtained during slow crack growth — by identifying and evaluating several key parameters. The predicted strength characteristics are illustrated using fracture mechanics data obtained for a soda lime silicate glass. Finally, the predicted strengths are compared with strengths measured in flexure on abraded soda lime silicate glass specimens. A good correlation is obtained, indicating an equivalence between micro- and macro-crack propagation conditions for this material.

Journal ArticleDOI
TL;DR: In this paper, the axial compression fracture of carbon fibres was studied by embedding single fibres in epoxy resin and compressing the specimens parallel to the fibre axis.
Abstract: Axial compression fracture of carbon fibres was studied by embedding single fibres in epoxy resin and compressing the specimens parallel to the fibre axis. By careful optical monitoring of the fibre surface the earliest stages of fracture were identified leading to estimates of the fibre axial compression failure strengths. Compression strength decreases markedly from about 2.2 GN m−2 for moderately oriented fibres to <1 GN m−2 for highest modulus filaments. The trend towards decreasing compression strength with increasing anisotropy is explained on the basis of an increasing fibre microfibrillar nature. However fracture morphology studies show that the unduly rapid strength decrease results from an increasing degree of fibre outer layer ordering which accompanies increasing axial anisotropy in carbon fibres since cracking occurs first on the more highly aligned filament surfaces. It is suggested that fibre compression fracture changes from a shear to a microbuckling or kinking mode with increasing fibre anisotropy, where the latter initiates in individual, well-aligned but uncoupled microfibrils. The similarity of fine axial compression fractures in oriented carbon fibres to those found in elastica loop experiments is noted as are the possible implications which the low strain-to-failure in compression of very high modulus fibres might have for practical composites.