Showing papers in "Journal of Materials Science in 1974"
550 citations
TL;DR: The mechanisms which have been suggested to explain the deformation of crystalline polymers are reviewed in this article, where emphasis has been placed upon the type of information that can be gained from experimental observations and on the extent to which those observations are consistent with suggested deformation mechanisms and current ideas on polymer structure and morphology.
Abstract: The mechanisms which have been suggested to explain the deformation of crystalline polymers are reviewed. Emphasis has been placed upon the type of information that can be gained from experimental observations and on the extent to which those observations are consistent with suggested deformation mechanisms and current ideas on polymer structure and morphology.
437 citations
TL;DR: In this article, a composite material with the mixed spinel cobalt ferrite-cobalt titanate and the perovskite barium titanate as coexisting phases has been prepared.
Abstract: A eutectic composite material with the mixed spinel cobalt ferrite-cobalt titanate and the perovskite barium titanate as co-existing phases has been prepared, which shows a magnetoelectric effect due to the mechanical coupling of the piezomagnetic spinel and the piezoelectric perovskite. The maximum value of the magnetoelectric effect ΔE/ΔH obtained up till now is 5.0 × 10−2 V cm−1 Oe−1 at room temperature.
413 citations
319 citations
TL;DR: In this paper, the pertinent thermodynamic relations, nucleation and growth and the influence of stress are considered and applied to thermoelasticity and the memory effects, and the effects of stress on memory are investigated.
Abstract: The pertinent thermodynamic relations, nucleation and growth and the influence of stress are considered and applied to thermoelasticity and the memory effects.
309 citations
TL;DR: A condensed description of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers, is given in this paper, where it is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments.
Abstract: A condensed description is given of the fundamental processes involved in radiation damage and the effects of radiation on the physical and chemical properties of organic materials, particularly polymers It is shown that the radiation doses received by specimens in the electron microscope are extremely high, very much greater than those used in radiation chemistry experiments Because of this, only qualitative predictions of behaviour in the electron microscope can be made A number of authors have described the changes in the image or diffraction pattern of particular specimen types during observation in the electron microscope and their work is reviewed here In general, contrast features in the image may disappear, due to loss of mass or crystallinity, or new features may appear due to distortion of ordered regions The effects of radiation damage on attainable resolution, and possible methods of improving the resolution are then discussed
225 citations
TL;DR: In this paper, the fracture toughness of PMMA has been determined in the temperature range −190 to + 80° C and over the crack speed range of 10−2 to 102 mm sec−1.
Abstract: Experiments are described in which the fracture toughness,K
c, of PMMA has been determined in the temperature range −190 to + 80° C and over the crack speed range of 10−2 to 102 mm sec−1. Single edge notch tension was used for instability measurements but the other data were obtained using the double torsion method. In the range −80 to + 80°C the variations inK
c may be described in terms of modulus changes and a constant crack opening displacement criterion. Crack instabilities are correlated with isothermal-adiabatic transitions at the crack tip. Below −80° C there is an inverted rate dependence associated with thermal effects during post-instability crack propagation.
202 citations
TL;DR: In this article, a technique for studying high temperature crack propagation in ceramic materials is developed, which is used to obtain relationships between the crack propagation rate and the stress intensity factor for hot-pressed silicon nitride up to 1400° C.
Abstract: A technique for studying high temperature crack propagation in ceramic materials is developed. The technique is used to obtain relationships between the crack propagation rate and the stress intensity factor for hot-pressed silicon nitride up to 1400° C. The data are then used to develop proof test diagrams which give values for the safe working stress levels for this material after proof testing (or any other flaw detection procedure).
197 citations
TL;DR: In this article, the stability of the three known phases in the Y2O3-Al 2O3 pseudo-binary system has been investigated and an optical and scanning electron microscope study of the associated morphological changes in YAlO3 has been conducted.
Abstract: The stability of the three known phases in the Y2O3-Al2O3 pseudo-binary system has been investigated. YAlO3 (YAP) and Y4Al2O9 (YAM) decompose at elevated temperatures, the products of the reaction being the third compound Y3Al5O12 (YAG) and an unknown phase (designated X). The decomposition is most evident in powders but can also be initiated on the surface of bulk single crystals. X-ray diffraction studies have been performed in an attempt to identify the structure and composition of the unknown phase. The thermal decomposition has been found to be surface controlled and an optical and scanning electron microscope study of the associated morphological changes in YAlO3 indicates that the reaction involves localized surface melting, probably with the loss of oxygen which effectively moves the composition off the binary join.
186 citations
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TL;DR: In this paper, the development of our present understanding of the phenomenon of creep cavitation is reviewed, and the status of research into nickel-base superalloys is reviewed with reference being made to such effects as regenerative heat-treatment.
Abstract: Metals often fail in service under creep conditions because of the formation of cavities on the grain boundaries which are approximately normal to the applied stress. This phenomenon of creep cavitation is becoming of increasing technological importance. As a result a complete understanding of it is desirable so that alloys with improved cavitation resistance can be designed. This paper reviews the development of our present understanding of the phenomenon which is one of nucleation, growth and linkage leading to failure. Several mechanisms of nucleation, such as at grain-boundary ledges or precipitates, have been postulated and experimental evidence in support of each has been cited. Similarly, deformation- or vacancy-controlled growth mechanisms have been discussed. It is apparent from the literature thatno single mechanism is applicable, indeed, the work discussed here suggests that several mechanisms may operate and each may become dominant at different stages of the creep life. Finally, the status of research into nickel-base superalloys is reviewed with reference being made to such effects as regenerative heat-treatment.
174 citations
TL;DR: The low compressive strength of unidirectional composites cannot be satisfactorily explained in terms of current theories which assume that failure is due to the matrix material.
Abstract: The low compressive strength of Kevlar 49® unidirectional composites cannot be satisfactorily explained in terms of current theories which assume that failure is due to the matrix material. For a given matrix, Kevlar 49 composites are considerably weaker in compression than those based on other comparable high strength, high modulus filaments. Fracture is found to occur before any plastic deformation of the matrix is observed.
TL;DR: In this paper, the graph of yield stress versus spherulite size goes through a maximum at a critical spherula size, which represents a changeover from spherulate yield to boundary yield, caused by an increased segregation of impurities at the boundaries coupled with voidage owing to contraction of the spheruleites on cooling.
Abstract: Tensile tests show that for isotactic polypropylene the graph of yield stress versus spherulite size goes through a maximum at a critical spherulite size. Scanning electron and transmission optical microscopy indicate that this represents a change-over from spherulite yield to boundary yield, caused by an increased segregation of impurities at the boundaries coupled with voidage owing to contraction of the spherulites on cooling.
TL;DR: In this paper, the present knowledge of crystal-melt interfacial energies is examined critically, consideration being given to the full range of metallic, inorganic and organic materials, both pure and impure.
Abstract: The present knowledge of crystal-melt interfacial energies is examined critically, consideration being given to the full range of metallic, inorganic and organic materials, both pure and impure. The methods currently available for measuring crystal-melt energies are discussed, and the significance of the experimental values in elucidating processes of crystal nucleation and growth is pointed out. The application of solid-liquid energy values to the measurement of other interphase boundary energies is indicated.
TL;DR: In this article, a fracture-mechanics theory is developed which gives fracture criteria for solids in general, without limitations as to their linearity, elastic behaviour or infinitesimal strain.
Abstract: A fracture-mechanics theory is developed which gives fracture criteria for solids in general, without limitations as to their linearity, elastic behaviour or infinitesimal strain. Besides the “standard” results of the theory which reduce to familiar forms like the Griffith equation for linear, elastic solids, several new results emerge from the theory. These include a relationship between the surface work and the true surface energy of the solid, an explanation of certain departures from standard fracture mechanics obtained with inelastic materials, and a prediction and explanation of the phenomenon of notch brittleness. Further applications of the theory, such as adhesive failure and fatigue, will be explored in a subsequent paper.
TL;DR: In this article, the microstructure of silicon nitride hot-pressed with a magnesium oxide additive has been studied by transmission electron microscopy, and the observations substantiate a solid/liquid/solid transformation mechanism, whereby Si and N are transported from α grains through a silicate liquid phase to nucleation sites for β at α/liquid interfaces or to β grains nucleated homogeneously in the liquid phase.
Abstract: The microstructure of silicon nitride hot-pressed with a magnesium oxide additive has been studied by transmission electron microscopy. This includes material at various stages in a hot-pressing process: the initial (∼ 90%α) silicon nitride powder; specimens partially densified and partially transformed from α-silicon “nitride” (Si11.5N15O0.5) to β-silicon nitride (Si3N4); and almost fully dense and fully transformed β-Si3N4. The observations substantiate a solid/liquid/solid transformation mechanism, whereby Si and N are transported from α grains through a silicate liquid phase to nucleation sites for β at α/liquid interfaces or to β grains nucleated homogeneously in the liquid phase.
TL;DR: In this article, the sessile drop method was used to measure the contact angle made by molten aluminium with vitreous carbon in vacuum at temperatures up to 1100° C. The effect on wetting behavior of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation.
Abstract: The contact angle made by molten aluminium with vitreous carbon was measured by the sessile drop method in vacuum at temperatures up to 1100° C. The effect on wetting behaviour of the oxide layer on the molten metal was highlighted by using two samples of aluminium in different states of oxidation. The investigation involved the variation of certain parameters affecting the stability of the oxide film, e.g. the temperature, additions of Ti, Si, Cr, Be, Ca and Li to aluminium and the time held at a certain temperature. The state of the molten aluminium surface under various experimental conditions was determined indirectly by surface tension measurements.
TL;DR: In this article, it is shown that conservative failure prediction based on an equivalence between inclusion size and crack size is usually acceptable if the shear modulusμ or thermal expansion coefficientα for the inclusion is larger than the matrix values.
Abstract: The stress concentrations that occur at inclusions due to thermal expansion and elastic modulus mismatch are discussed and the stress intensity factors at interface cracks that result from these stresses are calculated. It is shown that conservative failure prediction based on an equivalence between inclusion size and crack size is usually acceptable if the shear modulusμ or thermal expansion coefficientα for the inclusion is larger than the matrix values. If, however,μ andα are smaller for the inclusion than the matrix, extensive cracking can develop at the inclusions which may lead to premature failure. For this case the only effective methods for failure prediction are techniques which give directly the maximum stress intensity factor, i.e., proof testing and/or acoustic emission.
TL;DR: In this article, the authors discuss the way in which the features found on some tensile fracture surfaces of amorphous metals are formed, and the relevance of the strongly inhomogeneous plastic flow present in these solids to the formation of the particular fracture topography discussed.
Abstract: This paper discusses the way in which the features found on some tensile fracture surfaces of amorphous metals are formed. The relevance of the strongly inhomogeneous plastic flow present in these solids to the formation of the particular fracture topography discussed is pointed out, as well as features common to the well-known fracture micromechanisms, cleavage and dimpled rupture.
TL;DR: The cyclic stress-strain behavior of a wide variety of rigid polymers has been studied as mentioned in this paper, and three classes of fatigue response can be defined, each class displaying a characteristic evolutionary pattern in the stressstrain relation as deformation proceeds from the initial fatigue cycle to fatigue-crack propagation.
Abstract: The cyclic stress-strain behaviour of a wide variety of rigid polymers has been studied Three classes of fatigue response can be defined, each class displaying a characteristic evolutionary pattern in the stress-strain relation as deformation proceeds from the initial fatigue cycle to fatigue-crack propagation Ductile polymers undergo a marked decrease in deformation resistance prior to crack formation; the detailed mechanism by which this “softening” develops can be related to the material microstructure and thermomechanical history Amorphous polymers with a moderate degree of ductility soften slightly; in these materials crazing plays a dominant role in both the cyclic stress-strain response and the structural fatigue resistance Brittle and nearly-brittle polymers are essentially stable in cyclic deformation; the fatigue resistance of these materials is very sensitive to strain amplitude in cyclic deformation
TL;DR: The work of fracture of four different carbon fiber reinforced glass and glass-ceramic composites has been measured to determine the effects of the different properties of the components on fracture behaviour as discussed by the authors.
Abstract: The work of fracture of four different carbon fibre reinforced glass and glass-ceramic composites has been measured to determine the effects of the different properties of the components on fracture behaviour. Differences in fracture energies can be explained in terms of the fibre pull-out model and differences in the fibre-matrix interfacial shear bond. The work of fracture of the glass-ceramic is independent of crack velocity while that of the Pyrex matrix composite decreases with increasing velocity at low velocities, the decrease stopping at higher velocities. Work of fracture values agree well with linear elastic fracture mechanics toughness values.
TL;DR: In this paper, the macroscopic mechanical behavior associated with pseudoelasticity and the memory effects is extensively reviewed and the particular features of the tension and compression curves (the stress to induce or reorient the martensite, total elongation, reversibility and hysteresis) are analyzed and their dependence on temperature and crystal orientation is discussed.
Abstract: The macroscopic mechanical behaviour (stress-strain-temperature relations in tension, compression and internal friction) associated with pseudoelasticity and the memory effects is extensively reviewed. The particular features of the tension and compression curves (the stress to induce or reorient the martensite, total elongation, reversibility and hysteresis) are analysed and their dependence on temperature and crystal orientation is discussed.
TL;DR: In this article, powder and single-crystal X-ray techniques have been employed to obtain precise lattice parameters of silicon uniformly doped with boron or phosphorus, and good agreement is found between the two methods.
Abstract: Powder and single-crystal X-ray techniques have been employed to obtain precise lattice parameters of silicon uniformly doped with boron or phosphorus. Good agreement is found between the two methods. Previous accurate determination of the CuKα1, effective wavelength has yielded λ=1.540621±0.000006 A. Particular care has been devoted to the chemical and electrical characterization of the alloys, whose maximum dopant concentrations were 8×1019 atoms cm−3 for P and 4.4×1020 atoms cm−3 for B.
TL;DR: In this paper, the authors discussed the strength variations in boron-epoxy composites with differing shear strengths of the interfacial bond and suggested how to tailor interfacial shear strength in order to obtain a reasonable toughness.
Abstract: The premises upon which prevailing composite toughness theories are based are discussed in the light of observed strength variations in boron-epoxy composites with differing shear strengths of the interfacial bond. None of the extant toughness theories (pull-out, debonding, stress redistribution) successfully predicts the work of fracture of the boronepoxy system. However, incorporation of the work to create new surfaces into the total toughness analysis gives better agreement with experiment, and work of fracture predictions for other sytems, such as carbon-polyester, can also be modified. The approach is more generalized than the Outwater/Murphy debonding explanation for toughness, which in the way usually presented only applies when the filament fracture strain is greater than the matrix fracture strain. The present analysis suggests how to tailor the interfacial shear strength in order to obtain a reasonable toughness yet still maintain strengths of the order of the rule of mixtures.
TL;DR: In this article, an analytical treatment of the development of a general contour under ion bombardment is proposed, which relates the properties of the eroded material through its yield variation upon the angle of incidence,S (θ).
Abstract: An analytical treatment of the development of a general contour under ion bombardment is proposed. The derived equations relate the properties of the eroded material through its yield variation upon the angle of incidence,S (θ). New specific angles (θs
1 andθs
2) are introduced which limit regions where the evolution process of the surface may be different. The theory allows prediction of the number of angular points which will appear in each region. A computer simulation program is used to describe the evolution of sine-type surfaces. With infinite time, such profiles in relief above a horizontal plane, tend towards the steady state which exists in a horizontal plane. The model is compared to one previously described.
TL;DR: In this paper, the dislocation arrangements produced around microhardness indentations made in silicon at room temperature have been studied by transmission electron microscopy and it is suggested that, during indentation, the theoretical shear strength is exceeded locally and that the observed dislocations arise as a result of the accommodation of the displacements due to block slip.
Abstract: The dislocation arrangements produced around microhardness indentations made in silicon at room temperature have been studied by transmission electron microscopy. Loops consisting of 30°- and 60°-dislocations are produced and move on the {111} planes. It is suggested that, during indentation, the theoretical shear strength is exceeded locally and that the observed dislocations arise as a result of the accommodation of the displacements due to block slip. On annealing up to 1030° C the loops do not appear to be mobile, rather new loops consisting of edge and screw components are formed which can move large distances.
TL;DR: In this article, the possibility of influencing the effects of chemically active environments on fracture processes in some controlled and predictable manner, such that their potentially detrimental effects on mechanical reliability are minimized, and their ability to facilitate fracture is utilized when this is desirable, as in materials removal processes.
Abstract: This paper is concerned with the possibility of influencing the effects of chemically active environments on fracture processes in some controlled and predictable manner, such that their potentially detrimental effects on mechanical reliability are minimized, and their ability to facilitate fracture is utilized when this is desirable, as in materials removal processes. Phenomena such as stress-corrosion cracking, liquid metal embrittlement and chemomechanical effects are considered as they relate to the fracture behaviour of metals, ceramics, minerals, rocks, glasses, organic crystals and polymers.
TL;DR: The effect of the orientation of metal wires on the opening of a crack in a brittle-matrix composite has been studied in this article, where the force arising from the plastic bending of a wire which is weakly bonded to the matrix and which crosses the matrix crack at an angleθ to the crack face normal has been measured in model resin-wire composites.
Abstract: The effect of the orientation of metal wires on the opening of a crack in a brittle-matrix composite has been studied. The force arising from the plastic bending of a wire which is weakly bonded to the matrix and which crosses the matrix crack at an angleθ to the crack face normal has been measured in model resin-wire composites and good agreement is found with a simple theory based on the calculation of the force needed to produce a plastic hinge in a cantilever beam. The force passes through a maximum at a small crack opening, of the order of one wire diameter, and decreases with further crack opening. The The largest force is obtained for a value ofθ of approximately 45°. For wires whose length approaches the critical length, the force and the total work of fracture arising from the bending of the wire are small compared to the values arising from the interfacial shear stress resisting pull-out; the contributions due to bending and interfacial shear stress are of comparable magnitudes for wires which are approximately one-fifth of the critical length.
TL;DR: In this article, two types of stage I fatigue crack initiation were observed, (a) along α/β interfaces and (b) transcrystalline initiation across α grains in partly transformed microstructures and across αβ interfaces in fully transformed micro structures.
Abstract: Fatigue deformation and stage I (shear mode) crack initiation in Ti-6Al-4V alloy test pieces have been studied using optical microscopy. Two types of stage I fatigue crack initiation were observed, (a) alongα/β interfaces and (b) transcrystalline initiation acrossα grains in partly transformed microstructures and acrossαβ interfaces in fully transformed microstructures. The α/β interface cracking occurred predominantly in the low stress regions of the test pieces. These observations suggested that a microstructure with a smallα grain size, to minimize the mean free slip path, and with minimum lengths ofα/β interface, would have a high fatigue strength. Such a microstructure, with anα grain size of < 10 μm, and spheroidal or near spheroidalβ particles, was produced by thermo-mechanical processing. The rotating cantilever fatigue strength of this microstructure, ± 670 MN m−2 at 10−7 cycles, compares with fatigue strengths in the range ± 480 to ± 590 MN m−2 for commercial Ti-6Al-4V bars.