Showing papers in "Journal of Materials Science in 1981"
TL;DR: In this article, a wide ranging critical analysis of the existing wealth of data shows that the dielectric loss obeys power-law dependences on frequencies, both below and above any loss peaks that may be present.
Abstract: The frequency dependence of the dielectric response of solids shows an apparently bewildering variety of patterns, virtually none of which corresponds to the classical Debye behaviour. However, a wide ranging critical analysis of the existing wealth of data shows that the dielectric loss obeys power-law dependences on frequencies, both below and above any loss peaks that may be present. This corresponds to power-law dependences on time under step-function excitation and it applies completely generally regardless of the detailed physical and chemical nature of the materials in question and also applies equally to dipoles, ions and hopping electrons as the polarizing species. Moreover, the power-law responses persist down to the lowest temperatures in the milliKelvin range, thus proving the importance of non-thermal transitions. The power laws are characterized by exponents in the range ± 1 and they cover as special cases the complete range of the observed types of response, from virtually frequency-independent “flat” losses often seen in low-loss materials, through various forms of asymmetric loss peaks to strongly dispersive behaviour in which both the real and the imaginary components of the susceptibility vary almost inversely with frequency. The “universality” of the power law strongly suggests the dominance in all materials of a common mechanism of dielectric relaxation and this is found in many-body interactions which provide a model capable of explaining the totality of the observed responses of solids, including both the frequency- and the temperature-dependence. In this interpretation, the classical one-particle Debye law represents but a singularity in a more general behaviour and is usually overshadowed by the new many-body mechanisms.
487 citations
TL;DR: In this article, the authors performed tension tests on re-healed and welded glassy polymers (PMMA-PMMA, SAN-SAN and PMMA-SAN) and found that the facture toughness in the interface increased with contact time, asKIi ∝t 1/4 as predicted by a diffusion model.
Abstract: Compact tension tests have been performed on re-healed and welded glassy polymers (PMMA-PMMA, SAN-SAN and PMMA-SAN). At temperatures above the glass transition temperature,Tg, it was observed that the facture toughness,KIi, in the interface increased with contact time,t, asKIi ∝t1/4 as predicted by a diffusion model. The self-diffusion constantD(Tg + 15 K) of chains of molecular weight 1.2×105 can be estimated as 1×10−21sec−1 with an activation energy of 274 kJ mol−1. For full material resistance, the depth of interdiffusion, 〈Δx2〉1/2, was calculated to be between 2 and 3 nm. Vacuum drying of the specimens, as well as polishing the interfaces, decreases the speed of interdiffusion.
467 citations
TL;DR: SEM observation of the fracture surfaces indicates a predomination of transgranular failures in polycrystalline hydroxyapatite, which is similar to that of cortical bone, dentine and enamel.
Abstract: The compressive, flexural, torsional and dynamic torsional strengths of polycrystalline hydroxyapatite sintered at a temperature of 1300° C for 3 h were found to be 509, 113, 76 and 68 MPa, respectively. The mechanical properties of polycrystalline hydroxyapatite are compared with those of cortical bone, dentine and enamel. SEM observation of the fracture surfaces indicates a predomination of transgranular failures.
450 citations
TL;DR: In this article, the activation energy for nucleation of particles, for growth of particles and for the total process can all be determined independently by experiment, and the agreement between the theory and the experiments is very satisfactory.
Abstract: In crystallization or precipitation, the activation energy for nucleation of particles,En, for growth of particles,Eg, and for the total process,Ec, can all be determined independently by experiment. Formulae relating these three values are developed. Cases of linear and parabolic growth are included for different nucleation rates and morphologies. The formulae are tested experimentally on amorphous alloys (metallic glasses) based on Fe-Ni. The agreement between the theory and the experiments is very satisfactory.
325 citations
TL;DR: In this paper, the mechanics of hardness indentation are considered and an expression for the relative depth recovery of the impression as a function of hardness/modulus, H/E, is derived.
Abstract: The mechanics of hardness indentation are considered. On the basis of a cycle in which the loading is elastic-plastic and the unloading (and subsequent reloading) elastic, an expression is derived for the relative depth recovery of the impression as a function of hardness/modulus,H/E. Experimental observations on indented surfaces of selected materials, mostly ceramics, using a tilting procedure in the scanning electron microscope to measure the residual depths, confirm the predicted trends. The analysis offers a simple means of characterizing the deformation properties of materials and should provide a basis for evaluating a range of contact-related properties, particularly surface damage phenomena in sharp-particle impact.
287 citations
TL;DR: In this paper, the elastic properties, fracture toughness, strength and sub-critical crack growth of hydroxy apatite ceramic blocks were investigated, and it was shown that very serious slow crack growth is present.
Abstract: Hydroxy apatite ceramic blocks of varying density have been prepared from a commercial powder. The elastic properties, fracture toughness, strength and sub-critical crack growth of these materials have been investigated. Young's modulus for the nearly fully dense material is 112 GPa while the compressive strength is about 800 MPa. For the same material the strength and fracture toughness under dry conditions are 115 MPa and 1.0 MPa m1/2, respectively. Substantial slow crack growth was found under these conditions. Under wet conditions the values for strength and fracture toughness drop to about 75% of their “dry” values. In this case very serious slow crack growth is present.
287 citations
TL;DR: In this paper, a casting technique for preparing aluminium-alumina, aluminium-illite and aluminium-silicon carbide particle composites has been developed, which essentially consists of stirring uncoated but suitably heat-treated ceramic particles of sizes varying from 10 to 200 μm in molten aluminium alloys using the vortex method of dispersion of particles, followed by casting of the composite melts.
Abstract: A casting technique for preparing aluminium-alumina, aluminium-illite and aluminium-silicon carbide particle composites has been developed. The method essentially consists of stirring uncoated but suitably heat-treated ceramic particles of sizes varying from 10 to 200 μm in molten aluminium alloys (above their liquidus temperature) using the vortex method of dispersion of particles, followed by casting of the composite melts. Recoveries and microscopic distribution of variously pretreated ceramic particles in the castings have been reported. Mechanical properties and wear of these composites have been investigated. Ultimate tensile strength (UTS) and hardness of aluminium increased from 75.50 MN m−2 and 27 Brinell hardness number (BHN) to 93.15 MN m−2 and 37 BHN respectively due to additions of 3 wt % alumina particles of 100 μm size. As a contrast, the tensile strength of aluminium-11.8 wt % Si alloy decreased from 156.89 MN m−2 to 122.57 MN m−2 due to the addition of 3 wt % alumina particles of the same size. Adhesive wear rates of aluminium, aluminium-11.8 wt % Si and aluminium-16 wt % Si alloys decreased from 3.62×10−8, 1.75×10−8 and 1.59×10−8 cm3 cm−1 to 2.0×10−8, 0.87×10−8 and 0.70×10−8 cm3 cm−1, respectively, due to the additions of 3 wt % alumina particles.
272 citations
TL;DR: In this article, a model based on the Weibull strength distribution of the carbon fibre reinforced composite phase was used to relate the two-parameter WeibULL strength distribution to that of single carbon fibres, and experimental observations of the failure process support this hypothesis.
Abstract: When carbon fibre is combined with less-stiff higher-elongation glass fibre in a hybrid composite an enhancement of the failure strain of the carbon fibre reinforced phase is observed. This “hybrid effect” is only partially accounted for by internal compressive strains induced by differential thermal contraction during fabrication. The predominant factor is shown to be a relationship between the strength and effective bundle size of the carbon fibre ligaments which is a consequence of the statistical distribution of strengthreducing flaws in the carbon fibres. A lamina or ligament (bundle) of carbon fibres fails when there is a local critical accumulation of fibre fractures. A model based on this concept is used to relate the two-parameter Weibull strength distribution of the carbon fibre reinforced composite phase to that of single carbon fibres. The model suggests that the critical number of fibre fractures is of the order of 3, and experimental observations of the failure process support this hypothesis.
258 citations
229 citations
TL;DR: In this article, the product of the electrostriction coefficientQ and the Curie-Weiss constantC is constant for all perovskite crystals and the Q value is proportional to the square of the thermal expansion coefficient,α.
Abstract: Properties of new electrostrictive materials for displacive transducers are reviewed including theoretical, material and design studies. Intensive investigation of the electrostrictive effects in ferroelectric and antiferroelectric perovskites have led to some empirical rules: the product of the electrostriction coefficientQ and the Curie-Weiss constantC is constant for all perovskite crystals and theQ value is proportional to the square of the thermal expansion coefficient,α. Consistent with the empirical rules, the relaxor ferroelectric ceramic 0.9 Pb(Mg1/3Nb2/3)O3 −0.1 PbTiO3 possesses much larger strain with lower hysteresis, aging effects and thermal expansion than that obtained with piezoelectric lead zirconate titanate (PZT). Using a multilayer configuration similar to commercial capacitors, a new mirror control device capable of large strains with high reproducibility, up toΔL/L ∼ 10−3, with only 200 V applied has been developed.
222 citations
TL;DR: In this article, a simple method based on the shift of the differential thermal analysis (DTA) crystallization-peak temperature, for evaluating the influence of temperature and time of heat-treatments on bulk nucleation, is described.
Abstract: The crystal nucleation of Li2O-2SiO2 glass is studied by differential thermal analysis. A simple method, based on the shift of the differential thermal analysis (DTA) crystallization-peak temperature, for evaluating the influence of temperature and time of heat-treatments on bulk nucleation, is described. The experimental results are in good agreement with results obtained by other workers.
TL;DR: In this paper, the theory of non-equilibrium grain-boundary segregation is discussed with particular reference to recent ideas and data relating to boron grain boundary segregation in Type 316 austenitic steel and a model is developed which, it is hoped, will more realistically describe the magnitude and extent of the process.
Abstract: The theory of non-equilibrium grain-boundary segregation is discussed with particular reference to recent ideas and data relating to boron grain-boundary segregation in Type 316 austenitic steel. The kinetics of the non-equilibrium grain-boundary segregation process are considered in depth and a model is developed which, it is hoped, will more realistically describe the magnitude and extent of the process. Reasonable agreement is found between the predictions of the model and experimental evidence for non-equilibrium boron, aluminium and titanium segregation to grain boundaries in austenitic steels. The model predicts, generally, that elements with large misfits with the matrix atoms will segregate most. Larger grain sizes lead to greater grain-boundary segregation. Also, the two critical heat-treatment parameters in non-equilibrium segregation are the solution-treatment temperature and the cooling rate from the solution-treatment temperature. Predictions of the worst combinations of these parameters for maximum non-equilibrium segregation to grain boundaries in austenitic steels are presented.
TL;DR: In this paper, the influence of substrate roughness on wettability has been investigated at room and high temperatures using sixteen material combinations, mostly liquid metals and solid ceramics but also water, glycerol and solid nickel.
Abstract: The influence of substrate roughness on wettability has been investigated at room and high temperatures using sixteen material combinations, mostly liquid metals and solid ceramics but also water, glycerol and solid nickel. The contact angles assumed by both wetting and non-wetting drops of all but two material combinations increased linearly with the relative steepness of the surface features, the effect being less for experiments conducted at high temperatures. In contrast, the contact angles of good wetting drops of glycerol and exceptionally good wetting drops of Easy-flo decreased when their silica and nickel substrates were roughened. Similarly, contact angles of both wetting and non-wetting drops were decreased by ultrasonic vibration. The experimental data can best be interpreted in terms of the metastable equilibrium configuration models in which an advancing liquid front has to overcome energy barriers associated with surface features. This occurs more readily if these barriers are small relative to the energy of the liquid which our data suggest can be equated with the enthalpy of the liquid. This interpretation enables the effects of substrate roughness at one temperature or with one liquid to be used to predict behaviour at other temperatures and with other liquids.
TL;DR: In this article, a quantitative model is proposed, based on the dynamics of plastic waves which accounts for the transition from "normal" to "inverse" transient behaviour with increasing strain, and also explains the opposite effects of stress relaxation and specimen unloading on the restraining transients.
Abstract: Tensile tests were performed on seven commercial polymers at 22° C and at constant true strain rates of 10−4 to 10−1 sec−1. The constant strain rates were imposed on the minimum section of each sample with the aid of a diametral transducer, an exponential function generator and a closed-loop hydraulic testing machine. The polymers investigated were: high and low density polyethylene, polytetrafluoroethylene, polypropylene. polyvinylchloride and polyamide 6 and 66. True yield drops were observed in the rigid glassy polymers, whereas yielding was more gradual in the semi-crystalline or plasticized polymers. Strain rate change tests were also performed, during which one order of magnitude increases and decreases were imposed on the specimens. “Normal” transients were observed at small strains in the samples containing a rubbery phase, while the transients were of an “inverse” nature in the samples containing a glassy phase. With an increase in the strain at which the change was initiated, the “normal” transients changed in character to “inverse”. Transient tests were also performed in which straining was interrupted to permit a period of stress relaxation or of holding in the unloaded condition prior to the resumption of straining. A quantitative model is proposed, based on the dynamics of plastic waves which accounts for the transition from “normal” to “inverse” transient behaviour with increasing strain, and also explains the opposite effects of stress relaxation and of specimen unloading on the restraining transients.
TL;DR: In this article, the authors present a survey of charged particle emission from a number of materials including crystalline insulators, glass, graphite, polymers and composites, focusing on fibre-reinforced epoxy systems which yield unique forms of charge emission.
Abstract: The emission of electrons and positive ions from materials undergoing fracture is investigated. We present a survey of charged particle emission from a number of materials including crystalline insulators, glass, graphite, polymers and composites. Particular attention is given to fibre-reinforced epoxy systems which yield unique forms of charge emission. Energy distributions of the emitted particles are given for E-glass-epoxy strands, polybutadiene filled with glass beads, and mica. Evidence is presented that interfacial failure and charge separation play important roles in the observed emission.
TL;DR: In this paper, a novel polytitanocarbosilane was synthesized to examine the process of converting a multielement organometallic polymer into an inorganic compound, which was investigated by the techniques of infra-red spectroscopy (IR), gel permeation chromatography (GPC), number average molecular weight measurements and 29Si nuclear magnetic resonance (NMR) measurements.
Abstract: The novel polytitanocarbosilane, formed by the cross-linking of polycarbosilane with titanium tetra-alkoxide, was synthesized to examine the process of converting a multielement organometallic polymer into an inorganic compound. The chemical structure of this polymer was investigated by the techniques of infra-red spectroscopy (IR), gel permeation chromatography (GPC), number average molecular weight measurements and29Si nuclear magnetic resonance (NMR) measurements. The pyrolysis products in N2 gas at 1400° C and 1700° C were the microcrystalline and crystalline states of silicon carbide and titanium carbide, respectively.
TL;DR: SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silicon, aluminium chloride and starch, and the resulting single-phase SiC-ain powder was hot-pressed without additives to a high density.
Abstract: SiC-AIN alloys were prepared by the carbothermal reduction of silica and alumina, derived from an intimate mixture of silica, aluminium chloride and starch. The resulting single-phase SiC-AIN powder was hot-pressed without additives to a high density. The dense bodies had a fine-grained uniform microstructure. The Young's elastic modulus, microhardness, fracture toughness, thermal expansion and thermal conductivity were measured as functions of composition. The creep behaviour of the SiC-AIN alloy was compared with that of silicon carbide.
TL;DR: In this article, a low-temperature X-ray diffraction study was undertaken in order to fix the compositional limit of the tetragonal phase of the Nb-Sn A15 phase.
Abstract: Bulk samples covering the entire homogeneity range of the Nb-Sn A15-phase were prepared by a new method: levitation melting under high argon pressure. The variations of the lattice parameter, superconducting transition temperature, resistivity and critical field slope were measured as a function of composition. A low-temperature X-ray diffraction study was undertaken in order to fix the compositional limit of the tetragonal phase. The theoretical expectations for the critical field slopes at the transition temperature, Tc, based on actually-observed alloy parameters, were found to be in good agreeement with measured values.
TL;DR: A literature survey of aluminium powder metallurgy (PM) for high-strength applications was undertaken in this article, with particular emphasis on high strength, corrosion-resistant alloys and alloys developed for use at elevated temperatures.
Abstract: A literature survey of aluminium powder metallurgy (PM) for high-strength applications was undertaken. Improvements in aluminium—base alloys made via ingot metallurgy (IM) are reaching the point of diminishing returns. PM offers an alternative technology, capable of producing alloys having improved fatigue, corrosion, and stress-corrosion resistance, as well as improved strength and toughness at room or elevated temperatures. The steps involved in powder metallurgy: powder manufacture, powder processing, de-gassing, and consolidation, are described. The merits and deficiencies of the various processes for each step are compared. The key to successful application of Al powder metallurgy alloys appears to be the de-gassing and consolidation of the powder. The properties of several new PM alloys are compared, with particular emphasis on highstrength, corrosion-resistant alloys and alloys developed for use at elevated temperatures.
TL;DR: Using both a parabolic law for crystal growth and an exponential law for dissolution of solids in liquids, an equation describing the diffusion-controlled growth of a single-phase intermetallic layer has been derived as discussed by the authors.
Abstract: Using both a parabolic law for crystal growth and an exponential law for dissolution of solids in liquids, an equation describing the diffusion-controlled growth of a single-phase intermetallic layer has been derived. This equation enables calculation of the interlayer thickness as a function of time under given conditions of interaction of a solid metal with a liquid one. The growth rate of the Fe2Al5 interlayer follows the predicted time dependence.
TL;DR: In this article, the fracture energies of elastomer-modified epoxy polymers have been determined over a range of strain rates from 10−2 to 103 sec−1.
Abstract: The fracture energies of elastomer-modified epoxy polymers have been determined over a range of strain rates from 10−2 to 103 sec−1. The modifiers included a liquid carboxyterminated butadiene acrylonitrile and a solid rubber. They were used alone and also in combination. In all cases, the modifiers increased the toughness of the base resin by orders of magnitude and one combination of liquid and solid rubber increased toughness by 60 times. There was a general decrease in fracture energy with increasing strain rate but even during impact testing the modified epoxys were 10 to 20 times tougher than the base polymer. Scanning electron microscopy revealed that, when combined with the liquid rubber, the solid rubber induced a localized shear yielding.
TL;DR: The self-diffusion of 30Si in high purity and N-doped α-SiC single crystals has been measured in the temperature range 2273 to 2573 K as mentioned in this paper.
Abstract: The self-diffusion of30Si in high purity and N-doped α-SiC single crystals has been measured in the temperature range 2273 to 2573 K. The diffusion (DSi*) in N-doped crystals exceeds that in the pure crystals because of the increase in the concentration of the charged acceptor-type Si vacancies in the presence of the N species. A comparison ofDC* andDSi* shows that the former exceeds the latter by approximately 102, primarily because of the greater entropy of migration of C. Possible crystallographic paths of transport for both species are also discussed.
TL;DR: The effect of high-energy radiation on n-alkanes and polyethylene (PE) is reviewed in this article. But the authors focus on the effects of high energy radiation on PE.
Abstract: The effect of high-energy radiation on n-alkanes and polyethylene (PE) are reviewed. The article includes a description of (a) primary radiation events, formation, spatial distribution and decay of free radicals and radical migration mechanisms, (b) formation of cross-links and other stable products, (c) the effects of crystallinity, crystalline modifications and morphology on radiation cross-linking, and (d) radiation-induced changes in the crystal lattice and the destruction of crystallinity at high irradiation doses. An attempt is made to bring together conflicting views on various unsolved problems of the radiation physics and chemistry of these important and much studied substances. Long-chain paraffins are given considerable attention since their radiation behaviour often provides a link between that of PE and its short-chain analogues.
TL;DR: In this paper, the deformation behavior of an AISI 316 stainless steel under uniaxial tension was examined at 25, − 70 and − 196° C. X-ray diffraction analyses showed that the transformation to α-martensite commenced at these values of plastic strain and thereafter the volume fraction ofα increased steadily with strain.
Abstract: The deformation behaviour of an AISI 316 stainless steel under uniaxial tension was examined at 25, − 70 and − 196° C. The flow curves exhibited peculiar shapes and the work hardening rates were found to increase with strain beyond certain values of plastic strain. X-ray diffraction analyses showed that the transformation toα-martensite commenced at these values of plastic strain and thereafter the volume fraction ofα increased steadily with strain. On the other hand, the amount of the∈-martensite was found to increase with plastic strain initially, reach a maximum and then decrease gradually. The contribution of theα-phase to the flow stress of the alloy was found to be directly proportional to the volume fraction ofα. It is shown that the analysis of the flow curves provides a simple method of detecting the onset of the strain-induced martensitic transformation as well as estimating the amount of this martensite during further deformation.
TL;DR: In this paper, the Raman spectra of sodium borosilicate glasses with a wide range of Na2O/B2O3 ratios were systematically measured and various variations of the spectra with glass composition were studied to interpret the implied distribution of Na+ ions between silicate and borate units.
Abstract: Raman spectra of sodium borosilicate glasses with a wide range of Na2O/B2O3 ratios were systematically measured Variations of the spectra with glass composition were studied to interpret the implied distribution of Na+ ions between silicate and borate units When Na2O/B2O3 is less than 1, all Na+ ions are associated with borate units as indicated by the absence of the 1100 cm−1 band of Si-O− non-bridging bond stretching For the (1−x)Na2O · SiO2 ·xB2O3 glass withx≦04 the peak-height ratio of the 950 cm−1 band to the 1080 cm−1 band was used to analyse semiquantitatively the distribution of the Na+ ions between silicate and borate units Sodium ions are divided between silicate and borate units approximately in proportion to the amount of SiO2 and B2O3 present in these glasses Some of the high sodium content glasses were crystallized and their spectra were compared with the bulk glass spectra The distribution of Na+ ions in the glass was quite different from their distribution after crystallization Spectra of high silica glasses that had been heat-treated for phase separation indicated exclusion of borate units from the silica network and the formation of borate groups For high boron content glasses, no change was observed on heat treatment Raman bands due to borate groups seem to be little affected by their environments
TL;DR: In this article, the authors measured the electrical resistivity, Hall coefficient, and thermoelectric power of the most silicon-rich silicide of manganese, MnSi∼1.73, in the Boules of the Bridgman method in the composition range from 62.96 to 63.64 at% Si.
Abstract: Boules of the most silicon-rich silicide of manganese, MnSi∼1.73, were grown by the Bridgman method in the composition range from 62.96 to 63.64 at% Si. There are plate-like MnSi precipitates parallel to thec-plane of Mn15Si26 matrix in all boules except at their upper and lower ends. The amount of the MnSi precipitates was about 2 vol%. Measurements of electrical resistivity, Hall coefficient, and thermoelectric power of the boules were made in the temperature range from 77 to 1200 K. Thermoelectronic properties of Mn15Si26 were estimated on the basis of the distribution state of MnSi precipitates in the boule by assuming that metallic MnSi and semiconducting Mn15Si26 alternately crystallized in lamellae. Although the resistivities and thermoelectric powers measured in thec- anda-axis directions of Mn15Si26 showed anisotropy, the former were proportional to exp (4073/T) in the intrinsic region in both directions. The Hall coefficients showed isotropy over the whole temperature range. The degenerate holeconcentration of Mn15Si26 was determined to be 2.1×1027 m−3. Hall mobilities of Mn15Si26 in both thec- anda-axis directions obey aT−3/2-law above 600K. The Hall coefficient calculated from this relationship was in good agreement with the one found for Mn15Si26 in the intrinsic region. The effective-hole masses of Mn15Si26 along thec- anda-axis were found to be, respectively, 15 and 11 times larger than those of a free electron. Assuming that acoustic lattice scattering is dominant and that carriers obey Fermi-Dirac statistics, the temperature dependence of the calculated thermoelectric power was in reasonable agreement with the one estimated for Mn15Si26 in the temperature range from 400 to 1200K.
TL;DR: In this article, it was shown that at least three possible densification mechanisms might be operative during the gel to glass conversion: volume relaxation, condensation reactions and viscous sintering.
Abstract: Multicomponent silicate glasses of composition (wt%) 66SiO2-18B2O3-7Al2O3-6Na2O-3BaO were prepared by three sol-gel processes which differed primarily in the extent of hydrolysis of the metal alkoxide precursors. Gels which were prepared from solutions in which a stoichiometric excess of water was added, causing extensive replacement of OR groups (R ≡ (C
x
H(2x+1))s−1 by hydroxyl groups, were converted to fully dense, organic-free, monolithic glasses at temperatures near the glass transition temperature. Gels containing large numbers of OR groups showed enhanced densification at lower temperatures due to condensation reactions, but these gels could not be converted to fully dense, organic-free glasses. This investigation has shown that at least three possible densification mechanisms might be operative during the gel to glass conversion: volume relaxation, condensation reactions and viscous sintering.
TL;DR: In this article, spherical indentation measurements were made on enamel surfaces of intact human teeth and Young's modulus was found to be typically 8.3×1010 Pa and the yield stress to be 3.3 ×108 Pa.
Abstract: Spherical indentation measurements were made on enamel surfaces of intact human teeth. From the load versus depth of indentation curve Young's modulus was found to be typically 8.3×1010 Pa and the yield stress to be 3.3×108 Pa. Young's modulus was observed to vary with moisture content and with the orientation of the enamel surface. Viscoelastic behaviour was evident, also depending on the moisture content of the enamel.
TL;DR: In this paper, the de-oxidation of two submerged-arc, high-strength, low-alloy (HSLA) steel weld metals has been shown to depress γ→α transformation temperatures and produce a marked change in the resultant microstructures.
Abstract: Reducing the oxygen content of two submerged-arc, high-strength, low-alloy (HSLA) steel weld metals has been shown to depress γ→α transformation temperatures and produce a marked change in the resultant microstructures. In weld metal of composition 0.12wt% C, 1.35wt% Mn, 0.29 wt% Si, 0.03 wt% Nb reducing the oxygen content from about 300 ppm to about 60 ppm decreased the transformation initiation temperature by about 30° C and changed the microstructure from acicular ferrite to parallel lath ferrite. In weld metal of composition 0.1 wt% C, 0.8 wt% Mn, 0.1 wt% Si, 0.01 wt% Nb reducing the oxygen content from about 600 ppm to about 300 ppm decreased the transformation initiation temperature by approximately 20° C and favoured the development of ferrite side-plates and acicular ferrite at the expense of the polygonal ferrite microstructure. In both weld metals the depressed transformation temperature is thought to be due to the larger γ-phase grain size developed when the volume fraction of small de-oxidation products is reduced. The marked microstructural change from fine-grained acicular ferrite to parallel lath ferrite which occurred when virtually all the de-oxidation products were removed suggests that these small de-oxidation products may also be of fundamental importance to the nucleation of acicular ferrite.
TL;DR: In this article, the deformation-fracture pattern during contact with a Vickers pyramid is described, and a precursor stage of stable growth is observed prior to attaining a failure configuration, consistent with augmentation of applied tensile loading by the residual contact component.
Abstract: The micromechanics of indentation-induced flaws in monocrystalline silicon have been studied in relation to strength determination. In the first part, the evolution of the deformation-fracture pattern during contact with a Vickers pyramid is described. Emphasis is thereby placed on the vital role of the residual component of the elastic-plastic contact field in driving the cracks. In the second part, the response of the cracks in subsequent strength testing is followed. A precursor stage of stable growth is observed prior to attaining a failure configuration, consistent with augmentation of the applied tensile (flexural) loading by the residual contact component. No detectable slow crack growth due to environmental influence is found. Nevertheless, silicon is revealed as a material of extreme susceptibility to brittle fracture, with significant strength degradation from contacts on the microscale. The relevance of this brittleness to the mechanical behaviour of silicon components as a function of fabrication and prospective service conditions is discussed.