Showing papers on "Ultimate tensile strength published in 1975"

Continuous silicon carbide fiber of high tensile strength

Abstract: Continuous silicon carbide fiber of high-tensile strength (about 350 Kg/mm2) was synthesized by means of the heat-treatment of organosilicon polymer obtained from dodecamethylcyclohexasilane. X-ray analysis and high voltage electron microscopic observations revealed that the obtained continuous fiber is an ultrafine grain structure of β-silicon carbide.

Uniaxial Failure of Composite Laminates Containing Stress Concentrations

Abstract: Two previously developed failure criteria for predicting the uniaxial tensile strength of a laminated composite containing through-the-thickness material discontinuities (notches) are subjected to further experimental scrutinization. In particular, the two-parameter (unnotched tensile strength of the laminate and a characteristic length) models, which are capable of predicting observed discontinuity size effects without resorting to the concepts of linear elastic fracture mechanics, are based on limited experimental verification. In the present paper, and experimental program is presented which examines the effect of changes in the material system, the laminate fiber orientations, and the notch shape and size (stress gradient), on the model predictions. This is accomplished by obtaining experimental data on two material systems, glass/epoxy and graphite/ epoxy, in conjunction with two orientations of fiber-dominated laminates containing through-the-thickness circular holes and sharp tipped cracks of several sizes. In addition to the test results, two observations based on the models are presented. First, the statistical failure distribution for a composite containing a circular hole is predicted using the models and shown to agree well with experimental observations. Second, an Irwin type correction factor applied to the stress intensity factor is shown to result in nearly constant values of the critical stress intensity factor for all values of crack length. The correction factor is shown to be related to the characteristic length of the present models.

The concept of one polymer composites modelled with high density polyethylene

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.

Dynamic Response of Anisotropic Laminated Plates Under Initial Stress to Impact of a Mass

Abstract: : The central impact of a mass on a simply-supported laminated composite plate under initial stress is investigated. The contact force and the dynamic response of the plate are obtained by solving a non-linear integral equation. The energy transferred from the mass to the plate during impact is also obtained by use of a normalized contact force. It is found that a higher initial tensile stress elevates the maximum contact force, but reduces the contact time, the deflection, and the stresses. It is also noted that a higher tensile initial stress results in less energy transfer from the striking mass to the plate.

Tensile and creep strengths of hot-pressed Si3N4

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.

The Deformation of aluminum foams

Abstract: The compressive flow behavior of Al, Al−7 pct Mg and 7075 Al alloy foams has been determined in structures whose void fraction varies from 0.80 to 0.95 of the total volume. In all cases, a greater than linear increase in flow strength with increase in density was exhibited, indicating that bending stresses within the foam structure are an important feature of the collapse mode. The flow strength did not follow proportionately changes in bulk flow strength in comparisons of either alloy or of heat-treatment conditions. Ancillary tensile and metallographic observations show that this lack of correlation arises because the different foams collapse by different modes with localized fracture becoming dominant in the higher strength 7075 alloy. The energy absorbing efficiency was found to be independent of foam density for all the materials. However, the efficiency was found to be a strong function of the alloy and heat treatment increasing from about 30 pct in Al, to 43 pct in Al−7 pct Mg and to 50 pct in the solution heat treated and aged 7075 alloy. The increase in efficiency occurs because of an increase in the propensity to fracture in the higher strength alloys which introduces the potential for a propagating constant-stress collapse process.

The compression strength of unidirectional carbon fibre reinforced plastic

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.

Estimation of mechanical properties for rigid polyurethane foams

Abstract: Rigid plastic foams find application in construction mainly as core materials for loaded sandwich structures—in buildings, ground vehicles, and airplanes. This work provides an equation for the mechanical behavior of polyurethane foams as a function of foam density. Starting from a model conception and the qualitative microscopic consideration of the deformation and failure mechanism, simple relations are found for the tensile, compressive and shear strength and the elastic modulus, which sufficiently express the measured results.

Intermittent bonding for high toughness/ high strength composites

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.

Structural analysis in continuous silicon carbide fiber of high tensile strength

Abstract: The starting material of a continuous silicon carbide fiber with very high tensile strength is a polycarbosilane. It begins to decompose from 300°C in vacuum and is gradually converted into a β-silicon carbide fiber by the heat-treatment at the temperature above 800°C.

Root strength in some Populus and Salix clones

Abstract: The tensile strength of the roots of six Populus and Salix clones, and its relation to their anatomy and chemical composition, was investigated to assist selection of improved varieties for soil conservation planting. The amount of stele in the roots and its specific gravity were the most important factors determining tensile strength. Variation in specific gravity accounted for 79% of the intra-clonal variation in the tensile strength of the stele, and was also correlated with inter-clonal and seasonal variation. Fibre wall strength and specific tensile strength were correlated with S2 microfibril angle intra-clonally, cellulose content inter-clonally, and the lignin/cellulose ratio seasonally. The load required to break the roots did not increase linearly with the diameter of the roots. The results show that, in future, tensile testing is not essential in the selection of clones with the strongest roots, because these can be identified from the amount of stele in their roots and its specific gr...

Cast vs. wrought cobalt‐chromium surgical implant alloys

Abstract: The measured tensile and fatigue strengths of wrought and heat-treated cobalt chromium-molybdenum-carbon alloys such as HS21 were found to be more than twice those of as cast alloys of the same composition. The resistance of wrought HS21 to crevice corrosion at metal-Teflon contacts in isotonic salt solution at 37 degrees C was found to be considerably greater than that of cast HS21, wrought HS25, wrought MP35, or 316L stainless steel which are currently used for surgical implants. The increased crevice corrosion resistance and mechanical strength of wrought HS21 as compared to as cast HS21 was attributed to greater chemical and structural homogeneity as well as to finer grain size and distribution of secondary phases. Fabrication of shaped implants from wrought HS21 is possible by techniques currently used for the fabrication of industrial parts from other wrought cobalt-chromium base alloys.

The tensile and fatigue behaviour of Kevlar-49 (PRD-49) fibre

Abstract: The tensile, creep and tension-tension fatigue properties of Kevlar-49 fibre (formerly known as PRD-49) have been determined. The fracture morphology of the fibre has been examined and is shown to be complex due to considerable splitting. The fibre quickly stabilizes under a steady load but failure due to creep can occur when it is loaded very near to its simple tensile breaking load. Kevlar-49 has been found to fail by fatigue, and its fatigue lifetime is dependent on the amplitude of the applied oscillatory load as well as the maximum load to which the fibre is cycled.

Multiple Failure State and Strain Controlled Triaxial tests

Abstract: In this paper new methods are reported for the determination of the triaxial compressive strength of rocks. The “Multiple Failure State Test” with several single failure states in the same specimen, represents an extension of the classical testing procedure. The “Strain Controlled Test” is based, however, on a new concept and permits the determination of the failure envelope for a single test specimen. This type of test yields in addition useful information concerning the influence of changing lateral pressures and the influence of plastic deformations on the ultimate strength. A large number of tests with the different experimental methods and on several types of rock show good agreement in the results for the peak strength of intact rock as well as for the residual strength in the broken condition.

Viscoelasticity of polystyrene melts in tensile creep experiments

Abstract: An apparatus for measuring properties of polymer melts in tensile creep is described. Elongational viscosityµ, recoverable straine 0 , and complianceD 0 in the steady-state of deformation are determined from the creep curves of ten polystyrene samples with various molecular weights and molecular weight distributions. The elongational viscosityµ is three times the zero shear viscosity in the stress independent region. It decreases slightly for larger stresses. The temperature dependence of the viscosity is found to be the same in shear and elongation. The recoverable deformatione r 0 is independent of temperature but increases with stress. It follows thatµ 0 is an exponential function of molecular weight whereasD 0 reflects the molecular weight distribution.

Tensile strength and work hardening of ultrafine‐grained high‐purity copper

Abstract: Sputter‐deposited high‐purity copper specimens with grain sizes from 8.4 to 0.056 μm were tested in tension to investigate the influence of grain size on yield strength for small grain sizes. The smallest grain size in the sputter‐deposited copper was a factor of 40 smaller than the smallest grain size previously available for yield‐strength–grain‐size studies of high‐purity copper. The 0.2% offset yield strengths varied from 73.4 MPa for the coarsest‐grained copper to 481 MPa for the finest‐grained copper. The hardening was related to grain‐ and twin‐boundary spacings. The yield strength obeyed the Hall‐Petch relation even for the finest grain size of 0.056 μm, giving σy=6.39+3.74(l)−1/2 MPa, where σy is the 0.2% offset yield strength and l is the mean intercept length (mm) between boundaries. The data agreed with the Ashby model, σ∼ (e/l)1/2, only at very low strains (e<0.001) for the specimens with very fine grain sizes (l⩽0.077 μm).

Properties of polypropylene-polyethylene blends

Abstract: High-density polyethylene (PE) and isotactic polypropylene (PP) were melt-blended in the following percentages of PE by weight: O, 10, 33.3, 40, 50, 66.6, 90, and 100. For these blends we obtained data on shear stress vs shear rate; tensile modulus and strength; density; and rates of water-vapor transmission for films. The shear-rate/shear-stress data at 190 and 210°C are well fitted by the Ellis model with a maximum relative error of 5 percent. At 190°C all the mixtures were found to exhibit flow instabilities at high shear rates except the 90 percent and pure PE compositions. These, however, were unstable at 140, 150, and 160°C. The 10, 33.3, 40, 50, and 66.6 percent PE mixtures ruptured at elongations of less than 15 percent at the maximum tensile stress. The maximum tensile strength and modulus pass through maxima at 10 percent PE. Density is given by the equation ρ = 0.9029 + 0.0544 (wt fraction PE). Water-vapor permeability was measured using wax-sealed permeability cups, according to ASTM E96-66. Valid results were obtained for only a few compositions because of faulty seals that could be detected only during careful dismantling of the specimen dishes. Faulty seals could account for the value, about ten times ours, reported in the literature for linear PE.

The crystallization and interfacial bond strength of nylon 6 at carbon and glass fibre surfaces

Abstract: The nucleation and crystallization of nylon at the interface in glass-fibre and carbon-fibre reinforced nylon 6 composites has been investigated by electron microscope studies of sectioned and etched bulk specimens and solution cast and melt crystallized thin films. The fracture energies of the composites were obtained from tensile strength tests and the interfacial bond strengths were calculated from fibre pullout measurements. The fibres are shown to nucleate a columnar structure at the interface with marked differences between the structures nucleated by glass fibres and by carbon fibres and also between that nucleated by type I and type II carbon fibres. The structure around glass fibres was non-uniform and influenced to some extent by the presence of the size coating on the fibre surface. In the carbon-fibre composites the columnar structure was due primarily to physical matching of the graphite crystallites. Surface treatment of the carbon fibres to improve chemical bonding is shown to have a significant effect on bond strength which cannot be explained in terms of the columnar structure at the fibre surface. The treated fibres gave rise to only small amounts of fibre pull-out and low fracture energies whereas the untreated fibres showed extensive pull-out which was reflected in high fracture energies.

The pressure and temperature effects on brittle‐to‐ductile transition in PS and PMMA

Abstract: : Tensile experiments in polystyrene (PS) and poly(methyl methacrylate) (PMMA) conducted at constant strain rate over a wide range of pressure and temperature have shown that a brittle to ductile transition is induced in these amorphous polymers by the superposition of hydrostatic pressure as well as by the raise of the experimental temperature. A detailed stress-strain analysis permits explanation of the mechanism for the brittle to ductile transition in terms of interaction between two competing processes of plastic yielding -- crazing and shear banding phenomena. The crazing and shear banding processes respond quite differently to changes of pressure or temperature. The evidence that the brittle to ductile transition pressure becomes lower with increasing temperature refutes a previously suggested concept that the transition relates primarily to mechanical relaxation phenomena.

Residual strength characterization of laminated composites subjected to impact loading

Abstract: : An analogy between damage inflicted by a single point hard particle impact and damage inflicted by inserting a flaw of known dimensions in a static tensile coupon is discussed. The results suggest that residual strength can be predicted as a function of kinetic energy of impact by executing two experiments, a static tensile test on an unflawed specimen and a static tensile test on a coupon previously subjected to a single point impact. The model appears to be accurate for impact velocities which are less than the penetration velocity. For velocities above complete penetration, the residual strength is identical to the static strength of a coupon with a hole having the same diameter as the impacting particle. Comparison of various materials indicates that the impact strength of composite materials is strongly influenced by the strain energy to failure of the reinforcement. (Author)

The effect of polymerization conditions and crystallinity on the mechanical properties and fracture of spherulitic nylon 6

Abstract: The molecular and structural parameters controlling the mechanical properties, deformation and fracture of spherulitic nylon 6 have been investigated. The nylon was prepared by the anionic polymerization of e-caprolactam and the polymerization conditions were varied to give samples having a range of spherulite diameter, molecular weight and degree of crystallinity. The tensile properties and fracture mode of the nylon varied considerably with degree of crystallinity and polymerization temperature. High crystallinity and low polymerization temperatures below 423 K gave a brittle material. Polymerization above 423 K resulted in a ductile material which showed a yield drop. In this material final fracture was preceded by the formation of inter and trans spherulitic cracks which coalesced to form a large cavity that led to final failure. In nylon having a low degree of crystallinity, fracture was fibrillar in nature and occurred by the ductile drawing of the material to strains greater than 250%.

Polyurethane—polystyrene interpenetrating polymer networks

Abstract: Two component interpenetrating polymer networks (IPN) of the SIN type (simultaneous interpenetrating networks), composed of a polystyrene network (crosslinked with divinyl benzene) and a polyester-polyurethane network (crosslinked with trimethylolpropane), were made. Electron microscopy and glass-transition measurements showed that phase separation had resulted with some interpenetration, presumably occurring at the boundaries. At a composition of about 75 percent polyurethane, a phase inversion occurred, the continuous phase being polystyrene at polyurethane compositions of less than 75 percent. The stress-strain properties and hardness measurements agreed with these results. Enhanced tensile strength was observed in the IPN's in a concentration range where modulus reinforcement was not evident. A small enhancement in tear strength and thermal stability was also noted.