Showing papers on "Ultimate tensile strength published in 1982"

Restorative resins: hardness and strength vs. quantity of remaining double bonds

Abstract: It has been hypothesized that the Wallace indentation hardness of smooth surface resins is a factor of prime importance for the abrasion by food of Class 1 restorations. In the present work factors affecting the hardness of polymers were investigated. In addition the tensile strength of composite resins was measured and related to the catalytic system of the polymer. It was found that for a given composition of the monomer the Wallace hardness number increased with increasing content of inhibitor, decreased with increasing content of peroxide, and was unaffected by changes in the content of amine. The hardness was well correlated with the quantity of double bonds remaining in the polymer. BISGMA-based polymers showed no variation in hardness when the originating monomer varied with respect to content of a bi- or a trifunctional diluting monomer. Light-polymerized polymers were relatively hard as compared to chemically cured materials of adequate setting time. The tensile strength of composite resins was predominantly determined by the monomer content of peroxide and increased herewith. The tensile strength was well correlated with the quantity of remaining double bonds in the constituting polymer.

The response of solids to elastic/plastic indentation. I. Stresses and residual stresses

Abstract: A new approach for analyzing indentation plasticity and for determining indentation stress fields is presented. The analysis permits relations to be established between material properties (notably hardness, yield strength, and elastic modulus) and the dimensions of the indentation and plastic zone. The predictions are demonstrated to correlate with observations performed on a wide range of materials. The indentation stress fields are computed along trajectories pertinent to three dominant indentation crack systems: radial, median, and lateral cracks. The peak load and residual tensile stresses are shown to be consistent with observed trends in indentation fracture.

Strength of the cement-bone interface.

Abstract: The fixation of total joint components to bone using acrylic bone cement is by the penetration of the cement into the microstructure of cancellous bone to achieve a mechanical interlock. It has been shown that the method of cement application and the preparation of the cancellous surface significantly affects both the tensile and shear strengths of the cement-bone interface. Doughy cement finger-packed on an uncleaned surface resulted in a very low interface strength compared to a low-viscosity cement made to penetrate a cleaned bone surface. Maximum strengths were achieved for cancellous bone cleaned by using either a high-intensity water lavage or a polyethylene brush and by facilitating penetration of the cement for distances of 5 to 10 mm into the bone.

FRP-encased concrete as a structural material

Abstract: Synopsis Plastics reinforced with continuous glass fibres have outstanding tensile strength in the fibre direction and excellent corrosion resistance, but are characterized by low modulus and low compressive strength. It is proposed to develop composite members in which a prefabricated FRP (fibreglass-reinforced-plastic) casing is used initially as the form to cast plain concrete, and thereafter to confine the concrete, act as tensile reinforcement and provide corrosion protection. Significant cost savings are possible with the proposed combination of materials, especially in exposed structures, such as bridges. An experimental investigation of FRP-encased concrete cylinders in axial compression and of rectangular FRP-encased beams in bending is presented. The results demonstrate the excellent strength and ductility characteristics of FRP-encased members. The behaviour of circular FRP-encased concrete beam-columns is described also, in terms of analytically obtained moment-axial-load and ductility-axial-l...

Relationship between the tensile properties of articular cartilage from the human knee and age.

Abstract: The relationship between the tensile properties of articular cartilage and age has been investigated in vitro in the human knee joint. Specimens orientated parallel to the articular surface were excised from the superficial and deep zones of the femoral condyles of knee joints of persons in the age range from 8 to 91 years. The results showed that the tensile strength of the superficial zone increased with age to reach a maximum value in the third decade. Thereafter the strength decreased markedly with increasing age. The tensile strength of cartilage from the deep zone did not show an increase in the early years but decreased continuously with age. The tensile stiffness of the superficial layer at stresses of 5 MN/m2 and 10 MN/m2 increased to maximum values in the third decade and thereafter decreased with increasing age. The stiffness of the deep zone decreased continuously with age. It is suggested that these results reflect changes in the organisation of the collagen fibre mesh with age and possibly also changes in the collagen cross-links.

Structure property studies of fibres from various parts of the coconut tree

Abstract: Fibres from different structural parts of the coconut palm tree (Cocos nucifera, linn.) have been examined for properties such as size, density, electrical resistivity, ultimate tensile strength, initial modulus and percentage elongation. The stress-strain diagrams, fracture mode, microfibrillar angle as well as cellulose and lignin contents of these fibres have been determined. The observed properties have been related to the internal structure and chemical composition of the fibres. Some potential uses of these fibres have been listed.

Process for producing a high strength porous polytetrafluoroethylene product having a coarse microstructure

Abstract: Porous polytetrafluoroethylene materials having high strength and coarse microstructure are produced by densifying the materials after removal of lubricant and then stretching. The term, "coarse," is used to indicate that the nodes are larger, the fibrils are longer, and the effective pore size is larger than conventional materials of the same matrix tensile strength. Densification can be achieved through the use of such devices as a densification die, a calender machine, or a press. This invention can be used to produce all kinds of shaped articles.

Tensile Strength of Unidirectionally Reinforced Composites — I

Abstract: Between 1964 and 1980 most micromechanical analyses of composite strength have been based on the chain-of-bundles model. The present in vestigation abandons this model and concentrates instead on the formation and growth of multiple fiber fractures (cracks). This permits treating interac tion of cracks in different bundles and assignment of different ineffective lengths to fiber breaks of different multiplicity.Weakest link theory is used to determine the number of isolated fiber frac tures (singlets), double fractures (doublets), and multiplets of arbitrary order as a function of stress. It turns out that if the fracture of individual fibers obeys Weibull's equation, a plot of nQi vs lnσ is a straight line of slome im. Here o is applied stress, Qi is the number if i-plets formed during loading to stress σ, and m is the Weibull modulus. The envelope of the Qi curves serves as a failure line. Use of the failure line leads directly to a rational failure criterion based on a Griffith-type instability and sho...

Mechanical properties of Fe-Si-B amorphous wires produced by in-rotating-water spinning method

Abstract: Amorphous wires with high strength and good ductility have been produced in Fe-Si-B alloy system by the modified melt-spinning technique in which a melt stream is ejected into a rotating water layer. These wires have a circular cross section and smooth peripheral surface. The diameter is in the range of about 0.07 to 0.27 mm. Their Vickers hardness (Hv) and tensile strength (σf) increase with silicon and boron content and reach 1100 DPN and 3920 MPa, respectively, for Fe70Si10B20, exceeding the values of heavily cold-drawn steel wires. Fracture elongation(e f ), including elastic elongation, is about 2.1 to 2.8 pct. An appropriate cold drawing results in the increase of σf and ef by about eight and 65 pct, respectively. This increase is interpreted to result from an interaction among crossing deformation bands introduced by cold drawing. The undrawn and drawn amorphous wires are so ductile that no cracks are observed, even after closely contacted bending. Further, it is demonstrated that the σf of the Fe75Si10Bl5 amorphous wire increases by the replacement of iron with a small amount of tantalum, niobium, tungsten, molybdenum, or chromium without detriment to the formation tendency of an amorphous wire. Such iron-based amorphous wires are attractive as fine gauge, high strength materials because of their uniform shape and superior mechanical qualities.

The Confined Compressive Strength of Polycrystalline Ice

Abstract: Triaxial tests were carried out on randomly oriented, laboratory-made, polycrystalline ice, between strain-rates of 10–7 and 10–1 s–1 and with confining pressures from 0.1 to 85 MN m–2, at –11 ± 1°C. Below strain-rates of about 10–5 s–1 the confining pressure has little effect, but at higher strain-rates the confining pressure prevents cracking which allows the compressive strength to rise to a value greater than the unconfined compressive strength. At 1.4 ×10–2 s–1, the unconfined strength of 12 MN m–2 rises to 26 MN m–2 with a confining pressure of 25 MN m–2, before dropping slowly with greater confining pressures. Above 10–2 s–1 the unconfined strength decreases rapidly with increasing strain-rate, but the confined strength continues to increase. The dependence of strain rate on the maximum compressive stress is discussed.

Solvent Effects on Bonding Organo-silane to Silica Surfaces:

Abstract: Interfacial bonding and stability of gamma-methacryloxypropyltrimethoxysilane with silica surfaces have been studied by means of infrared spectroscopy The addition of n-propylamine enhances silanization of gamma-methacryloxypropyltrimethoxysilane to silica surfaces in normal aliphatic hydrocarbons, and cyclohexane yields a more water-resistant silica-silane bond, and improves the diametral tensile strength of the composite

Apparatus and method for protection of electrical contacts

Abstract: An apparatus and method for protection of electrical contacts. The protection apparatus ensures that the electrical contacts are protected when they are otherwise located in an adverse environment. To this end, the protection apparatus includes an insulating gel that is characterized by a cone penetration value from approximately 150 to 350 (10 -1 mm); an ultimate elongation of at least approximately 200%; a maximum tensile strength of approximately 20 psi; and a cohesive strength greater than its adhesive strength. The protection apparatus further includes a first means to contain the gel, a second means to retain the gel within the first means and a force means which acts on the first means so that the gel is maintained in compressive contact with the electrical contacts and substantially encapsulates a conductive portion of the electrical contacts.

Deformation characteristics of dual-phase steels

Abstract: An investigation was made to determine the effect of volume fraction of martensite on the strength, ductility, and fracture behavior of dual-phase steels. For both V-and Mo-bearing alloys, a linear relationship was found to exist between the amount of martensite and both tensile strength and uniform elongation. Contrary to previous reports that predict microcracking of martensite above 0.2 volume fraction to be responsible for a drop-off in ductility, no martensite cracking was found. Fracture was caused by void formation at small inclusions or at the ferrite/martensite interface. In severely banded structures, the strength/ductility relationship was detrimentally affected because of the tendency for crack propagation in the less ductile martensite without the cracks being blunted by the ferrite matrix.

The importance of root strength and deterioration rates upon edaphic stability in steepland forests

Abstract: The additional strength provided by roots to the soil is generally considered to be in the form of a cohesive strength hC which may range in magnitude from 1 kPa to 20 kPa. Studies of the tensile strength of tree roots show that small roots sampled from living trees range in mean tensile strength from about 10 MPa to about 60 MPa. After tree felling small roots lose their strength at average rates between 300 and 500 kPa per month. Root biomass also decreases rapidly after clearfelling. The reduction in K after forest removal is a prime cause of landsliding on many steep slopes.

A method for fabrication of aluminum-alumina composites

Abstract: A process was used to produce Al-Mg alloy composites containing discontinuous A12O3 fibers. In the first step of the process, induced convection of the melt permits intimate contact between the fibers and the melt which invariably results in chemical interaction between the two. The presence of MgAl2O4 spinel on the fiber surface was confirmed. The composites produced contained randomly distributed fibers and were further processed both to increase the volume fraction of fibers and to align them in two dimensions (planar random alignment). Examination of composite specimens fractured under tension indicated that the interfaces were strong enough to permit transfer of load from the matrix to the fiber. For example, modulus of elasticity and ultimate tensile strength of the alloy were improved approximately 50 pct and 40 pct, respectively, by the addition of 23 vol pct A12O3 fibers.

Tensile strength of highly oriented polyethylene. II. Effect of molecular weight distribution

Abstract: The tensile strength of oriented polyethylene filaments is discussed in relation to molecular weight. Short-term tensile properties at room temperature were obtained in our laboratory and from the literature for polymer samples covering the molecular weight (Mw) range from 54 × 103 to 4 × 106, and polydispersities ranging from 1.1 to 15.6, oriented by solid-state extrusion, melt spinning/drawing, solution spinning/drawing, and “surface growth.” It was found that both the molecular weight and its distribution markedly affected tensile strength. The breaking stress σ of highly oriented fibers varied with molecular weight roughly as σ ∝, M0.4, at constant Mw/Mn over the entire range studied. Reduction of polydispersity from 8 to 1.1 by an increase of Mn with Mw approximately constant at 105 increased tensile strength of oriented polyethylene filaments by a factor of nearly 2.

Kinking and compressive failure in uniaxially aligned carbon fibre composite tested under superposed hydrostatic pressure

Abstract: Initiation and propagation of failure in uniaxially aligned 60% volume-fraction Type III carbon fibre-epoxide compressive specimens, strained parallel to the fibre axis, was studied at atmospheric and superposed hydrostatic pressures, H, extending to 300 MN m−2. The atmospheric axial compressive strength was approximately 1.5 GN m−2 and equal to the tensile strength, but mechanisms involving shear-operated failure of the fibres must be discounted since the failure process was very pressure sensitive above H∼ 150 MN m−2. The results also could not be satisfactorily interpreted by theories involving micro-buckling of individual fibres or laminae when the matrix shear modulus controls the compressive strength. For atmospheric tests and for H<150 MN m−2 the initiation of failure was associated with transverse cracking (longitudinal splitting) which was followed by kinking. Ahead of the propagating kink band, groups of fractured fibres were observed, which is consistent with failure of these groups by buckling; this process causes composite catastrophic failure. At higher pressures splitting was suppressed, as was interlaminar cracking in doubly-notched (in-plane shear) specimens, but kinking, which became increasingly more difficult to initiate, was the precursor of the failure process. An attempt was made to analyse failure using the fracture mechanics model of Chaplin with some success for the notched specimens.

Deformation modes of the α-phase of ti-6al-4v as a function of oxygen concentration and aging temperature

Abstract: The tensile properties of lamellar Ti-6A1-4V and the deformation modes of the α-phase of this alloy were investigated as a function of oxygen concentration and as a function of aging heat treatment. Oxygen affects the mechanical properties through microstructural modifications which depend on the choice of aging parameters. The variations in Young's modulus, yield strength, ultimate tensile strength, and ductility, are correlated with α/β volume ratio and with α-deformation characteristics. Homogeneityvs inhomogeneity of slip, change of the predominant slip modes from prismatic slip to fine planar slip on pyramidal planes, and the occurrence of Ti3Al precipitates influence the deformation behavior of the α-phase and thus influence the mechanical properties of the alloy. The deformation behaviors of the lesser β-phase regions were not investigated, and only speculations can be made on the extent of their influence on the alloy's mechanical properties.

A Study of the Deformation and Fracture of a Dual-Phase Steel

Abstract: A metallographic study of the tensile deformation and fracture of a commercial dual-phase steel shows that extensive plastic deformation of the martensite occurs mainly in the neck of the tensile specimen. The average load-transfer stress in martensite was roughly calculated from a shear-lag model, and it was found that it exceeds the estimated martensite yield stress value at strains corresponding to the ultimate uniform elongation, and beyond. Ductile fracture begins with void formation at martensite-ferrite interfaces, most frequently at the poles of closely spaced martensite particles situated on ferrite grain boundaries. Large inclusions and martensite banding also affect the fracture process.

Behavior of discontinuous fiber composites: Fiber orientation

Abstract: The behavior of polymeric materials reinforced by discontinuous. Descriptors for the planar and axial orientation distributions are discussed. Predictions of micromechanical models and experimental data are presented to illustrate the influence of orientation state upon elastic constants, thermal coefficients of expansion and tensile strength. Results are presented for the notched strength and compressive creep behavior of the glass/phenolic composite of two orientation states. Finally, the implications of these results upon the design of elements molded of discontinuous fiber composites are discussed.

The effect of addition of high-density polyethylene on the crystallization and mechanical properties of polypropylene and glass-fiber-reinforced polypropylene

Abstract: High-density polyethylene up to about 30% by weight was melt-mixed with polypropylene and short-glass-fiber-reinforced polypropylene. The presence of high-density polyethylene and glass fibers in the polypropylene matrix affects its crystallization characteristics, which were studied with the help of differential scanning calorimetry. The blend and composite samples have a large number of polypropylene domains apparently due to an abundance of surface nuclei; as a result, the tensile strength, tensile modulus, and toughness are enhanced. The temperature dependence of shear modulus and logarithmic decrement indicate that high-density polyethylene can have plasticizing effect below the glass transition temperature of polypropylene. The scanning electron micrographs of fractured ends show the presence of dispersed domains in the composite samples.

The effect of pH on the in vitro degradation of poly(glycolide lactide) copolymer absorbable sutures

Abstract: The pH effect on the hydrolytic degradation of Polyglactin 910 copolymer was studied in terms of the tensile properties of the suture specimens. The use of a cord/yarn grip, newly designed specifically for fibrous materials, eliminated the grip-induced failure. Different degrees of hydrolytic degradation of this copolymer at 3 different pH levels were observed. The suture specimens exhibited the best retentions of breaking strength at the physiological pH of 7.44, while the specimens at pH = 10.09 showed the fastest loss of breaking strength. Thus, a maximum retention of tensile properties occurred around the pH level of 7.0, whereas smaller percentages of retention of tensile properties were observed at both acidic and strong alkaline solutions. This synthetic absorbable suture material exhibits the basic characteristic of hydrolysis which is catalyzed by both acid and base.

Three-Parameter Failure Criterion for Concrete

Abstract: A general, three-dimensional failure criterion for plain concrete and mortar is proposed. This criterion is formulated in terms of the first and the third stress invariants of the stress tensor, and it involves only three independent material parameters. Although these parameters interact with one another, each parameter corresponds to each of three failure characteristics of concrete behavior. These material parameters may be determined from simple tests such as uniaxial compression and triaxial compression or biaxial tests. For the purpose of including reasonable values of tensile strengths in the failure criterion, it is advisable to include the uniaxial tensile strength in the parameter determination. A simple expression for evaluation of the uniaxial tensile strength on the basis of the uniaxial compressive strength is given. Twenty-two sets of good quality data for concrete and mortar have been included in this study, and comparisons between the proposed failure criterion and the experimental data are made in biaxial, triaxial, octahedral, and τ\N - σ\N planes. The ability of this criterion to capture the characteristics of failure in concrete and mortar appears to be quite good with accuracies generally within the natural scatter of the test data.

Influence of layer thickness on the strength of angle-ply laminates

Abstract: Experimental results are presented showing that the strength and toughness of finite width angle-ply laminates can be increased significantly by using an alternating layer stacking sequence as opposed to a clustered configuration. The ultimate tensile stress of an alternating plus/minus theta laminate of the form (+ or - theta) sub 2 sub s can be much as 1.5 times that of a clustered configuration of the form theta sub 2/-theta sub 2 sub s. Further, the toughness of the alternating layer configuration can be as much as 2.7 times that of the clustered configuration. These differences are explained analytically through consideration of the influence of layer thickness on the magnitude of the interlaminar shear stress and by examination of failed specimens. It is shown that the two laminate configurations exhibit distinctly different failure modes for some fiber angles. Both laminate configurations exhibit catastrophic failure with the damage limited essentially to a small region defined by the length of a single crack across the width of the specimen, parallel to the fiber direction. Results are presented for T300/5208 graphite-epoxy for fiber orientations of 10, 30, and 45 deg.

Short Jute Fiber Reinforced Carboxylated Nitrile Rubber

Abstract: Silica is not an essential component in the bonding system in XNBR-jute fiber systems. Mechanical anisotropy is observable only at the higher fiber loadings (40 phr and above) in XNBR-jute fiber composites. In composites containing sufficient amounts of bonding agent and fibers for tensile-strength anisotropy to be observed, tensile failure occurs by both fiber breakage and debonding. Fibers increase the aging resistance of XNBR composites. Mill shrinkage and green strength of XNBR improve, while Mooney viscosity increases and scorch time decreases with the addition of jute fiber to XNBR.

A comparison of the effect of pH on the biodegradation of two synthetic absorbable sutures.

Abstract: The differences in hydrolytic degradation of two size 2-0 synthetic absorbable sutures, Polyglycolic acid (Dexon) and Poly(glycolide-lactide) (Vicryl), in the buffer media of three different pH levels ranging from 5.25 to 10.09, were compared in terms of the percentage retention of tensile strength. It was found that Vicryl sutures, in general, exhibited better retention of tensile strength than Dexon sutures within the studied pH range and extent of hydrolysis. When comparing Vicryl with Dexon sutures, the former was only slightly better than Dexon sutures, in the case of an acid environment. The former, however, retained better strength than the latter in a physiological pH (7.44) and under high-alkaline conditions (10.09). Among the three pH levels tested, Vicryl sutures retained the highest tensile strength in a physiological pH and showed a faster loss of tensile strength in both acidic and high-alkaline conditions. Dexon sutures, however, exhibited better retention of tensile strength in the acidic medium than in an alkaline medium. This pH dependent hydrolysis of Dexon and Vicryl sutures should command surgeons' attention in their selection of synthetic absorbable suture materials for particular needs.