Showing papers on "Ultimate tensile strength published in 1988"

Hydroxyapatite-coated titanium for orthopedic implant applications.

Abstract: The interface mechanical characteristics and histology of commercially pure (CP) titanium- and hydroxyapatite- (HA) coated Ti-6Al-4V alloy were investigated. Interface shear strength was determined using a transcortical push-out model in dogs after periods of three, five, six, ten, and 32 weeks. Undecalcified histologic techniques with implants in situ were used to interpret differences in mechanical response. The HA-coated titanium alloy implants developed five to seven times the mean interface strength of the uncoated, beadblasted CP titanium implants. The mean values for interface shear strength increased up to 7.27 megaPascals (MPa) for the HA-coated implants after ten weeks of implantation, and the maximum mean value of interface shear strength for the uncoated CP titanium implants was 1.54 MPa. For both implant types there was a slight decrease in mean shear strength from the maximum value to that obtained after the longest implantation period (32 weeks). Histologic evaluations in all cases revealed mineralization of interface bone directly onto the HA-coated implant surface, with no fibrous tissue layer interposed between the bone and HA visible at the light microscopic level. The uncoated titanium implants had projections of bone to the implant surface with apparent direct bone-implant apposition observed in some locations. Measurements of the HA coating material made from histologic sections showed no evidence of significant HA resorption in vivo after periods of up to 32 weeks.

Aluminum-Based Amorphous Alloys with Tensile Strength above 980 MPa (100 kg/mm2)

Abstract: New Al-based amorphous alloys with high strength and good ductility were produced in an Al-Y-Ni system by liquid quenching. The tensile fracture strength ( σf) and Vickers hardness reach 1140 MPa and 300 DPN for Al87Y8Ni5. The specific strength defined by the ratio of σf to density is as high as 38, being much higher than that for conventional alloy steels. The high-strength Al-base amorphous alloys are expected to attract strong attention as a new type of high-strength material with low density.

Composition dependence of tensile yield stress in filled polymers

Abstract: Examen de divers polymeres: ABS, polypropylene, polyethylene et diverses charges: verre, CaCO 3 , talc, silice, etc

Acceleration of Tensile Strength of Incisions Treated with EGF and TGF-β

Abstract: The ability of surgeons to accelerate wound healing through pharmacologic intervention is limited. The effects of locally applied, biosynthetic human epidermal growth factor (EGF) and transforming growth factor-beta (TGF-beta) on tensile strength of experimental incisions were investigated. A single dose of EGF in saline failed to increase tensile strength over controls. Thus, EGF was incorporated into multilamellar liposomes, which prolonged the exposure of incisions to EGF (p less than 0.001). A single dose of EGF in multilamellar liposomes produced a 200% increase in wound tensile strength over controls between 7 and 14 days (p less than 0.05). Light and electron microscopy of the wounds revealed increased collagen formation and fibroblast proliferation. A single dose of TGB-beta in a collagen vehicle stimulated a 51% increase in wound tensile strength at 9 days (p less than 0.01). We conclude that addition of EGF and TGF-beta in appropriate vehicles stimulates early transient increases in wound tensile strength in normal rats.

Plate separation and anchorage of reinforced concrete beams strengthened by epoxy-bonded steel plates

Abstract: This paper deals with the problem of Anchorage at the ends of steel plates glued to the tensile faces of reinforced concrete beams. A simple theoretical study of the force systems at the plate/glue and the glued concrete interfaces is presented. This suggests that high stress concentrations and peeling forces are present at the ends of the plates when the composite beam is loaded in flexure. Tests carried out to investigate the effectiveness of different Anchorage arrangements are described in detail. The results from these tests confirm that, at the ends of the plates, interface stress concentrations exist, which have limiting peak values in the region of root 2 x tensile splitting strength of the concrete. Theoretical interface bond stresses, based on simple elastic behaviour, are found to have no consistent relationship to the measured peak values. However, if the maximum (unreduced) plate thickness is always used in these calculations, a simple method is proposed for obtaining a reasonable assessment of the peak stress. The efficiency of the different Anchorage details is discussed, and it is shown that the use of additional glued anchor plates gives the best results. These plates overcome the problem of Anchorage failure and enable the full theoretical flexural strength to be achieved, together with ductile behaviour.(a)

Structure of skin layer in injection‐molded polypropylene

Abstract: The structure of skin layer in injection-molded polypropylen which displayed a clear two-phase structure of skin and core has been studied by means of wide-angle x-ray diffraction, small-angle x-ray scattering, melting behavior, density, dynamic viscoelasticity, and tensile test. In skin layer, the c-axis and a*-axis were highly oriented to the machine direction (MD), and the plane of the lamellar structure of about 160 A in thickness was in normal to MD. The density was about 0.907 g/cm3, which was nearly the same as that of core layer. Although the majority of crystallites melted in the same temperature range as in that of the core layer, there was about 5.3% higher temperature melting structure (Tm = 182°C). The dynamic tensile modulus E′ in MD decreased more slowly with increasing temperature than that of the core layer and held high modulus in the range of ca. 30°C, just above the temperature at which E′ of the core layer suddenly dropped. E′ in MD was higher than that in TD in the temperature range below 33°C, which was slightly higher than the primary absorption temperature, and the order reversed above 33°C. The tensile yield stress in MD was 1.5 times higher than that of the core layer. The skin layer in MD ruptured just after yielding and did not show necking. The tensile yield stress in TD was about half of that in MD about 0.7 times that of the core layer. The necking stress in TD was about 0.6 times that of the core layer. In general, a polypropylene melt crystallizes under a high shear stress in injection molding. From these facts, it was concluded that the skin layer is composed of so-called “shishkebab”-like main skeleton structures, whose axis is parallel to MD, piled epitaxially with a*-axis-oriented imperfect lamellar substructure.

Composite technology for total hip arthroplasty.

Abstract: Composite materials, which can be very strong while having a low modulus of elasticity, are being studied because such materials have potential to be made into isoelastic hip prostheses. Composites intended for medical applications incorporate carbon or polyamide as a fiber component, while polysulfone, polyetheretherketone, or polyethylene is used as a matrix component. Mechanical properties (especially the modulus of elasticity) are emphasized because of the desire to match those properties of the proximal femur. Many of the variables that affect the mechanical properties of these materials are explained. The application of stress to different fiber orientations demonstrates the mechanical properties of the composite, and this is proved mathematically. It is shown that in composites with fibers oriented in the same direction, the modulus of elasticity in the direction of the fibers generally approaches that of the fibers as the amount of matrix decreases. Perpendicular to the fibers, the modulus of elasticity of the composite is only slightly greater than that of the matrix material. For isotropic chopped-fiber composites, the modulus of elasticity approaches that of the matrix as the fiber content decreases; at high-fiber content, the modulus is significantly less than that of oriented long-fiber composites. In general, the modulus of elasticity and fiber content have a linear relationship. Composites have fatigue properties that vary with direction and approach ultimate strength in tension but are lower in compression. The fatigue properties of proposed composites are discussed. Abrasion as a cause of stress concentration sites and wear particles is considered.

Rising Fracture Toughness from the Bending Strength of Indented Alumina Beams

Abstract: The analytical function of crack extension to a fractional power is used to represent the fracture resistance of a vitreous-bonded 96% alumina ceramic. A varying flaw size, controlled by Vickers indentation loading between 3 and 300 N, was placed on the prospective tensile surfaces of four-point bend specimens, previously polished and annealed. The lengths of surface cracks were measured by optical microscopy. Straight lines were fitted to the logarithmic functions of observed bending strength versus indentation load in two series of experiments: (I) including the residual stress due to indentation and (II) having the residual stress annealed out at an elevated temperature. Within the precision of measurement these lines have the same slope, being about 32% less than the -1/3 slope which a fracture toughness independent of crack extension would indicate. Considering the criteria for crack extension and specimen failure, the fracture mechanics equations were solved for the conditions of the two series of experiments. Approximately the same values of fracture toughness, rising as a function of indentation flaw size, were obtained from both series of experiments.

Influence of Filler Type and Water Exposure on Flexural Strength of Experimental Composite Resins

Abstract: The objective of this investigation was to determine the influence of water exposure on the flexural strength of three experimental composite materials. The composites consisted of an experimental resin system which contained silane-treated filler particles of quartz, barium glass, and porous silica. The amorphous silica particles were spheres approximately 5 micron in diameter. In addition to the different composites, pure resin samples were investigated as a control group. The results of this investigation did not support the hypothesis that use of porous amorphous silica filler particles reduced the hydrolytic degradation effect of composites containing such silica particles. Instead, the results indicated that water may have a more detrimental effect on the strength of the matrix than on the filler-matrix interface. However, the relatively high frequency of fracture lines in the porous silica particles after storage in water indicate that water had a weakening effect on this type of filler.

Development of a new continuous Si−Ti−C−O fibre using an organometallic polymer precursor

Abstract: A polytitanocarbosilane, which is useful as the precursor polymer for ceramic fibre, was synthesized using polydimethylsilane, polyborodiphenylsiloxane and titanium tetraisopropoxide. The polytitanocarbosilane was melt-spun and using the continuous heat-treatment process from the polymer fibre to ceramic fibre, flexible Si-Ti-C-O fibre was produced. The density, tensile strength and Young's modulus of this amorphous ceramic fibre were found to be 2.35 g cm−3, 3.0±0.2 and 220±10 GPa, respectively. The Si-Ti-C-O fibre retained its high tensile strength to higher temperatures (about 1200° C). The specific resistance of this ceramic fibre covered a wide range of 107 to 10−1ωcm. This ceramic fibre is considered to be useful as reinforcement fibre for composites.

Cast metal matrix composites

Abstract: Metal matrix composites have been available in certain forms for at least two decades, e.g. boron fibre reinforced aluminium and various dispersed phase alloys and cermets. Recently, a range of alumina and silicon carbide fibres, whiskers, and particles with diameters <20 μm have become available. The possibilities of incorporating these materials into metals to improve stiffness, wear resistance, and elevated temperature strength without incurring weight penalties have attracted the attention of design engineers in the aerospace and automobile industries. The aim of the present paper is to outline the manufacturing processes for such composites, in particular those based upon liquid metal technology, e.g. squeeze casting and spray forming. Some of the mechanical and physical properties which have been determined for these materials are described. An analysis of how matrix alloy selection may influence tensile and fracture behaviour of short fibre and particle reinforced composites is attempted.MS...

Engineering Properties of Concrete Affected by Alkali-Silica Reaction

Abstract: A detailed study of the effects of alkali-silica reaction (ASR) on the engineering properties of concrete such as compressive and tensile strength, elastic modulus, and pulse velocity is presented. Two types of reactive aggregate - a naturally occurring Beltane opal and synthetic fused silica - were used. The tests wee carried out at 20 C and 96 percent relative humidity (RH). The results showed that losses in engineering properties do not all occur at the same rate or in proportion to the expansion undergone by the ASR-affected concrete. The two major properties affected by ASR were flexural strength and dynamic modulus of elasticity. Compressive strength was not a good indicator of ASR, but the flexural strength proved to be a reliable and sensitve test for mointoring ASR. Nondestructive tests like dynamic modulus and pulse velocity were also able to identify deterioration of concrete by ASR. The data indicate that critical expansion limits due to ASR would vary depending on the type and use of a concrete structure.

Coiled perimysial fibers of papillary muscle in rat heart: morphology, distribution, and changes in configuration.

Abstract: The morphology, distribution, and configuration of coiled perimysial fibers of rat heart papillary muscle were studied. Methods included bright-field light microscopy of silver-stained sections, scanning and transmission electron microscopy, and differential interference contrast light microscopy of unfixed and unstained specimens. Coiled fibers, elliptical in cross section, are arranged in a branched network that diverges from the muscle-tendon junction and is continuous throughout the length of the muscle and into the ventricle wall. Most fibers range in diameter from less than 1 micron to 10 micron and are parallel with the long axis of the muscle, although branching is common and oblique orientations are seen. Several myocytes are associated with each coiled perimysial fiber. Constituent fibrils (diameter, 40-50 nm) occur in bundles twisted within the fiber. Small satellite elastic fibers are parallel to the collagen fiber axes. Stereo analysis of the coiled perimysial fibers reveals helical configurations, as opposed to planar waviness, that become less convoluted or even straighten as the resting muscle is stretched. Calculations based on cross-sectional areas of fibers, changes in fiber configurations, and tensile moduli reported for collagen fibers of other tissues show that the potential tensile strength of the network of coiled perimysial fibers is sufficient to contribute significantly to the mechanical properties of papillary muscle. Detailed evaluations of possible roles of the coiled perimysial collagen fiber system as a function of passive stretch and contraction in ventricular wall, as well as in papillary muscle, warrant further study.

Strength and stiffness of ships' plating under in-plane compression and tension

Abstract: New data curves are presented describing the behavior of imperfect rectangular plates under uniaxial or biaxial longitudinal and/or transverse compression and tension. The data curves, developed by a combination of nonlinear finite element analysis and regression analysis of a large body of test results, provide a definition not only of plate strength (maximum load-carrying capacity) but also of effective stress-strain relationships throughout the tensile and compressive strain ranges, from which plating "effective widths" and "effective breadths" may be determined. In addition to mean plate stiffness and strength, upper and lower-bound stress-strain and strength curves are described.

Prediction of the compressive strength of vertebral bodies of the lumbar spine by quantitative computed tomography.

Abstract: The ultimate compressive strength of 36 thoracolumbar vertebrae was determined experimentally. In addition, the trabecular bone mineral content was measured by single energy quantitative computed tomography. The areas of fractured endplates were also determined by computed tomography. The results show that a linear relationship exists between the compressive strength and the product of bone density and endplate area. These data allow an in vivo prediction of vertebral body strength using a noninvasive method with a standard error of estimate amounting to less than 0.95 kN.

Residual Strength of a Carbon/Epoxy Composite Material Subjected to Repeated Impact:

Abstract: The residual tensile and compressive strengths of specimens cut from composite plates subjected to repeated impact at various energy levels were measured. The 16-ply quasi- isotropic composite plates were 2 mm thick, fabricated from Hercules AS4/3501-6 car bon/epoxy prepreg. Impact energy level and number of impacts were found to be major factors influencing strength degradation. However, strength degradation was limited to the region near the impact point.

Microstructure effects on tensile properties of tungsten-Nickel-Iron composites

Abstract: Controlled processing of heavy alloys containing 88 to 97 pct W resulted in high sintered densities and excellent bonding between the tungsten grains and matrix. For these alloys, deformation and fracture behavior were studiedvia slow strain rate tensile testing at room temperature. The flow stress increased and the fracture strain decreased with increasing tungsten content. The tradeoff between strength and ductility resulted in a maximum in the ultimate tensile strength at 93 pct W. Microstructure variations, notably grain size, explain sintering temperature and time effects on the properties. During tensile testing, cracks formed on the surface of the specimens at tungsten-tungsten grain boundaries. The crack density increased with plastic strain and tungsten content. The surface cracks, though initially blunted by the matrix, eventually increased in density until catastrophic failure occurred. An empirical failure criterion was developed relating fracture to a critical value of the surface crack tip separation distance. Application of the model explains the effects of microstructural variables on tensile properties.

Distribution of bone strength in the proximal tibia

Abstract: Indentation tests were used to determine the ultimate strength of the proximal tibia. Measurements were made at the subchondral bone surface and on transverse planes up to 25 mm below the surface. Medial condyles were stronger than lateral condyles, and in both cases bone strength decreased abruptly with distance from the surface, especially over the first 5 mm. The mean bone strength was greater in men than in women in both condyles, especially in the harder upper layers. The areas of greatest strength on both the medial and lateral sides varied with depth. At the surface, maximum strength in the medial region was more posterior in men than in women. With increasing depth, the area shifted medially in the medial region and laterally in the lateral region. Spatial distribution of strength across planes of the tibia seems consistent with anticipated patterns of load distribution in weight bearing and with the contiguity of the trabecular bone. The data are relevant to an understanding of normal joint mechanics and to the design and placement of prostheses in total knee arthroplasty.

The effect of fiber-matrix stress transfer on the strength of fiber-reinforced composite materials

Abstract: A model for the mechanism of tensile failure in oriented fiber composites based on random fragmentation of the reinforcing fibers biased by stress concentrations at fracture sites has been developed. Single-fiber composites and composite strands of 34 to 36 volume percent fiber were prepared from an epoxy resin reinforced with Hercules AS4, HMS4, and IM6G carbon fibers. Fiber strength distributions and single-fiber composite fragmentation data were used to calculate theoretical composite tensile strengths, which were then compared with experimental values. The fractures in single-fiber composites were observed in situ under cross-polarized light, and the mechanisms of interfacial failure were discussed.

Mechanical properties of concrete at low temperature

Abstract: Laboratory studies were conducted on concrete compressive and splitting tensile strength, modulus of elasticity, and Poisson's ratio and on the local bond strength between concrete and steel under ...

Tensile fracture of doubly-convex cylindrical discs under diametral loading

Abstract: Doubly-convex cylindrical gypsum discs have been fractured under the action of two diametrically opposed in-plane forces. The disc diameter was constant throughout the test series. The ratio of cylinder length to diameter ranged from 0.06 to 0.30; the ratio of cylinder diameter to radius of curvature of the disk faces was varied from 0 to 1.43. The fracture loads obtained have been correlated with stress data obtained from the photoelastic analysis of Pitt et al. An empirical equation, valid for any brittle material, relating the tensile strength of the material to the fracture load and dimensions of a doubly-convex disc has also been developed.

Dynamic Testing and Reinforcement of Rubber

Abstract: A series of experiments have been run to determine which mechanisms dominate carbon black reinforcement of rubber. A broad range of compounds using oil-extended and non-oil-extended rubbers and carbon blacks covering the spectrum of tread blacks have been tested. The results for measurements made in an all-SBR formulation are reported here. The primary experiment consisted of measurement of the dynamic modulus and hysteresis of the cured and uncured compounds over a broad range of frequencies, temperatures, and strains. Ternperatures ranged from −70°C to +90°C; frequencies varied from 0.01 to 10 Hz; double strain amplitudes varied from 0.5% to 35%. From a discussion of the literature and evaluation of the experimental results, two mechanisms have been found to control the primary effects of carbon black on rubber reinforcement, where reinforcement refers to a general enhancement of properties, such as modulus, as well as the tensile strength of the compound. Hydrodynamic interaction, which is the...

Miscible blends from rigid poly(vinyl chloride) and epoxidized natural rubber

Abstract: Mechanical properties and fracture of melt-blended poly(vinyl chloride) (PVC) and epoxidized natural rubber (ENR) having 50 mol % epoxidation level are studied at different compositions. The effect of blend ratio on tensile strength, tear strength, elongation at break, tension set after failure, and hardness are determined. The stress-strain behaviour of low ENR blends exhibits yielding and necking, whereas that of high ENR blends exhibits soft elastomeric deformation. At higher compositions of ENR, plots of tensile strength, tear strength, and hardness against blend composition are concave in nature; and plots of the elongation at break deviate markedly from the additive value with a pronounced maximum occurring at the 70wt% composition of ENR. The scanning electron microscopic examination of fracture surfaces of blends does not show any features of phase separation of ENR or PVC. The tensile fracture surface of rigid PVC exhibits partially fused particle structures of PVC and that of blends exhibits features of shearing and horizontal discontinuous striations. The torn surface of rigid PVC shows evidence of intrinsic crazing and that of blends shows features of shear fibrils, vertically changed discontinuous striations, steps, and unstable and stable tear fronts.

New Amorphous Alloys with Good Ductility in Al-Ce-M (M=Nb, Fe, Co, Ni or Cu) Systems : Condensed Matter

Abstract: New Al-based amorphous alloys were formed in Al-Ce-M (M=Nb, V, Cr, Mn, Fe, Co, Ni or Cu) ternary systems by melt spinning. The compositional range is the widest for Al-Ce-Ni alloys and extends from 2 to 15 at% Ce and below 30%Ni. The Al-Ce-M (M=Nb, Fe, Co, Ni or Cu) alloys containing over 80%Al have good bending ductility. The crystallization temperature (Tx) and hardness (Hv) of the ductile alloys increase to 625 K and 400 DPN with increasing M and Ce content and the highest tensile strength reaches 935 MPa. The effect of M elements on Tx and Hv is interpreted by taking the bonding nature of Ce and M atoms into consideration.