Showing papers on "Ultimate tensile strength published in 1979"

Effect of hydrostatic pressure on the deformation behavior of polyethylene and polycarbonate in tension and in compression

Abstract: The stress-strain response of crystalline high density polyethylene and of amorphous polycarbonate has been determined in tension and in compression at superimposed pressures up to 1104 MPa(160 ksi). Strain softening occurred in the polycarbonate at low pressures but was inhibited by pressure. Tensile necking occurred in both materials, but was promoted by pressure in polyethylene and inhibited in polycarbonate. The initial modulus, E, and the flow stress, σ, at a given offset strain varied linearly with the mean pressure, P, with essentially the same pressure coefficient, α. Thus, E = (1+αP)E0 and σ = (1+αP)σ0, where E0 and σ0 are values at zero mean pressure. In polyethylene, the coefficient, σ0, was the same in tension and compression, indicating that the strength differential between tension and compression was a simple manifestation of pressure-dependent yielding. In polycarbonate the coefficient, σ0, was different in tension and in compression, implying an effect due to the third stress invariant or to anisotropy. The results suggest a constitutive model for polymers in which the flow stress is linearly dependent on mean pressure, but in which inelastic volume change is negligible. The results also suggest that the pressure dependence of flow stress in polymers is the same as that of the initial modulus.

Mechanical, thermal, and electrical properties of metal fiber‐filled polymer composites

Abstract: The critical concentration at which a metal-filled composite becomes electrically conductive can be dramatically reduced by adding the metal as randomly dispersed fibers. The higher the aspect ratio of the fibers, the lower the concentration needed to induce electrical conductance. Composites exhibiting resistivities below 20 ohm-cm have been produced with less than 8 volume percent aluminum fibers, having an aspect ratio of 24:1. At low fiber loadings the tensile strength of the composites is similar to that of the unfilled polymer. The thermal properties of these composites are shown to increase monotonically in accordance with the theoretical development of Nielsen.

Ultrahigh-strength polyethylene filaments by solution spinning/drawing, 2. Influence of solvent on the drawability†

Abstract: High-modulus structures of linear polyethylene with Young’s moduli of 70 GPa may be generated, for example, by drawing meltspun fibers to very high draw ratios’), solid-state extrusion (e. g., cf.’)) and by the solution-crystallization technique referred to as surface growth3). The tensile strength of the drawn and extruded materials is usually found below 1 GPa, whereas the longitudinal crystals of Zwijnenburg and Pennings may have a strength as high as 3 GPa. The superior strength of the latter filaments, which have comparable Young’s moduli, is due to the high molecular weight of the polymer sample used4*’). Previous attempts to draw or extrude polyethylene of similar molecular weight to high draw ratios only succeeded at relatively high temperatures, in fact above the melting point, where the effectiveness of the chain-extension process is known to be low (see6)). The structures thus produced, therefore, exhibited but moderately improved mechanical properties6). In a wide-ranging study on the processability of high molecular weight polymers it has been found that the effective drawability of these materials is drastically enhanced by spinning” or casting from dilute solutions. This effect will be illustrated in the present paper for polyethylene, and this improved drawability will be discussed in terms of a favourable intermolecular topology of the polymer.

Ultrahigh-strength polyethylene filaments by solution spinning and hot drawing

Abstract: The past decade has seen a rapidly growing interest in highmodulus and high-strength polymeric fibers (see e.g. CIFERBI, WARD 1979). The methods to prepare these filaments are based on cold/ hot drawing (CAPACCI0, WARD 1974), two-stage drawing (CLARK, SCOTT 1974), hydrostatic (GI~SON et al. 1974) and direct (SOUTHERN, POR~ER 1970; TAKAYANAGI et al. 1966) extrusion, elongational flow (PENNINGS et al. 1972; ZWIJNENBURG, PENNINGS 1976) and on the intrinsic rigidity of particular macromolecules in solution (e.g. CIFERRI 1975). High-modulus polyethylene filaments with Young's moduli of about 70 GPa have been produced by CAPACCI0 and WARD (1974) through drawing. PORTER et al. (1970) performed solid-state extrusion to obtain polyethylene structures with similar mechanical properties. The tensile strength of these materials is usually found below I GPa (CAPACCI0, WARD 1975; KOJIMA, PORTER 1978). Longitudinal crystals of polyethylene with a Young's modulus of 100-120 GPa and a tensile strength of 3-4 GPa have been obtained from solution by ZWIJNEN~JRG and P~NNINGS (PENNINGS 1977) in a Couette-type apparatus employing a crystallization technique referred to as surface growth. This short communication describes some preliminary results on alternative routes to produce high-strength and high-modulus polyethylene filaments with a uni-axial Young's modulus of 90 GPa and a tensile strength of 3 GPa. The method is based on a simple solution-spinning and drawing process that can be performed continuously.

Synthesis and fabrication of β-tricalcium phosphate (whitlockite) ceramics for potential prosthetic applications

Abstract: A novel process is described for preparing dense, polycrystalline tricalcium phosphates. Singleβ-phase compositional integrity is achieved by introducing catalytic amounts of sulphate ion and this pore free material has close to theoretical density. Preliminary mechanical properties include a compression strength of 687 MN m−2 and a tensile strength of 154 MN m−2. The relationship between processing variables and phase composition, microstructure, strength and translucence is described. The material has promise for bone implant applications.

Effects of Texture and Composition on Mechanical Behavior of Experimentally Deformed Carbonate Rocks

Abstract: Dry, low-porosity carbonate rocks with a wide range of texture and dolomite content were experimentally deformed at room temperature, strain rate of 10-4 sec-1, and at confining pressures of 0, 50, and 100 MPa (1 MPa = 10 bars = 145 psi) to evaluate the effects of texture and composition on ultimate strength and ductility. Of all the factors considered, weighted mean grain size and microcrystalline carbonate (micrite) content have the highest linear correlation coefficients with ultimate strength. Grain size is, therefore, the dominant intrinsic rock property that affects ultimate strength in low-porosity carbonate rocks. Systematic increases in total dolomite content (determined by X-ray diffraction) do not correlate significantly with ultimate stre gth when all of the variously textured rocks are compared. However, ultimate strength does increase with increasing dolomite content in rocks of similar texture. The approximate ultimate strengths of carbonate rocks with intermediate dolomite and/or micrite content can be predicted by the best-fit plane to the ultimate strengths of "pure end members" (Yule marble, Solenhofen limestone, Hasmark dolomite, Blair dolomite). For experiments at 100 MPa confining pressure, this plane is defined by the equation: 0.90 D + 2.07 M + 269 = ^sgru, where D is dolomite content in percent, M is microcrystalline carbonate content in percent, and ^sgru is ultimate strength in MPa. The equation of the plane defined by ultimate strengths of rocks of intermediate composition and texture is: 1.07 D + 2.29 M + 258 = ^sgru. The mean difference between the strengths predicted by these two planes is only 9 MPa. Most precursive microfractures in nonmicritic elements are intragranular. Although the density of intragranular microfractures increases with increasing confining pressure, grain boundary cracks are suppressed by confining pressure. Very few microfractures occur in the micrite itself. At a given confining pressure, highly micritic rocks exhibit much less abundant precursive microfractures than coarser grained rocks, and hence they are stronger.

Tensile strength of water

Abstract: THE measured tensile strength of water has long been known to be significantly less than theoretical predictions and the reduced strength is normally attributed to the presence of solid impurities that serve as nucleation sites for rupture of the liquid1. A favourite method of measuring tensile strength is through the dynamic stressing of a liquid by an acoustic field. At sufficiently large values of the peak negative acoustic-pressure amplitude the liquid ruptures and forms a rapidly growing vapour cavity that collapses violently during the positive portion of the cycle. This cavity collapse is normally violent enough to be observed easily with the unaided eye or ear. Such an event is termed the acoustic cavitation threshold and is a measure of the tensile strength of a liquid. Although some successes have been obtained in achieving measured values of the tensile strength comparable to theoretical predictions for extremely small samples2 or after extensive filtration3, I know of no current theory for the prediction of values of the dynamic tensile strength for ordinary distilled water. Using a modified version of a recent theory by Apfel4, an equation is presented here that correctly predicts the variation of the acoustic cavitation threshold of water with surface tension, dissolved gas content and temperature.

Formability of sandwich sheet materials in plane strain compression and rolling

Abstract: The stress states developed during room temperature, plane strain compression modes of deformation of stainless steel clad aluminum and aluminum clad strainless steel sheets have been investigated in order to gain insight into the formability of bonded ductile sandwich sheet materials in primary metalworking processes Assuming uniform, isostrain deformation in the component layers, sandwich compression stress-strain curves were predicted to be rule of mixtures averages of component compression stress-strain curves These predictions showed good agreement with experimental data when friction and in-homogeneous deformation were taken into account Since the through-thickness applied pressure can be assumed to be the same in both components of thin sandwich sheet materials, in-plane stresses which are tensile in the harder component and compressive in the softer component of a clad sheet are developed in order to satisfy the yield conditions The nature of these in-plane stresses was confirmed by measurements of residual stress distributions in rolled clad sheet specimens, and it was shown how the tensile stress in the harder component may lead to unstable flow and failure of this component during forming The observed failures were similar in both plane-strain indentation and rolling tests Although the initiation of instability in symmetric clad sheet metals appears to be independent of the arrangement of the component layers, the process of final localization leading to fracture was observed to depend heavily on the layer arrangement

Age-related changes in the density and tensile strength of human femoral cortical bone.

Abstract: In order to ascertain whether the intrinsic strength of human bone changes with age or not, we have determined the ultimate tensile strength and density of strips of femoral cortical bone. These femora were collected from cadavers varying in age from 13 to 97 years. The results show that both density and intrinsic strength of bone increase up to about the fourth decade of life and then decrease with age. However, the rate of decrease of strength is greater than that of density. This indicates that the density of bone is not the sole determining factor of its strength, and that some other factors play an important part.

Correlation of Fiber Composite Tensile Strength with the Ultrasonic Stress Wave Factor

Abstract: An acoustic-ultrasonic technique was used to indicate the strength variations of tensile specimens of a graphite/epoxy composite. A “stress wave factor” was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), [0 deg/±45 deg/0 deg] symmetrical, and [±45 deg] symmetrical. Correlations indicated that the stress wave factor can predict variations of the tensile and shear strengths of composite materials. The method was also found to be sensitive to strength variations associated with microporosity and differences in fiber/resin ratio.

Retention of dowels subjected to tensile and torsional forces.

Abstract: This investigation measured the maximal tensile and torsional forces sustained by four different designs of dowels. 1. Under tensile force, the threaded screw-in dowels were significantly more retentive than the unthreaded dowels. 2. Under torque, both the threaded screw-in and serrated dowels were significantly more retentive than the smooth-sided dowels.

Tensile strength of composites with brittle reaction zones at interfaces

Abstract: A theoretical model of the longitudinal strength of brittle fibre-reinforced composites with brittle reaction zones was presented for both cases of strongly and weakly bonded fibre/brittle zone interfaces. First, on the basis of the fracture mechanics, a model of the strength of the fibres coated with strongly adhering brittle zones was proposed as a function of the thickness of the brittle zones. Next, the conditions under which debonding occurs at the interfaces were investigated with the aid of the shear lag analysis proposed by Cox. The theoretical model was then examined using composites with strongly and weakly bonded interfaces. The proposed model agreed fairly well with the experimental results. Finally, the permissible thickness of the brittle zone below which no reduction in fibre strength appears was calculated, using the proposed theory, under the condition of strong interfacial bonding, for carbon, boron and silicon carbide fibres which are of practical use. The calculated values of the thickness were smaller than 1 μm.

Deformation of sandwich sheet materials in uniaxial tension

Abstract: The stable and unstable plastic flow of stainless steel-clad aluminum and aluminum-clad stainless steel sandwich sheet materials deformed in uniaxial tension have been investigated. For the clad sheet materials studied experimentally, stable deformations were uniform in the component layers, and the assumption of isostrain was used in modeling the deformation behavior. The rule of mixtures, an average of component properties weighted by cross-sectional area fractions, was applied to determine sandwich uniaxial true stress-true strain curves from those of the components. In addition, measurements of residual stress distributions in deformed tensile specimens gave insight into states of stress during loading. A model to determine the magnitude of stresses which are generated by component normal plastic anisotropy differences was developed as well. With this knowledge of the stress state, predictions of uniform elongation of the clad sheet materials were made which compared favorably to experimental measurements. As for ductile monolithic sheet materials, stable flow of sandwich sheet materials in tension was limited by diffuse necking, which leads to local instability at higher strains. This local instability gives rise to a through-thickness localized thinning which terminates macroscopic deformation. Conditions for local instability in uniaxial tension have been developed for sandwich as well as monolithic sheet materials. Predictions from these models are in agreement with measurements.

Biaxial and Uniaxial Data for Statistical Comparisons of a Ceramic's Strength

Abstract: The uniaxial and equibiaxial tensile strengths of a brittle material were measured in bending. Equibiaxial tension was attained by concentric ring loading of disks and uniaxial tension by four-point line loading of plates. The two specimen designs give equal volumes, surface areas, and stress gradients. Ground surfaces and lapped surfaces were tested. The equibiaxial tensile strength of a dense alumina was lower than the uniaxial tensile strengths for both ground and lapped surfaces, 8.5 and 8.1%, respectively. The Batdorf theory of flaw statistics, in which biaxial tensile strengths can be predicted from the statistical distribution of uniaxial tensile strength measurements, agreed with the data.

Optical communication cable

Abstract: An improved optical cable (10) having increased bending flexibility along with increased tensile strength comprises means for controlling coupling between a cable jacket (28) and its reinforcing strength members (26). In one embodiment, a reinforcement bedding layer (23) is applied between a plastic-extruded inner jacket (22) and the outer cable jacket (28). Before extrusion of the outer jacket (28), the reinforcing strength members (26) are helically applied onto the bedding layer with predetermined strength member surfaces (27) making intimate surface contact with the bedding layer. Because the bedding layer is impervious to the plastic extrudant used to construct the outer jacket and is capable of rendering the predetermined strength member surfaces sufficiently inaccessible to the plastic extrudant, encapsulation of strength member lengths (25) containing the predetermined strength member surfaces (27) by the plastic extrudant is prevented. In another embodiment, the cable sheath (57) includes two separate layers (64, 70) of strength members, each layer having predetermined lays in opposite directions such that under a tensile load they produce equal but oppositely directed torques about the cable's longitudinal axis. The coupling between each layer of strength members and its surrounding jacket can also be controlled.

The role of microstructure in hydrogen-assisted fracture of 7075 aluminum

Abstract: Underaged, peak strength (T6), and overaged (T73) microstructures were studied in 7075 plate material. Hydrogen charged and uncharged tensile specimens of longitudinal orientation were tested between −196°C and room temperature. The results confirm a hydrogen embrittlement effect, manifested mainly in the temperature dependence of the reduction of area loss; a classical behavior of hydrogen embrittlement. The maximum embrittlement shifted to lower temperatures with further aging. The effect of hydrogen was largest for the underaged condition and smallest for the overaged, thus following the pattern found for the sensitivity to stress-corrosion cracking in high strength aluminum alloys. The fracture path was predominantly transgranular, with minor amounts of intergranular fracture.

Titanium alloys of the TiAl type

Abstract: Cast and forged titanium alloys suited for use at temperatures over 600° C. are based on TiAl gamma phase structure. Useful alloys have about 1.5% or greater tensile ductility at temperatures of 260° C. and below, thereby making them fabricable and suited for engineering applications. Disclosed are alloys having weight percent compositions of 31-36 aluminum, 0-4 vanadium, balance titanium (in atomic percent, about: 45-50Al, 0-3V, bal Ti). The inclusion of about 0.1 weight percent carbon improves creep rupture strength. To obtain high tensile strength, the alloys are forged at about 1025° C. and aged at about 900° C.; to obtain higher creep rupture strength and tensile ductility, a solution anneal at about 1150° C. is interposed before aging.

A mathematical description of the strength properties of concrete under generalized stress

Abstract: Synopsis A mathematical description of the ultimate strength envelope of concrete under axisymmetric stress states has been derived by analysing experimental data obtained in previous investigations of the Concrete Materials Research Group at Imperial College. The derived equations, when combined with an proposed elsewhere for the description of the effect of the intermediate stress σ2 upon the ultimate strength level, define a surface in stress space which provides a simple mathematical representation of the ultimate strength of concrete under generalized short-term loading conditions. The resulting ultimate strength surface conforms with generally accepted shape requirements and has been found to provide a close fit for most biaxial and triaxial strength data published to date.

Diametral Compressive Testing Method

Abstract: A new approach of diametral compressive testing with circular anvils is proposed. The circular anvils are used to select a suitable contact width or to avoid the collapse of the specimen in the contact edge. Furthermore, the statistical corrections on the diametral compressive strength for the effects of the size and stress distribution are explained by the application of Weibull’s statistical theory. The experimental results of the diametral compressive testing are compared with the uniaxial tensile strengths for some kinds of graphite and marble, and the discrepancies between the two strengths are discussed. According to our macroscopic brittle fracture criterion under biaxial stress state, which was proposed recently, the tensile strength can be deduced from the diametral compressive strength σHC* and the uniaxial compressive strength σC as follows, σt* = KICKIIC 12 σCσHC*(1+σx/σH)+σC {σHC*(1−σx/σH)−σC}+σC2 where σt* is the deduced tensile strength, σx /σH is the ratio of maximum and minimum principal stresses at the center of the disk, and KIC and KIIC are the values of Mode I and Mode II fracture toughness. The deduced values σt* are ascertained experimentally to agree very well with the uniaxial tensile strength in wide range of brittle materials, such as graphite and marble.

The influence of strain path on subsequent mechanical properties—Orthogonal tensile paths

Abstract: Several aluminum alloys have been subjected to two stage tensile straining, an initial prestrain followed by a subsequent tensile strain at 90 deg to the initial direction. In AA1100-0 and AA3003-0 the prestrain produces dislocation tangling and diffuse cell walls resulting in an enhanced flow stress and decrease in ductility when the material, is subsequently strained in the orthogonal direction. In a fine grained experimental Al−Fe−Ni alloy the prestrain is accompanied by a very low accumulation of dislocations and in this case the flow stress is reduced and ductility enhanced in subsequent orthogonal straining. The commercial alloys AA2036-T4 and AA5182-0 are unaffected by the two stage tensile strain path. The results are considered in terms of the forming limit curve and it is also shown that the behavior is consistent with the concept of an “alien” dislocation distribution being generated during the prestrain.

Humid aging of plastics: Effect of molecular weight on mechanical properties and fracture morphology of polycarbonate

Abstract: Polycarbonate tensile bars were aged up to 18 months at 0%, 75%, and 100% relative humidity and temperatures of 65–93°C. In the humid aged samples hydrolysis caused progressive reductions in molecular weight. Below a critical molecular weight (Mw = 33,800, Mn = 14,300) tensile strength dropped off rapidly. A transition from ductile to brittle failure was also observed at that point. Extrapolations indicate that the ductile–brittle transition at 38°C will be reached after 5 years at 100% relative humidity for the polycarbonate studied. Elongation was affected even in the early stages of hydrolysis. This suggests that whenever the degradation mechanism is a molecular weight reduction, toughness will be affected before the strength properties are lost. Mechanical properties are affected by annealing and antiplasticization which reduce localized stresses and increase short-range order. The brittle fracture surfaces of polycarbonate consist of four distinct regions. The size of the regions and the prominence of the features changed as the molecular weight decreased.

Size Effect in Model Concretes

Abstract: The paper reviews current research on the effect of specimen size on compressive, indirect tensile and flexural tensile strengths, the stress-strain characteristics, and related quantities. The measured compressive and tensile strengths were observed to increase with a decrease in specimen size in all investigations. The nondimensional stress-strain curves in compression tests were noted to be homologous for prototype and model concretes. A higher tensile-compressive strength ratio is observed in smaller specimens. The effects of duration and conditions of curing compactions, shape of specimen, and other factors are reported. Techniques are suggested to select the cylinder size to evaluate the concrete compressive strength in a model specimen. To assist with the determination of size effects and standardization, the ACI Committee 444 on Models of Concrete Structures has recommended that model investigations should include compression tests on 2-in.x4-in. (50-mmx100-mm) cylinders along with any other cylinder sizes used.

Brittle interface layers and the tensile strength of metal matrix-fibre composites

Abstract: The influence of brittle layers on the ultimate tensile strength of metal matrix composites is discussed. An equation has been derived to calculate the first critical thickness of the layer. The brittle layers have two effects on the fracture of the fibre, one of which is the value of the local stress near the tip of the crack, situated at the fibre-layer interface. Methods have been developed for the theoretical calculation of the critical stress intensity factor, KIC, of brittle materials. Experimental results with B-SiC fibres have shown that their tensile strength is reduced with increasing thickness of the SiC layer. The critical thickness of the layer, tl*,for B-SiC fibres is about 1.0 to 7.5 μm, which coincides well with the theoretical value of tl*.

Influence of Silicon and Phosphorous on the Mechanical Properties of Both Ferrite and Dual-Phase Steels

Abstract: A study has been made of the influence of up to 2 pct Si and 0.42 pct P upon the strength and ductility of ferrites over a wide grain size range; the grain size was varied fromd −1/2 mm−1/2 = 4 to 14. Although the ductility decreased with increasing strength for all the alloys, the 2 pct Si alloy had the best combination of strength and ductility. The ferrites containing 2 pct Si and 0.2 pct P had greater uniform elongations than conventional HSLA steels at the same tensile strength; it is thought that the ductility of the ferrites is enhanced by the presence of Si while the ductility of conventional HSLA steels is reduced by the presence of carbide precipitates. With the theory for a composite of two ductile phases and the results for the fine-grained alloyed ferrites, the change in uniform elongation as a function of tensile strength was predicted for dual-phase (martensite plus ferrite) steels. Good agreement was found between the prediction and experimental results for dual-phase steels containing up to 0.2 pct P or 2 pct Si; the 2 pct Si alloy had the best combination of strength and ductility of all dual-phase steels so far reported. This study again emphasizes the importance of the high strength, high ductility ferrite in controlling the properties of dual-phase steels.