Showing papers on "Ultimate tensile strength published in 1971"

Stress-strain behavior of styrene-acrylonitrile/glass bead composites in the glassy region

Abstract: The effects of temperature, strain rate and filler content on tensile properties of SAN/glass bead composites are studied. A point of discontinuity on the stress-strain curves for unannealed composites is investigated, annealing results in smooth curves with no discontinuities. A simple model for the filler effect on yield stress is suggested and shown to be in a good agreement with experimental data. A double shifting procedure to account for the temperature and filler effects on yield stress as a function of strain rate is proposed. A single master curve that can be represented by the equation: relates composite yield stress to strain rate, temperature and filler volume fraction.

The mechanical behaviour of polymers under high pressure

Abstract: The effect of pressure on the tensile deformation of amorphous polycarbonate and poly(ethylene terephthalate) and semi-crystalline polychlorotrifluoroethylene and polytetrafluoroethylene was investigated up to 8 kb. Tensile deformations of polycarbonate at atmospheric pressure at temperatures down to 116°K were also performed. The former three polymers showed increases of yield stress, yield strain and elastic modulus, and decreases of fracture strain. Polytetrafluoroethylene behaved in an analogous manner up to 4 kb, beyond which both the ‘yield’ stress and elastic modulus deviated systematically from the lower-pressure behaviour. This was found to correlate with changes of bulk modulus at a solid–solid phase transition near 5 kb. The pressure dependence of yield stress was fitted by modified von Mises and Mohr–Coulomb yield criteria. A material parameter describing this pressure dependence was obtained for these and other polymers and was found to correlate qualitatively with the strength-limit...

Adhesion of viscoelastic materials to rigid substrates. III. Energy criterion for failure

Abstract: Measurements are described of the strength of a model adhesive joint subjected to (1) tensile rupture, with the interface containing a small unbonded region of varying size, and (2) pure shear deformation, in the form of a partly unbonded sheet. These, and previous measurements of resistance to peeling separation, are all shown to be consistent with an energy criterion for adhesive failure. The characteristic failure energy per unit area of interface has been determined for the model adhesive material as a function of the effective rate of detachment, over a wide range covering almost the entire spectrum of viscoelastic response. The values obtained are found to increase from levels only slightly higher than thermodynamic considerations would predict, i.e., 102−103 ergs/cm2, at low rates of crack propagation, up to a value of about 106 ergs/cm2 at high rates when the material responds in a glasslike manner. These results suggest that the failure energy has two components: the (reversible) work of adsorption and the (irreversible) work of deformation of the adhesive in effecting separation.

The effect of omega phase on the mechanical properties of titanium alloys

Abstract: The effect of the precipitation of the metastable ω phase on the tensile properties of β-phase titanium alloys has been studied. The volume fraction of ω phase was varied by controlling the heat treatment temperature and the alloy content. It is shown that provided the volume of ω phase is less than 0.6, significant increases in yield strength can be obtained while retaining reasonable ductility. Higher volume fractions results in complete macroscopic embrittlement, but fracture still occurs by microvoid coalescence. Thin film microscopy of deformed samples shows that dislocations bypass the omega particles. The results are discussed in relation to current theories of deformation and fracture of two-phase alloys.

Deformation of UO2 at High Temperatures

Abstract: The effects of temperature, strain rate, and grain size on the mechanical properties of UO2 were investigated using the four-point bending technique. Strain rates were varied by two orders of magnitude, and test temperatures up to 1800°C were used. Data are presented on the ultimate tensile stress, yield stress, and plastic strain-to-fracture. Below the brittle-to-ductile transition temperature, Tc, the material fractured in a brittle manner, with no macroscopic plastic deformation. Between Tc and a second transition at a higher temperature, Tt, a small amount of plastic deformation was measured before fracture. Beyond Tt, the strength of UO2 decreased continuously, and extensive plasticity was observed. This high-temperature plasticity was characterized by a thermally activated rate-controlling process; this behavior is consistent with observations of creep behavior under high stresses. The following phenomenological equations for the strain rate fit the data for the material with 8-μm grain size above Tt: and where σp and σ88f are the proportional limit and steady-state flow stress, respectively, and temperature T is in °K.

The mechanical properties of an epoxy resin with a second phase dispersion

Abstract: The mechanical strength of an anhydride-cured epoxy resin was studied by means of tensile tests as a function of particle size and volume fraction of an alumina trihydrate particulate-dispersed phase. These results and those of the microscopic examination imply that the poor strength of the system may be attributed to the intrinsically low strength of the dispersion. The tensile strength can be maximised by correct formulation on the basis of either particle size or volume fraction of the dispersed second phase. The modulus increases with increasing volume fraction, but is unaffected by particle-size variation at a constant volume fraction. The addition of a silane coupling agent increases the modulus of the composite, while having a negligible or adverse effect on the other properties.

Bearing capacity of anisotropic cohesive soil

Abstract: A new description of anisotropic cohesive strength provides a simple solution for the bearing capacity of a strip load, based on previous work by Hill This solution and a survey of published data on anisotropic shear strength indicate that the bearing capacity at worst is 85% of what would be predicted using conventional shear strength data for vertical compression and bearing capacity theory The bearing capacity is 90% of that predicted by conventional theory and the average of strength from vertical and horizontal compression When compressive strength is available for three orientations of loading, the shear strength can be represented as an ellipse, and the bearing capacity depends on the shape of the ellipse and on the average of vertical and horizontal compressive strengths

Porous titanium surgical implant materials

Abstract: Porous pure titanium and titanium-6% aluminum-4% vanadium alloy materials, made by several powder metallurgy techniques, have been studied for potential use as surgical implant materials. Tissue ingrowth into open porosity and favorable physical properties have been found. Tensile strength and ductility data are presented as a function of density. Microscopic observations include scanning electron microscope pictures of the surface of specimens prior to implantation in animals, photomicrographs of the internal pore structure, macrophotographs of surfaces before and after polishing, and histological photomicrographs illustrating the nature of the tissue ingrowth found.

Plastic deformation of polyethylene II. Change of mechanical properties during drawing

Abstract: The crystallinity, elastic modulus, and tensile strength of samples of various draw ratios together with the true stress—strain curves of high-density polyethylene were determined to establish correlations with morphological changes occurring during deformation. Changes of crystallinity at draw ratios below 5, i.e., constancy during drawing of quenched film and a decrease during drawing of annealed film, are explained by the formation of microfibrils with crystallinity independent of the thermal history of the film. The microfibrils slide past each other at higher draw ratios, generating an increasing number of interfibrillar tie molecules, which is reflected in the increasing number of interfibrillar tie molecules, which is reflected in the increase of crystallinity, elastic modulus, and tensile strength. From the true stress—strain curves, the differential work density for the deformation of the volume element was calculated as a function of the draw ratio. It contains two components which reflect two different mechanisms of deformation. The first component, decreasing with increasing draw ratio, can be associated with the destruction of the original microspherulitic structure; the second one, increasing with increasing draw ratio, can be associated with the deformation of the new fiber structure, i.e., with the sliding motion of the microfibrils formed during the first deformation step.

Polylactide fabric graphs for surgical implantation

Abstract: Absorbable surgical sutures that are dimensionally stable within the body may be prepared by the extrusion of polylactide polymer, including copolymers of L(-) lactide with up to 35 mole percent of glycolide. Said polymers are characterized by an inherent viscosity of at least 1.0, and the extruded filaments are oriented by drawing at a temperature of about 50* to about 140* at a draw ratio of up to 11 X , and annealed. Sutures so prepared have a tensile strength of from 25,000 p.s.i. to 100,000 p.s.i.

Aqueous degradation of polyimides

Abstract: The effect of an aqueous environment on the tensile properties of Kapton polyimide film has been investigated. Immersion of specimens in distilled water at 25° to 100°C for time periods ranging from one hour to several hundred hours resulted in a decrease in the ultimate tensile strength of the polymer from 23 ksi to approximately 14 ksi, and a corresponding decrease in elongation to failure from 38% to approximately 5%. The kinetics of this decrease in mechanical properties are second order and yield an activation energy of approximately 15.6 kcal/mole. The reaction is slightly dependent on pH in the range 2.0 to 12.0, but is highly dependent on the pH in the range 0.4 to 2.0. The decrease in mechanical properties at pH 2.0 to 6.0 appears to be due to hydrolysis of either uncyclized amic acid linkages or diamide functional groups present in the polyimide, whereas that at pH below 2.0 is probably the result of hydrolysis of both imide and amide bonds. Prolonged reflux of the polyimide in water resulted in the extraction of a water-soluble, amide-containing material.

Cellulosic sheet material having a thermosetting resin bonder and a surfactant debonder and method for producing same

Abstract: Cellulosic sheet materials having an improved ratio of wet tensile strength to dry tensile strength comprise cellulosic fibers; at least one debonder selected from the group consisting of anionic and cationic surface active agents; and a cationic thermosetting resin such as those normally employed to increase the wet strength of paper.

Hot‐Pressing and Mechanical Properties of Al2O3 with an Mo‐Dispersed Phase

Abstract: Compositions of alumina with a molybdenum dispersed phase were investigated in the 0 to 5 vol% Mo range. These compositions were also prepared with a 0.5 wt% MgO addition. All specimens were fabricated by hot-pressing, and near theoretical densities were achieved. Specimens were characterized by metallographic and X-ray diffraction analyses, and microhardness, elastic moduli, tensile strength, and fracture energy were determined. Results revealed that Mo additions did not affect grain growth; in contrast, MgO additions significantly inhibited grain growth. However, Mo additions did reduce the elastic moduli and microhardness but did not measurably affect the tensile strength. Tensile strength was dependent on grain size and fitted the G−1/3 relation. The fracture energy of Al2O3+5% Mo was 50% greater than that of Al2O3. Specimens were successfully hot-pressed with a micro-structure graded from that of Al2O3 to that of the 5% Mo composition.

The influence of nonmetallic inclusions on the mechanical properties of steel: A review

Abstract: The literature regarding the influence of nonmetallic inclusions on the mechanical properties of steel is reviewed, with critical comments on various studies. A brief discussion of inclusion rating methods and a synopsis of the effects of applied stress on inclusions in an isotropic, elastic matrix are presented. The parameters considered are tensile strength, impact strength, reduction of area, fatigue properties and fracture toughness. It is concluded that in many applications, the type of inclusions are more important than the total content and as matrix strength increases, the notch effect of inclusions becomes more significant. Also, mechanical properties can be influenced by any one or a combination of the following inclusion parameters; shape, size, quantity, interspacing, distribution, orientation, interfacial strength, and physical properties relative to the matrix.

A Novel Technique for Measuring the Strength of Liquids

Abstract: A novel technique has been effectively utilized in studying the properties of liquids under conditions that are not ordinarily accessible. This technique involves the use of an acoustic standing‐wave field established in a column of one liquid in order to trap an immiscible droplet of another liquid. In the experiment reported here, a filtered ether droplet suspended in filtered glycerine was superheated and acoustically stressed until the combination produced an explosive liquid‐to‐vapor phase transition. The experiment was performed under atmospheric conditions at which the normal boiling point of ether is 35.6°C. The measured tensile strength varied linearly from 17 bars at 130°C to 0 bars at 146°C. Previous measurements of the tensile strength of liquids have not come within a factor of 2 or 3 of the theoretical predictions based on homogeneous nucleation theory, a theory which describes the vaporization conditions for pure liquids. The results reported here are in good agreement with that theory. This novel agreement is attributed to the ability to obtain pure liquid samples by utilizing small (0.5‐mm‐diam) filtered droplets.

Modified cellulosic fibers and method for preparation thereof

Abstract: Modified cellulosic fibers, characterized by improved properties, such as reduced swellability and reduced natural fiber-to-fiber bonding, are produced by a process which comprises treating an aqueous slurry of the fibers with a substantive polymeric compound, drying the treated fibers to cause the polymeric compound to react with itself and with the fibers, and refiberizing in water to separate the individual, treated fibers. The fibers are useful in the preparation of improved cellulosic sheet materials which exhibit increased bulk and reduced tensile strength.

Stability and Load Capacity of Members with No Tensile Strength

Abstract: A mathematical solution is derived which permits the computation of critical load, deflection and stresses for eccentrically loaded slender prismatic compression members made of materials that have compressive strength but no tensile strength. A graphical presentation of the solution facilitates its applicaiton. In an example of application, the solution is used to compute the strength of masonry walls which were tested by the Structural Clay Products Institute. Even though there are limitations to our ability of predicting the behavior of a complex material such as masonry by a mathematical solution based on a simplified model, there is good agreement between computed and measured strength.

Dynamic Tensile Strength of Concrete Materials

Abstract: THE DYNAMIC TENSILE STRENGTH OF PLAIN CONCRETE, FIBER REINFORCED CONCRETE, AND A POLYESTER CONCRETE IS EVALUATED IN TERMS OF THE CRITICAL FRACTURE STRAIN ENERGY. BASED ON THE FRACTURE STRAIN ENERGY REMAINING CONSTANT, IT WAS SHOWN THAT THE FRACTURE STRAIN SHOULD VARY AS THE ONE-THIRD POWER OF STRAINING RATE OR THE INVERSE ONE-HALF POWER OF RISE TIME. THIS WSA EXAMINED ON PRISMATIC SPECIMENS OF THREE TYPES OF CONCRETE AND FOUND TO AGREE WITH EXPERIMENTAL RESULTS. THE TESTS WERE ACCOMPLISHED USING AN IMPACT LOADER AND A STRAIN GAGE SYSTEM. THE PAPER ALSO POINTS OUT THE RELATIONSHIP OF THIS TYPE OF TEST TO THE GENERAL PROBLEM OF SPALLATION OF CONCRETE BY DYNAMIC TENSILE PULSES. /ACIJP/

Unusual film‐forming properties of aromatic heterocyclic ladder polymers

Abstract: A new method of obtaining films of aromatic heterocyclic ladder polymers has been found which circumvents casting from high-boiling acidic solvents. The BBL ladder polymer has been formed into tough, durable films by collecting suspensions of the polymer obtained from acid reprecipitations upon a fritted glass funnel. After drying, the polymer can be removed as film, with thickness dependent upon the amount of material used. Such a film has a tensile strength of 9,600 lb/in.2 as compared to a tensile strength of 16,000 lb/in.2 obtained from the same polymer when cast from methanesulfonic acid solution.

Effect of porosity content on the tensile strength of porous materials

Abstract: A theory that takes into account the stress-concentrating effect of the pores in porous materials is proposed. Upper and lower limits between which the strengths of porous materials must lie are predicted. A pore-sensitivity factor is defined and, assuming that this is proportional to the fractional porosity, an equation is derived which describes the variation in relative strength with porosity content and which empirically can take account of the matrix ductility. The equation is shown to agree well with published experimental data.

Deformation and failure of brazed joints—macroscopic considerations

Abstract: Experimental data are presented on the influence of component yield strength and joint geometry on the mechanical behavior of transverse brazed joints. The systems studied were various iron alloys brazed with dilute silver alloys. From these data a model is developed for the deformation and ductile failure of brazed joints. In thick and thin joints, macroscopic plastic instability and hydrostatic tension respectively are the major causes of void growth and ductile fracture. Strain hardening in the braze metal is found to be an important factor in delaying fracture in both cases. Increases in the braze metal yield strength are accompanied by increases in the tensile strength of a brazed joint if the yield strength of the base metal exceeds the fracture strength of the joint. The loss of stress triaxiality which accompanies base metal yielding severely limits joint strength.

Fatigue strength of high-yield reinforcing bars

Abstract: The stress range to which a reinforcing bar is subjected is the primary factor determining its fatigue life. For design purposes, there is a limiting stress range, the fatigue limit, above which a reinforcing bar will have a finite fatigue life and is certain to fracture. At stress ranges below the fatigue limit, a reinforcing bar will have a long fatigue life and may be able to sustain a virtually unlimited number of stress cycles. The magnitude of the fatigue limit depends on the minimum stress during each stress cycle and on the shape of the deformatins rolled onto the bar surface. It may also depend on the diameter and the grade of the bar. Increasing a tensile minimum stress was found to result in a decrease in fatigue strength. On the other hand the fatigue was found to incrase with an increasing compressive minimum stress. Bar diameter and grade of bar were found to influence the finite-life fatigue strength of reinforcing bars. The existence of a long-life fatigue effect due to these variables could not be established. Larger size bars have a lowered fatigue strength while higher grade bars have an increased fatigue strength. The effect of lug geometry on fatigue strength was found to be coupled with that of bar diameter. The larger the bar diameter, the greater was the effect of lug geometry.