Showing papers on "Tensile testing published in 1977"

Tensile strength of hybrid composites

Abstract: This paper presents an approximate, statistical analysis for the tensile strength of unidirectional hybrid composite materials consisting of two-dimensional arrays of alternating low elongation and high elongation fibres in a common matrix. Expressions for ineffective length and fibre strain concentration factor in hybrid composites are developed. The analysis identifies a number of important material properties that affect the failure process in hybrids: statistical fibre tensile failure strain characteristics, and fibre extensional moduli and cross-sectional areas. The influence of these parameters on the failure process is examined and differences between failure mechanisms in hybrids and composites containing only one type of fibre are considered. The analysis predicts that, in general, the failure strain of a hybrid should be different from those of composites reinforced with either of the “parent” fibres alone. It is found that the theory can explain the “hybrid effect” that has been observed by several authors: hybrids made by combining high elongation and low elongation fibres, such as graphite and glass, often display tensile failure strains greater than those of composites made from the low elongation fibres alone. Predicted failure strains are compared with available experimental data. Suggestions for future work in the area are presented.

Ten Deg Off-Axis Test for Shear Properties in Fiber Composites

Abstract: A combined theoretical and experimental investigation was conducted to assess the suitability of the 10 deg off-axis tensile test specimen for the intralaminar shear characterization of unidirectional composites. Composite mechanics, a combined-stress failure criterion, and a finite variation across the specimen width and the relative stress and strain magnitudes at the 10 deg plane. Strain gages were used to measure the strain variation across the specimen width at specimen midlength and near the end tabs. Specimens from Mod-I/epoxy, T-300/epoxy, and S-glass/epoxy were used in the experimental program. It was found that the 10 deg off-axis tensile test specimen is suitable for intralaminar shear characterization, and it is recommended that it should be considered as a possible standard test specimen for such a characterization.

Mechanical properties of mixtures of two compatible polymers

Abstract: The properties of mixtures of poly(2, 6-dimethyl p-phenylene oxide) and poly(styrene) have been measured by DSC, density gradient, dynamic mechanical response, and tensile testing. The mixtures are found to have single glass trasitions that vary continuously with the composition. They also have small negative excess volumes of mixing, indicative of strong polymerpolymer interaction. The dynamic mechanical response of the mixtures shows that the low temperature secondary relaxations are suppressed whereas those at high temperatures are enhanced. These observations imply that mixing on the segmental levc l has occurred. A plot of tensile strength vs composition at different strain rates reveals two regions of failure behavior. The high PS, high strain rate region is brittle, and the high PM2PO, low strain rate region is ductile. When the tensile yield data are treated according to the Ree-Eyring equation, the addition of PS to PM2PO is found to reduce the flow volum, e of the mixture. The overall effect on mechanical properties of adding small amounts of one component to the other is similar to that of anti-plasticization. Our experimental observations are consistent with the shifting of the relaxation mechanisms to longer times due to the negative excess volume of mixing.

The influence of particle size on the tensile strength of particulate — filled polymers

Abstract: The tensile strengths of a particulate-filled rigid polyurethane resin are presented at varying volume fractions and a wide range of particle sizes. These results are compared with exisiting theories of the strength of particulate-filled composite systems. A linear relationship is proposed to exist between the mean particle diameter and the tensile strength at a given volume fraction. A method of normalizing data is presented which removes the stress-concentration effects of finite particle sizes and allows comparison of the data with a simple equation relating tensile strength and volume fraction. The effects of particle size and volume fraction in relation to crack propagation are discussed, and the proposed method of analysis is shown to give similar results when applied to published data.

A numerical analysis of the tensile test for sheet metals

Abstract: The strain hardening, strain-rate hardening, and plastic anisotropy properties of metal sheets are normally determined in a tensile test during the nearly uniform deformation prior to the maximum load. Beyond this point, strain nonuniformity leading to a neck is poorly understood in terms of interaction of these material properties with changes in strain-rate and stress-state within the neck, and the resulting load-extension plot. Satisfactory modeling of this problem has been achieved by using a rigid/plastic constitutive law including strain hardening and strain-rate hardening. Progressive cessation of deformation starting from elements in the specimen fillet region toward the center is demonstrated. This effect is shown to generate a strain peak (neck) at the gage length center. The predicted load-extension plots and strain distributions in the neck agree well with experiments conducted on a number of test materials. This work provides a quantitative measure of the influence of various material parameters on tensile ductility and identifies the proper constitutive law for input into mathematical models of more complex forming operations.

Laser shock hardening of weld zones in aluminum alloys

Abstract: The feasibility of using a high energy, pulsed laser beam to shock-harden weld zones in 5086-H32 and 6061-T6 aluminum sheet was investigated. The tensile strength, hardness, and microstructure of samples 0.3 cm thick were studied before and after laser shocking. After laser shocking, the tensile yield strength of 5086-H32 was raised to the bulk level and the yield strength of 6061-T6 was raised midway between the welded and bulk levels. The increases in ultimate tensile strength and hardness were smaller than the increases in the yield strength. The microstructures after shocking showed heavy dislocation tangles typical of cold working.

The tensile fatigue behavior of para‐oriented aramid fibers and their fracture morphology

Abstract: Samples of Fiber B and PRD 49 which were the forerunners of current Kevlar aramid fibers were subject to a limited number of tensile tests and tensile fatigue tests in order to determine their fracture morphology. The fibers were examined by optical and scanning electron microscopy. Both tensile and fatigue failure occurs by axial splitting, with the fatigue splits being much longer. Compressive effects in snap-back cause kink bands to form. The fatigue strength is only marginally less than the tensile strength.

Non Hookean Behaviour in the Fibre Direction of Carbon-Fibre Composites and the Influence of Fibre Waviness on the Tensile Properties

Abstract: In the literature the tensile behaviour in the fibre direction of unidirec tional carbon fibre reinforced plastic (c.f.r.p.) is assumed to be linearly elastic up to failure.Some authors distinguish a primary and a secondary part in the stress- strain curve each showing Hookean behaviour.The experimental results of this paper show that Young's modulus of laminates increases proportionally with the tensile stress, as found in Ref. [1] for single non-impregnated fibres.An empirical relation between Young's modulus and the tensile stress is derived and the influence of fibre misalignment on this relation is exam ined.In addition, the influence of fibre misalignment on the tensile strength and Poisson's ratio is discussed.

Characterization of asphalt pavement materials using the indirect tensile test

Abstract: The techniques and procedures for obtaining the needed fundamental properties through use of the indirect tensile test are reviewed and the evaluation of these properties is summarized The indirect tensile test described can be used to characterize asphalt materials in terms of resilient elastic properties, properties related to thermal cracking, properties related to fatigue cracking, and properties related to permanent deformation

A general relation between tensile strength and specimen geometry for concrete-like materials

Abstract: The tensile strength of concrete-like materials varies wiries when different test procedures or even different shapes and sizes of specimens are employed. Correlations have previously been established but restricted to particular test conditions. The approach here presented, based on the “weakest link of the chain” concepts, offers the possibility of correlating the results of the different tensile tests of concrete-like materials. For that purpose, the amount of material under a tensile stress greater than 0.95 of the maximum tensile stress in the specimen must be evaluated. Relating the maximum tensile stress at the moment of failure with the above mentioned volume (Highly Stressed Volume), a decreasing function is obtained. The function fitted can be used to obtain a tensile strength value of the material, free from the influence of the characteristics of tests and specimens. In this experimental work, the function is established by testing seven different mortar mixes, subjected to nine different test conditions. Centered-point and third-point loading flexural tests and splitting tests were carried out on specimens of different sizes. Direct tension on a briquertte was also applied. The test results showed a decreasing linear regression between the logarithm of the maximum tensile stress at the moment of failure and the logarithm of the highly stressed volume. The slope of that line remained fairly constant for the seven mortar mixes tested.

Investigation of Adhesive Properties of Dental Composite Materials Using an Improved Tensile Test Procedure and Scanning Electron Microscopy

Abstract: A standardized tension test was used to evaluate the adhesive properties of several composite materials when used on both dentin and enamel specimens. The nature of the test surfaces was examined by roughness tests using a Talysurf machine and also in more detail by means of a scanning electron microscope. Poor results were obtained for the adhesion of composite materials to dentin whereas good retention to enamel was obtained.

The Fracture Toughness of Boron Aluminum Composites

Abstract: A test and analysis program concerning the fracture toughness of 0/sup 0/, 90/sup 0/, 0/sup 0//90/sup 0/ and +-45/sup 0/ boron filament reinforced aluminum matrix composites is described. Two different analytical techniques were used to determine fracture toughness based on the tensile testing of prenotched compact tension specimens over a wide range of (a/w). It is shown that good agreement exists between these two techniques for both uniaxially and biaxially reinforced material. Comparisons were also made between specimens of two thicknesses and between the behavior of specimens having as-machined and propagating cracks. Values of fracture toughness for boron aluminum are presented and compared with similar data for other engineering materials.

Energy Absorption of High-Strength Steel Tubes Under Impact Crush Conditions

Abstract: The energy absorption of automotive sheet steels was determined at impact speeds to 40 mph by crushing tubular structures at 70 and -40 F. The test program was designed to provide an intermediate step between tensile and vehicle tests aimed at understanding material behavior at high impact speeds. Energy absoprtion increased with impact velocity, strength, thickness, and lower temperature. Energy absorbed was also influenced by tube geometry. These results show that the new HSLA steels provide excellent energy absoprtion and that designers can use these steels at relatively light gages to reduce vehicle weight without sacrificing crashworthiness, even at low temperature. /GMRL/

Comparison of mechanical properties of 2Cr-Mo and O.5Cr-Mo-V simulated heataffected zones

Abstract: Reheat cracking during the stress relief of 0.5Cr-Mo-V weldments can occur in the coarse-grained region of the HAZ and necessitates expensive, time-consuming repairs. An HAZ thermal-simulation technique has been used to produce coarsegrained material similar to that obtained in welds of commercial 2Cr-Mo and 0.5Cr-Mo-V material. The mechanical properties of the two material HAZs, measured by slow strain-rate tensile testing, have been compared to establish whether the 2Cr-Mo composition, an alternative low-alloy creep-resistant, steam pipe material, offers any significant advantages in terms of its resistance to reheat cracking. Some practically relevant effects of thermal-cycle and welded-joint restraint variables on the structure and the hot-tensile properties of HAZ material have also been investigated. The results indicate that 2Cr-Mo material has the greater inherent resistance to reheat cracking. However, a change in steam pipe composition should not be necessary as substantial improvements...

Studies in Non‐Isothermal Rheology

Abstract: Almost all basic work in rheology, both experimental and theoretical, has dealt with isothermal flows, with the temperature being held constant during any one measurement. The present paper presents systematic studies of the nonisothermal behavior of two polystyrenes (a commercial sample and a sample of sharp molecular weight distribution). The experiments involve stress growth and stress relaxation during elongation in an Instron tensile tester, with rapid changes of temperature being imposed during the pulling and after it. Generalized non‐isothermal viscoelastic theory is proposed and tested. The generalized time‐temperature superposition involved there works well in simple stress relaxation (when the temperature changes are imposed after the pulling) but in the simultaneous type of experiments (when the temperature changes are imposed during the pulling), the accommodation to the new state seems to be more rapid than expected from theory.

The influence of molecular weight on the large deformation behavior of SBS triblock copolymer elastomers

Abstract: Engineering stress–strain properties were determined for two polystyrene–polybutadiene–polystyrene (SBS) triblock copolymer elastomers, one consisting of blocks of molecular weight 7000/43000/7000 and the other, 16000/85000/17000. In addition, various blends of these two materials were prepared in order to vary the number-average molecular weight of the blocks in a systematic way while maintaining polystyrene content in the range of 25–28 wt %. Samples were solvent cast from benzene or benzene/heptane mixtures and annealed before testing. Ring specimens were extended to rupture at varying strain rates on an Instron tensile tester. Results indicate that number-average molecular weight has a marked influence on stress–strain behavior over the range of molecular weights and testing conditions employed. The observed behavior is consistent with a systematic increase in the proportion of a mixed interfacial region between the pure polystyrene and polybutadiene domain as molecular weight decreases. The interfacial region contributes to mechanical hystersis, rate sensitivity, and toughness in the SBS materials. Scanning electron photomicrographs of fracture surfaces also showed systematic changes with molecular weight.

Tensile and Shear Testing of Some Pharmaceutical Powders

Abstract: Twelve pharmaceutical diluents have been characterized by determination of particle size distribution, tensile strength and the shear cell parameters cohesiveness (C), flow factor (FF) and the effective angle of friction (dL). Nine materials possessed a size distribution approximating log-normal. Avicel and the starch samples exhibited highest cohesiveness and lowest flow factors. The correlation between C and FF was good, but T was unrelated to either. Values of C/T varied from 0.19 to 3. 16. It is suggested that in many cases, estimates of T may not fit the yield locus at the corresponding bulk density because of different modes of consolidation in the tensile tester and shear cell.

Fe-Cr-Mn microduplex ferritic-martensitic stainless steels

Abstract: An alloy development program has been undertaken with the aim of identifying an Fe-Cr-Mn stainless steel with ferritic-martensitic microduplex phase balance of sufficient stability to produce moderate strength and ductility, good impact resistance and acceptable as-welded properties. A microduplex, low C and N, Ti stabilized composition of Fe-11.5 pct Cr-3 pct Mn has been found to provide a yield strength of ⋍550 MPa, a tensile strength of ≃650 MPa, tensile elongation of 20 pct, a CVN impact transition temperature of-115°C (at 0.33 cm gage) and good weldability as determined by bend, impact, and intergranular corrosion testing. The alloy possesses general corrosion resistance roughly comparable to T405 and T430 ferritic stainless steels. The impact resistance achieved with the mixture of ferrite and martensite is inconsistent with previous concepts of second phase toughening in microduplex alloys, with the mixture apparently being significantly tougher than either of its components in bulk form.

Opto-electronic tensile testing system

Abstract: A tensile testing system for use with a specimen of rubber or other material having a test region defined on its reduced midportion by a marking or markings of, for example, higher lightness than the other specimen surface. The system comprises a scanning device for repeatedly translating the optical characteristics of the specimen or specimens into an electrical signal as the specimen or specimens are subjected to increasing tensile stress, and a gate circuit for deriving from the output signal of the scanning device its portions corresponding to the test region or regions. The varying length of the test region or regions can be represented either by pulse durations or by pulse numbers. The scanning device can be either an "area scanner" such as a television camera or a "line scanner" such as a solid-state line image sensor. Various embodiments are disclosed.

The anisotropy of deformation and fracture in a directionally solidified Ni/Ni 3 Al-Ni 3 Cb lamellar eutectic alloy

Abstract: The orientation dependence of deformation and fracture modes was investigated for a directionally-solidified Ni−Ni3Al−Ni3Cb lamellar eutectic alloy (Ni-20 wt pct Cb-2.5 wt pct al-6.0 wt pct Cr) using optical and transmission microscopy to examine tensile and compression specimens tested at temperatures below the softening point of the δ (Ni3Cb) reinforcing phase (∼1050 K). In this temperature range there is a large difference between longitudinal and transverse tensile ductibility (>5 pct longitudinalvs<1 pct transverse). No single preferred fracture path (such as interfacial delamination) could be found to account for the low transverse tensile ductility. Analysis of the δ twinning geometry, however, indicated that the twinning strains for twins of the type {211}, which operate copiously in longitudinal tension, are negative in most transverse orientations, with Schmid factors being very low (<0.013) in the limited range of transverse orientations where {211} twin strains are positive. Examination of transverse tension test specimens broken at 1033 K confirm the absence of {211} twins, with only limited {011} twinning being found in selected grains, leading to the conclusion that the relatively low transverse tensile ductility of the eutectic results from the very limited number of deformation systems which operate in the δ reinforcing phase below the softening temperature.

Tensile strength of hybrid composites

Abstract: This paper presents an approximate, statistical analysis for the tensile strength of unidirectional hybrid composite materials consisting of two-dimensional arrays of alternating low elongation and high elongation fibres in a common matrix. Expressions for ineffective length and fibre strain concentration factor in hybrid composites are developed. The analysis identifies a number of important material properties that affect the failure process in hybrids: statistical fibre tensile failure strain characteristics, and fibre extensional moduli and cross-sectional areas. The influence of these parameters on the failure process is examined and differences between failure mechanisms in hybrids and composites containing only one type of fibre are considered. The analysis predicts that, in general, the failure strain of a hybrid should be different from those of composites reinforced with either of the “parent” fibres alone. It is found that the theory can explain the “hybrid effect” that has been observed by several authors: hybrids made by combining high elongation and low elongation fibres, such as graphite and glass, often display tensile failure strains greater than those of composites made from the low elongation fibres alone. Predicted failure strains are compared with available experimental data. Suggestions for future work in the area are presented.

Method for testing sheet metals

Abstract: A method of determining properties of sheet metal uses a specimen having a full width section and a reduced width section about 95% the width of the full width section in a tensile test. The strain hardening exponent is calculated from thickness and width measurements made before and after the specimen is strained to failure. The same and other measurements are used to calculate yield strength, elongation, ultimate strength and plastic strain ratio. Particularly useful for continuously yielding materials, the yield strength may also be determined from calculations using the strain hardening exponent and the ultimate strength.

An experimental investigation on the tensile moduli and strengths of graphite/epoxy laminates

Abstract: The results of a series of tensile tests on some graphite/epoxy laminates, at rates varying from 0.002 to 2 in./min are examined. The loads were applied at various angles to the fiber directions in each case. The rate-dependent behavior of the stress-strain response is assessed. Evidence is presented to indicate that failure first occurs on inner plies, and that, in some cases, moduli increase with increasing stress (or strain) level. Lamination theory is used to predict the moduli, and comparisons with experiment are given. This theory is also used in conjunction with three failure theories to predict ultimate strengths (with varying degrees of success). Further, two approaches to ply unloading after first-ply failure are used and discussed. One is a standard method found in the literature while the other is a proposed 'strength-of-materials' type of technique which is computationally much simpler.

Properties of superplastic Cr-Ni steel

Abstract: Superplastic flow has been investigated in the steel X5 CrNiTi 26.6 by means of the hot tensile test. Particular attention has been paid to the magnitude of flow stresses, strain-rate sensitivity, and total elongation with its dependence on microstructure (controlled by technological treatment), strain rate, and temperature. Of all the microstructural parameters examined, the matrix grain size seems to have the predominant influence. The steel exhibits superplastic behaviour if the matrix has a grain size Dα, ≤4.5μm,if the strain rate e is <10−1 min−1, and if the temperature is above 875° C. At temperatures ≥ 1000°C in the α- and γ- regions, grain growth occurs, and the superplastic flow consequently terminates. As temperature and strain rate are connected in an Arrhenius-type relationship, an activation energy for flow processes in the ferrite-austenite phase mixture can be determined for the range of ferrite grain sizes Dα,= 3.2 to 5.4 μm.The activation energy depends linearly on matrix grain si...

Mineral-filled polyethylene compsotion with improved characteristics

Abstract: PURPOSE:A mineral-filled polyethylene composition with improved tensile elongation, which is composed of a polyethylene resin and a specific inorganic filler treated on the surface.

Test for predicting fatigue life of bituminous concrete

Abstract: An examination of several simple test methods revealed that the indirect tensile test can be used to predict the fatigue life of bituminous concrete. This replaces the traditional, expensive, and time-consuming flexural fatigue test. The tests examined--indirect tensile, double punch, resilient modulus, flexure, resonant frequency, and pulse velocity--were selected from a literature search for use on several mixes obtained from variaous locations in the United States and containing a variety of asphalt cements and aggregates. The traditional flexural fatigue test was also performed on each mix, and the results were correlated with those from the simple tests. The correlations indicated that indirect tensile strength and stiffness can be used to predict the fatigue behavior of bituminous concrete. The indirect tensile method can be used for designing mixes with adequate fatigue service lives. /Author/