Showing papers on "Tensile testing published in 1989"

Tensile strain dependence of Brillouin frequency shift in silica optical fibers

Abstract: Brillouin frequency shift in a single-mode optical fiber has been measured as a function of tensile strain. The strain coefficient of normalized Brillouin frequency shift C identical to (dv/sub B//d epsilon )/v/sub B/ is found to be 4.4 for silica fibers. This result shows the potential of Brillouin spectroscopy to evaluate tensile strain in the fiber with the strain resolution of about 2*10/sup -4/. The origin of the large strain coefficient is discussed. >

On the estimation of the tensile strength of carbon fibres at short lengths

Abstract: Generally, to determine the fibre-matrix interfacial properties in fibre reinforced plastics, it is necessary to know the tensile strength of the fibre at very short lengths, for which direct measurements are not possible. Accordingly, in this study, the determination of the tensile strength of high strength carbon fibres and their gauge length dependence are analysed by means of the Weibull model. The influence of the estimator chosen and of the sample size on the calculated value of the tensile strength of the fibre are first determined. Secondly, the accuracy of the three- and the two-parameter Weibull distributions is examined. Finally, it is shown that the most appropriate extrapolation at short length is performed by means of a linear logarithmic dependence on gauge length of the tensile strength. This method seems to be valid for untreated as well as for surface-treated high strength carbon fibres.

Study of copper-alumina bonding

Abstract: Bonding between copper and alumina can be obtained by the “solid state bonding” process and the “liquid phase bonding” process The strength of interfaces has been tested mechanically using shear tests, tensile tests and fracture toughness tests The effects of bonding parameters on bond strength have been studied Observations by transmisssion electron microscopy have been performed to detect and analyse the nature and evolution of interfacial compounds as a function of copper oxidation and bonding time Chemical reactions lead to the formation of the binary oxide CuAlO2 The stability of this compound and the reversibility of chemical reactions appear to be very dependent on the amount of oxygen present in the system

The bovine pericardial xenograft: I. Effect of fixation in aldehydes without constraint on the tensile viscoelastic properties of bovine pericardium

Abstract: Tensile testing of tissue strips has been used to examine the effect of simple fixation in glutaraldehyde and formaldehyde on the viscoelastic properties of bovine pericardium. To assess tissue anisotropy, tissue strips were cut at 0 degree, 30 degrees, 60 degrees, and 90 degrees relative to the base-to-apex direction. Fresh anterior pericardium was modestly anisotropic, being least extensible in the base-to-apex direction; however, fixation removed this anisotropy. Fixation also produced a marked change in the response of the material to initial cyclic loading during preconditioning. Overall extensibility of the fixed material was significantly greater than that for the fresh tissue, consistent with a 10.7% shrinkage in aldehydes calculated from strain at fracture data. Reductions in stress relaxation and creep after fixation were noted as well, consistent with intrafibrillar crosslinking. Cyclic hysteresis and ultimate tensile strength were unaffected. Since the observed changes in the stress-strain response were largely attributable to shrinkage, control of shrinkage by physical means would allow for engineering modification of bovine pericardial mechanics for controlled anisotropy.

Microdamage analysis of fibrous composite monolayers under tensile stress

Abstract: The quasi-static deformation and fracture modes of several types of fibrous composite materials are studied from a fundamental viewpoint using a new experimental approach. Microcomposite monolayers, consisting of single fibres accurately positioned into a thin poly-meric matrix, were manufactured using a specially developed technique, and tested for strength by means of a custom-made miniature tensile testing machine. The materials used were E-glass, and Kevlar 29, Kevlar 49 and Kevlar 149 para-aramid fibres, and a room-temperature curing epoxy resin. The tensile testing machine was fitted to the stage of a polarized light stereozoom microscope and the fracture process was recorded both via a standard 35 mm camera and a colour video camera. The fibre content of the first generation of micro-composite monolayers used in this work was low (<0.025) but definite effects on the modulus and strength were obtained as the experimental data followed the rule-of-mixtures quite accurately in most cases. The failure process was different in each type of composite and current statistical models for strength are unable to account for the modes of failure observed in some of the systems studied. The experimental approach proposed is potentially useful in the study of the effects of interface chemistry modifications, fibre-fibre interactions, matrix toughness modification, misalignment effects, and more, on the deformation and failure micromechanics of composites.

Mechanical properties of Al–Li alloys Part 1 Fracture toughness and microstructure

Abstract: Mechanisms influencing the ambient temperature mechanical properties of commercial Al–Li alloys 2090, 8090, 8091, and 2091 are examined as a function of plate orientation, with specific emphasis on the role of microstructure. In Part 1, results on the uniaxial tensile and plane strain fracture toughness properties are presented and the behaviour is discussed in terms of the role of the matrix and grain boundary precipitates, associated precipitate free zones (PFZs), and the occurrence of short-transverse delamination. It is seen that in general peak aged microstructures show an excellent combination of strength and toughness (L–T, T–L), equal to or exceeding that shown by traditional 2000 and 7000 series high strength aluminium alloys. The superior toughness of peak aged compared with naturally aged microstructures seems to be associated with widespread matrix precipitation of platelike precipitates (T1 in Al–Li–Cu alloys and S in Al–Li–Cu–Mg alloys), β′-dispersoids and second phase particles whi...

Adhesive for low temperature applications

Abstract: Adhesive compositions are made from methacrylate ester monomers, elastomeric polymers having a Tg below -25° C. and which are soluble in the monomers, core-shell polymers which swell in the monomers but do not dissolve therein, and free radical producing catalysts. These adhesive compositions when used in bonded assemblies exhibit a combination of high adhesive bond impact strength and high bulk tensile elongation.

Study of interfaces of high‐performance glass fibers and DGEBA‐based epoxy resins using single‐fiber‐composite test

Abstract: The single-fiber-composite (SFC) technique was used to study the interfacial behavior between two flexible blends of diglycidylether of bisphenol A (DGEBA)-based epoxy and polyglycol epoxide and three glass fibers. Dog-bone-shaped SFC specimens were made and strained to obtain a distribution of fragment lengths. The fibers were tension-tested at two different gauge lengths. The fragment length distributions, the fiber strength data, and a Monte Carlo simulation of a Poisson/Weibull model for fiber strength and flaws were used to obtain the effective interfacial shear strength values. The results show that the interface does not fail. Instead, penny-shaped transverse cracks appear at every fiber break and grow as the specimen is strained. The interfacial shear strength values are many times higher than the yield shear strength values of bulk epoxy obtained from the tension test.

Plastic deformation and solid-phase transformation in β-phase polypropylene

Abstract: Tensile specimens of isotactic polypropylene, initially crystallized in the β-form with high purity, were tested at various temperatures. It was observed by WAXD that the most important phenomenon occurring in the course of a tensile test is the β-smectic transformation for specimens drawn at lower temperature and β-α transformation for specimens drawn at higher temperature, which takes place in the crystalline lamellae and is induced by plastic deformation. c-Axis oriented β-crystals have never been found in the drawn specimens. It was also shown that the β-smectic transformation propagates inside the spherulites from the equatorial regions, in which the chain axes are nearly parallel to the drawing direction, towards the diagonal and polar regions. Finally, it was noted that microvoids are formed simultaneously during plastic deformation, which may be due to the volume contraction induced by the β-α or β-smectic transformation.

Composition and temperature dependence of tensile properties of austenitic FeMnAlC alloys

Abstract: The effects of aluminium addition (0–4 wt%) to Fe-26MnAl alloys and carbon addition (01 – 03 wt%) to Fe-30Mn-1AlC alloys on tensile properties, especially tensile elongation, were investigated from room temperature to 4 K The transformation of austenite to deformation twins during the tests was very beneficial in enhancing tensile elongation at cryogenic temperatures The amount of deformation twins formed during plastic deformation was not the major factor for maximum elongation, but the optimum work hardening rate by the gradual formation of deformation twins played an important role The maximum elongation peak shifted to lower temperatures with increased aluminium (5 aluminium wt%), but moved to higher temperatures with increased carbon content (03 wt%) The new flow equation σ = Kϵ N exp ( Mϵ ) was applied to calculate uniform elongations The calculated values were in reasonable agreement with the measured values

Method for fabricating high-temperature tensile test specimens

Abstract: A carbon composite tensile test specimen for high temperature testing and a method of fabricating the same are disclosed. A plurality of holes are drilled in first and second end sections of the specimen and then the end sections are electroplated with nickel. The nickel plating of the end sections prevents breakage of the ends in the jaws of a tensile testing apparatus. For high-temperature testing, a standard-sized specimen may be used with the jaws in the hot zone.

Mechanical properties of Co3Ti polycrystals alloyed with various additions

Abstract: Third elements including vanadium, tantalum, chromium, molybdenum, tungsten, iron, nickel, aluminium and germanium, were added to L12-type Co3Ti polycrystals with a composition of 23 at % Ti. Tensile tests from 77 to 1273 K were carried out to investigate the mechanical properties of these alloys. Anomalous increases of the yield stress with increasing temperature were observed from 473 to 973 K (or 1100 K depending on the strain rates) for all tested alloys. It was also observed that the yield stress increased with decreasing temperature below 473 K and decreased with increasing temperature above 973 K (or 1100 K). The yield stresses above the peak temperature were very sensitive to the strain rate and grain size. Microstructural observation showed that gram-boundary sliding had a considerable contribution to the fall in yield stress at high temperatures. The elongation showed a maximum around 673 K and a minimum around 1073 K for all alloys. Microstructural and fractographic observation showed that most alloys tested suffered from hydrogen-related embrittlement at ambient temperatures and grain-boundary cavitation-related embrittlement around 1073 K. Addition of aluminium and iron was found to produce a significant improvement in hydrogen-related embrittlement at room temperature.

Effects of microstructure of the behavior of an aluminum alloy and an aluminum matrix composite tested under low levels of superimposed hydrostatic pressure

Abstract: Experiments have been conducted on an aluminum alloy and an aluminum matrix composite tested in tension under the influence of superimposed hydrostatic pressure. Monolithic alloys heat-treated to underaged (UA) and overaged (OA) conditions exhibited significant differences in their responses to the superimposition of hydrostatic pressure during tension testing. Significant increases in ductility were obtained with moderate increases in confining pressure for the OA alloy, while the UA alloy exhibited little effect of pressure. In contrast, significant increases in ductility were obtained for the composites, regardless of the matrix aging condition. The effects of pressure on frature are determined in light of the micromechanisms of fracture in these materials.

Experimental Characterization of Delamination Fracture

Abstract: Experimental methods for characterizing interlaminar fracture behavior of composite materials are discussed The classic short-beam shear test is presented along with a number of methods based on linear elastic fracture mechanics These methods include the double cantilever beam test, the edge-delamination test, the end-notch flexure test, both the single and double cracked-lap shear test, and the off-axis center notch tensile test Each test method is discussed from an applied mechanics point-of-view Such an approach is appropriate in light of the complex nature of composite materials In addition, relationships between fundamental experimental data and structural performance are considered This includes consideration of mixed-mode failure criteria and a parametric study involving a one-dimensional delamination buckling model for evaluating the materials characterization/structural performance interface Consideration is also given to relationships between basic resin properties and in situ performance as a matrix material in the composite

Tensile behaviour of grass

Abstract: The tensile behaviour of ryegrass (Lolium perenne L.), which was grown, harvested and tested under controlled conditions, is described. Whereas some of the grass leaf specimens behaved in a predominantly brittle manner, others evinced a semi ductile mode such that a proportional limit could be identified. Results indicated that the tensile properties depended upon specimen location and the tensile test strain rate. The data showed that as strain rate was increased, the stiffness, toughness and strength increased, while ductility decreased. Comparison of test results as a function of water content did not reveal statistically significant differences in any of the mechanical parameters. Analysis of the leaf structure suggests that the epidermal cells play a major role as a load-bearing component.

Relating Resin Mechanical Properties to Composite Delamination Fracture Toughness

Abstract: The relationship between resin mechanical properties and the resultant composite Mode I and Mode II delamination fracture toughnesses in graphite-epoxy systems was examined. The tensile property that best correlated with composite delamina tion toughness was the resin tensile elongation. Resins with higher tensile elongations pro duced composites with a higher delamination toughness, though the relationship between the two may not be a simple one.The method used to toughen the resin affected the resulting composite delamination toughness. A rubber toughened resin would produce a tougher composite than would a resin that had the same tensile elongation (but with a lower crosslink density rather than rubber particle additions).

On microstructure-property correlation of thermally aged type 316L stainless steel weld metal

Abstract: This paper deals with the microstructural changes and consequent deterioration in the room temperature tensile properties of type 316L stainless steel weld metal when exposed to elevated temperatures (773 to 973 K) for prolonged periods (up to 5000 hours). The microstructure-property correlation derived in this study is based on a variety of techniques: Magne-Gage, electrochemical extraction, X-ray diffraction, tensile testing, and both optical and electron microscopy. It has been established that the amount and morphology of the sigma phase are the key factors in determining the changes in the strength levels, total elongation, and extent of work hardening. The amount and morphology of sigma, in turn, is seen to depend on the relative kinetics of the various transformations, such as dissolution of delta-ferrite, growth of carbides,etc., shape changes in sigma, and the relative stabilities of the phases at the corresponding temperature of aging. The complicated dependence of the tensile properties on the microstrutural changes has been explained with direct quantitative evidence.

Polyester fibers in asphalt paving mixtures

Abstract: The primary objective of this study was to determine whether homogeneously dispersed polyester fibers improve the tensile strength and moisture susceptibility properties of asphaltic concrete. The secondary objective was to analyze the effects of changing the denier, length, and percentage of a single fiber type. The first phase of the experimental plan was to perform a Marshall method of mix design on all the fiber and nonfiber asphaltic concrete mixtures. The optimum asphalt cement contents that were determined from these tests were then used when producing the mixtures for the indirect tensile tests. The indirect tensile test was selected for the second phase of this study because it enables simultaneous analyses of tensile and moisture susceptibility properties.