Showing papers on "Tensile testing published in 1980"

Tensile fracture of cancellous bone

Abstract: Excised specimens of cancellous bone from human femora were subjected to compressive or tensile testing, and the resulting force-displacement curves were recorded. The relationships between bone strength and apparent density were similar for specimens tested in these two loading modes. The modulus of elasticity was also comparable for the tensile and compressive specimens. Specimens loaded in compression absorbed considerable energy after the initial fracture because of progressive impaction of the trabeculae. In the specimens loaded in tension, the fractured bone fragments separated and therefore absorbed little additional energy after the initial failure. The energy absorption capacity was thus significantly lower for the tensile specimens. The results of this study show that the primary difference in mechanical properties of cancellous bone tested in tension and compression is the energy absorption capacity. This finding suggests that tensile and avulsion fractures of cancellous bone observed clinically are associated with minimal energy absorption and therefore may be precipitated by relatively minor trauma.

Fracture mechanism of plant fibres

Abstract: This paper, which describes work from an extensive study of various plant species, is aimed at presenting the best common physical description of the mechanism of failure in tension of cellulose-based fibres. A correlation coefficient of r=0.69 was observed between the mean tensile strengths and Young's moduli of fibres extracted from leaves, stems, and other miscellaneous sources. This observation is attributed to increases in Young's modulus and tensile strength with decreasing microfibril angle and increasing cellulose content. A cylindrical cell model was applied to the mean tensile strengths of fibres preconditioned at 24 to 27° C and 60% relative humidity. A modification of the resulting expression was used to produce the best correlation coefficient of r=0.89 between predicted and measured mean tensile strengths. However, the importance of cellulose content for strength which is presently illustrated for various plant species is not reflected in terms of mean fracture strain, which was increased by increasing microfibril angle showing why high works of fracture can be obtained from different species.

The relationship between tensile strength and flexure strength in fiber-reinforced composites

Abstract: Tensile data on unidirectional composites generated from a flexure test usually yield a higher strength than observed from a standard tensile coupon. According to a statistical-strength theory based on a Weibull distribution, the presence of a stress gradient in the flexure-test results in an apparent increase in tensile strength as compared to the tensile test under uniform stress. In the present paper, this concept is explored by utilizing data from unidirectional graphite-epoxy composites to compare with theoretical results generated from a two-parameter Weibull distribution. A larger variation in tensile strength is observed from tensile-coupon data than from flexure data. Such differences are not in accordance with strength theories based on a uniform flaw distribution and raise questions concerning variability of the test methods, as well as sources of material variability.

On the law of mixtures in dual-phase steels

Abstract: The applicability of the equation of the stress in the ferrite at the ultimate tensile strain to dual-phase steels obtained by heating 1010 and 1020 grades was tested. The law of mixtures describe the tensile strength of 1010 steels provided the dislocation hardening is included. The equation application to other dual phase systems may require modification to account for differences in metallurgical parameters. (FS)

Tensile Strength of Concrete: Double-Punch Test

Abstract: The tensile strength of concrete is most commonly measured by the indirect split-cylinder test. Recently, an alternative new test, known as double-punch test, has been proposed. It is the purpose of this paper to summarize the present stand on the double-punch test method for the determination of tensile strength of concrete. The summary deals with two equally important aspects of progress — new solutions emerging from the analytical study and experimental results reported from laboratory tests. This paper attempts to evaluate critically this new test method and to determine the range of their applicability, relative merits, and limitations as compared to the well-established split-cylinder tests. Throughout this development and evaluation, it has been recognized that a balance must be struck between the requirement of realistic representation of tensile strength of concrete and the requirement for simplicity in practical use. It is considered that in both these respects, the double-punch method is satisfactory.

Morphology and properties of short segment block copolymers

Abstract: The structural, mechanical, and thermal properties of a polyetherpolyester segmented copolymer system [poly(tetramethylene oxide)/poly(tetramethylene terephthalate)] and two polycaprolactone-polyurethane elastomeric systems (based on 4, 4′-diphenylmethane diisocyanate or 4, 4′-dicylohexylmethane diisocyanate) were investigated. Experimental techniques employed in the analysis include DSC, dynamic mechanical testing, IR dichroism, small-angle x-ray and laser light scattering, and tensile testing. Results show that material properties can be explained in terms of system compatibility, crystallization characteristics, and domain morphologies.

The effect of chain structure on the annealing and deformation behaviour of polymers

Abstract: In a tensile test ductile thermoplastics may give either uniform deformation or necking. Recently it has been found that those giving uniform deformation either, are known to have extended chain configurations in solution, or have chemical formulae with linear structures and relatively few flexible bonds. The observed differences in behaviour can be predicted from a viscosity retarded rubber elasticity model in which a constant related to chain flexibility is introduced, which quantifies the strain hardening of the material. It is argued that the early development of strain hardening generally interferes with the localization of plastic strain in shear bands or crazes (as well as in a neck) and correlates with the stress cracking performance of high density polythenes.

Dynamic Tensile Testing of Structural Materials Using a Split Hopkinson Bar Apparatus

Abstract: : Stress-strain curves in tension obtained on a large number of structural materials at strain rates up to 1000/s are presented. A modified split Hopkinson bar apparatus used for high strain rate tensile testing is described. Data are compared with other published results. The flow stress of all the materials tested is seen to increase to some extent over the range in strain rates from 0.001 to 1000/s.

Order-Strengthening in a nickel-base superalloy (hastelloy alloy S)

Abstract: HASTELLOY* alloy s is a commercial, solid solu* HASTELLOY is a registered trademark of Cabot Corporation tion-strengthened, nickel-base superalloy developed for applications where oxidation resistance, low thermal expansion and retained ductility after long-time exposure at elevated temperatures are prerequisites. Its typical heat treatment consists of annealing at 1340 K (1950 °F) followed by air cooling to produce an essentially single phase material. When specimens from annealed heats were aged at 810 K (1000 °F) for 1000 to 8000 h and then tensile tested at room temperature, it was found that relative to the annealed condition, the 0.2 pct yield strength had nearly doubled while about 70 pct of the tensile elongation was retained. It is the objective of this note to report on the formation of a long-range ordered phase that caused the observed strengthening.

The effect of ordering on the hydrogen embrittlement susceptibility of Ni2Cr

Abstract: Isothermal annealing at 500 °C for various lengths of time after rapid quenching from 900 °C results in different degrees of ordering in Ni2Cr. Tensile specimens of disordered and ordered Ni2Cr were subjected to hydrogen embrittling and nonembrittling environments before and during tensile testing. The hydrogen embrittlement susceptibility was determined by reduction-in-area losses (RA loss) after failure. The results of the tensile tests indicated that the disordered alloy and highly ordered alloy were the most susceptible to hydrogen embrittlement. The RA loss in each case was approximately 70 pct. The tests revealed a minimum susceptibility to hydrogen embrittlement between 40 and 50 pct order. The fracture surfaces of the specimens, as examined by scanning electron microscopy, showed that the extent of embrittlement is correlated with the amount of intergranular failure. The mechanisms for failure in Ni2Cr appear to depend upon the extent of aging in the alloy.

Effect of strain wave shape on high temperature fatigue life of a type 316 steel and application of the strain range partitioning method

Abstract: Effects of strain rate and strain wave shape on low-cycle fatigue life of a Type 316 stainless steel were investigated at 600 and 700 °C. A great reduction in the fatigue life corresponded with a variation in the fracture mode. Especially extensive grain boundary microcracks such as wedge- and cavity-type cracks were observed in slow-fast sawtooth wave shape tests and in tension hold time tests, respectively. The test results were analyzed by the strain range partitioning method proposed by Manson, Halford and Hirschberg. In applying the method, a new technique of partitioning the inelastic strain range was proposed and used. Four component strain range vs life relationships were dependent on the testing temperature between 600 and 700 °C. However, the difference between 600 and 700 °C was eliminated by using normalized component strain range by dividing by ductility of creep rupture test and tensile test.

Tensile strength of restorative resins

Abstract: The purpose of the present work was to measure the tensile strength of restorative resins and to study the effect of the method of measurement on the recorded results. A direct pull method using dumb-bell shaped specimens was used. The tensile strength of the resins was also tested using the diametral compression method suggested by the A.D.A. It was found that the method of testing affects the results. Although the diametral compression method is a simple method, it cannot be considered reliable for all types of material. The tensile strength of the conventional composites was significantly higher than the tensile strength of the microfilled composites.

An examination of diffusion bonded interfaces in a mild steel

Abstract: A study of the interface surfaces of fractured diffusion bonds in a mild steel was made in order to further understanding of the mechanisms of bond formation and of the mechanical properties of such bonds. The results show that parent-metal tensile strengths are achieved with some 20% of the interface still unbonded and that these unbonded areas are present as grooves rather than as isolated voids as had previously been thought. The relative orientation during bonding of any directional surface finish on the two component halves affects the geometry of the unbonded grooves and, to a slight extent, the resultant tensile strengths. The results also suggest that tensile testing alone is not a sufficient criterion by which bond quality should be assessed; impact or fracture toughness testing also must be considered.

Polymer dope composition, composite fibers made therefrom and process for making same

Abstract: There is provided a shaping composite dope composition comprising a cellulose derivative, an acrylonitrile polymer and a solvent capable of substantially dissolving these polymeric materials simultaneously therein, and exhibiting flow birefringence or optical anisotropy. A composite fiber made from the dope has a strucute such that the cellulose derivative is present in the form of a dispersed phase of fine fibers in a matrix of the acrylonitrile polymer, the crystalline orientation angle of the acrylonitrile polymer phase is 18° to 63° as measured by wide angle X-ray diffractiometry, and the ratio of the crystalline orientation angle of the cellulose derivative phase to the crystalline orientation angle of the acrylonitrile polymer phase satisfies a specified requirement. The composite fiber is excellent in the thermal dimensional stability and mechanical properties, such as tensile strength and tensile elongation and loop strength and loop elongation.

Cyclic creep of type 304 stainless steel during unbalanced tension-compression loading at elevated temperature

Abstract: Samples of Type 304 stainless steel were subjected to cyclic stresses with a positive mean stress at 300 and 560°C. Very rapid net elongation was observed whenever the stress limits were such as to produce a plastic strain amplitude of the same order of magnitude as the elastic strain at the peak stress. The maximum mean strain-rate, or cyclic creep rate, for a given peak tensile stress was achieved when the mean stress was just slightly above zero. Increasing the mean stress caused the mean strain rate to de-crease. The sensitive dependence of the mean strain-rate on the plastic strain ampli-tude and inverse dependence on the mean stress indicates that remobilization of disloca-tions by the reverse strain is an important mechanism for cyclic-creep acceleration. Although rapid cyclic creep was observed at both temperatures, a measurable mean strain rate was found for a much narrower range of stress conditions at 560 than at 300°C. The strain accumulated during cyclic creep did not produce any strain hardening, but did influence the shape of the stress-strain curve in a subsequent tensile test.

Mechanical properties of Stycast-1266 at low temperatures

Abstract: Young’s modulus, the critical tensile stress, and the fracture stress of Stycast‐1266 have been determined by the tension test as functions of temperature between room temperature and 2.2 K.

Ductile fracture initiation in pure α-Fe: Part I. Macroscopic observations of the deformation history and failure of crystals

Abstract: Single crystalα-Fe whiskers, grown by the reduction of ferrous chloride by hydrogen have been strained to fracture in an Instron tensile testing machine and in a bench straining device at various elongation rates at room temperature. Whiskers were found to exhibit macroscopic slip behavior strongly dependent upon elongation rate while the geometric reduction in area and the fracture mode remained in all cases identical. Ductile rupture of iron whiskers produces a characteristically shaped chisel-edge fracture whose geometry is sensitive to crystal orientation, due to the geometry of active slip systems, but which isnot a function of strain rate. The micromechanisms of ductile rupture of these single crystals are strongly affected by dislocation dynamics. The development of dislocations necessary to accomodate an extensive reduction in area appears to be independent of the nature of surface slip observed. Dislocation structures form small volume elements which are separated from one another by dislocation cell walls. The accommodation of large strains as well as the reduction in area is determined by the movement of dislocations on the order of a distance equal to that of the dislocation cell size. The boundaries of the cell and/or the cell volume could then be expected to be specifically related to the site where the initiation of fracture occurs.

Evaluation of low-temperature pavement cracking on elk county research project

Abstract: The Elk County Research Project in Pennsylvania consists of six test pavements constructed in September 1976 by using AC-20 asphalt cements from different sources Two test pavements developed extensive low-temperature non-load-associated cracking during the first severe winter After 25 years in service and two more severe winters, the remaining four test pavements do not exhibit any significant cracking Periodic performance evaluation of these pavements has been conducted Cracking of the two test pavements was attributed to high stiffness moduli of asphalt cement and asphaltic concrete, determined by indirect nomograph methods It was felt that the stiffness moduli should also be determined by direct measurements on actual pavement cores Split tensile tests were conducted at four below-freezing temperatures at a deformation rate of 127 mm/s (005 in/min) to determine such basic mix properties as stiffness modulus, tensile strength, and tensile strain at failure Stiffness moduli of the aged pavements were also determined by the indirect Heukelom and McLeod methods The data from the tensile test indicate that tensile strength or tensile strain at failure, considered independently, does not explain the low-temperature cracking phenomenon on this project Both direct measurements and indirect methods show that the stiffness modulus of the asphaltic concrete is a better indicator of potential low-temperature cracking Stiffness moduli determined from the tensile test were generally found to be lower than those obtained by the two indirect methods A maximum permissible stiffness modulus of 269 MPa (3900 lbf/sq in) for original asphalt cement (at minimum pavement design temperature and 20,000s loading time) has been selected to develop AC-20 asphalt cement specifications for the cold regions of Pennsylvania (Author)

Effect of hydrogen on the fracture properties and microstructure of Ti-6Al-4V

Abstract: A Ti-6Al-4V alloy was hydrogenated to various levels and subjected to fracture toughness and conventional tensile testing. The results indicate that these particular properties are not unduly influenced by hydrogen contents of up to 490 ppm. Furthermore, the fracture resistance was not affected by a 20 h hold on load, although sustained load cracking did occur at high hydrogen contents. Nevertheless, transmission electron microscopy revealed that, at hydrogen concentrations in excess of 225 ppm, strain-induced hydride precipitation occurred ahead of the loaded crack tip.

Tensile Strength and Ultimate Elongation of Rubber-Fibrous Compositions

Abstract: Data are presented which show that the mechanism of fracture in rubber-fiber composites is governed by the adhesion of the matrix material to the fiber as well as the strength of the matrix. Degree of orientation of the fiber is also important.

Safety tires for automobiles.

Abstract: A safety tire for automobile, which comprises a tire body (A) and a number of closed hollow elements (6) of a thermoplastic synthetic resin having a tensile modulus of 200 to 30 000 kg/cm , a tensile strength of 100 kg/cm or more, preferably 200 to 1000 kg/cm , and a tensile elongation of 10% or more, preferably 100 to 800%, said hollow elements being arranged in series along the outer circumference of a wheel rim (4) which supports the tire body An automobile can be run on the safety tire even after the tire body is punctured