Showing papers on "Ultimate tensile strength published in 1983"

A tensile testing technique for fibre-reinforced composites at impact rates of strain

Abstract: A brief review is given of techniques which have been employed in attempts to determine the mechanical properties of composite materials under tensile impact loading. The difficulties encountered in the design of a satisfactory tensile impact testing machine for composite materials are discussed and a new method, using a modified version of the standard tensile split Hopkinson's pressure bar (SHPB), is described. Dynamic stress-strain curves for unidirectionally-reinforced carbon/epoxy composite, in which failure occurs in less than 30 μsec at a mean strain rate of about 400 sec−1, are presented and their validity is established. An extension of the technique to allow the testing of wovenroving reinforced glass/epoxy composites is described and dynamic stress-strain curves obtained for which the times to failure approach 100 μsec and the average strain rate is of the order of 1000 sec−. Comparative stress-strain curves at low and intermediate rates of strain are obtained and the effect of strain rate, over about 7 orders of magnitude, on the tensile modulus, and strength, fracture strain and energy absorbed in fracturing is determined. The limitations of the technique are discussed.

Alkali treatment of coir fibres for coir-polyester composites

Abstract: Coir fibres were subjected to alkali treatment with a view to improving the wettability of coir fibres by a commercially available resin such as polyester. Tensile strength of the fibres increases by 15% when the fibres are soaked in 5% aqueous solution of NaOH at 28±1° C for 72 to 76 h after which it shows a gradual decrease. This decrease is much more pronounced when the alkali is replenished after every 24 h. SEM observations showed the removal of cuticle and tyloses from the surface of coir as a result of alkali treatment, resulting in a rough fibre surface with regularly spaced pits. The debonding stress of alkali-treated fibres from polyester matrix was 90% higher than that of untreated fibres from the same matrix. Untreated fibres tended to float in the polyester whereas alkali-treated fibres were uniformly dispersed in polyester. Incorporation of 0.30 volume fraction of untreated and treated fibres in polyester resulted in composites having 11% and less 5% porosity, respectively. Flexural strength, modulus and impact strength of composites containing alkali-treated fibres were 40% higher than those containing the same volume fractions of untreated fibres. Longitudinal ultrasonic velocity and sound attenuation measurements indicated less fibre segregation and better fibre-matrix bonding in composites containing alkali-treated fibres.

Differential stress magnitudes during regional deformation and metamorphism: Upper bound imposed by tensile fracturing

Abstract: Veins occupying tensile fractures are a common feature of metamorphic rocks of all grades. It can be shown in many cases that such veins are synmetamorphic and that they underwent repeated cycles of fracturing and healing throughout deformation and foliation development. Theoretical failure models have predicted that tensile failure is limited to differential stresses less than four times the tensile strength of the material (σ 1 −σ 3 ⩽ 4 T ), and this condition can therefore be used to place an upper bound on differential stress intensities during deformation and foliation development where they are concurrent with vein formation. The tensile strengths of rocks are generally less than 10 MPa, and in the presence of a high temperature metamorphic fluid, a value of 5 MPa may be more reasonable, due to subcritical crack growth. It is thus concluded that differential stress intensities during crustal orogenesis will be less than 40 MPa, and they may be lower than 20 MPa.

Biomechanical properties of bone allografts.

Abstract: The biomechanical properties of allograft bone can be altered by the methods chosen for its preservation and storage. These effects are minimal with deep-freezing or low-level radiation. Freeze-drying, however, markedly diminishes the torsional and bending strength of bone allografts but does not deleteriously affect the compressive or tensile strength. Irradiation of bone with more than 3.0 megarad or irradiation combined with freeze-drying appears to cause a significant reduction in breaking strength. These factors should be considered when choosing freeze-dried or irradiated allogeneic bone that will be subjected to significant loads following implantation.

Mechanical properties of electrochemically prepared polypyrrole films

Abstract: The mechanical and conducting properties of free-standing films of polypyrrole toluenesulfonate depend on the preparation conditions. Films prepared in aqueous ethylene glycol solvent mixtures show a variation of two orders of magnitude in the conductivity and of a factor of three in the tensile strength.

Structural behaviour of reinforced concrete beams strengthened by epoxy bonded steel plates.

Abstract: The development of synthetic adhesives based on epoxy resins has opened new possibilities for bonding structural materials together. The present work was concerned with the use of epoxy resins to strengthen reinforced concrete beams by externally bonded steel plates. It was found in the first part that the assessment of the properties of the epoxy adhesive is of paramount importance as they varied considerably with the thickness of the test specimen and the rate of loading. The adhesive proved to offer a bond stronger than concrete in shear and resulted in a composite action between the beams and steel plates. Preloading the beams prior to strengthening them did not have any adverse effect on their behaviour. The added strength from the plates was fully exploited even in beams which were held under a preload of 70% of their ultimate strength while being strengthened. Stopping the plate in the shear span, short of the support, created a critical section where premature bond failure occurred beyond a certain plate thickness. Failure was caused by the combination of high peeling and bond stresses present in the region where the plate was stopped. These stresses were due to the transfer of tensile forces from the plate to the bars in that region and were higher with thicker plates. Bonding steel plates on the tension face of the beams increased their shear capacity by 9 to 15%. This may have been due to dowelling action from the plates which had a greater contact area with concrete than an equivalent amount of internal steel bars. The use of externally bonded steel as shear reinforcement was effective but requires further investigation. The external web strips failed prematurely as compared to equivalent stirrups. The long term deformations in plated beams were highly affected by the conditions of their environment but despite 47 month exposure no visual deterioration of the concrete-epoxy-steel joint was observed.

Mechanical properties of banana fibres (Musa sepientum)

Abstract: The stress—strain curve for banana fibre is determined. Properties such as the initial modulus (YM), ultimate tensile strength (UTS) and percentage elongation are evaluated as a function of fibre diameter, test length and speed of testing. It is found that YM, UTS and % elongation show little variation in their values for fibres of diameter ranging from 50 to 250 μm. The UTS and breaking strain are found to decrease with an increase in the test length while both breaking strength and breaking strain remain constant with the increase of speed of testing from 0.5 to 100 × 10−3 m and thereafter they both decrease. These observed properties are explained on the basis of the internal structure of the fibre, namely, the number of cells, spiral angle and the number of defects. Scanning electron microscopic (SEM) studies of the fractured surfaces of these fibres indiacte that the failure is due to pull-out of microfibrils accompanied by tearing of cell walls; the tendency for fibre pull-out seems to decrease with increasing speed of testing.

Cycle-dependent and time-dependent bone fracture with repeated loading

Abstract: Fatigue tests of human cortical bone (up to 1.74 X 10(6) cycles) were conducted under tension-compression (T-C) and zero-tension (O-T) modes with a 2Hz, stress controlled, sinusoidal loading history. Tensile creep-fracture tests at constant stress levels were also performed. The relationship between the initial cyclic strain range and cycles to failure with the T-C specimens were consistent with that derived previously in low-cycle fatigue under strain control. Using a time-dependent failure model, the creep-fracture data was found to be consistent with previous studies of the influence of strain rate on the monotonic tensile strength of bone. The model also predicted quite well the time to failure for the O-T fatigue specimens, suggesting that creep damage plays an important role in O-T fatigue specimens.

Adhesive bonding of various materials to hard tooth tissues: forces developing in composite materials during hardening.

Abstract: Reported measurements show that significant tensile stresses develop during the hardening of composite resins if there is bonding to the cavity walls.

Microstructure, tensile deformation, and fracture in aged ti 10V-2Fe-3Al

Abstract: In the /3-Ti alloy Ti-10V-2Fe-3Al a variety ofα-andω-aged microstructures with different yield stresses was established by combinations of forging and heat treatment. Tensile tests have shown that plastic deformation and fracture are strongly influenced by the morphology, size, and volume fraction of the different types of a-phase (primary a, secondaryα, grain boundaryα), as well as by the-phase. A detailed microscopical study revealed several deformation and fracture modes. It appears that at several sites stress and strain concentrations and subsequent void nucleation can occur and that the quantitative combinations of the differentα-types determine which sites are active. The dominant deformation mode for the (α +gb) solution treated andα-aged conditions was a strain localization in theα-aged matrix leading to voids at the interface between aged matrix and primary a-phase. In case of theβ-solution treated andα-aged microstructures the grain boundaryα leads to a strain localization in the softα-film and to void nucleation at grain boundary triple points at low macroscopic strains. Based on the above mechanisms it is discussed in detail how varying size, volume fraction, and morphology of theα-phase affect the ductility. The embrittling effect ofω-particles can be largely reduced by a grain refinement.

Statistical analysis of multiple fracture in 0°/90°/0° glass fibre/epoxy resin laminates

Abstract: Measurements of the distributions of crack spacings developed in the 90° ply of 0°/90°/0° glass fibre/epoxy resin laminates under tensile loading show that the ply has a variable strength. As a consequence the strain at which cracking begins is very dependent on the specimen length. The observed distributions of crack spacing are not consistent with the assumption of a uniform strength for the 90° ply. A statistical model provides a good description of the cracking behaviour particularly when the cracks are widely spaced. Magnification of the stress in the matrix between the relatively stiff glass fibres leads to debonding which is observed as a reversible “stress-whitening.” The distributions reveal a lower probability of crack formation in the under-stressed region close to the existing cracks and provide estimates of the size of this region. The method of analysis can be applied to many systems which exhibit multiple fracture.

Effects of nitrogen on dislocation behavior and mechanical strength in silicon crystals

Abstract: The characteristics of dislocation behavior and mechanical strength in tensile tests are investigated on the silicon crystals that are doped with nitrogen at the time of crystal growth by the floating‐zone technique. These are compared with those in the usual floating‐zone‐grown silicon crystals. Nitrogen atoms dispersed in a silicon crystal are shown to have no influence on the velocities of dislocations in motion in the temperature range above 600 °C. Dislocations in the nitrogen‐doped crystal are, however, immobilized while the crystal is kept under a low or zero applied stress at elevated temperatures. Like Czochralski‐grown silicon, nitrogen‐doped silicon shows a much higher yield strength than usual floating‐zone‐grown silicon when crystals are dislocated. It is concluded that interstitial nitrogen atoms bring about the hardening of silicon crystals through locking of dislocations upon congregating on the latter.

Effect of reducible properties of temperature, rate of strain, and filler content on the tensile yield stress of nylon 6 composites filled with ultrafine particles

Abstract: The yield stress of nylon 6 (Ny6) composites filled with ultrafine and micron-sized (SiO2 and glass) particles was measured as a function of temperature, rate of strain, and filler content. The yield stress of the composites filled with ultrafine SiO2 particles increased with filler content and decreased with filler size, whereas for composites filled with glass particles, this relation was reversed. For ultrafine SiO2 filled composites, the tensile yield stress was found to be reducible with regard to temperature, rate of strain, and filler content. At a given filler content, composite curves were obtained for yield stress plotted against the logarithm of the strain rate. The Arrhenius plot of the shift factors for composing the strain rate-temperature master curve formed a single curve irrespective of the filler content and size. The curve comprised two linear regions with a break appearing at 110[ddot], corresponding to a transition of the matrix polymer. The master curves obtained for differe...

Age-dependent influence of strain rate on the tensile failure of rat-tail tendon.

Abstract: Sensitivity of tensile strength, failure strain, and failure energy density to strain rate was studied for rat-tail tendon (RTT), a collagen-rich connective tissue. Tendons from animals aged 1-27 months were stretched at a high (720 percent/s) and low (3.6 percent/s) strain rate. Each failure parameter increased with strain rate. However, the sensitivity of tendon failure to rate of strain decreased rapidly during growth and sexual maturation of the animal. The study provides basic data on the rate-sensitive strength of collagen fibers using RTT.

Tensile yield stress of polypropylene composites filled with ultrafine particles

Abstract: For polypropylene composites filled with ultrafine or particles of the order of microns, (SiO2 and glass, respectively), yield stress was measured as functions of temperature, the rate of strain and filler content. The yield stress of the composites filled with ultrafine particles increased with the filler content and decreased with the filler size, while for the composites filled with glass particles, these relations were reversed. For SiO2 filled composites, the tensile yield stress was found to be reducible with regard to temperature, the rate of strain and the filler content. The Arrhenius plot of the shift factors for composing the logarithmic strain rate — temperature master curve formed a single curve irrespective of the filler content and size. The curve comprised three linear regions with breaks appearing at 60 and 110° C, where the transition of the matrix polymer took place. The master curves obtained for different contents of a given size filler could be further reduced into a grand composite curve by shifting them along the axis of logarithmic strain rate, with the logarithmic second shift factors proportional to the square root of the volume fraction of the filler. The dependence of the filler volume fraction on the second shift factor was related to the dispersion state of fillers in PP matrix, namely, the promotion of the aggregation with filler content. The dependences of the yield stress on the filler volume fraction and size were explained by a modified equation based on the dispersion strength theory, with an aggregation parameter incorporated.

Use of wood fibers in thermoplastic composites

Abstract: Wood fibers from aspen and spruce have been used for filler and reinforcement of polystyrene. The wood fibers used were in the form of refined wood. In order to improve compatibility of wood fibers with polymeric matrices, fibers have been modified by copolymerization with styrene. The kanthate method of grafting employing the ferrous-hydrogen peroxide catalytic system was used for fiber treatment. The following properties of composites have been measured: elastic-modulus, tensile strength, and energy absorbed at break. In summary, it has been found that the composites from grafted fibers showed superior mechanical properties to those with original fibers. In general, as a filler, the aspen fibers were superior to spruce, and the shorter fibers superior to longer ones. Mechanical properties of composites as compared to polystyrene were improved as follows: elastic modulus +37 percent; tensile strength +35 percent and energy at breakup by 43.5 percent. The best composites properties have been achieved at 40 percent of fiber fraction present.

Effect of stress triaxiality on neck propagation during the tensile stretching of solid polymers

Abstract: Cylindrical samples of high density polyethylene were tested in tension at 21° C and a nominal strain rate of 8.5 × 10−4 sec−1. The occurrence of necking in the centre of the specimens was provoked by the introduction of area defects of various sizes. The stabilization of this constriction and its propagation towards the ends of the specimens was studied photographically. An analytical method for the description of neck development is outlined, based on the use of strain and strain rate gradients. The times corresponding to neck initiation and stabilization are shown to be associated with critical values of the local strain hardening coefficient of the material. The role of area, strength and temperature inhomogeneities in the kinetics of strain localization is discussed. A further inhomogeneity term based on the axial variation of the Bridgman triaxiality factor FT is introduced. It is shown that the transverse compressive stresses associated with the shoulders of the neck can play a significant role in neck propagation in otherwise homogeneous materials.

The effect of interfacial adhesion on the tensile behavior of polystyrene–glass‐bead composites

Abstract: The tensile behavior at 20 DegC of polystyrene (I) [9003-53-6]-glass bead composites was studied at glass concns. from 0 to 25 vol.%. To gain insight into the role of interfacial adhesion, the bonding between glass and I was varied by using different silane coupling agents [Z-6032 [34937-00-3] and CH2:CHSi(OEt)3 [78-08-0]]. In contrast to the elastic behavior, the crazing behavior (i.e., the crit. applied tensile strength for craze formation at beads) of the composites was considerably affected by the degree of interfacial adhesion. This is explained by different mechanisms for craze formation at adhering and nonadhering glass beads, resp. Both elastic and crazing behavior of the composites were influenced by the glass bead concn

The dynamic tensile strength of ice and ice‐silicate mixtures

Abstract: We determined the dynamic tensile strength of ice and ice silicate mixtures at strain rates of ∼10^4 s^(−1). At these strain rates, ice has a tensile strength of ∼17 MPa, and ice-silicate mixtures with 5 and 30 wt % sand content have strengths of ∼20 and 22 MPa, respectively. These values lie significantly above tensile strengths of ∼1.6 MPa for ice and of ∼5−6 MPa for frozen silt, measured at strain rates of ∼10^(−2) to 10° s^(−1), but markedly below values found for a variety of rocks at comparable strain rates. Results of the present experiments are used to derive parameters for continuum fracturing models in icy media, which are used to determine relations between tensile strength and strain rate, and to predict stress and damage histories as well as size frequency distributions for ice and ice-silicate fragments. It is found that tensile strength σ_M is related to strain rate by σ_M ∝ e_0^[0.25–0.3], similar to results obtained for other geological materials. The increase of small fragments relative to larger fragments with increasing strain rate, as predicted by the continuum model, is a result which parallels findings in laboratory impact experiments.

Response of the Bond in Reinforced Concrete to High Temperatures

Abstract: Synopsis The effect of high temperutures upon the bond between the steel und concrete in reinforced concrete was examined over a temperature range of 20–750°C The concrete mix was constant throughout und 16 mm deformed reinforcing bar (Tor bar) was used in most tests Various parameters were examined including different test conditions and depths of cover The four test conditions used were: (l) stressed during heating (a steady-state bond stress of 3·70 N/mm2 was applied) and loaded to failure when hot, (2) stressed during heating and loaded to failure when cooled, (3) no applied stress during heating and loaded to failure when hot, and (4) no stress during heating and loaded to failure when cooled Four different depths of concrete cover (25, 32, 46 und 55 mm) were l for the stressed/residual test condition, but only tht 55 mm cover was used with the other three test conditions The effect of heat upon the compressive und tensile strength of the concrete was also considered, together with its effect up

Effect of Re-Compression on the Properties of Tablets Prepared by Moist Granulation

Abstract: The effect of re-compression on the tableting properties of some direct compression excipients (directly compressible starch, dicalcium phosphate dihydrate and microcrystalline cellulose) and their formulations was examined. Re-compression generally reduced the tablet strength and this reduction was more significant when the initial compaction was carried out at a higher pressure. The reason for the reduction of tensile strength upon re-working is attributed to work hardening and the production of robust granules, which have increased resistance to deformation compared to unworked granules.This paper is based on a presentation made to the 31st National meeting of the Academy of Pharmaceutical Sciences, American Pharmaceutical Association, held at Orlando, Florida, U.S.A. on November 15-19th, 1981.

Resorbable materials of poly(L‐lactide). II. Fibers spun from solutions of poly(L‐lactide) in good solvents

Abstract: Fibers of poly(L-lactide) (PLLA) with a tensile strength up to 1.2 GPa and Young's modulus in the range of 12–15 GPA were obtained by a hot drawing of fibers spun from solution of PLLA in good solvents such as dichloromethane and trichloromethane. The tensile strength of fibers was strongly dependent on the molecular weight of PLLA and on polymer concentrations in the spinning solution. Changing of the polymer concentration in the spinning solution gives rise to formation of fibers with different shape and porosity. Fibers spun from 10–20% solutions at room temperature exhibit a regular structurization, due to the melt fracture. These fibers had knot strengths up to 0.6 GPa, whereas fibers with a smooth surface spun from more dilute solutions had weaker square knots up to 0.3 GPa.

Single‐valued strength of ‘‘perfect’’ silica fibers

Abstract: An analysis has been made of the tensile strength statistics of two silica fibers with quite different degrees of diameter uniformity. It has been found that the coefficient of variation in diameter (νd) is equal to that in minimum diameter (νd,min) and that the measured coefficient of variation in breaking load (νL) and breaking stress (calculated assuming constant d) are twice this value. Since νL =νσ =2νd =2νd,min it is clear the apparent variability in strength is the result of the variability in diameter and therefore the real strength is essentially single valued. Because of this lack of statistical variation in breaking strength, it is suggested that these fibers are flaw‐free as drawn.

Improvement in lower temperature mechanical properties of 0. 40 Pct C-Ni-Cr-Mo ultrahigh strength steel with the second phase lower bainite

Abstract: A study has been made of the effect of the second phase lower bainite on lower temperature mechanical properties from ambient temperature (287 K) to 123 K of a commercial Japanese 0.40 pct C-Ni-Cr-Mo ultrahigh strength steel corresponding to AISI 4340. When 25 vol pct lower bainite, which appeared in acicular form so as to partition prior austenite grains, was associated with martensite at 473 K, it provided a better combination of strength and ductility than that achieved using 1133 K direct water quenching irrespective of the test temperature. With the lower bainite, notch tensile strength was dramatically improved over the temperature region studied about 2150 MPa even at 123 K; whereas, in the case of 1133 K direct water quenching, it remained at about 1700 MPa. Similar trends were observed in the relationship between the lower bainite and the Charpy V-notch impact energy at and above 238 K. The lower bainite also produced superior fracture ductility and notch toughness results with decreased temperature of testing as compared to those obtained using a y γ α′ ’ repetitive heat treatment for the same steel. The above beneficial effects of the second phase lower bainite on lower temperature mechanical properties are briefly discussed in terms of metallographic examinations, the law of mixtures, and so on.

A Study on the Tensile Strength of Ice as a Function of Grain Size

Abstract: : An analysis of ice fracture that incorporates dislocation mechanics and linear elastic fracture mechanics is discussed. The derived relationships predict a brittle to ductile transition in polycrystalline ice under tension with a Hall-Petch type dependence of brittle fracture strength on grain size. A uniaxial tensile testing technique, including specimen preparation and loading system design was developed and employed to verify the model. The tensile strength of ice in purely brittle fracture was found to vary with the square root of the reciprocal of grain size, supporting the relationship that the theory suggests. The inherent strength of the ice lattice and the Hall-Petch slope are evaluated and findings discussed in relation to previous results. Monitoring of acoustic emissions was incorporated in the tests, providing insights into the process of microfracture during ice deformation.

Mechanical properties of ductile Fe-Ni-Zr and Fe-Ni-Zr (Nb or Ta) amorphous alloys containing fine crystalline particles

Abstract: Melt-quenched Fe60–80Ni10–30Zr10 and Fe70Ni20Zr10−x(Nb or Ta) x (x≲2 at %) alloy ribbons with the duplex structure consisting of amorphous and bcc phases were found to exhibit hardness and tensile strengths higher than those of the totally amorphous alloys. The volume fraction of the bcc phase was intentionally allowed to alter in the range 0% to 60% by changing the composition and sample thickness. The bcc phase has an average particle size of 75 nm for the Fe-Ni-Zr alloys and 50 nm for the Fe-Ni-Zr-Nb alloys, and the lattice parameter is much larger than that of pure α-Fe because of the dissolution of large amounts of zirconium, niobium and/or tantalum. The hardness and tensile strength of the duplex alloys increase with amount of bcc phase and reach about 880 DPN and 2580 MPa, which are higher by about 20% to 30% than those of the amorphous single state, at an appropriate volume fraction of bcc phase. As the volume fraction of the bcc phase increases further, the duplex alloys become brittle and the tensile strength decreases significantly. The enhancement of strength was considered to be due to the suppression of shear slip caused by fine bcc particles dispersed uniformly in the amorphous matrix. It was thus demonstrated that an optimum control of melt-quenched structure results in the formation of ductile Fe-based amorphous alloys containing fine crystalline particles.