Showing papers on "Tensile testing published in 1979"

Constitutive Model for Short-Time Loading of Concrete

Abstract: A constitutive model based on nonlinear elasticity is proposed, where the secant values of Young’s modulus and Poisson’s ratio are changed appropriately. This alteration is obtained through the use of a nonlinearity index that relates the actual stress state to the failure surface. The model simulates the strain hardening before failure, the failure itself and the strain softening in the post-failure region. The dilation of the concrete and the influence of all three stress invariants are considered. All stress states including those where there are tensile stresses can be dealt with; however, the model is calibrated using experimental data obtained by a uniaxial compressive and tensile test only. The model predictions are demonstrated to be in good agreement with experimental results involving a wide range of stress states and different types of concrete.

Correlation of Fiber Composite Tensile Strength with the Ultrasonic Stress Wave Factor

Abstract: An acoustic-ultrasonic technique was used to indicate the strength variations of tensile specimens of a graphite/epoxy composite. A “stress wave factor” was determined and its value was found to depend on variations of the fiber-resin bonding as well as fiber orientation. The fiber orientations studied were 0 deg (longitudinal), 10 deg (off-axis), 90 deg (transverse), [0 deg/±45 deg/0 deg] symmetrical, and [±45 deg] symmetrical. Correlations indicated that the stress wave factor can predict variations of the tensile and shear strengths of composite materials. The method was also found to be sensitive to strength variations associated with microporosity and differences in fiber/resin ratio.

Biaxial and Uniaxial Data for Statistical Comparisons of a Ceramic's Strength

Abstract: The uniaxial and equibiaxial tensile strengths of a brittle material were measured in bending. Equibiaxial tension was attained by concentric ring loading of disks and uniaxial tension by four-point line loading of plates. The two specimen designs give equal volumes, surface areas, and stress gradients. Ground surfaces and lapped surfaces were tested. The equibiaxial tensile strength of a dense alumina was lower than the uniaxial tensile strengths for both ground and lapped surfaces, 8.5 and 8.1%, respectively. The Batdorf theory of flaw statistics, in which biaxial tensile strengths can be predicted from the statistical distribution of uniaxial tensile strength measurements, agreed with the data.

Formation of longitudinal, midface cracks in continuously-cast slabs

Abstract: Based on a series of related investigations, a mechanism for the formation of longitudinal, midface cracks in strand-cast slabs has been elucidated. Metallographic studies, X-ray analyses, and high-temperature tensile testing of as-cast slab samples, together with computer predictions of heat flow, have been combined to show that the cracks open first close to the solidification front where the ductility is extremely low. Tensile strains in the solid shell, resulting from rapid surface cooling or inadequate end-plate taper, concentrate in local regions of high temperature near the meniscus or at the level of nozzlestream impingement on the broad face. While the interior of the shell is opening, the surface which is cooler and more ductile, flows plastically to form a local surface depression. The subsurface cracks may subsequently break through to the surface in the mold or upper sprays if the tensile strains are sufficiently high. The influence of the impinging metal stream, mold-powder practice, metal-level control, steel composition, end-plate taper, submold support and spray practice on the formation of longitudinal, midface cracks is explained in terms of this mechanism.

Brittle interface layers and the tensile strength of metal matrix-fibre composites

Abstract: The influence of brittle layers on the ultimate tensile strength of metal matrix composites is discussed. An equation has been derived to calculate the first critical thickness of the layer. The brittle layers have two effects on the fracture of the fibre, one of which is the value of the local stress near the tip of the crack, situated at the fibre-layer interface. Methods have been developed for the theoretical calculation of the critical stress intensity factor, KIC, of brittle materials. Experimental results with B-SiC fibres have shown that their tensile strength is reduced with increasing thickness of the SiC layer. The critical thickness of the layer, tl*,for B-SiC fibres is about 1.0 to 7.5 μm, which coincides well with the theoretical value of tl*.

An investigation of tensile strength of dental solder joints

Abstract: Tensile specimens of dental solder joints were tested to determine the effect of gap distance on the strength of solder joints. Two dental alloys were used; a Type III gold alloy and a gold-palladium (Au-Pd) alloy. The Type III alloy was joined with the recommended gold solder. The Au-Pd alloy was joined using preceramic and postceramic application soldering techniques. Gap distances of 0.13 mm, 0.5 mm, and 1 mm were used with each soldering technique. All solder specimens were machined to a uniform diameter and then tested for tensile strength. It was concluded that: 1. There was a significant increase in strength for the Type III gold as the gap distance was increased. 2. The trend toward stronger joints at narrow gap distances for Au-Pd alloy joined with presolder was not statistically significant. 3. The trend toward stronger joints at wide gap distances for the Au-Pd alloy joined with the postsolder was not statistically significant. 4. The postsolder joints were statistically stronger than the presolder joints. 5. The trends observed could be partially explained in terms of competing effects of yield strength (triaxially), wettability, and void or inclusion content at the various gap distances.

Pore Formation and Its Effect on Mechanical Properties in W—Ni—Fe Heavy Alloy

Abstract: W–Ni–Fe heavy alloy tensile specimens were sintered at 1450°C for various times up to 44h. The W content varied between 90 and 96 wt-%, and the Ni to Fe weight ratio was 1:1. The specimens are fully densified after 15 min to 1 h of sintering and show high strength and ductility. During the tension test, cracks are formed at the interface between tungsten grains when the grain deformation reaches critical levels. The number of these intergranular cracks increases with deformation until the specimens fracture. When the specimens are over-sintered for 4 and 8 h, large irregular pores are formed with a sharp decrease of strength and ductility. Upon further sintering, the porosity decreases again with a recovery of the mechanical properties. The results demonstrate that small amounts of porosity, even 1 or 2%, can cause drastic reduction of the mechanical properties in tungsten heavy alloys.

Mechanical Properties Characterization of an SMC-R50 Composite

Abstract: Materials scientists and design engineers considering the use of composites molded from sheet molding compound (SMC) for structural applications need reliable mechanical property data for these composites. In response to this need, the mechanical properties of a well documented, carefully prepared SMC-R50 composite over a temperature range of - 40 degree C to 121 degree C are reported. The properties determined include Young's modulus, shear modulus, and Poisson's ratio, thermal coefficient of expansion, tensile fatigue, tensile creep, and ultimate strengths in tension, compression, shear and flexure. All tests are based on one composite material, thus, conclusions about the relationship between different mechanical properties can be made. For example, the tensile and compressive moduli of SMC-R50 composite are virturally the same. Also, Young's modulus, shear modulus, and Poisson's ratio obey an established equation relating these constants. In addition, this study establishes the existence of a fatigue limit for SMC-R50 composite.

In-situ estimates of the tensile strength of snow utilizing large sample sizes

Abstract: Experimental procedure and measured estimates of the tensile strength of snow are given by a new method utilizing large sample sizes of naturally deposited snow. Data are presented as a function of average sample density, temperature, loading rate, and snow type. The results show less scatter in the data than previous in-Jitu estimates and lower mean strength values as a function of density. The relevance of the data to tensile fracture as observed in slab avalanche release is discussed. RESUME. Estimation in situ des e{forts de traction dons la neige sur des 'ehan/ilions de .grande dimension. On donne un procede experimental et des estimations des efforts de traction dans la neige par une nouvelle methode utilisant des echantillons de grandc dimension de neige deposee naturellement. Les resultats sont presentes en fonction de la densite moyenne de l'echantillon, de la temperature, de la surcharge et du type de neige. Les resultats montrent une dispersion moindre que les estimations anciennes et des moindres valeurs moyennes d es efforts en fonction de la densitc. On discute le rapport entre les resultats et les ruptures a la traction observees dans les declenchements d'avalanches de plaques. ZUSAMMENFASSUNG. In-,itu-AbJChiit z ullgen der Zugfestigkeit von Sehnee an groJfformatigell Proben. Das experimcntdle Verfahrcn und die Abschatzungsergebnisse .. iner neuen Methode zur Bestimmung der Zugfestigkeit von Schnee, bei der grossformatige Proben natlirlich abgelagerten Schnees benutzt werden, werden mitgeteilt . Die \\OVert .. stellen sich in Abhangigkeit von der mittlcren Probendichte, der Temperatur, der Bclastungsrate und der Schnecart dar. Die Ergebnisse zeigen gcringere Streuung als fruhere Abschatzungcn und kleinere mittlere Festigkeit in Abhangigkeit von der Dichte. Die Bedeutung der Daten fur Zugbruehc, \",ie sic in Brcttlawincn zu beobachten sind, wird diskuti,·rl. INTRODUCTION The tensile strength of snow is an important quantity in snow mechanics. Destructive tensile fractures are habitually observed on the line where snow slabs break away from their anchoring zones (Haefeli, 1967; Peria, [1975]). The tensile strength of snow is a function of many variables including density, temperature, and snow type. In addition , any test introduces additional variables which must be considered including loading rate, sample size, boundary conditions at the places where the sample and testing equipment are in contact, and sample disturbance in mounting the specimens. Experiments with small sample sizes using centrifugal tensile testers consistently show large scatter in the strength values and high mean strength values (Sommerfeld, 1974). In addition, centrifugal testers cannot be used in situ and therefore may subject the sample to damage upon insertion of the sample tubes. Jarring of the samples against the walls of the tester at fast acceleration rates is also possible in centrifugal tests. The procedure used in the present paper to estimate the tensile strength of snow is intended to provide estimates for larger sample sizes closer to the expected sample size in natural slab avalanches. In addition, the tests were made in situ and the loads were applied slowly to prevent effects of jarring and sample damage. The boundary conditions at the places where the snow specimen and the testing equipment were in contact were such that the conditions expected prior to destructive tensile fracture observed in snow-slab release were approximately simulated. EXPERIMENTAL PROCEDURE The experiments were done during the winters of 1971 72 and 197273 in the Cascade Mountains, U .S.A. The apparatus consisted of a series of large tables set out on a horizontal snow surface to collect samples of snow. The tables had removable, wooden sides such that the • Present address: Environment Canada, Canmorc, Alberta ToL 01\\10, Canada. 321 322 ./O ll R:'>IAL OF GLACIOLOGY samples .were ·collec ted in a box on top of th e ta bl cs. Following collect ion of a sample, t hc top was carcfull y trimmed o ff a nd the woodcn sidcs were removed to provide uniforml y shaped and sized samples . The surface of th e tables was partly roug h and partly smooth . It was hoped that d estruc tive tensil e fracture would occur on the line between the rough and smooth sections as th e table was slowly tilt ed by lifting onc cnd resulting in slow loading by body forces. This proved to be th e casc for each test. The fra c ture surfaces \\WIT, in gcneral , smooth and perpendic ular tn the ta hle sudacc. The stress field in t he sa mples in th e present tes ts is not hornogencous. The tests welT d esigned to simulate conditions of tensil e fa ilure in slabs whose resistan ce to sustaining basal shear stress is diminished . Thcre will , therefore, be small differences whcn the present dat a arc compared to uniaxial test results . However, a small er cffec t is to be expected when comparing the results 10 fi eld es timates.

The influence of biaxial prestrain on the tensile properties of three aluminum alloys

Abstract: We have investigated the influence of planar biaxial prestrain on the subsequent tensile behavior of three aluminum alloys. The flow stability encountered in the uniaxial stage is explained in terms of the reduced tensile hardening following biaxial prestraining. A critical stress value approximately equal to the nonprestrained ultimate tensile strength is shown to be the controlling factor for the onset of failure.

Temperature dependence of the tensile strength of glass fiber–epoxy and glass fiber–unsaturated polyester composites

Abstract: Epoxy and unsaturated polyester resins reinforced with random-planar orientation of short glass fibers were prepared and the temperature dependence of their tensile strength was studied. The tensile strength decreases as the temperature increases, and this tendency can be expressed in terms of critical fiber length lc and apparent interfacial shear strength τ: where σcs is the tensile strength of composite reinforced with random-planar orientation of short fibers, L is the fiber length, d is the fiber diameter, σf is the tensile strength of fiber, σm is the tensile strength of matrix, uf is the volume fraction of fiber, vm is the volume fraction of matrix, and σ′m is the stress of the matrix at fracture strain of the composite. The experimental strength values at room temperature are considerably smaller than the theoretical values, and this difference can be explained by the thermal stress produced during molding due to the large difference in the thermal expansion coefficient between glass fiber and matrix resin.

Transverse tensile characteristics of fiber composites with flexible resins: Theory and test results

Abstract: A theoretical and experimental investigation has been conducted of the transverse tensile properties of flexible-resin/glass-fiber composite lamina. The objective is to increase the elongation at failure of a lamina in a state of transverse tension so that when a lamina is used in a laminate configuration, it does not suffer premature failure (e.g., failure at a lower strain level than that for a lamina in fiber direction tension). We show that the mode of failure in the transverse tensile lamina differs greatly from that in the neat resin. The failure mode in the lamina form is found to be brittle fracture. From this, it follows that the controlling neat resin property is the low elongation modulus rather than the elongation at failure. Significant improvements in the transverse tensile strain at failure were obtained for the flexible-resin/glass-fiber systems studied. 9 figures, 3 tables.

The heat treatment of the commercial aluminum alloy 7075

Abstract: A systematic study has been carried out on the effects of aging on various properties of the commercial aluminum alloy 7075, viz, the tensile yield strength, the ultimate tensile strength, the fracture toughness, the hardness, the electrical conductivity and the resistance to stress-corrosion cracking. When duplex aging was carried out the primary aging parameters did not affect the mechanical properties. Good correlations were found between the different properties. In particular, a linear correlation was found between the strength properties, tensile yield stress, ultimate tensile stress and hardness, whereas the correlation of the strength properties with the electrical conductivity resulted in non linear relationships. Also, a maximum in strength was found to correlate with a minimum in fracture toughness.

Method of determining the plating properties of a plating bath

Abstract: A band of material is formed by plating the material onto a cylindrical cathode sandwiched between a pair of insulating end pieces and is supported in a plating bath spaced a short distance from an anode. The cathode is rotated about its axis to provide uniform, reproducible mass transport to the plating surface. In order to determine the tensile properties of the plated material, the band is removed from the cathode and pulled apart in a tensile machine. During tensile testing, the band is held using a pair of pins and clevis, or it is formed into a strip and gripped in a standard fixture. In order to determine the stress condition of the plated material, the band is cut open and its change in diameter measured.

Acoustic emission interpretation of ductile fracture processes

Abstract: Detailed analyses of acoustic emission from several material classes have established that the predominant source in tensile testing is particle decohesion and fracture. Acoustic emission is a smoothly varying parameter with plastic strain in 4340 steel where small carbides predominate; however, in an IN 718 superalloy, it is both bimodal and exhibits a burst phenomena where very large carbides and nitrides as well as a medium size laves (δ) phase contribute. From microscopic and acoustic emission observations, it is found that the fracture process is sulfide decohesion followed by void sheet instability associated with carbides in 4340 steel. In IN 718, large carbide or nitride fractures are followed by void sheets associated with laves phase. Identification of the major particle nucleation sites have allowed an initial interpretation of ductile hole growth models. Application of McClintock hole growth and a Hahn and Rosenfield void sheet instability criterion to the ductile fracture process has provided a good correlation to tensile ductilities, plane-strain crack tip ductilities, and plane-strain fracture toughness, K IC.

The tensile strength of hardmetals

Abstract: In conventional bend tests on hardmetal specimens with a rectangular cross-section the strength values exhibit a wide scatter as a result of fracture being initiated from pores and inclusions. A new bend test-piece geometry has been devised which subjects a relatively small volume of material to a high tensile stress and so reduces the probability of fracture starting from defects. The test gives reproducible results with low scatter, and, by suppressing defect initiated failures, it enables a more accurate assessment to be made of the effect of metallurgical variables, such as grain-size and composition, on strength.

Multiparameter system for investigation of the effects of high-power ultrasound on metals.

Abstract: A multiparameter system has been developed which, for the first time, permits simultaneous measurement of sufficient quantities to test all of the proposed mechanisms for the influence of high‐power ultrasound on metal specimens. Results of measurements using this system give new insight into the mechanical and thermal processes involved. Data are presented which show typical results obtained during tensile elongation of polycrystalline and single‐crystal aluminum specimens.