Showing papers on "Tensile testing published in 1990"

Influence of Test Method on Failure Stress of Brittle Dental Materials

Abstract: A bi-axial flexure test (piston-on-three-balls), a four-point flexure test, and a diametral tensile test were used to measure the failure stress of four brittle dental materials: zinc phosphate cement, body porcelain, opaque porcelain, and visible light-cured resin composite. Furthermore, the fracture probability of the bi-axial test specimens was predicted from the results of the four-point flexure test, with use of statistical fracture theory. Bi-axial failure stresses calculated from an equation developed by Marshall (1980) exhibited no significant difference for zinc phosphate cement as a function of piston size, specimen thickness, presence or absence of a stress-distributing film, and loading rate. The four-point flexure strength values of zinc phosphate cement and opaque procelain were significantly lower (p less than 0.05) than the corresponding mean bi-axial strength values, while the mean four-point flexure strength values of body porcelain and resin composite were not significantly lower (p greater than 0.05) than the corresponding mean bi-axial strength values. The diametral tensile strength of all materials was significantly lower than the bi-axial flexure strength. The mean bi-axial flexure strengths of zinc phosphate cement and opaque porcelain were much higher than the theoretical values predicted from surface flaw theory, while the strength values for body porcelain and resin composite were comparable with those determined from the four-point flexure test. These results demonstrate that the strength of zinc phosphate cement depends not only upon the geometric factors, but also upon sample preparation conditions.

Influence of Water Exposure on the Tensile Strength of Composites

Abstract: The objective of this study was to investigate whether water storage causes permanent damage to composites by determining how the tensile strength of nine different composite materials changes with both water storage and water storage followed by dehydration. Eighteen samples (ASTM-D Specification 1708-66) of each of the nine materials were prepared and divided into three groups of six samples each. Group I was stored dry at 60°C, while Groups II and III were stored in distilled water at 60°C. After six months, Groups I and II were subjected to tensile testing, while Group III was transferred to a desiccator and dehydrated for two weeks at 60°C before this group was tested in tension. Mean values, pooled by storage group independent of material, revealed a significant (p<0.05) reduction in strength for both Groups II and III relative to Group I. These findings prove that water has an irreversible effect on most dental composites. A comparison of Group II with Group III data revealed that the samples which...

Strengthening and ductilization of Ni3Si by the addition of Ti elements

Abstract: The mechanical properties of Ni 3 Si polycrystals alloyed with Ti and doped with boron were investigated by compressive and tensile tests. The yield stress increased with increasing Ti concentration and with decreasing Ni concentration at all testing temperatures. The peak temperature in the yield stress increased with increasing Ti concentration. The activation energy for the thermal stress term producing the positive temperature dependence decreased with increasing Ti concentration and was correlated with the phase stability of L1 2 (Ni 3 Si) relative to D0 24 (Ni 3 Ti). Ductility was obtained by the addition of Ti. Higher elongation values were observed in the alloys consisting of higher Ti concentration and higher Ni concentration. Further improvement of the tensile elongation was found by the addition of a small amount of boron. The variation of the elongation with temperature showed a peak at intermediate temperature. The elongation behavior correlated well with the variation of the fracture patterns. The ductilization of the Ni 3 Si observed in this work verified the alloying method to improve the grain boundary cohesion of L1 2 type ordered alloys which has been proposed by the present authors.

Superplasticity in β-silicon nitride whisker-reinforced 2124 aluminium composite

Abstract: The aim of this study is to establish whether Si 3 N 4 whisker-reinforced 2124 Al composite fabricated by a simple powder metallurgical method without TMP could produce superplastic behaviour. The relationship between mechanical properties and strain rate in this composite is then investigated by performing tensile tests at a temperature of 525°C

Chromium addition and environmental embrittlement in Fe3Al

Abstract: Iron aluminides based on Fe[sub 3]Al afford excellent oxidation properties at relatively low cost, making them candidates for use as structural material in corrosive environments. Recently, efforts have been devoted to understanding and improving their ductility through control of grain structure, alloy additions and material processing. Studies at this laboratory have shown that the ambient temperature ductility can be increased significantly by additions of up to 6% Cr. This increase in ductility was earlier attributed to increased cleavage strength, easier cross slip due to lower antiphase boundary (APB) energy, and solid softening. Very recent studies of FeAl and Fe[sub 3]Al in various tensile testing environments have indicated that both alloy systems are relatively more ductile at room temperature when tested in vacuum or dry oxygen. Ductilities of 12--18% were attained in both iron aluminide systems in an oxygen pressure of 6.7 [times] 10[sup 4] Pa, while only 2--4% ductility was achieved in normal laboratory air. It seems appropriate to reexamine the mechanism by which chromium produces improved ductility at room temperature in laboratory air and to correlate it with the environmental effects on mechanical properties. In the current investigation, the authors have evaluated room temperature tensile properties of the binary more » alloy (Fe-28Al, at.%) and ternary alloy containing chromium (Fe-28Al-4Cr) as a function of surface condition and heat treatment. The results indicate that, although chromium may affect cleavage strength and APB energies, its most significant effect on room temperature ductility is to modify the protective surface oxide, resulting in a minimization of environmental embrittlement. « less

Tensile and fracture properties of epoxy resin filled with flyash particles

Abstract: The ultimate tensile strength, modulus of elasticity and fracture properties of epoxy resin filled with flyash particles have been evaluated by the tensile test. The tensile strength of epoxy resin filled with flyash particles decreases the fracture properties and the modulus of elasticity increases with increasing percentage of flyash. It is advisable to use flyash when the void formation cannot be controlled effectively.

Tensile tests of ceramic-matrix composites. Theory and experiment

Abstract: A model describing the salient features of tensile stress-strain curves of ceramic–fiber composites has been developed. The model incorporates statistics of fiber failure. Furthermore, the compliance of the testing machine is included so that the onset of instability can be predicted. An experiment conducted on a composite consisting of a glass-ceramic matrix reinforced with SiC fibers exhibits excellent agreement with the predicted behavior.

Microstructure and fracture behaviour of short and long fibre-reinforced polypropylene composites

Abstract: Microstructure and fracture mechanical behaviour of injection-moulded, longer glass fibrereinforced polypropylene (Verton* aspect ratio ≈ 320) were studied as a function of fibre volume fraction and compared to that of shorter fibre-filled polypropylene (aspect ratio ≈ 70). Toughness was measured using instrumented notched lzod and falling weight impact tests, as well as compact tension specimens. It was found that the addition of longer fibres generally increased the toughness of the material, although more significant increases were seen in the impact tests than were seen in the compact tension test. For the latter results, a correlation between toughness improvement and microstructural details was performed on the basis of the microstructural efficiency concept, a semi-empirical approach of the formKc,C = (a* +nR)Kc,M, where,Kc,C andKc,M are the fracture toughnesses of the composite and the matrix, respectively,a* is a matrix stress correction factor,n is a scaling parameter andR is a fibre reinforcement effectiveness factor. The latter corrects for differences in the composite microstructures, and incorporates effective fibre orientation factors, layering of injection moulded parts, and fibre volumes in the different layers.

Tensile properties of synthetic fiber reinforced mortar

Abstract: This paper reports on an experimental study of synthetic fiber reinforced mortar. The fibers used included aramid, high-strength high-modulus polyethylene, and polypropylene, and they were randomly mixed in the matrix at volume fractions below 3%. Tensile properties of the composites were measured by the direct tensile test under both monotonic and cyclic loading. Workability and the drying shrinkage of the composites are also reported.

Influence of testing environment on the room temperature ductility of FeAl alloys

Abstract: The effects of testing atmospheres (air, O2, N2, and vacuum) on the room-temperature ductility of Fe-40Al, Fe-40Al-0.5B, and Fe-50Al alloys were investigated. The results confirmed the decrease in room-temperature ductility of Fe-rich FeAl alloys by the interaction of the aluminide with water vapor, reported previously by Liu et al. (1989). The highest ductilities were measured in the atmosphere with the lowest moisture levels, i.e., in vacuum. It was found that significant ductility is still restricted to Fe-rich alloys (Fe-40Al), as the Fe-50Al alloy remained brittle under all testing conditions. It was also found that slow cooling after annealing was beneficial, and the effect was additive to the environmental effect. The highest ductility measurements in this study were 9 percent elongation in furnace-cooled Fe-40Al and in Fe-40Al-0.5B, when tested in vacuum.

Silicon Wafer Bonding Mechanism for Silicon-on-Insulator Structures

Abstract: X-ray diffraction topography and tensile testing are used to study the perfection of bonded interfaces in the sandwich structure where one of the two silicon wafers used had an SiO2 layer applied to it first. The tensile strength and the formation of unbonded areas (voids) were compared to the cases where two bare silicon wafers were used and where both wafers were coated with oxide. There are two mechanisms for wafer bonding: one is for a lower temperature and another is for a higher temperature range. It is concluded that a strong affinity between the two wafers at low temperatures is essential to obtaining tight bonding after a high-temperature anneal. A proper amount of H, OH and H2O on the wafers plays an important role in good chemical bonding below 800°C. Above 1000°C an interaction between adjacent atoms to create covalent bonding and deformation of the SiO2 layer are effective in establishing good bonding.

Isothermal and Nonisothermal Fatigue Behavior of a Metal Matrix Composite

Abstract: The isothermal and nonisothermal fatigue resistance of a metal matrix composite (MMC) consisting of Ti-15V-3Cr-3Al-3Sn (Ti-15-3) matrix reinforced by 33 vol pct continuous SiC fibers was investigated. The fibers were nominally oriented parallel to the specimen axis. Isothermal fatigue tests were performed in air at 300 and 550 C. The MMC had good isothermal fatigue resistance at low cyclic stress, with fatigue cracks initiating from fiber-matrix interfaces and foil laminations. At high cyclic stresses, stress relaxation in the matrix reduced isothermal composite fatigue resistance at 550 C. Nonisothermal fatigue loading substantially degraded composite fatigue resistnce. This degradation was produced by a thermomechanical fatigue damage mechanism associated with the fiber-matrix interfaces.

Considerations in Electrodeposition of Compositionally Modulated Alloys

Abstract: High‐quality specimens of sufficient thickness for reliable testing are needed if the enhanced properties observed for ultrastructured multilayered metals are to be understood and exploited. In the present paper, factors affecting the quality of multilayers electrodeposited from a single electrolyte, via concerted modulation of the electrode potential and electrolyte mass transport, are discussed. The importance of precise control of the potential during deposition of the more noble metal is emphasized. Results obtained by a pulse technique show that Ni passivation does not occur under the conditions used to electrodeposit Ni‐Cu multilayers. Attainable deposit quality is illustrated by tensile test data for a series of 90%Ni‐10%Cu specimens that are twice as strong as Ni and for which the standard deviations for the ultimate tensile strength and modulus are only 1.5 and 3.9%, respectively.

A fibre coating process for advanced metal-matrix composites

Abstract: A fibre coating process has been used to produce continuously reinforced advanced metal-matrix composites with up to 8% volume fraction of SiC fibre. Matrix materials were an α/β titanium alloy (Ti-Al-V), a dispersion-strengthened titanium alloy (Ti-Al-V-Y), a rapid solidification processed aluminium alloy (Al-4.3Cr-0.3Fe), and intermetallic compounds Ti3Al and TiAl. Thick metal coatings are shown to adhere well to the fibres, no evidence is found for chemical reaction between the coating and the fibre during the coating process, and the coated fibres can be handled and bent without damage. Tensile test data for Ti-Al-V alloy reinforced with 21% SiC fibre show a modulus near to a theoretical prediction, but tensile strength significantly below prediction. Loss of strength is attributed to the formation of a brittle reaction product during hot consolidation. The advantages and potential of the coated-fibre route for MMC production are discussed.

Experimental determination of tensile behavior of fiber reinforced concrete

Abstract: With reported improvements in tensile behavior of concrete due to fiber reinforcement, considerable interest has been generated in tensile testing techniques for cementitious composites. Such methods are reviewed and a novel method for direct tensile tests on fiber reinforced concrete (FRC) is described. The method requires only a simple loading fixture yet gives satisfactory test results. The results of tensile measurements are reported for various synthetic FRC with mortar matrix. It is expected that direct tensile test of FRC can be widely performed by using this method.

Improvement of room temperature ductility of stoichiometric Ni3Al by unidirectional solidification

Abstract: Stoichiometric polycrystalline Ni3Al was grown undirectionally by a floating zone method. The solidification structure was strongly dependent on the growth rate. A columnar grained structure with a strong 〈111〉 texture was obtained with the growth rate over 13 mm/h. The alloy exhibited a large tensile elongation of 17% at room temperature without the addition of boron. The combined mode of transgranular fracture and intergranular fracture was observed on the fracture surfaces, with traces of crystallographic slip. It is considered that the large room temperature ductility in this alloy is attributed to the substantial suppression of intergranular crack initiation and its catastrophic propagation.

Tensile fracture and fractographic analysis of 1045 spheroidized steel under hydrostatic pressure

Abstract: Void formation in tensile test under hydrostatic pressure is characterized through quantitative metallography, and the fracture mechanism under pressure is analyzed by fractography. Transition of the fracture surface from the cup-and-cone under atmospheric pressure to a slant structure under high pressure is explained on the basis of the void development leading to fracture and the concomitant change in fracture mechanism. The concept of “shear blocks” is introduced to illustrate the features observed on the fracture surface of specimens tested under high pressure. It is postulated that shear blocks evolve to connect the central crack regions with the shear crack initiated on neck surface due to the severe necking deformation under applied pressure.

Tensile Fracture Toughness of Ceramic Materials: Effects of Dynamic Loading and Elevated Temperatures

Abstract: Experimental methods are presented for the determination of fracture initiation toughness of ceramics and ceramic composites in pure tension under quasi-static and dynamic loading conditions over a range of temperature spanning 20° to 1300°C. Circumferentially notched and cyclic fatigue precracked rods of a variety of ceramic materials were subjected to quasi-static tensile fracture (rate of stress intensity factor loading, K1∼ 0.1 MPa ∼ m1/2∼ s−1) in an electroservohydraulic test machine and to dynamic tensile fracture (K1∼ 106 MPa ∼ m1/2· s−1) using a modified tensile Kolsky (split-Hopkinson) bar. For the quasi-static and dynamic fracture tests at elevated temperatures, the ceramic specimen was inserted into an air furnace where either friction grips or stress wave loading outside the furnace subjected the specimen to fracture. Dynamic finite-element analyses of the circumferentially notched cylindrical rod have been conducted to develop the optimum specimen dimensions and test procedures for the measurement of dynamic fracture toughness at ambient and elevated temperature. Experiments conducted on Al2O3, Si3N4, and SiC, and an Al2O3-25 vol% SiC whisker composite at room temperature indicate that the dynamic to quasistatic fracture initiation toughness ratio KId/KIc is in the range of 1.1 to 1.4. Elevated-temperature fracture tests for the polycrystalline Al2O3 of 3-μm average grain size reveal that KId is only mildly sensitive to temperature over a range of 20° to 1100°C, whereas it suffers a precipitous drop above 1100°C. Over the temperature range 20° to 1300°C, the ratio KId/KIc is found to be in the range 1.2 to 1.5. Scanning electron microscopy observations show that failure above 1100°C usually evolves by the nucleation, growth, and coalescence of cavities. The mechanisms of elevated-temperature quasi-static and dynamic fracture in polycrystalline Al2O3 are examined and possible causes for the apparently higher dynamic fracture initiation resistance are discussed. The significance and limitations of the proposed experimental techniques are highlighted.

Random glass mat reinforced thermoplastic composites. Part I: Phenomenology of tensile modulus variations

Abstract: The mechanical properties of random continuous glass mat reinforced composites, as determined by standard tensile tests, are known to have a very large scatter. To understand this scatter, new test procedures were developed to map the local tensile elastic moduli in a large plaque at 12.7-mm (½-in) intervals. Surprisingly, the tensile modulus in these materials can vary by a factor of two over the 12.7-mm distance. The elastic modulus is shown to vary by a factor of three in a 150 × 305-mm (6 × 12 in) plaque. Expressions have been obtained for the average moduli measured by tensile and bend tests. These expressions have been used to compare measured flexural moduli with values predicted by using measured tensile moduli.

Mechanisms influencing the cryogenic fracture-toughness behavior of aluminum-lithium alloys

Abstract: Cryogenic strength-toughness relationships for advanced aluminum-lithium alloys 2090, 8090, 8091 and 2091 are examined as a function of microstructure, plate orientation and wrought-product form (plate vs sheet), with specific emphasis on the underlying micro-mechanisms associated with crack advance. It is found that, with decrease in temperature from 298 K to 77 and 4 K, strength, tensile elongation and strain-hardening exponent are increased for all alloy chemistries, microstructures and product forms; however, the longitudinal (L-T, T-L) fracture toughness may increase or decrease depending upon the prevailing microscopic mechanism (microvoid coalescence vs transgranular shear) and macroscopic mode (plane strain vs plane stress) of fracture. In general, alloy microstructures that exhibit changes in either the fracture mechanism or mode at low temperatures show a decrease in L-T toughness. Conversely, when the fracture mechanism is unchanged between ambient and 4 K, observed variations in toughness with temperature are a strong function of the degree of local stress-triaxiality that develops at the crack tip. In very thin sheets, where the fracture mode remains one of plane stress (“slant” fracture), the elevation in toughness at low temperatures is associated with the concurrent increase in tensile strength and ductility; conversely, in thick plate, the increased occurrence of through-thickness delaminations (due to the weak short-transverse properties) at low temperatures locally promotes plane-stress conditions, thereby enhancing toughness by relaxing triaxial constraint. In sheets of intermediate thickness, however, the absence of such through-thickness delaminations permits the expected transition from plane-stress to plane-strain conditions, with the result that the toughness now decreases with reduction in temperature.

Fracture features of a silicon-dispersed aluminium alloy extruded from rapidly solidified powder

Abstract: The tensile fractography of an AI-20Si-3Cu-1 Mg alloy consolidated from rapidly solidified powder by extrusion has been investigated using optical and electron microscopy, and related to the processing conditions as well as the tensile behaviour of the alloy at room and elevated temperatures. The alloy studied shows distinct fracture features owing to the presence of dispersed silicon crystal particles with a bimodal distribution in size and of prior powder particle boundaries in the extrudate. It has been found that at room temperature cracks initiate by cracking the primary silicon crystal particles. Crack propagation occurs along the interfaces between the eutectic silicon crystal particles and the matrix and also between the prior powder particles, where microvoids are formed by the interfacial decohesion. At 300 °C, the fracture of the alloy involves microvoid nucleation, growth and coalescence at the interfaces between the silicon crystal particles and the aluminium matrix and between the prior powder particles. It has also been observed that the fractographic features of the alloy correspond well to the processing conditions including extrusion temperatures and subsequent heat treatment. The importance of minimizing the coarsening of the silicon crystals in processing in order to use the full strength potential of the alloy investigated is emphasized.

Determination of the local tensile axis direction in a tem in situ strained γ′ single crystal—a finite element approach

Abstract: An in situ study of the plastic deformation mechanisms occurring in the ordered γ′ phase of the CMSX 2 superalloy has been performed inside a Jeol 200 CX electron microscope. This type of study necessitated the development of a single crystal tensile test specimen with a special curved profile which allowed us to concentrate the stresses at the edge of a hole generated by a polishing treatment. We then deformed this highly resistant material in a wide temperature range within the microscope. Since the mechanical properties of this material are strongly orientation dependent, we were interested in determining the orientation of the local tensile axis in the specimen produced during the experiment. This was obtained by performing a finite element analysis using the code MSC/NASTRAN® and extracting the state of principal stresses near the edge of the hole. By recalculating the Schmid factors in the vicinity of the hole, we were able to explain the development of the slip systems observed during the experiments. We will show that the orientation of the stresses occurring in the in situ experiments can be accurately predicted, and that there exists a zone, the extent depending on the diameter of the hole, in which the major principal stress axis is parallel to the global tensile direction. These results from the particular study of the CMSX2 γ′ phase can be of interest to all in situ straining experiments.

Random glass mat reinforced thermoplastic composites. Part III: Characterization of the tensile moudulus

Abstract: Random glass mat thermoplastic composites, which can be thermostamped to form complex deep-drawn parts with ribs and bosses, are excellent materials for making low-cost stiff parts with relatively high impact strength. However, the mechanical properties of these materials, as determined by standard tensile tests, are known to exhibit large scatter. And the tensile modulus in these materials can vary by a factor of two over a 12.7-mm distance. In an earlier effort, measurements of the local tensile moduli of long, thin, 12.7-mm-wide strips along both thin edges (left and right) of the specimen and across the face were used to show that the local tensile modulus is well approximated by the arithmetic mean of the local left- and right-edge tensile moduli. To establish the tensile strength of these materials, the local tensile moduli of long dog-bone specimens are first characterized along the length, after which the specimens are pulled to failure. The tensile strength is shown to correlate well with the arithmetic mean of the local left- and right-edge tensile moduli.

The effect of specimen size and stress rate for the Brazilian test—A statistical analysis

Abstract: The Brazilian test is a widely accepted method for the determination of the tensile strength of intact rock. Specifications for the Brazilian tensile strength test have been established by the American Society for Testing and Materials (ASTM), ASTM D 3967-86 and a suggested approach is provided by the International Society for Rock Mechanics (ISRM). The ASTM and ISRM allow a relatively wide range of values for specimen geometry defined in terms of length to diameter ratio and loading rates defined as either time to failure or stress rate.