Showing papers on "Ultimate tensile strength published in 1991"

Theory of mechanical-properties of ceramic-matrix composites

Abstract: A theory is presented to predict the pullout work and ultimate tensile strength of ceramic-matrix composite (CMC) materials tested under uniaxial tension as functions of the underlying material properties. By assuming that the fibers fracture independently and that global load redistribution occurs upon fiber fracture, the successive fragmentation of each fiber in the multifiber composite becomes identical to that of a single fiber embedded in a homogeneous large-failure-strain matrix, which has recently been solved exactly by the present author. From single-fiber fragmentation, the multifiber composite distribution of pullout lengths, work of pullout, and ultimate tensile strength are easily obtained. The trends in these composite properties as a function of the statistical fiber strength, the fiber radius and fill fraction, and the sliding resistance-tau-between the fibers and the matrix easily emerge from this approach. All these properties are proportional to a characteristic gauge length-delta-c and/or the associated characteristic stress-sigma-c, with proportionality constants depending only very weakly on the fiber Weibull modulus: the pullout lengths scale with delta-c, the work of pullout scales with sigma-c-delta-c, and the ultimate strength scales with sigma-c. The key length-delta-c is the generalization of the "critical length," defined by Kelly for single-strength fibers, to fibers with a statistical distribution of strengths. The theory also provides an interpretation of fracture-mirror measurements of pulled-out fiber strengths so that the in situ key strength sigma-c and Weibull modulus of the fibers can be determined directly. Comparisons of the theoretical predictions of the ultimate tensile strength to literature data on Nicalon/lithium aluminum silicate (LAS) composites generally show good agreement.

Aspects of fracture in particulate reinforced metal matrix composites

Abstract: The tensile deformation and fracture behaviour of the aluminium alloy 6061 reinforced with SiC has been investigated. In the T4 temper plastic deformation occurs throughout the gauge length and the extent of SiC particle cracking increases with increasing strain. In the T6 temper strain becomes localised and particle cracking is more concentrated close to the fracture. The elastic modulus decreases with increasing particle damage and this allows a damage parameter to be identified. The fraction of SiC particles which fracture is less than 5%, and over most of the strain range the damage controlling the tensile ductility can be recovered, indicating that other factors, in addition to particle cracking are important in influencing tensile ductility. It is suggested that macroscopic fracture is initiated by the SiC particle clusters that are present in these composites as a result of the processing. The matrix within the clusters is subjected to high levels of triaxial stress due to elastic misfit and the constraints exerted on the matrix by the surrounding particles. Final fracture is then produced by crack propagation through the matrix between the clusters.

Hopkinson Techniques for Dynamic Recovery Experiments

Abstract: Novel techniques are introduced to render the classical split Hopkinson bar apparatus suitable for dynamic recovery experiments, where samples can be subjected to a single pulse of pre-assigned shape and duration, and then recovered without any additional loading, for post-test characterization; i.e., techniques for fully controlled unloading in Hopkinson bar experiments. For compression dynamic recovery tests, the new design generates a compressive pulse trailed by a tensile pulse (stress reversal), travelling toward the sample. Furthermore, all subsequent pulses which reflect off the free ends of the two bars (incident and transmission) are rendered tensile, so that the sample is subjected to a single compressive pulse whose shape and duration can also be controlled. For tension recovery experiments, the new design provides for trapping the compression pulse reflected off the sample, and the tensile pulse transmitted through the sample. In addition, a sample can be subjected to compression followed by tension, and then recovered, allowing the study of, e.g. the dynamic Bauschinger effect in materials.

A Progressive Failure Model for Composite Laminates Containing Openings

Abstract: A progressive failure model is developed for laminated composites containing stress concentrations subjected to in-plane loading. The fundamental approach is to model a damaged lamina using a damaged ply constitutive relation in a simplified manner. The environmental effects including the thermal residual stresses and hygroscopic stresses arc taken into consideration. Parametric studies show that load increment only has little effect on the ultimate strength. When the number of elements for the finite element mesh increases to a certain value, the predicted ultimate strength approaches a stable value. The predictions for the ultimate strength, stress-strain behavior and the damage progression agree reasonably well with the experimental result.

Intrinsic stress in diamond films prepared by microwave plasma CVD

Abstract: The stress in diamond films prepared by microwave plasma CVD was investigated as a function of methane concentration (0.2%–3.0%) and deposition temperature (600–900 °C). Tensile and compressive total (thermal and intrinsic) stress were observed, depending on the deposition conditions. The thermal stress is compressive and relatively constant (0.215–0.275 GPa) over the temperature range investigated. The intrinsic stress is tensile and its origin is interpreted in terms of the grain boundary relaxation model. Calculations indicate a value of 0.84 GPa, using the grain boundary model, which is in fair agreement with the measured value. For the methane series, the tensile intrinsic stress decreases with increasing the methane fraction. The increasing compressive stress is ascribed to increased impurity (hydrogen and nondiamond phase carbon) incorporation with increasing methane fraction. 15N nuclear reaction analysis shows a linear correlation between hydrogen in the film and methane in the supply gas while spectroscopic ellipsometry shows a direct correlation between optically absorbing nondiamond (sp2) carbon incorporation and methane. For the temperature series, the intrinsic tensile stress increases with deposition temperature. The increase is ascribed to decreasing sp2 C incorporation with temperature, as confirmed by spectroscopic ellipsometry measurements.

The Effect of Local Interfacial Geometry on the Measurement of the Tensile Bond Strength to Dentin

Abstract: The local detail of the geometry of the adhesive interface can have a significant effect on the measurement of dentin bond strengths and may be a contributory factor in the discrepancies among data in the published literature. The potential effect on the dentin bond strength due to modifications of the local stress distribution at the adhesive/dentin interface has been assessed. Tensile bond strength measurements for specimens with and without an adhesive flash were carried out and compared with the stress distribution at the adhesive interface determined by finite element stress analysis. The results showed that when the adhesive was constrained to the interface only, the tensile bond strength was 3.10 MPa, which increased to 6.90 MPa when a flash of adhesive was present. For a realistic measurement of dentin bond strength, the adhesive should be constrained to the interface only. Extension of the adhesive beyond the interface will result in an artificially high value for the dentin bond strength. A standardized method for the measurement of dentin bond strength is urgently needed, but must take these as well as all other known factors into account if results from different testing centers are to be directly comparable.

Intrinsic stress in sputtered thin films

Abstract: A review of the literature reveals that the intrinsic stress in sputtered thin films can be tensile or compressive depending on the flux and energy of particles striking the film. Stress data indicates that the normalized momentum P*n=γ√ME (where γ is the energetic particle/atom flux ratio, M the mass, and E the energy) may be the appropriate stress scaling factor. The forward sputtering model predicts a √E dependence. An idealized stress–momentum curve is constructed consisting of three regimes:(1) a region of increasing tensile stress at low P*n, due to a porous microstructure, followed by (2) a sharp transition from tensile to compressive stress at intermediate momentum, accompanied by a conversion to zone T‐type microstructure and (3) a saturation region at high momentum, due to plastic flow. For any deposition process the sign and magnitude of the stress depends on P*n, which is a function of several deposition parameters. Calculations indicate that stress reversal in sputtered and ion‐assisted evapo...

Fiber-Matrix Adhesion and Its Effect on Composite Mechanical Properties: II. Longitudinal (0°) and Transverse (90°) Tensile and Flexure Behavior of Graphite/Epoxy Composites:

Abstract: An optimum level of interfacial bond strength between reinforcing fiber and a polymeric matrix in which it is placed is essential for acceptable composite mechanical properties and performance. The...

Damage Tolerance of Laminated Composites Containing an Open Hole and Subjected to Tensile Loadings

Abstract: An investigation was conducted to study tensile failure of laminated composites containing an open hole This investigation was especially concerned with determining the response, type and extent of damage in composites as a function of applied load Both an analysis and experiments were performed for graphite/epoxy composites during the study A progressive damage analysis was developed to study the problem The analysis was verified by an extensive comparison between the numerical calculations based on the analysis and the experimental data obtained during the investigation as well as from published literature Different graphite/epoxy composite materials were considered in the study Overall, good agreements were found between the calculations and the data Based on the study, it was found that the types and extent of internal damage in the notched composites strongly depend on the ply orientation of the laminates The types and the size of damage directly affect the strength and failure mode of the co

Mechanical properties of high-strength lightweight concrete

Abstract: Information is presented on the mechanical properties of high-strength lightweight concrete up to 100 MPa with a corresponding density of 1865 kg/ sq m. Five different types of lightweight aggregates were investigatged and the strength of the aggregate appears to be the primary factor controlling the strength of the high strength lightweight concrete. The tensile/compressive strength ratio appears to be lower for high strength lightweight concrete than that for high strength normal weight concrete, and the elastic modulus, which varied from 17.8 to 25.9 GPa, is much lower than that of normal weight concrete. For the high strength lightweight concrete, the shape of the ascending part of the stress-strain curve was more linear than that of lightweight concrete with low to medium strength.

Mean stress effects on low cycle fatigue for a high strength steel

Abstract: — ASTM A723 Q & T steel with a yield strength and ultimate strength of 1170 and 1262 MPa respectively was evaluated for mean stress-strain effects under smooth specimen axial strain controlled low cycle fatigue conditions with strain ratios R of −2, −1, 0, 0.5 and 0.75. Cycles to failure ranged from 15 to 105. Cyclic stress-strain response based upon half-life hysteresis loop peaks were similar for all R ratios. Mean stress relaxation occurred for R≠−1 only when plastic strain amplitudes were present and this occurred above total strain amplitudes of 0.005. Thus, mean stress relaxation was completely dependent upon cyclic plasticity. Mean strains did not affect low cycle fatigue life unless accompanied by half-life mean stress. Tensile mean stress was detrimental and compressive mean stress was beneficial and these effects only occurred at strain ampltidues below 0.005. Three different mean stress models were used to evaluate the low cycle fatigue data and the SWT log-log linear model best represented the data. These results can be used with the local notch strain fatigue life prediction methodology.

Micromechanical modeling of fiber/matrix interface effects in transversely loaded SiC/Ti-6-4 metal matrix composites

Abstract: The transverse tensile behavior of a composite composed of unidirectional silicon-carbide fiber (Textron SCS-6) in a Ti-6AL-4V matrix is examined with emphasis on the effects of fiber-matrix interface strength. The residual stresses as a result of a mismatch in the coefficients of thermal expansion of silicon carbide and titanium are estimated analytically and compared with measurements made using X-ray diffraction techniques. Idealizing the composite as a regular rectangular array of fibers in an elasto-plastic matrix, the transverse tensile stress-strain behavior is predicted under the assumptions of an infinitely strong interface as well as an interface without tensile strength. These results are compared with experiments conducted at three different temperatures. The agreement between experiment and predictions based on an interface without tensile strength is extremely close. The modeled stress-strain curves predict a well-defined knee in the transverse tensile stress-strain curve associated with the separation of fiber and matrix at their interface. The same stress-strain behavior is observed experimentally. Results of edge replica experiments and mechanical unloading from stress levels above the knee are also presented as additional evidence of the association of fiber-matrix separation with the knee in the transverse tensile stress-strain curve.

The effect of plastic deformation on Al2CuLi (T1) precipitation

Abstract: The enhancement ofT1 precipitation in Al-Li-Cu alloys by plastic deformation prior to aging (that is, cold work) and the subsequent increase in alloy strength is investigated. The increased understanding of the role of matrix dislocations in the nucleation and growth ofT1 plates, discussed in the previous paper,[1] permits a detailed study of the phenomenon. In this paper, the effect of different levels of plastic strain on theT1 particle distributions as a function of aging time at 190 °C is quantified, and the subsequent influence on tensile properties is thereby described. The effect of plastic deformation is shown to decrease theT1 plate length and thickness, increase the number density by almost two orders of magnitude, increase the yield strength by 100 MPa, while simultaneously reaching peak strength in 20 pct of the time required without plastic deformation.

Relationship Between Petrographic Characteristics, Engineering Index Properties, and Mechanical Properties of Selected Sandstones

Abstract: Six different sandstone units were studied to investigate and quantify the relationship between their mechanical properties (compressive strength, tensile strength, Young's modulus, Poisson's ratio), petrographic characteristics, and engineering index properties. Sandstones investigated included the Sharon sandstone, the Juniata sandstone, the Morgantown-Grafton sandstone, and three Berea sandstone units. These sandstones were tested for percent absorption, density, slake durability, total pore volume, uniaxial compressive strength, tensile strength, Young's modulus, and Poisson's ratio. Petrographic characteristics studied included grain size, grain shape, grain sorting, packing density, packing proximity, degree of grain interlocking, and mineral composition. The data were analyzed statistically to determine the quantitative relationships between various properties. Results indicate that compressive strength, tensile strength, and Young's modulus values for the sandstones studied are closely related (r>0.7) to their density, percent absorption, total pore volume, and type of grain-to-grain contacts. Generally, sandstones with higher densities, lower percent absorption, lower total pore volume, and higher percentage of sutured contacts exhibited higher values of compressive strength, tensile strength, and Young's modulus. For Poisson's ratio, however, inverse relationships were observed with compressive strength and Young's modulus. Based on these results, equations were developed for predicting mechanical properties from values of density, percent absorption, total pore volume, and percent sutured contacts.

Dilatation balloon fabricated from low molecular weight polymers

Abstract: A low molecular weight, flexible, biaxially oriented, dilatation catheter balloon comprising oriented polyethylene terephthalate, and having a calculated radial tensile strength of greater than about 25,000 psi.

Mechanical and barrier properties of edible corn and wheat protein films

Abstract: Published methods for production of homogeneous edible films from com and wheat proteins were adapted. Barrier and mechanical properties of the edible films were evaluated with procedures commonly used on polymeric films. Mechanical property data included thickness, elongation, tensile strength, tear strength, and burst strength measurements. Barrier property data included water vapor, oxygen, and carbon dioxide gas transmission rate measurements. Homogeneous com and wheat protein films were found to have low tensile strengths, far less than cellophane. Com films were brittle while wheat films were elastic in comparison to cellophane. All three types of film had low permeabilities for dry gases but relatively high water vapor permeabilities.

Increase in Mechanical Strength of Al–Y–Ni Amorphous Alloys by Dispersion of Nanoscale fcc-Al Particles

Abstract: Ni-base amorphous alloys with the homogeneous dispersion of nanoscale fcc-Ni particles have been produced in the composition range of 5 to 14 at%Si and 7 to 15%B. The particle size and interparticle spacing are 10 and 20 nm, respectively. The alloys exhibit tensile fracture strength (σ f ), Young's modulus (E) and hardness (H v ) which are higher than those of the corresponding amorphous single phase alloys, accompanying an increase in fracture elongation (∈ f )

Mechanical Strength of Clay Minerals as Influenced by an Adsorbed Polysaccharide

Abstract: The water-stabilizing action of polysaccharides on soil aggregates has been ascribed to the binding together of soil particles by polymer bridges. This study was conducted to investigate the ability of polysaccharides to increase the strength of interparticle bonds by measuring the mechanical strength of clay-polysaccharide complexes. Kaolinite, montmorillonite, and the polysaccharide scleroglucan were used. Cores were prepared from dilute suspensions of the complexes, air dried, and manufactured either into small briquets or into spherical aggregates to measure respectively the modulus of rupture and the tensile strength. The polysaccharide increased the mechanical strength of both clay minerals. The modulus of rupture of montmorillonite increased from 265 to 580 × 10⁵ Pa at the maximum adsorption of scleroglucan, which was 140 g kg⁻¹ clay. In the case of kaolinite, modulus of rupture measurements indicated that particle-orientation effects were small and could be neglected. The tensile strength of kaolinite increased from 1 to 20.6 × 10⁵ Pa at the maximum adsorption of scleroglucan (29.9 g kg⁻¹ clay). In this case, the mechanical properties were not due to changes in the clay microorganization, since scleroglucan affected neither the fabric nor the porosity of the kaolinite. Increases in strength were thus intercepted as the formation of polymer bridges between the clay particles and were related to the progressive coverage of the surface area of the clay by the polysaccharide. We concluded that the aggregating action of polysaccharides is predominantly due to an increased strength of interparticle bonds.

Prediction of concrete tensile strength from compressive strength: evaluation of existing relations for normal weight concrete

Abstract: The 0.5 power relation adopted by ACI Committee 318 predicting the splitting tensile strength of concrete from its compressive strength has been investigated. Research has consistently indicated that the relation in the Building Code Requirement does not agree particularly well with test results. Consequently, researchers have proposed alternative relations. The research for this paper investigated the validity and accuracy of these alternate relations. Tensile strength preditions from these relations were compared with test results assembled from various sources. It was found that the splitting tensile strength is not proportional to the 0.5 power of compressive strength. Although most of the alternate relations appear to be good, the assembled test data revealed that 0.69 is the most accurate power relation. Thus 0.69 power relation is proposed as an alternative to the ACI 318 relation.

Shear bond strength of composite resin to porcelain.

Abstract: This study evaluated the effect of porcelain surface treatment on the shear bond strength of composite resin to various porcelains and porcelain combinations. A variety of feldspathic porcelains with low and medium alumina content were tested. Porcelain/composite resin samples were stored in 37 degrees C water, thermocycled 1,000 times, and tested in shear. A 3-minute etching using hydrofluoric acid significantly increased the bond strength of most of the feldspathic porcelains with low and medium alumina content. Silane application to all types of etched porcelain had no significant effect on bond strength.

Development of high‐strength, high‐conductivity Cu–Ag alloys for high‐field pulsed magnet use

Abstract: A wire‐conductor fabrication method has been developed for Cu–Ag alloys containing 2–60 at. % Ag where high strength and high conductivity conductors are obtained by cold working combined with intermediate heat treatment. The intermediate heat treatment is repeated 3–4 times at 350–450 °C for 1–2 h at appropriate stages of reduction of area. The optimized Cu‐16 at. % Ag alloy wire with 99% reduction of area showed a tensile strength of 1000 MPa and an electrical conductivity of 80% IACS at room temperature. This suggests that the wires fabricated may be very promising for high‐field pulsed magnet use.

Do fibers increase the tensile strength of cement-based matrixes

Abstract: Many of the current applications of fiber reinforced concrete involve the use of fibers ranging around 1 % by volume of concrete It is usually assumed that fibers do not influence the tensile strength of the matrix, and that only after the matrix has cracked do the fibers contribute by bridging the cracks Recently, it has been possible to incorporate relatively large volumes (ranging up to 15%) of steel, glass, and synthetic fibers in concrete With such a large volume of fibers in concrete, some evidence presented in this paper indicates that the fibers may substantially increase the tensile strength of matrixes If this is true, then it is important to define conditions under which such beneficial interactions can occur

Mechanical properties of i-PP/CaCO3 composites

Abstract: Tensile and impact behavior of CaCO3-filled polypropylene was studied in the composition range 0–60 wt % filler. Tensile modulus increased while tensile strength and breaking elongation decreased with increase in CaCO3 content. The modulus increase and elongation decrease were attributed to increased filler–polymer interaction resulting in reduction in molecular mobility, while increased amorphization and obstruction to stress transfer accounted for the tensile strength decrease. Analysis of tensile strength data showed introduction of stress concentration in the composites. Izod impact strength at first increased up to a critical CaCO3 content, beyond which the value decreased. Surface treatment of CaCO3 with a titanate coupling agent LICA 12 enhances the adhesion of the filler and polymer, which further modifies the strength properties. Scanning electron microscopic studies indicated better dispersion of CaCO3 particles upon surface treatment, which effected the changes in the strength properties of the composites.

Toughening of MoSi2 with a ductile (niobium) reinforcement

Abstract: The effect of interfacial reactions and Y2O3 coatings on toughening of MoSi2 by ductile phase Nb reinforcements has been investigated. In the absence of coating the interfacial reaction layer exhibits parabolic growth with Mo5Si3, (Mo, Nb)5Si3, (Nb, Mo)5Si3 and Nb5Si3 phases forming. In precracked laminates subjected to tensile loads the ductile phase deformation is partially constrained, with debonding occurring within the interfacial reaction zone. Dense Y2O3 coating inhibits interdiffusion and results in more extensive debonding. In either case, significant toughening is expected with measured work of rupture values χ ≈ 5.7 to 6.3. Bulk composite MoSi2 reinforced with 20 vol.% Nb particles subjected to a chevron-notched three point flexure test had a work of rupture almost five times larger than the unreinforced MoSi2 matrix.

Wood Flour/Polypropylene Composites: Influence of Maleated Polypropylene and Process and Composition Variables on Mechanical Properties

Abstract: The mechanical properties of wood flour/polypropylene composites may be improved by using coupling agents to enhance the bonding between filler and matrix. We used a two-level, full-factorial experiment to examine the effectiveness of a commercially available additive, Epolene E-43, on strength (tensile, flexural, and cantilever-beam), modulus, impact energy, density, and melt viscosity of composites. The effect of Epolene E-43 was studied alone and in combination with three other variables: the weight ratio of wood flour to total polymer in the composites (45/55 or 55/45), size of wood flour particles (nominal 20 or 40 mesh), and extruder residence time (one or three extrusions). Of all the variables, Epolene E-43 had the greatest effect on strength. This effect was somewhat enhanced by using the 40-mesh wood flour and three extrusions; for this combination of variables, Epolene E-43 caused a 30 percent increase in strength. The combination of Epolene E-43 with a 55/45 wood flour/polymer ratio a...

The Effect of Laves Phase on the Mechanical Properties of Wrought and Cast + HIP Inconel 718

Abstract: The effect of varying amounts of Laves phase on the mechanical properties of wrought and cast + HIP Inconel718 is discussed. When present as a continuous or semicontinuous grain boundary network in wrought Inconel718, Laves phase dramatically reduces room temperature tensile ductility and ultimate tensile strength, with room temperature impact and fracture toughness properties and elevated temperature ductility also reduced. Laves may also act as a preferred crack initiation and propagation site, resulting in reduced low cycle fatigue (LCF) p blty d ca a i i an accelerated fatigue crack growth rates. Laves present as large globular aggregates in cast+HIP Inconel 718 significantly reduces room temperature tensile and elevated temperature stress rupture properties. In addition, the phase acts as a preferred crack initiation and propagation site, resulting in significant reductions in smooth and notch LCF capability and an accelerated fatigue crack growth rate. Methods for controlling Laves phase in wrought and cast +HIP Inconel 718 are discussed. Superalloys 718,625 and Various Derivatives Edited by Edward A. JJxia The Minerals, Metals & Materials Society, 1991

Effects of Silicon and Manganese Addition on Mechanical Properties of High-strength Hot-rolled Sheet Steel Containing Retained Austenite

Abstract: An 80 kgf/mm2 grade high-strength hot rolled sheet steel with a significantly high product of tensile strength and total elongation (TS×EI=3 000) has been developed by utilizing transformation-induced plasticity of retained austenite in 0.2% carbon sheet steels by optimizing the silicon and manganese content and hot rolling conditions. Finish rolling temperature and coiling temperature are important factors in terms of introducing a large amount of retained austenite. Silicon addition over 1.0% results in a significant increase in the volume fraction of retained austenite due to the change in second phase from bainite+pearlite to bainitic ferrite. The maximum volume fraction of retained austenite and the consequential optimum combination of tensile strength and ductility is obtained in a 0.2%C-2.0%Si-1.5%Mn steel. The effect of retained austenite on ductility becomes small with further addition of manganese over 1.5%, because the retained austenite transforms in the early stage of the straining process due to the presence of martensite.