Showing papers on "Ultimate tensile strength published in 1996"

Properties and modification methods for vegetable fibers for natural fiber composites

Abstract: SYNOPSIS Studies on structure and properties of natural vegetable fibers (NVF) show that composites made of NVF combine good mechanical properties with a low specific mass. The high level of moisture absorption by the fiber, its poor wettability, as well as the insufficient adhesion between untreated fibers and the polymer matrix lead to debonding with age. To build composites with high mechanical properties, therefore, a surface modification of the fibers is necessary. The existing physical and chemical NVF modification methods-e.g., plasma treatment or graft copolymerization-which are used for the development of NVF-polymer composite properties is discussed. It is shown that modified cellulose fiber-polymer interaction mechanisms are complex and specific to every definite system. By using an coupling agent, like silanes or stearin acid, the Young's modulus and the tensile strength increases, dependent on the resin, until 50%. Simultaneously, the moisture absorption of the composites decreases for about 60%. With other surface modifications, similar results are obtained. 0 1996 John Wiley & Sons, Inc

Mechanical and barrier properties of edible chitosan films as affected by composition and storage

Abstract: Oxygen permeability coefficients (OP), water vapor permeability coefficients (WVP), ethylene permeability coefficients (EP), tensile strength (TS) and percent elongation (%E) at break values were determined for chitosan films plasticized with glycerin at two concentrations (0.25 and 0.50 mL/g chitosan). Film samples were tested after 0, 2, 4, 8 and 12 wk of storage. After an initial drop in permeability during the first 2 wk of storage, mean OP (4.6 × 10−5 cc/m-day-atm) and mean EP (2.3 × 10−4 cc./m.day.atm) remained constant while mean WVP (2.2 × 10−1 g/m-day-atm) decreased with respect to storage time. TS values (15–30 MPa) decreased and %E values (25%–45%) increased with respect to storage time. The stability of OP and EP values with storage was not expected, while the change in mechanical properties was as expected.

Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene: 1. Tensile and flexural modulus

Abstract: In this report we present the results from the first part of a study on the influence of fibre length (0.1–50mm) and concentration (3–60% w/w) on the properties of glass-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method, and are compared with samples prepared on a commercial melt-impregnation GMT line. We found that laminate stiffness increased linearly with fibre concentration up to 40% w/w. However, stiffness was virtually independent of fibre length above 0.5 mm. Predictions of tensile modulus using the Cox model correlated well with the experimental data. High concentrations of long fibres(>40% w/w) resulted in fibre packing problems and an increase in void content which lead to a reduction in modulus. The matrix molecular weight and the fibre-sizing compatibility had little effect on the laminate stiffness.

The balance of mechanical and environmental properties of a multielement niobium-niobium silicide-based in situ composite

Abstract: This article describes room-temperature and high-temperature mechanical properties, as well as oxidation behavior, of a niobium-niobium silicide basedin situ composite directionally solidified from a Nb-Ti-Hf-Cr-Al-Si alloy. Room-temperature fracture toughness, high-temperature tensile strength (up to 1200 °C), and tensile creep rupture (1100 °C) data are described. The composite shows an excellent balance of high- and low-temperature mechanical properties with promising environmental resistance at temperatures above 1000 °C. The composite microstructures and phase chemistries are also described. Samples were prepared using directional solidification in order to generate an aligned composite of a Nb-based solid solution with Nb3Si- and Nb5Si3-type silicides. The high-temperature mechanical properties and oxidation behavior are also compared with the most recent Ni-based superalloys. This composite represents an excellent basis for the development of advanced Nb-based intermetallic matrix composites that offer improved properties over Ni-based superalloys at temperatures in excess of 1000 °C.

Tensile properties of short sisal fiber reinforced polystyrene composites

Abstract: The tensile properties of polystyrene reinforced with short sisal fiber and benzoylated sisal fiber were studied. The influence of fiber length, fiber content, fiber orientation, and ben-zoylation of the fiber on the tensile properties of the composite were evaluated. The ben-zoylation of the fiber improves the adhesion of the fiber to the polystyrene matrix. the benzoylated fiber was analyzed by IR spectroscopy. Experimental results indicate a better compatibility between benzoylated fiber and polystyrene. the benzoylation of the sisal fiber was found to enhance the tensile properties of the resulting composite. The tensile properties of unidirectionally aligned composites show a gradual increase with fiber content and a leveling off beyond 20% fiber loading. The properties were found to be almost independent of fiber length although the ultimate tensile strength shows marginal improvement at 10 mm fiber length. The thermal properties of the composites were analyzed by differential scanning calorimetry. Scanning electron microscopy was used to investigate the fiber surface, fiber pullout, and fiber–matrix interface. Theoretical models have been used to fit the experimental mechanical data. © 1996 John Wiley & Sons, Inc.

High-temperature deformation measurements using digital-image correlation

Abstract: The ability of the computer-vision technique of digital-image correlation to measure full-field in-plane surface deformations at elevated temperatures was evaluated by a series of experiments. Samples were subjected to pure translation, free thermal expansion and uniform tensile loads. Results are presented which show that the digital-image-correlation technique remains fully capable of accurate measurement of the displacements and strains on the surface of a planar object at temperatures up to 650°C.

Mechanical behaviour of laminated metal composites

Abstract: Laminated metal composites (LMCs) are a unique form of composite material in which alternating metal or metal containing layers are bonded together with discrete interfaces. The mechanical properties of these materials are reviewed. The tensile properties at low and high temperatures are described. At low temperature, very high tensile strengths can be achieved in deposition processed laminates and very high tensile ductilities can be achieved in roll bonded laminates by layer thickness refinement. At high temperature, superplasticity has been observed and agrees with predictions from constitutive creep relations. Damage critical properties (such as fracture toughness, fatigue, and impact behaviour) and damping can be superior to those exhibited by the component materials. The damage critical properties are strongly influenced by local delaminations at layer interfaces. Mechanisms responsible for many of the unique properties of LMCs have been proposed. The influence of processing, laminate archit...

Degree of hydration-based description of mechanical properties of early age concrete

Abstract: For the evaluation of the risk of thermal cracking in hardening massive concrete elements, knowledge of the development of strength and deformability of early-age concrete is extremely important. Based on an extensive experimental research program on hardening concrete elements, a degree of hydration-based description for the compressive strength, Young's modulus, the uniaxial tensile strength, the splitting tensile strength, the flexural tensile strength, Poisson's ratio and the peak strain are all worked out. An extension of the formulation of Sargin for the stress-strain relation for short-term compressive loading leads to a degree of hydration-based stress-strain relation for hardening concrete. Good agreement with experimental results is reported.

Casting defects and the tensile properties of an AlSiMg alloy

Abstract: Samples containing either entrapped dross and oxide films, gas porosity or small drilled holes have been used to study the effect of different types of defects on the tensile behaviour of an Al 7Si 0.4Mg casting alloy. The tensile properties show little or no correlation with the bulk porosity content, especially in the case of samples containing dross and oxide films. In contrast, the decrease in tensile ductility and strength correlates with the area fraction of defects in the fracture surface of the samples. The experimental results are in agreement with the predictions of a simple analysis based on models for the growth of a plastic instability in a tensile sample.

Influence of fibre length and concentration on the properties of glass fibre-reinforced polypropylene: Part 3. Strength and strain at failure

Abstract: In this report we present the results from the third part of a study on the influence of fibre length (0.1–50 mm) and concentration (3–60% w/w) on the properties of glass fibre-reinforced polypropylene laminates. These laminates were prepared in the laboratory using a wet deposition method and compared with samples prepared on a commercial melt impregnation GMT line. We found that laminate tensile strength increased linearly with fibre concentration up to 60% w/w. Laminate strength was also found to increase with increasing fibre length. At high values of fibre length (> 3–6 mm) the strength reached a plateau level which was directly dependent on fibre content. The matrix molecular weight appeared to have little direct influence on the level of laminate strength. However, the glass fibre sizing compatibility was found to have a strong effect on the tensile strength of both laboratory made wet deposited laminates and commercially prepared GMTs. The tensile strength of the GMT samples also showed a clear correlation with the measured fibre strength. A modified version of the Kelly-Tyson model gave calculated values of laminate strength which correlated well with the experimental data. We propose that the tensile strength of these laminates is governed by the properties of the fibres which have an orientation close to parallel with the loading direction.

Antimicrobial and physicochemical properties of methylcellulose and chitosan films containing a preservative

Abstract: The methylcellulose was mixed with chitosan as well as 4% of sodium benzoate or potassium sorbate to form a film. Investigations of the antimycotic activity of the film on Penicillium notatum and Rhodotomla nibra revealed that it possessed significant antifungal properties. At 25C, approximately 43-45 % of the preservatives were released from the film to the glycerol-water mixture in the first 30 min. The maximum amount of preservative that could be released from the film at 25C was approximately 5745%. At 4C, 38-39% of preservatives were released from the film within 30 min, and reached a maximum amount of 49 % in approximately 6 h. The IT-IR spectrum showed that the ionic interaction between -COO of preservatives and -NH,+ of chitosan existed in the film. However, the incorporation of preservatives did not affect the tensile strength and elongation propeny of the methylcellulose/chitosan film.

Thermal and mechanical properties of aluminum powder-filled high-density polyethylene composites

Abstract: Thermal conductivity and mechanical properties such as tensile strength, elongation at break, and modulus of elasticity of aluminum powder-filled high-density polyethylene composites are investigated experimentally in the range of filler content 0–33% by volume for thermal conductivity and 0–50% by volume for mechanical properties. Experimental results from thermal conductivity measurements show a region of low particle content, 0–12% by volume, where the particles are distributed homogeneously in the polymer matrix and are not interacting with each other; in this region most of the thermal conductivity models for two-phase systems are applicable. At higher particle content, the filler tends to form ag-glomerates and conductive chains resulting in a rapid increase in thermal conductivity. The model developed by Agari and Uno estimates the thermal conductivity in this region. Tensile strength and elongation at break decreased with increasing aluminum particles content, which is attributed to the introduction of discontinuities in the structure. Modulus of elasticity increased up to around 12% volume content of aluminum particles. Einstein's equation, which assumes perfect adhesion between the filler particles and the matrix, explains the experimental results in this region quite well. For particle content higher than 30%, a decrease in the modulus of elasticity is observed which may be attributed to the formation of cavities around filler particles during stretching in tensile tests. © 1996 John Wiley & Sons, Inc.

Modification of poly(L-lactides) by blending: Mechanical and hydrolytic behavior

Abstract: Two different poly(L-lactides) (PLLAb and PLLAa) were blended with poly(e-caprolactone) (PCL) and an elastic poly(e-caprolactone/L-lactide) P(CL/L-LA) copolymer to modify the mechanical properties of PLLA. Blends of both PLLAs with 20 wt.-% of PCL were prepared. PLLAa was blended with 20 wt.-% of P(CL/L-LA) copolymer, and blends of PLLAb and P(CL/L-LA) copolymer were made with copolymer contents of 5, 10, 20 and 30 wt.-%. The tensile properties and impact and shear strengths were determined as a measure of the mechanical properties. The hydrolytic behavior of the blends was investigated, and the changes in shear strength as a function of hydrolysis were followed. The structure of the hydrolyzed samples was studied by means of scanning electron microscopy (SEM). The properties of PLLA changed considerably when blended with PCL or P(CL/L-LA) copolymer. An increasing amount of copolymer in PLLAb decreased tensile modulus and shear strength, but improved the strain and impact strength. In hydrolysis, blends containing PLLAa degraded slower than blends of PLLAb because of the higher initial molar mass and purity of PLLAa. The molar masses of PLLAb blends decreased dramatically, and less than 10% of the initial molar masses and shear strengths were left after 12 weeks in vitro. The morphology of the blends affected the degradation. The blends containing P(CL/L-LA) copolymer had a porous structure which facilitated water absorption into the blend.

Corrosion resistance and corrosion fatigue strength of new titanium alloys for medical implants without V and Al

Abstract: The corrosion resistance and the corrosion fatigue strength of Ti-15Zr-4Nb-4Ta-0.2Pd-0.2O-0.05N and Ti-15Sn-4Nb-2Ta-0.2Pd-0.2O alloys were compared with those of Ti-6Al-4 V extra low interstitial (ELI), Ti-6Al-2Nb-1Ta, pure Ti grade 2 and β type Ti-15%Mo-5Zr-3Al alloys. Anodic polarization and corrosion fatigue testings were performed in various physiological saline solutions at 310 K. The corrosion fatigue test was carried out under the condition of a tension to tension mode with a sine wave at a stress ratio of 0.1 and at a frequency of 10 Hz. The tensile properties of these alloys were measured at room temperature. The change in current density was small up to passivity zone in 1 wt.% lactic acid, PBS(−), calf serum and eagle's MEM + fetal bovine serum solutions except 5 wt.% HCl. The current density of Ti-15Zr-4Nb-4Ta-0.2Pd-0.2O-0.05N alloy at potential up to 5 volt tend to be lower than that of Ti-6Al-4V ELI. Otherwise passive current density of the β type Ti-15Mo-SZr-3Al alloy was higher than that of α + β type alloys. The passive films formed on Ti-15Zr-4Nb-4Ta-0.2Pd-0.2O alloy in the calf serum consisted mainly of TiO2, ZrO2, Nb2O5, Ta2O5 and Pd or PdO as demonstrated using X-ray photoelectron spectroscopy. The cycle to failure of Ti-15Zr-4Nb-4Ta-0.2Pd-0.2O-0.05N and Ti-15Sn-4Nb-4Ta-0.2Pd-0.2O alloys annealed at 973 K for 7.2 ks increased with decreasing applied maximum stress. The fatigue strength at 108 cycles in those alloys was about 600 MPa. The fatigue strength of Ti-6Al-2Nb-1Ta alloy at 108 cycles was about 700 MPa. The fatigue strength of β type Ti-15Mo-5Zr-3Al alloy at 107 cycles was lower than that of α + β type alloys.

Influence of ferrite-martensite microstructural morphology on tensile properties of dual-phase steel

Abstract: The influence of ferrite-martensite microstructural morphology, volume fraction of martensite, epitaxial ferrite on the tensile behaviour of dual-phase steels, was studied. It was observed that increasing the martensite content and its aspect ratio raised tensile strength and ductility. Epitaxial ferrite in rolled material strongly reduced the strength and improved the ductility, suggesting that substructure strengthening of material, as well as increased stress transfer to the hard phase, contribute to the strength of thermo-mechanically processed material. Mettallographic analysis of deformed samples revealed that void nucleation occurs predominantly along the ferrite-martensite interface. The void density in the necked region increased towards the fracture surface in all samples and was higher for samples which exhibited localized necking.

Effects of β-α transformation on the static and dynamic tensile behavior of isotactic polypropylene

Abstract: It was demonstrated that the mechanical stress-induced βα-transformation in isotactic polypropylene (iPP) is associated with considerable toughness enhancement. This toughness improvement depends on the test conditions (loading frequency). The toughness of β-iPP was superior to the α-iPP by 13% under static (characterized by a load frequency of ca. 5 × 10−4 Hz) and 70% under dynamic (tensile impact with a loading frequency in the range of ca. 3 × 102…103 Hz) conditions, respectively. By applying the essential work of fracture (EWF) concept to single-edge notched tensile (SEN-T) specimens it was shown that for the toughness upgrading observed, energy dissipation in the enlarged plastic zone is responsible. The occurrence of the βα-transformation was evidenced by differential scanning calorimetry (DSC). Based on DSC measurements it was found that the degree of βα-trans-formation depends on the local strain. At high strain values the βα-conversion is complete (at elogation at break in uniaxial static tensile test), while this transformation is only partial at lower strains (at tensile impact). In addition, in the plastic (or deformation) zone the βα-conversion changed locally, and can be used for mapping of this region. © 1996 John Wiley & Sons, Inc.

Tensile properties of particulate-reinforced metal matrix composites

Abstract: Room temperature tensile tests have been carried out on MMCs, all based on the Al alloy 7075 and on monolithic material. The particulate reinforcements used were SiC in three nominal sizes, 5, 13 and 60 μm. Three matrix ageing conditions were studied, peak aged and equivalent underaged and overaged matrix conditions, based on microhardness measurements. The effects of ageing condition on the tensile properties of the composites follow those produced in unreinforced material. Composites containing 5 and 13 μm particles both had greater 0.2% proof stress and tensile strength values than unreinforced material. However, the composite reinforced with 60 μm particles had reduced 0.2% proof stress and tensile strength in the underaged and peak aged condition, and a greater 0.2% proof stress in the overaged condition compared to the monolithic alloy. All the composites had lower ductility than the unreinforced material. with the material containing 5 μm SiC being the most ductile and that reinforced with 60 μm SiC having very low ductility. Failure appears to occur by the accumulation of internal damage to particles either by particle fracture or interfacial failure. Such damage introduces voids which grow and lead to reduced ductility in these composites. Large 60 μm particles fracture easily at low applied stresses, leading to reduced 0.2% proof stress and premature failure compared to the other composites. The small 5 and 13 μm particles damage less easily and so these composites are stronger than the monolithic material and are more ductile than the composite reinforced with 60 μm particles.

Spall fracture properties of aluminum and magnesium at high temperatures

Abstract: Measurements of the dynamic tensile strength of aluminum and magnesium have been carried out by investigations of the spall phenomena over a wide range of temperatures, shock‐wave intensities, and load durations. Free‐surface velocity profiles were recorded with VISAR and used to provide the spall strength measurements. The initial temperature of samples was varied from room temperature to near the melting point. The peak compressive pressure in the shock waves was varied from 5 to 50 GPa for aluminum and from 2 to 10 GPa for magnesium. The load duration was varied by more than one order of magnitude. The free‐surface velocity measurements showed a precipitous drop in the spall strength of preheated samples as temperatures approached the melting point. No significant influence of the peak pressure on the spall strength was observed. The strain‐rate dependencies of the spall strength could be represented as power functions with a power index of 0.060 for aluminum and 0.072 for magnesium. Unexpectedly large amplitudes for the Hugoniot elastic limit of both aluminum and magnesium were observed at temperatures approaching the melting point.