Showing papers on "Ultimate tensile strength published in 2012"

Tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete

Abstract: The effects of blending fibers on the tensile behavior of Ultra High Performance Hybrid Fiber Reinforced Concrete (UHP-HFRC) are investigated. Four types of steel macro-fibers (of differing length or geometry) and one type of steel micro-fiber are considered. In producing the specimens, the volume content of the macro-fiber was held at 1.0%, whereas the volume content of the micro-fiber varied from 0.0% to 1.5%. The overall shape of tensile stress–strain curves of UHP-HFRC is primarily dependent upon the type of macro-fiber, although the addition of micro-fibers favorably affects the strain hardening and multiple cracking behaviors. UHP-HFRC produced from macro-fibers with twisted geometry provides the best performance with respect to post cracking strength, strain capacity and multiple micro-cracking behavior, whereas UHP-HFRC produced with long, smooth macro-fibers exhibits the worst performance.

Tough and highly stretchable graphene oxide/polyacrylamide nanocomposite hydrogels

Abstract: Polyacrylamide (PAM)/graphene oxide (GO) nanocomposite hydrogels (PGH) with GO nanosheets as cross-linkers were synthesized via in situ free radical polymerization of acrylamide in an aqueous suspension of GO. The tensile properties of the hydrogels were investigated in terms of type and content of cross-linkers. Compared to conventional PAM hydrogels (PBH) cross-linked chemically with N,N′-methylenebisacrylamide, PGH exhibits high tensile strength, high toughness and especially a large elongation at break. The tensile strength of PGH is about 4.5 times higher than that of PBH, and the elongation at break is over 3000%, nearly one order higher than that of PBH even when the content of GO is only 0.0079 wt%. By analyzing the cross-linked structure of PGH and the theoretical calculation on the number of cross-linked polymer chains per unit volume of gels, a structure model was thus proposed.

Probing topological protection using a designer surface plasmon structure.

Abstract: The ideal elastic limit is the upper bound to the stress and elastic strain a material can withstand. This intrinsic property has been widely studied for crystalline metals, both theoretically and experimentally. For metallic glasses, however, the ideal elastic limit remains poorly characterized and understood. Here we show that the elastic strain limit and the corresponding strength of submicron-sized metallic glass specimens are about twice as high as the already impressive elastic limit observed in bulk metallic glass samples, in line with model predictions of the ideal elastic limit of metallic glasses. We achieve this by employing an in situ transmission electron microscope tensile deformation technique. Furthermore, we propose an alternative mechanism for the apparent 'work hardening' behaviour observed in the tensile stress-strain curves.

Ideal strength and phonon instability in single-layer MoS 2

Abstract: Ideal tensile stress strain relations for single-layer MoS${}_{2}$ are investigated based on first-principle calculation, for biaxial tension and uniaxial tension along zigzag and armchair directions. The predicted ideal tensile strengths and elastic moduli are in excellent agreement with the very recent experimental measurements of Bertolazzi et al. [ACS Nano 5, 9703 (2011)] and Castellanos-Gomez et al. [Adv. Mater. 24, 772 (2012)]. It is identified that the tensile strength of single-layer MoS${}_{2}$ are dictated by out-of-plane soft-mode phonon instability under biaxial tension and uniaxial tension along the armchair direction. This failure mechanism, different from that of the truly two-dimensional material graphene, is attributed to the out-of-plane atomic relaxation upon tensile strain. Investigation of the electronic structures of single-layer MoS${}_{2}$ under tensile strain shows the material becomes an indirect semiconductor at small tensile strain ($l2$$%$) and turns into metallic before reaching the ideal tensile strength.

Dispersion of carbon nanotubes and its influence on the mechanical properties of the cement matrix

Abstract: An appropriate dispersion of carbon nanotubes (CNTs) is a prerequisite for their use in improving the mechanical properties of cement-based composites In this study two types of carbon nanotubes (CNTs) having different morphologies were investigated To obtain a uniform distribution of CNTs in the cement matrix, the effect of sonication on the deagglomeration of CNTs in combination with anionic and nonionic surfactants in varying concentrations was quantitatively investigated when preparing aqueous dispersions of CNTs for the subsequent use in cement paste The relationships between the quality of CNT-dispersion on the one hand and the sonication time and surfactant concentration on the other were determined using UV–vis spectroscopy After dispersion, nitrogen-doped CNTs were found mostly as individual, broken CNTs In contrast, after the treatment of the mixture of single-, double-, and multi-walled CNTs, a net-like distribution was observed where destruction of the CNTs due to sonication could not be distinguished Modification of the cement pastes with dispersions of CNTs led to a pronounced increase, up to 40%, in compressive strength and, in some cases, to a moderate increase in tensile strength under high strain-rate loading However, no significant improvement in strength was observed for quasi-static loading Microscopic examination revealed that the bridging of the C–S–H phases differed depending on the type of CNT This explained, at least partly, the observed effects of CNT-addition on the mechanical properties of hardened cement pastes

Improving the mechanical properties of natural fibre fabric reinforced epoxy composites by alkali treatment

Abstract: In this article, three bio-composites, i.e. flax, linen and bamboo fabric reinforced epoxy resin, were manufactured using a vacuum bagging technique. The influence of alkali treatment (with 5 wt% NaOH solution for 30 min) on tensile properties of flax, linen and bamboo single-strand yarns, surface morphology and mechanical properties (with respect to tensile and flexural properties) of the composites were investigated. It was found that the failure mechanism of single-strand fibres under tension consists of fibre breakage and slippage simultaneously. The alkali treatment had a negative effect on the tensile strength and modulus of the flax, linen and bamboo single-strand yarns. However, after the treatment, the tensile and flexural properties of all the composites increased, e.g. the tensile and flexural strength of the treated flax/epoxy composite increased 21.9% and 16.1%, compared to the untreated one. After the treatment in all the composites, the tensile fractured surfaces exhibited an improvement of...

Recent Progress in Fabrication, Structure, and Properties of Carbon Fibers

Abstract: This paper reviews recent developments in carbon fibers. Intensive studies focus on relationships among processing conditions, chemical/physical structures and tensile properties of polyacrylonitrile and meso-phase pitch based carbon fibers. Carbon fibers with specific geometry, such as hollow, porous, and patterned, have been fabricated for specific applications. Additionally, carbon nanotubes (CNTs), which have excellent mechanical properties, have been processed into macroscopic continuous fibers. Incorporating CNTs in precursor fiber also improves tensile strength and modulus of the resultant carbon fiber. Although extensive studies have been conducted for improving carbon fiber tensile strength and modulus as well as for reducing their production cost, these issues remain amongst the main challenges for broadening their applications.

Ultra-high performance concrete and fiber reinforced concrete: achieving strength and ductility without heat curing

Abstract: Ultra-high performance concrete (UHPC) and ultra-high performance fiber reinforced concrete (UHP-FRC) were introduced in the mid 1990s Special treatment, such as heat curing, pressure and/or extensive vibration, is often required in order to achieve compressive strengths in excess of 150 MPa (22 ksi) This study focuses on the development of UHP-FRCs without any special treatment and utilizing materials that are commercially available on the US market Enhanced performance was accomplished by optimizing the packing density of the cementitious matrix, using very high strength steel fibers, tailoring the geometry of the fibers and optimizing the matrix-fiber interface properties It is shown that addition of 15% deformed fibers by volume results in a direct tensile strength of 13 MPa, which is 60% higher than comparable UHP-FRC with smooth steel fibers, and a tensile strain at peak stress of 06%, which is about three times that for UHP-FRC with smooth fibers Compressive strength up to 292 MPa (42 ksi), tensile strength up to 37 MPa (54 ksi) and strain at peak stress up to 11% were also attained 28 days after casting by using up to 8% volume fraction of high strength steel fibers and infiltrating them with the UHPC matrix

Effect of fiber surface treatments on mechanical and abrasive wear performance of polylactide/jute composites

Abstract: The main focus of this work is to improve the adhesion of jute fiber with polylactide (PLA). For this purpose, surface of the jute fiber was modified by alkali, permanganate, peroxide and silane treatments. The surface modified fibers were characterized by FTIR spectroscopy. Unidirectional composites were prepared with treated jute fibers and PLA matrix by hot pressing of solvent impregnated prepregs. Surface treatments resulted in enhancement of tensile and flexural properties and reduction in Izod impact strength. Dynamic mechanical analysis (DMA) results showed that, treated composites have higher storage modulus and lower tangent delta with respect to untreated composite. The degree of interfacial adhesion between the jute fiber and PLA was estimated using adhesion parameter obtained through DMA data. The results of thermogravimetric analysis (TGA) showed a higher thermal stability for silane treated composites. Experimental results on abrasive wear tests revealed that the wear resistance of composite is sensitive to fiber/matrix adhesion.

Tensile properties of an AlCrCuNiFeCo high-entropy alloy in as-cast and wrought conditions

Abstract: Extensive multistep forging at 950 °C was applied to the cast AlCuCrFeNiCo high-entropy alloy to transform the cast coarse dendritic structure into a fine equiaxed duplex structure consisting of the mixture of BCC and FCC phases, with the average grain/particle size of ∼1.5 ± 0.9 μm. Tensile properties of the alloy in the as-cast and forged conditions were determined in the temperature range of 20–1000 °C. The hot forged alloy was stronger and more ductile during testing at room temperature, than the as-cast alloy. The yield stress (YS), ultimate tensile strength (UTS), and tensile ductility ( δ ) of the forged condition were 1040 MPa, 1170 MPa, and 1%, respectively, against 790 MPa, 790 MPa and 0.2% for the as-cast condition. In both conditions, the alloy showed brittle to ductile transition (BDT), with a noticeable increase in the tensile ductility within a narrow temperature range. In the as-cast condition, this transition occurred between 700 and 800 °C, while in the forged condition, it was observed between 600 and 700 °C. With an increase in the testing temperature above the BDT, a continuous decrease in tensile flow stress and an increase in tensile ductility were observed. In the temperature range of 800–1000 °C, the forged alloy showed superplastic behavior. The tensile elongation was above 400% and reached 860% at 1000 °C.

Prediction of tensile properties of hybrid-natural fiber composites

Abstract: The tensile strength and modulus of short, randomly oriented hybrid-natural fiber composite was found out experimentally and also predicted using Rule of Hybrid Mixture (RoHM). Hybrid composites were prepared using banana/sisal fibers of 40:0, 30:10, 20:20, 10:30, and 0:40 ratios, while overall fiber volume fraction was fixed as 0.4 V f . The comparison between experimental and RoHM showed that they are in good agreement.

Size effects on elasticity, yielding, and fracture of silver nanowires: In situ experiments

Abstract: This paper reports the quantitative measurement of a full spectrum of mechanical properties of fivefold twinned silver (Ag) nanowires (NWs), including Young's modulus, yield strength, and ultimate tensile strength. In-situ tensile testing of Ag NWs with diameters between 34 and 130 nm was carried out inside a scanning electron microscope (SEM). Young's modulus, yield strength, and ultimate tensile strength all increased as the NW diameter decreased. The maximum yield strength in our tests was found to be 2.64 GPa, which is about 50 times the bulk value and close to the theoretical value of Ag in the $\ensuremath{\langle}110\ensuremath{\rangle}$ orientation. The size effect in the yield strength is mainly due to the stiffening size effect in the Young's modulus. Yield strain scales reasonably well with the NW surface area, which reveals that yielding of Ag NWs is due to dislocation nucleation from surface sources. Pronounced strain hardening was observed for most NWs in our study. The strain hardening, which has not previously been reported for NWs, is mainly attributed to the presence of internal twin boundaries.

Cassava starch biodegradable films: Influence of glycerol and clay nanoparticles content on tensile and barrier properties and glass transition temperature

Abstract: In this study, glycerol content and its incorporation method on tensile and barrier properties of biodegradable films (BF) based on cassava starch were analyzed. ANOVA showed that the glycerol incorporation method did not influence the results (P > 0.05), however the glycerol content influenced significantly the tensile and barrier properties of the films (P 0.05).

The effects of alkali-silane treatment on the tensile and flexural properties of short fibre non-woven kenaf reinforced polypropylene composites.

Abstract: Kenaf fibre reinforced polypropylene composites were manufactured by compression moulding. The kenaf fibre was considered in three forms; untreated, treated with sodium hydroxide solution and treated with sodium hydroxide solution followed by three-aminopropyltriethoxysilane. The effects of these chemical treatments on the tensile and flexural properties of the composites were investigated. Mechanical test results show that alkali treatment followed by three-aminopropyltriethoxysilane treatment (alkali–silane treatment) significantly improves the tensile and flexural properties of short fibre non-woven kenaf polypropylene composites. In particular, the specific tensile and flexural strengths of alkali–silane treated kenaf composites with 30% fibre mass fraction are, respectively, only 4% and 11% lower than those of composites made using glass fibre. Scanning electron microscopy examination shows that the improvements in the tensile and flexural properties resulting from alkali–silane treatment can be attributed to better bonding between the fibres and matrix.

Welding of polymers using a 2 μm thulium fiber laser

Abstract: Absorber-free transmission and butt-welding of different polymers were performed using thulium fiber laser radiation at the wavelength 2 μm. The relations between the laser process conditions and the dimensions and quality of the seam were investigated by means of optical and phase-contrast microscopy. Mechanical properties of the weld joints were studied in tensile strength tests. Laser-welded polyethylene samples revealed a tensile strength of greater than 80% of the bulk material strength. Transmission welding of different polymer combinations featured the formation of different joint classes depending on the spectral properties. The experiments demonstrate new application areas of mid-IR fiber laser sources for materials processing.