Uniaxial Tension (uniaxial + tension)

Distribution by Scientific Domains
Distribution within Polymers and Materials Science

Selected Abstracts

Localization Events and Microstructural Evolution in Ultra-Fine Grained NiTi Shape Memory Alloys during Thermo-Mechanical Loading,

Andreas Schaefer
Subjecting a thin NiTi specimen to uniaxial tension often leads to a localized martensitic transformation: macroscopic transformation bands form and propagate through the specimen, separating it into regions of fully transformed martensite and original austenite. In the present study, the alternating current potential drop (ACPD) technique is used to analyze the change in electrical resistance of ultra-fine grained NiTi wires subjected to a broad range of thermo-mechanical load cases: (i) uniaxial tensile straining at constant temperatures (pseudoelastic deformation); (ii) cooling and heating through the transformation range at constant load (actuator load case); (iii) a combination of mechanical and thermal loading. We monitor the ACPD signals in several zones along the gauge length of specimens, and we demonstrate that a localized type of transformation is a generic feature of pseudoelastic as well as of shape memory deformation. Moreover, the ACPD signals allow to differentiate between temperature-induced martensite (formed during cooling at no or relatively small loads), stress-induced martensite, and reoriented martensite (formed under load at low temperatures). [source]

Mechanical Properties and Corrosion Resistance of a Novel Ni-Cr-Mo Alloy,

P. Huang
A new Ni-23Cr-18Mo (wt.%) alloy, designated as Nistelle Super C, was developed recently at Deloro Stellite Inc. for high corrosion resistance applications. Microstructure and phase transformation behaviour of the alloy were studied using SEM and DSC techniques, respectively. Mechanical properties such as stress - strain relation of the alloy and load , depth relation of individual phases of the alloy were determined under uniaxial tension and under nano indentation, respectively. Corrosion resistance of the alloy in oxidizing and reducing acids was evaluated in accordance with ASTM standard test designation G31-72. [source]

Description of fatigue damage in carbon black filled natural rubber

ABSTRACT The present paper describes macroscopic fatigue damage in carbon black-filled natural rubber (CB-NR) under uniaxial loading conditions. Uniaxial tension-compression, fully relaxing uniaxial tension and non-relaxing uniaxial tension loading conditions were applied until sample failure. Results, summarized in a Haigh-like diagram, show that only one type of fatigue damage is observed for uniaxial tension-compression and fully relaxing uniaxial tension loading conditions, and that several different types of fatigue damage take place in non-relaxing uniaxial tension loading conditions. The different damage types observed under non-relaxing uniaxial tension, loading conditions are closely related to the improvement of rubber fatigue life. Therefore, as fatigue life improvement is classically supposed to be due to strain-induced crystallization (SIC), a similar conclusion can be drawn for the occurrence of different types of fatigue damage. [source]

A meso-level approach to the 3D numerical analysis of cracking and fracture of concrete materials

ABSTRACT A meso-mechanical model for the numerical analysis of concrete specimens in 3D has been recently proposed. In this approach, concrete is represented as a composite material with the larger aggregates embedded in a mortar-plus-aggregates matrix. Both continuum-type components are considered linear elastic, while the possibilities of failure are provided with the systematic use of zero-thickness interface elements equipped with a cohesive fracture constitutive law. These elements are inserted along all potential crack planes in the mesh a priori of the analysis. In this paper, the basic features of the model are summarized, and then results of calculations are presented, which include uniaxial tension and compression loading of 14-aggregate cubical specimen along X, Y and Z axes. The results confirm the consistency of the approach with physical phenomena and well-known features of concrete behaviour, and show low scatter when different loading directions are considered. Those cases can also be considered as different specimens subjected to the same type of loading. [source]

Cover Picture: Structural Modifications to Polystyrene via Self-Assembling Molecules (Adv. Funct.

Abstract The cover shows tensile failure of a sample of pure polystyrene (left), and a polystyrene sample with greater impact strength containing 1% by weight of dispersed nanoribbons (right), as reported in work by Stupp and co-workers on p.,487. The nanoribbons are formed by self-assembly of molecules known as dendron rodcoils (DRCs) in styrene monomer, resulting in the formation of a gel. This gel can then be polymerized thermally. We have previously reported that small quantities of self-assembling molecules known as dendron rodcoils (DRCs) can be used as supramolecular additives to modify the properties of polystyrene (PS). These molecules spontaneously assemble into supramolecular nanoribbons that can be incorporated into bulk PS in such a way that the orientation of the polymer is significantly enhanced when mechanically drawn above the glass-transition temperature. In the current study, we more closely evaluate the structural role of the DRC nanoribbons in PS by investigating the mechanical properties and deformation microstructures of polymers modified by self-assembly. In comparision to PS homopolymer, PS containing small amounts (,,1.0,wt.-%) of self-assembling DRC molecules exhibit greater Charpy impact strengths in double-notch four-point bending and significantly greater elongations to failure in uniaxial tension at 250,% prestrain. Although the DRC-modified polymer shows significantly smaller elongations to failure at 1000,% prestrain, both low- and high-prestrain specimens maintain tensile strengths that are comparable to those of the homopolymer. The improved toughness and ductility of DRC-modified PS appears to be related to the increased stress whitening and craze density that was observed near fracture surfaces. However, the mechanism by which the self-assembling DRC molecules toughen PS is different from that of conventional additives. These molecules assemble into supramolecular nanoribbons that enhance polymer orientation, which in turn modifies crazing patterns and improves impact strength and ductility. [source]

Localized failure of fibre-reinforced elastic,plastic materials subjected to plane strain loading

Dunja Peri
Abstract We consider discontinuous bifurcations as the indicator of a localized failure for a class of composites that are characterized by elastic fibres reinforcing an elastic,plastic matrix. A macroscopic tangent stiffness tensor for the fibre-reinforced composite is developed by consistently homogenizing the contribution of fibres in a spherical representative volume element. Analytical solutions are derived for the critical hardening modulus and corresponding bifurcation directions for the case of plane strain loading. Properties of the solutions are further illustrated on the example of the non-associated Drucker,Prager model at onset of yielding. Results show that presence of fibres decreases the critical hardening modulus, thus inhibiting the onset of strain localization. The rate of decrease in the critical hardening modulus is the highest for pure shear, followed by uniaxial tension, uniaxial compression, biaxial tension and biaxial compression. The main fibre parameters that control the onset of strain localization are their volumetric content and their stiffness modulus whereby very stiff fibres can produce the most significant decrease in the critical hardening modulus, especially for the state of biaxial tension. The critical hardening modulus for the non-associated Drucker,Prager model exhibits a full range of localization modes including compaction bands, dilation bands, and transition in the form of shear bands regardless of the presence of fibres. Presence of fibres affects bifurcation directions, except in the case when Poisson's ratio of the matrix is equal to 0.25. The results demonstrate stabilizing effects of fibres by which they provide the control against the onset of strain localization. Copyright © 2006 John Wiley & Sons, Ltd. [source]

Strain rate mediated microstructure evolution for extruded poly(vinylidene fluoride) polymer films under uniaxial tension

F. Fang
Abstract The deformation and fracture mechanism during uniaxial tension under controlled strain rates are investigated for extruded poly(vinylidene fluoride) (PVDF) polymer films at room temperature. It was found that both the longitudinal and transversal film-samples exhibited pronounced strain rate effect, that is, the yield stress increases while the fracture strain decreases with the increasing of strain rates. For the longitudinal film samples, phase transformation from the nonpolar ,-phase to the polar ,-phase occurs during the uniaxial tension, and the extent of the phase transformation enhances when the strain rate decreases. For the transversal film samples, no phase transformation was detected in all tested strain rates. By combining the stress,strain behavior and the X-ray results, it can be inferred that the conformational change from , to , phase during uniaxial tension contributes to the higher fracture strain of the longitudinal films than that of the transversal films. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 103: 1786,1790, 2007 [source]

Use of a bioscaffold to improve healing of a patellar tendon defect after graft harvest for ACL reconstruction: A study in rabbits

Sinan Karaoglu
Abstract Following harvest of a bone-patellar tendon-bone (BPTB) autograft, the central third of the patellar tendon (PT) does not heal well. The healing tissues also form adhesions to the fat pad and can cause abnormal patellofemoral joint motion. The hypotheses were that a bioscaffold could enhance patellar tendon healing through contact guidance and chemotaxis, and the scaffold could serve as a barrier to decrease adhesion formation between the neo-PT and infrapatellar fat pad. In 20 New Zealand White rabbits, a central-third PT defect was created. One strip of porcine small intestinal submucosa (SIS) was attached to both the anterior and posterior sides of the PT defect of the SIS-treated group (n,=,10). For comparison, a central defect was left nontreated (n,=,10). At 12 weeks, histomorphology was examined using Masson's trichrome staining. The cross-sectional area (CSA) was determined with a laser micrometer, and the central BPTB complexes were tested in uniaxial tension. SIS-treated samples showed a greater amount of healing tissue with denser and well-oriented collagen fibers and more spindle-shaped cells. There was no noticeable adhesion formation in the SIS-treated group. For the nontreated group, there were significantly more and diffuse adhesive formations. The SIS-treated group also had a 68% increase in neo-PT CSA, 98% higher stiffness, and 113% higher ultimate load than that in the nontreated group. SIS treatment increased the quantity of healing tissue, improved the histological appearance and biomechanical properties of the neo-PT, and prevented adhesion formation between the PT and fat pad. © 2007 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res 26:255,263, 2008 [source]

Long-term effects of porcine small intestine submucosa on the healing of medial collateral ligament: A functional tissue engineering study

Rui Liang
Abstract Porcine small intestinal submucosa (SIS) was previously shown to enhance the mechanical properties of healing medial collateral ligaments (MCL), and the histomorphological appearance and collagen type V/I ratio were found to be close to those of normal MCL. We hypothesized that at a longer term, 26 weeks, SIS could guide a better organized neo-ligament formation, increasing mechanical properties and increasing collagen fibril diameters mediated by a reduction in collagen type V. A 6 mm gap injury in the right MCL was surgically created in 38 rabbits, while the contralateral intact MCL served as a sham-operated control. In half the animals, a strip of SIS was sutured onto the severed ends. In the other half, no SIS was applied. The cross-sectional area (CSA) was determined with a laser micrometer system. The femur,MCL,tibia complex was mechanically tested in uniaxial tension. Histomorphology was determined through H&E and immunofluorescent staining and transmission electron microscopy (TEM). Sodium-dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) was used to determine collagen type V/I ratio. SIS-treated MCLs displayed a 28% reduction in CSA, a 33% increase in tangent modulus, and a 50% increase in tensile strength compared with the nontreated group (p,<,0.05). TEM showed groups of collagen fibrils with larger diameters in the SIS-treated ligaments in comparison with uniformly small fibrils for the nontreated group. H&E staining showed more densely stained collagen fibers in the SIS-treated group aligned along the longitudinal axis with more interspersed spindle-shaped cells. Immunofluorescent staining showed less collagen type V signals, confirmed by a 5% lower ratio of collagen type V/I compared with the nontreated controls (p,<,0.05). The findings extend the shorter term 12-week results, and support the potential of porcine SIS as a bioscaffold to enhance ligament healing. © 2006 Orthopaedic Research Society. Published by Wiley Periodicals, Inc. J Orthop Res [source]

Distribution Function and Thermodynamic Potentials of a Self-Avoiding Chain

Aleksey D. Drozdov
Abstract Summary: An explicit expression is derived for the distribution function of end-to-end vectors for a flexible self-avoiding chain. Based on this relation, analytical formulas are developed for the free and internal energies of a chain with excluded-volume interactions. Force,stretch relations are obtained at uniaxial tension and compression. The effects of strength of segment interactions on the shapes of the distribution function and the force-displacement diagram, as well as on the mean-square end-to-end distance and stiffness of a chain are studied numerically. The dimensionless distribution function P versus the dimensionless end-to-end vector Q* for self-repellent chains with ,,=,0.0, 0.4, 0.8, 1.2, and 1.6, from top to bottom, respectively. [source]

Lateral compaction effects in braided structures

Robert A. Dasilva
This paper addresses the phenomenology of strand interaction in biaxial non-embedded braided textile structures under uniaxial tension. The specific interest in the development of new braided textile structures is a result of the shortcomings of current rope, belt, and cable performance under large strain controlled conditions. However, this work also holds particular significance in the area of textile composite preforms. In composites forming, the lateral strand compaction mechanism, which drives braid behavior under tension, may be applied to woven fabrics for predicting wrinkling during forming processes. Additionally, manufacturing models produced in this study may be used to predict shape and size limitations of braided composite preforms. In this paper, a generalized model is developed for these structures with the intent of characterizing and predicting mechanical behavior. The methodology consists of a modular framework, which includes the prediction of manufacturing parameters. Lateral strand compaction tests were performed to generate constitutive material curves for use in analytical geometric models. Model predictions correlate well with data generated from braid uniaxial tension tests. Results suggest that lateral strand strain drives braid tensile behavior. [source]

Mechanical properties of Al2O3/polymethylmethacrylate nanocomposites

Benjamin J. Ash
Alumina/polymethylmethacrylate (PMMA) nanocomposites were produced by incorporating alumina nanoparticles, synthesized using the forced gas condensation method, into methylmethacrylate. The particles were dispersed using sonication and the composites were polymerized using free radical polymerization. At an optimum weight percent, the resulting nanocomposites showed, on average, a 600% increase in the strain-to-failure and the appearance of a well-defined yield point when tested in uniaxial tension. Concurrently, the glass transition temperature (Tg) of the nanocomposites dropped by as much as 25°C, while the ultimate strength and the Young's modulus decreased by 20% and 15%, respectively. For comparison, composites containing micron size alumina particles were synthesized and displayed neither phenomenon. Solid-state deuterium NMR results showed enhanced chain mobility at room temperature in the nanocomposites and corroborate the observed Tg depression indicating considerable main chain motion at temperatures well below those observed in the neat polymer. A hypothesis is presented to relate the thermal and mechanical behavior observed in the composites to the higher chain mobility and Tg depression seen in recent ultrathin polymer film research. [source]

Mechanical properties and volume dilatation of HDPE/CaCO3 blends with and without impact modifier

Yu-Lin Yang
Different blends of high-density polyethylene (HDPE) with calcium carbonate (CaCO3) were mechanically tested under uniaxial tension with or without poly(ethylene- co -octene) elastomer grafted with maleic anhydride (POEg), as an impact modifier. In some materials, the surface of the CaCO3 was treated with an amino acid and in others the mineral particles were left untreated. The stress,strain behavior were determined at constant true strain rate by using the VidéoTraction© system. Also, the volume changes upon stretching was assessed by means of the video extensometer and correlated with X-ray densitometry measurements. The dependence of modulus, yield stress, and cavitation is shown to depend on the relative percentage of the three constituents. In particular, the cavitation rate increases markedly with the CaCO3 content and decreases with the POEg content. By contrast, the surface pretreatment of the CaCO3 particles appear to be of much lesser importance. POLYM. ENG. SCI., 46:1512,1522, 2006. © 2006 Society of Plastics Engineers [source]

Melt processed microporous films from compatibilized immiscible blends with potential as membranes

M. Xanthos
Microporous flat films with potential as membranes were produced via melt processing and post-extrusion drawing from immiscible polypropylene/polystyrene blends containing a compatibilizing copolymer. The blends were first compounded in a co-rotating twin-screw extruder and subsequently extruded through a sheet die to obtain the precursor films. These were uniaxially drawn (100%,500%) with respect to the original dimensions to induce porosity and then post-treated at elevated temperatures to stabilize the resultant structure, which consisted of uniform microcracks in the order of a few nanometers in width. The effects of blend composition and extrusion process parameters on surface and cross-sectional porosity and solvent permeability of the prepared films are presented and related to specific microstructural features of the films before and after drawing. Finite element modeling of the stretching operation in the solid state yielded a successful interpretation of the blend response to uniaxial tension that resulted in microcrack formation. Comparison of some of the novel microporous structures of this work with commercial membranes prepared by solvent-based phase inversion processes suggests comparable pore size and porosity ranges, with narrower pore size distribution. [source]