Tensile Test Method Research Articles

Reliable in-plane shear modulus for pultruded-fibre-reinforced polymer sections

A simple test method to determine the in-plane shear properties of pultruded materials, where the mat reinforcement is of randomly oriented continuous fibres, is presented. Existing standard test methods have a number of weaknesses, but a number of them can be overcome by using the 10° off-axis tensile test method proposed by Chamis and Sinclair in 1976. Straight-sided specimens have unidirectional fibre reinforcement oriented at 10° to the direction of tensile load. Tension generates a biaxial in-plane stress state that, by employing stress and strain transformations, enables the shear modulus to be determined. The mean shear moduli of web material in four shapes, from 20 coupon tests in batches of five, were found to be consistent at 4·2–4·8 GPa. Given that 10° off-axis coupons are easy to prepare, with no technical difficulties, this non-standard method is recommended to characterise the in-plane shearing of pultruded materials having continuous-filament (or strand) mat reinforcement.

A Tensile Strength Apparatus with the Facility to Monitor Negative Pore-Water Pressure

Abstract This article presents a new testing method for investigating the behavior of clayey geomaterials subjected to a tensile (negative) total stress. The method includes the use of high-capacity tensiometers to measure the pore–water pressure of the test specimen, an aspect which has not been demonstrated in any other direct tensile testing method. This addition allows interpretation of failure data in terms of effective stress rather than total stress, which is the approach that should be pursued in the saturated range. The test specimen shape and loading method have been modified from those commonly seen in existing literature to ensure that the direction of the major principal stress in the failure zone coincides with the direction of the externally applied tensile force, allowing for a more accurate analysis of tensile failure. Results are shown for saturated specimens and compared to results obtained for the same soil in uniaxial compression, using a modified version of the presented uniaxial tensile method, and a triaxial compression test. It is demonstrated that crack initiation occurs by shear failure if the data are interpreted in terms of effective stress rather than total stress and that the failure mechanisms under tension do not differ from compression.

Specimen size effects on fracture behaviour of SiC/SiC tubes during circumferential tensile test

SiC fiber-reinforced SiC matrix (SiC/SiC) composites are expected as a high-temperature structural material for the application of aerospace and nuclear energy system due to their high-temperature stability, reduced-activation property, and excellent irradiation resistance. It was investigated the size effects of test specimen on the fracture behaviour and apparent strength of SiC/SiC tubes in order to minimize the size of test specimen, as well as to develop circumferential tensile test method for SiC/SiC fuel cladding of nuclear reactor. The tube specimens with a narrow width (less than 5 mm) represented the stable value of apparent strength. In case of wide width (>5 mm), the apparent strength of test specimen decreased with the increase in specimen width. It was observed that the fracture of the test specimen with wide width was initiated from the sides of test specimen due to the local contact between loading pin and the test specimen. It is required to use the material with high modulus as a loading pin material in order to avoid the stress concentration caused by local contact.

Melamine-based poly(azomethine) hydrogels: Mechanical, biodegradability, drug loading and antibacterial properties

In the present paper, a new series of biodegradable poly(azomethine) gels were prepared to investigate the usability as biomaterials. The structures of the hydrogels were characterized by using FT-IR and SEM analyses. Contact angle measurements were also performed to investigate hydrophobicity of the hydrogels. Thermal behavior of melamine-based poly(azomethine)s and hydrogels was performed using TG-DTA and DSC techniques. Mechanical properties of poly(azomethine) hydrogels were investigated using a tensile testing method. Biodegradability, drug loading or release performance, protein absorption, water uptake and antibacterial properties were also studied due to investigate usability of melamine-based hydrogels as biomaterials.

Substructure Development and Deformation Twinning Stimulation through Regulating the Processing Path during Multi‐Axial Forging of Twinning Induced Plasticity Steel

Multi‐axial forging (MAF) at room temperature is employed to investigate the effects of deformation processing path and the amount of imposed strain on the deformation mechanisms of a twinning‐induced plasticity (TWIP) steel. The results indicate that the twin frequency is decreased by applying the 2nd compression (∑ɛ = 0.8), however, an unexpected increase is realized at the end of first MAF pass (∑ɛ = 1.2). This is attributed to the change in strain path and orientation dependence of deformation twinning. The latter is phenomenal considering the previous researches reporting the suppression of twinning at the early stage of deformation (ɛ < 0.4). The same sequence is followed during the second pass of MAF process. Interestingly, the progressive and continues substructure development along with dynamic Hall–Petch effect results from deformation twinning leads to an appreciable grain refinement. The latter is accompanied by the sharp drop of hardening rate in corresponding flow curves. The microtexture analysis indicates the strengthened texture of the 1 pass‐processed specimens which is weaken at the end of 2 pass due to the recrystallization and increasing the number of texture component. The current work also explores the room temperature mechanical properties of the multi axial forged workpiece through elaborating the miniaturized tensile testing method.

A new biaxial tensile shear test method to measure shear behaviour of coated fabrics for architectural use

Shear properties of coated fabrics is poorly understood and the effects of shear stiffness on the behaviour of tensile fabric structures are usually ignored in the current design practice. The paper presents a new test method for the investigation of architectural coated fabric shear properties. The method relies on the biaxial pretension of cruciform specimens, where warp and weft yarns are oriented 45° with respect to the loading directions. Loading protocol is used to generate consecutive shear stress wave with specific biaxial tensile stress aligned with the yarns. An advanced biaxial tensile test system has been developed to implement biaxial loading by either displacement or force control strategy. Biaxial tensile shear tests of PVDF-coated polyester materials have been carried out to validate the new method. The implications of shear deformation, and material’s viscosity and plasticity from the experimental results are addressed. The determination of shear stiffness is described and a comparison of results derived from different methods has been made. The advantages of the new biaxial tensile shear test method and some experimental findings are concluded.

Hoop tensile strength of tubular carbon fiber reinforced silicon carbide matrix composites

C/SiC (carbon fiber-reinforced silicon carbide) composites are widely used in the aerospace industry and for the fabrication of high-temperature parts owing to their excellent heat and chemical resistances. In this study, the tensile properties of C/SiC composite tubes manufactured by a filament winding method were examined via hoop tensile testing, and the optimal testing conditions were determined by comparing them with the properties of a composite plate specimen. It was found that during tensile testing, bending stress was generated and the strain inside and outside of the gauge section of the composite specimen is shown as tensile and compressive, respectively; as a result, premature damage occurred, which was not observed for the plate specimen. In order to minimize this effect, tensile testing was performed under the improved conditions, at which the side of fixture was close to the side of the test specimen, and the distance between the upper and lower fixtures was small. However, the relatively low strain to failure (which is a unique characteristic of C/SiC composites) suppressed the induction of both strain inside and outside the specimen in the tensile direction, which led to lower tensile strengths of the composite tubes as compared to that of the plate specimen. Because the tensile modulus calculated in this study is very close to that of the plate specimen, the hoop tensile testing method is suitable for determining the modulus values of C/SiC composites.

Strength characteristic and failure criterion of flexible multi-axial warp-knitted fabrics coated with polyurethane on single side

Coated fabrics are widely used in tension structures. In order to investigate the tensile behaviors of the coated fabrics, one group of specimens was cut out from multi-axial warp-knitted polyester fabrics coated with polyurethane on one side. These failure strengths of polyurethane-coated multi-axial warp-knitted fabrics were obtained by the method of uniaxial tensile test and a failure stress criterion is presented for the kind of materials. The results show that the coated fabric is anisotropic material, and the coating has great influence on the mechanical properties of the material. Furthermore, the failure stress criterion can be used for references in material design and application.

Hybrid Nanocomposite Films of Starch, Poly(vinyl alcohol) (PVA), Starch Nanocrystals (SNCs), and Montmorillonite (Na‐MMT): Structure–Properties Relationship

Starch, as a natural, renewable, and biodegradable polysaccharide, is widely used in the food and pharmaceutical industries. However, the extreme water‐sensitivity and poor tensile strength of starch materials have limited its practical application as an engineering material. Here, the authors blended starch with PVA to improve its film formability, and then, added Na‐MMT and SNCs to the blend in order to enhance the mechanical properties. Nanofillers are used in pure and hybrid form to study the synergistic effect of these two types of nanofillers. SNCs, obtained by acidic hydrolysis of potato starch granules, have a z‐average particle size of ≈230 nm and crystallinity of 57%. Nanocomposite films, prepared via the solution casting method, are characterized by X‐ray diffraction (XRD) and tensile testing methods. XRD patterns confirmed the exfoliation dispersion of Na‐MMT in the polymer blend matrix. Additionally, the results of the tensile tests and thermogravimetric analysis (TGA) indicated that the presence of nanofillers in separate and hybrid forms in the matrix led to the improvement of the mechanical and thermal properties of nanocomposites. Finally, the findings revealed the synergistic effect of nanofillers of SNCs and Na‐MMT for improving the mechanical and thermal properties of starch/PVA blend, particularly in 3 wt% of the total filler content in 50:50 (w/w).

Influence of heating on spectroscopic, mechanical, and thermal properties of reduced graphene oxide-poly(vinyl alcohol) composite films

The spectroscopic, uniaxial tensile, and thermal properties of reduced graphene oxide (rGO)-poly(vinyl) alcohol (PVA) composite films produced by using rGO synthesized using modified Hummer's method with varying weight ratio of rGO up to 10% were investigated by using an uniaxial tensile tester, Fourier Transform Infrared (Ft-IR)/Attenuated Total Reflectance (ATR) spectroscopy, and Differential Scanning Calorimeter (DSC) methods after heating process at different temperatures from room temperature to 200 °C. For unheated composite films, with increasing rGO weight ratio up to 10%, the Young's modulus of rGO-PVA films increased by approximately 2–3 times, conversely the strain at break values decreased greatly by about 40–50%. The heating process led to the significant improvement in the tensile strength and the Young's modulus, and great decrease in extensibility with respect to the unheated samples, e.g., the tensile strength and Young's modulus increased by 3–4 times and 8–10 times, respectively, for the heating temperatures up to 150 °C. With increasing heating temperature, the stress-strain curve of rGO-PVA composite films turned from that of ductile and amorphous polymer to that of more brittle and rigid polymers. With increasing rGO content, the glass transition, the crystallization, and the melting temperatures increased and heating process generally shifted these temperatures to higher values. The great contribution of rGO content and the heating to the improvement of especially mechanical properties of rGO-PVA composite films thanks to the strong intermolecular interactions of rGO nanosheets with the PVA matrix molecules through hydrogen bonding and to the changes in the crystallinity ratio of PVA was shown in detail in the analysis of the spectral results. The relationship between the changes in the mechanical, structural, and thermal properties of the studied composite films was determined by using tensile testing, Ft-IR/ATR, and DSC methods.

Experimental evaluation of nanoindentation as a technique for measuring the hardness and Young’s modulus of Zircaloy-2 sheet material

Experiments have been performed on a Zircaloy-2 sheet material to evaluate nanoindentation as a technique for measuring the Young’s modulus and hardness of the nuclear material. Room temperature transverse and longitudinal mechanical properties of an unirradiated Zircaloy-2 sheet material were measured with nanoindentation. The results were compared with those of tensile testing and Vickers microindentation obtained on the same material. Anisotropy evaluated with the conventional methods of microhardness measurement and tensile testing could be accurately confirmed by the nanoindentation measurement technique. The results show that the nanoindentation technique can be used to measure the Young’s modulus and hardness of small-volume samples of the material. The constraint factor, employed for converting hardness to yield strength, has also been determined and is reported for the material.

Determination of the local constitutive properties of the welded steel joints using digital image correlation method

The digital image correlation (DIC) method has become popular to characterize the local constitutive properties distribution especially for the welded joints. Although the evaluation of the local constitutive properties of a specimen is possible using DIC, few research has been reported to characterize these properties of the welded steel joints. This paper presented a method to evaluate the local constitutive properties of a welded steel joint through tensile testing and DIC method. Firstly, tensile tests of the welded steel joint were carried out and the stress-strain curves of different locations of the welded steel joint were obtained by the DIC method. Then these experimental stress-strain curves were fitted by an appropriate material model. Constitutive properties at these specific locations of the welded steel joint were then determined using this model based on test standards and the Considère criterion. The results showed that the Young’s modulus of different sub-regions of the welded steel joints were almost constant. The yield and tensile strength decreased from the weld metal (WM) to the heat affected zone (HAZ) and the base metal (BM). It was also found that the hardening properties of different sub-regions of the welded steel joint followed the sequence of BM > WM > HAZ. This paper contributed a simple method to characterize the local material properties of welded steel joint.

Improving fluid flow in geothermal reservoirs by thermal and mechanical stimulation: The case of Krafla volcano, Iceland

The magmatic-hydrothermal system at Krafla Volcano, North-East Iceland, is an important source of fluids exploited for geothermal energy. Here, we employ laboratory measurements to constrain the porosity and permeability of the main lithologies forming the reservoir, and investigate the impacts of different thermal and mechanical stimulation practices to improve fluid flow.Six main rock types were identified and sampled: three basalts (a dense and a porous lava, and a surficial dyke); a hyaloclastite; an obsidian; an ignimbrite; a felsite; and a gabbro. Permeability measurements were made in a hydrostatic cell using the steady-state flow method at a range of confining pressures (1–100 MPa). The measurements show that permeability generally increases with porosity, but that permeability may vary significantly for a given porosity, depending on the presence of pore connectivity and micro-fractures. We note that an increase in effective pressure results in a decrease in permeability due to closure of pre-existing cracks, abundant in some rocks. When unloading, samples fail to recover pre-loading permeability, as cracks do not necessarily entirely reopen. To further examine the hysteresis imposed by crack closure, we cyclically loaded/unloaded a felsite sample ten times by varying pore pressure which resulted in a further nonlinear decreases in permeability with each pressurisation cycle; thus an understanding of the pressurisation path may be a requirement to constrain fluid flow variations in geothermal systems.To test the effects of thermal stimulation on fluid flow, samples of dense basalt and felsite were thermally stressed by heating to 450 °C and cooling at different rates (in air, in water and at a controlled rate of <5 °C·min−1). The results show that the permeability of originally highly fractured rocks is not affected by thermal stressing, but originally unfractured rocks show a nonlinear increase in permeability with each thermal stressing cycle, especially with the largest thermal shock imposed by quenching in water; thus thermal stimulation may not be expected to result in a similar magnitude of permeability creation along the length of a borehole.Finally, following the permeability measurements on intact rocks, the Brazilian tensile testing method was employed to impart one and two (orthogonal) macro-fractures, and permeability was measured after each step. The creation of one macro-fracture strongly enhanced the permeability of the rock (especially dense rocks), resulting in a narrower range of permeability (as a function of porosity) for the fractured rocks. Imparting a second fracture had trivial additional impact on the permeability of the rock. Yet, the presence of fine fragments and possible minor offset of fracture interfaces was found to obstruct fracture closure, which resulted in higher permeability irrespective of effective pressure; thus hydraulic fracturing may locally increase fluid flow, especially when employing proppants to obstruct fracture closure and ensure a stable permeable network in a reservoir.We discuss the implications of the findings for a first order constraint on the permeability of the reservoir rock and the potential of thermal and mechanical stimulation methods on energy production in geothermal systems nested in active volcanic fields.

The sequential twinning-transformation induced plasticity effects in a thermomechanically processed high Mn austenitic steel

Different initial microstructures with various bimodal grain size distributions (BGSD) were produced in a high Mn austenitic steel through applying a predetermined set of thermomechanical processing cycles. The corresponding room temperature mechanical properties and the related strain hardening behaviors were assessed using tensile testing method. The results indicated that in the microstructure with high grain size bimodality, the length and amplitude of rapid hardening region was well higher than the others. This was attributed to its higher capability to α'-martensite formation. In addition, the threshold strain to initiate martensitic transformation was shifted to the lower one in the microstructure with higher bimodal grain size distribution. The latter was related to the lower arisen back stresses in the interior regions of the coarser grains. Furthermore, different transformation paths were identified as the BGSD changed. The austenite could directly transform to α'-martensite (γ→α') in the microstructure with lower BGSD; in this case the α'-martensite mainly appeared at the intersections of deformation twins. In contrast, in microstructures with higher BGSD, the nucleation occurred at the intersections of ε-martensite platelets. The co-existence of these transformation paths provided an extended transformation induced plasticity effect ending to a higher elongation to fracture in the course of deformation. In order to summarize the contribution of various strain hardening mechanisms, a deformation map was also constructed. Accordingly, the enhanced ductility/strength properties were attributed to the sequential operation of extended transformation induced plasticity and twinning induced plasticity effects.

Quality Evaluation Tests for Tensile Strength of Reactive Powder Concrete

AbstractThis study presents a comparison between different testing procedures to determine the tensile strength of reactive powder concrete (RPC). The tensile strength test methods include a direct...

Adsorptive removal kinetics of anionic dye onto chitosan films doped with graphene oxide: An in situ fluorescence monitoring

ABSTRACTThe aqueous adsorption of a fluorescent dye (pyranine) onto crosslinked chitosan-graphene oxide composite films was studied. In situ fluorescence monitoring technique is introduced as easy and fast experimental technique to select optimal adsorbent conditions. The effect of ionic crosslinker on adsorption was studied with sodium tripolyphosphate, trisodium citrate, and sodium sulfate, respectively. Among the crosslinkers, it was realized that sodium sulfate crosslinked films showed a greater adsorption rate for pyranine than the other two types of crosslinked films. Recently, graphene oxide is of interest as a filler compound for many biopolymer applications due to its favorable thermal, mechanical and surficial properties. In the present study, graphene oxide incorporation increased adsorption rate of the dye and the mechanical strength of ionically crosslinked chitosan films. The adsorption behavior of the adsorbent was explained by a kinetic model. Samples were characterized using scanning electron microscopy, thermogravimetric analysis, swelling experiments and tensile testing method.

Adhesive properties of laminated veneer lumber poles for use in temporary soil nailing: development and evaluation of a test method for curved structures in a high-alkaline environment

Innovative circular, hollow, laminated veneer lumber (LVL) beech sections for use as temporary geotechnical soil reinforcement members are currently being developed. Appropriate surface gluing quality between the veneers is fundamental to this subsoil application of the permanently cement-embedded, engineered timber product. The circular cross-section geometry and the permanently high-alkaline environment of the structural member is not covered by presently standardized testing and conditioning methods for examining LVL surface bond line quality. The sample conditioning and tensile shear test method compliant with EN 302-1 (Adhesives for load-bearing timber structures—test methods—part 1: determination of longitudinal tensile shear strength, European Committee for Standardization, Brussels, 2013) was modified to determine bonding parameters for circular, hollow LVL sections. Bond line curvature, groove cutting depth and sample geometry were found to greatly influence stress distribution, percentage of wood failure and tensile shear strength. Short-term alkaline treatment of test samples did not significantly influence the bonding performance, wood failure percentage, tensile shear strength and fracture patterns. To improve tensile shear strength, adhesives with different material rigidities were used and compared. An orthotropic, elastic numerical analysis revealed a greater influence of adherent elasticity than adhesive elasticity on the stress distribution within the bond line. With regard to determining the bond line integrity of curved veneer poles, a sample geometry compliant with EN 302-1 (2013) was developed and numerically evaluated.

Heat Treatment, Mechanical Properties and Microstructure of T-Joint Steel Arc Welded

Heat treatment of T-Joint’s steel arc welded are performed are investigated in this research. The heat treatment process that used were annealing and quenching. The microstructure was investigated by optical microscope. The mechanical behavior of the samples was investigated using universal tensile testing machine for tensile test and Microvickers hardness method for hardness testing. The microstructure of welding zone of welding metals with various heat treatments is grain boundary ferrite, Widmanstatten ferrite and acicular ferrite. The weld metal with quenching treatment has a highest tensile strength with tensile strength 197.97 Mpa. The quenching process increases the tensile strength by 49.58 %. The distortion value in weld metal without heat treatment, quenching and annealing is 0.11mm; 0.04 mm and 0.08 mm respectively. The hardness number of weld metals with quenching process have a highest number base metal, HAZ and weld metals. Results showed that the mechanical properties of T-joints steel arc welded can be improved by various heat treatments.

Optimum manufacturing parameters in selective laser sintering of PA12 with white cement additives

Selective laser sintering (SLS) is a modern rapid prototyping method with which 3D objects with complex geometries can be manufactured precisely through the sintering of powders’ thin layers using the laser power. The effective manufacturing parameters in SLS are laser power, scanning speed, scan-spacing, and the part-bed temperature. In this work, selective laser sintering (SLS) is used to manufacture a composite material from white cement additives and polyamide 12 (PA12) and then, the influence of energy density (controlled by laser power, scanning speed, and scan-spacing) on the dimensions, density, mechanical properties, and morphology of sintered specimens is investigated. The criteria for obtaining optimum manufacturing parameters are the part dimensional accuracy, maximum density, and maximum strength. Hence, the optimum energy density for producing parts with maximum density and enhanced strength has been determined experimentally. The tensile, compressive, and flexural testing methods are used to evaluate the effects of laser power on the fabricated parts. The results show that the optimum energy density of 0.051 J/mm2 could achieve the highest density of sintered parts without any degradation of binder material. Also, it is found that a combination of a 0.051-J/mm2 energy density and 10% weight fraction of white cement is sufficient enough to enforce significant improvements on the mechanical properties of PA12-sintered specimens.

Precipitation Stages and Reaction Kinetics of AlMgSi Alloys during the Artificial Aging Process Monitored by In-Situ Electrical Resistivity Measurement Method

The precipitation process and reaction kinetics during artificial aging, precipitate microstructure, and mechanical properties after aging of AlMgSi alloys were investigated employing in-situ electrical resistivity measurement, Transmission Electron Microscopy (TEM) observation, and tensile test methods. Three aging stages in sequence, namely formation of GP zones, transition from GP zones to β″ phase, transition from β″ to β′ phase, and coarsening of both phases, were clearly distinguished by the variation of the resistivity. It was discussed together with the mechanical properties and precipitate morphology evolution. Fast formation of GP zones and β″ phase leads to an obvious decrease of the resistivity and increase of the mechanical strength. The formation of β″ phase in the second stage, which contributes to the peak aging strength, has much higher reaction kinetics than reactions in the other two stages. All of these stages finished faster with higher reaction kinetics under higher temperatures, due to higher atom diffusion capacity. The results proved that the in-situ electrical resistivity method, as proposed in the current study, is a simple, effective, and convenient technique for real-time monitoring of the precipitation process of AlMgSi alloys. Its further application for industrial production and scientific research is also evaluated.