Tensile Test Method Research Articles

Measurement of the Strength and Microstructural Characteristics of Epoxy Polymers Cured by Thermal and Microwave Methods

Epoxy polymer samples cured by thermal and microwave methods under different temperature-time conditions are studied. The physical and mechanical parameters of the epoxy polymer samples, as well as their microstructure and fractographic fracture patterns, are studied. A tensile test method is used is used to determine the dependence of their strength parameters on the curing regime. Optimal regimes are identified for both curing methods, which makes it possible to obtain samples with maximum strength. Electron microscopy is used for comparative fractographic analysis of the fracture surfaces of samples with similar strength characteristics with thermal and microwave curing. It is found that microwave curing yields an increased globule size and more nanopores, as well as more pronounced local plastic deformation during fracture, and a larger spread in the ratio of the propagation velocities of main and secondary cracks. The dependence of the optical density of the test samples on the thermal and microwave curing regimes is established for wavelengths of 360–2500 nm.

Effect of electrospinning parameters on the mechanical and morphological characteristics of small diameter PCL tissue engineered blood vessel scaffolds having distinct micro and nano fibre populations – A DOE approach

Electrospinning is a widely used technique in tissue engineered blood vessel (TEBV) scaffold research. Successful TEBV scaffolds must be produced in a way that balances tissue-like mechanical characteristics with morphologies that promote cellularity by supporting cell attachment whilst also permitting cell infiltration. Electrospun tubular poly (ε-caprolactone) (PCL) scaffolds combining interspersed nano and micro fibre morphologies have shown promise in this regard. A comprehensive design of experiments (DOE) approach examines the effect of production parameters on the mechanical and morphological properties of small diameter PCL vascular scaffolds created using a single-step electrospinning process and comprised of multi-modal fibre populations. Mechanical properties of the vessels are assessed using a modified uniaxial ringlet tensile test method while morphological properties, including mean fibre diameter, degree of fibre alignment and porosity, are also captured.Regression analysis showed that a diverse range of mechanical properties could be achieved through the careful adjustment of processing conditions. Constructs with a broad range of ultimate tensile strengths (~4–10 MPa) and Young's moduli (~1.5–3 MPa) were prepared. The speed of the rotating collector system was found to be a dominant factor influencing both the mechanical and morphological attributes of the fabricated scaffolds. Several other main effects and interactions terms were found to influence the scaffold attributes, including degree of fibre orientation and mean fibre diameter.The potential applicability of particular tubular scaffolds for vascular applications were then evaluated by comparison with literature obtained mechanical property values for human coronary arteries and the great saphenous vein. This study demonstrates an important step towards a readily available and tailorable set of multi-modal PCL scaffold designs for further biological and clinical investigation.

Mechanical spectroscopy of metal/polymer composite membranes for hydrogen separation

In the present work, mechanical properties of metal-polymer composite membranes for hydrogen separation have been investigated by tensile test and mechanical spectroscopy methods. The membranes were prepared by high-energy ball milling and subsequent thermal pressing of a powder mixture of polyethylene with 10 wt% hydride-forming intermetallic compound LaNi2.5Co2.4Mn0.1. The membranes were then subjected to activation by long exposure in a hydrogen atmosphere. The static tensile test showed a slight decrease in membrane tensile strength after hydrogen activation that may be explained by intermetallic particle embrittlement. Mechanical spectroscopy study reveals a shift of the internal friction peak of the activated membrane by 22 K towards lower temperatures and a small decrease of the activation energy of polyethylene viscoelastic transformation from 144 kJ/mol to 138 kJ/mol.

A harmless thin film elastic modulus measurement method through bending the nonlinear sliding cantilever beam

This paper presents the design of a novel elastic modulus measurement method through bending the specimen to estimate the elastic modulus of a small irregular thin-film specimen without causing damage. First of all, based on nonlinear Euler-Bernoulli beam theory, A measurement system is constructed with a laser displacement sensor and a dynamometer to obtain a relationship between deflection and force. The elastic modulus is estimated by the strain energy and the work of a constant force. Secondly, uniaxial tensile tests of specimens are conducted to evaluate the accuracy of the proposed method. The experimental results show good agreement between the elastic modulus obtained using the proposed method and the elastic module obtained through tensile test method. The relative error between them is less than 2.0%, which validates the proposed method’s performance on accuracy. To sum up, the proposed test method is a supplement to the harmless elastic modulus measurement method.

Investigating an Inverse Finite Element Approach for Characterising Soft Materials

ABSTRACT Soft materials, such as soft biological tissue and soft silicone rubber, are non-linear materials which require the classical uniaxial and biaxial tensile testing methods for characterisation. Unfortunately, in special cases, such as for soft biological tissue, the samples are smaller than 10 mm χ 10 mm in size and these classical tensile testing methods produce unwanted stress and strain gradients due to the fastening techniques associated with these methods. Micro-indentation is proposed as an alternative method for characterising soft materials. Using inverse Finite Element (FE) analysis and a known Mooney-Rivlin three parameter material model, six different micro-indentation tests were proposed. A theoretical approach was used to determine which indentation test best characterised a silicone sample, by using two FE models. The results showed that microindentation is capable of characterising a soft material in ideal conditions with a cylindrical indenter applied in a diagonal orientation over the sample, as the best indentation method. Finally, it was observed that the material model can either match the displacements with the smallest objective function or the stress vs. stretch curve can be matched to 99 % over the whole stretch range but not both simultaneously. Additional keywords: Inverse Finite Elements analysis, Micro-indentation, Gradient optimisation, Mooney-Rivlin hyper-elastic material model.

Failure Analysis of the Strain Clamp Steel Anchor Corrosion of a 500 kV Transmission Line

By macroscopic observation, composition analysis, mechanical properties test, SEM, energy spectrum, overall grip tensile test and finite element mechanics calculation method, the strain clamp steel anchor corrosion failure of a 500 kV transmission line is analysed. The results show that the corrosion of steel anchor for 31 years are the result of the natural corrosion, steel anchor corrosion rate is accelerated due to the galvanic corrosion, crevice corrosion, stress and damaged surface of the galvanized layer, and achieve C4 environment (zinc 2.1–4.2 um per year, carbon steel 50–80 um per year). The hardware are qualified. It is suggested to replace the steel anchor with yellow rust on the surface after 5 years, and to reevaluate the next maintenance cycle of the gold fittings without yellow rust on the surface at present, and replace it when the corrosion depth reaches 10%. Before replacement, all fittings should be monitored, especially steel anchor.

An effective method for determining necking and fracture strains of sheet metals

Biaxial tensile testing methods using cruciform specimens have been developed in the last few decades for the determination of forming limit diagrams (FLDs) and fracture forming limit diagrams (FFLDs) for sheet metals. One of the difficulties associated with this test geometry is the lack of a widely accepted method to determine the necking and fracture strains which are necessary to construct these diagrams. In this study, a novel spatio-temporal method has been proposed for the determination of necking and fracture strains. In the method, two rectangular zones: the base zone (BZ) and the reference zone (RZ) are selected at the location where fracture initiates. The zone RZ includes the zone BZ and both zones have the same side length in the direction parallel to the necking band but different side length in the perpendicular direction. By plotting the thickness reduction within RZ against that in BZ, the onset of localised necking can be determined by finding the intersection of the two straight lines fitted separately using the data in the initial and final stages of deformation. The corresponding limit strains are then determined using the strains within the zone BZ. The method has been successfully applied to uniaxial tensile tests on AA6082 and boron steel dog-bone specimens, and to equi-biaxial tensile tests on AA5754 cruciform specimens.• Compared to widely used existing methods, the novel spatio-temporal method has greater simplicity, stability and accuracy with regard to the determination of localised necking strains.• The spatio-temporal method has good potential to become a standard method for the determination of limit strains for sheet metals.

Measurement of True Stress-True Strain Curve up to Large Strain Extent at Elevated Temperature in Ti-6Al-4V Alloy with Image Analysis Tensile Test Method

The image analysis tensile test method was applied to obtain true stress-true strain curves at elevated temperature in Ti-6Al-4V alloy. A CCD camera successfully captured the profile change of a specimen during the tensile test. Minimum radius and neck curvature can be calculated from the profile, then used to determine true strain and true stress after necking using Bridgman’s equation. True stress-true strain curves up to a strain of 0.8 were obtained in the high temperature tensile test at 850 ℃. The true stress-true strain curves show work hardening at a strain rate of 0.2 s-1 and dynamic restoration at a strain rate of 0.01 s-1 in the tensile test at 850 ℃. On the other hand, in compression tests, the true stress-true strain curves show steep decrease in true stress after yielding. This might be due to the effect of barreling of the specimen, rather than any metallurgical structural change. The image analysis tensile test method is applicable to obtain accurate high-temperature true stress-true strain curves at elevated temperature up to large strain extent.

Giant hardening response in AlMgZn(Cu) alloys

This study presents a thermomechanical processing concept which is capable of exploiting the full industrial application potential of recently introduced AlMgZn(Cu) alloys. The beneficial linkage of alloy design and processing allows not only to satisfy the long-standing trade-off between high mechanical strength in use and good formability during processing but also addresses the need for economically feasible processing times. After an only 3-hour short pre-aging treatment at 100°C, the two investigated alloys, based on commercial EN AW-5182 and modified with additions of Zn and Zn+Cu respectively, show high formability due to increased work-hardening. Then, these alloys exhibit a giant hardening response of up to 184 MPa to reach a yield strength of 410 MPa after a 20-minute short final heat treatment at 185°C, i.e. paint-baking. This rapid hardening response strongly depends on the number density, size distribution and constitution of precursors acting as preferential nucleation sites for T-phase precursor precipitation during the final high-temperature aging treatment and is significantly increased by the addition of Cu. Minor deformation (2%) after pre-aging and before final heat treatment further enhances the development of hardening precipitates additionally by activating dislocation-supported nucleation and growth. Tensile testing, quantitative and analytical electron-microscopy methods, atom probe analysis and DFT calculations were used to characterize the alloys investigated in this work over the thermomechanical processing route. The influence of pre-strain on the hardening response and the role of Cu additions in early-stage cluster nucleation are discussed in detail and supported by in-situ STEM experiments and first-principles calculations.

A novel method for testing the fatigue performance of cement stabilized base field coring samples

Cement stabilized macadam (CSM) being widely used material in pavement base and subbase layers, its service performance and fatigue life need to be evaluated accurately. While laboratory testing using field coring samples seems to be a direct approach, there is no testing standard for CSM field coring or fatigue test over its service life yet. This paper proposes a novel testing method for field coring and laboratory testing for the fatigue life of CSM, which can be further used to estimate the residual life of the CSM base and subbase courses. The method makes use of the differential traffic loading in the transverse direction of a pavement section to build-up control groups. To reduce the errors caused by the variability in tensile strength between the specimens in one group, a Twin-Specimens Method is proposed, by which one specimen is tested for the tensile strength while the other one of the twin for the fatigue life. To further reduce the variability, the semi-circular bending (SCB) test was recommended becaues of its least variation of testing results among three competing tensile strength testing methods. Based on a comprehensive fatigue life experimental study based on 116 coring samples drilled from a 10-year-old freeway in central China, the SCB strength was found to be about 3 times of the indirect tensile (IDT) testing strength, and the four-point bending (4 PB) testing strength was about 1.15 times of the IDT strength. In conclusion, the optimal method for testing the fatigue resistance of CSM using field coring samples is recommended, which can also be further used to evaluate the existing performance CSM course.

A small specimen testing method to determine tensile properties of metallic materials

Abstract A stable uniaxial tensile testing method has been proposed for small specimens that can obtain stress-strain relations and strength of metallic materials. Based on energy equivalent assumptions, a semi-analytical model with five parameters has been put forward. Those parameters can be determined by a small amount of finite element analysis (FEA), and more extensive numerical validation is carried out on the model. By designing a simple installation fixture for the small specimens of which the parallel section is 1.2 mm in width and 5 mm in length, a series of uniaxial tensile tests have been performed with small specimens. It shows that the stress-strain relations and strength obtained by the small specimen testing method are consistent with those from standard round bar specimens. The small specimen test method will help to obtain the mechanical properties of materials in nuclear industry and other fields.

Study on Mesoscopic Mechanics of Recycled Asphalt Mixture in the Indirect Tensile Test

Reclaimed asphalt pavement (RAP) mainly contains asphalt binder and aggregates, and the RAP materials used in paving roads could save virgin materials. This paper studied the following: asphalt mixture with different RAP material contents was prepared; then the indirect tensile test was carried out, and the mesoscopic model of the recycled asphalt mixture was reconstructed digitally. Discrete element method (DEM) of indirect tensile test was carried out to analyze the mechanical properties of recycled asphalt mixture in mesoscopic perspective. The results showed that there were some gaps between the simulation result of the digital specimen model and the test value of the recycled asphalt mixture, but the velocity vector and the law of force chain development of the recycled asphalt mixture could be explained in mesoscopic perspective. It proved that the virtual simulation test of the mechanical test was effective. The damage process of recycled asphalt mixture was analyzed in mesoscopic perspective, and the unification of mechanical response and macroscopic appearance was completed. Meanwhile, the simulation method of mesoscopic mechanics was an effective supplement to traditional tests, and guided tests method theoretically.

Influence of rolling modes and the level of accumulated deformation on the mechanical and plastic properties of stainless austenitic steel AISI 304L

The paper presents the results of studies of rolling modes (direct, reverse, cross ones) at 500°C for samples of stainless steel AISI 304L and their influence on mechanical and plastic properties of the material. The stress-strain state was investigated using a numerical simulation program and the deformation parameters of processing were established. The mechanical properties were studied by microhardness measuring and tensile testing methods. The results of the experiment were analyzed and discussed, and conclusions were drawn. The regularities of the effect of strength parameters depending on the modes of processing and accumulated deformation during rolling have been established.

Investigation and optimization of Superplastic forming parameter in Aluminium alloy

Super plasticity is the capability of materials to parade very high tensile elongation which can be more than 2500%, appearing in eminent temperature under low stress dependent on strain rate. In this paper intentions to optimize superplastic parameters such as yield stress, ultimate stress, temperature, strain rate and strain rate sensitivity index by using hot tensile test method in AA 7075 alloy in experimental and numerical simulation method. In experimental method, the cross head velocity concept has been adopted to attain the permeability by achieving the material properties with the functions’ of temperatures conditions. Finite element method using ABAQUS software was modeled to compare the experimental results.

ОБОСНОВАНИЕ КОРРЕКТИРУЮЩИХ ВОЗДЕЙСТВИЙ, КОМПЕНСИРУЮЩИХ ПОНИЖЕННОЕ СОДЕРЖАНИЕ УГЛЕРОДА В СТАЛИ ПРИ ПРОИЗВОДСТВЕ ХОЛОДНОКАТАНОГО ЛИСТОВОГО ПРОКАТА ДЛЯ ШТАМПОВКИ

The relevance of the work. There are situations in the practice of metallurgical production when steel melting with a chemical composition intended to complete the determined order is reassigned to the production of rolled metal from another steel grade. With the formal accordance of chemical composition of melted steel to the requirements for a different steel grade, crucial control parameters of process that are traditionally used for a new grade of steel, may turn out to be inappropriate for structural and phase transformations in steel with real chemical composition. To prevent the re-lease of non-conforming products is necessary to develop and apply operational corrective actions. The purpose of the work is selection and rationale of operational corrective actions in the production of cold rolled sheet products of quality classes CQ, DQ and DDQ of mild quality steel to compensate for the reduced carbon content in meltings assigned to complete the respective orders. Microscopy methods were used to study the structure and phase composition of steel with a carbon content of 0,008 – 0,04 % in hot-rolled and cold-rolled states. Data on the mechanical properties of hot-rolled and cold-rolled steel were obtained by standardized tensile test methods. Based on the test results, re-liable multiple approximations of influence of control characteristics of the technology on properties of cold-rolled steel were constructed, which were subsequently used in optimization of thickness of semi finished rolled product for cold rolling as a compensating effect at the fluctuations of carbon content within the above limits. The novelty of the work lies in the identification and rationale of corrective actions for a technological system in which cold rolling is carried out on a continuous four-stand mill with roll feed. The results of the work consist in determining the temperature of the end of rolling and the increment of the thickness of the semi finished rolled product as operation-al compensating effects at assigning steel meltings with a low carbon content for rolling into a tech-nological system with a continuous four-stand mill with roll feed. The practical significance of the work is to prevent the yield of non-conforming products at using the proposed solution in the pro-duction of cold-rolled steel of quality classes CQ, DQ and DDQ 0,6–2,0 mm thick.

Experimental Investigation and Constitutive Modeling of the Uncured Rubber Compound Based on the DMA Strain Scanning Method.

Existing research tends to focus on the performance of cured rubber. This is due to a lack of suitable testing methods for the mechanical properties of uncured rubber, in particular, tensile properties. Without crosslinking by sulfur, the tensile strength of uncured rubber compounds is too low to be accurately tested by general tensile testing machines. Firstly, a new tensile stress testing method for uncured rubber was established by using dynamic thermomechanical analysis (DMA) tensile strain scanning. The strain amplitude was increased under a set frequency and constant temperature. The corresponding dynamic force needed to maintain the amplitude was then measured to obtain the dynamic force-amplitude curve observed at this temperature and frequency. Secondly, the Burgers model is usually difficult to calculate and analyze in differential form, so it was reduced to its arithmetic form under creep conditions and material relaxation. Tensile deformation at a constant strain rate was proposed, so the Burgers model could be modified to a more concise form without any strain terms, making mathematical processing and simulating much more convenient. Thirdly, the rate of the modified Burgers model under constant strain was in good agreement with the test data, demonstrating that the elastic stiffness was 1–2 orders of magnitude less than the tensile viscosity. In the end, it was concluded that large data dispersion caused by the universal tensile test can be overcome by choosing this model, and it may become an effective way to study the tensile modeling of uncured rubber compound.

A new technique for characterising mechanical properties of materials under hot stamping conditions

In order to characterise mechanical properties of materials (e.g. formability) under hot stamping conditions, significant efforts have been made to the development of the biaxial tensile testing method using cruciform specimens. However, no method for necking strain determination and no cruciform specimen design have been widely accepted. In this study, a new technique for characterising mechanical behaviour of materials under hot stamping conditions has been proposed. It includes two main parts: 1) a novel spatio-temporal method for determining necking and fracture strains, and 2) a cruciform specimen design for formability evaluation using biaxial testing method. In the first part, the theoretical base of the novel spatio-temporal method has been discussed, and the method has been validated by applying to uniaxial tensile tests on AA6082 specimens. The method has also been compared with several existing popular methods, in the determination of limit strain at onset of localised necking. It is found that the novel method has greater simplicity, stability and accuracy for the determination of localised necking strain. In the second part, a proposed cruciform specimen of AA5754 has been tested under the equi-biaxial tension, and both the necking initiation location and the strain path at the location where necking initiates, have been analysed. Furthermore, the novel spatio-temporal method has been applied to the biaxial tensile test for the determination of necking and fracture strains. The results show that the designed cruciform specimen enables to initiate fracture at the centre of the specimen and realisation of linear strain path under equi-biaxial tension.

Rifampin-Releasing Triple-Layer Cross-Linked Fresh Water Fish Collagen Sponges as Wound Dressings.

Objectives Surgical wounds resulting from biofilm-producing microorganisms represent a major healthcare problem that requires new and innovative treatment methods. Rifampin is one of a small number of antibiotics that is able to penetrate such biofilms, and its local administration has the potential to serve as an ideal surgical site infection protection and/or treatment agent. This paper presents two types (homogeneous and sandwich structured) of rifampin-releasing carbodiimide-cross-linked fresh water fish collagen wound dressings. Methods The dressings were prepared by means of the double-lyophilization method and sterilized via gamma irradiation so as to allow for testing in a form that is able to serve for direct clinical use. The mechanical properties were studied via the uniaxial tensile testing method. The in vivo rifampin-release properties were tested by means of a series of incubations in phosphate-buffered saline. The microbiological activity was tested against methicillin-resistant staphylococcus aureus (MRSA) employing disc diffusion tests, and the in vivo pharmacokinetics was tested using a rat model. A histological examination was conducted for the study of the biocompatibility of the dressings. Results The sandwich-structured dressing demonstrated better mechanical properties due to its exhibiting ability to bear a higher load than the homogeneous sponges, a property that was further improved via the addition of rifampin. The sponges retarded the release of rifampin in vitro, which translated into at least 22 hours of rifampin release in the rat model. This was significantly longer than was achieved via the administration of a subcutaneous rifampin solution. Microbiological activity was proven by the results of the disc diffusion tests. Both sponges exhibited excellent biocompatibility as the cells penetrated into the scaffold, and virtually no signs of local irritation were observed. Conclusions We present a novel rifampin-releasing sandwich-structured fresh water fish collagen wound dressing that has the potential to serve as an ideal surgical site infection protection and/or treatment agent.

Effect of cruciform specimen design on strain paths and fracture location in equi-biaxial tension

Abstract Hot stamping technologies require new methods for evaluating formability of sheet metal under various forming conditions. Biaxial tensile testing method using a cruciform specimen has been used for the applications, but a suitable cruciform specimen design has not yet been accepted. One of the challenges in designing a specimen for formability tests is to ensure proportional equi-biaxial strain paths arise at the location of fracture initiation. In this study, after reviewing existing cruciform specimen designs, three different geometries of cruciform specimen, named Type I, Type II and Type III, were proposed. Using numerical analysis and practical experiments, fracture initiation locations and corresponding strain paths in the specimens were investigated under equi-biaxial tension. Numerical simulations were performed to optimise the dimensions of Type I specimen to achieve a relatively high strain level near the centre point of the specimen. Based on the optimised dimensions, equi-biaxial tensile tests were carried out on cruciform specimens with different geometries, and strain paths at the fracture initiation locations were compared and analysed. It was found that in all cruciform specimens, equi-biaxial strain state appears only near the centre point. In the Type I and Type II specimens, fracture never initiates near the centre point, but at a location in the fillet transition zone where major strain is higher than that at the centre point. The Type III specimens have the ability to initiate fracture near the centre point, and to produce proportional strain paths with strain ratio β close to 1 in equi-biaxial tension, 0 in plane-strain tension, and -0.5 in uniaxial tension at the locations of fracture initiation. The research provides a cruciform specimen design, Type III, which has high potential to be used for evaluating formability for sheet metal.

Adhesive Characteristic and Mechanism of Ballastless Track Sealant in Hydrolysis Condition

The current evaluation method cannot predict accurately the hydrolysis resistance of sealants applied in ballastless slab track. And the degradation mechanism of sealant in hydrolysis condition has not been researched systemically. In this paper, the hydrolysis resistance of different sealants was researched with the aid of the self-developed direct tensile test method. The Atomic Force Microscope (AFM) was employed to analyze the micro-adhesion force on the surface of sealants, and thereby the correlation between macro-behavior and the micro-mechanism of sealants during hydrolysis was established. Results showed that the characteristics of the interface between sealants and substrates are reduced after hydrolysis, and that sealants with higher soft-segment content have good resistance to hydrolysis. Reduction of the bonding area after hydrolysis is also an important factor in the reduction of the characteristics of the adhesive interface. The micro-adhesion force of soft segments shows a fluctuating reduction tendency, and that of hard segments reduces more significantly during hydrolysis. The micro-adhesion force has good correlation with the maximum tensile force, but a poor correlation with failure displacement. The maximum tensile force is proved to be an optimal evaluation index in determining the hydrolysis resistance of sealants.