Standard Tensile Tests Research Articles

Inverse identification of the post-necking work hardening behaviour of thick HSS through full-field strain measurements during diffuse necking

A procedure is presented to identify the post-necking work hardening behaviour of thick HSS steels using a standard uniaxial tensile machine. The pre-necking strain hardening behaviour is available from standard quasi-static tensile tests in the rolling direction. The method is extended beyond necking by performing an inverse identification using the Finite Element Model Update technique and the heterogeneously. A synchronized Digital Image Correlation setup is employed to acquire experimental full-field strain fields at the surface of the diffuse neck and inversely identify the strain hardening behaviour beyond the point of maximum uniform strain. Double notched tensile specimens are used to inversely identify the 3D plastic anisotropy. Subsequently, the effect of plastic anisotropy on the identified post-necking work hardening behaviour is scrutinized. Finally, the robustness of the proposed procedure to identify post-necking strain hardening behaviour is experimentally assessed.

Analysis and Numerical Simulation of the Structural Performance of Fused Deposition Modeling Samples With Variable Infill Values

The prediction of the structural performance of additive manufacturing (AM) parts has become one of the main challenges to boost the use of AM in industry. The structural properties of AM are very important in order to design and fabricate parts not only of any geometrical shape but also with variable or customized mechanical properties. While AM experimental studies are common in the literature, a limited number of investigations have focused on the analysis and prediction of the mechanical properties of AM parts using theoretical and numerical approaches, such as the finite element method (FEM); however, their results have been not accurate yet. Thus, more research work is needed in order to develop reliable prediction models able to estimate the mechanical performance of AM parts before fabrication. In this paper, the analysis and numerical simulation of the structural performance of fused deposition modeling (FDM) samples with variable infill values is presented. The aim is to predict the mechanical performance of FDM components using numerical models. Thus, several standard tensile test specimens were fabricated in an FDM system using different infill values, a constant layer thickness, one shell perimeter, and polylactic acid (PLA) material. These samples were measured and modeled in a computer-aided design (CAD) system before performing the experimental tensile tests. Numerical models and simulations based on the FEM method were then developed and carried out in order to predict the structural performance of the specimens. Finally, the experimental and numerical results were compared and conclusions drawn.

Finite Element Modelling and Validation of Thermomechanical Behaviour for Layered Aluminium Parts Made by Composite Metal Foil Manufacturing

The paper presents finite element modelling and thermomechanical analysis on the tensile properties of layered aluminium 1050 metal foil parts made by composite metal foil manufacturing. In this paper, a three-dimensional finite element model was developed and validated through experiments to analyse thermal effects on the tensile properties of 200-μm-thick aluminium 1050 metal foils. The effects of thermal stress and strain were studied by carrying out transient thermal analysis on the heated plates used to join the 200-μm-thick metal foils together using a special brazing paste. A standard tensile test at ambient temperature was carried out on the resulting layered dog bone specimens to analyse the thermal effects on the individual layers of metal. The investigations were precisely designed to assess the effect of heat provided amid the brazing operation to join the metal thwarts together as a layered structure and whether it assumed a part in affecting the tensile properties of the final products when contrasted to a solid aluminium 1050 dog bone specimen of the same dimensions. Corrosion testing was also carried out on dog bone specimens made from varying thickness foils (50 μm, 100 μm, and 200 μm) of aluminium 1050 to assess the effect of corrosion on the tensile strength and elongation. The results showed that the specimens did not face the problem of galvanic corrosion of the foil–bond interface. Microstructural analysis was also carried out to analyse the fracture modes of the tested specimens after corrosion testing.

Direct usage of the wire drawing process for large strain parameter identification

Large strain hardening is the main material description ingredient for cold bulk forming process simulations. Hardening identification of large strains is a trade-off between cost, standardization and the ability to represent the experiment, but there are no standard procedures to date. In this proposed approach, large strains (larger than 1) are reached using an industrial wire drawing process, and measured data for identification are obtained from standard tensile tests. Fast semi-analytical post-processing was possible despite the significant process-inherited strain heterogeneity. The parameters of state-of-the-art hardening models were identified, and the robustness was demonstrated to reach far beyond the strain level attained in the experiments. As a consequence, accurate and robust large strain hardening modelling was achieved from standard (tensile test) acquisition by using industrial wire drawing pre-strains.

The Effect of Varying Almond Shell Flour (ASF) Loading in Composites with Poly(Butylene Succinate (PBS) Matrix Compatibilized with Maleinized Linseed Oil (MLO).

In this work poly(butylene succinate) (PBS) composites with varying loads of almond shell flour (ASF) in the 10–50 wt % were manufactured by extrusion and subsequent injection molding thus showing the feasibility of these combined manufacturing processes for composites up to 50 wt % ASF. A vegetable oil-derived compatibilizer, maleinized linseed oil (MLO), was used in PBS/ASF composites with a constant ASF to MLO (wt/wt) ratio of 10.0:1.5. Mechanical properties of PBS/ASF/MLO composites were obtained by standard tensile, hardness, and impact tests. The morphology of these composites was studied by field emission scanning electron microscopy—FESEM) and the main thermal properties were obtained by differential scanning calorimetry (DSC), dynamical mechanical-thermal analysis (DMTA), thermomechanical analysis (TMA), and thermogravimetry (TGA). As the ASF loading increased, a decrease in maximum tensile strength could be detected due to the presence of ASF filler and a plasticization effect provided by MLO which also provided a compatibilization effect due to the interaction of succinic anhydride polar groups contained in MLO with hydroxyl groups in both PBS (hydroxyl terminal groups) and ASF (hydroxyl groups in cellulose). FESEM study reveals a positive contribution of MLO to embed ASF particles into the PBS matrix, thus leading to balanced mechanical properties. Varying ASF loading on PBS composites represents an environmentally-friendly solution to broaden PBS uses at the industrial level while the use of MLO contributes to overcome or minimize the lack of interaction between the hydrophobic PBS matrix and the highly hydrophilic ASF filler.

A comparison process between hand lay-up, vacuum infusion and vacuum bagging method toward e-glass EW 185/lycal composites

This study about reinforced e glass fibers with processed of lycal composites resin by using hand lay-up, vacuum infusion, and vacuum bagging method. Plain-weave type woven glass fabric, commercial code: EW185 cloth, has been used as the GFRP. Experiments carried out include tensile testing to obtain tensile stress, tensile strain, and elastic modulus performed using UTM (Universal Testing Machine) tools. In addition, density, composite thickness, mass fraction and fraction of composite material volume and SEM (Scanning Electron Microscope) photographs can be determined to see the bond density between fibers and resins. Specimen preparation refers to ASTM D3039 which is the standard tensile test for composites with a polymeric matrix. Compared with hand lay-up, vacuum infusion, and vacuum bagging method, Vacuum infusion has the best ultimate tensile strength that is 346.15 MPa and average modulus elasticity is 10673.4 MPa. Failure Mode is also DAT.

Study on physico-mechanical and gamma-ray shielding characteristics of new ternary nanocomposites

In this study, a series of “Epoxy-Clay-PbO” nanocomposites under the name of ECPNCs were prepared by the molding method, and their physico-mechanical properties were investigated by different techniques. Focus of the work, was on the shielding ability of the ECPNCs for the gamma rays, emitted from Ir-192, Cs-137 and Co-60 with a wide range of energy. Scanning electron microscopy, and X-ray diffractometry demonstrated that clay platelets were fully exfoliated, and the PbO particles were homogenously distributed in the polymeric matrix. Thermo-gravimetric analysis and standard tensile tests revealed that PbO content has an “increasing/decreasing” effect on “thermal stability/mechanical strength” of the nanocomposites. Gamma shielding experiments showed that efficacy of ECPNCs containing 30 wt% PbO was 47% better than that of concrete. Experimental attenuation data were confirmed by theoretical calculations, so that the maximum difference between them was 14.1%. Furthermore, a correlation was developed between PbO content of the ECPNCs and their mass attenuation coefficient for all gamma sources.

Construction of whole stress-strain curve by small punch test and inverse finite element

Abstract Small punch test is applied to estimate mechanical properties and damage evolution by a miniature specimen. Combining small punch test and inverse finite element, the elastoplastic parameters in Hollomon model and damage parameters in Gurson-Tvergaard-Needleman (GTN) model were identified by the undamaged and damaged stages of the load-displacement curve. Then, the whole stress-strain curve of 316L austenitic stainless steel was constructed based on finite element simulation of a tensile specimen considering the constructed Hollomon model and GTN model. To validate the constructed whole stress-strain curve, standard tensile test was performed as a control group. The result demonstrates that the constructed stress-strain curve is in agreement with the experimental data obtained by standard tensile test. Finally, the plastic damage distribution and fracture mechanism of the miniature specimen were analyzed to understand the damage evolution of small punch test.

Mechanical and flow properties of blends of polypropylene and powder coating recyclates with and without addition of maleic anhydride

AbstractIn this research, from 10% to 40% by weight of hydrolyzed powder coating recyclates were used as filler in polypropylene (PP). Firstly, PP and filler were dry‐mixed and then, in order to get a homogeneous mixture, were extruded at 180°C. The resulting compounds were cooled and granulated, and by use of an injection molding machine at 180–200°C, standard tensile test bars were produced. Tensile stress, three‐point bending strength, and izod impact strength of these specimens containing different types of filler and different filler concentrations were tested. The results are presented, and the effects of type and content of hydrolyzed powder coating waste on the mechanical properties of polypropylene are discussed. Also, the change in melt flow index of polypropylene as a function of filler content is analyzed. Furthermore, the bonding mechanism of filler and matrix material was examined by electron microscopy.

Acoustic emission of material damages in glass fibre-reinforced plastics

The aim of this study is to compare two different standardized testing procedures, tensile testing and Mode-I double cantilever beam (DCB) testing, to evaluate a possible correlation between the dominant failure in glass fibre-reinforced plastics and their according acoustic emissions (AE). AE is processed by using a burst collection of all recorded transient signals and is further analysed with the k-means clustering algorithm. To generate damage related AE, a series of experiments for tensile testing and Mode-I DCB testing is performed on 16-layer glass fibre/epoxy specimens with a cross-ply lay-up for tensile and an unidirectional lay-up for Mode-I DCB testing. Three sensors at tensile testing and one sensor at Mode-I DCB testing gather AE data. The results of clustered burst signals show a good accordance between both testing procedures, with a similar weighted peak frequency (WPF) range in each classified cluster. In total, three different clusters are determined. An assignment of these three clusters to the three dominant damage mechanisms, visually observed by microscopy, is suggested.

Direct inscription and evaluation of fiber Bragg gratings in carbon-coated optical sensor glass fibers for harsh environment oil and gas applications.

In this research work, we show the successful inscription of fiber Bragg gratings into carbon-coated pure silica as well as germanium-doped glass fibers by applying the pulsed laser point-by-point manufacturing technique. First, the parameters used for the Ti:sapphire femtosecond laser process are demonstrated. Without removing the polymeric carbon coating, destruction-free formation of highly reflective Bragg gratings is performed with selected types of hermetically enclosed fibers. We demonstrate the advantage of the carbon coating by long-term exposure to a pure hydrogen atmosphere at an elevated temperature. Such harsh conditions exist in the oil and gas industry, which means there is high application potential for technologically advanced optical sensors. Compared to the also examined standard glass fibers with a distinct signal attenuation, carbon-coated fibers show no significant degradation. Finally, we analyze the mechanical stability of the processed fibers via standardized tensile tests. No substantial decrease in strength occurs among the sensor-integrated samples.

Trimming and sheared edge stretchability of automotive 6xxx aluminum alloys

Edge quality produced by shearing processes often leads to reduced material formability which was observed in multiple studies and summarized in the reference literature. The intention to make the sheared edge performance more predictable has motivated the development of several experimental techniques such as the hole expansion test and the tensile test with one side of the sample sheared in various cutting conditions. The paper presents a review of published results for both of these techniques and illustrates very limited research dedicated to sheared edge performance of aluminum alloys. The experimental study was performed on three broadly used in automotive industry 6xxx serious aluminum alloys which have similar mechanical properties and chemical composition with some variation in processing regimes and individual elements quantities. The effects of cutting clearance on longitudinal, transverse and diagonal orientations of the trim line relative to the rolling direction were discussed for all three alloys. The results of standard tensile test of all three materials were very similar with rather small difference in work hardening and almost no difference in total elongations measured by an extensometer. Measurements of elongations as a result of stretching of samples along orthogonally trimmed sheared surfaces indicated that the increase of the cutting clearance above 5% for Alloy 1 and above 15% for Alloy 2 usually leads to formation of burrs and reduced elongations of trimmed samples before fracture occurs. The effect of cutting clearance on sheared edge stretching performance for Alloy 3 is significantly less pronounced than for Alloys 1 and 2, which makes Alloy 3 very attractive for exterior panel automotive applications in which significant stretching of sheared edge can be anticipated. Detailed discussion of mechanism of blank separation during trimming process was based upon the results of 2D numerical simulation and interrupted trimming process with partially propagated cracks.

Mechanical behavior of high strength S690-QT steel welded sections with various heat input energy

Over the past two decades, there were a number of experimental investigations into mechanical properties as well as structural behaviour of high strength S690-QT steel welded sections. It is evident now that, similar to structural aluminium, these welded sections will suffer from a significant reduction in their mechanical properties, i.e. both yield and tensile strengths as well as ductility, due to change in microstructures if welding is not properly controlled. Owing to a lack of detailed understanding on effects of various welding procedures and parameters onto the mechanical properties of these steel welded sections, many design and construction engineers have serious concerns on adopting these S690-QT steel materials in buildings and bridges.This project aims to investigate and quantify effects of various line heat input energy onto the mechanical properties of the S690-QT steel welded sections through a series of carefully planned and executed standard tensile tests. A total of 12 standard tensile tests on cylindrical coupons of welded sections were conducted, and full range deformation characteristics of these coupons were obtained through use of strain gauges and measurements on high resolution digital images. Both welding methods, namely, GMAW and SAW, were employed to prepare full penetration butt-welded sections with various line heat input energy. It should be noted that GMAW was performed with a robotic welding system while SAW was performed with an automated welding machine to attain high quality welding consistently. Additional standard tensile tests on 3 reference coupons machined from the base plates, and another 3 reference coupons machined from the weld metal were also conducted to provide basic material properties for direct comparison.It was shown that in almost all coupons of the welded sections tested in the present study, fracture occurred within the heat affected zones of the welded sections without any failure in neither the weld metal nor the base plates. For welded sections prepared with a line heat input energy equal to 1.0 kJ/mm, there was almost no reduction in the mechanical properties of the welded sections. However, for those welded sections prepared with a line heat input energy equal to 5.0 kJ/mm, only 70% of the yield strength of the base plates was attained. Consequently, the effects of welding onto the mechanical properties of the S690-QT steel welded sections have been successfully quantified, and the information is readily adopted in assessing their mechanical behaviour according to various line heat input energy employed during welding.

Microstructures, Mechanical and Corrosion Properties of the Extruded AZ31-xCaO Alloys

The effects of the extrusion process and CaO addition amount on microstructure, mechanical, and corrosion properties of AZ31 alloys were investigated by means of optical microscopy (OM), scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), standard tensile testing, and so on. The grain size of AZ31 or AZ31-1%CaO alloy becomes larger with increasing extrusion temperature. The grain size of AZ31-1%CaO alloy is much smaller than that of AZ31 alloy at the same extrusion temperature. In addition, the formation of the Al2Ca phase caused by CaO addition refines the grain size, and the recrystallization of AZ31-1%CaO alloy is improved significantly. The recrystallization grains distribute more uniformly as the increase of extrusion ratio, and the completely recrystallized grains distribute uniformly in the form of equiaxed crystals with an extrusion ratio of 9. Tensile testing results show that extruded AZ31-1%CaO alloy at the extrusion temperature of 300 °C and an extrusion ratio of 9 exhibits the best mechanical properties. While corrosion properties of AZ31 alloys decreases due to the addition of CaO.

The Effect of Nano-Fillers on the In-Plane and Interlaminar Shear Properties of Carbon Fiber Reinforced Composite

In this study, the interlaminar region of a carbon fiber composites was reinforced with silica nano-particles, and its effect on the in-plane mechanical response was investigated. Also, the effect of particles on the dynamic interlaminar shear strength of composites was studied. Two batches of composite specimens, one batch made of only fiber and matrix and the other with nano-silica added as a third phase, were fabricated. The composite specimens were prepared through a high-temperature molding process, where the nanoparticles were dispersed on the surface of the prepreg layers before stacking. For in-plane properties, standard tensile test coupons were made with fibers oriented at a different angle relative to the loading direction. For interlaminar shear properties, a V-notch bending and three-point bending specimens were prepared. It was found that the nanoparticles have a sound influence on the in-plane mechanical response mainly on the in-plane shear property of the composite. On the other hand, the nano-filler has shown a significant effect on the dynamic interlaminar shear strength of the laminate.

Effects of heat accumulation on microstructure and mechanical properties of Ti6Al4V alloy deposited by wire arc additive manufacturing

Complex thermal behaviour during fabrication plays an import role in the geometrical formation and mechanical properties of Ti6Al4V components manufactured using Wire Arc Additive Manufacturing (WAAM) technology. In this study, through in-situ temperature measurement, the heat accumulation and thermal behaviour during the gas tungsten wire arc additive manufacturing (GT-WAAM) process are presented. The effects of heat accumulation on microstructure and mechanical properties of additively manufactured Ti6Al4V parts were studied by means of optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS) and standard tensile tests, aiming to explore the feasibility of fabricating Ti6Al4V parts by GT-WAAM using localized gas shielding. The results show that due to the influences of thermal accumulation, the layer’s surface oxidation, microstructural evolution, grain size, and crystalline phase vary along the building direction of the as-fabricated wall, which creates variations in mechanical properties and fracture features. It has also been found that it is necessary to maintain the process interpass temperature below 200 °C to ensure an acceptable quality of Ti6Al4V part fabricated using only localized gas shielding in an otherwise open atmosphere. This research provides a better understanding of the effects of heat accumulation on targeted deposition properties during the WAAM process, which will benefit future process control, improvement, and optimization.

On fabric materials response subjected to ballistic impact using meso-scale modeling. Numerical simulation and experimental validation

Present work investigates the dynamic response of dry fabric materials subjected to ballistic impact loading. The purpose of this research is to simulate the dynamic fabrics behavior accurately in order to capture the maximum fabric deformation, the ballistic limit and the absorbed energy in case of fabric perforation. In particular, a meso-scale modeling approach was employed to capture the behavior of para-aramid fabrics using LS-DYNA software. The quasi-static mechanical properties of fabric yarns were defined by standard tensile tests, whereas the Johnson-Cook strain rate rule was applied to approximate the strain rate dependence of yarn tensile strength. The numerical results were validated against impact experiments using air-gun apparatus.

A mechanical system for tensile testing of supported films at the nanoscale

Standard tensile tests of materials are usually performed on freestanding specimens. However, such requirement is difficult to implement when the materials of interest are of nanoscopic dimensions due to problems related to their handling and manipulation. In the present paper, a new device is presented for tensile testing of thin nanomaterials, which allows tests to be carried out on specimens initially deposited onto a macroscopic pre-notched substrate. On loading, however, no substrate effects are introduced, allowing the films to be freely stretched. The results obtained from a variety of thin metal or polymeric films are very promising for the further development of this technique as a standard method for nanomaterial mechanical testing.

Damage identification parameters of dual-phase 600–800 steels based on experimental void analysis and finite element simulations

In this work, the damage behavior of cold-rolled zinc-coated dual-phase steel sheets 600 and 800 grades was evaluated by means of standard uniaxial tensile testing, microstructural characterization and finite element modeling. The void formation in both steels was investigated as a function of the plastic strain level from digital image processing of scanning electron micrographs to quantify the average void size and to determine the corresponding measures of void density, void area fraction and void aspect ratio. Based on the void analysis and the experimental uniaxial tensile test data, a four-step procedure is proposed to identify the parameters of the Gurson–Tvergaard–Needleman (GTN) damage model. Bearing in mind the non-uniqueness of the GTN model parameters, 3D finite element simulations using a single element and an 1/8 symmetry uniaxial tensile specimen model were performed in a systematic manner to investigate the role of both nucleation and failure parameters on the uniaxial behavior. At low straining levels, most of the void initiated by debonding of globular aluminum-oxide inclusions identified by EDS in both dual-phase steels. At higher straining levels, the void density evolution is found to be more pronounced in DP600 steel owing to the faster void nucleation rate at the ferrite grain boundaries. A good agreement between predictions and experimental load-elongation is achieved allowing for the identification of the full set of GTN damage model parameters of both DP600 and DP800 steels. The proposed damage calibration of dual-phase steels can be very helpful in simulations of practical sheet metal forming processes.

Mechanical Performance of Resistance Spot Welded Steel Sheets

Mechanical performance of resistance spot welded steel sheets was evaluated under quasi-static and dynamic loading conditions. Numerical inverse calibration method was mainly utilized to characterize mechanical properties especially for flow curves and ductile fracture criteria of constituent zones of the welded joints. For the base sheets, standard tensile test and high-speed tensile test was conducted under quasi-static and dynamic loading conditions, respectively. Mechanical properties of the weld zones were characterized using the developed miniature tensile specimen. Implementing the mechanical properties and structure to the finite element model, finite element simulation was used to evaluate the mechanical performance of two distinct weld coupons.