Standard Tensile Tests Research Articles

Elevated Temperature Effects on the Plastic Anisotropy of an Extruded Mg-4 Wt Pct Li Alloy: Experiments and Polycrystal Modeling

In this work, we study the deformation behavior of Mg-4 wt pct Li in uniaxial tension as a function of temperature and loading direction. Standard tensile tests were performed at temperatures in the range of 293 K (20 °C) ≤ T ≤ 473 K (200 °C) and in two in-plane directions: the extrusion and the transverse. We find that while the in-plane plastic anisotropy (PA) decreases with temperature, the anisotropy in failure strain and texture development increases. To uncover the temperature dependence in the critical stresses for slip and in the amounts of slip and twinning systems mediating deformation, we employ the elastic-plastic self-consistent polycrystal plasticity model with a thermally activated dislocation density based hardening law for activating slip with individual crystals. We demonstrate that the model, with a single set of intrinsic material parameters, achieves good agreement with the stress–strain curves, deformation textures, and intragranular misorientation axis analysis for all test directions and temperatures. With the model, we show that at all temperatures the in-plane tensile behavior is driven primarily by $$ \left\langle a \right\rangle $$ slip and both $$ \left\langle {c + a} \right\rangle $$ slip and twinning play a minor role. The analysis explains that the in-plane PA decreases and failure strains increase with temperature as a result of a significant reduction in the activation stress for pyramidal $$ \left\langle {c + a} \right\rangle $$ slip, which effectively promotes strain accommodation from multiple types of $$ \left\langle a \right\rangle $$ and $$ \left\langle {c + a} \right\rangle $$ slip. The results also show that because of the strong initial texture, in-plane texture development is anisotropic since prismatic slip dominates the deformation in one test, although it is not the easiest slip mode, and basal slip in the other. These findings reveal the relationship between the temperature-sensitive thresholds needed to activate crystallographic slip and the development of texture and macroscopic PA.

Practical failure analysis of resistance spot welded advanced high-strength steel sheets

In this study, a practical numerical procedure to analyze the failure behavior of resistance spot welded structures, especially for structures composed of advanced high-strength steels (AHSS) sheets, was developed for the first time. The root cause of the difference in failure modes between the welded structures of AHSS and conventional mild steel sheets was also elucidated. Given that the characterization of detailed mechanical properties of base sheets and weld nuggets is extremely complex, considerable effort was exerted to identify and properly simplify critical mechanical properties that are essential for failure analysis. This was achieved by developing a simple but effective experimental procedure to characterize the key properties by mainly utilizing standard and miniature-specimen tensile tests that are commonly available in any laboratory. In this study, two AHSS sheet grades, TRIP980 and DP980, as well as a conventional mild steel (GMW2) sheet grade were considered. The study involved the macroscopic characterization of mechanical properties including hardening behavior and fracture criterion. Furthermore, electron backscattered diffraction analysis of the base sheets and weld nuggets was also performed. The failure mode and strength of the lap-shear and U-shape tension tests were then analyzed for similar welded sheets under quasi-static loading conditions.

In situ nonlinear ultrasonic probing during plastic deformation

In is well known that nonlinear ultrasound is sensitive to micro-structural changes in materials. Here, we present recent results obtained during tensile tests of aluminum samples. Using continuous ultrasonic waves, we study the second harmonic generation and its relationship with dislocation proliferation during plastic deformation. The experimental setup is based on two transducers, an emitter and a receiver, both coupled face to face to a probe mounted on a standard tensile test machine. We measure both the first and second harmonic received amplitudes, Aω and A2ω respectively, for several amplitudes of the emitted signal. These are related by a nonlinear parameter β, through A2ω = βAω2. We observe that β is independent of the applied stress during the elastic regime, whereas it presents strong variations once plasticity occurs, presenting a pronounced maximum before fracture. This maximum can be considered as a signature, a warning, of a fracture that is soon to come.

Fatigue safety evaluation of newly developed contact wire for eco-friendly high speed electric railway system considering wear

Since carbon emission level of electric railway system is much lower than that of automotive transportation, electric railway system has been known as eco-friendly and low-carbon transportation. Recently, to expand the use of such railway system, there is global tendency of developing high speed railway system. In parts of high speed railway system, contact wire which supplies electricity to railway vehicles is exposed to continuous wear and bending fatigue through the contact with pantographs of running railway vehicles. In the past, only wear life of contact wire was considered since it is known that wear life is shorter than fatigue life. However, after the report of the fatigue failure on contact wire of Shinkansen in Japan, bending fatigue of contact wire has become a very important issue to be considered for the safety of contact wire. In this paper, based on the fatigue damage evaluation process that Yamashita et al. suggested for pure copper contact wire, cumulative fatigue damage on Cu-Mg contact wire which is newly developed for 400km/h-level railway system was calculated, and fatigue safety factor on Cu-Mg contact wire at allowable strain condition was investigated. In addition, to simplify such tests, a simpler method to obtain cumulative fatigue damage on contact wire from standard tensile test result is suggested.

Theoretical model for predicting uniaxial stress-strain relation by dual conical indentation based on equivalent energy principle

For conical indentation, the strain energy is a function of the semi-vertical cone angle, the indentation depth and the stress-strain relation. According to equivalent energy principle of representative volume elements (RVE) and the classical cavity assumption for material deformation region, the function with dual-parameters about volume and deformation is theoretically derived in the present study. This original equivalent-energy indentation model (EIM) is capable of forward-predicting load-depth relation and reverse-predicting uniaxial stress-strain relation for ductile materials only based on loading part of indentation. Further analyses show that the forward and reverse predicted results from EIM method are in excellent agreement with those by finite element analyses (FEA). Macro conical indentation experiments on five types of metals have been conducted using conventional indenters which are similar to Rockwell sclerometer. Consequently, the stress-strain relations predicted by EIM are quite close to those from standard tensile tests.

Small punch test methodologies for the analysis of the hydrogen embrittlement of structural steels

In the present study, a new small punch test (SPT) methodology has been used to analyse the effect of hydrogen embrittlement on the tensile properties of three different grades of CrMoV steel: the base metal (CrMoV-1), weld metal (CrMoV-2) and this same weld metal subjected to an intermediate heat treatment (CrMoV-3). SPT results were compared with those obtained in standard tensile tests carried out in a hydrogen environment. Moreover, a new SPT methodology was used to analyse the environmental effects on a CrNiMn steel under cathodic protection and cathodic charge.Results obtained shows the usefulness of the SPT to estimate the grade of deterioration induced by hydrogen embrittlement, especially when a lack of testing material makes impossible the test of standard specimens.

Study of pseudoelastic systems for the design of complex passive dampers: static analysis and modeling

This work presents an experimental and numerical analysis of several parallel systems of NiTi pseudoelastic wires. Standard tensile tests were accomplished to evaluate the global damping capacity, the energy dissipated per cycle and the maximum attenuated force in a static condition. Besides, a numerical model was implemented to predict the damping response of more complex pseudoelastic arrangements. It was found a damping capacity upper limit of 0.09 regardless the number and the length of the NiTi components. In addition, it was found that the energy dissipated per cycle is related to the strain and to the number of the NiTi components; furthermore, the system composed of NiTi wires with different length allows for an elastic region that is related to the numbers of wires and that presents a modulation of the stiffness. Finally, the proposed numerical model allows a precise design of complex pseudoelastic combinations as it is able to represent the rhombohedral characteristic.

Effect of Gd on microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn alloy

Effect of minor Gd addition on the microstructure, mechanical properties and wear behavior of as-cast Mg–5Sn-based alloy was investigated by means of OM, XRD, SEM, EDS, a super depth-of-field 3D system, standard high-temperature tensile testing and dry sliding wear testing. Minor Gd addition has strong effect on changing the morphology of the Mg–5Sn binary alloy. Gd addition benefits the grain refinement of the primary α-Mg phase, as well as the formation and homogeneous distribution of the secondary Mg2Sn phase. The mechanical properties of the Mg–5Sn alloys at ambient and elevated temperatures are significantly enhanced by Gd addition. The wear behavior of the Mg–5Sn alloy is also improved with minor Gd addition. The alloy with 0.8% Gd addition exhibits the best ultimate tensile strength and elongation as well as the optimal wear behavior. Additionally, the worn surface of the Mg–5Sn–Gd becomes smoother in higher Gd-containing alloys. The best wear behavior of alloy was exhibited when Gd addition was up to 0.8%, showing a much smoother worn surface than that of control sample. The improvement of tensile properties is mainly attributed to the refinement of microstructure and the increasing amount and uniform distribution of Mg2Sn phase. The larger amount of Mg2Sn phase uniformly distributed at the grain boundary of Mg–Sn–Gd alloys act as a lubrication during sliding, and combined with smaller grain size improve wear behavior of the binary alloy.

The effect of beta-tricalcium phosphate on mechanical and thermal performances of poly(lactic acid)

Orthophosphates are bioactive crystals with similar structure, in terms of elemental composition and crystal nature, to human bone. In this work, biocomposite materials were prepared with poly(lactic acid) (PLA) as matrix, and beta-tricalcium phosphate (β-TCP) as osteoconductive filler by extrusion-compounding followed by conventional injection molding. The β-TCP load content was varied in the 10–40 wt% range and the influence of the β-TCP load on mechanical performance of PLA/β-TCP composites was evaluated. Mechanical properties of composites were obtained by standardized tensile, flexural, impact, and hardness tests. Thermal analysis of composites was carried out by means of differential scanning calorimetry; degradation at high temperatures was studied by thermogravimetric analysis; and the effect of the β-TCP load on dynamical response of composites was studied by mechanical thermal analysis in torsion mode. The best-balanced properties were obtained for PLA composites containing 30 wt% β-TCP with a remarkable increase in the Young’s modulus. These materials offer interesting properties to be used as base materials for medical applications such as interference screws due to high stiffness and mechanical resistance.

The Effects of Graphene and Flame Retardants on Flammability and Mechanical Properties of Natural Fibre Reinforced Polymer Composites

The effects of incorporating three different types of flame retardant (FR) and two variants of graphene into 10 %wt palm EFB natural fibre (NF) filled epoxy composites were investigated in term of the flammability, thermal and mechanical properties through standard Bunsen burner experiment, bomb calorimetry, TGA and tensile tests. The types of FR employed include zinc borate (ZB), ammonium polyphosphate (APP) and alumina trihydrate (ATH) while a lab synthesised and a commercial form of graphene were used in the current work. Compared to the neat NF filled epoxy composite, specimens loaded with 15 %wt of either ZB or APP demonstrated a drip-free condition as observed from the Bunsen burner tests, which could be attributed to the strong char forming characteristic of the compositions. In specimens containing 15 %wt of either ZB or ATH, results from Bomb calorimetry revealed that these specific formulations produced the lowest mean gross heat release amongst others, suggesting better resistant to flame. Relative to the graphene incorporated composites, the post TGA measured mass residue was observed to be greater in FR rich formulations, suggesting that FR additives capable of yielding a much superior flame retardancy compared to graphene. While a slight increases in Young’s modulus was recorded in composites loaded with FR, such formulations produced several main drawbacks whereby reduction in ultimate tensile strength and elongation to break were being measured in large proportion of the specimens.

Crystal plasticity extended models based on thermal mechanism and damage functions: Application to multiscale modeling of aluminum alloy tensile behavior

The mechanical anisotropic properties of aluminum alloy are studied using multi-level approaches for strain-rate and temperature-sensitive large plastic deformation of polycrystalline aggregates. Unlike previous researches, the thermal effect and the damage evolution process are considered simultaneously and integrated in the CPFEM method. In the microscopic constitutive equation of crystal plasticity, the shear strain rate on the slip system is described by an advanced exponential function based on thermal activated mechanism, instead of traditional phenomenological power-law function. To determine the rate-sensitive material parameters in this new model, the strain rate and temperature jump tests are performed. In addition, a simulation of one representative volume element is compared to the results of conventional tensile tests to obtain other thermal parameters. Coupled with the continuum damage evolution formula, this thermal affected crystal plasticity model is then implemented in a single crystal analysis for different orientation, temperature and strain rate conditions. Finally, this extended crystal plasticity model is applied in the finite element method to simulate the mechanical properties of 5052 aluminum alloy at absolute temperature 473 K. Taylor model is also used to compare these simulations as well as the experimental data. The results show that the damage model coupled in the crystal plasticity is able to predict the mechanical response of 5052 aluminum alloy; moreover, this model can simulate the explicit evolution of damage factor and local stress concentration in the deformation of standard tensile test specimen. In the simulation, the specimen is meshed by rectangular elements and each element is given an initial orientation at the first time increment step. This study argues that even in high temperature, the orientation mismatch between adjacent grains could lead to early cavity or crack initiation and the damage development is similar to the void evolution theory. An explanation of the possible fracture angle is given in the thermal tensile test due to polycrystalline anisotropy. At last, the analysis of stress heterogeneity and texture evolution is also shown in this study.

Nonlinear time dependent behaviour of epoxy resins

The nonlinear behaviour of epoxy resins is studied on standard tensile tests. A strain field measurement system is applied (Aramis) in order to monitor local strains. The residual strain is measured by recovering the specimens for up to 68 hours after unloading. The time span the specimen is exposed to load has a large influence on the creeping process and the residual strain after recovering. This is studied by comparison of instantaneous unloading with keeping the specimen under permanent load for thirty minutes. It is shown that moderate differences in the initial strain can lead to large differences in the creep behaviour as well as in the residual strain.

Tensile Test and Analysis of the Geometry of Kevlar/Epoxy Composites

This paper is concerned with the analysis of geometric composites, whose reinforcement was made of plain weave fabric with different geometries. They were determined following the basic parameters of the textiles e.g. crimp length, crimp amplitude, thickness of the woven fabric, dimensions of the cross-sectional tow (tow width, tow height) and crimp angle. The number of fibers in the warp and tow strands and number of layers in the composites were also determined. These composites comprised of the same materials were subjected to a standard tensile test, according to DIN EN ISO 14 129. The mechanical properties of the composite as a whole were determined by tensile test.

Assessing the potential of wood welding for Australian eucalypts and tropical species

The wood welding potential of Australian and tropical species has been investigated. Optimized parameters for Eucalyptus saligna, Eucalyptus pilularis, Corymbia maculata, Ochroma pyramidale, and Tectona grandis were determined using a standard tensile strength test. The results confirmed the importance of density in the optimisation process. The grain direction also proved to have a significant impact on the welded joint strength of species featuring large wood rays or vessels in diagonal and/or radial pattern. Wood welding could therefore be an alternative for such species where gluing is required.

Ductile Behaviour Characterization of Low Carbon Steel: a CDM Approach

In this paper, the ductile behaviour of two different low carbon steels, C-Mn-440 and interstitial free high strength (IFHS), is presented using a continuum damage mechanics (CDM) approach. The damage growth law is adopted to predict the ductile response of the specified materials. Cyclic load-unload tensile tests in combination with standard uniaxial tensile tests helped to estimate the necessary parameters: damage variable, D, fracture stress, σf, threshold damage strain, e0, and strain hardening exponent, n, required to apply the model. The strain hardening exponent estimated from the cyclic test data is used to predict the damage variable, D. Increase of damage shows deterioration of the hardening exponent magnitudes varying nonlinearly. The simulated flow curve by the damage variable, D, corresponding to the loadunload test is observed to approximate the experimental true stress-true strain curve very closely up to the onset of necking for both the materials. The experimental values of D, as obtained for C-Mn-440 and IFHS steels, vary from 0.10 to 0.44 and 0.09 to 0.45, respectively. The critical damage parameters, DC, for the considered materials are 0.44 and 0.45, representing their good ductile response.

Effects of high-dose gamma irradiation on tensile properties of human cortical bone: Comparison of different radioprotective treatment methods

There are growing interests in the radioprotective methods that can reduce the damaging effects of ionizing radiation on sterilized bone allografts. The aim of this study was to investigate the effects of 50kGy (single dose, and fractionated) gamma irradiation, in presence and absence of l-Cysteine (LC) free radical scavenger, on tensile properties of human femoral cortical bone. A total of 48 standard tensile test specimens was prepared from diaphysis of femurs of three male cadavers (age: 52, 52, and 54 years). The specimens were assigned to six groups (n=8) according to different irradiation schemes, i.e.; Control (Non-irradiated), LC-treated control, a single dose of 50kGy (sole irradiation), a single dose of 50kGy in presence of LC, 10 fractions of 5kGy (sole irradiation), and 10 fractions of 5kGy in presence of LC. Uniaxial tensile tests were carried out to evaluate the variations in tensile properties of the specimens. Fractographic analysis was performed to examine the microstructural features of the fracture surfaces. The results of multivariate analysis showed that fractionation of the radiation dose, as well as the LC treatment of the 50kGy irradiated specimens, significantly reduced the radiation-induced impairment of the tensile properties of the specimens (P<0.05). The fractographic observations were consistent with the mechanical test results. In summary, this study showed that the detrimental effects of gamma sterilization on tensile properties of human cortical bone can be substantially reduced by free radical scavenger treatment, dose fractionation, and the combined treatment of these two methods.

Effect of hydrogen embrittlement on the tensile properties of CrMoV steels by means of the small punch test

In the present study, a new small punch test (SPT) methodology has been used to analyse the effect of hydrogen embrittlement on the tensile properties of three different grades of CrMoV steel: the base metal (CrMoV-1), weld metal (CrMoV-2) and this same weld metal subjected to an intermediate heat treatment (CrMoV-3). SPT results were compared with those obtained in standard tensile tests carried out in a hydrogen environment.The SPT was fully able to detect the deterioration induced by hydrogen in all steels. However, a higher level of embrittlement was obtained in the tensile tests. Furthermore, due to the aggressiveness of the environment meant, it was not possible to compare the results for CrMoV-2, which is highly susceptible to embrittlement due to its microstructure composed of low tempered bainite. As regards CrMoV-1 and CrMoV-3, the results obtained by means of the SPT fully agreed with those obtained in the tensile tests. It was observed that the poor behaviour of CrMoV-2 in a hydrogen environment was improved by applying a heat treatment of 680°C for 4h (CrMoV-3), although the excellent performance of CrMoV-1 when in contact with hydrogen was not achieved. The feasibility of the small punch test to estimate the deterioration of the tensile mechanical properties of CrMoV steels due to hydrogen embrittlement has been demonstrated.

Effect of weld on the mechanical properties of high strength and ultra-high strength steel tubes in fabricated hybrid sections

The effect of welding on the mechanical properties of high and ultra-high strength tubes in hybrid sections is a critical factor which influences the global performance of fabricated members and should be considered in the design and incorporation of these materials. To investigate and quantify these effects on the material of welded steel, a specific type of hybrid section composed of plates and tubes is considered in which two scales of experimental analysis are conducted at different positions from weld. In the macro scale, standard tensile tests are performed at various distances from weld to obtain the mechanical properties of heat affected steel in the axial direction parallel to the weld. Comparisons are made among three different welded materials: mild steel, high strength steel and ultra-high strength steel. The original and after-weld alteration in the ultimate tensile strength (UTS) and the strain corresponding to the UTS are investigated giving particular attention to the effect of yield strength and strain hardening rate. At the micro level, the microstructure of three above-mentioned materials in addition to microhardness profiles have been examined providing extensive data of the material behavior after welding. It is shown that the welding and post welding process, such as heat input and cooling rate affect the local material properties at different distances from weld leading to an overall heterogeneity in the material influencing the mechanical behavior.

Study on MIG-TIG double-sided arc welding-brazing of aluminum and stainless steel

MIG-TIG double-sided arc welding (DSAW)-brazing process was firstly conducted to join aluminum alloy and stainless steel using Al-Si filler metal and Nocolok flux. The joints were made at different welding parameters. The formation and microstructure of the weld interface were investigated. The bonding quality of the joints was examined by standard tensile tests. Based on the results, a sound welding-brazing joint with excellent front and back formation was formed. Compared with conventional welding, the welding heat input of T/M-GSAW was smaller and more uniform along the joint thickness. The thickness of the intermetallic compound layer, equal under the same welding condition, was thinner and altered with the welding heat input. The tensile strength of most joints reached 80MPa and fracture occurred in the HAZ of aluminum.

Experimental validation of a flat punch indentation methodology calibrated against unconfined compression tests for determination of soft tissue biomechanics

Mechanical characterisation of soft biological tissues using standard compression or tensile testing presents a significant challenge due to specimen geometrical irregularities, difficulties in cutting intact and appropriately sized test samples, and issues with slippage or damage at the grips. Indentation can overcome these problems but requires fitting a model to the resulting load–displacement data in order to calculate moduli. Despite the widespread use of this technique, few studies experimentally validate their chosen model or compensate for boundary effects. In this study, viscoelastic hydrogels of different concentrations and dimensions were used to calibrate an indentation technique performed at large specimen-strain deformation (20%) and analysed with a range of routinely used mathematical models. A rigid, flat-ended cylindrical indenter was applied to each specimen from which ‘indentation moduli’ and relaxation properties were calculated and compared against values obtained from unconfined compression. Only one indentation model showed good agreement (<10% difference) with all moduli values obtained from compression. A sample thickness to indenter diameter ratio ≥1:1 and sample diameter to indenter diameter ratio ≥4:1 was necessary to achieve the greatest accuracy. However, it is not always possible to use biological samples within these limits, therefore we developed a series of correction factors. The approach was validated using human diseased omentum and bovine articular cartilage resulting in mechanical properties closely matching compression values. We therefore present a widely useable indentation analysis method to allow more accurate calculation of material mechanics which is important in the study of soft tissue development, ageing, health and disease.