Maximum Tensile Strain Research Articles

Effect of nano-sized Al2O3 reinforcing particles on uniaxial and high cycle fatigue behaviors of hot-forged AZ31B magnesium alloy

Abstract The effect of hot-forging process was investigated on microstructural and mechanical properties of AZ31B alloy and AZ31B/1.5vol.%Al2O3 nanocomposite under static and cycling loading. The as-cast alloy and composite were firstly subjected to a homogenization heat treatment at 450 °C and then an open-die forging at 450 °C. The results indicated that the presence of reinforcing particles led to grain refinement and improvement of dynamic recrystallization. The forging process was more effective to eliminate the porosity in the cast alloy workpiece. Microhardness of the forged composite was increased by up to 80% and 16%, in comparison with those of the cast and forged alloy samples, respectively. Ultimate tensile strength and maximum tensile strain of the composite were improved by up to 45% and 23%, compared with those of the forged alloy in similar regions. These enhancements were respectively 50% and 37% in the compression test. The composite exhibited a fatigue life improvement in the region with low applied strain; however, a degradation was observed in the high applied strain region. Unlike AZ31B samples, tensile, compressive and high cycle fatigue behaviors of the composite showed less sensitivity to the applied strain, which can be attributed to the amount of porosity in the samples before and after the hot-forging.

Crystallographic orientation and spatially resolved damage in a dispersion-hardened Al alloy

The in-situ neutron diffraction technique, in combination with both the full-field crystal elasto-viscoplastic finite element model and microstructural characterization, was used to study the deformation-induced damage anisotropy in a commercial Al alloy, subjected to uniaxial tensile and cyclic loading. The simulations capture well the crystallographic-orientation-dependent lattice strain behavior. The hard grains, e.g. those orientated with the <111> and <422> orientations parallel with the uniaxial loading direction (LD), feature large Taylor factors and seem more prone to form damage-related band structures. Their effective elastic moduli decrease with the accumulation of damage, which are different from the soft grains orientated with the <200> orientation along the LD. Correlation between the distribution of voids and that of the residual lattice strain developed after failure may exist. The maximum tensile type residual lattice strain observed after failure may be resulted from the band structure formed in the hardest <111> grains. It was revealed that the band structure triggered by the hard particles could be one of sources of damage. In addition, while the specimen was obviously damaged, a fast stress relief was evidenced after unloading from the tension, especially at the beginning of unloading. Our present investigations provide a novel method for exploring the damage mechanisms of polycrystalline materials during plastic deformation.

Stretchable and conductive composites film with efficient electromagnetic interference shielding and absorptivity

The development of high-performance stretchable and electromagnetic interference (EMI) shielding materials is crucial to the rapidly growing industry of next-generation flexible electronics such as portable electronics and wearable devices. The common approach to EMI shielding is to increase the contents of conductive materials and improve the conductivity. However, this approach is limited by the worse stretchable property. An intrinsically stretchable conductive and EMI shielding thin film (thickness of 0.7 mm) based on functional adhesive (FA) composited by silver nanoparticles (Ag NPs), nickel nanoparticles (Ni NPs), and liquid polydimethylsiloxane (PDMS) is proposed in this paper. The FA is coated onto cured PDMS substrates to fabricate the film, achieving maximum tensile strain of 250% and EMI shielding effectiveness (SE) of 57.1 dB. Up to 35% absorptivity makes an important contribution to SE. This film can withstand more than 20000 stretching-releasing cycles at tensile strain of 0–100% and 0–150%, with no delamination, demonstrating its superior stretchability and repeatability. The mechanism of EMI shielding of silver and nickel nanoparticles is discussed. The durability of these films in terms of electrical and EMI SE properties are also tested. In addition, a device to change the output power of a transformer is constructed.

Achieving 5.9% elastic strain in kilograms of metallic glasses: Nanoscopic strain engineering goes macro

The ideal elastic limit is the upper bound of the achievable strength and elastic strain of solids. However, the elastic strains that bulk materials can sustain are usually below 2%, due to the localization of inelastic deformations at the lattice scale. In this study, we achieved >5% elastic strain in bulk quantity of metallic glass, by exploiting the more uniform and smaller-magnitude atomic-scale lattice strains of martensitic transformation as a loading medium in a bulk metallic nanocomposite. The self-limiting nature of martensitic transformation helps to prevent lattice strain transfer that leads to the localization of deformation and damage. This lattice strain egalitarian strategy enables bulk metallic materials in kilogram-quantity to achieve near-ideal elastic limit. This concept is verified in a model in situ bulk amorphous (TiNiFe)-nanocrystalline (TiNi(Fe)) composite, in which the TiNiFe amorphous matrix exhibits a maximum tensile elastic strain of ∼5.9%, which approaches its theoretical elastic limit. As a result, the model bulk composite possesses a large recoverable strain of ∼7%, a maximum tensile strength of above 2 GPa, and a large elastic resilience of ∼79.4 MJ/m3. The recoverable strain and elastic resilience are unmatched by known high strength bulk metallic materials. This design concept opens new opportunities for the development of high-performance bulk materials and elastic strain engineering of the physiochemical properties of glasses.

Effects of strain gradients in the onset of global buckling in slender walls due to earthquake loading

Global buckling of slender walls, reported only in a few laboratory tests before 2010, became a critical issue in design of reinforced concrete buildings after it was observed following the 2010 Mw 8.8 Chile earthquake and the 2011 Mw 6.3 New Zealand earthquake. Researchers have proposed theoretical buckling models based on prismatic columns subjected to uniform tension/compression cycles, where the key parameters are slenderness ratio, number of curtains of reinforcement, and maximum tensile strain before buckling during load reversal. These models have shown sufficient accuracy in comparison with laboratory tests on columns under such loading conditions. However, buckling in walls is more complex because of variation of strains through the wall depth and variation of moment along the wall height. Nonlinear finite elements are used to evaluate the effects of these more complex loadings on buckling of wall boundary elements. Analyses showed that the maximum tensile strain (averaged over the wall out-of-plane unsupported height) required to buckle the wall during load reversal does not depend on the moment variation along the wall height. Moreover, for typical wall lengths, the wall boundary behaves like an isolated column subjected to axial force cycles, with minimal apparent bracing provided by the wall web. This allows to analyze a broad range of practical cases for buckling susceptibility using simplified approaches based on buckling models of axially loaded columns.

Mechanistic analysis and cost-effectiveness evaluation of asphalt rubber mixtures

Traffic loading has been associated with different main distresses occurring in the pavements. Fatigue cracking and rutting can be considered as the main distresses occurring in the pavement structure. Studies conducted in the past have shown improved mechanical performance of asphalt rubber mixtures, but only few of these studies are inclined in investigating the long-term mechanistic performance and the cost-effectiveness of the addition of rubber into asphalt mixtures. A mechanistic analysis utilising 3D Move software package was performed to assess the long-term fatigue performance and rutting performance of two different mixtures, namely: conventional hot mixed asphalt (HMA) and asphalt rubber (AR). Two different pavement construction scenarios were investigated as a newly constructed pavement structure and a rehabilitated overlay. Each mixture was analysed for two different vehicle speeds and two different pavement thicknesses that totalled 16 different 3D Move mechanistic analysis scenarios (2 asphalt mixtures × 2 construction scenarios × 2 vehicle speeds × 2 pavement thicknesses). The maximum tensile strain at the bottom of the asphalt layer for each scenario was utilised to establish a fatigue ratio that compared AR to the corresponding conventional HMA pavement sections. In addition, a cost-effectiveness analysis was carried out for the same 16 scenarios. Overall, the mechanistic analysis showed that the fatigue life of an AR was six times greater than that of conventional HMA layer for a new construction, and for the overlay, AR had 40 times more fatigue life than a conventional HMA. The rutting life was also increased with the use of asphalt rubber. In the case of cost-effectiveness analysis, AR exhibited four times lower cost per 1000 fatigue life cycles and three times lower cost per cycle of rutting when compared to a conventional HMA in a new construction. For an overlay scenario, AR exhibited 23 times lower cost per 1000 fatigue life cycles and around four times lower cost per cycle of rutting compared to a conventional HMA overlay.

Self-Induced Strain in 2D Chalcogenide Nanocrystals with Enhanced Photoelectrochemical Responsivity

Strain engineering has become an emerging strategy to tailor the performance of nanocatalysts. However, current strained catalysts overwhelmingly rely on stresses originated at catalyst–support interfaces. Self-standing strained nanostructures are extremely challenging to produce, and thus their impact on catalytic and photocatalytic activities remains largely unknown. Herein, we propose a ligand-based colloidal strategy for the one-step growth of bended metal chalcogenide nanoplates with a built-up strain. This strategy is based on the seeded growth of strained nanostructures from sacrificial seeds which provide a proper lattice mismatch. We demonstrate this strategy for the synthesis of strained orthorhombic SnSe and SnS nanoplates from rock salt SnS seeds. We probe not only the presence of atomic distortions in the periodic lattice but also its coupling with the generation of a large density of selenium vacancies. Geometrical phase analysis evidences the formation of a strain field in self-bended SnSe nanoplates, with a maximum tensile strain up to 12%. Theoretical and experimental results further reveal that the strain-related selenium vacancies strongly affect the electronic structure of SnSe and facilitate the mobility of photogenerated charge carriers, which result in a significantly improved photoelectrochemical activity. The strategy presented here opens a new avenue for precisely tuning semiconductor functionalities via strain engineering.

3D printing of continuous kevlar reinforced polymer composite through coextrusion method

The major drawbacks of 3D printed thermoplastic using fused deposition method (FDM) are exhibit weak mechanical properties. This reduces the usability of the printed part as the functional structure for part replacement in a real-world application. Therefore, in this study a co-extrusion of a continuous fibre of twisted Kevlar using FDM is conducted to examine the improvement of mechanical strength of the 3D printed part with reinforcement of continuous fibre. The coextruded reinforced plastic (CRP) parts consisting of polylactic acid (PLA) as matrix and twisted Kevlar as core fibre. The mechanical performance of printed parts was evaluated in a tensile test under ASTM D638 standard. The results of both CRPs were compared against unreinforced PLA which. It has been demonstrated that CRPs with twisted Kevlar was able to achieve significant increment in Ultimate tensile strength (+179.7%, 104.64MPa), maximum tensile strain (+257%, 5.384%) and relative similar Young’s modules (3.29GPa) compared to unreinforced PLA. As a result, this study created a unique material print which CRP with twisted Kevlar which offer high stiffness and high strength structure.

Study on Grinding and Deformation Fracture Control of Cold Rolled Titanium Strip

Surface defects of titanium strip need to be removed by local grinding, but local cracking or band breaking then occurs during subsequent cold rolling. Tensile properties and deformation resistance of 3 mm thick commercially pure titanium strip with grinding pits on the surface were simulated by a finite-element method using a multi-pass cold-rolling deformation process. The stress and strain of grinding pits with depths of 0.25–2 mm were analyzed. During cold-rolling deformation, the stress and strain in the center of a grinding pit were larger than at the edge region. The strip was first subjected to tensile stress in the rolling direction, which then decreased and gradually changed to compressive stress. Partial stress was larger in the rolling direction than in the transverse direction. When the tensile stress and true strain both exceeded the stress and strain limits during second-pass rolling, the strip with a grinding depth of 2 mm cracked, but shallower grinding pits were repaired. The criterion for cracking during rolling after grinding is that the maximum tensile strain at the bottom of the pit must be less than the critical strain of the material: ln ( 1 + h / H ) ≤ ε C r . Results of numerical simulation were verified by the data for cold-rolling tests.

Development of carbon fiber acrylonitrile styrene acrylate composite for large format additive manufacturing

The increasing interest of Large Format Additive Manufacturing (LFAM) technologies in various industrial sectors mainly lies on the attainable production of pieces reaching several cubic meters. These new technologies require the development of optimized materials with two-folded capabilities, able to satisfy functional in-service requirements but also showing a proper printability. Acrylonitrile Styrene Acrylate (ASA) is among the most interesting thermoplastic materials to be implemented in a LFAM device due to its excellent wettability and mechanical properties.This research focuses on the development and characterization of ASA and carbon fiber (CF) ASA composites suitable for LFAM. The rheological, thermal and mechanical properties of neat ASA and ASA containing 20 wt% CF are addressed. The results evidence the higher performance of the CF loaded composite compared to the raw ASA polymer (i.e., the 20 wt% CF composite shows a 350% increase in flexural Young's Modulus and a 500% increment in thermal conductivity compared with neat ASA). Additionally, both materials were successfully printed along perpendicular directions (X and Z), showing the maximum tensile strain for the composite printed along the X orientation as was expected. The results of the flexural tests are comparable or slightly higher than those of injected parts. Finally, the fracture surface was analysed, identifying different types of porosity.

Enhanced Stretchable and Sensitive Strain Sensor via Controlled Strain Distribution.

Stretchable and wearable opto-electronics have attracted worldwide attention due to their broad prospects in health monitoring and epidermal applications. Resistive strain sensors, as one of the most typical and important device, have been the subject of great improvements in sensitivity and stretchability. Nevertheless, it is hard to take both sensitivity and stretchability into consideration for practical applications. Herein, we demonstrated a simple strategy to construct a highly sensitive and stretchable graphene-based strain sensor. According to the strain distribution in the simulation result, highly sensitive planar graphene and highly stretchable crumpled graphene (CG) were rationally connected to effectively modulate the sensitivity and stretchability of the device. For the stretching mode, the device showed a gauge factor (GF) of 20.1 with 105% tensile strain. The sensitivity of the device was relatively high in this large working range, and the device could endure a maximum tensile strain of 135% with a GF of 337.8. In addition, in the bending mode, the device could work in outward and inward modes. This work introduced a novel and simple method with which to effectively monitor sensitivity and stretchability at the same time. More importantly, the method could be applied to other material categories to further improve the performance.

A flexural design methodology for UHPC beams posttensioned with unbonded tendons

This paper provides a framework for predicting the flexural behavior of ultra-high performance concrete (UHPC) beams posttensioned with unbonded tendons. A mechanics based phenomenological model is presented to predict flexural capacity, and a set of equations that can be used to predict strand stress at the ultimate limit state is proposed and considers how the nonlinear domain of UHPC in tension affects flexural behavior. It is demonstrated that predictions based on the proposed equations and the presented flexural design methodology are in close agreement with results obtained from validated numerical simulations. The strand stress at ultimate is expressed as a function of neutral axis depth, effective depth of tendon, tendon length, loading configuration, loading pattern, plastic hinge length, maximum usable UHPC compressive and tensile strain, and shape of the stress-strain curve of the tendon. The influence of tendon area, mild steel area and yield stress, specified UHPC compressive strength and tensile strength, as well as beam cross-sectional dimensions are captured indirectly through the calculation of the neutral axis depth. The flexural design methodology is presented in terms of the failure mode observed when the considered specimens reach their ultimate load carrying capacity. The failure mode is characterized as either a fiber tension controlled failure or a UHPC compression controlled failure. The change in strand stress at the ultimate limit state, Δfps, the strand stress at the ultimate limit state, fps, and the nominal moment capacity, Mn, of 221 UHPC posttensioned beams obtained based on the proposed methodology are compared with results obtained from validated numerical models and it is demonstrated that average predicted values are within 5% of computed ones and the coefficient of variation is not greater than 17%.

Prediction of Viscoelastic Pavement Responses under Moving Load and Nonuniform Tire Contact Stresses Using 2.5-D Finite Element Method

This study developed two-and-half dimensional (2.5-D) finite element method (FEM) to predict viscoelastic pavement responses under moving loads and nonuniform tire contact stresses. The accuracy of 2.5-D FEM was validated with two analytical solutions for elastic and viscoelastic conditions. Compared to three-dimensional (3-D) FEM, the computational efficiency of the 2.5-D method was greatly improved. The effects of loading pattern and speed on pavement surface deflection and strain responses were analyzed for asphalt pavements with four different asphalt layer thicknesses. The analyzed pavement responses included surface deflections, maximum tensile strains in the asphalt layer, and maximum compressive strains on top of subgrade. The loading patterns have influence on the mechanical responses. According to the equivalent rule, the point load, rectangle type, and sinusoid-shape contact stresses were studied. It was found that the point load caused much greater pavement responses than that of the area-based loading. When the tire loading was simplified as uniform contact stress in rectangular area, the maximum tensile strains in the asphalt layer varied with the width/length ratio of contact area. Additionally, it was shown that the dynamic responses of pavement structure induced by the sinusoid-shape contact stresses and realistic nonuniform stresses were quite similar to each other in all the cases. The pavement strain responses decreased as the speed increased due to viscoelastic behavior of asphalt layer. The study results indicate that asphalt pavement responses under moving load can be calculated using the proposed 2.5-D FEM in a fast manner for mechanistic-empirical pavement design and analysis.

Effects of overconsolidation ratio on tunnel responses due to overlying basement excavation in clay

Due to shortage of usable spaces in congested urban cities, deep basements for buildings are frequently constructed above or at a side of existing tunnels. Although much attention was paid to the basement-tunnel interaction, previous studies mainly simplified it as a plane strain problem and focused on excavation-induced tunnel responses in sand. In this study, three-dimensional centrifuge tests were conducted to investigate long-term tunnel responses due to overlying basement excavation in lightly (overconsolidation ratio (OCR) = 1.7) and heavily overconsolidated (OCR = 6.0) kaolin clays. Immediately upon completion of basement excavation, the measured heave and tensile strain of tunnel in heavily overconsolidated clay are up to 25% smaller than those in lightly overconsolidated clay. This is because a smaller void ratio in a stiffer clay possesses large soil stiffness around tunnel lining. Due to dissipation of excess negative pore water pressure, the maximum heave and tensile strain of tunnel increase by up to 210% and 50%, respectively, in heavily and lightly overconsolidated clays. To ensure the safety and serviceability of existing tunnel, special attention should be paid to long-term rather than short-term tunnel responses.

3D Printing of Polylactic Acid Bioplastic–Carbon Fibres and Twisted Kevlar Composites Through Coextrusion Using Fused Deposition Modeling

Polylactic acid (PLA) bioplastic is a common material used in Fused Deposition Modeling (FDM) 3D printing. It is biodegradable and environmentally friendly biopolymer which made out of corn. However, it exhibits weak mechanical properties which reduced its usability as a functional prototype in a real-world application. In the present study, two PLA composites are created through coextruded with 3K carbon fibres and twisted Kevlar string (as core fibre) to form a fibre reinforced parts (FRP). The mechanical strength of printed parts was examined using ASTM D638 standard with a strain rate of 1 mm/min. It has been demonstrated that the FRPs coextruded with 3K carbon fibres had achieved significant improvement in Young’s modulus (+180.6%, 9.205 GPa), ultimate tensile strength (+175.3%, 103 MPa) and maximum tensile strain (+21.6%, 1.833%). Although the Young’s modulus of Kevlar FRP was found to be similar to as compared to unreinforced PLA (~3.29 GPa), it has gained significant increment in terms of maximum tensile strain (+179.7%, 104.64 MPa), and maximum tensile strain (+257%, 5.384%). Thus, this study revealed two unique composite materials, in which the 3K carbon FRP can offer stiff and high strength structure while Kevlar FRP offers similar strength but at a higher elasticity.

Lognormal Distribution Function for Describing Seepage Damage Process of Single‐Cracked Rock

The precondition of rock stress and deformation analysis is a reasonable rock constitutive model. Most of the previous studies have described the heterogeneous microdamage by Weibull distribution or normal distribution. However, both of them have limitations. Therefore, this paper intends to use the lognormal distribution as the probability distribution model of rock microunit strength. Based on the tensile failure of the single‐fractured rock under the hydrodynamic force, the maximum tensile strain failure criterion is used as the distribution parameter of rock microunit strength. And, considering the multiphase properties of the filling fractured rock, the equivalent elastic modulus parameter is adopted in the model. We design a triaxial seepage test for the filled single‐fractured rock and analyze the applicability and rationality of the modified lognormal statistical damage model for characterizing the fractured rock by using the test data. According to the comparison of the experimental stress‐strain curve and the model stress‐strain curve and the analysis of the damage value test curve and the model curve, the rationality of the established statistical damage constitutive model is verified, and the advantages and limitations of the model are proposed.

Embankment responses to shield tunnelling considering soil-structure interaction: case studies in Hangzhou soft ground

As more and more under-river tunnels are constructed in urban areas, the deformations and potential damage of existing embankments due to tunnelling have become a major concern. This problem is complex because not only does tunnelling affect the existing embankments, but their presence also alters tunnelling-induced ground movements. An analytical method, which takes account of the effects of the embankment’s self-weight, the property of the soil-embankment interface, and the embankment’s bending and axial stiffness, is put forward to estimate the embankment’s deflections and horizontal strains due to tunnelling. Subsequently, a procedure is proposed to identify the embankment’s damage level based on its calculated maximum tensile strain. In the end, case studies of three embankments in Hangzhou soft ground are conducted to examine and validate the analytical method and the damage identification procedure. Further parametric studies show that the embankment’s bending stiffness has a significant effect on its deflections and damage level, while the influence of self-weight is mild.

Maximum tensile stress and strain of skin of the domestic pig-differences concerning pigs from organic and non-organic farming.

The purpose of this work has been to determine differences in biomechanical properties of porcine skin from organic and non-organic farming as porcine skin is widely used as a model for human skin. A test apparatus was used, using gravity to stretch and finally tear a dumbbell-shaped specimen of prepared abdominal skin with a testing surface area of 25 × 4mm. A total of 32 specimens were taken from seven individual pigs, three from organic and four from non-organic farming, in different orientations with respect to the Langer's lines. The tests were performed at a dynamic speed of around 1.66m/s (corresponding to a nominal strain rate of 67s-1). Engineering strain at rupture was higher in pig skin from non-organic farming with values up to 321% as opposed to 90% in organic pig skin. The maximum tensile stress found in non-organic pig skin was lower than in pig skin from organic farming with maximum values of 34MPa as opposed to 58MPa. The reason for the difference in biomechanical properties is unclear; the effect of sunlight is discussed as well as other factors like age and exercise. It seems that the biomechanical properties of porcine skin from organic farming are more similar to those of human skin.

Approaching diamond\u2019s theoretical elasticity and strength limits

Diamond is the hardest natural material, but its practical strength is low and its elastic deformability extremely limited. While recent experiments have demonstrated that diamond nanoneedles can sustain exceptionally large elastic tensile strains with high tensile strengths, the size- and orientation-dependence of these properties remains unknown. Here we report maximum achievable tensile strain and strength of diamond nanoneedles with various diameters, oriented in <100>, <110> and <111> -directions, using in situ transmission electron microscopy. We show that reversible elastic deformation depends both on nanoneedle diameter and orientation. <100> -oriented nanoneedles with a diameter of 60 nm exhibit highest elastic tensile strain (13.4%) and tensile strength (125 GPa). These values are comparable with the theoretical elasticity and Griffith strength limits of diamond, respectively. Our experimental data, together with first principles simulations, indicate that maximum achievable elastic strain and strength are primarily determined by surface conditions of the nanoneedles.

Thermal cycling effects on the creep-fatigue interaction in type 316LN austenitic stainless steel weld joint

Thermomechanical fatigue (TMF) tests under in-phase temperature-mechanical strain combination were performed on a type 316 LN austenitic stainless steel weld joint using temperature ranges of 573–823 K, 623–873 K and 673–923 K employing a mechanical strain amplitude (Δεmech/2) of ±0.4%. Isothermal low cycle fatigue (designated as IF) tests were also carried out at the maximum temperatures (Tmax) of TMF cycling. The interaction of creep deformation with IF and TMF cycling was assessed by incorporating hold periods of 1 min and 5 min at the maximum tensile strain. TMF cycling resulted in considerably lower lives compared to IF, with the life reduction being more significant under hold conditions. Further, a clear difference in the cyclic stress response (CSR) was observed between creep-TMF and creep-IF cycling, depending on the hold duration and temperature range. The contribution of creep deformation to the overall damage was found to be higher under TMF compared to IF cycling at the Tmax. The observed variations in the cyclic lives under IF and TMF cycling with and without hold times were explained on the basis of the dominant fracture mechanisms identified through detailed microstructural characterization of the crack initiation and propagation modes. The extent of intergranular damage was seen to increase with an increase in the temperature range and the hold period. The role of oxidation in the development of damage was observed to be different under creep-TMF and creep-IF cycling. Numerous grain boundary microvoids and their inter-linkages caused enhanced crack propagation under creep-TMF, compared to creep-IF cycling. A comparison of the deformation behaviour, cyclic life and damage developed in the material under IF and TMF suggested that the performance of the weld joint under TMF cycling cannot be satisfactorily represented through IF tests at the Tmax.