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In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress σ RD : σ ND = 2:1 was higher than that of the ND yield stress under stress ratio σ RD : σ ND = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases. [ABSTRACT FROM AUTHOR]

Multiaxial creep investigations at high temperatures are required to guarantee the integrity of structural materials such as boiler pipes for power generation and turbine blades for aviation and industrial applications. The multiaxial creep testing method using a cruciform specimen has several advantages, and the authors successfully downsized the specimen. The authors also developed a technique for the in situ observation of the specimen in an electric furnace and the non-contact displacement measurement in the development of a biaxial tensile creep testing machine for the miniature cruciform specimen. By observing the specimen at a target mark during the creep testing through an observation window installed at the bottom of the furnace, it was possible to visualize the specimen surface variations and obtain the axial strain from the locus of the target marks. The Mises-type equivalent strain was calculated from the axial strains obtained in the equi-biaxial tensile multiaxial creep testing and was compared with the strains obtained in the uniaxial creep testing. The Mises-type equivalent strain can be expressed using a unified method up to approximately 5% of the initial strain in the test, even in the multiaxial stress state.

In the present study, the mechanical response and deformation behavior of a Mg AZ31 plate with different types of pre-twins was systematically investigated under biaxial tension along the normal direction (ND) and transverse direction (TD) with different stress ratios. The results show that significant hardening was observed under biaxial tension. The yield values in the direction of larger stress values were higher than those under uniaxial loading conditions, and the solute atom segregation at twin boundaries generates more obvious strengthening effect. Noting that, for TRH (with cross compression along the rolling direction (RD) and TD and annealing at 180 °C for about 0.5 h) sample, the strength effect of the RD yield stress σRD:σND = 2:1 was higher than that of the ND yield stress under stress ratio σRD:σND = 1:2. There is a complex competition between twinning and detwinning under biaxal tension along the ND and TD of the pre-twinned samples with the variation in the stress ratio along the TD and RD. The variation in the twin volume fractions for all samples under biaxial firstly decreases and then increases with a higher stress ratio along the ND. As for the TDH sample (precompression along the TD and annealing), the changes of the twin volume fraction were lower than that of the TR sample (cross compression along the TD and RD). However, the amplitude of variation in twin volume fraction of the TRH sample is higher than that of the TR sample. This is because the relative activity of detwinning decreases and that of twinning increases, as the ND stress mainly leads to the growth of pre-twins and the TD stress often promotes detwinning of primary twins. With a higher stress ratio along the ND, the activity of twinning deformation increases and that of detwinning decreases.

The article discusses the conducted research, the purpose of which was to assess the effect of drying- thermal fixation on the breathability and relaxation processes of half-woollen worsted fabrics for costume purposes of different densities on the base and weft, with different wool and polyester content, and with the insertion of lycra into the weft thread. It was found that when exposed to hot air, the intensity of relaxation of efforts in all the studied tissues increases. The duration of relaxation on the base under the influence of hot air is less than at normal temperature. Across the weft the duration of relaxation varies significantly: in tissues that do not contain lycra, it is also lower, and in tissues containing lycra, on the contrary, higher. The percentage of increased air permeability of fabrics as a result of their thermal fixation can be raised by increasing deformation along the base and weft and the duration of exposure to hot air. Авторами статьи проведено исследование, целью которого являлось оценка влияния операции «Сушка-термофиксация» на воздухопроницаемость полушерстяных камвольных тканей с различным соотношением шерстяных волокон, полиэстера и лайкры и происходящие при этом релаксационные процессы. Для достижения по- ставленной цели были проведены исследования изменения длительности релаксации и воздухопроницаемости тканей различного волокнистого состава при двухосном растяжении и воздействии на ткань потока горячего воздуха (180 оС). Ткани исследовались во влажном и сухом состояниях. В результате исследования установлено, что процент повышения воздухопроницаемости тканей в результате их термофиксации можно поднять за счет увеличения деформирования по основе и утку и продолжительности воздействия горячего воздуха. Эффективность влияния этих параметров термофиксации можно повысить за счет снижения плотностей по основе и утку, снижения линейных плотностей нитей и повышения их крутки, а также за счет снижения доли шерстяных волокон в составе тканей.

In this paper, the free-edge effects which play an important role in the failure analysis of composite laminates are studied. Pure temperature change and its combination with biaxial tension are investigated for a composite plate with a centric circular hole that is adequately small in comparison to the dimension of the plate. Moreover, the laminate is assumed to be thin, the temperature change of all points of the plate is identical and the biaxial tensile load is applied far from the center of the hole. For this purpose, a semi-analytical method based on a two-dimensional thermoelastic boundary layer theory and a minimum potential energy principle is proposed. It is shown that the present method predicts the interlaminar peeling and shear stresses surrounding the hole with good agreement compared to the results obtained by FEM analysis. [ABSTRACT FROM AUTHOR]

The mechanical properties of soft tissues are driven by their complex, heterogeneous composition and structure. Interestingly, studies of soft tissue biomechanics often ignore spatial heterogeneity. In our work, we are therefore interested in exploring the impact of tissue heterogeneity on the mechanical properties of soft tissues. Therein, we specifically focus on soft tissue heterogeneity arising from spatially varying thickness. To this end, our first goal is to develop a non-destructive measurement technique that has a high spatial resolution, provides continuous thickness maps, and is fast. Our secondary goal is to demonstrate that including spatial variation in thickness is important to the accuracy of biomechanical analyses. To this end, we use mitral valve leaflet tissue as our model system. To attain our first goal, we identify a soft tissue-specific contrast protocol that enables thickness measurements using a Keyence profilometer. We also show that this protocol does not affect our tissues' mechanical properties. To attain our second goal, we conduct virtual biaxial, bending, and buckling tests on our model tissue both ignoring and considering spatial variation in thickness. Thereby, we show that the assumption of average, homogeneous thickness distributions significantly alters the results of biomechanical analyses when compared to including true, spatially varying thickness distributions. In conclusion, our work provides a novel measurement technique that can capture continuous thickness maps non-invasively, at high resolution, and in a short time. Our work also demonstrates the importance of including heterogeneous thickness in biomechanical analyses of soft tissues. [ABSTRACT FROM AUTHOR]

The multiaxial deformation behavior of magnesium alloys is an important factor in understanding the service performance of structures. In the present research, the deformation mechanism of a Mg AZ31 sheet under biaxial tension with various stress ratios ( σ RD : σ 45 ) along the rolling direction (RD) and the diagonal direction (45° direction) between the normal direction (ND) and transverse direction (TD) was systematically studied for the first time using cruciform specimens. The impacts of the stress ratio, σ RD : σ 45 , on the mechanical response, twinning behavior, texture and slip behavior were investigated. The results showed that the contribution of twinning to plastic deformation was limited and governed by the Schmid law. The activation of twinning induced a twin texture component with c-axes largely parallel to the 45° between ND and TD. The deformation induced by biaxial tension was accommodated mainly by prismatic and basal slips under the stress ratio of σ RD : σ 45 = 4 : 1 , and the fraction of grains favoring basal slip increased with lower stress ratio along the RD. The characteristics of flow stress can be effectively explained by the relative activities of twinning and slip with stress ratio. [ABSTRACT FROM AUTHOR]

A biaxial tension test considering temperature is crucial to predict the mechanical properties of airship envelopes. However, there is a lack of biaxial tensile test equipment for high- and low-temperature correlation. In this study, a temperature control device suitable for biaxial tension was designed based on the traditional device, and the biaxial tension test of the UN-5100 material in high- and low-temperature environments was realized. In addition, a series of tests were carried out to verify the effectiveness and rationality of the temperature control device. Then, a biaxial tensile test of UN-5100 specimens between −33 °C and 80 °C were carried out and the stress–strain relationship of the UN-5100 specimens under high- and low-temperature environments was obtained. Based on the test data, the elastic modulus and Poisson's ratio of the UN-5100 specimens at different temperatures were calculated. Finally, the test results showed that the elastic modulus and Poisson's ratio of the airship envelope were larger at low temperatures, indicating that the capsule is relatively safe at such temperatures. The relationships between the temperature and the mechanical properties of the airship were also summarized. [ABSTRACT FROM AUTHOR]

This paper explores the effects of woven fabric structures on the biaxial tensile mechanical properties and burst properties of woven fabric for layflat hose. A repeat unit cell finite element modeling for woven fabrics for layfalt hose is adopted. To investigate the effects of fabric structure, two parameters are studied: warp yarn spacing and weft yarn linear density. The mechanical response outcomes such as stress distribution, intensity, breaking elongation, and burst properties such as burst pressure, burst direction, are defined and the effects of structure parameters studied on these outcomes are studied. The effects of the warp yarn spacing and the weft yarn linear density on the biaxial tensile mechanical properties and the burst properties of woven fabric for layflat hose are determined. Moreover, the results suggest finite element method exhibits high accuracy in predicting the burst pressure of layflat hose. [ABSTRACT FROM AUTHOR]

The formability limits of bulk metal forming in principal strain space and in the effective strain vs. stress-triaxiality space are characterized by an uncertainty region in which cracks may be triggered by tension (mode I of fracture mechanics) or by out-of-plane shear (mode III). The problem in obtaining experimental data in this region has been known for a long time and the main objective of this paper is to present a new upset formability test geometry that can effectively contribute to the characterization of the formability limits of bulk metal forming parts subjected to biaxial tension. Alongside with this objective, this paper also presents an analytical expression for converting the fracture forming limit line corresponding to crack opening by mode III in principal strain space into a hyperbolic fracture limit curve in the effective strain vs. stress-triaxiality space. The overall methodology employed by the authors combines experimentation along with analytical and numerical modelling, and the contents of the paper is a step towards diminishing the actual lack of knowledge regarding failure by fracture in bulk metal forming parts subject to stress-triaxiality values beyond uniaxial tension. Results show that a new uncoupled ductile fracture criterion built upon combination of the integrands of the Cockcroft-Latham and McClintock criteria can be successfully used to model the physics of the bulk metal forming limits for the entire range of stress-triaxiality values corresponding to cracking on free surfaces. [ABSTRACT FROM AUTHOR]

• A complex strain partitioning in two loading axes is observed with the variation of stress ratio. • The observed strain transitions with stress ratio are related to the competition between { 10 1 ¯ 2 } twinning and basal slip. • For all the stress ratios, the accommodated strains by most { 10 1 ¯ 2 } twin variants are ε x x >0 and ε y y >0, while most basal variants accommodate a positive y-axis strain. The mechanical behavior of a hot-rolled Mg AZ31 plate was studied under biaxial tensions along two perpendicular loading axes of x and y in the ND-TD plane, with the x-axis aligned at a 45° counterclockwise angle from the TD (ND and TD refer to the normal direction and transverse direction). A complex strain partitioning in two loading axes is observed with the variation of stress ratio σ x x : σ y y . For σ x x : σ y y = 1:1 and 1:1.5, the strains along the x- and y-axes, ε x x and ε y y , are both positive. However, With the stress ratio of σ x x : σ y y = 1:3, ε y y remains positive, while ε x x becomes negative. Interestingly, for σ x x : σ y y = 1:2, ε x x changes from negative during the early stage of loading to positive upon failure. Crystal plasticity simulations and theoretical calculations reveal that the observed strain transition. The reasons for the strain transition with stress ratio is related to the competition between { 10 1 ¯ 2 } twinning and basal slip. For { 10 1 ¯ 2 } twinning, the accommodated strains by most of the twins are ε x x >0 and ε y y >0 for all the stress ratios considered. For basal slip, most of the basal variants accommodate a positive y-axis strain, while for loading cases with low stress ratios, most of the basal variants result in a negative x-axis strain. As the stress ratio decreases, basal slip becomes more active, while the activity of { 10 1 ¯ 2 } twinning gradually decreases, leading to the observed strain transition. For σ x x : σ y y = 1:2, the transition from negative to positive is related to the increasing activity of { 10 1 ¯ 2 } twinning with strain. Theoretical calculations reveal that the competition of basal slip and { 10 1 ¯ 2 } twinning under biaxial tension is determined by the variation of their Schmid factors with σ x x : σ y y . [ABSTRACT FROM AUTHOR]

The multiaxial deformation behavior of magnesium alloys is an important factor in understanding the service performance of structures. In the present research, the deformation mechanism of a Mg AZ31 sheet under biaxial tension with various stress ratios (σRD:σ45) along the rolling direction (RD) and the diagonal direction (45° direction) between the normal direction (ND) and transverse direction (TD) was systematically studied for the first time using cruciform specimens. The impacts of the stress ratio, σRD:σ45, on the mechanical response, twinning behavior, texture and slip behavior were investigated. The results showed that the contribution of twinning to plastic deformation was limited and governed by the Schmid law. The activation of twinning induced a twin texture component with c-axes largely parallel to the 45° between ND and TD. The deformation induced by biaxial tension was accommodated mainly by prismatic and basal slips under the stress ratio of σRD:σ45=4:1, and the fraction of grains favoring basal slip increased with lower stress ratio along the RD. The characteristics of flow stress can be effectively explained by the relative activities of twinning and slip with stress ratio.

A biaxial tension test considering temperature is crucial to predict the mechanical properties of airship envelopes. However, there is a lack of biaxial tensile test equipment for high- and low-temperature correlation. In this study, a temperature control device suitable for biaxial tension was designed based on the traditional device, and the biaxial tension test of the UN-5100 material in high- and low-temperature environments was realized. In addition, a series of tests were carried out to verify the effectiveness and rationality of the temperature control device. Then, a biaxial tensile test of UN-5100 specimens between −33 °C and 80 °C were carried out and the stress–strain relationship of the UN-5100 specimens under high- and low-temperature environments was obtained. Based on the test data, the elastic modulus and Poisson’s ratio of the UN-5100 specimens at different temperatures were calculated. Finally, the test results showed that the elastic modulus and Poisson’s ratio of the airship envelope were larger at low temperatures, indicating that the capsule is relatively safe at such temperatures. The relationships between the temperature and the mechanical properties of the airship were also summarized.

Background: Biaxial tests are important for complex mechanical behaviours of materials such as rubbers, soft materials, polymers and bio-materials, and commercial biaxial testing machines are usually expensive. Objective: For convenience and cost control, an equal-biaxial device for soft materials, with a load capacity up to 100 N and a maximum displacement of 50 mm, is designed and manufactured. Methods: A novel rope and pulley load system is applied in the designed biaxial device, and the device ensures automatically equal stress in two directions and minimizes possible installation deviation. The biaxial strain is measured from the central zone of the cruciform samples by a set of non-contact laser extensometer. Results: The device is calibrated through an array of tests for three different types of soft materials, silicon rubber, polyimide (PI) and polyethylene terephthalate (PET). The repeatability of equal-biaxial strain–stress curves of the three materials is excellent. Possible error sources of the device are examined and their respective contributions are quantified. Conclusions: Such a device offers a convenient way to carry out biaxial tests for many materials such as rubbers, polymers, and biomaterials. [ABSTRACT FROM AUTHOR]

Plastic deformation of polyethylene in uniaxial and biaxial loading conditions is studied using molecular dynamics simulation. Effects of tensile strain rates from 1 × 105 to 1 × 109 s−1, and mass density in the range of 0.923–0.926 g/cm3 on mechanical behaviour and microstructure evolution are examined. Two biaxial tensile deformation modes are considered. One is through simultaneous stretching in both the x and y directions and the other sequential stretching, firstly in the x -direction and then in the y -direction while strain in the x -direction remains constant. Tangent modulus and yield stress that are determined using the stress–strain curves from the molecular dynamics simulation show a strong dependence on the deformation mode, strain rate and mass density, and all are in good agreement with results from the experimental testing, including fracture behaviour which is ductile at a low strain rate but brittle at a high strain rate. Furthermore, the study suggests that the stress–strain curves under uniaxial tension and simultaneous biaxial tension at a relatively low strain rate contain four distinguishable regions, for elastic, yield, strain softening and strain hardening, respectively, whereas under sequential biaxial tension, stress increases monotonically with the increase of strain, without noticeable yielding, strain softening or strain hardening behaviour. The molecular dynamics simulation also suggests that an increase in the strain rate enhances the possibility of cavitation. Under simultaneous biaxial tension, with the strain rate increasing from 1 × 106 to 1 × 109 s−1, the molecular dynamics simulation shows that polyethylene failure changes from a local to a global phenomenon, accompanied by a decrease of the void size and increase of uniformity in the void distribution. Under sequential biaxial tension, on the other hand, the density of the cavities is clearly reduced. [ABSTRACT FROM AUTHOR]

The article discusses the research of the stress decrease along the warp and weft of half-woolen worsted fabrics by biaxial tension and exposure to hot air for a certain time. Based on the results of the research, mathematical models were constructed that enabled to predict a change in the stress during its relaxation after biaxial deformation during thermal fixation. It was revealed that the structural characteristics of the fabric, its composition, the amount of deformation and the duration of exposure to hot air influence the magnitude of the stress decrease. It was established that the maximum value of the stress arising in the process of stretching is observed at the greatest deformation, and the maximum stress decrease occurs when exposed to temperature for 220-300 seconds, depending on the amount of deformation and the type of fabric. Статья посвящена исследованию изменения усилий (напряжений) по основе и утку полушерстяных камвольных тканей различного волокнистого состава, возникших при их двухосной деформации, после воздействия сухого горячего воздуха в течение определенного времени. Для проведения данного исследования был применен центральный композиционный ортогональный план, позволяющий построить уравнение регрессии второго порядка для трех факторов. По результатам исследования были получены математические модели, позволяющие прогнозировать падение усилия по основе и утку тканей при их деформации по основе и утку и времени воздействия горячего воздуха, построены графики зависимости падения усилий по основе и утку от времени воздействия горячего воздуха при постоянных величинах деформаций по основе и утку, а также двумерные сечения падения усилия по основе и утку от величин деформации в обоих направлениях при постоянном времени воздействия температуры. Было выявлено, что на величину падения усилия по основе и по утку будут оказывать влияние состав, поверхностная плотность, плотность ткани по основе и утку, линейная плотность нитей основы и утка, а также величины деформации ткани по основе и утку и время воздействия горячего воздуха. Результаты исследования позволяют определить оптимальные условия проведения процесса термофиксации.

The uniaxial tensile test and Erichsen test are performed on the different deformation behavior under different stress states. The materials used in this paper had obvious anisotropy in the rolling plane because of the bimodal textures along the transverse direction. However, the Mg alloy with the weakest texture distribution did not get the better plasticity and formability, which was related to the enhanced grain boundary cohesion by more Zn addition. The rate of dislocations storage was independent of load direction for a given Mg alloy, even if Mg alloy has large in-plane anisotropy at lower stress levels. There was something different from the work hardening behavior in stage III between the ZXE0500 alloy and ZXE1500 alloy in three load directions because of the dynamic recovery. Tension twin is easier to be activated on ZXE1500 alloy rather than ZXE0500 alloy. Because the crack edge of samples used for the Erichsen test went through non-equal biaxial tensile stress, and the strain in the radial direction was much larger than that of the circumferential direction, so the texture evolution was similar to the uniaxial tensile stress. [ABSTRACT FROM AUTHOR]

Objective: This work evaluates the rate-dependent and relaxation properties of native porcine heart valves, glutaraldehyde fixed porcine pericardium, and decellularized sterilized porcine pericardium. Methods: Biaxial tension testing was performed at strain-rates of 0.001 s-1, 0.01 s-1, 0.1 s-1, and 1 s-1. Finally, relaxation testing for 300 s was performed on all heart valve biomaterials. Results: No notable rate-dependent response was observed for any of the three biomaterials with few significant differences between any strain-rates. For relaxation testing, native tissues showed the most pronounced drop in stress and glutaraldehyde the lowest drop in stress although no tissues showed anisotropy in the relaxation. Conclusions: Increasing the strain-rate of the three biomaterials considered does not increase the stress within the tissue. This indicates that there will not be increased fatigue from accelerated wear testing compared to loading at physiological strain-rates as the increase strain-rates would likely not significantly alter the tissue stress.

This paper aims to study the mechanical and electrical properties of the composite structure of PVC film and film cell under biaxial tension. The saddle PVC membrane structure with thin-film battery was obtained by biaxial tensile tests carried out on the composite structure along the fiber direction and at an angle of 45 degrees to the fiber, respectively. The deformation of the film cell and PVC membrane materials was tested using digital image technology, and the voltage of the film cell was tested using a multimeter. The results showed that the tensile strain occurred in both membrane batteries and PVC membrane at different loading levels, and the former was always less than the latter. At a tensile load with the ultimate load ratio of 60%, it was only at the film cell's outer edge that the stripping occurred. Under the illumination of a stable light source, the film cell voltage decreased gradually with the increasing tensile load. No more than 10% of the cell voltage drop occurred when the membrane material, the principal tensile strain of the cell, and the cell's expansion area ratio were less than 3.1%, 2.8%, and 1.03, respectively. The experimental results show that the film cell can be applied to the saddle membrane structure by controlling the appropriate load. [ABSTRACT FROM AUTHOR]

Two-way shear failure of slabs is a sudden one, which has catastrophic outcome. Slabs with large dimensions, may be subjected to in plane tensile forces due to restraint or earthquake loading. There is a lack of agreement between various design codes regarding the significance of in-plane tensile forces on the two-way shear strength. The purpose of this study is to explore, propose a simplified two-way shear strength model, which include the effect of in-plane tensile forces on the strength. A review for the experimental investigations, existing models, design codes for two-way shear of slabs is presented, with emphasis on in-plane tensile forces. The loading method used in the current experimental testing are misleading, where the two-way shear and the in-plane forces are independent. A comparative study was conducted between existing formula and design codes for this case. The comparison between different codes with the experimental results show that the new proposed Eurocode design code was found to be the most accurate one. However, it did not include the effect of the in-plane tensile forces in a physically sound manner. In addition, more full testing of concrete slabs under combined two-way shear and tensile forces are required to refine this existing two-way shear design code provisions or develop new formulas or mechanical model. [ABSTRACT FROM AUTHOR]

Combined cyclic tension and internal pressure tests with various proportions of each loading were run on a 2.5%Cr–1%Mo steel in air and in 3.5% NaCl solution, with and without cathodic protection to investigate the effect of positive stress biaxiality on corrosion‐fatigue lives and damage mechanisms. At free potential, a strong reduction in fatigue resistance was observed for uniaxial as well as for equibiaxial cyclic tension and attributed to multiple crack initiation from corrosion pits. Cathodic protection completely cancelled the detrimental effect of the corrosive environment on fatigue lives whatever the load biaxiality was, in spite of an obvious enhancement of intergranular fracture attributed to hydrogen embrittlement. [ABSTRACT FROM AUTHOR]

As the characterization of superplastic materials requires elevated temperatures and strain rate control, standard bulge testing procedure with optical measuring systems is not feasible for the determination of biaxial stress–strain curves. Standard superplastic bulge forming tests performed at constant pressure can be used for the identification of material constants or formability evaluation, but they are not applicable for accurate characterization of deformation behavior providing stress–strain curves at constant strain rates. The present paper is aimed to provide a technique for the direct characterization of stress–strain behavior of superplastic materials in conditions of biaxial tension. This technique is based on bulge forming testing with a closed-loop pressure control procedure allowing one to maintain the value of the effective stress at the dome pole at the predefined constant level. Thus, the variation of strain rate is reduced compared to the constant pressure testing. The results are evaluated using a double-step numerical procedure which provides the way to calculate the stress–strain curves, corresponding to constant referenced strain rates. The developed technique was used to characterize superplastic aluminum alloy Alnovi-U in conditions of biaxial tension at 500 °C. [ABSTRACT FROM AUTHOR]

The article deals with the determination of the stress state for an unbounded space in the vicinity of a cylindrical cavity (thick-walled slab with a hole), which has a cross-section of a shape close to a regular polygonal (Galin – Ivlev problem). As a model of the space material, we have used a model of the medium that takes into account the aging elastic-viscoplastic properties. The solution has been obtained within the framework of the method of a small parameter that characterizes the deviation of the hole shape from the circle, as well as the perturbation of static boundary conditions. In this case, the unperturbed state corresponds to an axisymmetric elastoplastic stress-strain state of a thick slab with a circular hole that is made of an aging elasto-viscoplastic material. As a result, analytical expressions for the stress components are obtained, as well as an equation for determining the shape and size of the interface between the domains of elastic and plastic deformation of the slab. [ABSTRACT FROM AUTHOR]

Biaxial behavior of various types of concrete is essential to be considered in construction design because construction structures normally experience multiaxial stresses rather than uniaxial stress. Research on biaxial behavior of steel fiber-reinforced concrete (SFRC) has been conducted in the past decades. Most of the research, however, is only limited to biaxial compression, whereas information regarding biaxial tension and biaxial tension-compression on SFRC is relatively scarce. This study presents a simple biaxial experimental setup to investigate the biaxial behavior of SFRC with 0.5, 1.0, and 1.5% steel fiber under biaxial tension and biaxial tension-compression. It is found that the smaller stress ratio enhanced the deformability and tensile capacity of SFRC under biaxial tension-compression, whereas the effect of stress ratio on biaxial tensile behavior of SFRC is negligible. The addition of steel fiber eventually enhanced the concrete strength by 15 to 41% under tension-compression compared with plain concrete. [ABSTRACT FROM AUTHOR]

This paper aims to study the mechanical and electrical properties of the composite structure of PVC film and film cell under biaxial tension. The saddle PVC membrane structure with thin-film battery was obtained by biaxial tensile tests carried out on the composite structure along the fiber direction and at an angle of 45 degrees to the fiber, respectively. The deformation of the film cell and PVC membrane materials was tested using digital image technology, and the voltage of the film cell was tested using a multimeter. The results showed that the tensile strain occurred in both membrane batteries and PVC membrane at different loading levels, and the former was always less than the latter. At a tensile load with the ultimate load ratio of 60%, it was only at the film cell’s outer edge that the stripping occurred. Under the illumination of a stable light source, the film cell voltage decreased gradually with the increasing tensile load. No more than 10% of the cell voltage drop occurred when the membrane material, the principal tensile strain of the cell, and the cell’s expansion area ratio were less than 3.1%, 2.8%, and 1.03, respectively. The experimental results show that the film cell can be applied to the saddle membrane structure by controlling the appropriate load.

Adverse remodeling of the left ventricle (LV) after myocardial infarction (MI) results in abnormal tissue biomechanics and impaired cardiac function, often leading to heart failure. We hypothesized that intramyocardial delivery of engineered stromal cell-derived factor 1α analog (ESA), our previously-developed supra-efficient pro-angiogenic chemokine, preserves biaxial LV mechanical properties after MI. Male Wistar rats (n = 45) underwent sham surgery (n = 15) or permanent left anterior descending coronary artery ligation. Rats sustaining MI were randomized for intramyocardial injections of either saline (100 μL, n = 15) or ESA (6 μg/kg, n = 15), delivered at four standardized borderzone sites. After 4 weeks, echocardiography was performed, and the hearts were explanted. Tensile testing of the anterolateral LV wall was performed using a displacement-controlled biaxial load frame, and modulus was determined after constitutive modeling. At 4 weeks post-MI, compared to saline controls, ESA-treated hearts had greater wall thickness (1.68 ± 0.05 mm vs 1.42 ± 0.08 mm, p = 0.008), smaller end-diastolic LV internal dimension (6.88 ± 0.29 mm vs 7.69 ± 0.22 mm, p = 0.044), and improved ejection fraction (62.8 ± 3.0% vs 49.4 ± 4.5%, p = 0.014). Histologic analysis revealed significantly reduced infarct size for ESA-treated hearts compared to saline controls (29.4 ± 2.9% vs 41.6 ± 3.1%, p = 0.021). Infarcted hearts treated with ESA exhibited decreased modulus compared to those treated with saline in both the circumferential (211.5 ± 6.9 kPa vs 264.3 ± 12.5 kPa, p = 0.001) and longitudinal axes (194.5 ± 6.5 kPa vs 258.1 ± 14.4 kPa, p < 0.001). In both principal directions, ESA-treated infarcted hearts possessed similar tissue compliance as sham non-infarcted hearts. Overall, intramyocardial ESA therapy improves post-MI ventricular remodeling and function, reduces infarct size, and preserves native LV biaxial mechanical properties. Engineered stromal cell-derived factor 1α analog (ESA) preserves the biaxial mechanical properties of myocardial tissue after infarction in rats. Image 1 • Rat left ventricular myocardium stiffens significantly by 4 weeks after infarct. • Engineered stromal cell-derived factor 1α analog is a promising angiogenic therapy. • Intramyocardial angiogenic therapy delivered at time of infarct reduces scar size. • Angiogenic therapy preserves biaxial mechanical properties at 4 weeks post-infarct. • Preserved cardiac biomechanics is associated with improved function after infarct. [ABSTRACT FROM AUTHOR]

Woven nanostructures have been acknowledged as a platform for solar cells, supercapacitors, and sensors, making them especially of interest in the fields of materials sciences, nanotechnology, and renewable energy. By employing molecular dynamics simulations, the mechanical properties of two-dimensional woven nanofabrics under biaxial tension are evaluated. Two-dimensional woven nanostructures composed of graphene and graphyne nanoribbons are examined. Dynamic failure process of both graphene woven nanofabric and graphyne woven nanofabric with the same woven unit cell initiates at the edge of interlaced ribbons accompanied by the formation of cracks near the crossover location of yarns. Further stress analysis reveals that such failure mode is attributed to the compression between two overlaced ribbons and consequently their deformation under biaxial tension, which is sensitive to the lattice structure of nanoribbon as well as the density of yarns in fabric. Systemic comparisons between nanofabrics with different yarn width and interval show that the strength of nanofabric can be effectively controlled by tuning the space interval between nanoribbons. For nanofabrics with fixed large gap spacing, the strength of fabric does not change with the ribbon width, while the strength of nanofabric with small gap spacing decreases anomalously with the increase in yarn density. Such fabric strength dependency on gap spacing is the result of the stress concentration caused by the interlace compression. The outcomes of simulation suggest that the compacted arrangement of yarns in carbon woven nanofabric structures should be avoided to achieve high strength performance. [ABSTRACT FROM AUTHOR]

Abstract With advantages of small folding volume, light weight, simple structure, low cost and so on, the flexible inflatable wing has attracted many researchers' attention. However, the change of ambient temperature has a significant influence on the bearing stress of the flexible inflatable wing. Here the typical flat inflatable wing was taken as the object, and the biaxial stress analysis and the Mises stress of the influence of the ambient temperature of the inflatable wing were constructed adopting the mechanical theory and balance principle. And the finite element simulation calculation under different ambient temperature was also performed with the theoretical model. It is found that the biaxial stress and strength of the flexible wing film are closely related to the ambient temperature, and the temperature changings will cause the wing stress to change the Mises stress distribution law of the upper and lower airfoil surfaces, and the wing skin is a two-phase plane stress state. Moreover, with the increase of the ambient temperature, the changes of the Mises stress of the wing root, middle and wingtips of the whole airfoil are inconsistent, but the overall warping deformation is improved, which provides a theoretical reference for the structural optimization design and strength analysis of the flexible inflatable wing. [ABSTRACT FROM AUTHOR]

In many engineering applications, 3D braided composites are designed for primary loading-bearing structures, and they are frequently subjected to multi-axial loading conditions during service. In this paper, a unit-cell based finite element model is developed for assessment of mechanical behavior of 3D braided composites under different biaxial tension loadings. To predict the damage initiation and evolution of braiding yarns and matrix in the unit-cell, we thus propose an anisotropic damage model based on Murakami damage theory in conjunction with Hashin failure criteria and maximum stress criteria. To attain exact stress ratio, force loading mode of periodic boundary conditions which never been attempted before is first executed to the unit-cell model to apply the biaxial tension loadings. The biaxial mechanical behaviors, such as the stress distribution, tensile modulus and tensile strength are analyzed and discussed. The damage development of 3D braided composites under typical biaxial tension loadings is simulated and the damage mechanisms are revealed in the simulation process. The present study generally provides a new reference to the meso-scale finite element analysis (FEA) of multi-axial mechanical behavior of other textile composites. [ABSTRACT FROM AUTHOR]

Uniformly dispersed graphene effectively improves the strain-sensing capability of the composite film under a low graphene load in nanocomposites prepared with polydimethylsiloxane (PDMS) and graphene (GNP) monolayer powder. The threshold concentration of graphene was determined by loading nanocomposites at different temperatures. For different concentrations, when using traditional uniaxial stretching, the rate of resistance change of films near the threshold concentration is five times higher than the rate of films with a high concentration. Compared with traditional uniaxial stretching, the biaxial stretching we introduced can effectively improve the sensitivity of the film by an order of magnitude. The change in the resistance of the film near the threshold concentration is due to the change of the tunnel length and the cross-section of the tunnel, whereas the high concentration of the film is due to the change of the conductive path inside the film. Biaxial stretching has different effects on films with different concentrations, but the final effect of increasing sensitivity is the same. This study provides guidance for improving the strain-sensing sensitivity of GNP/PDMS composite films and the application of biaxial tension in detecting human motions.

Based on the dynamic loading (1-100 s-1) experiments under different temperatures (223e298 K) and stress states, uniaxial and biaxial strength criterion of a Hydroxyl-terminated polybutadiene (HTPB) based composite solid propellant were further investigated. These experiments were conducted through the use of a new uniaxial INSTRON testing machine, different new designed gripping apparatus and samples with different configurations. According to the test results, dynamic uniaxial tensile strength criterion of the propellant was directly constructed with the master curve of the uniaxial maximum tensile stress. Whereas, a new method was proposed to determine the dynamic uniaxial compressive strength of the propellant in this study. Then uniaxial compressive strength criterion of the propellant was constructed based on the related master curve. Moreover, it found that the uniaxial tensilecompressive strength ratio of the propellant is more sensitive to loading temperature under the test conditions. The value of this parameter is about 0.4 at room temperature, and it reduces to 0.2e0.3 at low temperatures. Finally, the theoretical biaxial strength criterion of HTPB propellant under dynamic loading was constructed with the unified strength theory, the uniaxial strength and the typical biaxial tensile strength. In addition, the theoretical limit lines of the principal stress plane for the propellant under dynamic loading at different temperatures were further plotted, and the scope of the limit line increases with decreasing temperature. [ABSTRACT FROM AUTHOR]

By utilizing the modified strain energy function from Gao, uniaxial tension and biaxial tension of rubber like materials has been researched. For verification purposes, the proposed constitutive model from Gao has been implemented in a general-purpose FEA software. And then the nonlinear finite element procedure is presented for the analysis of rubber-like materials. The volumetric incompressibility condition of the deformation from rubber like materials is included in the formulation by using the penalty method. By utilizing the FEA software ABAQUS, uniaxial tension and biaxial tension model from rubber like materials have been established. In order to compare the FEA results with theoretical results, curve stress-principal stretch has been plotted with different material parameters, which indicate the correctness and rationality of theoretical analysis. In the end, analysis of cylindrical rubber membrane has been proposed based on the proposed strain energy function. The results show that the constitutive parameter n has a strengthening effect on the rubber membrane material and instability of cylindrical rubber membrane will be occur as the circumferential or longitudinal principal stretch increases. This research has revealed the deformational mechanism and provided reasonable reference for the design of rubber like materials. [ABSTRACT FROM AUTHOR]

This paper is concerned with the determination of limit loads for centrally cracked square plates subjected to biaxial tension. It briefly discusses the concept of limit loads and some aspects of numerical modelling. It presents results of numerical calculations conducted for two-dimensional (plane strain state and plane stress state) and three-dimensional cases. It also considers the relationship between the limit load and the crack length, the specimen thickness, the yield strength and the biaxial load factor, defined for the purpose of this work. The paper includes approximation formulae to calculate the limit load.