Stress Hysteresis Research Articles

Mechanical properties of CFRP and shrinkage compensating concrete actively confined and strengthened short columns under freeze–thaw cycles

AbstractThis paper investigates the use of CFRP precast tubes filled with shrinkage‐compensating self‐consolidating concrete (SSCC) for strengthening columns. Compared to ordinary self‐consolidating concrete (OSCC), SSCC can address the stress hysteresis issue caused by the poor cooperation between CFRP and concrete structures, while also enhancing the mechanical properties of columns. Experimental and theoretical studies were conducted to examine the tensile mechanical properties of CFRP materials and the axial compressive mechanical properties of CFRP precast tubes strengthened with OSCC or SSCC under freeze–thaw cycles. Various variables were considered, such as freeze–thaw cycles, types of strengthening concrete, and the number of CFRP layers. The results indicate that freeze–thaw cycles do not affect the ultimate tensile strength of CFRP but significantly reduce its ultimate tensile strain. SSCC‐strengthened specimens exhibit higher load‐carrying capacity and better ductility compared to OSCC‐strengthened specimens. In addition, compared to the strengthening of two‐layer CFRP and SSCC, the strengthening of one‐layer CFRP and SSCC more effectively demonstrates the advantage of the post‐tensioning effect. However, the ductility coefficient of the columns decreases with an increase in the number of freeze–thaw cycles, regardless of the number of CFRP layers or type of strengthened concrete. Modified theoretical model accurately predicts the normalized peak stress and strain of the strengthened specimens.

Elastocaloric effect of NiTi shape memory alloys manufactured by laser powder bed fusion

To address the challenges posed by the complex processing of NiTi alloys, the additive manufacturing technology has been employed for the preparation of NiTi alloys samples. Up to now, there is limited research on the elastocaloric effects of NiTi alloys manufactured by LPBF. This study focused on the utilization of laser powder bed fusion (LPBF) to fabricate NiTi samples, with a particular emphasis on the influence of laser power, scanning speed and hatch spacing on the microstructure and properties of NiTi alloys. The results indicated that the process parameters affect the stress hysteresis of superelasticity by influencing the Ni content in the NiTi alloys. The higher Ni content, the lower the stress hysteresis. In addition, the critical stress for plastic deformation of the texture in the <001> direction in NiTi alloys is the smallest. When only the P was changed, the proportion of the texture in the <001> direction in the sample increased with the increase of P, the proportion of plastic deformation increased, and the degree of recovery also gradually decreased. Furthermore, at a specific temperature, 10 K higher than the end temperature of austenite transformation, each sample exhibited good superelasticity. In particular, the 1st cooling capacity of the sample with the best elastocaloric effect reached 11.0 K, which was superior to other results obtained by LPBF under similar compressive strain levels.

Quasi-linear superelasticity and associated elastocaloric effect in boron-doped polycrystalline Ni-Mn-Ti alloys

Ni-Mn-Ti shape memory alloys show great potential in solid-state elastocaloric cooling owing to very prominent elastocaloric effect along with first-order stress-induced martensitic transformation. However, large stress hysteresis inherent to martensitic transformation greatly restricts the energy efficiency and cyclic stability of elastocaloric response. Here, we demonstrate the effective manipulation of stress hysteresis as well as the resulting elastocaloric effect through doping boron to Ni-Mn-Ti alloys. With the incremental boron content in (Ni50Mn31Ti19)100–xBx (x = 0, 0.2, 0.5, 1, 1.5) alloys, a plateau-type superelastic behavior with large stress hysteresis gradually evolves into a quasi-linear one with slim hysteresis, giving rise to significant improvement in the energy conversion efficiency of elastocaloric response. In a (Ni50Mn31Ti19)99B1 alloy, the coefficient of performance of material (COPmat) can be as high as 24 ∼ 33. Moreover, under a compressive strain of 4%, large cooling |ΔTad| values higher than 6.5 K in the (Ni50Mn31Ti19)99B1 alloy are maintained for over 8000 superelastic cycles, showing an enhancement of one order of magnitude in the cyclability with respect to that of boron-free Ni50Mn31Ti19 alloy. We attribute the enhanced elasocaloric response to the significantly improved mechanical properties but reduced stress hysteresis endowed by relatively high content of boron doping.

A Study on the Bearing Performance of an RC Axial Compression Shear Wall Strengthened by a Replacement Method Using Local Reinforcement with an Unsupported Roof

When compared with conventional replacement reinforcement methods, the method of replacement using a local reinforcement with an unsupported roof has the advantages of shortening the reinforcement cycle and reducing material loss, and many scholars have carried out useful explorations thereof. At present, the formula for the bearing capacity of reinforcement by replacing concrete in the Code does not consider the effect of stress hysteresis on the parts of the reinforcement; so when the initial stress level is greater than 0.4, the Code’s strength utilization coefficient of 0.8 for the new concrete in the replaced area is on the side of insecurity. In this study, we are trying to improve and supplement the formula in the Code through the following work. Firstly, 18 groups of shear wall models were constructed using a VFEAP finite element analysis program to analyze the bearing performances of the shear walls after the replacement. The results showed that the replacement concrete strength, the initial stress level and the size of the replaced area had a significant influence on the bearing capacity of the shear wall after the replacement. Secondly, utilizing the replacement concrete strength, the initial stress level and the size of the replacement area as key parameters, then introducing the strength improvement coefficient considering the constraints of the stirrups, the modified strength utilization coefficient of new concrete in the replaced area was formulated. Finally, based on the modified strength utilization coefficient, the replacement bearing capacity formulas for the one-batch, two-batch, and three-batch replacements were derived, and an N-batch replacement bearing capacity formula was regressed and fitted on the basis of these equations, which are less discrete and more secure than the Code’s formula.

Ultrastretchable, Ultralow Hysteresis, High-Toughness Hydrogel Strain Sensor for Pressure Recognition with Deep Learning.

Hydrogel, as a promising material for a wide range of applications, has demonstrated considerable potential for use in flexible wearable devices and engineering technologies. However, simultaneously realizing the ultrastretchability, low hysteresis, and high toughness of hydrogels is still a great challenge. Here, we present a dual physically cross-linked polyacrylamide (PAM)/sodium hyaluronate (HA)/montmorillonite (MMT) hydrogel. The introduction of HA increases the degree of chain entanglement, and the addition of MMT acts as a stress dissipation center and cross-linking agent, resulting in a hydrogel with high toughness and low hysteretic properties. This hydrogel synthesized by a simple strategy exhibited ultrahigh stretchability (3165%), high breaking stress (228 kPa), high toughness (4.149 MJ/m3), and ultralow hysteresis (≈2% at 100% of strain). The fabricated hydrogel flexible strain sensors possessed fast response and recovery times (62.5:75 ms), a wide strain detection range (2000%), a strain detection limit of 1%, and excellent cycling stability over 500 cycles. Furthermore, the hydrogel flexible strain sensor can be used for human motion monitoring, gesture recognition, and pressure recognition assisted by deep learning algorithms, showing enormous promise for applications.

Axial stress-strain behavior of pre-stressed CFRP confined concrete columns

Bonded carbon fiber reinforced polymer (CFRP) confined concrete presents issues such as stress hysteresis and easy detachment at the interface between CFRP and concrete. Applying prestress to CFRP can improve this situation. To investigate the stress-strain behavior of prestressed CFRP strengthened plain concrete columns (PC) under axial compression, a total of 1 unreinforced concrete column, 9 bonded CFRP strengthened concrete columns, and 27 prestressed CFRP strengthened concrete columns were designed. Including CFRP layers and the level of prestress were taken as the study factors, and axial compression tests were conducted on each specimen to analyze their axial compression performance. The test results indicated that applying prestress to CFRP results in the core concrete being constantly subjected to triaxial compression, with initial transverse compressive strain and longitudinal tensile strain, thereby increasing the initial stiffness of the core concrete. In contrast to bonded CFRP-strengthened columns, the ultimate axial stress, ultimate axial strain, and initial stiffness of prestressed CFRP-strengthened columns increased with the level of CFRP prestress, with a more pronounced improvement observed in columns wrapped with a higher number of layers of CFRP. For a 4-layer CFRP strengthened column prestressed at 0.3, the ultimate axial stress and ultimate axial strain increased by up to 13 % and 20 %, respectively, compared to bonded 4-layer CFRP strengthened columns, with the initial stiffness increasing by up to 30 %. On the other hand, applying prestress to CFRP can significantly enhance the effective utilization of CFRP, but it is negatively correlated with the number of CFRP layers. Compared to bonded 1-layer CFRP strengthened columns, the effective utilization rate increased from 0.63 to 0.91, a 44 % increase, when prestressing CFRP at 0.3. Finally, based on existing relevant research, a peak stress and strain model considering the ratio of confinement stiffness to strain ratio was proposed. Based on the fundamental assumptions of curve analysis, the design-oriented axial stress-strain model suitable for prestressed CFRP strengthened concrete columns was established, with good match between theoretical and experimental curves.

A one‐dimensional phenomenological constitutive model of shape memory alloys considering the cyclic degradation of two‐way memory effect

AbstractThis study introduces a one‐dimensional phenomenological constitutive model designed to describe two‐way shape memory effect (TWSME) and its associated cyclic degradation. The model utilizes the logistic function to formulate the phase transformation equation, incorporates the expansion of key parameters into their respective fatigue functions to characterize the fatigue phenomenon, and integrates a phase transformation rate regulation function into the differential form of the phase transformation equation. This integration facilitates the control over the entire phase transformation process and the simulation of incomplete transformations. The model is distinguished by its comprehensive functionality, simple form, ease of calculation, and the clear and direct influence of key parameters. Furthermore, it offers a degree of flexibility because each function within the framework is replaceable. The simulation of the TWSME strain and recovery stress hysteresis loop deformation has been successfully conducted, enabling the description of internal hysteresis loops caused by incomplete transformation. The validity of the model is corroborated by comparing it with existing experimental results.

Superelasticity with narrow stress hysteresis and high cyclic stability in Co–V–Al polycrystalline alloy

Superelasticity of shape memory alloy associated with the martensitic transformation is extremely attractive for applications in sensors and biomedical. This application requires narrow stress hysteresis to reduce energy dissipation and a stable superelasticity cycle is an important factor in their practical applications. Co–V–Al alloys have inimitable advantages due to their narrow stress hysteresis, low-cost, and corrosion resistance, but the low number of superelasticity cycles restricts its development. Here, we report an intrinsic Co58V29Al13 polycrystalline alloy with a superelasticity stress hysteresis of 30 MPa at room temperature, the lowest among the alloys in this system, and a superelasticity strain of 3.6%. In addition, the sample shows no significant decay trend after 500 loading and unloading cycles. The high number of superelasticity cycles is mainly due to the elastic stress field generated around the dislocation during the cycle, which provides internal stress for martensite nucleation and reduces energy dissipation during martensitic transformation. This work provides essential guiding significance for the design of high-performance superelasticity alloys.

Accelerated learning and co-optimization of elastocaloric effect and stress hysteresis of elastocaloric alloys

Accelerated learning and co-optimization of elastocaloric effect and stress hysteresis of elastocaloric alloys

Enhancing elastocaloric performance: Ti-doped Co–V-Ga bulk polycrystalline alloys with minimal stress hysteresis

Currently, practical applications of shape memory alloy (SMA) solid elastocaloric refrigeration materials are limited by low elastocaloric effect (eCE), high applied stress, and large stress hysteresis (Δσhys). Here, we introduce a composition design strategy using Ti-doped Co–V-Ga SMAs to address these challenges. We combine first-principles calculations and experiments to verify this strategy. Our results show that the lattice distortion caused by the significant difference in atomic radius after Ti doping produces a solid solution strengthening effect inside the alloy, which significantly improves the superelasticity of the alloy, delays the plastic deformation of the austenite phase, and the volume fraction of martensitic transformation increases significantly. The newly developed Co51.7V31.3Ga16Ti1 bulk polycrystalline alloy exhibits a remarkable adiabatic temperature change (ΔTad) of −10 K at room temperature under a low stress of 400 MPa, a minimum Δσhys of 18 MPa, and a high coefficient of performance COPmat of 31.9. Importantly, the 100-cycle loading-unloading test at 350 MPa is done, and it reveals that the ΔTad for the Ti0 alloy was only 3.9 K, while it reached 6.2 K for the Ti1 alloy, marking a noteworthy 59 % performance enhancement. From the simplicity of the fabrication process to the comprehensive performance of the material, it exhibits a promising advantage for practical cooling applications This study presents a feasible design strategy for large-scale production of high-performance bulk polycrystalline alloys with high eCE, low stress, and Δσhys.

Helicopter vibration control employing superelastic pitch link with shape memory alloy

One of the main applications of shape memory alloy (SMA) concerns vibration control, especially superelastic SMA (SMA-SE), which presents a significant stress hysteresis and can work as a damper while adding minimal weight to the structure. In helicopters, vibration is a phenomenon inherent to their operation, and although cannot be eliminated, must be minimized to acceptable levels of safety and comfort. In this context, this paper aims to present the design, testing, and dynamic behavior of a new device entitled smart pitch link, a device with superelastic material for passive vibration control. The paper depicts the design process, assembly, and device testing using a whirl tower that simulates a helicopter rotor in hover. The approach adopts a comparative analysis of the dynamic response on the prototype in reference condition, with a stiff pitch link, with the modified prototype, and with the superelastic pitch link installation. In addition, beyond hover tests, cyclic commands and an asymmetrical lateral gust were employed to observe the output response of the device under transient loadings. Contrary to the literature data about the low time response of SMA, the device presents satisfactory time response and attenuation in frequencies close to main rotor frequencies, with signal attenuations between 2 to 4 dB without any external energy consumption, which, in a comparative analysis, may exceed more than 50% of vibrational amplitude attenuation.

A Semi‐Interpenetrating Poly(Ionic Liquid) Network‐Driven Low Hysteresis and Transparent Hydrogel as a Self‐Powered Multifunctional Sensor

AbstractConductive hydrogels are gaining significant attention as promising candidates for the fabrication materials for flexible electronics. Nevertheless, improving the tensile properties, hysteresis, durability, adhesion, and electrochemical properties of these hydrogels remains challenging. This work reports the development of a novel semi‐interpenetrating network poly(ionic liquid) hydrogel named PATV, via the in situ polymerization of acrylamide, N‐[Tris(hydroxymethyl)methyl] acrylamide, and 1‐vinyl‐3‐butylimidazolium tetrafluoroborate. The density functional theory calculations reveal that the poly(ionic liquid) in the hydrogel network acts as physical cross–linking points to construct hydrogen‐bond networks. Furthermore, the hydrogen‐bond networks dissipate energy efficiently and quickly, and thus stress concentration and hysteresis are avoided. The prepared hydrogel has a low hysteresis (9%), high tensile properties (900%), fast response (180 ms), high sensitivity (gauge factor = 10.4, pressure sensitivity = 0.14 kPa−1), and wide sensing range (tensile range: 1–600%, compression range: 0.1–20 kPa). A multifunctional sensor designed based on the designed hydrogel enables real‐time, rapid, and stable response‐ability for the detection of human movement, facial expression recognition, pronunciation, pulse, handwriting, and Morse code encryption. Furthermore, the assembled triboelectric nanogenerator displays an excellent energy harvesting capability, thus highlighting its potential application in self‐powered flexible wearable electronic devices.

Reversible reorientation of martensite variants in stress-induced martensite aged Co35Ni35Al30 single crystals

The paper reports the temperature dependence of the reversible reorientation of martensite variants during loading/unloading along the [001]B2||[001]L10-direction in compression in stress-induced martensite (SIM) aged at 423 K for 0.5 h under a compressive stress of 500 MPa applied along the [110]B2||[100]L10-direction Co35Ni35Al30 single crystals. A wide temperature range of reversible strain from 203 K to 413 K (210 K) is observed due to the stabilisation of the tetragonal L10-martensite variant V1 ([001]B2||[001]L10) during SIM-aging in these single crystals. The reversible strain in the range of 157 K (203 K<Tt<As=Af=360 K) is because of the reorientation of the L10-martensite variants V1-V2/V3. The superelasticity at Tt>Af=360 K occurred due to the stress-induced B2-L10(V2/V3) martensitic transformation (MT). Rubber-like behaviour develops in the range of 52 K (203 K<Tt<Mf*=255 K) and is characterised by a narrow stress hysteresis of 13 MPa and a reversible strain of −12.0 % due to the movement of the twinning boundaries (reversible twinning) in L10-martensite. The reversible strain reaches −10.2 % in the temperature range from Mf*=255 K to As=Af=360 K. This strain is associated with a new mechanism of L10-martensite variant reorientation, which occurs through a sequence of reverse and forward stress-induced L10(V1)-B2-L10(V2/V3) MTs and leads to the stages on the stress–strain curves. The reverse L10(V1)-B2 MT at loading and forward B2-L10(V1) MT at unloading on the first stage of the stress–strain curves are characterised by low critical stresses of 8–23 MPa, a narrow stress hysteresis of 3–19 MPa and a completely reversible strain of −6.0 %, which is stable for 100 loading/unloading cycles.

Effect of burst-type martensitic transformation on superelastic and elastocaloric properties in a 〈116〉 oriented Cu70.5Al17.5Mn12 single crystal

We report the occurrence of stress-induced burst-type martensitic transformation in a 〈116〉A oriented Cu70.5Al17.5Mn12 single crystal. The burst-type transformation is observed in the reverse transformation of unloading from 250 K to 370 K in tension, showing strong coupling with plastic deformation in the temperature range between 310 K and 370 K. Such coupling greatly exacerbates the stress hysteresis and energy dissipation in association with the stress-induced transformation, resulting in a significant enhancement in the mechanical damping and degradation in the elastocaloric response. In particular, the merit index for damping exhibits a remarkably high value of 0.903 at 370 K, demonstrating the huge potential of coupled burst-type transformation and plastic deformation in manipulating damping properties. Moreover, it is evidenced that the microstructural evolution of burst-type transformation greatly deviates from that of the thermoelastic transformation.

Large Cyclability of Elastocaloric Effect in Highly Porous Ni-Fe-Ga Foams.

Solid-state refrigeration based on elastocaloric materials (eCMs) requires reversibility and repeatability. However, the intrinsic intergranular brittleness of ferromagnetic shape memory alloys (FMSMAs) limits fatigue life and, thus, is the crucial bottleneck for its industrial applications. Significant cyclic stability of elastocaloric effects (eCE) via 53% porosity in Ni-Fe-Ga FMSMA has already been proven. Here, Ni-Fe-Ga foams (single-/hierarchical pores) with high porosity of 64% and 73% via tailoring the material's architecture to optimize the eCE performances are studied. A completely reversible superelastic behavior at room temperature (297 K) is demonstrated in high porosity (64-73%) Ni-Fe-Ga foams with small stress hysteresis, which is greatly conducive to durable fatigue life. Consequentially, hierarchical pore foam with 64% porosity exhibits a maximum reversible ∆Tad of 2.0 K at much lower stress of 45 MPa with a large COPmat of 34. Moreover, it shows stable elastocaloric behavior (ΔTad = 2.0 K) over >300 superelastic cycles with no significant deterioration. The enhanced eCE cyclability can be attributed to the pore hierarchies, which remarkably reduce the grain boundary constraints and/or limit the propagation of cracks to induce multiple stress-induced martensitic transformations (MTs). Therefore, this work paves the way for designing durable fatigue life FMSMAs as promising eCMs by manipulating the material architectures.

High yield stress and narrow phase transformation hysteresis of thermomechanical-processing NiTiCu shape memory alloy

NiTiCu shape memory alloy is subjected to thermomechanical processing which deals with local canning compression followed by annealing at 300, 450 and 600 °C, respectively. Transformation temperatures of annealed NiTiCu specimens increase with elevating annealing temperature. Following annealing at 300 °C, NiTiCu specimen exhibits high yield stress of about 2000 MPa due to the existence of nanocrystalline grains. NiTiCu sample annealed at 600 °C possesses an extremely narrow phase transformation hysteresis width of about 1 °C. Nanotwins are found in NiTiCu sample annealed at 300 °C, while a large number of twin variants appear in NiTiCu samples annealed at 450 and 600 °C. Nanocrystalline grains contribute to suppressing the occurrence of twin variants. Furthermore, nanocrystalline grains are not beneficial to the formation of martensite variants. In the case of compressive loading, martensite reorientation and detwinning take place more readily in NiTiCu samples annealed at 450 and 600 °C.

Experimental characterization and constitutive modeling of thermoplastic polyurethane under complex uniaxial loading

This paper presents the testing and constitutive modeling of a Thermoplastic Polyurethane (TPU) compound used in commercial applications. The tested specimens were extracted directly from a TPU sphere used in check valves through water-jet cutting. The tests included tensile and compression tests under complex uniaxial loading protocols to capture different nonlinear phenomena, such as stress softening, hysteresis, relaxation, creep, and rate dependence. The material is modeled assuming a nonlinear elastic equilibrium path that may exhibit stress softening (i.e., Mullins effect), and a hysteretic viscoplastic response that presents rate dependence at three different time scales. To achieve this constitutive behavior, a Parallel Rheological Framework model is used. The nonlinear elastic equilibrium path is modeled using the generalized Yeoh hyperelastic model. The stress softening of the equilibrium path is modeled using the Ogden-Roxburgh damage model on the deviatoric response. The hysteretic viscous response is further split into three viscoplastic chains to represent time dependence at three different time scales in a decoupled way. Each viscoplastic chain is modeled using the Bergstrom-Boyce model with its standard evolution law of the creep strain. The model parameters were found using a stochastic optimization scheme to simultaneously fit all the considered tests. The outstanding agreement between the model and the experimental data across a wide range of loading scenarios provides additional insight into the time-dependent behavior and deformation mechanism of TPUs. Moreover, it shows that the mechanical behavior of these materials can be represented by decoupling the nonlinear viscoplastic behavior in different time scales.

Enhanced superelasticity and reversible elastocaloric effect in nano-grained NiTi alloys with low stress hysteresis

Solid-state cooling technologies have been considered as potential alternatives for vapor compression cooling systems. The search for refrigeration materials displaying a unique combination of pronounced caloric effect, low hysteresis, and high reversibility on phase transformation was very active in recent years. Here, we achieved increase in the elastocaloric reversibility and decrease in the friction dissipation of martensite transformations in the superelastic nano-grained NiTi alloys obtained by cold rolling and annealing treatment, with very low stress hysteresis (6.3 MPa) under a large applied strain (5%). Large adiabatic temperature changes (ΔT max = 16.3 K at ε = 5%) and moderate COPmater values (maximum COPmater = 11.8 at ε = 2%) were achieved. The present nano-grained NiTi alloys exhibited great potential for applications as a highly efficient elastocaloric material.

Room-temperature elastocaloric effect in Co49Ni21Ga30 shape memory wires

We demonstrate appreciable room-temperature elastocaloric effect in the Co49Ni21Ga30 microwires prepared using the Taylor-Ulitovsky method. By forming an almost excellent [001]B2-oriented single crystal along the wire axis, extraordinary superelasticity with low critical stress and narrow stress hysteresis was achieved. Moreover, the wire exhibits room-temperature elastocaloric effect (ΔTad = −4.1 K) with no apparent degradation for 100 cycles. Due to its easy fabrication and the small scale, the wire is of great potential for advanced applications in miniature intelligent devices requiring refrigeration. This work also paves the way for developing other high-performance shape memory wires.

A 3D viscoelastic–viscoplastic behavior of carbon nanotube‐reinforced polymers: Constitutive model and experimental characterization

AbstractDue to the widespread use of carbon nanotube (CNT)‐reinforced polymers in various industries, investigating the dynamic mechanical response of these materials under impact loading is of significant importance. A three‐dimensional viscoelastic (VE)–viscoplastic (VP) constitutive model for CNT/epoxy nanocomposites is developed. A proper rheological model is established using the generalized Maxwell model to represent the VE behavior and propose an exponential function to express the elasto‐VP response. Employing an empirical logarithmic relationship to estimate material properties at different strain rates, the VP behavior is modeled based on the overstress concept. The 3D numerical discretization of the proposed rate‐dependent material model is also carried out to develop a user‐defined material model (UMAT) for the commercial finite element (FE) software of Abaqus. The performed FE simulations based on the proposed rate‐dependent constitutive material can properly capture stress relaxation and hysteresis behaviors of the nanocomposites. Comparing the estimated tensile and shear stress–strain curves through developed material models with experimental measurements, an excellent agreement is observed.Highlights Tensile/shear properties of CNT/epoxy are measured at three strain rates. An empirical constitutive model is proposed for any arbitrary strain rates Viscoplastic behavior is captured based on over‐stress concept A 3D incremental form of a viscoelastic–viscoplastic material model is developed.