Cyclic Tensile Tests Research Articles

Strain-sensing fiber with a core–sheath structure based on carbon black/polyurethane composites for smart textiles

Fiber-shaped sensors have great potential for real-time monitoring of human physiological signals thanks to the merging of electronic and textile technologies. This work reports on the fabrication of a core–sheath structured strain-sensing fiber based on the wet-spinning method. The sensing fiber is composed of a core of non-conducting polyurethane and a conducting sheath of carbon black in a polyurethane matrix. Microscopic observation reveals the irregular shape or scattered appearance of the core as well as the porous structure of the fiber, the diameter of which is in the range 200–500 μm. The electro-mechanical properties and their dependence on carbon black concentration in the sheath and draw ratio between the spinneret and first drafting roller are experimentally investigated. It has been found that the percolation threshold of the fiber is in the range 15–16 wt%. The resistance of the fiber rises stably as the fiber is stretched up to a strain of 120% and increases with the increase of draw ratio between the spinneret and first drafting roller. In the cyclic tensile tests, the resistance of the fiber exhibits good repeatability in subsequent loading–unloading cycles after pre-stretching, despite partial recovery of the resistance in the first few cycles. The integration of the strain-sensing fiber into textiles is demonstrated by the core-spun yarn fabricated based on a modified vortex spinning method. The results of this study indicate the fiber could be a promising candidate for a sensor for smart textiles.

Experimental Analysis of Plantar Fascia Mechanical Properties in Subjects with Foot Pathologies

Plantar Fascia (PF) is a fibrous tissue that plays a key role in supporting the foot arch; it can be affected by several pathologies that can alter foot biomechanics. The present study aims at investigating the mechanical behavior of PF and evaluating possible correlations between mechanical properties and specific pathologies, namely diabetes and plantar fibromatosis (Ledderhose syndrome). PF samples were obtained from 14 human subjects, including patients with Ledderhose syndrome, patients affected by diabetes and healthy subjects. Mechanical properties of PF tissues were evaluated on three samples from each subject, by cyclic uniaxial tensile tests up to 10% of maximum strain and stress relaxation tests for 300 s, in hydrated conditions at room temperature. In tensile tests, PF exhibits non-linear stress–strain behavior, with a higher elastic modulus (up to 25–30 MPa) in patients affected by Ledderhose syndrome and diabetes with respect to healthy subjects (elastic modulus 10 ÷ 14 MPa). Stress-relaxation tests show that PF of patients affected by Ledderhose syndrome and diabetes develop more intense viscous phenomena. The results presented in this work represent the first experimental data on the tensile mechanical propertied of PF in subjects with foot diseases and can provide an insight on foot biomechanics in pathological conditions.

Yield strength estimation of X65 and X70 steel pipe with relatively low t/D ratio

During the pipe forming process, a steel plate undergoes inelastic behavior multiple times under a load condition repeating tension and compression in the circumferential direction. It derives local reduction or increase of yield strength within the thickness of steel pipes by the plastic hardening and Bauschinger effect. In this study, a combined hardening model is proposed to effectively predict variations of yield strength in the circumferential direction of API-X65 and X70 steel pipes with relatively low t/D ratio during the forming process, which is expected to experience accumulated plastic strain of 2~3%, the typical Luder band range in a low-carbon steel. Cyclic tensile tests of API-X65 and X70 steels were performed, and the parameters of the proposed model for the steels were calibrated using the test results. Bending–flattening tests to simulate repeated tension and compression during pipe forming were followed for API-X65 and X70 steels, and the results were compared with those by the proposed model and Zou et al. (2016), in order to verify the process of material model calibration based on tension–compression cyclic test, and the accuracy of the proposed model. Finally, parametric analysis for the yield strength of the steel plate in the circumferential direction of UOE pipe was conducted to investigate the effects of t/D and expansion ratios after O-forming on the yield strength. The results confirmed that the model by Zou et al. (2016) underestimated the yield strength of steel pipe with relatively low t/D ratio, and the parametric analysis showed that the t/D and expansion ratio have a significant impact on the strength of steel pipe.

Effect of strain rate history on the piezomagnetic field of ferromagnetic steels

The goal of this research is to investigate the effect of strain rate history on the piezomagnetic behavior of ferromagnetic steels. Cyclic tensile tests were carried out to record the magnetic fields on the surfaces of Q345 and X80 steel specimens. The impacts of different strain rate histories on the magnetic signals were investigated and the evolutions of piezomagnetic fields of Q345 and X80 steels are closely related to the strain rate history. The magnetic fields demonstrate a systematic evolution when the strain rate history increases from 0.03 min−1 to 0.3 min−1. When the strain rate history decreases from 0.3 min−1 to 0.03 min−1, the magnetic fields remain relatively stable. The results were explained by the movement of magnetic domains and the strength of pinning sites induced by the external stress. This study shows that strain rate history should be considered as one of the variables that influence the piezomagnetic field of ferromagnetic steels.

A Biologically Muscle‐Inspired Polyurethane with Super‐Tough, Thermal Reparable and Self‐Healing Capabilities for Stretchable Electronics

AbstractPolymeric elastomers play an increasingly important role in the development of stretchable electronics. A highly demanded elastic matrix is preferred to own not only excellent mechanical properties, but also additional features like high toughness and fast self‐healing. Here, a polyurethane (DA‐PU) is synthesized with donor and acceptor groups alternately distributed along the main chain to achieve both intra‐chain and inter‐chain donor‐acceptor self‐assembly, which endow the polyurethane with toughness, self‐healing, and, more interestingly, thermal repair, like human muscle. In detail, DA‐PU exhibits an amazing mechanical performance with elongation at break of 1900% and toughness of 175.9 MJ m−3. Moreover, it shows remarkable anti‐fatigue and anti‐stress relaxation properties as manifested by cyclic tensile and stress relaxation tests, respectively. Even in case of large strain deformation or long‐time stretch, it can almost completely restore to original length by thermal repair at 60 °C in 60 s. The self‐healing speed of DA‐PU is gradually enhanced with the increasing temperature, and can be 1.0–6.15 µm min−1 from 60 to 80 °C. At last, a stretchable and self‐healable capacitive sensor is constructed and evaluated to prove that DA‐PU matrix can ensure the stability of electronics even after critical deformation and cut off.

Engineering mechanical properties by controlling the microstructure of an Fe–Ni–Mn martensitic steel through pre-cold rolling and subsequent heat treatment

Experiments were conducted to examine the effects of prior cold rolling and subsequent heat treatment on the microstructure, phase evolution and mechanical properties of an Fe–10Ni–7Mn martensitic steel. The results show that 70% cold rolling leads to deformation-induced austenite formation in the microstructure and reduces the size of the martensite blocks. Prior cold rolling increases the reversed austenite volume fraction under post-deformation intercritical annealing (PDIA) at 600 °C compared with the solution annealed condition. Electron back scattering diffraction and dilatometric studies showed that under PDIA there is a reverse transformation of martensite to austenite through a sequential combination of martensitic and diffusional mechanisms. There is also a precipitation of θ-NiMn particles in the PDIA specimen after subsequent ageing leading to an increase in the ultimate tensile strength in tensile testing. Cyclic tensile testing revealed pseudoelastic behavior in the cold-rolled specimen but this disappeared after PDIA and appeared again after subsequent ageing. • Cold rolling produces deformation-induced austenite formation and also refines the martensite blocks. • The prior austenite and the smaller martensite blocks are the primary potential sites for austenite nucleation during PDIA. • Ultimate tensile strength improves from ~695 MPa for the solution annealed sample to ~1215 MPa for the PDIA processed specimen followed by ageing. • Observed pseudoelasticity in the cold rolled specimen disappears after PDIA. • Pseudoelasticity appears again in the PDIA processed specimen followed by ageing.

Self-adaptive multiblock-copolymer-based hybrid solid-state electrolyte for safe and stable lithium-metal battery

The dramatic volume change during the Li plating/stripping process has aroused brittle solid electrolyte interphase as well as weak interfacial compatibility between electrolyte and electrode, which results in capacity fading and safety hazards. We design elastic multiblock copolymers (mBCPs) with excellent extensibility up to 600% to address this problem. The best recovery rate of mBCP is 82% after 100 times of cyclic tensile tests. The mBCPs are regarded as elastomers that enable close contact with electrode surface during cycling. The elastic mBCPs are then mixed with lithium salt and high ionic conductivity inorganic ceramics to prepare hybrid solid-state electrolytes (HSSEs). The HSSEs are expected to possess self-adaptive property making good interfacial connection due to the mBCPs. The best HSSEs demonstrate high ionic conductivity of 0.14 mS cm−1 with a Li ion transference number of 0.55 and wide electrochemical window of 5.2 V at 25°C. Excellent cycling performance with long battery life is achieved by utilizing the self-adaptive HSSE: the Li metal electrode cycled for 150 times retains 96% coulombic efficiency in Li/HSSE/LiFePO4 cells, and stable cycling of 500 h is achieved in the symmetric cells.

A comprehensive insight into the superelasticity measurement of laser welded NiTi shape memory alloys

In this work, superelastic response of laser welded NiTi wires were studied using nanoindentations and cyclic tensile tests. At high power laser condition ~0.4 wt% of Ni content evaporated, which resulted in the formation of the martensite phase due to about 40 °C shift in the Af temperature. This caused in 500 nm residual depth after the cyclic load-unload nanoindentation test and 1.9% residual strain after the cyclic tensile test, both signs of superelasticity deterioration. However, by adopting the possible lowest power laser condition, these parameters became 200 nm and 1%, respectively. By increasing the cyclic tensile test temperature to 60 °C (above Af), similar superelastic responses were achieved due to the elimination of any unfavorable martensite phases inside their fusion zones.

Seismic performance of steel columns corroded in general atmosphere

Steel structures exposed to general atmosphere for a long time are highly susceptible to corrosion damage, which would lead to the degradation of service performance of the components and even structures. This article focuses on the effect of corrosion on the seismic performance of steel column. The accelerated corrosion tests in general atmosphere were conducted on 7 H-shaped steel columns and 20 steel plates. Then the obtained plate specimens were subjected to monotonic tensile tests and cyclic loading tests, and the steel columns were subjected to pseudo-static tests, respectively, to study the effects of corrosion on their mechanical properties and seismic performance. Then, a simplified three-dimensional finite element model (FEM) capable of accurately simulating the hysteretic response of corroded steel columns under low-cycle loading was established. Experimental results indicated that the yield strength, tensile strength, elastic modulus and peak strain of corroded steel plate decreased linearly with the proposed corrosion damage parameter Dn, and the energy dissipations under low-cycle loading were significantly reduced. There is a correlation between the cyclic hardening parameters of corroded steel and the yield-tensile strength difference (SD), and then a simplified formula was proposed. Corrosion could result in the premature entrance of each loading stage of corroded columns and the deterioration of buckling deformation range, bearing capacity and energy dissipation, etc. In addition, a larger axial compression ratio (CR) would further accelerate the failure process of corroded columns. The parametric finite element analysis (FEA) indicated that greater damage was found for steel columns with non-uniform corrosion, and hysteretic performance degraded more significantly when corrosion distributed at flanges or foot zone.

Experimental and Numerical Analysis of the Mechanical Properties of a Pretreated Shape Memory Alloy Wire in a Self-Centering Steel Brace

As a stimulus-sensitive material, the difference in composition, fabrication process, and influencing factors will have a great effect on the mechanical properties of a superelastic Ni-Ti shape memory alloy (SMA) wire, so the seismic performance of the self-centering steel brace with SMA wires may not be accurately obtained. In this paper, the cyclic tensile tests of a kind of SMA wire with a 1 mm diameter and special element composition were tested under multi-working conditions, which were pretreated by first tensioning to the 0.06 strain amplitude for 40 cycles, so the mechanical properties of the pretreated SMA wires can be simulated in detail. The accuracy of the numerical results with the improved model of Graesser’s theory was verified by a comparison to the experimental results. The experimental results show that the number of cycles has no significant effect on the mechanical properties of SMA wires after a certain number of cyclic tensile training. With the loading rate increasing, the pinch effect of the hysteresis curves will be enlarged, while the effective elastic modulus and slope of the transformation stresses in the process of loading and unloading are also increased, and the maximum energy dissipation capacity of the SMA wires appears at a loading rate of 0.675 mm/s. Moreover, with the initial strain increasing, the slope of the transformation stresses in the process of loading is increased, while the effective elastic modulus and slope of the transformation stresses in the process of unloading are decreased, and the maximum energy dissipation capacity appears at the initial strain of 0.0075. In addition, a good agreement between the test and numerical results is obtained by comparing with the hysteresis curves and energy dissipation values, so the numerical model is useful to predict the stress–strain relations at different stages. The test and numerical results will also provide a basis for the design of corresponding self-centering steel dampers.

Rate dependent free energy formulations for dynamically excited superelastic SMA wires

AbstractSuperelastic shape memory alloys (SMAs) are metallic two‐phase polycrystal alloys. The transformation between austenite and martensite phases allows superelastic SMAs unique hysteretic energy dissipation capacity, which is particularly interesting for the development of new‐type of intelligent vibration control systems for structures. However, in structural control, most of the vibrations occur in high strain rate regimes, which interfere the release of self‐generated heat and cause atomic lattice destabilization and thus influence the hysteretic dissipation. The present work proposes two different strain rate dependent free energy formulations and aims to improve the accuracy of existing one‐dimensional macroscopic models of SMA wires. The approaches are developed and implemented in different continuum thermomechanical frameworks, without impairing the simplicity and robustness of the solution process. The first approach introduces an additional control variable for the entropy evolution. The second approach uses a phenomenological formulation of the latent heat evolution. The proposed formulations are validated by cyclic tensile tests conducted on SMA wires. The results show that the calculations using the new formulations can represent the superelastic SMA wire response more accurately.

Poly(glyceryl sebacate)/silk fibroin small-diameter artificial blood vessels with good elasticity and compliance

Small-diameter artificial blood vessels do not match the compliance of the host blood vessels after transplantation, will directly affect the blood compatibility of small-diameter artificial blood vessels and resulting in problems such as thrombosis and intimal hyperplasia that can lead to transplantation failure. Since the compliance of small-diameter artificial blood vessels is directly related to the elasticity of the component materials, the poly(glyceryl sebacate) (PGS), a type of bioelastomer, and silk fibroin (SF) were blended to fabricate small-diameter artificial blood vessels by electrospinning. The morphology, structure, elasticity, tensile properties, suture retention strength, compliance, and in vitro degradation and biological properties of the samples were studied. Results showed that the small-diameter artificial blood vessel samples were composed of micro-fibers or nano-fibers, and had satisfactory compliance and elasticity. The compliance of the PGS/SF (70/30) samples was 3.58 %/100 ​mmHg, which were higher than or comparable to natural blood vessels. The results of radial cyclic tensile tests showed that the energy loss per cycle of PGS/SF tubular samples was very low. Adding PGS accelerated the degradation rate of small-diameter artificial blood vessel samples, and PGS/SF electrospun small-diameter artificial blood vessel samples promoted the adhesion and proliferation of human umbilical vein endothelial cells (HUVECs). The samples’ anticoagulant performance were also increased after adding heparin. PGS/SF blends have potential advantages in the preparation of small-diameter artificial blood vessels that can meet the requirements of elasticity and compliance.

A Constitutive Model for Alginate-Based Double Network Hydrogels Cross-Linked by Mono-, Di-, and Trivalent Cations

In this contribution, a micro-mechanically based constitutive model is proposed to describe the nonlinear inelastic rubber-like features of alginate-based double network hydrogel cross-linked via various counterions. To this end, the lengthening of the polysaccharide polymer chain after a fully stretched state is characterized. A polymer chain is firstly considered behaving entropically up to the fully stretched state. Then, enthalpic behavior is accounted for concerning the following lengthening. To calculate enthalpic behavior, the macroscopic material properties, such as elastic modulus, are integrated into the proposed model. Thus, a new energy concept for a polymer chain is proposed. The model is constituted by the proposed energy concept, the network decomposition model, the Arruda–Boyce eight chain model and the network alteration theory. The model is compared against the cyclic tensile test data of alginate-based double network hydrogels cross-linked via mono-, di-, and trivalent cations. Good agreement between the model and experiments is obtained.

Analysis of tensile behavior of recycled aggregate concrete using acoustic emission technique

Recycled concrete aggregate (RCA) was processed from reinforced concrete edge beams sourced from a demolished bridge. This material replaced different ratios of coarse aggregate in a benchmark concrete. The tensile behavior of the developed concrete mixes was characterized via monotonic and cyclic uniaxial tensile tests performed on notched cylinders. Such tensile tests allow for the quantification of the fracture energy and softening behavior of the concrete. Moreover, acoustic emission (AE) measurements were conducted in conjunction with the cyclic tests to characterize e.g. micro-crack initiation and development, as well as crack localization. The tensile behavior of the various materials was found to be similar with minimal variation in the results. However, the softening behavior suggests that the RCA materials are slightly more brittle compared to both the mother and benchmark materials. The corresponding AE measurements also indicated similarities between the micro-crack initiation and development for these mixes. It can be constituted that if the concrete used to produce RCA is of high quality and from one source, the resulting RAC will have adequate tensile properties with minimal variation, despite the aggregate replacement ratio.

A Lattice-misfit-dependent Micromechanical Approach in Ni-based Single Crystal Superalloys

In Ni-based single crystal superalloys, the macroscopic properties are intertwined with their complex bi-phased γ (NiAl)/γ’ (Ni3Al) microstructure. This study aims to better understand the coupled effect of lattice misfit and microstructural state on the macro-scale performance by utilizing a faithful representation of the microstructure, via a phase-field model, as a starting point for a micromechanical model embedded in a finite-element crystal plasticity framework. We outlined a micromechanical model with a lattice-misfit-dependent isotropic hardening that takes a unique description depending on the phase: an Eshelby tensor (sphere or penny) for the precipitates (γ’ phase) and a continuous medium for the matrix (γ phase). Finite-element simulations of strain-controlled monotonic tensile and alternate cyclic tests were performed on a set of realistic 3D phase-field microstructures (cuboidal states and directionally coarsened rafted states) defined by their natural (undeformed) or constrained (deformed) lattice misfits and the width of the γ matrix channels. As the magnitude of the natural lattice misfit gets larger for the cuboidal microstructural states, the tensile test simulations predict smaller macroscopic yield stress and strain hardening as well as smaller stress triaxiality at the microstructure level. The model also predicts that having a more pronounced rafted microstructure yields a smaller stress triaxiality at the microscale. The cyclic simulations showed that the averaged stress triaxiality at the microscale during five simulated cycles is the smallest for a natural lattice misfit of -0.3% and a 60% completed rafting process. These insights allow to better understand the experimental studies that investigated the effect of microstructural states on the mechanical response during monotonic and cyclic loading.

The effect of high-pressure torsion on the microstructure and outstanding pseudoelasticity of a ternary Fe–Ni–Mn shape memory alloy

Abstract Experiments were conducted to examine the effect of high-pressure torsion (HPT) processing on the microstructure and pseudoelastic behavior of a ternary Fe–10Ni–7Mn (wt.%) shape memory alloy in both the solution-annealed and intercritically-annealed conditions. X-ray diffraction (XRD) patterns and electron backscatter diffraction (EBSD) analyses showed that the initial microstructure of the alloy in the solution-annealed condition was a fully lath α′-martensite which partially transformed to a strain-induced austenite (α′→γ) by HPT processing. Also, the austenite formed in the dual phase (α′+γ) specimens after intercritical annealing treatment at 600 °C for 7.2 ks underwent a γ→e→α′ transformation during subsequent HPT processing such that a multi-phase microstructure was formed consisting of α′-martensite, austenite and e-martensite. The HPT processing led to a significant increase in the microhardness value to ~690 Hv due to a high density of dislocations and the associated grain refinement of the microstructure. Cyclic loading-unloading tensile tests at room temperature revealed a strain hysteresis and pseudoelastic behavior in the HPT-processed specimens with different initial microstructures. Outstanding pseudoelasticity values of about 67% and 75% were obtained at the fourteenth loading-unloading cycle after 20 HPT turns in the solution-annealed and intercritically-annealed specimens, respectively.

Strain rate dependent formulation of the latent heat evolution of superelastic shape memory alloy wires incorporated in multistory frame structures

Due to their unique hysteretic energy dissipation capacity, shape memory alloy (SMA) wires are particularly interesting for the development of new-type of intelligent vibration control systems for structures. However, in structural control, most of the vibrations occur in high strain rate regimes, which interfere the release of self-generated heat and thus influence the hysteretic dissipation. This paper proposes a strain rate dependent formulation of the latent heat evolution and aims to improve the accuracy of existing macroscopic modeling approaches developed for SMA wires particularly for the dynamic load cases. The proposed formulation is determined phenomenologically and implemented in a continuum thermomechanical framework based constitutive SMA wire model without impairing the simplicity and robustness of the solution process. The proposed formulation is validated by cyclic tensile tests conducted on SMA wires. Results show that the calculations using the formulation can predict the wire response more accurately than the strain rate independent formulation. For the simulation of multistory frame structures incorporating multiple SMA wires, the governing equations are driven. Shaking table tests are conducted on a 3-story frame structure under harmonic and seismic excitation. The responses of the structure are successfully replicated using the strain rate dependent latent heat formulation.

Fatigue and Tensile Properties of Aramid Fibers Measured by Single Fiber Mechanical Tests

Aramid fibers, with superior mechanical properties, have been widely used in a lot of industrial fields. From a safety point of view, long-term durability is required for these aramid fibers. In this study, the fatigue and tensile properties of two types of single aramid fibers, poly(para-phenylene terephthalamide) (PPTA) and poly(para-phenylene-co-3,4′-oxydiphenylene terephthalamide) (PPODTA), were investigated. Single fiber tensile and fatigue tests, cyclic tensile tests, tensile tests for post-fatigue test specimens, and optical microscopic observations were conducted. The stress–strain curves of the cyclic tensile tests indicated that PPTA and PPODTA fibers could be deformed above the elastic limit, and the strain at 2.0 GPa stress and the initial tensile modulus in subsequent tensile tests were changed by the cyclic stress. In fatigue tests, the cumulative probabilities of fatigue failure increased with the number of stress cycles for both the PPTA and PPODTA fibers. The fatigue behavior was influenced by the stress conditions and gauge length of the specimens. The initial tensile modulus in subsequent tensile tests was increased by the fatigue tests for both the PPTA and PPODTA fibers. However, regarding the tensile strength, significant decreases due to the fatigue tests were not observed. Fibrils detached from the fiber surface were observed in the post-fatigue test PPTA and PPODTA fiber specimens by optical microscope observations, with the loss of these fibrils contributing to the changes in modulus.

Shear driven deformation and damage mechanisms in High-performance carbon Fibre-reinforced thermoplastic and toughened thermoset composites subjected to high strain loading

High strain loading response of high-performance aerospace grade polyether-ether-ketone (PEEK) and toughened epoxy carbon fibre-reinforced composites has been investigated in pre-impregnated laminates having identical carbon fibre volume fraction, i.e. nearly 65%. Tensile cyclic loading tests have been carried out on the laminates with [±45°]8S stacking sequence, in order to characterise inelastic (plasticity) parameters for the two laminates progressively up to high strains (up to 11% strains), in correlation with the fibre and matrix micro-scale deformation and damage characteristics. The most suitable processes to achieve ultimate mechanical performance were used for manufacturing of the laminates. It has been observed that the PEEK composite exhibits higher mechanical performance at high strains under cyclic loads compared to epoxy composites (150% ultimate failure strain, 380% strain hardening and 200% ultimate failure stress) due to having superior micro-scale shear deformation in PEEK attributed to interfacial strength of fibre–matrix prior to the ultimate failure, as opposed to extensive micro-cracking, coalescence and fibre–matrix debonding in the epoxy composite.

Hysteretic behavior and cyclic constitutive model of corroded structural steel under general atmospheric environment

To study the hysteretic behavior of corroded steel under cyclic loading, corrosion morphology tests, monotonic tensile tests and cyclic loading tests were conducted on 7 groups of accelerated corrosion specimens and 10 groups of natural corrosion specimens. A new corrosion damage parameter Dn for corrosion degree evaluation and mechanical properties prediction and an extracting method based on corrosion morphology were proposed. It was found that corrosion reduced the strength, ductility and hysteretic energy of steel, and the degradation law of monotonic/hysteretic performance with corrosion damage parameter Dn was obtained. By analyzing the degradation laws of material parameters in classical combined hardening model with the corrosion degree and studying the relationship between the material parameters in monotonic and cyclic loading conditions, a plastic constitutive model of corroded steel was established. The simulated stress-strain curves of corroded steel were in good agreement with the experimental data, indicating that the proposed model successfully simulated the monotonic/cyclic loading performance of corroded steel.