Small Strain Range Research Articles

A photocurable ultra-tough eutectic gel with coordination crosslinking used for wearable sensors and TENG flexible electrodes

Flexible polymer molecular chains are of great interest to researchers in the field of flexible wearable electronics due to their unrivaled flexibility and ductility. However, achieving high toughness, high elasticity, environmental stability and easy machining of flexible electronic materials remains a challenge. In this study, we present a photocurable eutectic gel mainly composed of DMAPS, AAc, Zr4+ and deep eutectic solvents (DES). Due to the strong coordination between zirconium ions and polymer networks, the gel can be endowed with excellent properties, such as excellent tensile strength (1.14 MPa), low hysteresis (5 kJ·m−3) and good adhesion (above 40 kPa). DES can not only give the gel good electrical conductivity, but also maintain the stability of the gel to ensure that the leakage or volatilization of the solvent will not occur in use. The properties mentioned above allow the gel to achieve a sensitivity factor of up to 1.7 over a small strain range, demonstrating its potential applications in the field of flexible strain sensors and triboelectric flexible electrode materials. What’s more, the gel can be used to prepare complex geometric shapes with high precision through digital light processing (DLP) based 3D printing technology. Therefore, this work introduces a novel approach for the development of highly stable flexible wearable devices, which has the potential to expand the applications of eutectic gels.

Investigation of Gnetum Gnemon and Ramie Natural Fiber on the Mechanical Properties of Composites with the Combination of Aramid and Carbon Fiber as Reinforcement for Military Personnel Applications

Every equipment infrastructure in a TNI unit will be needed to support an operation in the defence system to maintain the integrity of the Unitary State of the Republic of Indonesia. Personal protective equipment is needed for a war operation’s safety or continuity. Protective components made from composite fibers have the advantage of being resistant to corrosion caused by the environment. The natural and carbon fibers will be mixed/reinforced with epoxy resin to become composite materials. This study aims to identify Gnetum Gnemon fiber composites with carbon fiber and aramid fiber to determine the mechanical properties of the composite material resulting from a collision. Natural fiber Gnetum gnemon has not been widely studied as a reinforcing material for polymer composites. Gnetum gnemon fiber chemical composition is hemicellulose approx. 25%, 40% alpha cellulose, 10% lignin and 3-5% benzene extractive. Its density is quite light, 1.2087 g/cm³ - 1.8069 g/cm³. Because this fiber has a continuous fiber structure and a strong natural weave, its use is still minimal. Special treatment such as alkali treatment on Gnetum gnemon, can increase the strength of natural fibers. Due to its exceptional mechanical properties, Kevlar or aramid fibre are extensively used in industrial and military applications. The aramid fiber exhibited a transversely anisotropic nature in a small strain range, with its stress-strain behavior as linear and elastic. The anisotropic nature of the aramid fiber was due to its high tensile-to-shear modulus ratio. The high strength and modulus were also found to be scattered due to the larger distribution of defects in the longer fiber. Epoxy resin is a type of polymer characterized often by one or more epoxide functional groups, with at least one of the epoxide functional groups acting as a monomer and terminal unit of the polymer within the structural chain.

Experimental Study on the Mechanical Properties of Nano-Silicon-Modified Polyurethane Crack Repair Materials

This study aims to solve the problem of dynamic crack repair in concrete. Although conventional polyurethane has good strength, its tensile and shear properties are poor. It was found that nano-silicon had an overall enhancing effect on the mechanical properties of polyurethane; therefore, five sets of tests with different dosages (0%, 2%, 5%, 7.5%, and 10%) were designed. The compressive, tensile, and shear mechanical properties of nano-silicon-modified polyurethanes were tested by compression, tensile, and straight shear tests, and the microscopic appearance of the materials was observed by scanning electron microscopy. The results showed that nano-silicon could enhance the mechanical properties of polyurethane. The best filling effect on polyurethane was achieved at a dosage of 5%, which increased the compressive, tensile, and shear strengths by 29.4%, 257.6%, and 202.1%, respectively, compared with the substrate. The compressive and tensile moduli in the small strain range were enhanced by 268.5% and 511.8%, respectively. After exceeding 5%, the mechanical properties of the materials decreased due to the enhanced nanoparticle agglomeration effect, which led to the appearance of voids inside the materials. The comprehensive analysis shows that nano-silicon can better enhance the mechanical properties of polyurethane with an optimal dosage of 5%, which is stronger relative to other repair materials and does not require time maintenance.

Uniaxial carbon nanotube fiber reinforced dielectric elastomer actuator with self-sensing

Compared to the isotropic dielectric elastomer (DE), uniaxial fiber reinforced DEs have larger deformation capabilities in specific directions, showing great application prospects. However, there are still significant challenges in achieving self-sensing without introducing additional sensing components. Inspired by the control method of biological muscles, in this article, we used carbon nanotube (CNT) fibers as reinforcing fibers that resistance changes are highly sensitive to tensile strain and exhibit a linear relationship within a small strain range. Based on the developed uniaxial reinforced strain behavior model of DEs, a shear lag model was adopted to introduce an interface transition layer between the DEs and CNT fiber to consider the strain difference caused by the difference in elastic modulus. The relationship between CNT fiber strain and DE strain was established, and the influence of CNT fiber mechanical properties on self-sensing performance was explored. The verification results under 0.05 Hz, 20 kV/mm signals show that the model has 4 % error, providing new ideas for the self-sensing function of uniaxial fiber reinforced DEs.

Estimating Hardening Soil-Brick model parameters for sands based on CPTU tests and laboratory experimental evidence

The Hardening Soil-Brick model for soils is designed to carry out complex numerical analyses of soil-structure interaction problems taking into account strong stiffness variation in the range of small strains. However, to calibrate its parameters advanced triaxial and oedometric tests are required. In case of uncemented sands laboratory testing is usually difficult. Therefore, to facilitate calibration procedures, a CPTU based method, enhanced by an experimental evidence derived from advanced triaxial drained and oedometric tests, has been proposed and verified. It is shown in the paper that using exclusively the CPTU test results one can calibrate most important model parameters for sands with accuracy that is sufficient for solving real life problems. The major goal of this paper is to identify correlations between all reference stiffness moduli, then verify them, and finally link with the CPTU based identification procedures. It is shown in the paper that such correlations exist and they exhibit very high coefficients of determination. Moreover, as the seismic version of the CPTU test is not often available in the practice, an enhanced procedure for identification of very small strain shear stiffness modulus has been proposed and then verified, using set of the SCPTU tests conducted in Gdańsk sands (Poland).

Dynamic Properties of Undisturbed Guiyang Red Clay in the Small-Strain Range

Dynamic Properties of Undisturbed Guiyang Red Clay in the Small-Strain Range

Auxetic Two‐Phase Chevron Mechanical Metamaterial

This investigation explores novel two‐phase chevron mechanical metamaterials that exhibit auxetic properties. Unlike traditional foam‐like cellular or porous auxetic materials, these designs are composed of chevron patterned layers embedded in anisotropic matrix. This innovation design allows for auxeticity in two orthogonal in‐plane directions (bi‐auxeticity) or in all in‐plane directions (complete auxeticity), providing not only a general strategy but also detailed guidelines for designing non‐porous auxetic mechanical metamaterials with tunable auxetic behaviors. One goal of this work is to explore the mechanical behavior, specifically effective stiffness and Poisson's ratio, of these new designs and to identify the design space for auxetic behavior using numerical and experimental methods. Systematic finite element (FE) simulations are conducted using ABAQUS and Python scripts to quantify effective stiffness and Poisson's ratio within a small strain range. To validate the numerical predictions, three representative designs are selected and fabricated via multi‐material polymer jetting. Uniaxial tension experiments are conducted on these specimens. Design spaces for non‐auxeticity, partial‐auxeticity, and complete auxeticity are identified through an integrated numerical approach. Theoretical criteria for determining the completeness of auxeticity are proposed and verified via FE simulations.

A non-linear stress–strain relationship for soil and rock

While many employ a hyperbolic stress–strain relationship for soils, it is known that such a relationship is accurate over the small-strain range as encountered in earthquake and soil dynamics problems. For large strains, a relationship with different input parameters is needed, as is required for finite-element analyses of large-deformation behaviour. These separate characterisations do not carry over into the other application. Here, a proposed power relationship is presented that was developed to characterise the triaxial test stress–strain behaviour of cohesionless material from lubricated or ‘frictionless’ cap and base tests (144 tests) covering a range in the natural variation in particle size, particle shape and surface roughness, over low to high confining pressure. This relationship covers the strain range from 10−6 to soil failure. To date, it has been successfully used in laterally loaded pile response characterisation (the strain wedge model) and shallow-foundation load–settlement–bearing capacity response. Most recently, it has been extended to assess the behaviour of rock-like material (caliche). The relationship and its comparison with the hyperbolic relationship for large strain and the shear modulus reduction curve for seismic behaviour are presented.

Computational Evaluation of Weaving Process on Mechanical Stiffness of Plain Weave Fabric

Inherent structural stress in a plain weave is induced during the formation process of fabrics, and its evaluation is useful for estimating the mechanical stiffness of weaves. In this study, the effect of inherent stress distributed in a weave fabric was investigated to estimate its mechanical stiffness. Here, a numerical simulation method that imitates the fabrication process of fabrics is proposed to evaluate stiffness. A diagram illustrating the weaving process is defined in this evaluation method. For computational analysis, a unit cell model used in homogenization was developed based on the structural periodicity of the plain weave structure using the finite element method. The weaving state was accomplished by simulating the weaving behavior in this model. The weaving state included the geometric shape and stress/strain data. Subsequently, a model was built to estimate the mechanical stiffness based on the weaving state data. Finally, a uniaxial tensile simulation was conducted using the numerical model. Using this evaluation method, the effect of inherent stress on the mechanical stiffness of weaves was quantified, which indicated that the tensile stiffness improved in a small strain range. The effect gradually decreased as the tension progressed.

Influence of Static and Repeated Surface Surcharge Loadings on Tunnel Displacement Considering Small-Strain Stiffness of Soft Clay

With the rapid development of urban metro tunnels, the effect of surface surcharge loading on existing tunnels is unavoidable. Accurate evaluation of soil deformation and tunnel displacement under surface surcharge loading is of great significance for practical engineering. In this research, the effect of static and repeated surface surcharge loadings on tunnel displacement in soft clay was investigated numerically. The hardening soil model with small-strain stiffness (HSS model) was adopted to simulate the soil response. The parameters of the HSS model were obtained through geotechnical tests. The result indicates that Shanghai layer 4 soft clay exhibits large soil shear stiffness in the small strain range. Tunnel displacement is closely related to parameters of surface surcharge loading width, burial depth of tunnel, and the horizontal distance from the centerline. The overlapping influence range of tunnel displacement was proposed. Under repeated surface surcharge loadings, the first cycle of the repeated surface surcharge loading has the greatest effect on the tunnel displacement, and the subsequent cycles of loadings still cause further increases in the tunnel displacement. The effect of repeated surface surcharge loadings on tunnel displacement gradually decreases as the burial depth of tunnel and the number of cycles increase.

Dynamic Shear Responses of Combined Contaminated Soil Treated with Nano Zero-Valent Iron (nZVI) under Controlled Moisture

Nano zero-valent iron (nZVI) technologies have gained recognition for the remediation of heavily contaminated sites and reused as backfilling soil. The moisture environment at these sites not only impacts the reactions and reactivity of nZVI but also the dynamic responses of compacted backfilled soils. The research explored the effects of different nZVI dosages (0.2%, 0.5%, 1%, 2%, and 5%) on Lead-Zinc-Nickel ions contaminated soil under a controlled-moisture condition. Cyclic triaxial tests were performed to evaluate the dynamic responses of treated soil samples prepared using a consistent moisture compaction method. Particle size distribution and Atterberg limits tests assessed changes in particle size and plasticity. The study revealed a minor reduction in the particle size, liquid limit, plastic limit, and plasticity index of the contaminated soil. Notably, increasing nZVI dosages in treated soils led to growing Atterberg limits. An increase in the specific sand fraction of treated soils was observed with nZVI, suggesting nanoparticles–soil aggregations favoring existing larger particles. Stepwise loading cyclic triaxial tests indicated an optimal dynamic response of soil treated with 1% nZVI under the controlled-moisture condition, proven by notable enhancements in the maximum shear modulus, maximum shear stress, less shear strain, and higher damping ratio within the small strain range. It should be noted that moisture content in treated soils declined significantly with higher nZVI dosages during preparation, potentially impeding effective aggregation and the formation of a solid soil skeleton. These findings advance the importance of considering the balanced nZVI dosage and moisture content when employing the safety assessment of practical applications in both nano-remediation techniques and soil mechanics.

Curve beam for strengthening the negative Poisson's ratio effect of rotating auxetic metamaterial: Experiments and simulations

This article described a three-dimensional lattice design method for customizing the negative Poisson’s ratio effect in a rotating rigid structure. By using bent beams as the basic building blocks of the lattice, a new class of curved beam rotating auxetic (CBRA) lattice was proposed. Through a combination of numerical simulations and experimental tests, the mechanical responses of representative three-dimensional auxetic lattice structures under compressive load were systematically studied, including Poisson’s ratio, energy absorption, and a multi-stage deformation mode that facilitated the tuning of mechanical properties. Additionally, the influence of structural geometric parameters on the elastic performance was discussed in detail. Unlike most rotating auxetic materials that could only achieve the negative Poisson’s ratio effect within a small strain range, the results demonstrated that the uniform Poisson’s ratio of the proposed three-dimensional lattice structure could achieve positive and negative adjustment within a strain range of 0–0.5. The design flexibility would contribute to making it a promising candidate for industrial and biomedical applications, such as scaffolds and skin grafts. The acceleration of the application of new three-dimensional expandable lattice structures in engineering applications made this system more versatile than similar non-graded systems.

Experimental Study of Hardening Small Strain Model Parameters for Strata Typical of Zhengzhou and Their Application in Foundation Pit Engineering

The hardening small strain (HSS) model, which considers the non-linear characteristics of the shear modulus of soil in the small strain range, is commonly utilized in the numerical analysis of excavations in sensitive environments. In order to ascertain the parameters of an HSS model for strata typical of Zhengzhou, an extensive series of laboratory tests was executed. Subsequently, a statistical analysis was utilized to establish the relationships between the principal parameters. A three-dimensional finite element model was established based on the excavation of representative strata in Zhengzhou. The accuracy and applicability of the model parameters were verified using the field measurement data. In addition, an analysis of the sensitivity of the main HSS model parameters to the foundation pit deformation was also carried out. The results show that the HSS model can analyze excavation deformation with greater precision than the hardening soil (HS) model or the Mohr–Coulomb (MC) model. The small strain parameters G0ref and γ0.7 have a great influence on the horizontal displacement of the support and the vertical displacement of soil behind the wall, respectively. The research results serve as a reliable foundation for both the analysis of excavation deformation and the determination of HSS model parameters for strata typical of Zhengzhou.

Nacre-Inspired MXene Nanocomposite-based Strain Sensor with Ultrahigh Sensitivity in a Small Strain Range for Parkinson's Disease Diagnosis.

Nowadays, chronic diseases are the primary threat to public health and are getting younger. By taking the advantages of continuousness, convenience, and real-time response, wearable strain sensors have been given great attention to diagnose chronic diseases via analyzing the patient's health state. However, most physiological signals, such as limb tremor of Parkinson's disease, microexpression, and slight joint movement, are tiny and difficult to be detected. Therefore, the development of strain sensors characterized with ultrahigh sensitivity in a small strain range (ε < 10%) is urgent. Inspired by nacre's hierarchical structure, we have fabricated nacre-mimetic nanocomposites with "brick-and-mortar" architecture by employing polyacrylamide (PAM) and Ti3C2Tx MXene nanosheets through a layer-by-layer (LBL) spin-coating technique. The resultant nanocomposite-based strain sensor exhibits ultrahigh sensitivity in a small strain range (GF = 296.8, ε < 10%), attributed to the bioinspired hierarchical structure and hydrogen bond-enhanced interfacial interactions. In addition, a high reliability, broad working sensing range (453%), short response time (183 ms), skin-like tensile stress (7.2 MPa), and excellent durability (2000 cycles) are also achieved. Due to the ultrahigh sensitivity within a small strain, the reported strain sensor can accurately diagnose and distinguish Parkinson's disease symptoms, including thumb pill-rolling tremor, masked face (microexpression), intermittent shaking of the head, and limb cogwheel motion. This work provides new insights to design strain sensors with high sensitivity for monitoring tiny signals and for disease diagnosis.

Comparison of anisotropic yield functions and calibrations for accurate thickness prediction in hole expansion test

The hole expansion test is an appropriate evaluation method for assessing the formability of automotive parts, where fracture prediction using simulated localized thickness is crucial. However, the accurate thickness prediction in the hole expansion test remains challenging. In this study, the selection of yield functions and calibration strategies were investigated to accurately predict the thickness of advanced high-strength steel subjected to the hole expansion test. An accurate description of the material anisotropy is important for thickness prediction because of the generation of various multiaxial stress states. To describe plastic anisotropy, a series of uniaxial tension, bulge, and in-plane biaxial tension tests were conducted on DP980 steel. Because conventional biaxial tension tests for DP980 steel showed a small strain range owing to its low ductility, a new laser-welding-reinforced biaxial tension test was developed to investigate the anisotropy of the plane strain at large strains. Differences in the ratio of the plastic strain rates were observed between the conventional and new tests. Finally, a hole expansion test and corresponding finite element simulations were conducted with different yield functions and calibrations for the Yld2000-2d yield function. The thickness strain profiles along the hole circumference and 3 mm inward were measured and predicted using simulations. In conclusion, both the yield stress and the ratio of plastic strain rates in the plane strain state were equally important for accurate thickness prediction during the DP980 hole expansion test. Furthermore, the crack location was inconsistent with the thinnest region in the experiment, which might be because of the shear fracture anisotropy encountered in DP980 steel.

High throughput construction for the deformation mechanism diagram and dynamic recrystallization of a bimodal‐sized particle‐reinforced Ti‐2.5Zr‐2Al‐1(Si,C) titanium alloy

AbstractAn in situ autogenous particle‐reinforced Ti‐2.5Zr‐2Al‐1(Si,C) titanium alloy is prepared by vacuum induction melting. The wide range of an effective strain between 0.2 and 1.2 and the corresponding microstructure are obtained by the double‐cone high‐throughput compression test and finite element simulation. The deformation mechanism diagram with strains of 0.2–1.2 and strain rates of 0.7–1.5 s−1 at 900°C is constructed. When the strain rate is 1.3 s−1, dynamic recovery occurs in the small strain range (&lt;0.377), dynamic recrystallization (DRX) occurs in the medium strain range (0.377–1.182), and deformation instability occurs in the large strain range (&gt;1.182), resulting in the deformation bands. High‐angle annular dark field and high‐resolution transmission electron microscopy are used to determine the existence of bimodal particle distribution, namely micron‐scale TiC particles and nano‐scale Ti5Si3 and (Zr, Si) particles. The average radius of the (Zr, Si) nanoparticles measured by small angle neutron scattering is 19.3 nm, and the volume fraction is 0.35%. DRX grains with an average size of 0.49 μm are obtained at 900°C, strain rate of 1.3 s−1, and strain of about 0.6. Micron‐scale particles stimulated DRX nucleation, while nanoscale particles hindered the growth of new grains, resulting in grain refinement.

Chemically derived graphene quantum dots for high-strain sensing

Graphene quantum dots (GQDs) refer to graphene fragments with a lateral dimension typically less than 100 nm, which possess unique electrical and optical properties due to the quantum confinement effect. In this study, we demonstrate that chemically derived graphene quantum dots show great potential for making highly stretchable and cost-effective strain sensors via an electron tunneling mechanism. Stretchable strain sensors are critical devices for the field of flexible or wearable electronics which are expected to maintain function up to high strain values (> 30%). However, strain sensors based on conventional materials (i.e. metal or semiconductors) or metal nanoparticles (e.g. gold or silver nanoparticles) only work within a small range of strain (i.e. the former have a working range < 1% and the latter < 3%). In this study, by simply dropcasting solution-processed GQDs between the interdigitated electrodes on polydimethylsiloxane, we obtained devices that can function in the range from 0.06% to over 50% tensile strain with both the sensitivity and working range conveniently adjustable by the concentration of GQDs applied. This study provides a new concept for practical applications of GQDs, revealing the potential of this material for smart applications such as artificial skin, human-machine interfaces, and health monitoring.

Some remarks on the performance of three advanced soil constitutive models in the small-strain region

ABSTRACT This short communication identifies some inconsistencies in the numerical predictions of three advanced soil constitutive models. The chosen constitutive models are subject to simple numerical tests in the small-strain range relevant to the cyclic response of soil in seismic, offshore and urban applications. The numerical tests comprise a cyclic simple shear test in the small-strain range, a simple shear test with very small strain unloading-reloading loops and a test on the dependence of the rate of the shear stiffness degradation on the changing mean confining stress. The results are briefly discussed and, in some cases, the reasons for the observed inconsistencies and potential improvements in the formulations of the investigated constitutive models are initially drafted.

Experimental Research on the Dynamic Characteristics of Several Model Soils in Small Strain Range and Application in Shaking Table Model Test

Reasonable model soil is very important in shaking table model tests to reduce the distortion of the soil structure stiffness ratio. Several model soils, such as sawdust soil, sawdust sand, rubber granular soil, rubber powder soil, and sawdust kaolin were prepared and a dynamic triaxial test proceeded to determine their dynamic characteristics. The experimental results showed that the variation of the dynamic shear modulus and dynamic damping ratio with dynamic shear strain was consistent with that of undisturbed soil. Finally, sawdust soil was adapted to a shaking table test of complex interaction systems and achieved good results. The results showed that sawdust soil is feasible as model soil. The research results can provide helpful references for the design of a similar shaking model test.

Compressive Strain Sensing Elastic Foam Based on Sericin Dispersed Carbon Nanotubes

The flexible strain sensor can transform the micro or macro deformation into the visual electrical signals for monitoring the physiological and motor characteristics of human body. However, the current commercial strain sensors generally have some shortcomings such as large stiffness and small strain range. In this work, a flexible compressive strain sensor with the 3D conductive network was fabricated by using biomacromolecule sericin protein dispersed carbon nanotubes (SSCNTs) as the conductive material and melamine foam (MF) as the elastic matrix. The results showed that the sensitivity of MF/SSCNTs elastic foam was 1.36 in the strain range of 0-70% with the CNTs content of 10 wt% and the cyclic compressive sensing performance was stable for at least 1600 cycles. This kind of flexible compressive strain sensor is environmentally friendly, low cost, simple process, and provides a new method for the preparation of green flexible sensor.