Limited Strain Range Research Articles

Transient Dual‐Response Iontronic Strain Sensor Based on Gelatin and Cellulose Nanocrystals Eutectogel Nanocomposites

AbstractThe emergence of wearable strain sensors in soft electronics has the potential to revolutionize healthcare and robotics. However, current sensors are based on petroleum‐based conductive composites that have a limited strain range. Ionic conductors such as hydrogels offer expanded strain range but have poor long‐term stability and restricted temperature operating window. Deep eutectic solvents (DESs) are promising nonaqueous electrolytes alternatives with green credentials. By combining DES electrolytes with biopolymers, transient ionic conductors are developed with high stretchability, and excellent chemical and thermal stability. Herein, cellulose nanocrystals (CNC) are incorporated, bearing ─OSO3H or ─COOH groups, to gelatin‐based eutectogels to produce nanocomposites with enhanced properties and additional functionalities. The eutectogel nanocomposite containing 1.0 wt.% COOH‐CNC demonstrate enhanced stretchability (375%) and ionic conductivity (3.0 mS cm−1) compared to the pristine gelatin‐based eutectogel (300% strain and 2.0 mS cm−1, respectively). Moreover, the spontaneous assembly of CNC within the eutectogel results in birefringence, which changes when stretching the nanocomposites. Thus, CNC incorporation provides the gelatin‐based eutectogel with a dual‐response capabilities when stretched, expanding their applications to new areas such as transient multi‐responsive strain sensors for wearable electronics, and multifunctional substrates for soft robotics, without compromising overall performance or sustainability.

Advantageous Strain Sensing Performances of FBG Strain Sensors Equipped with Planar UV-Curable Resin.

The existing optical strain sensors based on fiber Bragg grating (FBG) have limitations, such as a complex structure, a limited strain range (±200 με) and poor linearity performance (R-squared value < 0.9920); these limitations affect their potential practical applications. Here, four FBG strain sensors equipped with planar UV-curable resin are investigated. The proposed FBG strain sensors have a simple structure, a large strain range (±1800 με) and excellent linearity performance (R-squared value ≥ 0.9998); they further produce the following performances: (1) good optical properties, including an undistorted Bragg peak shape, narrow bandwidth (-3 dB bandwidth ≤ 0.65 nm) and a high side mode suppression ratio (SMSR, the absolute value of SMSR ≥ 15 dB); (2) good temperature sensing properties with high temperature sensitivities (≥47.7 pm/°C) and a good linearity performance (R-squared value ≥ 0.9990); and (3) excellent strain sensing properties with no hysteresis behavior (hysteresis error ≤ 0.058%) and excellent repeatability (repeatability error ≤ 0.045%). Based on their excellent properties, the proposed FBG strain sensors are expected to be applied as high-performance strain sensing devices.

Novel Isotropic Anti-Tri-Missing Rib Auxetics with Prescribed In-Plane Mechanical Properties Over Large Deformations

Analogy with the standard anti-tri-chiral auxetic structure, a novel anti-tri-missing rib structure is proposed in this work. Finite element (FE) analyses (on one unit-cell) were carried out first to investigate the auxeticity and the underlying deformation mechanisms of the proposed structure with linear elastic base material. FE results show that the structure exhibits constant NPR over a relatively large strain range at few specific orientations. However, its auxetic behavior is inconspicuous and the in-plane isotropy only holds over limited strain range owing to the deficient rotational mechanism. An enhanced design with increased interior angle of the ligament and triangle reinforcement within the rotational central core was then proposed to improve the auxeticity and its in-plane isotropy. A theoretical formulation of the elastic modulus and Poisson’s ratio for the enhanced design was further developed based on Castigliano’s theorem. Tunable elastic modulus in the linear elastic regime and controllable isotropic constant NPRs over large strain ranges were thus achieved for the enhanced design without significantly compromising the overall stiffness. The targeted NPR performances were also verified with nonlinear base materials. Uniaxial tensile experiments and finite size simulations for lattice structures comprising an array of enhanced anti-tri-missing rib unit cells were finally performed to validate the FE and theoretical results obtained from unit-cell analyses.

Evaluación de la capacidad de carga de tubos de hormigón reforzado con fibras híbridas

En las últimas décadas, se ha extendido el uso de un solo tipo de fibras, ya sean de acero o sintéticas, como refuerzo del hormigón en tubos premoldeados. Sin embargo, el hormigón tiene comportamiento a la fractura en múltiples escalas y un tipo de fibra proporciona refuerzo solo en un nivel y dentro de un rango limitado de deformaciones. Por ello, un refuerzo más eficiente podría lograrse utilizando la combinación de fibras de diferentes materiales, geometría y/o características mecánicas. El hormigón reforzado con dos o más tipos de fibras, combinadas racionalmente, se denomina Hormigón Reforzado con Fibras Híbridas (HRFH). En este trabajo, se presentan los resultados de una campaña experimental en la que se estudió la capacidad de carga de tubos de HRFH (THRFH), sometidos al ensayo de compresión diametral de tres aristas. Los resultados se comparan con los obtenidos para tubos de hormigón con refuerzo tradicional de barras de acero (THA) y tubos de hormigón reforzado con fibras de acero (THRFA), elaborados y ensayados en la misma campaña. Los resultados mostraron que los THRFH alcanzaron una capacidad de carga equivalente a los THA y superior a la de los THRFA.

Wearable and Skin‐Mountable Fiber‐Optic Strain Sensors Interrogated by a Free‐Running, Dual‐Comb Fiber Laser

AbstractWearable and skin‐mountable strain sensors are highly demanding for monitoring skin deformations induced by human activities. Realization of such sensor devices based on fiber‐optic approaches offers attractive advantages such as electromagnetic immunity and inherent electric safety in comparison to their electronic counterparts. However, fiber‐optic sensors, conventionally made of stiff silica fibers, are not mechanically compliant with the soft human skins and have limited strain range (&lt;1%) for measuring large deformations. Here, a stretchable fiber Bragg grating (FBG)‐based optical (SFO) strain sensor with skin‐like compliance for human activity monitoring is presented. The SFO sensor is fabricated by a sinuous‐shaped FBG incorporated with a stretchable substrate that responds to strain deformations by shifting of the Bragg wavelength. This structural design enables measurement of various dynamic strains associated with tension, bending and torsion in a large sensing range up to 50%. To facilitate wearable integrations, a novel free‐running fiber laser with coherent dual‐comb output is developed to interrogate the SFO sensors by dual‐comb spectroscopy, which enables fast spectral acquisition with a single photodiode. It is shown that the SFO strain sensors can be used for wearable and skin‐mountable detection of diverse human activities including breathing, phonation, facial expression, and joint movements in real time.

Characterization of semisolid deformation behavior of a high Zr-containing WE magnesium alloy

The effects of temperature and strain rate on the semisolid deformation behavior of a high Zr WE54 magnesium alloys were studied at temperatures of 570, 595 and 620 °C. A flow stress peak was appeared during deformation of the feedstock experimental material at deformation conditions of 570 °C, 0.010 and 0.100 s−1, and 595 °C, 0.100 s−1. The latter results were connected to the occurrence of dynamic recrystallization in solid globules. Also, these conditions were gauged to be able to activate “lubricated flow” mechanism. At 570 °C and strain rate of 0.001 s−1 as well as 595 °C and rates of 0.010 and 0.001 s−1, the flow stress increases and reaches a plateau, where dynamic recovery is considered as the dominant mechanism. However, at 620 °C under all the strain rates, the flow stress drops for a limited strain range and then increases again. The results show that as the liquid removes from the boundaries between the solid parts, the densification of the globules occurs at higher strains, causing an increase in the flow stress. Comparative analysis points out that the feedstock material exhibits a lower flow stress than as-cast alloy associating with a modified morphology of Zr particles after deformation.

Inclusions Size-based Fatigue Life Prediction Model of NiTi Alloy for Biomedical Applications

Current standards consider the size and distribution of inclusions in semi-finished material, but do not place requirements on final biomedical devices made of NiTi shape memory alloys. In this paper, we analyze this by comparing the fatigue performances of NiTi superelastic wires obtained by different processes through a simple bilinear model of fatigue response in terms of strain life. The fracture surfaces of failed wires are analyzed through SEM microscopy and data regarding the presence of particles, and their morphology is recorded and analyzed using Type-I extreme value distribution. The results show a strong correlation between the fatigue limit of wires (in terms of strain) and the predicted extreme values of inclusions at fracture origin. Then, following the concept of treating the inclusions as ‘small cracks,’ a simple relationship between fatigue limit strain range and inclusion size is proposed based on ΔKth data from the literature. The model is compared with the fatigue data obtained from the tested wires.

An innovative procedure for characterising a coupled elastoplastic damage model of behaviour using the Virtual Fields Method

The characterisation of material behaviour models can be challenging, especially when dealing with strongly non-linear constitutive laws. Classical procedures are restricted to the treatment of homogeneous mechanical fields. They can therefore not be applied after strain localisation and behaviour model can be characterised only over a very limited strain range. In addition, several tests are generally needed to characterise complex behaviour models. On the contrary, the Virtual Fields Method (VFM) enables the treatment of inhomogeneous mechanical fields. The VFM therefore allows to take advantage of the increasingly powerful full-field measurement techniques. Moreover, its ability to process data enriched by heterogeneities can be used to significantly decrease the number of tests that are required for the identification of complex behaviours. In this paper, the VFM is developed for the characterisation of a fully coupled elastoplastic-damage behaviour model, using one uniaxial tensile test only. The process of identification is assessed using two kinds of thin-specimen geometries (numerically simulated strain fields). Results demonstrate the efficiency of the VFM for the simultaneous identification of plastic and damage parameters from a unique uniaxial tensile test, but also highlight that the definition of a suitable specimen geometry is a key factor for result accuracy.

Experimental Methodology for Limit Strain Determination in a Carbon/Epoxy Composite under Tensile Fatigue Loading

This work proposes a methodology to obtain the carbon fiber/epoxy composite limit strain for structures surviving 120000 cycles. The damage progression was also evaluated using stiffness reduction and hysteresis loop analysis in order to obtain dynamic and secant modulus. The results provide information about composite fatigue behavior. This approach determined a limit strain range from 0.83 to 0.87%, a fatigue stress limit of 0.8% of the static strength, stiffness degradation (damage index) of about 5% (within the limit strain). The methodology presented herein may be used for determining of material design allowable when fatigue is key consideration.

Blank optimization for free bulging of Inconel 718 to maximize bulged height at high temperatures

Thickness profiled blank is designed via the optimization technique to maximize the bulged height in free bulging for Inconel 718. The thickness of the blank is described by the Bezier curve by using four control points. The location of each control points is used for the design variables of optimization. The material parameters for the flow stress equation of Inconel 718 are obtained from the free bulging test at constant pressure condition by using a flat blank and verified via numerical analysis. The objective function and constraints for optimization are the maximization of the bulged height within a limited strain range. The equivalent static load method for non-linear static response structural optimization with a move limit scheme is used for optimization. The result of optimization shows 21.95% increased bulged height and uniformly distributed strain after bulging. The free bulging test using blank with optimized profile is conducted to verify the optimization process. The results of bulged height and deformed shape are compared with those from numerical analysis, and the comparison shows good agreement.

가스압력을 이용한 자유벌징에서 성형양 최대화를 위한 두께 분포 최적화

자유벌징에 있어서 성형 높이를 최대화하기 위하여 블랭크의 두께 분포를 최적화 하였으며, 등가정하중을 이용한 구조최적화법을 사용하였다. 두께형상은 부드러운 곡선으로 나타내기 위하여 베지어곡선을 사용하였고 제어점의 위치가 설계변수이며, 최대 변형률을 일정 값으로 제한하였다. 사용된 소재는 인코넬 718 이며 최적화된 두께분포로 가공된 블랭크를 이용한 자유벌징 시험을 수행하여 평판형 블랭크를 사용한 결과보다 22% 더 높은 성형 높이를 얻었다. 최적화결과에서 예측된 변형형상, 정점에서의 변형 경향, 두께분포가 실험에서 얻은 결과와 유사하여 최적화 과정의 유효성을 입증하였고, 최적화 결과가 실제 구현될 수 있음을 검증하였다. Thickness profiled blank is designed using optimization techniques for maximizing the bulged heights during the free bulging of Inconel 718. The thickness of the blank was described by the Bezier curve and the locations of the control points were used as the design variables for optimization. The maximization of the bulged heights within the limited strain range served as the objective function and constraints for optimization. The equivalent static loads method for non-linear static response structural optimization (ESLSO) was used and the result of the optimization revealed 22 increased bulged heights. A free bulging test using a blank with an optimized profile was conducted to verify the optimization process. The results were compared with those of numerical analysis in terms of bulged height and deformed shape.

Two-Stage Stress-Strain Models for Light-Gauge Steels

An accurate stress-strain relationship is needed for use in the advanced numerical modelling of cold-formed light-gauge steel members covering a wide range of strains. Existing stress-strain models for carbon steels are either capable of accurate predictions over a limited strain range or defined using many material parameters for a full range of strains. The values of some material parameters are not always available in existing design codes. This paper presents two stress-strain models for light-gauge carbon steels, which are capable of accurate predictions over the full range of tensile strains up to the strain at the ultimate stress. Both stress-strain models are solely defined using either three basic Ramberg-Osgood parameters ( E0, σ0.2, and n) or even two basic parameters ( E0, and σ0.2), and are based on a careful interpretation of existing experimental data of virgin materials and materials from flat portions of cold-formed steel sections. The accuracy of these two proposed models is demonstrated by comparing their predictions with experimental stress-strain curves.

An investigation on the stress–strain relationship of cold-rolled steel sheets used in the automotive industry

Cold-rolled steels are used in every stage of the automotive industry, from engineering design to manufacturing, and advanced numerical studies of these steels require knowledge of their stress–strain behaviour. Existing stress–strain models for these steels either are only capable of accurate predictions over a limited strain range or are defined by many material parameters and the values of some of these parameters are not available in most of the existing design codes. This study presents an analytical approximation of the stress–strain relationship for cold-rolled steels. For this purpose, tensile tests were conducted with some commercial cold-rolled sheets used in the automotive industry. Data were analysed to construct a robust mathematical model. The residual sum of squares was employed as the common analysing parameter for both linear and non-linear models; residual diagnosis was also applied towards achieving robustness of the model.

Immune Responses to Mucosal Vaccination by the Recombinant S1 and N Proteins of Infectious Bronchitis Virus

Infectious bronchitis virus (IBV) is prevented primarily by the use of live attenuated vaccines, which are known to have a limited strain range of protection. Alternative vaccines against the emerging new virus strains can improve control of the disease. The aim of this study was to evaluate the immunogenic potential of two recombinant viral proteins, when administered by eyedrop, without the assistance of a vector. The recombinant S1 (rS1) and N (rN) proteins of the M41 strain expressed in E. coli were tested, and the live attenuated vaccine H120 was used as a positive control. Protection was evaluated by re-isolation of virus from tracheas of vaccinated chickens after challenge with strain M41. After three immunizations, rS1 glycoprotein induced 40% protection, while vaccination with rN provided no protection. Vaccination with rS1, rN, or H120 induced a cellular immune response as demonstrated by in vitro ChIFN-γ production by splenocytes of vaccinated birds. Vaccination with H120, and to a lesser extent rS1, induced HI and virus-specific IgG antibody production. These findings indicate that recombinant viral proteins administered through the mucosal route can evoke an immune response without the assistance of a vector.

Cyclic stress–strain response of compacted gravel

The positive effect of artificial densification on the stress–strain performance of granular materials is acknowledged from very ancient times but its importance greatly increased after the development of powerful machineries for the construction of large earth and rockfill dams. It is, however, pointed out that the extensive exploitation of gravelly soil is rarely supported by a thorough analytical assessment of the compaction effects on the constitutive relationships of materials, as would be desirable considering the massive dimension of these works and the complexity of typical loading conditions. The present research aims to fill this gap by means of a detailed experimental investigation and a theoretical analysis on the stress–strain response of dense gravels under monotonic and cyclic loading. The experimental campaign consists of a large number of triaxial tests performed at different initial mean effective stresses, following different stress paths and sequences, on artificially reconstituted samples of large dimensions compacted at different initial densities. The great care placed in the accuracy of laboratory instrumentation enables a high repeatability of experimental results, which is necessary to provide a clear focus on non-linearity in the limited strain range of the pre-failure response of the gravel. Based on the curve-fitting method the ingredients of an elasto-plastic constitutive model have been defined to predict the response of gravel under monotonic and cyclic loading. Elastic stiffness is simulated with a model derived from the literature which assumes a dependency on soil density together with inherent and stress-induced anisotropy. Plastic strain development from different initial stress and volume states of gravel is simulated by a critical state, multiple yielding constitutive model. Hardening and flow rules for the latter have been obtained by modifying previously existing laws in order better to reproduce the observations under monotonic compression, extension and cyclic loading. Validation of the proposed model is finally provided by comparing simulations and experimental results in a variety of testing conditions.

Stress-Strain Models for Light Gauge Steels

Advanced numerical modeling for cold-formed light gauge steel structures, from manufacturing to the structural response under the applied loading, requires the knowledge of the stress-strain behavior of the material over the full range of tensile strains. Existing stress-strain models for carbon steels are either only capable of accurate predictions over a limited strain range or defined by many material parameters and the values of some material parameters are not available in most of existing design codes. Therefore, a new stress-strain relationship for light gauge carbon steels up to the ultimate strength is required for the advanced numerical modeling and needs to be modeled on the basis of three basic material parameters, the so-called Ramberg-Osgood parameters (the 0.2% proof stress σ0.2, the initial elastic modulus 0 E and the strain-hardening exponent η). This paper presents such new stress-strain models for light gauge carbon steels, which are able to describe the stress-strain relationship over the full range of tensile strains by using only three basic Ramberg-Osgood parameters. In the present study, the stress-strain data obtained from tensile coupon tests reported in existing literatures have been collected and analyzed, and these tested coupons were cut from both virgin steel sheets and cold-formed steel sections. The new models have been developed by a careful interpretation of these existing experimental data. The accuracy of the proposed models has been demonstrated by comparing their predictions with experimental stress-strain curves.

The extensional viscoelasticity of protein-coated interfaces

In shear or dilational testing, the interfacial rheology of a protein film adsorbed at a fluid–fluid interface is often determined by its response to dynamic deformation. In order to extract characterising parameters from the response data, a model must be assumed in order to fit the response, yet the assumption is difficult to validate due to the limited strain range accessible by most instruments. In this work, a modelling approach was developed to extract characterising parameters from stress–strain curves measured in a high-strain extensional mode of deformation. This mode of testing is insensitive to interfacial tension gradients, making it particularly useful for the study of interfacially adsorbed materials, such as proteins, where the relationship between interfacial tension and interfacial rheology is complex. A four-parameter version of the Generalised Maxwell Model (GMM) for three-dimensional viscoelastic materials successfully describes the response of a two-dimensional β-lactoglobulin interfacial film over a full linear strain range of 0–100%. The GMM asserts that viscoelastic relaxation occurs on multiple timescales, and in this case the two associated time constants give new insights into the nature of interfacial rheology, and its dependence on mass transfer with the bulk solution. In particular, washing out protein from the bulk solution has little effect on the initial response of the system, but a significant effect on the larger-strain response. Fitting a smaller strain range with a less parameterised model (e.g. 0–5% strain fitted with 2 parameters, or 0–20% fitted with 3 parameters) yielded a result that was reasonable up to the strain rate fitted, although the model did not predict well the response to greater strains. The major consequence is that unless a strain range large enough to allow significant influence of viscosity on observed response is tested, unreliable values of viscosity may be determined. Three other common proteins (lysozyme, bovine serum albumin and β-casein) were also tested. In each case, the films showed viscoelastic behaviour that could be well described by the 4-parameter GMM, allowing the viscous components for these protein films to be estimated more accurately than has been possible to date.

The ultrastructure and contractile properties of a fast-acting, obliquely striated, myosin-regulated muscle: the funnel retractor of squids.

We investigated the ultrastructure, contractile properties, and in vivo length changes of the fast-acting funnel retractor muscle of the long-finned squid Doryteuthis pealeii. This muscle is composed of obliquely striated, spindle-shaped fibers ~3 mum across that have an abundant sarcoplasmic reticulum, consisting primarily of membranous sacs that form 'dyads' along the surface of each cell. The contractile apparatus consists of 'myofibrils' approximately 0.25-0.5 microm wide in cross section arrayed around the periphery of each cell, surrounding a central core that contains the nucleus and large mitochondria. Thick myofilaments are approximately 25 nm in diameter and approximately 2.8 microm long. 'Dense bodies' are narrow, resembling Z lines, but are discontinuous and are not associated with the cytoskeletal fibrillar elements that are so prominent in slower obliquely striated muscles. The cells approximate each other closely with minimal intervening intercellular connective tissue. Our physiological experiments, conducted at 17 degrees C, showed that the longitudinal muscle fibers of the funnel retractor were activated rapidly (8 ms latent period following stimulation) and generated force rapidly (peak twitch force occurred within 50 ms). The longitudinal fibers had low V(max) (2.15 +/-0.26 L(0) s(-1), where L(0) was the length that generated peak isometric force) but generated relatively high isometric stress (270+/-20 mN mm(-2) physiological cross section). The fibers exhibited a moderate maximum power output (49.9 W kg(-1)), compared with vertebrate and arthropod cross striated fibers, at a V/V(max) of 0.33+/-0.044. During ventilation of the mantle cavity and locomotion, the funnel retractor muscle operated in vivo over a limited range of strains (+0.075 to -0.15 relative to resting length, L(R)) and at low strain rates (from 0.16 to 0.91 L(R) s(-1) ), corresponding to a range of V/V(max) from 0.073 to 0.42. During the exhalant phase of the jet the range of strains was even narrower: maximum range less than +/-0.04, with the muscle operating nearly isometrically during ventilation and slow, arms-first swimming. The limited length operating range of the funnel retractor muscles, especially during ventilation and slow jetting, suggests that they may act as muscular struts.

Leishmania major Glycosylation Mutants Require Phosphoglycans (lpg2−) but Not Lipophosphoglycan (lpg1−) for Survival in Permissive Sand Fly Vectors

BackgroundSand fly species able to support the survival of the protozoan parasite Leishmania have been classified as permissive or specific, based upon their ability to support a wide or limited range of strains and/or species. Studies of a limited number of fly/parasite species combinations have implicated parasite surface molecules in this process and here we provide further evidence in support of this proposal. We investigated the role of lipophosphoglycan (LPG) and other phosphoglycans (PGs) in sand fly survival, using Leishmania major mutants deficient in LPG (lpg1 −), and the phosphoglycan (PG)-deficient mutant lpg2 −. The sand fly species used were the permissive species Phlebotomus perniciosus and P. argentipes, and the specific vector P. duboscqi, a species resistant to L. infantum development.Principal FindingsThe lpg2 − mutants did not survive well in any of the three sand fly species, suggesting that phosphoglycans and/or other LPG2-dependent molecules are required for parasite development. In vitro, all three L. major lines were equally resistant to proteolytic activity of bovine trypsin, suggesting that sand fly-specific hydrolytic proteases or other factors are the reason for the early lpg2 − parasite killing. The lpg1 − mutants developed late-stage infections in two permissive species, P. perniciosus and P. argentipes, where their infection rates and intensities of infections were comparable to the wild type (WT) parasites. In contrast, in P. duboscqi the lpg1 − mutants developed significantly worse than the WT parasites.ConclusionsIn combination with previous studies, the data establish clearly that LPG is not required for Leishmania survival in permissive species P. perniciosus and P. argentipes but plays an important role in the specific vector P. duboscqi. With regard to PGs other than LPG, the data prove the importance of LPG2-related molecules for survival of L. major in the three sand fly species tested.

Comparison of the work hardening of metallic sheets in bending–unbending and simple shear

Constitutive equations for sheet metals are important input data for the numerical simulation of forming processes. Their identification usually comes from uniaxial tensile tests at several orientations to the rolling direction and from equibiaxial tests. To characterize the kinematic part of the work hardening, strain path reversals are needed and different mechanical tests have been developed, such as tension–compression and simple shear. The aim of this work is to investigate the influence of the database used for identification, by using either bending–unbending or simple shear for strain path reversal. This study is performed both on an aluminum alloy and a TRIP steel. The presented results show that, for a limited strain range, the experiments are consistent.