Stretch Ratio Research Articles

Peculiarities of using dumbbell specimens made of elastomeric materials subject to finite deformation in complex loading tests

The features of experiments with dumbbell specimens performed to determine the mechanical properties of filled elastomers are analyzed. Emphasis is placed on testing materials that experience a complex loading history. Experiments such as cyclic loading with increasing amplitude of deformations and with nested stress / strain cycles are considered. It has been established that the rate of change of the stretch ratio in the central part (gauge section) of the specimen significantly differs from that calculated from the analysis of the positions of the grips. This difference manifests itself more prominently in the experiments with complex loading algorithms. The reason is that the viscoelastic properties and the Mullins effect of the filled elastomer are different in the central part of the specimen and at its ends near the grips. The presence of inhomogeneous deformation in the gauge section leads to additional difficulties associated with finding constants for constitutive equations. Besides, this phenomenon complicates a comparison of the mechanical properties of different materials, because detailed information on their behavior can be obtained in complex experiments only. So, experiments with straight specimens or rings with a rectangular cross-section offer more possibilities for studying the mechanical properties of filled elastomers than the experiments with dumbbell specimens.

Metal-Coordinated Dynamics and Viscoelastic Properties of Double-Network Hydrogels

Biological soft tissues are intrinsically viscoelastic materials which play a significant role in affecting the activity of cells. As potential artificial alternatives, double-network (DN) gels, however, are pure elastic and mechanically time independent. The viscoelasticization of DN gels is an urgent challenge in enabling DN gels to be used for advanced development of biomaterial applications. Herein, we demonstrate a simple approach to regulate the viscoelasticity of tough double-network (DN) hydrogels by forming sulfonate-metal coordination. Owing to the dynamic nature of the coordination bonds, the resultant hydrogels possess highly viscoelastic, mechanical time-dependent, and self-recovery properties. Rheological measurements are performed to investigate the linear dynamic mechanical behavior at small strains. The tensile tests and cyclic tensile tests are also systematically performed to evaluate the rate-dependent large deformation mechanical behaviors and energy dissipation behaviors of various ion-loaded DN hydrogels. It has been revealed based on the systematic analysis that robust strong sulfonate-Zr4+ coordination interactions not only serve as dynamic crosslinks imparting viscoelastic rate-dependent mechanical performances, but also strongly affect the relative strength of the first PAMPS network, thereby increasing the yielding stress σy and the fracture stress at break σb and reducing the stretch ratio at break λb. It is envisioned that the viscoelasticization of DN gels enables versatile applications in the biomedical and engineering fields.

Notch sensitivity of polymer-based thermal interface materials

Thermal interface materials (TIMs) used between the chip and the heat spreader play an indispensable role in effective heat removal to ensure the chip's performance and reliability. As they suffer from stresses in practical applications, TIMs need to have high toughness to resist fracture. The notch sensitivity of TIMs is considered an important parameter to evaluate its toughness. However, the notch sensitivity of TIMs is seldom mentioned, and the mechanism to enhance the toughness is still unclear. Here, using polymer-based TIMs consisting of polydimethylsiloxane/aluminum as a model, we specifically investigate notch sensitivity of TIMs and analyze the mechanical mechanism in detail from the macroscopic and microscopic scales. It was found that a transition from notch insensitive to notch sensitive will happen with a notch length of 2.0 mm, which is much higher than typical soft materials, such as hydrogels. We interpret the notch sensitivity of the TIM by finite element analysis at macroscopic scales and the Lake–Thomas theory at microcosmic scales. The relationship between the area of the strain concentration region to the notch length in finite element analysis is in good agreement with the fracture stretch ratio with different notch lengths measured in a uniaxial tensile experiment. This investigation gives an insight into designing notch-insensitivity TIM and understanding their fracture behavior.

Effect of Salt on Dynamic Mechanical Behaviors of Polyampholyte Hydrogels

Understanding the dynamic mechanical behaviors of tough hydrogels with ionic dynamic bonds in saline solution is crucial for applications, particularly in the biomedical field. In this work, using polyampholyte hydrogels, dually crosslinked with a primary network from covalent crosslinkers and/or trapped entanglements, and a dynamic network from ionic bonds, as a model system, we investigate the salt effect on rheological response and mechanical behaviors. Through a systematic study on one gel without a chemical crosslinker and one gel with a chemical crosslinker, we demonstrate that the salt effect on mechanical properties, including small-strain moduli, large deformation energy dissipation, and fracture stretch ratio, can be effectively converted into frequency or strain rate dependences following the time–salt superposition principle. Accordingly, we access a wide range of observation time scales from 10–11 to 102 rad/s at room temperature, covering three regimes: (I) the high-frequency plateau regime from the dynamic and primary networks, (II) the viscoelastic regime from sticky Rouse motion of ionic associations, and (III) the low-frequency plateau regime from the primary network. Moreover, we disclose an in-depth understanding of the entanglement’s behavior in the long-timescale regime III. This work not only provides a guide to biological applications of hydrogels in saline environments but also gives important insights into the toughening mechanism via dynamic bonds in other systems with dually crosslinked structures.

Effect of Mealworm Powder Substitution on the Properties of High-Gluten Wheat Dough and Bread Based on Different Baking Methods.

Mealworms (Tenebrio molitor) are protein-rich edible insects that have been regarded as novel food ingredients. In this study, high-gluten wheat flour was formulated with dried mealworm powder at various levels (0%, 5%, 10%, 15%, and 20%) to study its influence on the pasting, farinograph, and extensograph properties and microstructure of the dough. A subsequent decrease in the pasting parameters was observed due to starch dilution. The water absorption, dough development time, and dough stability time decreased gradually from 71.9% to 68.67%, 13.6 min to 10.43 min, and 14.1 min to 5.33 min, respectively, with the increase in the substitution of mealworm powder from 0% to 20%. The farinograph characteristics corresponded to a weak gluten network formed through the dilution of gluten by the replacement of wheat flour with a non-gluten ingredient. The stretch ratio of the high-gluten dough increased gradually from 4.37 (M0) to 6.33 (M15). The increased stretching resistance and extensibility of the dough with 5% and 10% mealworm powder indicated that mealworm powder can act as a plasticizer in the gluten network, which might contribute to the decreased strength and increased elasticity and flexibility of the dough network. The bread made with three different baking methods showed similar increases in specific volume and decreased hardness up to the 10% substitution level, owing to the increased elasticity and flexibility of the dough. The GB/T 35869-2018 Rapid-baking method, GB/T 14611-2008 Straight dough method, and automatic bread maker method exhibited the highest specific volumes of 3.70 mL/g, 3.79 mL/g, and 4.14 mL/g when the wheat flour was substituted with 10% mealworm powder. However, 15% and 20% mealworm powder substitution markedly reduced the bread quality owing to the dilution effect and mealworm powder phase separation. These results provide a perspective on the relationship between the rheological properties of mealworm powder-substituted high-gluten dough and application suggestions for insect food development in the food industry.

Semi-analytical model for stretch ratio determination in inflation test for isotropic membranes

This article wishes to contribute to the understanding of principal strains distribution in inflation test for circular isotropic soft membranes, combining analytical, numerical, and experimental investigations. The method developed gives a relatively simple and original solution of the deformation and thus of the stresses during an inflating test, provided that the measurement is sufficiently close to the pole. For this purpose, a semi-analytical model (SAM) is proposed and to evaluate that theory, two complementary approaches are used. The first approach is experimental. Inflation and uniaxial tensile tests are set up on medical silicone sheets to identify their hyperelastic constitutive parameters, using Digital Image Correlation. Then these mechanical properties are injected into a 3D finite element model (FEM) of membrane, simulating the inflation test, to compare the strains that had been obtained with those of the SAM. Numerical results show that the strain calculated by the SAM follows the pattern of the circumferential strain obtained by the FEM. Up to a certain distance from the center of the disk (half of the disk for our example), strain calculated by the SAM give a correct approximation of the deformation with respect to radial and circumferential FEM strains.

Liquid Moisture Transport in Stretched Knitted Fabrics

Abstract Transport of moisture is an important aspect of physiological comfort of clothing usage. The moisture originating from sweat can be in the form of vapour or liquid. Sweat in the form of liquid occurs, whereas the sweat in the form of vapour cannot be efficiently evaporated to the environment. For the stretchable fabrics, it is important to know the influence of stretching on their liquid moisture transport performance. The aim of the present work was to analyse the liquid moisture transport in knitted fabrics at varying degrees of stretch: 0, 15, 20 and 20%, and to assess the effect of stretch ratio on the ability of fabrics to transport the liquid moisture. Measurement was done using the M290 Moisture Management Tester supplemented with the MMT Stretch Fabric Fixture device. The obtained results confirmed that the stretching influences the values of the parameters characterizing the knitted fabrics from the point of view of their ability to transport liquid moisture.

Intrinsically stretchable ionoelastomer junction logic gate synchronously deformable with liquid metal

Liquid-free ionic conductors, known as ionoelastomers, are of great interest because of their potential for developing reliable and resilient ionic devices with elastic mechanical properties. This study presents an intrinsically stretchable diode consisting of a highly stretchable ionoelastomer bilayer vertically stacked with liquid metal electrodes. The bilayer contains two types of ionoelastomer networks: one containing fixed anions with mobile cations and one containing fixed cations with mobile anions. Both ionoelastomers use 2-hydroxyethyl acrylate to provide high stretchability. The junction between the two ionoelastomers creates a diode with excellent non-Faradaic ionic current rectification. The voltage-dependent modulation of the ionic double layer at the interface between the two ionoelastomers provides the rectification. The elastic diode works under cyclic loading to a uniaxial stretch ratio of 6 (strain of 500%), allowing the development of a highly stretchable ionic OR logic gate.

Realizing high stretch ratio of flexible wavy circuit via laser carving

Stretchable wavy circuit is an essential component in flexible devices, which have wide applications in various fields. In the industrial field, the stretching ability of the circuit is a crucial factor for flexible devices. Therefore, this study proposes laser carving method to increase both stretch ratio and device resolution of the flexible device. The results obtained from the experiment and finite element analysis verifies that laser carving on the wavy circuit increases the maximum stretch ratio of wavy circuit. The obtained analytic model confirms that laser carving generates tilted section on the wavy circuit, and reduces the bending rigidity of the curvy point of the wavy circuit. The study also verified that laser carved groove induces crack propagation into vertical to the circuit direction, so that the laser carved wavy circuit is less likely to disconnect than uncarved wavy circuit. Due to the reduced bending rigidity and crack induce, the wavy circuit stretches more than the conventional uncarved wavy circuit.

Online magnetic flux leakage detection of inclusions and inhomogeneities in cold rolled steel plate

Abstract Cold rolled steel plate is found in different applications. In manufacturing processes with high stretch ratios like bending or deep drawing, non-metallic inclusions, or segregations, which remain in the material during slab casting, can lead to ruptures of the plate. While not being visible optically, those inclusions are detectable by magnetic flux leakage inspection. Therefore, an online inspection system using giant magnetoresistance gradiometers was developed. The individual components were optimized by researching the magnetic properties of the cold rolled plate and natural as well as artificial defects on a laboratory setup for moving material simulation. Correlations between defect properties, inspection parameters and the resulting signals were determined. By optimizing components and configuration accordingly, a sensor module containing 48 sensors, signal conditioning, digitization, and an adjustable magnet was arrived at. Due to the necessarily small distance to the moving material, attention was paid to mechanical repeatability and ruggedness. An inclusion detection system, fully covering 1344 mm strip width, was installed in a coating line. Operating in production for over a year, the inspection system has shown high sensitivity and is, in addition to internal defects, able to detect various strip damages like roll marks and scratches.

Manufacturing and characterisation of 3D printed thermoplastic morphing skins

Morphing aircraft are one promising solution to reducing the aviation industry’s environmental impact because they can make aircraft more aerodynamically efficient, thereby reducing greenhouse gas emissions. The design of morphing skins is inherently challenging due to the competing design constraints of needing to be stiff out-of-plane to resist pressure loads while being compliant in-plane to minimise actuation energy. Previous work by these authors introduced the novel concept of Geometrically Anisotropic Thermoplastic Rubber (GATOR) morphing skins that take advantage of multi-material 3D printing and structural scaling laws to allow for better compromises between these competing design constraints. In this work, multi material Fused Filament Fabrication methods were used to 3D print the proposed GATOR sandwich panels from two different stiffnesses of thermoplastic polyurethane to demonstrate the manufacturing process and experimentally quantify the performance of some simple embodiments of the GATOR concept. The panels were mechanically tested to determine their flexural and extensional stiffnesses. Results show that the panels can be extended to a stretch ratio of λ = 1.6 with a linear response at low stretch ratios. The results from the flexural experiments show that the flexible face sheets are capable of withstanding some compression before buckling, which results in a linear behaviour at small forces. These results show the promise of the GATOR skin concept and motivate future development of designs that further exploit the underlying principles of the concept.

Universality of dilute solutions of ring polymers in the thermal crossover region between θ and athermal solvents

Due to their unique topology of having no chain ends, dilute solutions of ring polymers exhibit behavior distinct from their linear chain counterparts. The universality of their static and dynamic properties, as a function of solvent quality z in the thermal crossover regime between θ and athermal solvents, is studied here using Brownian dynamics simulations. The universal ratio URD of the radius of gyration Rg to the hydrodynamic radius RH is determined, and a comparative study of the swelling ratio αg of the radius of gyration, the swelling ratio αH of the hydrodynamic radius, and the swelling ratio αX of the mean polymer stretch X along the x-axis, for linear and ring polymers, is carried out. The ratio URD for dilute ring polymer solutions is found to converge asymptotically to a constant value as z→∞, which is a major difference from the behavior of solutions of linear chains, where no such asymptotic limit exists. Additionally, the ratio of the mean stretch along the x-axis to the hydrodynamic radius, (X/RH), is found to be independent of z for polymeric rings, unlike in the case for linear polymers. These results indicate a fundamental difference in the scaling of static and dynamic properties of rings and linear chains in the thermal crossover regime.

Hybrid Cache Management in IoT-Based Named Data Networking

Internet of Things (IoT) and named data network (NDN) are innovative technologies to meet up the future Internet requirements. NDN is considered as an enabling approach to improving data dissemination in IoT scenarios. NDN delivers in-network caching, which is the most prominent feature to provide fast data dissemination as compared to Internet protocol (IP)-based communication. The proper integration of caching placement strategies and replacement policies is the most suitable approach to support IoT networks. It can improve multicast communication which minimizes the delay in responding to IoT-based environments. Besides, these approaches are playing a most significant role in increasing the overall performance of NDN-based IoT networks. To this end, in this article, the challenges of NDN-IoT caching are identified with the aim to develop a new hybrid strategy for efficient data delivery. The proposed strategy is comparatively and extensively studied with NDN-IoT caching strategies through an extensive simulation in terms of average latency, cache hit ratio, and average stretch ratio. From the simulation findings, it is observed that the proposed hybrid strategy outperformed to achieve a higher caching performance of NDN-based IoT scenarios.

Propagation and attenuation of Lamb waves in functionally graded fractional viscoelastic soft plates with a pre-deformation

An improved understanding of the wave propagation in incompressible soft structures with a pre-deformation, especially the grasp of viscoelastic effect, could fundamentally catalyze technical developments in many areas including medicine, and rubber. Based on the nonlinear elasticity and linear incremental theories, a fractional-order hyper-viscoelastic model is established to derive dynamic equations of Lamb waves in functionally graded pre-deformed viscoelastic soft plates. The fractional-order Kelvin-Voigt model is applied to concern the viscoelasticity. An improved Legendre polynomial method is employed to analytically solve wave equations. The complex wave solutions are obtained without the iterative. The correctness of the present method is validated by a comparison with the finite element method. The influence of viscoelasticity and pre-formation on dispersion and attenuation curves is investigated. Some new wave phenomena are revealed: Phase velocity and attenuation of Lamb waves can be controlled by altering stretch ratios λi, and the pre-stretching restrains the viscoelastic effect; The minimum attenuation frequency can be adjusted by altering the material component distributions. Results provide the foundation for the design of biomaterials with the controllable viscoelasticity to greatly promote their applications in the regenerative medicine.

Self-Stretchable Fiber Liquid Sensors Made with Bacterial Cellulose/Carbon Nanotubes for Smart Diapers.

Liquid sensors for detecting water and body fluids are crucial in daily water usage and health monitoring, but it is challenging to combine sensing performance with high tensile deformation and multifunctional applications. Here, a substrate-free, self-stretchable bacterial cellulose (BC)/carbon nanotube (CNT) helical fiber liquid sensor was prepared by the solution spinning and coiling process using BC as the water-sensitive matrix and CNTs as the active sensing materials. The BC/CNT (BCT) fiber sensor has a high stretch ratio of more than 1000% and a rapid response for a current change rate of 104% within 1 s, which is almost unaffected under washing and various stretching or knotting deformations. By combination of the BCT fiber, we can design smart diapers or water level detectors, which rapidly monitor the status of smart diapers or water level, and the monitoring result can be transferred on time through an alarm device or smartphone. In short, the scalable and continuous preparation of the self-stretchable BCT helical fiber will provide a capacious platform for the development of a wearable sensor applied in daily life (such as smart diapers, water level detection, etc.).

Extensional rheology and flow-induced crystal alignment in polypropylene ionomers

The nonlinear response to the uniaxial extension of a series of isotactic polypropylene (iPP) ionomers is studied by melt rheology and ex situ small and wide-angle x-ray scattering measurements. These ionomers bear iPP backbones decorated with pendant aluminum carboxylate groups. Minuscule amounts of ion groups (<0.1 mol. %) are sufficient to produce remarkably high extensional strain hardening ratios of up to 200 and maximum stretch ratios (before breakage) of up to 50. Small and wide-angle scattering measurements from an iPP ionomer sample quenched during an extensional flow reveal monotonic correlations between Hencky strain, crystallinity, and crystal alignment. These results indicate a direct correlation between extensional stress and the chain alignment in the ionomer melt. Intriguingly, the ion clusters in the ionomer show no alignment induced by extensional deformation, suggesting undetermined rearrangements involving cluster dissociation and reassociation that occur during the flow. Slow stress relaxation, after flow cessation, was measured in the ionomers, in sharp contrast to much faster relaxation typically observed in the iPP homopolymer. Stress relaxation is not concomitant with a decrease in crystal alignment, which indicates that chain recoiling is not the stress relaxation mechanism in iPP ionomers.

An Efficient Traffic-aware Caching Mechanism For Information-centric Wireless Sensor Networks

This paper proposes a traffic-aware caching mechanism (TCM) for resource-constrained nodes in information-centric WSNs. TCM pushes up popular upstream content objects to be cached nearby the sink. Less popular content objects are cached farther from the sink compared to popular content objects. TCM also pushes down popular downstream content objects to be cached inside the network. The objective of TCM is to reduce the number of interest messages required forwarding in multiple hops inside WSNs to optimize stretch ratio, energy efficiency, and content retrieval latency. We implement TCM on the top of existing popularity-based caching schemes to improve their performance. Through analysis and experimental results, we show that TCM achieves a significant improvement in terms of energy efficiency, content retrieval latency, cache hit ratio, and stretch ratio compared to state-of-the-art popularity-based caching schemes.

Geometrical interpretation of the Timoshenko–Ehrenfest theorem

In this paper, geometrical interpretation of the Timoshenko–Ehrenfest theorem is given. It is based on a vector-valued version of continuum mechanics, which considers the deformed body as a surface in extended coordinate space. Scalar parameters of the metrics of this hypersurface determine the strain. In the bending beam case, this surface is formed by a twisted cylinder rolled into a cone. Accordingly, three kinds of metric parameters, the stretch ratio, the twist and cone angles responsible for stretching, shear, and bending determine the shape of the elastic curve. The balance equations for generalized forces taking into account shear deformation and rotational bending effects are derived. A new formula for the shear coefficient comes out of the derivation. It is shown that its magnitude 5/6 for quasistatic Timoshenko beam remains fair for the exact form of the cross-section at the free end.

High performance piezoelectric polymer film with aligned electroactive phase nanofibrils achieved by melt stretching of slightly crosslinked poly(vinylidene fluoride) for sensor applications

Flexible, transparent and lightweight polymer piezoelectric films are promising for emerging sensor applications, including wearable electronics and human–machine interfaces. However, it remains a great challenge for large-scale fabrication of high-quality polymer piezoelectric films by a cost-effective melt processing approach, mainly due to the difficulty of acquiring well-defined electroactive phases. Herein, a readily implementable and scalable strategy is reported to achieve poly(vinylidene fluoride) (PVDF) film with ultrahigh content of electroactive β-phase (∼96%) via melt stretching of slightly crosslinked PVDF. Upon controlled temperature and stretch ratio, the β-phase adopts an oriented nanofibril (diameter, 21.6 nm) morphology, while nanofibrils are further densely and parallelly aligned to fill the film space. The hierarchical nanoscale phase morphology endows the slightly crosslinked film with high optical transmittance (∼90%), good flexibility and also superior mechanical properties. Moreover, flexible piezoelectric device constructed on the film is demonstrated to have excellent electrical output with sensitive and repeatable responses in sensing dynamic pressure (0–250 kPa), temperature variation (3.3 mV oC-1), human motions and subtle physiological activities. This study therefore paves the way towards scalable manufacturing of high-performance piezoelectric polymer film through simple melt stretching.

Stretch-Induced Crystallization of Cellulose Spun from Ionic Liquid Solution.

With the emergence of efficient green solvents, structural regulation of regenerated cellulose is highly desired in the solution process from an industrial perspective. Cellulose fiber and films are viewed as a "composite" comprising amorphous and crystalline fractions. The regulation of the crystalline structure is of great importance for the properties of cellulose materials. In this study, we found stretch-induced crystallization behavior during the transition from solution to gel via coagulation. The crystallinity index of the hydrogel fiber increases with the stretch ratio (SR). X-ray diffraction revealed that the cellulose II hydrate formed in the stretched hydrogel fibers. The mechanical properties and thermal stability of the dry fibers greatly improved against the SR. This crystallization behavior depends on the concentration of the solution and the type of ionic liquid. This stretch-induced crystallization provides an efficient method for structural regulation in cellulose solution processing.