Stretch Ratio Research Articles

Facile Preparation of High‐Performance Stretchable Fiber‐Like Electrodes and Supercapacitors

AbstractA facile preparation method was proposed to fabricate core‐sheath structured elastic cord/carbon nanotube (CNT)/polyaniline (PANI) composite fibers with excellent electrochemical performance and good mechanical stretchability. Specifically, we developed a “surface melting for stable attachment” strategy to combine CNT/PANI composite film tightly with elastic cord fiber. The fabricated fiber‐like elastic cord/CNT/PANI composite electrode displays a large gravimetric capacitance of 394 F g−1(corresponds to a linear specific capacitance of 15.4 mF cm−1) and superior rate capability. The electrode capacitance has no obvious decrease when the electrode was stretched from original state to a large stretch ratio of 100%, and the capacitance maintains 98% after 100 stretch‐release cycles; besides, the electrode at stretching state possesses almost same cycling stability and rate capability as it at original state. These results indicate robust micro‐structure and outstanding stretchability of our fiber‐like elastic cord/CNT/PANI composite electrode. Consequently, all‐solid‐state supercapacitors assembled based on the fiber‐like electrode also exhibit impressive stretchability. Overall, the proposed facile method for producing stretchable fiber‐like electrodes/supercapacitors is believed to further boost the practical application of stretchable and wearable energy storage devices.

A Study of Pore Formation and Methanol Vapor Permeability in Stretched Polytetrafluoroethylene Films Used as a Precursor of Composite Ion-Exchange Membranes

Methanol vapor permeability and pore formation features in stretched polytetrafluoroethylene (PTFE) films used as a precursor of composite cation-exchange membranes have been studied. Porous structures of the precursor have been formed via stretching PTFE films in air, toluene, isopropyl alcohol, and CCl4. Permeability has been determined according to the evaporation of a liquid through a porous film; porosity, according to the increase in the film volume during stretching; pore formation features, according to optical microscopy images of porous films and their transverse microsections. It has been found that, with an increase in the stretch ratio, the porosity of PTFE films increases almost linearly, while the methanol vapor permeability increases exponentially. The permeability of the films stretched in liquids is 20 times higher than the permeability of the films stretched in air at comparable stretch ratio and porosity values. The considerably higher permeability of the films stretched in liquids and the observed differences in their porous structure suggest that the liquids are actively involved in the formation of through pores in the direction connecting the film surfaces, i.e., in the direction that determines the transport and conductive properties of composite membranes based on stretched PTFE films.

Physical ageing response of polystyrene subjected to the large deformation: The increase in fictive temperature

Film stretch was incorporated in the enthalpy relaxation experiment in order to examine physical ageing response of polystyrene subjected to large deformation. It was stretched in the midst of ageing step, where ageing temperature was located slightly higher than the onset of the glass transition shoulder to minimise the stretching effect on the enthalpy decay, and then heat capacity, cp(T), versus temperature curve was acquired by DSC (differential scanning calorimetry) as functions of the ageing time and stretch ratio. Pre-hold and post-hold stretches are both carried out, those are stretching-and-ageing and ageing-and-stretching, respectively. As a result, the stretching effect appeared as the shift of glass transition shoulder in cp(T) curve; its onset temperature increased with the increase in the stretch ratio. A remarkable discrepancy for the shift of glass transition shoulder was observed between the samples of pre-hold and post-hold stretches. The experimental cp(T) was reproduced by the modelling data calculated on the basis of Tool-Narayanaswamy-Moynihan framework to derive the data of fictive temperature (Tf). It was revealed that Tf isothermally increases with stretching. The amount of Tf increase depends on both the ageing time and stretch ratio. The discrepancy of the shift amount appeared between pre-hold and post-hold stretches was interpreted in terms of the increase in Tf.

Highly Stretchable and Conductive Superhydrophobic Coating for Flexible Electronics.

Superhydrophobic materials integrating stretchability with conductivity have huge potential in the emerging application horizons such as wearable electronic sensors, flexible power storage apparatus, and corrosion-resistant circuits. Herein, a facile spraying method is reported to fabricate a durable superhydrophobic coating with excellent stretchable and electrical performance by combing 1-octadecanethiol-modified silver nanoparticles (M-AgNPs) with polystyrene- b-poly(ethylene- co-butylene)- b-polystyrene (SEBS) on a prestretched natural rubber (NR) substrate. The embedding of M-AgNPs in elastic SEBS matrix and relaxation of prestretched NR substrate construct hierarchical rough architecture and endow the coating with dense charge-transport pathways. The fabricated coating exhibits superhydrophobicity with water contact angle larger than 160° and a high conductivity with resistance of about 10 Ω. The coating not only maintains superhydrophobicity at low/high stretch ratio for the newly generated small/large protuberances but also responds to stretching and bending with good sensitivity, broad sensing range, and stable response cycles. Moreover, the coating exhibits excellent durability to heat and strong acid/alkali and mechanical forces including droplet impact, kneading, torsion, and repetitive stretching-relaxation. The findings conceivably stand out as a new tool to fabricate multifunctional superhydrophobic materials with excellent stretchability and conductivity for flexible electronics under wet or corrosive environments.

Mechanical behavior of carbon nanotube yarns with stochastic microstructure obtained by stretching buckypaper

The development of yarns composed primarily from carbon nanotubes (CNTs) has been pursued recently with the intent of transferring to the yarn the exceptional mechanical and transport properties of individual nanotubes. In this work we study the process of yarn formation by dry stretching buckypaper, and the mechanical behavior of the resulting yarns, function of the CNT length and of the state of the CNT assembly before stretching. The analysis is performed using a coarse grained, bead-spring representation for individual CNTs. It begins with a random buckypaper structure composed from CNTs of diameter 13.5 Å. This structure is stretched to form a yarn. This occurs once the stretch ratio becomes larger than a threshold which depends on the CNT length. At the threshold, adhesion stabilizes a highly aligned packing of CNT bundles. Packing defects and pores, reminiscent of the initial structure of the buckypaper, are incorporated in the yarn. The yarn is further tested in uniaxial tension. The defects have little effect on the mechanical behavior of the resulting yarns. However, the behavior depends sensitively on the degree of packing of the CNTs in the sub-bundles forming the yarn. Therefore, the initial structure of the buckypaper has little effect on the performance of the yarn. Increasing the CNT length increases the yarn flow stress and this is associated with the residual tortuosity of the CNTs in the yarn. Decreasing the temperature or increasing the strain rate lead to a small increase of the flow stress. These results have implications for yarn design, which are discussed in the article.

Fluid-structure interaction modeling of aneurysmal arteries under steady-state and pulsatile blood flow: a stability analysis

Tortuous aneurysmal arteries are often associated with a higher risk of rupture but the mechanism remains unclear. The goal of this study was to analyze the buckling and post-buckling behaviors of aneurysmal arteries under pulsatile flow. To accomplish this goal, we analyzed the buckling behavior of model carotid and abdominal aorta with aneurysms by utilizing fluid-structure interaction (FSI) method with realistic waveforms boundary conditions. FSI simulations were done under steady-state and pulsatile flow for normal (1.5) and reduced (1.3) axial stretch ratios to investigate the influence of aneurysm, pulsatile lumen pressure and axial tension on stability. Our results indicated that aneurysmal artery buckled at the critical buckling pressure and its deflection nonlinearly increased with increasing lumen pressure. Buckling elevates the peak stress (up to 118%). The maximum aneurysm wall stress at pulsatile FSI flow was (29%) higher than under static pressure at the peak lumen pressure of 130 mmHg. Buckling results show an increase in lumen shear stress at the inner side of the maximum deflection. Vortex flow was dramatically enlarged with increasing lumen pressure and artery diameter. Aneurysmal arteries are more susceptible than normal arteries to mechanical instability which causes high stresses in the aneurysm wall that could lead to aneurysm rupture.

Pelvic muscles’ mechanical response to strains in the absence and presence of pregnancy-induced adaptations in a rat model

Maternal birth trauma to the pelvic floor muscles is thought to be consequent to mechanical demands placed on these muscles during fetal delivery that exceed muscle physiological limits. The above is consistent with studies of striated limb muscles that identify hyperelongation of sarcomeres, the functional muscle units, as the primary cause of mechanical muscle injury and resultant muscle dysfunction. However, pelvic floor muscles' mechanical response to strains have not been examined at a tissue level. Furthermore, we have previously demonstrated that during pregnancy, rat pelvic floor muscles acquire structural and functional adaptations in preparation for delivery, which likely protect against mechanical muscle injury by attenuating the strain effect. We sought to determine the mechanical impact of parturition-related strains on pelvic floor muscles' microstructure, and test the hypothesis that pregnancy-induced adaptations modulate muscle response to strains associated with vaginal delivery. Three-month-old Sprague-Dawley late-pregnant (N= 20) and nonpregnant (N= 22) rats underwent vaginal distention, replicating fetal crowning, with variable distention volumes. Age-matched uninjured pregnant and nonpregnant rats served as respective controls. After sacrifice, pelvic floor muscles, which include coccygeus, iliocaudalis, and pubocaudalis, were fixed in situ and harvested for fiber and sarcomere length measurements. To ascertain the extent of physiological strains during spontaneous vaginal delivery, analogous measurements were obtained in intrapartum rats (N= 4) sacrificed during fetal delivery. Data were compared with repeated measures and 2-way analysis of variance, followed by pairwise comparisons, with significance set at P < .05. Gross anatomic changes were observed in the pelvic floor muscles following vaginal distention, particularly in the entheseal region of pubocaudalis, which appeared translucent. The above appearance resulted from dramatic stretch of the myofibers, as indicated by significantly longer fiber length compared to controls. Stretch ratios, calculated as fiber length after vaginal distention divided by baseline fiber length, increased gradually with increasing distention volume. Paralleling these macroscopic changes, vaginal distention resulted in acute and progressive increase in sarcomere length with rising distention volume. The magnitude of strain effect varied by muscle, with the greatest sarcomere elongation observed in coccygeus, followed by pubocaudalis, and a smaller increase in iliocaudalis, observed only at higher distention volumes. The average fetal rat volume approximated 3 mL. Pelvic floor muscle sarcomere lengths in pregnant animals undergoing vaginal distention with 3 mL were similar to intrapartum sarcomere lengths in all muscles (P > .4), supporting the validity of our experimental approach. Vaginal distention resulted in dramatically longer sarcomere lengths in nonpregnant compared to pregnant animals, especially in coccygeus and pubocaudalis (P < .0001), indicating significant attenuation of sarcomere elongation in the presence of pregnancy-induced adaptations in pelvic floor muscles. Delivery-related strains lead to acute sarcomere elongation, a well-established cause of mechanical injury in skeletal muscles. Sarcomere hyperelongation resultant from mechanical strains is attenuated by pregnancy-induced adaptations acquired by the pelvic floor muscles prior to parturition.

The Turning Point for Morphomechanical Remodeling During Complete Intestinal Obstruction in Rats Occurs After 12-24h.

Intestinal obstruction prompts luminal dilation and wall remodeling proximal to the site of obstruction. Studies on temporal and spatial morphomechanical remodeling are needed for comprehending the pathophysiology of acute intestinal obstruction. The aim was to estimate the no-load and zero-stress morphomechanical properties in circumferential and longitudinal direction at 0, 6, 12, 24, 36, and 48h after complete intestinal obstruction. Obstruction of the distal ileum was created surgically by placement of a polyethylene ring for up to 48h in 30 rats. Sham and normal groups were also studied (n=12). Five 6cm-long intestinal segments proximal to the obstruction site were used for histological, morphometric and mechanical analysis at the designated times. Morphomechanical changes were huge but only subtle changes were observed between the 5 segments during the obstruction period. Due to dilation, the serosal length and mucosal length increased continuously from 6 to 48h (p<0.001). The wall area increased at 24h and beyond (p<0.001), demonstrating tissue growth. The opening and bending angle decreased to minimum values at 24h where after the opening angle increased and the bending angle returned to pre-obstruction levels. For the residual stretch ratios and the position of the neutral axis the turning point was found after 24h. Histologically, the thickness and area of most wall layers were quite stable for the first 12h but with an increase at the 24h time point that continued to the 48h time point. The most pronounced change was found for the circumferential muscle layer (p<0.05). Analysis of picrosirius red stained slides showed that submucosal type 3 collagen fraction increased significantly (p<0.001), whereas the fraction of type 1 collagen decreased (p<0.001). In conclusion, pronounced time-dependent morphomechanical remodeling was found. The obstructed intestine went from dilation remodeling to growth remodeling during the interval 12-24h after creating the obstruction.

Performance investigation of a dissipative dielectric elastomer generator by the damping model

This paper proposes an analytical model to investigate the performance of a dissipative dielectric elastomer generator (DEG) by considering the damping effect and the leakage current. Based on the analytical model, we study the effect of the cycle period, the maximum stretch ratio, and the pre-stretch ratio on the performance parameters of DEGs: the energy density, the average power density, and the conversion efficiency. The simulation results show that increasing the cycle period contributes to improving the energy density and the conversion efficiency. Moreover, the energy density and the average power density increase with the increase in the maximum stretch ratio. In addition, as the pre-stretch ratio increases, the energy density and the average power density can decrease. These methods and conclusions can better guide the optimal design and assessment of DEGs.

Biaxial Orientation of Poly(ethylene 2,5‐furandicarboxylate): An Explorative Study

AbstractThe biaxial orientation behavior of poly(ethylene 2,5‐furandicarboxylate) (PEF) is studied in comparison to poly(ethylene terephthalate) (PET). PEF is a polyester that can be produced through similar steps as PET but using 100% biobased 2,5‐furandicarboxylic acid instead of terephthalic acid. This work highlights the stress–strain behavior of PEF during biaxial orientation at various temperatures. Strain hardening and strain‐induced crystallization in the oriented PEF samples generally appeared at higher stretch ratios for PEF than for PET at comparable molecular weight, while somewhat lower degrees of crystallinity are reached in PEF. Shrinkage in oriented PEF is found to be on par with PET in the region of the glass transition. Higher modulus and improved barrier properties, compared to PET, are found in the oriented materials when sufficiently high stretch ratios are applied in biaxial orientation.

Heat Transfer of Springs in Oblique Crossflows

An experimental program is presented of heated tension springs in an external crossflow over a range of laminar Reynolds numbers, spring stretch ratios, and angles of attack. Extensive measurements of the forced convection heat transfer of helical wire within a wind tunnel reveal an interesting nonmonotonic dependence on angle of attack. Computational fluid dynamics (CFD) simulations, showing good agreement with the experimental data, are used to explore the behavior and gain a better understanding of the observed trends. A dimensionless correlation is developed that well captures the experimental and CFD data and can be used as an efficient computational tool in broader applications.

Dependence of the birefringence of polystyrene film on the stretching conditions.

We investigated the dependence of the birefringence of polystyrene (PS) film with a negative optical birefringence on the stretching conditions. We varied the stretching ratio (SR), stretching speed (SS), and stretching temperature (ST), and measured the inplane birefringence and the Nz coefficient of the PS film. The inplane birefringence was increased with greater SR and SS but decreased with greater ST. The Nz coefficient of the stretched PS film was around zero and showed similar dependence on the stretching conditions like inplane birefringence.

Caching in Information-Centric Networking: Strategies, Challenges, and Future Research Directions

Information-Centric Networking (ICN) is an appealing architecture that has received a remarkable interest from the research community thanks to its friendly structure. Several projects have proposed innovative ICN models to cope with the Internet practice, which moves from host-centrism to receiver-driven communication. A worth mentioning component of these novel models is in-network caching, which provides flexibility and pervasiveness for the upturn of swiftness in data distribution. Because of the rapid Internet traffic growth, cache deployment and content caching have been unanimously accepted as conspicuous ICN issues to be resolved. In this article, a survey of cache management strategies in ICN is presented along with their contributions and limitations, and their performance is evaluated in a simulation network environment with respect to cache hit, stretch ratio, and eviction operations. Some unresolved ICN caching challenges and directions for future research in this networking area are also discussed.

Study on Thermo-Oxidative Aging of EPDM Vulcanizates : Relationship between Tensile Breaking Stretch Ratio and Average T&lt;sub&gt;2&lt;/sub&gt; Relaxation Time of Rubber Phase

Study on Thermo-Oxidative Aging of EPDM Vulcanizates : Relationship between Tensile Breaking Stretch Ratio and Average T&lt;sub&gt;2&lt;/sub&gt; Relaxation Time of Rubber Phase

An anisotropic hyperelastic constitutive model for plain weave fabric considering biaxial tension coupling

A nonlinear anisotropic hyperelastic constitutive model is developed for plain weave fabrics by considering biaxial tensile coupling. The strain energy function is decomposed into two parts to represent tensile energy, including the biaxial tensile coupling effect from fiber elongation and shearing energy from relative rotation between warp and weft yarns. A simple and efficient material parameter identification method is proposed. The model is exemplified on a balanced plain weave glass fabric. Experimental data from the literature are used to identify material parameters in the constitutive model. Model validation is implemented by comparing numerical results with various experimental data, including biaxial tension tests under different stretch ratios and the picture frame shearing test. The developed constitutive model is applied to numerical simulation of a double-dome stamping of the plain weave fabric. The influences of binder force and initial fiber yarn orientation on forming are investigated. Numerical results demonstrated that the biaxial tensile coupling effect could not be neglected in forming simulation. The developed constitutive model is suitable to characterize the nonlinear behavior of plain weave fabrics under large deformation.

Urinary Bladder vs Gastrointestinal Tissue: A Comparative Study of Their Biomechanical Properties for Urinary Tract Reconstruction

To evaluate the mechanical properties of gastrointestinal (GI) tissue segments and to compare them with the urinary bladder for urinary tract reconstruction. Urinary bladders and GI tissue segments were sourced from porcine models (n = 6, 7 months old [5 male; 1 female]). Uniaxial planar tension tests were performed on bladder tissue, and Cauchy stress-stretch ratio responses were compared with stomach, jejunum, ileum, and colonic GI tissue. The biomechanical properties of the bladder differed significantly from jejunum, ileum, and colonic GI tissue. Young modulus (kPa-measure of stiffness) of the GI tissue segments was on average 3.07-fold (±0.21 standard error) higher than bladder tissue (P < .01), and the strain at Cauchy stress of 50 kPa for bladder tissues was on average 2.27-fold (±0.20) higher than GI tissues. There were no significant differences between the averaged stretch ratio and Young modulus of the horizontal and vertical directions of bladder tissue (315.05 ± 49.64 kPa and 283.62 ± 57.04, respectively, P = .42). However, stomach tissues were 1.09- (±0.17) and 0.85- (±0.03) fold greater than bladder tissues for Young modulus and strain at 50 kPa, respectively. An ideal urinary bladder replacement biomaterial should demonstrate mechanical equivalence to native tissue. Our findings demonstrate that GI tissue does not meet these mechanical requirements. Knowledge on the biomechanical properties of bladder and GI tissue may improve development opportunities for more suitable urologic reconstructive biomaterials.

Research on Uniaxial Tension Test of Brain Tissue

Corresponding to low targeting accuracy due to tissue deformation during the process of electrode insertion in sub-thalamic nucleus deep brain stimulation (DBS), biomechanical properties of brain tissue are essential to investigate. In this paper the isolated porcine brain tissue is used in the uniaxial tensile test. Moreover, cylindrical samples of diameter (10 mm) and height (10 mm) are used to measure tensile length by single degree of axis at 5mm/s, until specimen was broken. The stretch ratio of brain tissue has been explored. The material failure criterion parameters, K, 1, 2, of MAT-QUASILINEAR-VISCOELASTIC biological material model in LS-DYNA are fitting calculated according to the experimental results. Six uniaxial failure data obtained from uniaxial tests are 4.81, 5.00, 4.07, 4.62, 4.28, 4.45 respectively. Three failure material constants 1, 2, K are -0.0084, -3.1944, -4.8095. The failure criterion is being implemented in LS-DYNA to simulate brain tissue.

Muscle activity monitoring with fabric stretch sensors

In this paper, development of a fabric stretch sensor embedded system has been proposed for muscle activity monitoring. It is expected that this product will be proper for monitoring a wide range of human activities mainly due to the characteristics of light-weight and high sensitivity. The fabric sensors developed can be easily attached to almost any types of clothing due to their thin and stretchable natures. The mechanism and performance of the sensors have been characterized by measuring the mechanical and electrical performance along with stretch ratio or strain percent. The data collected would be successfully transmitted to mobile phones through low power consumption BLE connection, and thus muscle activities in real time. As expected, the resultant smart muscle pants could achieve realistic goals through monitoring body movements without any significant loss of wear comforts in normal clothing. This work significantly contributed in enhancing the utility of strain/stretch sensors for development of e-textiles and intended to be a starting point for data collection and analysis of smart fabric embedded sensing technologies.

An electromechanical model for the estimation of breakdown voltage in stretchable dielectric elastomer

Dielectric elastomer (DE) is capable of large deformation under electrical excitation. However, DE is susceptible to breakdown failure in this electromechanical actuation. Using an analogy of fracture mechanics, we establish an energetic model to estimate the breakdown voltage of DE in actuation. The non-linear characteristics, including material parameters, stretch ratios, and ambient temperature are involved to determine the critical condition of breakdown failure. The model is verified by experimental data of VHB membranes, and then extended to different DE materials. With respect to applications, two types of classic dielectric elastomer actuators (DEAs) are analyzed, and their breakdown voltages are evaluated. This study can provide a path for optimization of DE in electromechanical actuator and insulator applications.

A high-resolution gas-kinetic scheme with minimized dispersion and controllable dissipation reconstruction

In order to simulate multiscale problems such as turbulent flows effectively, the high-order accurate reconstruction based on mini- mized dispersion and controllable dissipation (MDCD) is implemented in the second-order accurate gas-kinetic scheme (GKS) to improve the accuracy and resolution. MDCD is firstly extended to non-uniform grids through the modification of dissipation and dispersion coefficients for uniform grids based on the local stretch ratio. Remarkable improvements in accuracy and resolution are achieved on general grids. Then a new scheme, MDCD-GKS is constructed, with the help of MDCD reconstruction, not only for conservative variables, but also for their gradients. MDCD-GKS shows good accuracy and efficiency in typical numerical tests. MDCD-GKS is also coupled with the improved delayed detached-eddy simulation (IDDES) hybrid model and applied in the fine simulation of turbulent flow around a cylinder, and the prediction is in good agreement with experiments when using the relatively coarse grid. The high accuracy and resolution of the developed GKS guarantee its high efficiency in practical applications.