Elastomer Tube Research Articles

Coaxial direct ink writing of shear stiffening gel/Ecoflex composite for customized insoles

Traditional sports insoles could reduce plantar pressure and protect against external dynamic shock during exercising, while their performance was limited severely for individuals with abnormal gait. Thus, it was in urgent need to develop insoles with both safeguarding and orthopedic functions. Here, shear stiffening gel (SSG), whose storage modulus rose dramatically with the shear frequency, was encapsulated in elastic elastomer (Ecoflex) tubes by using the coaxial direct ink writing technique to prepare customized insoles. The printing parameters were investigated to optimize the mechanical property of SSG/Ecoflex composite core-sheath fibers and hybrid films. Due to the rate-dependent mechanical property of inner SSG, the hybrid films could dissipate 53.4% impact acceleration, 46.9% penetrated force and increase buffer time by 1.6 times under dynamic loadings, thus presenting excellent safeguarding performance. Compared with commercial insoles, coaxial additive manufactured SSG/Ecoflex hybrid insoles not only exhibited better protection against sudden shocks during mild and violent exercises but also provided physical corrections to abnormal walking gaits, such as varus and valgus foot. Therefore, the programmable coaxial additive manufacture technique for constructing SSG/Ecoflex composite sports armors hold great promise for future advanced safeguarding and customized health improvement.

Preferential alignment of two-dimensional montmorillonite in polyolefin elastomer tube via rotation extrusion featuring biaxial stress field

Preferential alignment of two-dimensional (2D) nanofillers in polymer matrix is essential to realize the transition of distinct properties from individual nanofiller into bulk nanocomposites, but this is an impossible task in conventional melt-processing because 2D nanofillers with two degrees of freedom experience transition and rotation movements along or around the two axes of the plate. Here, we proposed a flow manipulation strategy to control the preferential alignment of 2D montmorillonite (MMT) plates in polyolefin elastomer (POE) tube by superposing a hoop drag flow from rotation of mandrel and die onto axial flow caused by conventional extrusion. The biaxial stress field simultaneously restricted the axial and hoop rotation movements of the major and minor axes of the MMT plates, leading to preferential alignment along the hoop and longitudinal directions with the planar surface perpendicular to radial direction of the tube. As a result, the as-prepared tube exhibited strong resistance to various mechanical deformations (hoop kinking, axial and radial compression) as well as enhanced barrier property, holding the promising potential as an advanced tube in clinical interventional therapy and transportation of polar substances. Compared with the state-of-the-art techniques with complicated process and low productivity efficiency, this flow manipulation strategy for tailoring preferential alignment of 2D nanofillers was featured with a simple melt-processing, which was suitable for massive production and easily extended to the other composite tubes.

Soft dielectric elastomer tubes in an electric field

Soft dielectric elastomers with high relative permittivity, very low modulus and high electric breakdown strength have emerged as promising materials for various applications as sensors, actuators and in energy harvesting and soft robotics. We study the intricate deformation behaviour of a soft dielectric elastomer tube of finite length and closed ends, that carries a dead load, is internally pressurised by an injected fluid and has a high electric potential applied across its walls. As for soft tubes in the absence of a potential, this electro-hyperelastic problem involving very large deformations, exhibits a multitude of possibilities, including homogeneous deformation, inhomogeneous bifurcation, snap-through instabilities and post bifurcation behaviour in the form of propagation of axisymmetric bulges. We develop a coupled Finite Element procedure for the situation where the domains of the mechanical and electrostatic problems coincide. The procedure can handle volume flow rate controlled electro-elastic problems. We use it to study the many aspects of the deformation behaviour and limitations placed by competing failure mechanisms on practical utilisation of the large areal strains and axial actuations that can be produced. If electrical breakdown can be avoided by ingenious design of loading sequences, the large volume increase in the tube due to the triggering of instabilities can be harnessed and has far-reaching technological implications.

Assessment of organic carbon migration and biofilm formation potential on polymeric tubes in contact with water

Biofilm formation has been frequently identified as a pathway of nosocomial infection in polymeric tubes used for patients of all ages. Biofilm formation on tube surfaces can lead to hygienic failure and cause diarrhea, stomach pain, inflammation, and digestive system disease. This study investigated the influence of polymeric tube materials in contact with water on the biomass formation potential and migration potential of microbially available carbon from plasticizers using a BioMig test. The thermoplastic elastomer tube, which is reusable, leached a relatively low amount of assimilable organic carbon to water. In contrast, the assimilable organic carbon migration potential of polyurethane was the most significant, 6-fold greater than that of the thermoplastic elastomer. Moreover, the same materials (e.g., silicone) produced via different manufacturing processes showed significant differences in migration behaviors. The potential biomass formation observed in polyurethane was approximately 7 × 109 cells cm−2 for both Aeromonas hydrophila and Escherichia coli strains. This study highlights the importance of choosing the correct material characteristics of polymeric tubes in contact with water to protect them from bacterial contamination. Therefore, manufacturers can use the BioMig test to evaluate and produce more hygienic and biostable tubes.

Voltage-controlled instability transitions and competitions in a finitely deformed dielectric elastomer tube

This work compares the transition and competitive mechanism between three types of instabilities of an incompressible dielectric tube: wrinkling, pull-in instability and electric breakdown. We also see how to select one type of instability mode on demand. First, we investigate the finite response and the wrinkling of a tube subject to a combination of applied radial voltage, torsion and axial force (or stretch). We use the surface impedance matrix method to determine the wrinkling threshold, and obtain the corresponding two-dimensional pattern shape of wrinkled surface. Second, we look at illustrative numerical calculations for ideal Mooney-Rivlin dielectrics and study the effects of actuation methods, electric voltage, torsion and geometrical parameters on the three types of instabilities. Results show that the deformation of the solid will influence the true electric field in the solid, and induce competitive effects between the applied voltage and the mechanical loading. We find that in addition to the expected contractile buckling, buckling may also occur in extension in an electrically actuated dielectric tube, a departure from the purely elastic wrinkling. Moreover, the electro-elastic behavior of the DE elastomer can be enhanced by introducing torsion. We also find that large stable actuation can be achieved and that the wrinkling pattern can be selected on demand in the tube by finely tuning the actuation, voltage, torsion and geometry, without encountering material failure.

Bifurcation of a finitely deformed functionally graded dielectric elastomeric tube

Soft functionally graded materials have attracted intensive attention owing to their special material inhomogeneity and are realized as various applications. In this paper, we theoretically investigate the finite deformation and superimposed bifurcation behaviors of an incompressible functionally graded dielectric tube subject to a combination of axial stretch and radial voltage. The theoretical framework of nonlinear electroelasticity and the related linearized incremental version is employed. We assume that the modulus and permittivity of the elastomer vary linearly along the thickness of the tube. The surface impedance matrix method is adopted to obtain the bifurcation equation for buckling of the tube. We present numerical calculation for the ideal neo-Hookean dielectric elastomer to study the effects of the applied voltage, geometrical size and material grading parameters on the nonlinear response and the incremental buckling behavior of the tube. We validate our results through comparison with those of the elastic problem. The results can provide solid guidance for the design and realization of dielectric actuators.

A mechanical model for McKibben pneumatic artificial muscles based on limiting chain extensibility and 3D application of the network alteration theories

Pneumatic Artificial Muscles (PAMs) mimic the behavior of skeletal muscles by generating contractile force when they are pressurized. Stiffness of these actuators depends on the applied pressure because the inner elastomeric tube exhibits non-linear mechanical behavior which also makes control of the actuator difficult. Therefore, it is crucial to obtain a precise mechanical model for these actuators. In this work, based on the theory of limiting chain extensibility, a new continuum mechanics-based model is developed for elastomeric McKibben PAMs to predict stiffness and output parameters such as free contraction, blocked force, and dead-band pressure during the actuation course. The developed model is consistent with network alternation theories, which allow predicting the softening observed in first cycles of inflation-deflation (Mullins effect). The established relations can predict variations of the actuation force due to the alternation of the material network parameters as a result of Mullins softening. In order to determine the material parameters of the bladder, uniaxial tensile tests have been conducted on a virgin silicon rubber. Cyclic tests have also been conducted on the fabricated PAMs in virgin and completely softened states to obtain their characteristic curves. It is concluded that, fractional evolution laws can be well combined with the developed model to predict the behavior of PAMs during cyclic deformations. It is observed that, even for contractions less than 25%, the maximum principal stretch in a PAM can exceed three which implies that, simple strain energy functions such as NeoHookean and Mooney-Rivlin should not be employed for PAMs. It is also concluded that, the Mullins softening increases the free contraction while makes no remarkable effect on the blocked force.

Magnetorheological elastomer peristaltic pump capable of flow and viscosity control

In this article, a magnetorheological elastomer peristaltic pump capable of bidirectionally conveying Newtonian and non-Newtonian fluids with precise net pumped volume and required viscosity patterns of fluids is presented and numerically investigated. The basic element is very succinct, which is composed of only a magnetorheological elastomer tube and an electromagnet. Two basic elements in series constitute a magnetorheological elastomer peristaltic pump. The maximum pumped volume can be achieved using maximum lag between voltage parameters gap1 and gap2. The Nelder–Mead optimization method is applied to realize the precise control of the net pumped volume during a steady working cycle. For a certain net pumped volume, the viscosity of fluids can also be adjusted through the modulation of the driving voltage parameters obtained from the Nelder–Mead optimization method.

Forming of thin-walled AA6061-T4 tubular joint by elastomeric bulging: experiment and computation

Tubular joint forming by elastomeric bulging (EB) is a feasible way to connect aluminum alloy tubes to high-strength sleeve fittings. It is critical to fully and deeply understand the deformation-induced sealing performance of tubular joints for precise manufacturing of high performance tubular joints. In this paper, thin-walled AA6061-T4 tubular joints fabricated by EB was investigated experimentally and numerically. Firstly, the anisotropic AA6061-T4 tube, the polyurethane elastomer (PUE) tube with hyperelasticity and the 15-5PH stainless steel (SS) sleeve fitting were characterized and modeled. Compared with the explicit algorithm, the implicit axisymmetric finite element (FE) models of the whole joining process, including EB forming and springback, were established. The influence of the groove structure of the sleeve fitting on the shearing-related pull-out strength and sealing-related bonding strength was discussed, and then the reasonable sleeve fitting’s structure with two grooves was obtained. Thus, the accurate ranges of extrusion pressure and tube bulging heights were derived for precise control of forming quality. Finally, the experimental set-up and forming dies for EB joining tests were established, and the reliability of these parameters determined by the FE model was verified experimentally. It is concluded that the forming quality of this tubular joint can be controlled precisely based on FE modeling of whole joining process, and thin-walled AA6061-T4 tubular joint fabricated by EB has a reliable seal performance.

1D Stretchable Block Copolymer Yarn‐Based Energy Harvesters via BaTiO3/Polydimethylsiloxane Composite‐Carbon Conductive Ink

AbstractHighly stretchable self‐powered energy sources are promising options for powering diverse wearable smart electronics. However, commercially existing energy sources are disadvantaged by tensile strain limitations and constrained deformability. Here, 1D thread‐based highly stretchable triboelectric nanogenerators (HS‐TENGs), a crucial step toward overcoming these obstacles, are developed based on a highly stretchable coaxial‐type poly[styrene‐b‐isoprene‐b‐styrene] (SIS) elastomer tube. Carbon conductive ink is injected into the SIS tube as a core 1D electrode that remains almost unaffected even under 250% stretching because of its low Young's modulus. To further facilitate power generation by the HS‐TENG, a composite of barium titanate nanoparticles (BaTiO3 NPs) and polydimethylsiloxane (PDMS) is coated on the initial SIS tube to modulate the dielectric permittivity based on variations in the BaTiO3 NPs volume ratio. The 1D PDMS/BaTiO3 NP composite‐coated SIS and a nylon 6‐coated 2D Ni–Cu conductive fabric are selected as triboelectric bottom and top layers, respectively. Woven HS‐TENGs textiles yield consistent power output under various extreme and harsh conditions, including folded, twisted, and washed states. These experimental findings indicate that the approach may become useful for realizing stretchable multifunctional power sources for various wearable electronics.

A Stretchable Capacitive Strain Sensor Having Adjustable Elastic Modulus Capability for Wide‐Range Force Detection

Stretchable strain sensors are important components of soft robotics, rehabilitation assistance, and human health monitoring systems. However, strain sensors capable of wide‐range force detection with adjustable modulus facilities are highly desirable to obtain mechanical feedback in various scenarios. Herein, a stretchable capacitive strain sensor capable of adjustable modulus and wide‐range force detection is reported. The sensor consists of two liquid metals (LMs) filled thermoplastic elastomer (TPE) tubes encapsulated in flexible silicone. The adjustable modulus capability of the sensor is attained by mounting the sensor with springs of different elastic coefficients. During electromechanical tests, the elastic coefficient‐dependent adjustable modulus is obtained in the range of 0.78–10.3 MPa. After optimizing the performance, a sensor capable of wide force‐sensing range (0.07–74 N), high cyclic stability (>3500 cycles), with low hysteresis, good linearity, and fast response time (<50 ms) is achieved. Finally, a digital display system is developed to display the amount of detected force during the loading of the sensor, which confirms the great capability of the sensor to be applied in joint rehabilitation and soft robotic fields.

Time-dependent electromechanical phase transition and bulging propagation in a viscoelastic dielectric elastomer tube

When a dielectric elastomer (DE) tube is subjected to mechanical pressure and electrical voltage, electromechanical (EM) phase transition may happen. In recent experiment, it has been shown that the EM phase transition process can be highly time-dependent: the bulged section can propagate along the tube under fixed voltage. In this article, we adopt a nonlinear viscoelastic model for the DE material to investigate the time-dependent EM phase transition of a DE tube under fixed amount of air and fixed voltage. Using the model of viscoelasticity, we demonstrate that a DE tube may experience a transition from a homogeneous shape to an inhomogeneous shape with bulged and unbulged sections coexisting in the tube under electrical loading, then the bulged section can gradually propagate at the expense of the unbulged section under the fixed initial coexistent voltage, which well captures the experimental observations. We have further shown that the EM phase transition condition and propagation of the bulged section of the DE tube also depend on the volume of the air chamber connected to the tube and the ramping rate of the applied voltage.

Reliability and optimal replacement interval of flexible hose assemblies in drinking water installations

The paper presents theoretical considerations and questionnaire examinations concerning reliability and replacement interval of flexible hose assemblies for washbasins, sinks and water closets. The topic is vitally important for providing home safety. The impact of operational temperature on durability of elastomeric tube was theoretically assessed. Questionnaire examinations covered 356 hoses installed in a block of flats in Poznan (Poland) and detached houses. The analyzed period of hoses’ operation was 11 years or less in the case of earlier failure. During that time 41 hoses (approximately 12%) had failed. Reliability functions were obtained separately for cold and hot water installations. It was found that flexible hose assemblies for hot water were less reliable than those for cold water. The optimal time to replace hoses was estimated as 6–7 years.

Unsteady streaming flow based TENG using hydrophobic film tube with different charge affinity

This paper proposes a simple, eco-friendly and economical fluid-based triboelectric nanogenerator (Flu-TENG), which is based on polyvinylidene fluoride (PVDF) between elastomeric tubes (P-TENG) and biaxially oriented polypropylene (BOPP) between elastomeric tubes (B-TENG). We examined the interactions based on the relation between the hydrodynamics of pipe flow and electrostatic induction at the electrical double layer (EDL). This is the first study to focus on the hydrodynamics of the unsteady pipe flow. From the experimental results, it was verified that the peak to peak current from unsteady flow is 70 times higher than that of steady flow. We also investigated the effect of triboelectric series to generate higher output. When the PVDF and Ground/PVDF/BOPP are connected respectively, it is called as P-TENG/PP-TENG/PB-TENG. The measured short circuit current at 15.9 Hz for P-TENG/PP-TENG/PB-TENG are 0.29 μA, 1.59 μA and 2.40 μA, respectively. And the measured open circuit voltage of P-TENG/PP-TENG/PB-TENG are 3.71 V, 14.6 V and 29.7 V, respectively. Finally, we verified the maximum power reaches 11.5 μW in the case of PB-TENG. This provides a new approach for improving the output power of the FluTENG for special applications.

Biomodeling: Perforated and Endothelialized Elastomeric Tubes for Vascular Modeling (Adv. Mater. Technol. 9/2019)

A tubular silicone elastomer platform comprising arrays of perforations generated using focused laser ablation is described for modeling blood vessels in vitro by Weijia Zhang, Yu Shrike Zhang, and co-workers, in article number 1800741. When populated with endothelial cells on the interior surfaces and embedded within an extracellular matrix, cells can sprout out from the tubes into the surrounding matrix through the open pores, providing an enabling system for studying angiogenesis.

Harvesting liquid stream energy from unsteady peristaltic flow induced pulsatile Flow-TENG (PF-TENG) using slipping polymeric surface inside elastomeric tubing

Flow in small size tubing or channels in multidisciplinary field such as Chemistry, medical and lab on chip sensors can be a potential candidate for energy scavenging. Recently, energy harvesting techniques have been developed utilizing the steady flow under induced pressure gradient in lab on chip device. Here, for the first-time harnessing energy from unsteady pulsatile water flow over hydrophobic polymeric surface attached in the inner wall of the elastic tubing that induces slip boundary and causes electrostatic potential difference in the electrical double layer of the solid-liquid interface is described. This work demonstrates peristaltic flow driven triboelectric nano-generator based on the flow contact electrification between the hydrophobic micro porous PVDF (mpPVDF) membrane and water stream flowing through elastic silicon tubing. The efficiency of the PF-TENG as energy harvester was evaluated using deionized water (PF.DIw-TENG), tap water (PF.Tw-TENG). The mechanistic approach is discussed for the generation of alternating current based on the relation between the hydrodynamics of pipe flow and adsorbed ions at the Electrical Double Layer (EDL). The generated voltage and short-circuit currents (Isc) are superior in PF.Tw-TENG, in particular, the maximum peak to peak values of voltage and Isc are 20.93 V and 1.67 μA, respectively, over PF.DIw-TENG. The PF.Tw-TENG shows greater efficiency over PF.DIw-TENG due to the presence of dissolved free mobile ions which can enhance the power output. Moreover, we verify the possibility of the PF-TENG as self-powered average volumetric flow rate sensor. The developed PF.TENG can be potentially applied for fluid dynamic monitoring of peristaltic flow involved in pharmaceuticals and food industries.

Soft kink valves

Completely soft, autonomous fluidic robots require valves made of soft materials. Such a soft valve has been demonstrated recently to enable complex movements of soft robots using a single source of air of constant pressure. This paper studies the mechanics of the valve using a combination of experiments and calculations. The valve is made of an elastomeric tube, subject to axial compression. At critical compression, the tube snaps into a kink and blocks the flow of the air in the tube. At another critical compression, the tube snaps open the kink and lets the air flow in the tube. The instability functions as a digital, on-and-off valve, and this function is unaffected by inaccurate deformation of the ends of the tube. A kinked tube blocks fluid flow in the tube up to a certain pressure. Because the elastomer readily undergoes large and reversible deformation, the kink valve can close and open repeatedly without damage. We map out the functional characteristics of the kink valve—the kink-close compression, the kink-open compression, and the breakthrough pressure—in the design space of material and geometry. It is hoped that this study will stimulate further work to harness diverse elastic instabilities for functions needed in soft robots.

Efficient Thermobonding Process Forming a Polyurethane Based Diagnostic Catheter with Liquid Crystal Polymer.

Diagnostic and therapeutic catheters play an inevitable role in minimal invasive medical procedures. Unfortunately, standard catheters show a limited transducer density and high production efforts. We propose a novel catheter design and manufacturing method using a liquid crystal polymer (LCP)-based flexible printed circuit board (FPCB) and a thermoplastic polyurethane (TPU) elastomer tube. Both components are bond together with a low cost, additive free lamination process at a re-flow temperature of 250° C. The lamination process is improved with a laser welding seam and LCP-integrated microholes preventing delamination. Standardized Mechanical tests were conducted to characterize the bonding. A Peel strength of up to 8.5 N in the radial direction and a non plastic elongation in the axial direction of 10% provide evidence that the thermobonding process is suitable for the production of flexible and mechanically durable medical catheters featuring high electrode densities.

Perforated and Endothelialized Elastomeric Tubes for Vascular Modeling.

We report the fabrication of a tubular polydimethylsiloxane (PDMS) platform containing arrays of small pores on the wall for modeling blood vessels in vitro. The thin PDMS tubes are produced following our previously reported templating approach, while the pores are subsequently generated using focused laser ablation. As such, when these perforated PDMS tube are populated with a monolayer of endothelial cells on the interior surfaces and embedded within an extracellular matrix (ECM)-like environment, the endothelial cells can sprout out from the tubes into the surrounding matrix through the open pores. When a pair of perforated PDMS tubes are placed in parallel in the matrix, formation of an interconnected network of microvasculature or larger vessels occurs, which is dependent on the flow dynamics within the PDMS tubes. Moreover, when co-cultured with tumor spheroids, the onset of tumor angiogenesis is observed. Our perforated and endothelialized PDMS tubes are believed to enable convenient vascular modeling in vitro and will likely contribute to improved biological studies as well as therapeutic screening.

Magnetorheological elastomer peristaltic fluid conveying system for non-Newtonian fluids with an analogic moisture loss process

A magnetorheological elastomer peristaltic fluid conveying system consisting of a magnetorheological elastomer tube and two electromagnets implements controlled movements via an external magnetic field with varying periods of driving voltages to convey non-Newtonian fluids over a certain time period. The effects of backpressure at the outlet of the magnetorheological elastomer peristaltic fluid conveying system, the viscosity of fluids at zero shear rate, and moisture loss along the longitudinal direction on net pumped volume are investigated systematically. The results demonstrate that the net pumped volume declines linearly with backpressure under all driving voltage periods. An improvement of the viscosity of fluids at zero shear rate allows at first the decrease, then the increase, and finally the decrease of the net pumped volume. Moisture loss plays a second role in the net pumped volume and the change of the fluid viscosity profile. The compression of the magnetorheological elastomer tube, the maximum shear stress, and the maximum von Mises stress in the magnetorheological elastomer peristaltic fluid conveying system are investigated to evaluate the magneto-fluid-structure interaction. This research offers a new approach to biological fluid conveying with an analogic moisture loss process.