Elastomer Core Research Articles

Robust Control of a Cable-Driven Soft Exoskeleton Joint for Intrinsic Human-Robot Interaction.

A novel, cable-driven soft joint is presented for use in robotic rehabilitation exoskeletons to provide intrinsic, comfortable human-robot interaction. The torque-displacement characteristics of the soft elastomeric core contained within the joint are modeled. This knowledge is used in conjunction with a dynamic system model to derive a sliding mode controller (SMC) to implement low-level torque control of the joint. The SMC controller is experimentally compared with a baseline feedback-linearised proportional-derivative controller across a range of conditions and shown to be robust to un-modeled disturbances. The torque controller is then tested with six healthy subjects while they perform a selection of activities of daily living, which has validated its range of performance. Finally, a case study with a participant with spastic cerebral palsy is presented to illustrate the potential of both the joint and controller to be used in a physiotherapy setting to assist clinical populations.

Vibration analysis of a rotating magnetorheological tapered sandwich beam

This paper investigates the free vibration analysis of a doubly tapered magnetorheological rotating sandwich beam based on the Euler-Bernoulli theory. The beam is made of a magnetorheological elastomer core sandwiched between two elastic layers. Through energy approach the kinetic and potential energies of the system are written and using the Lagrange equation the discretized form of the governing equation is derived based on the Ritz method. The free vibration analysis is carried out to obtain the natural frequency and the corresponding loss factor of the beam. Finally, after validating the formulation in order to provide a deep insight the effects of different parameters on the free vibration characteristics of the beam are studied through a comprehensive survey.

Peculiarities of magnetic properties of magnetoactive elastomers with hard magnetic filler in crossed magnetic fields

The purpose of this work was to research the influence of interparticle interactions, the elastic properties of matrix and the method of particles preparation on the magnetic properties of the magnetoactive elastomers based on polyurethane rubber containing magnetic particles with high coercivity both conducting and non-conducting. Magnetostatic properties measurements of magnetoactive elastomers were carried out using Vibrating Sample Magnetometer. The diagonal components of susceptibility tensor were found. The dynamic magnetic susceptibility (non-diagonal components) of magnetoactive elastomers was found with immitance-meter using a coil with an elastomeric core. The measured static and dynamic parameters of different samples were compared with each other. Mechanisms of magnetization changes in parallel and crossed magnetic fields are discussed.

Dynamic Analysis of the Non-Linear Behavior of a Composite Sandwich Beam with a Magnetorheological Elastomer Core

This work deals with the active control of the vibrations of mechanical structures incorporating magnetorheological elastomer. The damping coefficient and shear modulus of the elastomer increase when exposed to a magnetic field. Compared with the vibration control where the elastomer is permanently exposed to a magnetic field, the control of this process through time reduces vibrations more effectively. The experimental study for the vibrations of a sandwich beam filled with an elastomer is conducted, followed by a numerical study using the Abaqus code. The vibration damping is found to be dependent on the loading rate of micro-size ferromagnetic particles in the elastomer.

Forced transverse vibration of composite sandwich beam with magnetorheological elastomer core

We studied, experimentally and numerically, the vibrational response of a magnetorheological elastomer sandwich beam, clampedfree, delimited by two skins aluminum 7075T6, first subjected to a variable magnetic field perpendicular to the skin of the beam, and second to a harmonic excitation by magnetic force applied at the free end. Our main objective was to predict the effect of the intensity of the current flowing through a coil on several dynamic factors. The maximum amplitude of resonance and the variation of the loss factor as a function of structural stiffness are adjusted simultaneously by the application of different magnetic fields. The results of both methods are compared.

Numerical simulation of the nonlinear static behavior of composite sandwich beams with a magnetorheological elastomer core

In this work the static behavior of magnetorheological elastomer (MRE) sandwich beams is studied in flexion with transverse shear. The beam is formed by two aluminum skins bonded to a core of elastomeric silicone oil and loaded with iron particles at 30%. The rigidity of the beam is given by the addition of a usual stiffness matrix of two aluminum skins and an MRE complex stiffness matrix. The latter is a function of the magnetorheological properties of the MRE. The results show the influence of MRE adaptive stiffness and the loss factor in the static behavior of the sandwich studied. The structure proposed can be directly applied to civil engineering, for example, building foundations, mechanical engineering and aircraft wings.

On Dynamic Characteristic of Damaged Elastomeric Vibration Isolators

This paper deals with structural damage identification at vibration isolators with elastomeric-based composite, through continuous or periodical evaluation of behavioral changes of the dynamic characteristics. It has supposed only structural damages of passive isolators, appearing inside the elastomeric core. Theoretical approaches has been provided, computer simulation scenarios regarding some potential critical cases has been developed, and experimental tests has been performed, in order to evaluate main correlation between the levels of structural integrity and the operational performance respectively. Partial results indicate an acceptable sensitivity of this dynamic method with damage detection, and establish next goal of the research in evaluation of the failure imminence and accurately localizing techniques.

The fabrication and mechanical properties of a novel 3-component auxetic structure for composites

Abstract Functional auxetic composite materials can be fabricated from conventional or from auxetic components. The helical auxetic yarn (HAY) is a recently invented auxetic reinforcing component for composite materials. This paper investigates the Poisson's ratio behaviour of a further development of the HAY, needed for many practical applications. The 3-component auxetic yarn is based on a stiff wrap fibre (the first component) helically wound around an elastomeric core fibre (the second component) coated by a sheath (the third component). The resultant structure can overcome problems such as slippage of the wrap and changes in wrapping angles previously encountered during the manufacture and utilisation of the two-component HAY. The mechanical performance of conventional and novel systems is investigated; with emphasis on the differences between the engineering and true Poisson's ratio. The importance of the utilisation of a true tensile modulus and a true Poisson's ratio is demonstrated. This is the first time reported in the literature that an experimental auxetic effect analysis of HAYs was carried out by comparing true and engineering Poisson's ratio. We show that depending on the coating thickness of the third component, the 3-component auxetic system can demonstrate auxetic behaviour, and the coating thickness can be employed as a new design parameter to tailor both the Poisson's ratio and modulus of this novel composite reinforcement for a wide range of applications.

Synthesis and Redispersibility of Poly(styrene-block-n-butyl acrylate) Core–Shell Latexes by Emulsion Polymerization with RAFT Agent–Surfactant Design

A coagulatable and redispersible poly(styrene-block-n-butyl acrylate) (PS-b-PnBA) copolymer latex system was developed. A series of PS-b-PnBA diblock copolymers with the PnBA content up to 70 wt % were prepared via a reversible addition–fragmentation chain transfer (RAFT) emulsion polymerization. An amphipathic poly(acrylic acid-b-styrene) trithiocarbonate was synthesized and employed as macro-RAFT agent and surfactant. The resulted latex particles contained a soft poly(n-butyl acrylate) core and a hard polystyrene shell. The hard plastic shell could prevent the elastomer core from deformation and fusion at room temperature. It was found that the latex particles with the nBA content ⩽60 wt % could be easily coagulated by HCl and redispersed by NaOH with some ultrasound treatment. The coagulation and redispersion processes were repeatable. When the nBA content reached 70 wt %, the plastic shell became too thin, resulting in collapsed sticky particles. The critical shell thickness for redispersible latexes was about 8 nm.

SPS bridge decks for new bridges and strengthening of existing bridge decks

AbstractThe sandwich plate system (SPS) is a structural composite material made up of two metal plates bonded to a polyurethane elastomer core. SPS delivers high strength and stiffness, making it an excellent alternative to conventional stiffened steel and reinforced concrete. For strengthening of orthotropic bridge decks, SPS Overlay can be used to create a stiff bridge deck without removing the original plates. The renewed deck improves the distribution of wheel loads across the longitudinal stiffening elements, decreases deck curvatures associated with large concentrated wheel loads, extends the fatigue life of fatigue‐critical welds and increases the life of the wearing surface and the whole bridge. For new bridge applications, prefabricated SPS bridge deck plates reduce the dead load by up to 70 % compared with concrete bridge decks, thus allowing bridges to carry significantly greater live load without the need for girder or pier strengthening. Deck replacement can be completed while leaving the steel or concrete girders in place or, where speed of erection is critical, pre‐assembled longitudinal deck‐girder units can be used.

Development and in vitro/in vivo Evaluation of a Silastic Intravaginal Ring for Mifepristone Delivery.

Preparation and in vitro/in vivo evaluation of mifepristone intravaginal ring formulations were investigated. In the present study, it is reported that a mifepristone intravaginal ring of reservoir design comprising of a mifepristone silicone elastomer core enclosed in a silicone layer. During the preparation of intravaginal ring solid dispersion method was employed which improved the release rate of drug from the intravaginal ring. In vitro release studies performed under sink conditions and the released drug amounts were estimated using UV spectrometry at 310 nm. In addition, the in vivo release profile of in-house devices was evaluated in female New Zealand white rabbits. The rabbit plasma samples were processed and analyzed using a validated HPLC-MS method. Norgestrel was used as internal standard, and plasma samples contained mifepristone and internal standard were deproteinized, and then subjected to HPLC-MS analysis under condition of electrospray ionization in the selected ion monitoring mode. The drug release from intravaginal ring made in house was constant for 21 days in rabbits, which suggested the mifepristone intravaginal ring release system would be useful in clinical practice in the future. The result indicated the in vitro/in vivo correlation is perfect, which explained in vitro release analysis method developed was feasible.

Probing the Interplay of Ultraviolet Cross-Linking and Noncovalent Interactions in Supramolecular Elastomers

Ultraviolet (UV) irradiated supramolecular polybutadienes (PBs) containing 2-ureido-4-[1H]-pyrimidone (UPy) linkages were examined as a simple model for curable supramolecular elastomers. Via precise control of UV exposure, the cure and the degradation of the vinyl groups within the PB elastomeric core were investigated. The combination of UPy binding and covalent cross-linking by UV irradiation dramatically enhanced mechanical properties of these UPy-functionalized elastomers, yielding toughness enhancement up to ∼200× at the 5 min UV cure. UV-initiated cross-linking dominated the curing process up to ∼50 min exposure time. Beyond this cure time, dominant degradation of the vinyl linkages was observed. Control of this UV-initiated process yielded supramolecular elastomers with a covalently cross-linked phase induced by UV irradiation combined with a noncovalent UPy cross-linked phase induced by secondary hydrogen bonding interactions. Of particular note, it was determined that the presence of UPy hydrogen-bonded aggregates accelerated the UV cross-linking process during the initial stage of exposure. This observation was attributed to microphase-separated structure of UV-irradiated supramolecular elastomer, where UPy aggregation increased the probability of interaction between the pendant vinyls responsible for UV cross-linking. The systematic study of uniaxial tensile behavior of the UV-irradiated supramolecular elastomers offers new insight into the design and architecture of mechanically tunable supramolecular elastomers.

Dynamic behavior analysis of a magnetorheological elastomer sandwich plate

Abstract The design of magnetorheological materials with mechanical properties adjusted to the action of dynamic loads is a recent field of research. The few bibliographic literatures in this area concern the beams. This paper is devoted to a numerical and an experimental study of the dynamic behavior of sandwich plates consisting of two aluminum skins and a magnetorheological elastomer (MRE) core of different loads of micron-size ferromagnetic particles elaborated under the action of a magnetic field. Firstly, the rheological properties of the loaded elastomer with and without the impact of the magnetic field have been evaluated experimentally. Secondly, an experimental analysis of the impact of the loading rate of micron-size ferromagnetic particles of the elastomer as well as the magnetic field intensity on the vibration behavior of the elaborated plates is conducted. To evaluate the variation of the plate rigidity and damping factor, a confrontation of experimental values against numerical results, using the finite elements software Abaqus and the Ritz method of approximation for an appropriate model, was made for various dimensions and boundary conditions of the plate.

Dynamic stability of a rotating sandwich beam with magnetorheological elastomer core

Abstract In this work the dynamic stability of a rotating three layered symmetric sandwich beam with magnetorheological elastomer (MRE) core and conductive skins subjected to axial periodic loads has been investigated using finite element method (FEM). The derived governing equation of motion is in the form of a multi-degree of freedom Mathieu–Hill's equation with complex coefficients. The instability regions of the sandwich beam for the principal parametric resonance case have been determined by using the harmonic balance method. Effects of applied magnetic field, rotating speed, setting angle, hub radius, static load and dynamic load on the dynamic characteristics and instability regions of the sandwich beam are investigated. This work will find application in the passive and active vibration reduction of rotating sandwich structure using magnetorheological elastomer core, magnetic field and periodic axial load.

Continuously Stiffened Composite Web Shear Links: Tests and Numerical Model Validation

AbstractExperiments were carried out on shear links with webs made from two metal sheets vulcanized to an elastomeric core to investigate the concept of utilizing continuous web stiffening as means of enhancing the hysteretic behavior. The links were designed for the same nominal strengths and were subjected to increasing cyclic deformations. Two different link aspect ratios were considered with two different core thicknesses. The composite web increased the maximum strength and postbuckling capacity of deep shear links dominated by elastic buckling, but the links were not able to achieve the link plastic shear capacity. Although the use of the elastomer core increased the out-of-plane stiffness of the web, the failure mode was still characterized by web tearing caused by localized regions of reversing out-of-plane buckling zones. Performance expectations were exceeded by an unstiffened base link that achieved the American Institute of Steel Construction (AISC) deformation requirement with minimal strengt...

Vibration Characteristics Analysis of Orthotropic Rectangular Sandwich Plate with Magnetorheological Elastomer

Vibration characteristics of orthotropic rectangular sandwich plate with magnetorheological (MR) elastomer core and constraining layer is presented in this study. In order to improve the vibrational behaviors of the system, the orthotropic rectangular plate is covered a MR fluid core and a constraining layer. Finite element method is adopted to derive the finite element equations of motion for the orthotropic sandwich system. The effects of the natural frequencies and loss factors of the orthotropic sandwich plate are discussed. The rheological property of the MR material can be changed and controlled by applying various magnetic fields. The modal dampings and the natural frequencies for the orthotropic sandwich plate are calculated for various magnetic fields. Besides, the effects of the strength ratio of the base plate on the natural frequencies and modal loss factors are also discussed.

Influence of elastomeric core–shell impact modifiers on mechanical properties of cellulose diacetate resin

Cellulose diacetate (CDA) plasticized with triacetine was blended by melting extrusion with two different kind of elastomeric core–shell impact modifiers: methyl methacrylate (MMA, shell) grafted onto styrene–butadiene–rubber (SBR, core) (MSBR) and MMA (shell) grafted onto butyl acrylate rubber (BAR, core) (MBAR). The different CDA/MSBR and CDA/MBAR blends were characterized by mechanical properties and morphological observation with various impact modifier contents. The highest impact strength was observed in the case of the blend with 5 wt% of MSBR and 3 wt% of MBAR, respectively. The tensile strength and Young’s modulus of CDA blends were decreased with increasing both MSBR and MBAR. According to SEM observation, MBAR was dispersed more effectively in CDA matrix than that of MSBR, thus indicating improved impact strength.

Vibration analysis of sandwich rectangular plates with magnetorheological elastomer damping treatment

In this study, the vibration analysis of sandwich rectangular plates with magnetorheological (MR) elastomer damping treatment is presented. The rectangular plate is combined with a magnetorheological elastomer core layer and a constraining layer to improve the vibration behaviors of the sandwich system. The MR material shows variations in the rheological properties when subjected to varying magnetic fields. Additionally, the MR material exhibits a rapid time response and is applicable to structures or devices when a tunable system is required. The magnetorheological elastomer is found to have a significant effect on the vibration characteristics of the sandwich rectangular plate. The modal damper and the natural frequencies for the sandwich plate system are calculated for various magnetic fields and some designed parameters by utilizing the finite element method. The damping effects of the sandwich plate system can be controlled and changed when different magnetic field strengths are applied.

Vibration Response Analysis of MRE Cantilever Sandwich Beam under Non-Homogeneous Magnetic Fields

A three layer sandwich beam with an aluminum face sheet and a magnetorheological elastomer (MRE) core was fabricated. The transverse motion equations of MRE cantilever sandwich beam under non-homogeneous magnetic fields were derived with the fine Mead-Markus model, and the first natural frequency of the beam were calculated. Meanwhile, the first natural frequency of the beam was also simulated using ANSYS software. The numerical simulations accorded with theoretical results in general. The results are expected to provide guidance to develop broadband vibration isolation devices for railways and rolling stock.

Quantitative Analysis of the Polyurethane Composites with Non-Organic Nanofiller for Use in Implants of Intervertebral Disc

Quantitative Analysis of the Polyurethane Composites with Non-Organic Nanofiller for Use in Implants of Intervertebral DiscThe aim of this research was to develop a composite material to be used as an elastomeric core of the artificial intervertebral disc. Two types of polyurethane composites with non-modified SiO2and SiO2modified NH2group were obtained. The composites made of these materials have different filler content. The effect of modifying fillers for the structure and properties of these materials were investigated.