Elastomer Layer Research Articles

Characterization of Brake Shims Using Analytical Constrained Layer Damping Theories

AbstractShims in automotive brake systems are applied to suppress brake squeal resulting from self‐excited vibrations. These composite structures consist of thin metal plates and elastomer layers having high damping potential. The characterization and subsequent selection of shims is mainly based on a wide range of experimental investigations so far. To reduce measuring efforts significantly a systematic modeling of shims is focused. Therefore, approaches from literature describing surface damping treatments analytically are considered. The damping effect is mainly based on the shearing of the viscoelastic core which is taken into account by the applied theory. The dissipation potential is characterized by the complex shear modulus of the elastomer layer. Hence, sandwich beam theories enable the prediction of natural frequencies and in particular loss factors of bending mode shapes. In this contribution shims bonded on rectangular steel plates are examined. The main focus is on the determination of rheological influencing variables as well as the impact of boundary conditions in detail. Moreover, the impact of the shim length on the damping behavior is investigated experimentally.

Experimental and numerical characterisation of fibre‐metal‐elastomer laminates by using DMA regarding its damping behaviour

AbstractHybrid carbon fibre‐elastomer‐metal laminates consist of alternating layers of carbon fibre reinforced plastics, elastomer layers and aluminium sheets. These laminates offer great potential for a lightweight structural material with adjustable damping properties. The material damping is strongly influenced by the viscoelastic properties of the elastomer layers which damp by the principle of constrained layer damping when the laminate is vibrated. In this study the material damping was experimentally characterised by three point bending dynamic mechanical analysis (DMA). In this regard, HyCEML specimens were tested on different frequencies and temperatures. The loss factor, storage‐ and loss modulus were measured to characterise the damping over the temperature and the frequency range. Time‐temperature superposition was applied to determine the damping characteristics at higher and lower frequencies. The experimental results were compared to numerical studies on the basis of a characterisation of the single constituents. A test setup with a cantilever beam under free vibration was chosen for the comparison of experimental and numerical results. Detailed multi‐layer finite element models were generated offering high flexibility in terms of type and number of finite elements especially in the direction of laminate thickness. For this purpose, existing material models were used to investigate the influence of each component on the system's damping behaviour. The damping in the free vibration experiments was determined with the logarithmic decrement at the free end. Also the numerically and experimentally determined first eigenfrequencies were compared. It could be shown that the laminate damping is strongly dependent on the glass transitions of both the carbon‐fibre reinforced plastics and the elastomers. The numerically determined first eigenfrequency matched the experimental with a deviation of 10 %, the logarithmic decrement of the experimental results was more than 50 % higher. The damping behaviour of the HyCEM laminate, however, is underestimated by the numerical investigation, since nonlinear viscoelastic effects are not yet considered.

Evaluation of Mechanical Properties of Carbon Fiber Reinforced Polyamide 12 Laminates with Polyamide 12 Elastomer Layers

Evaluation of Mechanical Properties of Carbon Fiber Reinforced Polyamide 12 Laminates with Polyamide 12 Elastomer Layers

A Non-Linear Model of an All-Elastomer, in-Plane, Capacitive, Tactile Sensor Under the Application of Normal Forces.

In this work, a large deformation, non-linear semi-analytical model for an all-elastomer, capacitive tactile unit-sensor is developed. The model is capable of predicting the response of such sensors over their entire sensing range under the application of normal forces. In doing so the finite flat punch indentation model developed earlier is integrated with a capacitance model to predict the change-in-capacitance as a function of applied normal forces. The empirical change-in-capacitance expression, based on the parallel plate capacitance model, is developed to account for the fringe field and saturation effects. The elastomeric layer used as a substrate in these sensors is modeled as an incompressible, non-linear, hyperelastic material. More specifically, the two term Mooney-Rivlin strain energy function is used as a constitutive response to relate the stresses and strains. The developed model assumes both geometrical as well as material non-linearity. Based on the related experimental work presented elsewhere, the inverse analysis, combining finite element (FE) modeling and non-linear optimization, is used to obtain the Mooney-Rivlin material parameters. Finally, to validate the model developed herein the model predictions are compared to the experimental results obtained elsewhere for four different tactile sensors. Great agreements are found to exist between the two which shows the model capabilities in capturing the response of these sensors. The model and methodologies developed in this work, may also help advancing bio-material studies in the determination of biological tissue properties.

Active Compression Bandage Made of Electroactive Elastomers

Active compression bandages made of electromechanically active elastomers have recently been proposed to counteract dynamically, rather than statically, limb swelling due to various pathologies or conditions. To apply and modulate the compression pressure they exploit the ability of electroactive elastomer layer/s of changing size in response to a high voltage. For safety reasons, such devices must be properly insulated from the user limb. In this paper, we present an electroactive bandage made of two prestretched layers of an electroactive acrylic elastomer sandwiched between two insulating layers of a passive silicone elastomer. Moreover, uniaxial stiffening elements where introduced to maximize actuation along the radial direction. Prototypes of the bandage were tested with a pressurized air chamber, which mimicked the compliance of a human limb. Both experimental investigations and a finite electroelasticity analytical model showed that the passive layers play a key role for an effective transmission of actuation from the active layers to the load. The prototypes were able to actively vary the applied pressure up to 10%. The model showed that by increasing the number of electroactive layers the pressure variation could be further increased, although with a saturation trend, providing a useful indication for future designs of such bandages.

Impact and post-impact properties of hybrid-matrix laminates based on carbon fiber-reinforced epoxy and elastomer subjected to low-velocity impacts

The presented study investigates the impact behavior of hybrid matrix (HyMa) composite laminates under low-velocity impact loads. In the specific HyMa material system, carbon fiber-reinforced EPDM-rubber layers are combined with conventional carbon fiber-reinforced epoxy layers in a co-curing autoclave process. HyMa specimens with 1, 3 and 5 interlayers of fiber-reinforced elastomer (FRE) (21 plies in each specimen, 4.58 mm specimen thickness) and reference specimens were subjected to low-velocity impacts and compression after impact tests. Specimen response and damage were analyzed based on force-time curves, force-displacement curves, visual damage inspection, ultrasonic C-scans, micrographs and compression strength. Low-velocity impact experiments at different energy levels (16 J, 20 J, 25 J and 30 J) showed that peak forces, visual damage area and projected damage area could be dramatically reduced with increasing number of FRE layers. Energy absorption increased up to 21% and impact tolerance was significantly enhanced using HyMa laminates. We found that two main effects influenced the impact behavior: shear decoupling by the reinforced elastomer layers leading to higher deformation compliance and fiber fracture as a pronounced damage mechanism.

Performance of a large-scale magnetorheological elastomer–based vibration isolator for highway bridges

This study presents an experimental investigation on the magnetorheological effect of a new magnetorheological elastomer–based adaptive bridge isolation bearing system. Two identical magnetorheological elastomer–based adaptive bridge bearings (isolators) were designed and fabricated. Electromagnets were incorporated to create a closed-loop magnetic path in the magnetorheological elastomer layers. A double-lap shear and compression test setup was utilized to characterize the mechanical properties of the system subjected to scaled structural cyclic forces and strains. Experimental results demonstrated that the effective stiffness of adaptive bridge bearings increases with increased applied magnetic field and a compressive force resulted in larger apparent shear stiffness. Also, increasing loading frequency resulted in larger apparent shear stiffness and lower magnetorheological effect and similarly, however, a compressive force resulted in smaller magnetorheological effects.

Compact Dielectric Elastomer Linear Actuators

AbstractThe design and fabrication of a rolled dielectric elastomer actuator is described and the parametric dependence of the displacement and blocked force on the actuator geometry, elastomer layer thickness, voltage, and number of turns is analyzed. Combinations of different elastomers and carbon nanotube electrodes are investigated and optimized to meet performance characteristics appropriate to tactile display applications, namely operation up to 200 Hz with a combination of a 1 N blocked force and free displacement of 1 mm, all within a volume of less than 1 cm3. Lives in excess of 50 000 cycles have been obtained. Key to meeting these objectives is control of the multilayering fabrication process, the carbon nanotube electrode concentration, the selection of a soft elastomer with low viscous losses, and a proof‐testing procedure for enhancing life cycle reliability.

Large deformation mechanics of a soft elastomeric layer compressed by a finite flat rigid punch for tactile sensor applications

In this study, we develop a large deformation analytical–empirical model for a flat finite punch pinching on an incompressible, polymeric layer under plane strain conditions. The model could further advance the predictive capabilities of enhanced tactile sensor response models. The aforementioned model is developed based on the analytical model for an infinitely long layer under uniform compression which has been presented in Kalayeh and Charalambides (2015). Related non-linear finite element (FE) simulations with large strain, large deformation assumptions are carried out in this study. Using the FE finite flat punch simulations, the uniform layer compression model is properly adjusted to predicting the finite punch layer response. The mechanics of the polymeric layer in the vicinity of the symmetry plane, under the application of a flat finite rigid punch is fully analyzed and an expression for the indentation force as a function of the applied top surface deformation is developed. The relevance of this result to modeling the non-linear tactile sensor response over a broad sensing range is discussed. The reported results are compared to FE simulations for applied surface deformation levels of up to 40 percent of the layer initial thickness, and punch half-length to layer thickness ratios of 1 to 2. Great agreement is found to exist between the analytical–empirical model and the FE simulations. For completeness, this new semi-analytical model is fully summarized in the Appendix of this work.

SkinGest: artificial skin for gesture recognition via filmy stretchable strain sensors

ABSTRACTStretchable sensors are promising in the field of wearable robotics. To date, it is still a challenge to design an artificial skin with thin and sensitive stretchable sensors. In this paper, we present a new artificial skin, SkinGest, integrating filmy stretchable strain sensors and machine learning algorithms for gesture recognition of human hands. The presented sensor has a sandwich structure consisting of two elastomer layers on the outside and one soft electrode layer in the middle. Based on the improved fabrication process, we make the sensor’s thickness down to 150 µm, while keeping the gauge factor (GF) up to 8. Then, we integrate the machine learning algorithms (using LDA, KNN and SVM classifiers) with the stretchable sensors in our SkinGest system for gesture recognition. Supported by the experimental data from different subjects, our SkinGest system succeeds in identifying American sign language 0–9 with an average accuracy of 98%. The results demonstrate that the proposed SkinGest system provides a promising platform for future potential virtual reality and sign language recognition applications.

An experimental and numerical investigation of the effect of geometric parameters on the flexible joint nonlinear behavior for thrust vector control

Solid-propellant motors are used in a variety of space systems. This type of motor requires a guidance system, and a thrust vector control to function properly. One of the most effective methods for thrust vector control can be achieved by utilizing a flexible joint system. The flexible joint is the most widely used device in advanced nozzle system, such as space shuttle boosters, Vega, and Ariane 5. This setup includes multiple layers of elastomers to provide the flexibility, and a few metallic or composite rings as the scaffold of the system. In this study, a nonlinear simulation of the flexible joint is investigated using finite element method. These results are verified by construction and hydrostatic test, and there is a good consistency between predictions and empirical data. To the best of our knowledge, contemporary architecture does not provide the optimum result. Therefore, we propose delicately designed configuration, which can be mentored in a variety of motors, to improve the functionality of the flexible joints. A detailed study on the alteration of geometric parameters has been done to unravel its effect on the behavior of the flexible joint.

Experimental Characterisation of a Flat Dielectric Elastomer Loudspeaker

Conventional loudspeakers are often heavy, require substantial design spaces and are hard to integrate into lightweight structures (e.g., panels). To overcome these drawbacks, this paper presents a novel extremely flat loudspeaker which uses dielectric elastomer actuators with natural rubber for the elastomeric layers and metal electrodes as transduction mechanism. To facilitate the deformation of the elastomer, the electrodes are perforated. The microscopic holes lead to a macroscopically compressible stack configuration despite the elastomer incompressibility. The design is developed and the materials are chosen to guarantee low mechanical and electrical losses and a high efficiency in the entire frequency range up to several kilohertz. The loudspeaker was designed, built and afterwards experimentally investigated and characterised. Laser measurements of the surface velocity were performed to find dynamic effects present at the diaphragm. To further characterise the device, a semi anechoic chamber as used. Sound pressure levels emitted by the device were recorded at different bias and alternating voltages to study their influence. The nonlinearity of the loudspeaker, which is inherent for this kind of actuators, was quantified considering the total harmonic distortion. Here, a dependence on the amplitude of the alternating voltage is observed. Further, the distortion decreases rapidly the higher the frequency is, which qualifies the loudspeaker concept to properly work at high frequencies. Transfer functions between supplied voltage and on-axis sound pressure were measured and showed in principle potential for high frequency application. Further, the behaviour of the diaphragm changing from rigid piston to resilient disk with respect to frequency for different configurations was observed. Additionally, the directivity of the loudspeaker was investigated at several frequencies, and was in accordance with previously found research outcomes. The results, especially in the high frequency range, prove the usability of this design concept for practical applications.

Characterizing the effect of print orientation on interface integrity of multi-material jetting additive manufacturing

Relatively few engineering devices and structures are monolithic, as combinations of materials are often needed to meet the necessary functionality, performance, weight, and cost requirements. Progress in additive manufacturing (AM) now allows multiple materials to be produced in a single manufacturing process, opening new opportunities for expeditiously achieving functional and performance targets. Just as interactions at interfaces have long been of interest in the area of adhesive bonding, similar issues need to be addressed for printed composite materials, including how print orientation may affect failure. In this study, acrylic photopolymers were printed in a multi-material jetting process to produce fracture specimens consisting of an elastomeric layer sandwiched between two stiffer strips. Findings are offered as contributions to the three process modeling challenge topics conveyed in a recent NIST/NSF Measurement Science Roadmap (Pellegrino, 2016), as follows:•Specimen configuration guidelines for standards for validation, certification, and qualification of models/parts: Several test specimen configurations based on the double cantilever beam method were fabricated and evaluated to measure the fracture resistance of the assembled layers, leading to a recommended configuration that minimizes material usage and spurious dissipation.•Understanding interfacial science of AM polymers: Substantial differences are reported in the measured fracture energy and locus of failure (though nominally occurring at or near material interfaces) as a function of the print direction and interface architecture.•Non-equilibrium material/process measurements and models: All tests showed increased fracture energy at higher crack propagation rates; power-law relationships proved useful for comparing specimen configurations and describing this rate-dependent nature of the interface and materials involved.These studies, which additionally include encouraging preliminary results with graded multilayers, also suggest opportunities for designing printed interfaces with improved performance and durability for multi-material AM products.

Design of Multifunctional Soft Doming Actuator for Soft Machines

AbstractBilayer bending‐based soft actuators are widely utilized in soft robotics for locomotion and object gripping. However, studies on soft actuators based on bilayer doming remain largely unexplored despite the often‐observed dome‐like shapes in undersea animals such as jellyfish and octopus suction cup. Here, based on the simplified model of bending‐induced doming of circular bilayer plates with mismatched deformation, the design of a soft doming actuator upon pneumatic actuation and its implications in the design of multifunctional soft machines are explored. The bilayer actuator is composed of a patterned embedded pneumatic channel on top for radial expansion and a solid elastomeric layer on the bottom for strain‐limiting. It is shown that both the cavity volume and bending angle at the rim of the actuated dome can be controlled by tuning the height gradient of the pneumatic channel along the radial direction. Its potential multifunctional applications are demonstrated in swimming, adhesion, and gripping, including high efficient jellyfish‐inspired underwater soft robots with locomotion speed of 84 cm min−1 and rotation‐based soft grippers with low energy cost by harnessing the large rim bending angle, and octopus‐inspired soft adhesion actuators with strong and switchable adhesion force of over 10 N by utilizing the large cavity volume.

Ultrastretchable Conductor Fabricated on Skin-Like Hydrogel-Elastomer Hybrid Substrates for Skin Electronics.

Printing technology can be used for manufacturing stretchable electrodes, which represent essential parts of wearable devices requiring relatively high degrees of stretchability and conductivity. In this work, a strategy for fabricating printable and highly stretchable conductors are proposed by transferring printed Ag ink onto stretchable substrates comprising Ecoflex elastomer and tough hydrogel layers using a water-soluble tape. The elastic modulus of the produced hybrid film is close to that of the hydrogel layer, since the thickness of Ecoflex elastomer film coated on hydrogel is very thin (30 µm). Moreover, the fabricated conductor on hybrid film is stretched up to 1780% strain. The described transfer method is simpler than other techniques utilizing elastomer stamps or sacrificial layers and enables application of printable electronics to the substrates with low elastic moduli (such as hydrogels). The integration of printed electronics with skin-like low-modulus substrates can be applied to make wearable devices more comfortable for human skin.

A mortar formulation including viscoelastic layers for vibration analysis

In order to reduce the transfer of sound and vibrations in structures such as timber buildings, thin elastomer layers can be embedded between their components. The influence of these elastomers on the response of the structures in the low frequency range can be determined accurately by using conforming hexahedral finite elements. Three-dimensional mesh generation, however, is yet a non-trivial task and mesh refinements which may be necessary at the junctions can cause a high computational effort. One remedy is to mesh the components independently from each other and to couple them using the mortar method. Further, the hexahedral mesh for the thin elastomer layer itself can be avoided by integrating its elastic behavior into the mortar formulation. The present paper extends this mortar formulation to take damping into account such that frequency response analyses can be performed more accurately. Finally, the proposed method is verified by numerical examples.

Torsional vibration analysis of a rotating tapered sandwich beam with magnetorheological elastomer core

In this study, the torsional vibration analysis of a rotating tapered sandwich beam with a magnetorheological elastomer core has been investigated. The magnetorheological elastomer material is used as a constrained damping layer embedded between two elastic constraining skins in order to improve the vibrational behavior of the sandwich beam. The three layers of the sandwich beam have rectangular cross-sections with symmetric arrangement. The problem formulation is set up based on the torsional theory of rectangular laminated plates. The assumed modes method and the Lagrange equations are used to derive the governing equations of motion of the system. The validity of the presented formulation is confirmed through comparison of the obtained results with those available in the literature. A detailed parametric study is carried out to investigate the effects of applied magnetic field, tapering ratios, magnetorheological elastomer layer thickness, rotating speed, hub radius, and setting angle on the free vibration characteristics of the sandwich beam. The results show that magnetic field intensity, magnetorheological elastomer layer thickness, and tapering ratio have significant influences on the torsional vibrating characteristics of the sandwich beam, and the effects of rotating speed and hub radius are considerable. The setting angle has no substantial effect on the torsional vibration characteristics.

Elastic dependence of defect modes in one-dimensional photonic crystals with a cholesteric elastomer slab

We studied the transmission spectra in a one-dimensional dielectric multilayer photonic structure containing a cholesteric liquid crystal elastomer layer as a defect. For circularly polarized incident electromagnetic waves, we analyzed the optical defect modes induced in the band gap spectrum as a function of the incident angle and the axial strain applied along the same axis as the periodic medium. The physical parameters of the structure were chosen in such a way the photonic band gap of the cholesteric elastomer lies inside that of the multilayer. We found that, in addition to the defect modes associated with the thickness of the defect layer and the anisotropy of the elastic polymer, two new defect modes appear at both band edges of the cholesteric structure, whose amplitudes and spectral positions can be elastically tuned. Particularly, we showed that, at normal incidence, the defect modes shift toward the long-wavelength region with the strain; whereas, for constant elongation, such defects move toward larger frequencies with the incidence angle.

A Soft Three-Axis Load Cell Using Liquid-Filled Three-Dimensional Microchannels in a Highly Deformable Elastomer

The advances in soft robotics have increased the need of soft sensors in various applications involved with physical interactions between humans and robots. In this letter, we propose a soft multiaxis force sensor made of multimaterial elastomer layers and embedded microfluidic channels that are sensitive to compression perpendicular to the channel length. The microchannels are geometrically divided into multiple segments for detecting forces in three axes. When a force is applied to the top surface of the sensor, the microchannels are compressed by multisegmented force plates made of rigid plastic. While the microchannels located on the sides in the structure detect shear forces, the microchannel at the bottom detects normal force. The three-dimensional configuration of the microchannel physically separates the side channels from the bottom channel and consequently enables mechanical decoupling of shear forces from normal force. The letter describes the design and fabrication of the proposed sensor and discusses the experimental results for sensor characterization.

Highly Stretchable, Weavable, and Washable Piezoresistive Microfiber Sensors.

A key challenge in electronic textiles is to develop an intrinsically conductive thread of sufficient robustness and sensitivity. Here, we demonstrate an elastomeric functionalized microfiber sensor suitable for smart textile and wearable electronics. Unlike conventional conductive threads, our microfiber is highly flexible and stretchable up to 120% strain and possesses excellent piezoresistive characteristics. The microfiber is functionalized by enclosing a conductive liquid metallic alloy within the elastomeric microtube. This embodiment allows shape reconfigurability and robustness, while maintaining an excellent electrical conductivity of 3.27 ± 0.08 MS/m. By producing microfibers the size of cotton threads (160 μm in diameter), a plurality of stretchable tubular elastic piezoresistive microfibers may be woven seamlessly into a fabric to determine the force location and directionality. As a proof of concept, the conductive microfibers woven into a fabric glove were used to obtain physiological measurements from the wrist, elbow pit, and less accessible body parts, such as the neck and foot instep. Importantly, the elastomeric layer protects the sensing element from degradation. Experiments showed that our microfibers suffered minimal electrical drift even after repeated stretching and machine washing. These advantages highlight the unique propositions of our wearable electronics for flexible display, electronic textile, soft robotics, and consumer healthcare applications.