Thin Rubber Sheet Research Articles

Computational Study of Tear Testing of a Single Weld Formed by Fused Filament Fabrication

Abstract The tear test is widely used to measure the fracture toughness of thin rubber sheets and polymer films. More recently, the tear test has been applied to polymer materials produced by melt extrusion additive manufacturing to measure the fracture toughness of a single weld between two printed (extruded) filaments. This paper presents a finite element modeling study of the tearing of a weld between two printed filaments to investigate the mechanics of the tear test and the effects of geometry and material properties on the measured tear energy. The mechanical behavior of the printed filaments was described by a viscoplastic model for glassy polymers and the weld was represented using cohesive surface elements and the Xu–Needleman traction–separation relationship. The geometric model and the material parameters were chosen based on experimental measurements. The tear energy varied with the specimen dimensions, the curvature of the printed filaments, the yield stress relative to the cohesive strength of the weld, and the post-yield stress drop. The effects of the hardening modulus were small. These factors altered the viscoplastic dissipation in the material ahead of the propagating crack tip. The results showed that viscoplastic dissipation could constitute a large fraction of the tear energy and is strongly affected by the specimen dimensions and the geometry and material properties of the printed filament. There was also considerable mode mixty in the tear energy. The findings can be used to design tear tests to measure the intrinsic fracture toughness of the weld.

Real-time visualisation and optimisation of acoustic waves carrying orbital angular momentum

Travelling waves, such as light and sound, can carry angular momentum. Orbital angular momentum (OAM) is one of the components which is determined by the helicity of the phase fronts. The helical waveform is characterised in terms of an integer l and an azimuthal phase term of exp(−ilθ), but for |l| > 1 the resulting high-order beam structure is unstable to perturbation. In this work, using Fourier transform profilometry and stroboscopic imaging techniques, we demonstrate the real-time visualisation of the OAM-carrying acoustic waveform by imaging the pressure imprint of the acoustic wave on a thin rubber sheet. Furthermore, based on the visualised waveform, we are able to optimise high-order (|l| > 1) OAM states by controlling the individual elements of the acoustic source. Beyond the study of acoustic OAM, the real-time monitoring and optimising methods could be a benefit to other applications requiring acoustic waveform shaping, such as acoustic communications, acoustic holograms, etc.

Disk cavities in soft materials: Their bubble-like resonance and use in thin underwater sound blocking materials

The acoustics of gas-filled cavities in soft viscoelastic solids, such as rubber and gels, has been a renewed subject of research in recent years owing to usefulness in studies of multiple scattering and importance to sound insulating and anechoic materials. A brief review is followed by a presentation of recent research on disk cavity resonance done at the Naval Research Laboratory [J. Acoust. Soc. Am. 138, 2537–2547]. A lumped parameter analysis of the breathing mode of a disk cavity is presented which yields a natural frequency expression valid for a high-aspect ratio cavity embedded in an elastic medium. A verification approach using finite-element methods is also described which directly computes resonance in the framework of COMSOL Multiphysics. Calculation of scattering cross sections and visualization of the elastic displacement field indicates the importance of shear wave radiation. As an application example, a specially designed single layer array of disk cavities in a thin silicone rubber (PDMS) sheet was modeled that resonantly blocks underwater sound by nearly 20 dB for a favorable wavelength/thickness ratio of 240. Disk cavities are found to provide a wider bandwidth than near-spherical cavities. [Work sponsored by the Office of Naval Research.]

The ‘Coin-Through-the-Rubber’ Trick: An Elastically Stabilized Invagination

A spectacular trick of close-up magicians involves the apparent passing of a coin through a rubber sheet. The magic is based on the unusual elastic response of a thin rubber sheet: the formation of an invagination, stabilized by friction and elasticity, which holds the coin. By pressing on the coin, the invagination becomes unstable, and the coin is released. We describe the deformation analytically using a simple Hookean description, and examine the stability of the invagination. We finally compare the prediction of the Hookean analysis with numerical solutions of the neo-Hookean model, and provide a brief commentary on the origins of the trick.

Experimental validation of a simplified model for rolling isolation systems

SUMMARYRolling isolation systems (RISs) protect mission‐critical equipment and valuable property from earthquake hazards by decoupling the dynamic responses of vibration‐sensitive objects from horizontal floor motions. These responses involve the constrained rolling of steel balls between bowl‐shaped surfaces. The light damping of steel balls rolling between steel plates can be augmented by adhering thin rubber sheets to the plates, thereby increasing the rolling resistance and decreasing the displacement demand on the RIS. An assessment of the ability of lightly‐ and heavily‐damped RISs to mitigate the hazard of seismically induced failures requires high‐fidelity models that can adequately capture the systems' intrinsic nonlinear behavior. The simplified model presented in this paper is applicable to RISs with any potential energy function, is amenable to both lightly‐ and heavily‐damped RISs, and is validated through the successful prediction of peak responses for a wide range of disturbance frequencies and intensities. The validated model can therefore be used to compute the spectra of peak floor motions for which displacement demands equal capacity. These spectra are compared with representative floor motion spectra provided by the American Society of Civil Engineers 7–10. The damping provided by rolling between thin viscoelastic sheets increases the allowable floor motion intensity by a factor of 2–3, depending on the period of motion. Acceleration responses of isolation systems with damping supplied in this fashion do not grow with increased damping, even for short‐period excitations. Copyright © 2013 John Wiley & Sons, Ltd.

Recyclable thin TiO2-embedded rubber sheet and dye degradation

A new method for the preparation of thin rubber sheet embedded with TiO2 from natural rubber latex is presented. This method – simple and inexpensive – is based on the use of TiO2 powder (Degussa P25) mixing with small amount of natural rubber latex (60% HA) followed by vacuum filtration through a sintered glass to form a thin paper-like and flexible sheet. The characteristic of this thin and flexible TiO2 sheet (FT sheet) thus formed was studied by X-ray diffractometer (XRD) and scanning electron microscopy/energy dispersive X-ray spectrometer (SEM/EDS) techniques. The photocatalytic activity of FT sheet was evaluated using indigo carmine (IC) dye as a model for the organic dye pollutant in water. The results showed that the FT sheet containing TiO2 5wt% has the highest degradation efficiency than sheets containing higher TiO2 concentrations. The effects of pH and initial concentration of dye solution on the photodegradation were also investigated. Kinetics of the photocatalytic degradation was of the first-order reaction. The used FT sheet can be recovered and reused with no decline in the photodegradation efficiency over a long-term usage.

J022033 培養組織の球圧子押込試験による柔さ計測に関する研究

In this study, in order to measure the softness of cultured tissue, ball indentation tests were performed. As first step, the principle of ball indentation test was applied to the thin silicone rubber sheet (t=0.1mm), which achieved results confirm the validation of the measurement result. Next step, Young's modulus of monolayer cultured nerve cell (PCI2) was measured, and the validation of the measured results was confirmed by comparing with previous studies. The Young's modulus of the cell body is 36.5kPa, and distal, middle and proximal of neuritis are 50.2kPa, 21.8kPa and 51.5kPa, respectively. In addition, Young's modulus of three-dimensional gel-culture system consisting of primary human gingival fibroblasts (GF) and gingival epithelial (GE) cells in collagen gels were measured. The Young's modulus of whole gel and gingival epithelial cells are 3.46kPa and 81.9kPa, respectively. The results were shown the possibility of measuring the Young's modulus of each layer of cultured tissue in the case of laminate structure.

Numerical study of the mechanics of indentation bending tests of thin membranes and inverse materials parameters prediction

Indentation bending tests are an important testing method for thin rubber-like materials. The choice of material laws in finite element (FE) simulations of the test directly influences the accuracy of the numerical model and material properties predicted through inverse FE modelling. In this work, the effect of using a linear elastic or hyperelastic model on the material parameters predicted from indentation bending tests of a thin rubber sheet over a low strain range were studied. An inverse program has been developed based on the Kalman filter method to predict the material properties from experimental tests and to assess the uniqueness of the converged results for different material models. The predicted results were compared to standard tests carried out on the same material. Results showed that the Young’s modulus of the material with the linear elastic model can be accurately predicted while the converged parameters (C10 and C01) for the Mooney–Rivlin model were not unique; data analysis showed that parameters C10 and C01 of the converged data were associated with the shear modulus of the material.

A simple measuring device for laboratory indentation tests on cartilage / Eine einfache Prüfvorrichtung für Indentationsversuche am Knorpel

Mechanical testing of articular cartilage and repair tissue enables judgment of their capacity in withstanding mechanical loading. In the past, different methods have been developed requiring a complex technical setup and extensive data analysis. Therefore, the aim of the present project was to build up a simple measuring apparatus for laboratory indentation tests. The device consists of an incremental optical displacement transducer with a sleeve bearing guided plunger and a spherical tip made of polished steel (radius: 0.75 or 1.5 mm), a sensitive load cell and a stiff frame. The indentation force results from the plunger's gravity plus the force of the spring inside the displacement transducer and levels at 0.170 N or 0.765 N. The displacement transducer is fixed to the frame via the load cell that enables one to detect the initial contact of the tip with the tissue. The load cell has a standard uncertainty of 2 mN and the displacement transducer of 1 microm. From indentation-creep tests, a "0.25-s elastic modulus" is calculated. Measurements on thin rubber sheets were carried out to determine the quality of the measuring device. Compression tests on cylinders made of these rubber sheets yielded control data, and a good agreement with the "0.25-s elastic modulus" was found. Indentation tests on cartilage at different sites of sheep femoral condyles yielded a very good repeatability of the measurement results (+/-7.5%).

Laminated Rubber Bearing for Seismic Isolation

Seismic isolation system has absorbed much attention for a building construction method against earthquake road or buildings and badges. Laminated rubber bearing is an essential device of the seismic isolation system, which has a multi-layer ed structure composing of thin rubber sheets and steel plates.

Experimental study of cure process of foam rubber: observation of cell structure

Experimental study has been made during cure process of SBR/NR foam rubber. Rubber sample with 30 mm thick, made up by stacking thin rubber sheets in layers, was packed in a metal mold, and peroxide cure was performed by transient heat conduction. Rubber heating time was changed in several steps in order to study the effects of the cure time on the blowing characteristics. Also swelling test was conducted in order to study the relation between the cell structure and the crosslink density. Typical temperature field of one-dimensional, transient heat conduction was observed, and results of the observation studies showed that the cell structure changed depending on both the position from the heating surface and the heating time, and two extreme cell structure, open-cell foam, and closed-cell foam, was clearly observed. Image analyses of the cell structure showed that the porosity distribution increased with the increase of the distance from the heating surface, and the porosity was lower for longer heating time at a same position. Average area of the foam almost took similar results for the result of the porosity, and these various quantities were correlated to the crosslink density.

910 一様水流中の柔軟な弾性膜に発生するフラッタリング(GS-2 バイオエンジニアリング(2))

The fish's thrust results from actions of swimming fish that the fish's body is made to generate traveling waves by bending itself and transmits them downward. We think that fluttering has the possibility of drag reduction because it generates some thrust and assists main power. So we focus on fluttering in fluid. Study of fluttering was done using various kinds of elastic sheets having high and low stiffness. Our experimental models consisted of a flexible rear made of a very thin silicone rubber sheet which was easily deformed and a rigid front made of stainless steel. It was placed in a water tunnel. A laser light sheet method was used to visualize the deformation of the flexible sheet and the flow field around the model. From the visualization experiments, we measured the wave velocity, wavelength, frequency and amplitude of traveling wave on fluttering of a flexible sheet. We calculated fluttering of a flexible sheet with the model that the wave form was assumed and the principle of the energy conservation.

Relation between crack surface displacements and strain energy release rate in thin rubber sheets

The classical problem of a small crack in the center of a large, thin rubber sheet deformed in simple tension, pure shear or equi-biaxial extension is revisited. Following Key (1969) and Lake (1970), the strain energy release rate for crack growth is derived by examining the crack surface displacements (crack opening) and considering the work that would be done by forces applied to close the crack again. It is shown that the strain energy release rate may be expressed in the same form for all three modes of deformation. The results have been verified using non-linear finite element analysis. Differences arising from the use of different hyper-elastic material models are discussed.

Study of Direct-Measuring Skin-Friction Gauge with Rubber Sheet for Damping

This study concerns the direct measuring technique for skin-friction determination. Such a device measures the force on a small, movable surface element as a shear e ow passes over the surface. The typical direct-measuring skin-friction gauge uses a viscous liquid in the gap between the movable surface piece and the casing to dampen vibrations,tocreateanevensurface,tominimizetheeffectsofpressuregradients,andfortemperaturestabilization. In testing, the liquid slowly leaks out. Therefore, we have considered gauges with rubber to e ll all or some of the gap. This led to the development of a gauge with a thin rubber sheet to cover the face of the gauge instead of a previousdesign withrubbere lling theentireinternalvolume.First, ae niteelementmethodmodelwasemployed to fully understand the strain e eld involved and to e nalize the design. The resulting design consisted of a plastic skin frictiongaugewitha12.7-mm-diam e oatingelementonacantileverbeame exure,anapproximately0.51-mm-thick rubber sheet, a 1.6-mm-wide gap around the e oating element on a cantilever beam e exure, and semiconductor strain gauges at the beam base. Vibration tests were performed to determine if this design produced the required damping. These tests were successful. Supersonic wind-tunnel tests at Mach 2.4 with a total pressure of 3 atm and ambient total temperature demonstrated that the rubber sheet survived repeated tests and provided adequate damping. The skin-friction data obtained compared well with theory and other measurements.

Oscillating fracture paths in rubber.

We have found an oscillating instability of fast-running cracks in thin rubber sheets. A well defined transition from straight to wavy cracks occurs as the amount of biaxial strain increases. Measurements of the amplitude and wavelength of the oscillation near the onset of this instability indicate that the instability is a Hopf bifurcation.

Study on Rapid Curing for Laminated Rubber Using Induction Heating(1st Report, Fundamental Discussion of Heating Characteristics of Laminated Rubber and Applicability to Pre-Heater).

The rubber isolation bearing, which consists of thin rubber sheet and steel plate, is used to protect buildings from earthquake damage. In the manufacture of the bearing, the time required for the laminated rubber to be heated for valcanization is a serious problem, causing low productivity. Conventionally, the laminated rubber is heated using a hot plate press. However, with such an external heating method, it takes a long time for the internal rubber to heat up, because rubber has low thermal conductivity. Therefore, this paper proposed a new heating method. This method is focused on the steel laminated structure, whereby the confined steel plates are heated by induction heating. The possibility of using inductive heating for a laminated steel plate is discussed using the results from a small scale test and a simulation. As a result, it is demonstrated that this new heating method is available to pre-heating of the laminated rubber.

Surface modification processing of synthetic rubbers by ultraviolet irradiation and sputter ion etching treatment

The mechanism by which surface modification of two kinds of synthetic rubbers (ethylene-propylene and chloroprene) was brought about by ultraviolet (UV) irradiation and sputter ion etching treatments was studied from a physicochemical point of view. The most remarkable effect of this irradiation treatment was the rapid increase in adhesion properties and the simultaneous decrease in self-stickiness. This nonsticking effect was particularly important for the rapid production of articles from thin rubber sheets. The surface modification mechanism was studied by use of SEM, ESCA, FTIR, and related interfacial analytical procedures. It was shown that surface roughening with a quite thin layer of surface oxidation (∼0.5 μm in depth) is a key factor for the development of nonsticking properties. © 1997 John Wiley & Sons, Inc. J Appl Polym Sci 63: 1625–1633, 1997

Study of oscillation signals in instrumented charpy impact testing

AbstractThe effects of mechanical and electrical filtering were examined for signals obtained from a strain gauge installed at a dart of an impact tester. Mechanical filtering was provided by placing a thin rubber sheet on the impacted surface of the specimens. The electrical filtering was done using a 3 kHz low‐pass filtering circuit in the strain amplifier. It was shown from the results for polycarbonate Charpy specimens that mechanical filtering with a thickness of 0.5 and 1.0 mm gives good reliability for the impact velocity at both 2.8 and 4.0 m/s, not only in reducing the inertial oscillation effect but also in correctly providing values of impact energy.

The Stiffness of Human Apophyseal Articular Cartilage as an Indicator of Joint Loading

The stiffness and thickness distribution of healthy lumbar apophyseal cartilage was measured in 25 lumbar motion segments (L1–4). The cartilage indentation and needling techniques of Swann and Seedhom (37) were suitably altered to cope with the low modulus and small size of the joint surfaces. A load of 3.12 ± 0.19 N (mean ± s.d.) was applied to the cartilage through a hemispherical indenter of 4.756 mm diameter. The stiffness was calculated using the displacement and instantaneous load 150 ms and 2 s after the indenter first contacted the surface, and using the equations of both Waters (46) and Hayes et al. (47). The mean stiffness of apophyseal joint cartilage was 2.8 M Pa ± 4 per cent (mean ± 95 per cent confidence limit), and thickness 1.02 mm ± 3 per cent. Peripheral apophyseal joint cartilage was softer than central cartilage. The stiffnesses of the centres of the superior and inferior joint surfaces were 3.01 MPa ± 12 per cent and 3.55 MPa ± 11 per cent. Inferior surfaces had a mean thickness of 0.93 mm ± 5 per cent and stiffness of 2.88 MPa ± 7 per cent. Superior surfaces had a mean thickness of 1.10 mm ± 4 per cent and stiffness of 2.74 MPa ± 5 per cent. It was found that the stiffness of cartilage calculated according to the formula of Hayes et al. (47), based on a constitutive analysis of a thin isotropic elastic layer, was directly proportional to both the stiffness calculated using the semi-empirical formula of Waters (46), derived to describe indentation of thin rubber sheets, and the nominal compressive creep modulus calculated by dividing the mean contact stress by the strain at the deepest point of indentation. The creep modulus calculated 2 s after contact was directly proportional to the creep modulus calculated 150 ms after indenter contact, implying that deformation behaviour was uniform between these points despite variation of cartilage stiffness.

Estimation of the Load-Bearing Functions of the Patellar-Tendon-Bearing Orthosis.

Load-bearing functions and fracture-suspending effects of the patellar-tendon-bearing orthosis were evaluated by means of a contact pressure measurement system. The measurement of the dynamical skin/orthosis contact pressure distribution during walking was carried out using pressure-sensitive conductive rubber sensors. The sensor consists of a thin conductive rubber sheet sandwiched between a pair of copper electrodes and enabled determination of the contact pressure distribution in each of thirty-one equally sized areas covering the entire surface of the lower leg. Measurements were made using the three types of PTB, KBM and PTES orthosis under three sole conditions each. The relative pressure distributions measured were almost identical among the three types of orthosis, while for PTES the area around the patellar tendon made slightly low pressure contact. An experi-ment using an indentation device with an amputated above-the-knee specimen was also carried out to evaluate the fracture-suspending effects of the PTB orthosis. Results including the curve of the applied load-displacement for the specimens in the PTB orthosis were given.