Porous Elastic Materials Research Articles

Response of a thin coating of a porous elastic material whose generalised Young’s modulus depends on the density

Response of a thin coating of a porous elastic material whose generalised Young’s modulus depends on the density

Modeling Mass Transport Dynamics in Deformable Hydrogels during Evaporation.

Hydrogels possess exceptional mechanical properties and biocompatibility, making them widely used in contemporary bioengineering. Specifically, in the development of wearable and implantable health monitoring devices as well as drug delivery systems, hydrogels are utilized to enable precise control over the transport of solutes. Nonetheless, predicting the distribution of substances within hydrogels still poses a significant challenge due to the complex interplay between the movement of water content, migration of solutes, and deformability of the hydrogel polymer network, which presents challenges to theoretical modeling. Our work introduces a numerical model that addresses the movement of water and solute within a flexible hydrogel, accounting for evaporation and/or moisture absorption at the boundary. The model solves for water saturation, solute concentration, and hydrogel deformation iteratively at each time step while computing the boundary movement velocity based on the transport process. By comparing the modeled results of geometry deformation and water and solute distributions during evaporation with our experiments, we demonstrate the accuracy and applicability of our proposed model. This capability to precisely analyze water and solute concentrations in deformable and nonuniform hydrogel environments paves the way for advancements in biosensing and drug delivery methods that rely on elastic porous materials.

A Soft Robot Tactile Finger Using Oxidation-Reduction Graphene-Polyurethane Conductive Sponge.

Currently, intelligent robotics is supplanting traditional industrial applications. It extends to business, service and care industries, and other fields. Stable robot grasping is a necessary prerequisite for all kinds of complex application scenarios. Herein, we propose a method for preparing an elastic porous material with adjustable conductivity, hardness, and elastic modulus. Based on this, we design a soft robot tactile fingertip that is gentle, highly sensitive, and has an adjustable range. It has excellent sensitivity (~1.089 kpa-1), fast response time (~35 ms), and measures minimum pressures up to 0.02 N and stability over 500 cycles. The baseline capacitance of a sensor of the same size can be increased by a factor of 5-6, and graphene adheres better to polyurethane sponge and has good shock absorption. In addition, we demonstrated the application of the tactile fingertip to a two-finger manipulator to achieve stable grasping. In this paper, we demonstrate the great potential of the soft robot tactile finger in the field of adaptive grasping for intelligent robots.

Comparison of different methods for dynamic characterization of porous-elastic materials

Acoustical simulation of porous-elastic materials requires several properties to be characterized, one of them is the dynamic mechanical behavior of the structure. For this goal, quasi-static mechanical analysis (QMA) is the generally used method executed in the ca. 20-60 Hz frequency range, resulting constant (averaged) mechanical properties. Polymer-based materials, however, are well-known from their time- and frequency-dependent behavior. This implies the need for having frequency-dependent data in a wider frequency range, but the error induced by the fluid motion inside the pores increases with frequency. For that reason, dynamic mechanical analysis (DMA) together with frequency-temperature superposition method was chosen to analyze the possibility of extending the evaluable frequency range. Different measurement setups and strategies were tested and evaluated to minimize the errors coming from machine resonances and other influencing factors, and results were compared to those obtained from the classical QMA measurements. It was finally proven, that with thoroughly chosen technique, DMA can give high quality results for porous-elastic materials as well, in a remarkably wide frequency range.

Effect of porosity and pore size distribution on elastic modulus of foams

In this study, we investigate the impact of pore distribution and size on the mechanical response of elastic porous materials. Two-dimensional porous media with convex porosity are considered (e.g., foams and sponges). These structures are numerically generated by subtracting randomly dispersed circular holes from a solid square domain. The in-plane position vector of pore centers is given by a uniform probability density function (PDF). The pore diameters are, instead, drawn from a non-uniform two-parameter continuous probability distribution. The influence of the void ratio, i.e., the volume fraction of voids, and the parameters of the diameter PDF are studied over a wide range of values, including the percolation threshold, where the effective elastic modulus of the material abruptly drops to zero. This transition takes place at a critical value of the void ratio, which turns out to be unaffected by the parameters of the pore size distribution. Our results demonstrate that the elastic response of these structures is primarily governed by the void ratio, with the correlation length playing a secondary role. While the pore size distribution may affect the correlation length, it has a minimal impact on the foam’s overall behavior.

Study on the mechanism and controlling method for annulus pressure buildup problems in shale gas wells

The Annulus Pressure Buildup (APB) problems in shale gas wells is mainly caused by the crack at casing-cement interface. The stresses on casing-cement interface and cement-formation interface are calculated by the established model which the constrain of formation rock is considered. The elastic modulus of cement sheath has great effect on the stress on casing-cement and cement formation interface. The radial stress on interfaces changed linearly with fluid pressure. The cement rock is treated as a porous elastic material and the residual strain in cement sheath is mainly caused deformation or collapse of pore structure in the cement rock due to the large radial stress on interfaces. Ultimately, micro-annulus will be generated on the casing-cement interface due to the residual strain of cement sheath. High flexibility cement rock is proposed to decrease the radial stress on the interfaces which can reduce the residual strain of cement sheath. On the other hand, PABP is proposed to offset the decreased radial stress due to residual strain. A model for calculating the stress on interface by considering residual strain of cement sheath and PABP is established. The radial stress on the interfaces caused by PABP is quantitative calculated. The mechanism on how the method for solving APB problems in shale gas wells is clearly explained. The field application certificated the validity of method for solving the APB problems and it also proved the correctness of the calculation method.

Study of Cross-Scale Micro-Motion Wear Characteristics of Metallic Rubber

Abstract Metal rubber (MR) is a kind of elastic porous material with a complex and disordered internal structure, which results in wear characteristics that can only rely on tests but cannot meet the engineering application. This paper presents an exciting method for studying wear characteristics based on its virtual fabrication technology. By developing the intricate internal multipoint random contact mesh model of MR, a virtual real-time dynamic tracking contact point in a different state is captured. A thorough investigation is conducted into the contact point properties, point distribution, and the interaction of discrete contact points in MR interior space. Accordingly, a cross-scale micro-motion wear study method from micromorphology to macroscopic performance is proposed. The continuous wear cycle of MR is discretized into multiple single-turn metal wire elements by applying the principle of equal spacing. A statistical model of internal contact point wear of MR at the microlayer is developed considering the metal wire’s single-turn fretting wear prediction model. The cumulative prediction model of macroscopic wear damage of MR is based on the superposition of micro-element interval. Finally, the difference between the mass loss and that obtained from the simulation analysis after performing dynamic loading tests at different cycles was studied and found to be insignificant.

Wave attenuation and motion response of floating breakwater with sponge material

Floating breakwaters are essential for protecting coastal and offshore areas from strong waves. Sponge material (polyurethane) is a porous elastic material that is widely used in shock absorbers and anti-friction applications. To this end, a floating breakwater with sponge material (SMFB) was proposed and tested in a wave flume. Eight cases were tested, including three kinds of sponge materials with different porosity and two different arrangement modes. The motion response was analyzed using DeepLabCut, an open-source tool for markerless pose estimation of user-defined body parts with deep learning. The results showed that SMFB had better wave attenuation performance and a larger range of motion response with increasing sponge porosity. Furthermore, the SMFB with sponge material arranged on the deck of box-type floating breakwater had better wave attenuation performance. Lastly, floating breakwaters with sponge material had weaker wave reflection ability and stronger wave energy dissipation capacity than those without sponge material.

A cuboidal open cell model for constitutive modeling of surface effects in fluid-saturated porous materials

Fluid-saturated porous elastic materials, made up of connected networks of solid ligaments and characteristically having open pores, are commonly found in geological, biological and engineering materials. Surface effects can affect significantly the mechanical performance of such porous materials at macro scale, especially when the solid ligaments and the pores have micro or nano scale sizes. In the present study, in order to explicitly link pore-level geometrical parameters and surface effects with effective poroelastic properties as well as constitutive equations governing poroelastic deformation, we combine the top-down homogenization approach presented a previous study (Chen et al., 2021) with the bottom-up micromechanics approach. Inspired by the Gibson-Ashby cubic cell model for open-cell foams and the cellular networks typically found in fluid-saturated porous materials, we propose a cuboidal open cell model, with surface effects and fluid compressibility accounted for. For two limiting cases, i.e., the undrained state and the drained state, we demonstrate that both the surface moduli and residual surface stress (i.e., surface tension) prevent the deformation of solid ligaments, thus stiffening the porous material with enlarged effective Young's moduli. Further, we reveal that the two surface effect parameters (i.e., residual surface stress versus surface moduli) exhibit a coupling effect on effective moduli: when one parameter is large enough, the variation of the other affects significantly the effective moduli. As applications of the proposed model, we characterize mechanical behaviors of the porous material under typical loadings (e.g., uniaxial and non-proportional multiaxial tension) in both undrained and drained states; we also describe, for the first time, the stress concentration of a compressible liquid inclusion (e.g., a cell) with surface tension embedded in a fluid-saturated porous material with surface effects. Results of this study are beneficial for understanding and investigating how surface effects influence the poroelastic parameters of fluid-saturated porous materials having sufficiently small open pores.

Multilayered graphene oxide impregnated polyurethane foam for ultimate sound absorbing performance: Algorithmic approach and experimental validation

A multilayered graphene oxide-impregnated polyurethane (GO-PU) foam structure is proposed to maximize the sound absorption coefficient (SAC). The sound absorption properties of each PU layer were controlled via GO impregnation. The optimal multilayered structure was derived via theoretical predictions using matrix calculations. The elastic porous materials theory of Bolton et al. was applied to theoretical modeling of the sound-absorbing materials. The developed routine predicted the SAC with high accuracy for single and multilayered designs. The impregnation effect of GO was enormous and improved the average SAC by up to 153 % compared with the original PU. It is encouraging that the average SAC was improved by up to 49 % by simply optimizing the layer arrangement with the same amount of GO impregnation. Notably, the average SAC above 500 Hz of the optimized 54.6-mm -thick (±0.4 mm) GO-PU multilayered structure was enhanced to over 0.9. These remarkable results were verified by theoretical calculations and experiments.

Thermo-mechanical performances of elastic–porous materials with metallic wire mesh structures

Elastic–porous lightweight materials with metallic wire mesh structures are increasingly being used for vibration–reduction and thermal conduction under high temperatures or other harsh conditions. This is attributed to their special meso–scale functional structures. However, little is known about the intrinsic relationship between thermo-mechanical performances and the porous structure. We synthesized elastic–porous materials with metallic wire mesh (EPMWM) structures using entangling and weaving technologies. In addition, numerical models of microstructures were established, and experimentally validated using quasi–static and dynamic tests. Theoretical and experimental analyses of heat transfer behavior showed that the damping energy consumption of the entangled metallic wire mesh structure was better than that of the woven metallic wire mesh structure to a certain load condition. Moreover, pore air in EPMWM significantly affected the overall thermal conductivity, especially at high temperatures, due to the heat radiation between metallic wires.

Emulsion Gels as Precursors for Porous Silicones and All-Polymer Composites-A Proof of Concept Based on Siloxane Stabilizers.

In spite of its versatility, the emulsion templating method is rather uncommon for the preparation of porous silicones. In this contribution, two siloxane-containing stabilizers, designed to be soluble in polar (water) and non-polar (toluene) solvents, respectively, were used in low concentrations to produce stable emulsions, wherein polysiloxane gels were obtained by UV-photoinitiated thiol-ene click cross-linking. The stabilizers exhibited negative interfacial tension, as measured by Wilhelmy plate tensiometry. The emulsion gels evolved into porous silicones (xerogels), with tunable morphology and properties. According to TEM and SEM investigations, the emulsion template was preserved in the final materials. Several parameters (e.g., the structure of the polysiloxane precursors, composition of the emulsion gels, nature of the continuous phase, cross-linking conditions, or additives) can be varied in order to obtain porous elastic materials with desired properties, such as Janus membranes, absorbent monoliths, all-polymer porous composites, or silicone-swollen gels. The feasibility of these types of materials was tested, and exemplary porous silicones were briefly characterized by contact angle measurements, mechanical testing, and absorption tests. The proposed method is simple, fast, and economic, uses very little amounts of stabilizers, and can be adjusted as a green technique. In this contribution, all the silicon-based materials with a convenient design were prepared in house.

Multiscale stress analysis of porosity clusters as mechanical models of degenerated graphite defects in cast iron

We extend previous results for the stress analysis of a cluster of degenerated graphite in spheroidal cast iron, modelled as a multiscale three-dimensional composite. At the microscale, precipitates of degenerated graphite are modelled as spheroidal voids in a linear elastic matrix. At the mesoscale, clusters of degenerated graphite are aggregates of spheroidal voids. These aggregates are studied by means of a numerical analysis based on finite element simulations. As a second approach, the clusters are seen as homogeneous inclusions made of an equivalent porous elastic material. The average elastic properties of the porous material are calculated using an approach proposed by Tandon and Weng and based on Eshelby’s equivalent principle and Mori-Tanaka’s estimate. Comparison of the two approaches gives encouraging results in terms of average properties.

An a priori error analysis of a porous strain gradient model

AbstractIn this work, we consider, from the numerical point of view, a boundary‐initial value problem for non‐simple porous elastic materials. The mechanical problem is written as a coupled hyperbolic linear system in terms of the displacement and porosity fields. The resulting variational formulation is used to approximate the solution by the finite element method and the implicit Euler scheme. A discrete stability property and a priori error estimates are proved, from which the linear convergence of the numerical scheme is deduced under adequate regularity conditions. Finally, some numerical simulations are presented to show the accuracy of the finite element scheme studied previously, the evolution of the discrete energy and the behavior of the solution.

Optimization on hysteresis dynamic model of metal rubber material based on dry friction damping term

As one kind of porous elastic metal material, metal rubber is used in vibration isolation widely due to its better damping characteristic. During loading and unloading, the elastoplastic deformation and damping characteristics of this material are usually described by constructing its dynamic model. Although traditional models can describe the hysteresis performance, the accurate parameter identification of material structure under different preparation conductions is limited due to its complex expression or equivalent math form. In this paper, a dynamic hysteresis model is optimized through adding a dry friction damping term based on the micro-element analysis theory and analysis method of material mesoscopic structure. The relation among the manufacture technic, size of metal wire and vibration parameters were established, which accurately describes hysteresis characteristic of metal rubber by dry friction when the metal wires are in the state of slipping contact. The result is verified by the harmonic vibration experiment that the model has good adaptability and convenience, especially can improve the accuracy and convenience of parameter identification on the forming materials of metal rubber.

Effect of poroelastic material on vibroacoustic behavior of truncated conical shells

Acoustic transmission through single- and double-walled truncated conical shells lined with poroelastic material is analytically studied. The thin isotropic shells are excited by an oblique plane acoustic wave. The equations of motion of the shells are governed by Love's theory, and the wave propagation within the elastic porous material is described by an equivalent fluid model based on Biot's theory. To extract the acoustic pressures exerting on the surfaces of the conical shells, the shells are divided into several truncated segments which are narrow enough to be considered locally cylindrical. By employing a convergent power series solution the exact dynamic response of the conical shells is obtained. At first, the transmission loss results of this study are validated against those of previous works. Then, the results of various configurations of the single-walled conical shell lined with porous material are compared with those of its double-walled counterpart with equal mass. It is found that the single-walled shell lined with a porous layer is appropriate for sound insulation purposes at low frequencies below the first ring frequency, whereas, at higher frequencies, the double-walled sandwich shell provides better performance and more options for tuning the sound insulation. It is also shown that, except for low frequencies, the effects of the porous material and the method for bonding it to the facing shell are significant to improve the acoustic insulation ability. Finally, the influence of the porous layer thickness is investigated on the sound transmission loss.

Comparison between elastic and porous elastic material models for sediment acoustical behavior in an aluminum-sediment double layer

In this paper, Lamb waves dispersion curves are extracted for a double layer aluminum-sediment (gypsum) plate, both numerically and experimentally. For this purpose, the gypsum elastic properties are approximately calculated using ultrasonic bulk waves method. Then, by using the porous elastic behavior model for the gypsum, as well as the elastic model, available in ABAQUS commercial software, the dispersion curves are calculated numerically in the frequency range of 100–200 kHz for the sedimentary plate. In order to validate the numerical dispersion curves, an experimental setup consists of a 1-mm-thick aluminum plate covered by a 1.5 mm thick sediment (gypsum) area, equipped with two piezoelectric disks has been provided. The experimental dispersion curves for two fundamental symmetric and anti-symmetric modes, S0 and A0, have been extracted, using the time of flight method, applied on filtered experimental signals. Results show that the relative error between porous elastic and experimental models is 5.26% and 3.56% while relative error between numerical elastic model and the experimental model is 5.9% and 4.3%, for S0 and A0 modes, respectively. It is concluded that for dry sediments, the elastic mechanical behavior is acceptable. However, in case of wet sediments, dispersion curves should be extracted using a porous elastic model before defect detection in sedimentary structures. The unique capability of the porous elastic model is the possibility of wet sediment consideration, for dispersion curves evaluation.

Multiscale three-dimensional stress analysis of voids clusters for the modelling of degenerated graphite in cast iron

We propose a multiscale three-dimensional model for the stress analysis of a cluster of degenerated graphite in spheroidal cast iron. The model allows to study the effect of graphite microstructure on the average stress distribution inside the cluster. At the microscale, precipitates of degenerated graphite are modelled as spheroidal voids. At the mesoscale, clusters of degenerated graphite are viewed as spheroidal inclusions made of equivalent porous elastic material. The equivalent elastic properties of the porous material are calculated using an approach proposed by Tandon and Weng and based on Eshelby’s equivalent principle and the Mori-Tanaka’s estimate. FE simulations at the microscale and at the mesoscale are performed in order to numerically validate the multiscale model.

On the stability of linear porous elastic materials with microtemperatures effects and frictional damping

In this paper, we are interested in the study of a porous-elastic system in one-dimensional open bounded domain and with dissipation due to microtemperatures and frictional damping acting on the first equation (displacement of the solid elastic material). Using the energy method, we prove the exponential decay for the energy.

Development of a hierarchical model for voids clusters suitable for cast iron degenerated graphite

We develop a hierarchical model for the description of the stress state inside a cluster of degenerated graphite in spheroidal cast iron. The model is based on the following simplifying assumptions: at the microscale, the graphite particles are viewed as elliptical pores; at the mesoscale, clusters of graphite particles are modeled as elliptical inclusions made of an equivalent porous elastic material in plane strain. To calculate the equivalent elastic properties of the porous material, we adopt the Mori-Tanaka’s estimate. The accuracy of the model has been numerically verified by comparing the results of the model with FE simulations at three different levels: at the microscale, at the mesoscale, and coupling at the two scales. The model allows to study the effect of graphite microstructure on the average stress distribution inside the cluster.