Mechanical Properties Of Porous Materials Research Articles

An extended continuum-mechanics standard linear solid rheology for fluid-saturated porous rock

SUMMARY In a large body of rock-physics research, seismic wave velocity dispersion and attenuation in fluid-saturated porous rock are studied by constructing analytical or numerical models for time- or frequency-dependent dynamic (effective, or viscoelastic) moduli. A key and broadly used model of such kind is the Zener's, or the standard linear solid (SLS). This model is qualitatively successful in explaining many field and laboratory observations and serves as the key element of many generalizations such as the Burgers model for plastic deformations or the generalized SLS explaining band-limited or near-constant seismic attenuation. However, as a physical model of fluid-saturated porous rock, the SLS has several major limitations: disregard of inertial effects, absence of secondary wave modes and lack of key physical parameters such as porosity and Skempton coefficients. Grainy and porous rock is an unconsolidated material in which the effective density is frequency-dependent, and its effects on wave velocities may exceed those of the dynamic modulus. To overcome these limitations of the empirical SLS, we propose a rigorous rheologic model based on classical continuum mechanics and called the extended SLS, or eSLS. This rheology explains the available attenuation and dispersion observations equally well, but it is also close to Biot's model, honours all poroelastic relations, includes inertial effects, and reveals several new physical properties of the material. Detailed comparison of the eSLS and Biot's models gives a physical-mechanism-based classification of wave-induced fluid flow (WIFF) phenomena. In this classification, the so-called ‘global-scale’ flows occur in Biot's type structures within the material, whereas the ‘local-scale’ WIFF occurs in eSLS-type structures. Combining Biot's and eSLS models gives a broad class of rheologies for linear anelastic phenomena within rock with a single type of porosity. The model can be readily generalized to multiple porosities and different types of internal variables, such as describing squirt flows, wetting or thermoelastic effects. Modelling is conducted with relatively little effort, using a single matrix equation similar to a mechanical form of the standard SLS. By combining the eSLS and Biot's models, observations of dynamic-modulus dispersion and attenuation can be inverted for macroscopic mechanical properties of porous materials.

Mechanical properties of porous materials based on new triply periodic and minimal surfaces

In this study, the mechanical properties of eight new porous structures were investigated. These structures are based on triply periodic surfaces derived from zeolite frameworks AWW, CGF, HEU, NPT, FRA, IFY, LTL and TSC; the TPSs obtained from the last four frameworks were found to be new minimal. Samples of TSC-based porous structures were made of polyamide using 3D printing methods and their mechanical properties (loading curves, compression modulus, shear modulus, Poisson’s ratios, and yield strengths) were experimentally and numerically studied. Numerically calculated mechanical properties were found to be in good agreement with the experimental results. We revealed dependences of the mechanical characteristics on the relative density of the material and estimated mechanical properties of porous structures obtained from other seven zeolites. The results obtained enable one to choose porous materials that are the most suitable in terms of their mechanical properties for various engineering applications.

Importance of geometric parameters in modeling of porous materials – a finite element study

AbstractPorous materials consist of interconnected skeletal structure around a porous space. The skeletal structure is usually formed of a solid phase and the pores are typically filled with a fluid (liquid or gas). Porous materials are characterized by two essential geometric properties: porosity and pore size distribution (PSD), which influence their bulk mechanical properties. Porosity, which is defined in terms of the ratio between the envelope and the skeletal densities, is sufficient to describe the elastic bulk properties of porous materials. Gibson and Ashby developed a power scaling law expressing the linear relation between the elastic modulus and the relative density. The PSD describes the spatial variation of the pore sizes and has recently been shown to influence the mechanical properties of porous materials. In addition to porosity and PSD, the pore characteristics, namely pore size and shape, and pore‐wall size and shape, also determine the geometric properties that influence the bulk response of these materials. In this study, the importance of the above‐mentioned geometric parameters in the modeling of the porous materials is studied using a computational framework. The bulk mechanical response under large deformation of various porous structures with PSD based on different probability density functions (PDF) and different combinations of other geometric properties under uniaxial compression is investigated. The sensitivity of mechanical response to these geometric parameters is studied. Interdependent parameters which are significantly influential are identified. By controlling these parameters, the synthesis of porous materials can be guided and optimized.

Investigation into effective mechanical properties of porous material produced by the additive manufacturing method

Porous materials are defined as materials that contain holes, voids, or spaces in their structures, which can be interconnected or isolated. In the most complex forms of these materials, the holes can have irregular shapes with a random distribution in size, location, and direction, making studying their properties a challenging problem. Additive manufacturing techniques offer opportunities to create complex structures, and in this paper, we investigate the effective mechanical properties of porous material produced by the Fused Displacement Modeling (FDM) technique. We also propose an algorithm for generating a porous body containing irregularly shaped holes with arbitrary distributions in size and location while maintaining specific porosity. Due to the orthotropic properties of bodies created by the FDM technique, Reinforced Isotropic Solid Modeling (RISM) is combined with existing theories that calculate the effective properties of isotropic materials. For the experiments, some modified standard specimen with a porosity of 0.05 to 0.40 has been fabricated, and the elastic modulus and ultimate stress have been calculated using the tensile test. Finally, the results are compared with experimental data.

The effect of fillers’ composition on thermal swelling of silicate materials

The article presents the results of studies of the process of thermal pore formation of materials based on sodium alkaline silicates. The aim of the study is to substantiate fillers composition for liquid glass mixtures. Substandard rocks and technogenic materials were used as fillers. There were determined the temperature intervals of intensive formation of the gas phase during heat treatment of fillers. Comparative analysis of swelling characteristics revealed the preference for a combination of several fillers containing substances with different resistance to temperature transformations. The results of studies of the structure and physical and mechanical properties of porous materials confirmed feasibility of using multicomponent fillers. The cellular material developed is characterized by predominantly closed, high porosity, heat-shielding properties and resistance to mechanical stress.

Prediction of bulk mechanical properties of PVC foam based on microscopic model:Part I-Microstructure characterization and generation algorithm

The mechanical properties of porous materials greatly depend on their microstructures, so the generation of realistic microstructures is the premise for a sound numerical simulation and analytical prediction. This paper presented the microstructure generation of three kinds of transversely isotropic closed-cell polyvinyl chloride (PVC) foams with different densities based on the geometric characteristics obtained from the X-ray computed tomography (CT) technology. Advancing front method was used to densely pack a set of spheres whose volume distribution is proportion to the cell volume distribution and the microstructure was formed by Laguerre tessellation. Then the geometric characteristics of the numerical models were compared with those from the CT. The good consistence proves that the proposed method is accurate and efficient to produce the representative microstructure of the PVC foams. Finally, a method was proposed to optimize the microstructure of small size numerical specimens, by which the small specimens could give similar geometric characteristics to those of the large specimens.

Impact of pearl-necklace-like skeleton on pore sizes and mechanical properties of porous materials: A theoretical view

The structural and mechanical properties of open-porous cellular materials are often described in terms of simple beam-based models. A common assumption in these models is that the pore walls have a constant cross section, which may be in agreement for a vast majority of such materials. However, for many of those materials that are characterized by a pearl-necklace-like network, this assumption seems too idealized. Aerogels are perfect examples of such materials. In this paper, we investigate the effect of such pore walls having a string of pearls-like morphology on the properties of such open-porous materials. First, the pore size is mathematically modeled. Three scenarios are described, where the pore sizes are calculated for cells in 2D, 3D, and 3D with overlapping particles. The dependency of the skeletal features on the resulting pore size is investigated. In the second part, pore walls with 3D overlapping spheres are modeled and subjected to axial stretching, bending, and buckling. The effect of the particle sizes and the amount of overlap between the particles on the mechanical features is simulated and illustrated. The results are also compared with models that assume a constant cross section of pore-walls. It can be observed that neglecting the corrugations arising from the pearl-necklace-like morphology in open-porous cellular materials can result in serious miscalculations of their mechanical behavior. The goal of this paper is not to quantify the bulk mechanical properties of the materials by accounting for the pearl-necklace-like morphology but rather to demonstrate the significant deviations that may arise when not accounted for.

Tailoring centripetal metamaterial with superelasticity and negative Poisson’s ratio for organic solvents adsorption

Graphene metamaterials with a radial-like structure and negative Poisson’s ratio (NPR) were assembled using a unique centripetal freezing technique. Driven by the centripetal temperature gradient, ice crystals were grown toward the center of an aqueous graphene dispersion and form a radially arranged skeleton. A reentrant structure was formed at the diagonal of the monolith as the ice crystals sublimate. The obtained centripetal graphene metamaterial (CGM) was endowed with NPR response. CGM maintained NPR under 50% compression, which reached a minimum (−0.18) at 10% strain. After 50 compressive cycles at 50% strain, CGM retained approximately 96% of the original compressive strength. The radial channels endowed CGM with fast absorption kinetics, and the NPR response effectively accommodated the damage caused by volume shrinkage during repeated adsorption-regeneration cycles. This strategy is an effective method for achieving NPR response and improving the mechanical properties of porous materials.

Determining Mechanical Moduli of Disordered Materials with Hierarchical Porosity on Different Structural Levels.

The impact of synthesis parameters and structural properties, respectively, on mechanical properties of porous materials on different structural levels provides valuable information for designing materials for specific applications. Within this study, we apply two nonstandard approaches for determining the mechanical properties of the mesoporous backbone phase in a series of disordered SiO2-based monolithic materials possessing hierarchical meso-macroporosity, that is, deformation upon mercury porosimetry and in situ dilatometry during nitrogen adsorption analysis. By using ordered porous model materials, the latter method has been recently proven to provide reliable mechanical moduli. This concept was now applied to a SiO2 monolith developed for high-performance liquid chromatography exhibiting disordered hierarchical meso- and macroporosity, as well as a series of analogue phenyl-modified meso-macroporous SiO2 monoliths with up to 36.1 at% organic modification. The phenyl group was introduced by adding phenyltrimethoxysilane to the sol-gel mixture. The study aimed at investigating in detail the impact of the organic modification on the morphology of the porous solid and the resulting mechanical properties. The study shows that both Hg porosimetry and in situ dilatometry performed during N2 adsorption at 77 K provide similar and reasonable moduli of compression for the mesoporous backbone of the silica materials investigated. These data were compared with moduli of the macroscopic sample as determined from sound velocity measurements by describing the fully connected macroporous backbone with a foam model. The comparison reveals an otherwise overseen side effect of the organic modification of the silica framework: in contrast to the pure reference SiO2 meso-macroporous monoliths, the hybrid material is composed of a more particulate morphology on the mesoscale, that is, mesoporous particles and corresponding necks between them are formed, which results in significant softening of the porous solid on the macroscale.

Effect of electropolishing on mechanical property enhancement of Ti6Al4V porous materials fabricated by selective laser melting

ABSTRACT Metal additive manufacturing technologies such as laser powder bed fusion (so-called selective laser melting) have been widely applied in the field of aerospace or medical device. Moreover, porous materials have been extensively studied due to the maturity of metal additive manufacturing technology. The stress shielding effects can be reduced and the bone integration between the human bones and medical devices can be improved by introducing porous materials. Thus, the medical device would be more stable after implantation. However, in our previous study, the mechanical properties of porous materials are not only affected by the porous structure and porosity but also affected by the surface roughness and the ratio between surface roughness and strut diameter. In this study, to investigate and explore such issues, two major topics will be researched, which are (1) the formulation development of the electrolyte with a surfactant to increase the surface finish effectiveness during the electropolishing process of 3D printed Ti-6Al-4V porous materials; (2) the exploration of the relationship between the mechanical properties and the surface roughness/other factors. Also, the effect of surface roughness on mechanical properties was evaluated in terms of work of fracture and specific energy absorption.

Monte Carlo Simulation for Exploring Mechanical Properties of Porous Materials Based on Scaled Boundary Finite Element Method

The existence of pores is a very common feature of nature and of human life, but the existence of pores will alter the mechanical properties of the material. Therefore, it is very important to study the impact of different influencing factors on the mechanical properties of porous materials and to use the law of change in mechanical properties of porous materials for our daily lives. The SBFEM (scaled boundary finite element method) method is used in this paper to calculate a large number of random models of porous materials derived from Matlab code. Multiple influencing factors can be present in these random models. Based on the Monte Carlo simulation, after a large number of model calculations were carried out, the results of the calculations were analyzed statistically in order to determine the variation law of the mechanical properties of porous materials. Moreover, this paper gives fitting formulas for the mechanical properties of different materials. This is very useful for researchers estimating the mechanical properties of porous materials in advance.

Evaluation of mechanical properties of porous carbon material whose structure is formed by the polymerization-induced phase separation method

It is well known that the mechanical behavior of porous materials strongly depends on porosity and pore morphology. On the other hand, their complex shape and structure make the reproduction of deformation and failure by simulation difficult. In such a case, analyses using model reflecting the complex structure of porous material (image based modeling) are quite effective. Although model of porous carbon obtained by using FIB-SEM and X-ray CT have been conducted and material properties have been evaluated,(1) the relationship between geometric structure and mechanical properties has not yet been generalized. Therefore, the objective of this study is to evaluate the relationship between geometry and mechanical properties of carbon monolith, which is a porous material with controllable geometric factors and mechanical properties. Strut length, thickness and the joint diameter of struts are selected as geometric factors and image based modeling is conducted for reconstruction model obtained by X-ray CT. Design guidelines for mechanical properties of porous materials will be discussed in the presentation.

Preparation, microstructure, three-point bending strength and permeability of a vacuum sintering porous plate

The mechanical properties of porous materials made from metal powder rolling are generally low. In order to improve low bending properties of porous materials, wire mesh was used as reinforcement, vertical rolling, folding, pressing and sintering were adopted to prepare Stainless steel metal powder and wire mesh composite porous plate (SWMCP). The influences of vacuum sintering temperature, ultrasonic generator frequency and roll gap on microstructure and bending properties were studied. Bending behaviour and fracture morphology were also observed. The results revealed that the porous strip had unique characteristic of a powder-wire mesh-powder sandwich structure. Vacuum sintering temperature played a key role in preparing process. Samples sintered at 1330 °C got better metallurgical bonding quality and superior flexural strength than 1130 °C and 1230 °C. Quicker ultrasonic frequency and roller gap was 0 mm also brought better bending properties. The prepared SWMCP possessed excellent flexural strength and possibility of application.

3D‐multilayer simulation of microstructure and mechanical properties of porous materials by selective sintering

AbstractThis work presents multilayer phase‐field simulation of selective sintering process and the calculation of effective mechanical properties and residual stress of the microstructure using the finite element method. The dependence of the effective properties and residual stress on the process parameters, such as beam power and scan speed, are analyzed. Significant partial melting of powders is observed for large beam power and low scan speed, which results in low porosity of the microstructure. Nonlinear relationship between the effective mechanical properties and process parameters is observed. The increasing rate of effective mechanical properties decreases with increasing beam power, while increases with decreasing scan speed. The dependence of effective Young's modulus and Poisson's ratio on porosity are well established using power law models. Stress concentrations are found at the necking region of powders and the intensity increases with the level of partial melting, which results in increasing residual stress in the microstructure. The numerical results reveal quantitatively the process‐microstructure‐property relation, which implies the feasibility of the subsequent data‐driven approach.

A Study to Derive Equivalent Mechanical Properties of Porous Materials with Orthotropic Elasticity.

The need for diverse materials has emerged as industry becomes more developed, and there is a need for materials with pores in various industries, including the energy storage field. However, there is difficulty in product design and development using the finite element method because the mechanical properties of a porous material are different from those of a base material due to the pores. Therefore, in this study, a Python program that can estimate the equivalent property of a material with pores was developed and its matching was verified through comparison with the measurement results. For high-efficiency calculation, the pores were assumed to be circular or elliptical, and they were also assumed to be equally distributed in each direction. The material with pores was assumed to be an orthotropic material, and its equivalent mechanical properties were calculated using the equivalent strain and equivalent stress by using the appropriate material property matrix. The material properties of a specimen with the simulated pores were measured using UTM, and the results were compared with the simulation results to confirm that the degree of matching achieved 6.4%. It is expected that this study will contribute to the design and development of a product in the industrial field.

Investigation of frequency dependent mechanical properties of porous materials using dynamic mechanical analyzer and frequency-temperature superposition theory

In acoustic design of engineering applications - such as in the acoustic analysis of passenger vehicles - poroelastic materials are of great importance. One of the most influencing properties in determining their noise-reduction potential is the storage modulus. The purpose of this study is to examine the frequency dependence of storage modulus of selected porous acoustic materials at least up to 1000 Hz. This is executed by using the combined use of dynamic mechanical analyzer and frequency-temperature superposition theory. All other methods for measuring the storage modulus fall short in determining frequency-dependence above 100 Hz: quasi-static mechanical analyzer is mostly used for determining an averaged constant value deduced from low-frequency measurements, while the usage of an electromagnetic shaker capable for high-frequency excitation may include effects of fluid motion inside the pores, thus significantly modifying the results. Frequency-temperature superposition enables to determine the storage modulus values in a wide frequency range, based on low-frequency measurements, where fluid-structure interaction is negligible. It was found that the modulus varied significantly up to and beyond 1000 Hz, and thus, acoustical characterization of these materials can be significantly improved using the proposed method. The work concludes with recommendations to improve the accuracy of the results.

Research on Strength Prediction Model of Sand-like Material Based on Nuclear Magnetic Resonance and Fractal Theory

Micro-pore structure has a decisive effect on the physical and mechanical properties of porous materials. To further improve the composition of rock-like materials, the internal relationship between microscopic characteristics (porosity, pore size distribution) and macroscopic mechanical properties of materials needs to be studied. This study selects portland cement, quartz sand, silica fume, and water-reducing agent as raw materials to simulate sandstone. Based on the Nuclear magnetic resonance (NMR) theory and fractal theory, the study explores the internal relationship between pore structure and mechanical properties of sandstone-like materials, building a compressive strength prediction model by adopting the proportion of macropores and the dimension of macropore pore size as dependent variables. Test results show that internal pores of the material are mainly macropores, and micropores account for the least. The aperture fractal dimension, the correlation coefficient of mesopores and macropores are quite different from those of micropores. Fractal characteristics of mesopores and macropores are obvious. The macropore pore volume ratio has a good linear correlation with fractal dimension and strength, and it has a higher correlation coefficient with pore volume ratio, pore fractal dimension and other variable factors. The compressive strength increases with the growth of pore size fractal dimension, but decreases with the growth of macropore pore volume ratio. The strength prediction model has a high correlation coefficient, credibility and prediction accuracy, and the predicted strength is basically close to the measured strength.

Molecular scale insight of pore morphology relation with mechanical properties of amorphous silica using ReaxFF

Porous materials are typically heterogeneous and they contain large variations of micro-/nano-pore structures, causing complicated behaviors. In continuum models, most mechanical properties of porous materials are estimated based on porosity, while the variations of micro/nano structures are ignored. That could be problematic as the microscopic heterogeneity may affect the mechanical response of porous materials. Thus, understanding micro/nano heterogeneity impact has been the focus in many scientific and engineering subjects. In the present study, we investigated the effect of nanopore structure (including pore shape and orientation) as well as porosity on mechanical properties of amorphous silica (a-SiO2). The pore sizes in our simulations are comparable to the corresponding ones observed in a-SiO2 based materials. We found that the existing of nanopores strongly influences Young’s modulus (E) and critical energy release rate (GIC). These properties decrease with increasing porosity. Importantly, the impact of nanopores was characterized by structural parameters of porous materials. In addition to dependency on porosity, Young’s modulus also was found to vary as a function of potential energy per atom, which highly depends on nanopore shape. Furthermore, critical energy release rate was found to increase with increasing ligament length (also known as pore wall thickness). The results highlighted the importance of nanopore structures, which must be taken into account when studying fracture mechanisms in porous materials. Based on our findings, it was proposed that mechanical properties of porous materials can be controlled by nano-engineering pore structures.

THE FEATURES OF DEFORMATION AND DESTRUCTION OF POROUS DIATOMITEBASED CERAMICS

The experimental and theoretical investigations of mechanical properties of porous materials are one of the priority areas of development of condensed matter physics. Diatomite ceramics can serve as a raw material for structural heat and sound insulating materials and additives to some types of cement, as a polisher for metals and marble. Diatomite-based ceramics are also used for thermal insulation in aluminum production. The foamdiatomite ceramics is a promising porous material. But the properties of diatomite ceramics are not well studied, which determines the relevance of the study. The main task of the present work is the investigation of porosity and elastic moduli of diatomite ceramics, as well as the effect of thermal treatment on its physical-mechanical properties. The work deals with studying mechanical properties of porous ceramics based on diatomite – asedimentary rock composed predominantly of shells with micro- and nanopores of 50 to 500 µm. From the results of studying the microstructure of porous diatomite-based ceramics, the average porosity of samples (~50%) was determined, and the values of static (35 to 45 GP?) and dynamic (0.3 to 0.8 GP?) elastic moduli were experimentally measured. It was found that the values of elastic moduli decrease as material porosity increases. The experiment showed that the elastic modulus of the considered high-porous material was two orders of magnitude less than that of the crystalline one.

Influence of Manufacturing Parameters on Mechanical Properties of Porous Materials by Selective Laser Sintering.

This paper presents a study on the tensile properties of Alumide and polyamide PA2200 standard samples produced by Additive manufacturing (AM) based on selective laser sintering (SLS). Because of the orthogonal trajectories of the laser beam during exposure, different orientations of the samples may lead to different mechanical properties. In order to reveal this process issue, four orientations of the samples in building envelope were investigated. For data reliability, all the other process parameters were constant for each material and every orientation. The tensile tests highlight small differences in elastic properties of the two materials, while significant differences in strength properties and energy absorption were observed. Nevertheless, Young modulus indicates high stiffness of the Alumide comparing to PA2200 samples. The stereo microscopy reveals a brittle fracture site for Alumide and a ductile fracture with longitudinal splitting zones for PA2200. From the orientation point of view, similar properties of samples oriented at 0 and 90 degrees for all investigated mechanical properties were observed. However, tensile strength was less influenced by the sample orientations.