Macroscopic Pores Research Articles

Hierarchical porous carbon composite constructed with 1-D CNT and 2-D GNS anchored on 3-D carbon skeleton from spent coffee grounds for supercapacitor

In recent years, biomass-derived carbon electrode materials for energy storage have attracted intensive attention in terms of their natural unique structure, widespread availability and low cost. Herein, a unique hierarchical porous carbon composite material (CGCM@GNS&CNT) was facilely constructed on 3-D carbon skeleton by anchoring 2-D graphene nanosheet (GNS) and 1-D carbon nanotube (CNT) through self-assembling method. The CGs with abundant macroscopic pores were utilized as 3D carbon skeleton, CNT and GNS anchored on them were applied to enhance the specific surface area (SSA) and electrical conductivity. The composite material exhibits large SSA of 460 m2 g−1, interconnected conductive network and inherent N, O doping. The CGCM@GNS&CNT electrode achieves a high areal capacitance of 441 mF cm−2 and volumetric capacitance of 90 F cm−3 at 1 mA cm−2 in 1.5 M Na2SO4 electrolyte. More importantly, the CGCM@GNS&CNT-based symmetric supercapacitor affords a remarkable energy density of 31 μWh cm−2 at a power density of 800 μW cm−2 in 1.5 M Na2SO4. The capacitance retention and coulombic efficiency can retain 102.5% and 100.5% over 2000 cycles, respectively, confirming its superb charge/discharge stability and long-term reversibility. These signify that CGCM@GNS&CNT material holds a considerable promise for electrode application in high-performance supercapacitor.

Stability mechanism of AlSi12 aluminum foam under the action of Al–Si–Ca second phase

AlCa75 with equal Ca content was used to replace pure Ca for the preparation of AlSi12 foam in a stable pore structure after foaming for 20 min. The stability mechanism was studied based on the comparison between the macroscopic pore structure evolution and the second phase composition of AlCa75 and pure Ca aluminum foam. It was found that the porosity and average pore size of the AlSi12 foam with AlCa75 were stable without any abnormal large pores, and the foaming stage was prominent. The stability of AlSi12 foam with pure Ca is inferior. After 20 min of foaming, the foam bursts in the center. Combined with the microscopic characteristic analysis, it could see that the second phase produced by AlCa75 is mainly Al2Si2Ca, which can be uniformly dispersed in the matrix. The addition of pure Ca reduces the amount of the second phase and the main phase Al4Ca is easy to agglomerate. The stability mechanism shows that the Al2Si2Ca second phase, formed by AlCa75, demonstrates a better stabilizing effect in different foaming stages. Due to the premature agglomeration caused by Al4Ca and the low content of the second phase, the AlSi12 foam with pure Ca is challenging to long-term stability.

Two-step strategy for constructing hierarchical pore structured chitosan–hydroxyapatite composite scaffolds for bone tissue engineering

Chitosan (CS) combined with hydroxyapatite (HA) was injected into a composite braid, and a hierarchical pore structure scaffold was obtained by freeze drying and cold atmospheric plasma (CAP) technology. The CS/HA/braid scaffold with hierarchical pore structure was analyzed and characterized by scanning electronic microscopy, Fourier transform infrared spectroscopy, true color confocal microscopy, improved liquid replacement method, and phosphate buffer solution immersion. The mechanical properties and degradation ability of the scaffold were evaluated through compression test and degradation test. Results showed that HA addition endowed the core of the scaffold with macroscopic pore sizes of 80–180 μm, and CAP treatment endowed the shell of the scaffold with microscopic pore sizes ≤10 μm. All scaffolds exhibited high porosity and swelling rates of ≥80 % and ≥300 %, respectively. The scaffold with a hierarchical pore structure had good mechanical properties and twice the degradation rate. In addition, the treated scaffold precipitated intact spherical HA crystals. Under the synergistic effect of HA and CAP treatment, scaffolds achieved 277.6 % cell viability compared with pure CS scaffold. Overall, this method was feasible for preparing bone scaffolds with hierarchical pore structure for potential bone tissue engineering.

Experimental Study on the Effect of Long-Term Water Injection on Micropore Structure of Ultralow Permeability Sandstone Reservoir

During the long-term waterflooding (LTWF) in oil reservoirs, the formation is subject to permeability reduction as clay release and fine migration. At present, the mechanisms of permeability impairment in both macroscopic and microscopic pore structures in ultralow permeability reservoirs under LTWF are unclear. This statement epitomizes the main objective of this work: to understand how long-term waterflood changes porous structures and thus compromises permeability. The standard core flow experiments in conjunction with a couple of tests consisting of online nuclear magnetic resonance (NMR), high-pressure mercury intrusive penetration (HPMIP), X-ray diffraction (XRD), and scanning electron microscope (SEM) were performed to determine the mineral compositions, macrophysical properties, and micropore structures of two kinds of cores with different natures of pore distribution (i.e., unimodal and bimodal) before and after LTWF in Yan Chang field China. Results showed that the permeability decreased while the porosity increased after the LTWF. With respect to the pore size distribution, the small pores (SPs) decreased and the large pores (LPs) increased for both cores. For the unimodal core, the distribution curve shifted upwards with little change in the radius of the connected pores. For the bimodal core, the curve shifted to the right with an increasing radius of connected pores. With respect to the characteristic parameters, the average pore radius, median pore radius, structural coefficient, and tortuosity increased, while the relative sorting coefficient decreased. The relative changes of the parameters for the unimodal core were much smaller than those for the bimodal core. With respect to the clays, chlorite accounted for a majority proportion of the clays, and its content increased after LTWF. According to these changes, the mechanism of LTWF at different stages was interpreted. At the early stages, the blockage of the released clays occurred in SPs. Some of the middle pores (MPs) and LPs became larger due to the release and some of them became smaller due to the accumulation. At the middle stage, the blockage of SPs weakened. Some flow channels formed by MPs and LPs became dominant flow channels gradually. The effluxes of particles occurred, resulting in a significant increase in porosity. At the late stage, the stable flow channels have formed. The higher response of the bimodal core to LTWF could be attributed to its higher content of chlorite, which was more likely to accumulate. This study clarifies the mechanism of fine-migration-induced formation damage in microscopic pore structures and the migration pattern of clay minerals in ultralow permeability reservoirs. The work provides potential guidance for optimizing waterflood strategies in ultralow permeability reservoirs.

Solution of Tasks of Energy Efficiency of the Process of Drying Raw Plant Materials by Methods of Mathematical Modeling

Beet pulp has a high feed value, but after pressing it has a sufficiently high humidity, which leads to rapid spoilage. One of the ways to stabilize the quality of beet pulp is drying with superheated steam of reduced pressure. Mathematical modeling of heat transfer during convective drying of beet pulp is proposed. A feature of the model is the description of the drying process, which ensures its high intensity due to high heat and mass transfer ratios and preserves the quality of the finished product as a result of the process at a reduced pressure of transfer medium. In the period of a constant drying speed, dehydration of macroscopic pores topologically related to the sample surface, which are characterized by a relatively low binding energy of water molecules with the liquid phase, is taken into account. According to experimental data, the proportion of water content in these pores is 60…70% of the total moisture content. In the final stage of this period, an increase in the binding energy occurs due to the removal of water from microcapillaries, which is explained by the formation of structured clusters in thin wetting films of water molecules. The change in steam temperature as a result of passing through the product layer was 8 … 10 K, and the relative temperature change was 5 … 10%. The parameters of the models were identified in the following range of parameters: superheated steam temperature 393 … 453 K; speed of superheated steam 3 … 5 m/s; the pressure inside the drying chamber is 40 … 100 kPa; the specific load of the product on the grate is 8 … 24 kg/m2. The interpretation of the simulation results is presented by the dependences of the temperature difference between beet pulp and heat carrier T on the temperature of superheated steam Ts at various pressures P: 1 - 100 kPa; 2 - 80 kPa; 3 - 60 kPa; 4 - 40 kPa; υ = 4 m/s; at various specific loads of beet pulp on the gas distribution grid qsp: 1 - 8 kg/m2; 2 - 16 kg/m2; 3 - 24 kg/m2; υ = 4 m/s; P = 60 kPa and various speeds of superheated steam υ: 1 - 5 m/s; 2 - 4 m/s; 3 - 3 m/s. A sufficient convergence of the results was ensured, in which the deviation of the calculated data from the experimental data did not exceed 12, 5% in absolute value. The obtained results of the simulation can be used in the operational control of the technological parameters of the process of drying beet pulp with superheated steam of reduced pressure with a restriction on the temperature mode due to the receipt of a high quality product.

Shaking-table test on seismic motion compressed characteristics in a liquefied soil

The seismic motion compressed characteristic is a key issue on liquefied soil-structure shaking table model test. A series of shaking table tests were performed to study the seismic motion duration compression characteristics on the dynamic response of liquefied soil. Macroscopic phenomena and dynamic pore water pressure were measured and analyzed. Experimental results showed that the intensity and frequency of seismic motion had a significant influence on the dynamic response of the liquefied soil. Meanwhile, the phenomenon of soil liquefaction and the frequency filtering effects were obvious when inputting longer duration seismic motion. The liquefied soil was more sensitive to the seismic motion, which was compressed according to the predominant frequency of the foundation. In addition, it is suggested that the uncompressed seismic motion was more appropriate on the liquefied soil-structure model in 1g shaking table tests.

Improving mechanical and physical properties of ultra-thick carbon nanotube fiber by fast swelling and stretching process

We present a post-treatment method for directly-spun ultra-thick carbon nanotube fibers (CNTFs) with a high linear density of ∼ 6 tex (g km−1), which can possibly meet industrial-scale productivity. The treatment consists of consecutive steps of swelling of CNTFs in chlorosulfonic acid, stretching, and coagulation. The swelling of CNTFs makes even distribution of the CNT bundles, which are the subunits of CNTFs, and thereby promotes the removal of the interstitial voids and macroscopic pores during subsequent coagulation. The stretching straightens tortuous CNT bundles, and thereby facilitates dense packing of aligned bundles along the fiber axis that are evenly distributed by swelling. However, highly-tortuous CNT bundles in the high linear-density CNTF leads to incremental improvement of structure and properties. The stretching is only effective at stretching ratio (RS) > 20%, and both tensile strength and electrical conductivity gradually increase as RS increases, to 27- and 8.7-times at the maximum RS = 100%. We believe that our study on the influence of RS on the structure and properties of high linear-density CNTFs provide a new opportunity for designing the industrial process of the post-treatment to commercialize CNTFs.

Relationship between the Shear Strength and Microscopic Pore Parameters of Saline Soil with Different Freeze-Thaw Cycles and Salinities

Saline soil is a widely distributed special soil with poor engineering properties. In seasonally frozen regions, the poor properties of saline soil will cause many types of engineering damage such as road boiling, melt sinking, and subgrade instability. These engineering failures are closely related to the shear strength of saline soil. However, there are relatively few studies on saline soil in cold regions. The strength of the soil is always determined by its microstructure; therefore, the study aims to investigate the relationship between the shear strength and microscopic pore structure of saline soil with different freeze–thaw cycles and salinities. The shear strength characteristics of saline soil with different salinities subjected to different freeze–thaw cycles were obtained by triaxial tests. In addition, the microstructure of the soil samples was investigated by scanning electron microscopy (SEM) tests, and the microscopic pore parameters of the soil samples, including porosity (N), average pore diameter (D¯), average shape coefficient (K), surface fluctuation fractal dimension (F), and orienting probability entropy (Hm), were obtained by image processing software quantitatively. Based on the experimental results, the influence of freeze–thaw cycles and salinity on the shear strength characteristics and microstructure of the soil samples were analyzed. Besides that, in order to effectively eliminate the collinearity between independent variables and obtain a stable and reasonable regression model, principal component regression (PCR) analysis was adopted to establish the relationship between the microscopic pore parameters and the failure strength of the soil samples. The fitting results demonstrated that the failure strength of saline soil is mainly related to the size and direction of the pores in the soil, and it has little correlation with pore shape. The failure strength of the soil was negatively correlated with the average pore diameter (D¯) and porosity (N), and it was positively correlated with the orienting probability entropy of the pores (Hm). This study may provide a quantitative basis for explaining the variation mechanism of the mechanical properties of saline soil from a microscopic perspective and provide references for the symmetry between the changes of the macroscopic properties and microscopic pore structure of the saline soil in cold regions.

Assessment of mechanical, thermal, mineral and physical properties of fired clay brick made by mixing kaolinitic red clay and paper pulp residues

Among the largest producers of waste, the paper industry stands out due to its impact on human health and ecological balance. However, these residues may also contribute to a more environmental friendly brick industry, since the incorporation of fluxing agents may improve the firing process and the induced porosity reduces thermal conductivity of fired bricks. Therefore, this study aims to assess the feasibility of replacing clay with solid paper residue (PPR) from 2.5 to 17.5% in order to reduce resources depletion and improve brick performance. The original clay was characterized as a non-calcareous red clay with high contents of kaolinite. Several samples were made by extrusion and fired at 900 °C in accordance with industrial procedures. The addition of PPR led to increase shrinkage from 5 to 10% due to the effect of fluxing oxides which reduced pores volume and enlarged pores size. In addition, the impervious fraction was slightly reduced while the apparent porosity certainly increased (i.e. approx. 17%) due to the macroscopic pores developed by PPR combustion. This porosity produces lighter bricks (i.e. density decays from 1.76 to 1.39 g dm−3) with lower thermal conductivity (i.e. from 5.53 to 0.41 W m−1 K−1) but also reduces compressive strength (i.e. from 11 to 3 MPa) and increases water absorption (i.e. up to 24%). Nevertheless, toxicity is below the regulatory limits in all cases and fired bricks are easily adaptable to industrial procedures.

Effective hydro-mechanical material properties and constitutive behaviors of meso-structured RVE of saturated granular media

In the framework of the second-order concurrent computation homogenization method for saturated granular material, meso-structured RVE (Representative Volume Element) is modeled as a compact assembly of saturated discrete particles. The boundary conditions imposed on the RVE are comprised of the two parts: (1) the boundary displacements and pressures prescribed by downscaled macroscopic strain variables and pore pressure, and (2) constrained fine scale fluctuations of mesoscopic hydro-mechanical variables expressed in terms of periodic boundary conditions.The present paper focuses on the estimation of effective hydro-mechanical material properties and constitutive behaviors of meso-structured RVE of saturated discrete particle assembly via a proposed homogenization procedure. To achieve this target, a novel scheme for determining and imposing periodic boundary conditions on peripheral particles contacting with the RVE boundary of saturated discrete particle assembly is proposed.Numerical results demonstrate performances and capabilities of the proposed scheme in estimating effective hydro-mechanical non-linear material properties and predicting hydro-mechanical constitutive behaviors of saturated granular materials evolving with loading histories. They also demonstrate the significance and necessity of imposing periodic boundary conditions on the RVE in proper prediction of effective hydro-mechanical material properties and constitutive behaviors.

Thermal insulators with macroscopic and microscopic pore anisotropy created by gelation–freezing with alumina platelets

Thermal insulators with macroscopic and microscopic pore anisotropy created by gelation–freezing with alumina platelets

Porosity evolution in sequence stratigraphic framework: a case from Cretaceous carbonate reservoir in the Persian Gulf, southern Iran

Dariyan Formation (Aptian) is one of the important hydrocarbon reservoirs in the Persian Gulf. In this reservoir, porosity is controlled by various depositional and diagenetic factors. This study integrates petrographic, geochemical, petrophysical and reservoir quality data to distinguish various pore types and their evolution in two fields selected from the SE and NW Persian Gulf. Primary (depositional) and secondary (diagenetic) pore types are differentiated using the results of macroscopic (core) and microscopic (thin section and SEM) petrographic studies. Pore size distribution and reservoir importance are evaluated by MICP and porosity–permeability measurements on core-plug samples. Macroscopic pores are formed within the grain-dominated and dissolved mud-dominated facies that are located in the RST of third-order sequences, especially within the lower carbonate unit. Micropores are recorded in mud-dominated facies of middle to outer ramp settings with minor effects of meteoric dissolution. Accordingly, evolution in an open diagenetic system with high water/rock ratio is proposed for grain-supported facies, and a closed diagenetic system for mud-dominated intervals. There are close relationships between micrite micro-textures (MTCs) and reservoir properties of mud-dominated facies. A dynamic pore evolution model is presented for the Dariyan Formation that integrates all depositional and diagenetic features in sequence stratigraphic framework. This model can be used for ongoing reservoir studies of this formation in hydrocarbon fields of the Persian Gulf.

Capturing Subdiffusive Solute Dynamics and Predicting Selectivity in Nanoscale Pores with Time Series Modeling.

Fitting mathematical models with a direct connection to experimental observables to the outputs of molecular simulations can be a powerful tool for extracting important physical information from them. In this study, we present two new approaches that use stochastic time series modeling to predict long-time-scale behavior and macroscopic properties from molecular simulation, which can be generalized to other molecular systems where complex diffusion occurs. In our previous work, we studied long molecular dynamics (MD) simulation trajectories of a cross-linked HII phase lyotropic liquid crystal (LLC) membrane, where we observed subdiffusive solute transport behavior characterized by intermittent hops separated by periods of entrapment. In this work, we use our models to parameterize the behavior of the same systems, so we can generate characteristic trajectory realizations that can be used to predict solute mean-squared displacements (MSDs), solute flux, and solute selectivity in macroscopic length pores. First, using anomalous diffusion theory, we show how solute dynamics can be modeled as a fractional diffusion process subordinate to a continuous time random walk. From the MD simulations, we parameterize the distribution of dwell times, hop lengths between dwells, and correlation between hops. We explore two variations of the anomalous diffusion modeling approach. The first variation applies a single set of parameters to the solute displacements and the second applies two sets of parameters based on the solute's radial distance from the closest pore center. Next, we present an approach that generalizes Markov state models, treating the configurational states of the system as a Markov process where each state has distinct transport properties. For each state and transition between states, we parameterize the distribution and temporal correlation structure of positional fluctuations as a means of characterization and to allow us to predict solute MSDs. We show that both stochastic models reasonably reproduce the MSDs calculated from MD simulations. However, qualitative differences between MD and Markov state-dependent model-generated trajectories may in some cases limit their usefulness. With these parameterized stochastic models, we demonstrate how one can estimate the flux of a solute across a macroscopic length pore and, based on these quantities, the membrane's selectivity toward each solute. This work therefore helps to connect microscopic, chemically dependent solute motions that do not follow simple diffusive behavior with long-time-scale behavior, in an approach generalizable to many types of molecular systems with complex dynamics.

A comprehensive comparison of cell seeding methods using highly porous melt electrowriting scaffolds.

Cell seeding is challenging in the case of additively manufactured 3-dimensional scaffolds, as the open macroscopic pore network impedes the retention of the seeding solution. The present study aimed at comparing several seeding conditions (no fetal bovine serum, 10% or 100% serum) and methods (Static seeding in Tissue Culture Treated plate (CT), Static seeding of the MES in non-Culture Treated plate (nCT), Seeding in nCT plate placed on an orbital shaker at 20rpm (nCTR), Static seeding of the MES previously incubated with 100% FBS for 1h to allow for protein adsorption (FBS)) commonly utilised in tissue engineering using highly porous melt electrowritten scaffolds, assessing their seeding efficacy, cell distribution homogeneity and reproducibility. Firstly, we demonstrated that the incubation in 100% serum was superior to the 10% serum pre-incubation and that 1h only was sufficient to obtain enhanced cell attachment. We further compared this technique to the other methods and demonstrated significant and beneficial impact of the 100% serum pre-incubation, which resulted in enhanced efficacy, homogeneous cell distribution and high reproducibility, leading to accelerated colonisation/maturation of the tissue engineered constructs. We further showed the superior performance of this method using 3D-printed scaffolds also made of different polymers, demonstrating its capacity for up-scaling. Therefore, the pre-incubation of the scaffold in 100% serum is a simple yet highly effective method for enhancing cell adhesion and ensuring seeding reproducibility. This is crucial for tissue engineering applications, especially when cell availability is scarce, and for product standardisation from a translational perspective.

3D bio polybutylene succinate electrospun nanofiber scaffolds for biomimetic structure

In this study, the electrospinning machine was developed with a liquid bath support system, which is capable to achieve randomly organized three dimensional (3D) nanofibrous structure. These structures were fabricated using high speed stirring for liquid bath collector system resulting in fluffy and glibly structures. To investigate the optimal electrospinning conditions, as well as parameters like voltage, flow rate, distance between the electrodes with respect to polymer solution properties of poly(butylene succinate) (PBS), a series of experiments, were conducted. It was found that solution properties, such as combination of solvents, concentration of PBS, had significant effect on fiber morphology. The resultant scaffold can satisfy requirement of structural properties such as macroscopic external shapes, internal architectures, porosity, and pore size. The structure and morphology of the nanofibrous scaffold were characterized by SEM. Hydrolytic degradation was studied for 2D as well as 3D nanofibrous scaffolds. Our study encourages utilizing bio-PBS based nanofibrous scaffolds to have a great degree in biomimetic structures.

Effect of microwave pre-curing technology on carbide slag-fly ash autoclaved aerated concrete (CS-FA AAC): Porosity rough body formation, pore characteristics and hydration products

In objective to clarify the effect mechanism of microwave pre-curing method on carbide slag-fly ash autoclaved aerated concrete (CS-FA AAC), porosity rough body formation process, physic-mechanical properties, pore characteristics and hydration products were investigated. Slurry foaming course and rough body strength development were characterized to illuminate the porosity rough body formation process. Furthermore, bulk density and compressive strength were measured to expound physic-mechanical properties. Areometry, X-ray 3D imaging and MIP method were introduced to represent the total porosity, macroscopic pores and microscopic void, respectively. The hydration products of CS-FA AAC were comprehensively analyzed by detecting of morphology (FESEM), mineralogical (XRD), and thermal behavior (DSC-TG). As results demonstrated, the innovative microwave pre-curing technology accelerated slurry foaming and thickening rate, thus shorten the pre-curing duration and improve the stability of CS-FA AAC rough body. Furthermore, the total porosity of CS-FA AAC products was obviously enlarged which attributed to the magnification of foaming pores. However, in pore partition zone, the total porosity was decreased under microwave pre-curing, but the volume of pores between 0.01 and 1 μm were improved significantly. The microwave pre-curing technology significantly promoted the generation of intermediate hydration products and improved the crystallinity of strength contributing minerals in final products. Therefore, due to the divergence effect of microwave pre-curing technology on pore characteristics and hydration products, the subsequent effect on strength is nonlinear.

Reconstruction and Analysis of Tight Sandstone Digital Rock Combined with X-Ray CT Scanning and Multiple-Point Geostatistics Algorithm

Unconventional rocks such as tight sandstone and shale usually develop multiscale complex pore structures, with dimensions ranging from nanometers to millimeters, and the full range can be difficult to characterize for natural samples. In this paper, we developed a new hybrid digital rock construction approach to mimic the pore space of tight sandstone by combining X-ray CT scanning and multiple-point geostatistics algorithm (MPGA). First, a three-dimensional macropore digital rock describing the macroscopic pore structure of tight sandstone was constructed by micro-CT scanning. Then, high-resolution scanning electron microscopy (SEM) was performed on the tight sandstone sample, and the three-dimensional micropore digital rock was reconstructed by MPGA. Finally, the macropore digital rock and the micropore digital rock were superimposed into the full-pore digital rock. In addition, the nuclear magnetic resonance (NMR) response of digital rocks is simulated using a random walk method, and seepage simulation was performed by the lattice Boltzmann method (LBM). The results show that the full-pore digital rock has the same anisotropy and good connectivity as the actual rock. The porosity, NMR response, and permeability are in good agreement with the experimental values.

Study on the Pore and Microstructure Fractal Characteristics of Alkali-Activated Coal Gangue-Slag Mortars.

Just as it is regarding ordinary cement-based materials, the pore structure and microstructure of alkali-activated materials are disordered. It is essential to predict the macroscopic properties by studying the pore and microstructure fractal characteristics of materials. In this paper, the effects of slag content and alkali activator modulus on compressive strength, porosity, and microstructure of alkali-activated coal gangue-slag (AACGS) mortar were studied. Further, with the help of mercury intrusion porosimetry (MIP) data and the MATLAB programming, the pore and SEM photos fractal dimensions of AACGS mortar specimens were obtained, respectively, and the relationship between the microscopic fractal dimensions and the macroscopic strength and the structural characteristics of pores was established. The results show that the pore fractal dimension has a good linear relationship with the compressive strength and pore characteristic parameters (porosity, total pore area, and average pore diameter, etc.). With the increase of slag content, the SEM photos fractal dimension of AACGS mortar specimens increases, and the fractal dimension and compressive strength also show a significant positive linear relationship. The two fractal characterization methods can be used in the alkali-activated material system and have important guiding significance for predicting the macroscopic strength and pore characteristic parameters of the material.

Cholla cactus frames as lightweight and torsionally tough biological materials

Biological materials tested in compression, tension, and impact inspire designs for strong and tough materials, but torsion is a relatively neglected loading mode. The wood skeletons of cholla cacti, subject to spartan desert conditions and hurricane force winds, provide a new template for torsionally resilient biological materials. Novel mesostructural characterization methods of laser-scanning and photogrammetry are used alongside traditional optical microscopy, scanning electron microscopy, and micro-computed tomography to identify mechanisms responsible for torsional resistance. These methods, in combination with finite element analysis reveal how cholla meso and macro-porosity and fibril orientation contribute to highly density-efficient mechanical behavior. Selective lignification and macroscopic tubercle pore geometry contribute to density-efficient shear stiffness, while mesoscopic wood fiber straightening, delamination, pore collapse, and fiber pullout provide extrinsic toughening mechanisms. These energy absorbing mechanisms are enabled by the hydrated material level properties. Together, these hierarchical behaviors allow the cholla to far exceed bamboo and trabecular bone in its ability to combine specific torsional stiffness, strength, and toughness. Statement of SignificanceThe Cholla cactus experiences, due to the high velocity desert winds, high torsional loads. Our study has revealed the amazingly ingenious strategy by which the tubular structure containing arrays of voids intermeshed with wood fibers resists these high loads. Deformation is governed by compressive and tensile stresses which are greatest at 45 degrees to the cross section. It proceeds by stretching, sliding, and bending of the wood fibers which are coupled with the pore collapse, resulting in delayed failure and a high torsional toughness.

Pore characteristics analysis and numerical seepage simulation of antifreeze permeable concrete

The study of pore structure and seepage flow characteristics can help to reveal the structural and functional performance of permeable concrete from the macroscopic pores. This research aims to investigate the pore structure features and seepage characteristics of fiber-reinforced permeable concrete called antifreeze permeable concrete (AFPC) based on the images obtained by computer tomography (CT) and computed fluid dynamics method (CFD). The results show that the CT scanning and digital image processing technology is an efficient way to analyze the 2D and 3D pore structure of AFPC. 2D planar porosity and 3D connected porosity can generally represent the actual total porosity and connected porosity, respectively. The distribution of 2D Feret diameter and 3D equivalent diameter is in accordance with the normal distribution. The pore structure of AFPC shows fractal features of self-similarity and scale invariance. The fractal dimension shows a linear relationship with 2D planar porosity. CFD method can be applied on the generated 3D connected pore models to reveal the distribution of pressure and velocity in the pores of AFPC during seepage process. The relationship between seepage velocity and pressure gradient is described by Darcy’s law and Forchheimer’s law and the critical Reynolds numbers for AFPC with different pore structure are obtained.