Materials

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15 pages, 11369 KiB

Open AccessArticle

Study on Concave Direction Impact Performance of Similar Concave Hexagon Honeycomb Structure

by Guanxiao Zhao, Tao Fu and Jiaxing Li

Materials 2023, 16(8), 3262; https://doi.org/10.3390/ma16083262 - 21 Apr 2023

Cited by 5 | Viewed by 1726

Based on the traditional concave hexagonal honeycomb structure, three kinds of concave hexagonal honeycomb structures were compared. The relative densities of traditional concave hexagonal honeycomb structures and three other classes of concave hexagonal honeycomb structures were derived using the geometric structure. The impact [...] Read more.

Based on the traditional concave hexagonal honeycomb structure, three kinds of concave hexagonal honeycomb structures were compared. The relative densities of traditional concave hexagonal honeycomb structures and three other classes of concave hexagonal honeycomb structures were derived using the geometric structure. The impact critical velocity of the structures was derived by using the 1-D impact theory. The in-plane impact characteristics and deformation modes of three kinds of similar concave hexagonal honeycomb structures in the concave direction at low, medium, and high velocity were analyzed using the finite element software ABAQUS. The results showed that the honeycomb structure of the cells of the three types undergoes two stages: concave hexagons and parallel quadrilaterals, at low velocity. For this reason, there are two stress platforms in the process of strain. With the increase in the velocity, the joints and middle of some cells form a glue-linked structure due to inertia. No excessive parallelogram structure appears, resulting in the blurring or even disappearance of the second stress platform. Finally, effects of different structural parameters on the plateau stress and energy absorption of structures similar to concave hexagons were obtained during low impact. The results provide a powerful reference for the negative Poisson’s ratio honeycomb structure under multi-directional impact. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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12 pages, 14712 KiB

Open AccessArticle

The Effect of Particle Necks on the Mechanical Properties of Aerogels

by Lorenz Ratke, Ameya Rege and Shivangi Aney

Materials 2023, 16(1), 230; https://doi.org/10.3390/ma16010230 - 27 Dec 2022

Cited by 3 | Viewed by 1657

Abstract

Mechanical properties of open-porous materials are often described by constructing a cellular network with beams of constant cross sections as the struts of the cells. Such models have been applied to describe, for example, thermal and mechanical properties of aerogels. However, in many [...] Read more.

Mechanical properties of open-porous materials are often described by constructing a cellular network with beams of constant cross sections as the struts of the cells. Such models have been applied to describe, for example, thermal and mechanical properties of aerogels. However, in many aerogels, the pore walls or the skeletal network is better described as a pearl-necklace, in which the particles making up the network appear as a string of pearls. In this paper, we investigate the effect of neck sizes on the mechanical properties of such pore walls. We present an analytical and a numerical solution by modeling these walls as corrugated beams and study the subsequent deviations from the classical scaling theory. Additionally, a full numerical model of such pearl-necklace-like walls with concave necks of varying sizes are simulated. The results of the numerical model are shown to be in good agreement with those resulting from the computational one. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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16 pages, 20175 KiB

Open AccessArticle

Microstructure-Based Computational Analysis of Deformation Stages of Rock-like Sandy-Cement Samples in Uniaxial Compression

by Mikhail O. Eremin, Valentina A. Zimina, Aleksey S. Kulkov and Yurii P. Stefanov

Materials 2023, 16(1), 24; https://doi.org/10.3390/ma16010024 - 21 Dec 2022

Cited by 4 | Viewed by 1227

Abstract

This work presents a new finite-difference continuum damage mechanics approach for assessment of threshold stresses based on the mechanical response of a representative volume element of a sandy-cement rock-like material. An original experimental study allows validating the mathematical model. A new modification of [...] Read more.

This work presents a new finite-difference continuum damage mechanics approach for assessment of threshold stresses based on the mechanical response of a representative volume element of a sandy-cement rock-like material. An original experimental study allows validating the mathematical model. A new modification of the damage accumulation kinetic equation is proposed. Several approaches based on acoustic emission, instantaneous Poisson’s ratio and reversal point method are employed to determine the threshold stresses. Relying on the numerical modeling of deformation and failure of model samples, the threshold stresses and the deformation stages are determined. The model predicts the crack initiation stress threshold with less than 10% error. The model prediction of the crack damage stress threshold corresponds to the upper boundary of the experimental range. The model predicts the peak stress threshold with less than 0.2% error in comparison with the average experimental peak stress. The results of numerical modeling are shown to correlate well with the available experimental and literature data and sufficiently complement them. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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24 pages, 10568 KiB

Open AccessArticle

Gas Permeability Evolution of Coal with Inclusions under Triaxial Compression-Lab Testing and Numerical Simulations

by Yufeng Zhao, Heinz Konietzky, Thomas Frühwirt and H.W. Zhou

Materials 2022, 15(23), 8567; https://doi.org/10.3390/ma15238567 - 1 Dec 2022

Cited by 2 | Viewed by 1294

Abstract

Coalbed methane (CBM) exploitation leads to permanent stress redistributions in the coal bodies connected with fracturing processes and permeability changes due to deformation induced internal pore-fracture networks. Gas permeability evolution of coal samples is investigated with a newly developed three-dimensional fluid-mechanical coupled experimental [...] Read more.

Coalbed methane (CBM) exploitation leads to permanent stress redistributions in the coal bodies connected with fracturing processes and permeability changes due to deformation induced internal pore-fracture networks. Gas permeability evolution of coal samples is investigated with a newly developed three-dimensional fluid-mechanical coupled experimental system. X-ray CT is used to investigate the internal structure of the coal samples and delivers the basis to set-up numerical twins. The work focuses on coal samples with inclusions. A novel coupling procedure between two different tools—discontinuum and continuum codes—is established to simulate the permeability evolution. The permeability is related to the crack pattern in general, and crack width in particular. A prediction of permeability is proposed based on fracture distribution and microcrack behavior. The experimental studies validated the coupling approach. Shear fractures cause substantial permeability enhancement. Piecewise relations between permeability and volumetric strain can be used to fit the whole process, where a nonlinear exponential relation is established after the expansion point. The inclusions as important structural characteristics influence this relation significantly. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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17 pages, 3232 KiB

Open AccessArticle

Biocarbons Obtained from Fennel and Caraway Fruits as Adsorbents of Methyl Red Sodium Salt from Water System

by Aleksandra Bazan-Wozniak, Dorota Paluch, Robert Wolski, Judyta Cielecka-Piontek, Agnieszka Nosal-Wiercińska and Robert Pietrzak

Materials 2022, 15(22), 8177; https://doi.org/10.3390/ma15228177 - 17 Nov 2022

Cited by 4 | Viewed by 1640

Abstract

The aim of this study was to prepare biocarbons by biomass activation with carbon(IV) oxide. Fennel and caraway fruits were used as the precursors of bioadsorbents. The impact of the precursor type and temperature of activation on the physicochemical properties of the obtained [...] Read more.

The aim of this study was to prepare biocarbons by biomass activation with carbon(IV) oxide. Fennel and caraway fruits were used as the precursors of bioadsorbents. The impact of the precursor type and temperature of activation on the physicochemical properties of the obtained biocarbons and their interaction with methyl red sodium salt upon adsorption process have been checked. The obtained bioadsorbents were characterized by determination of-low temperature nitrogen adsorption/desorption, elemental analysis, ash content, Boehm titration, and pH of water extracts. The biocarbons have surface area varying from 233–371 m²/g and basic in nature with acidic/basic oxygen-containing functional groups (3.23–5.08 mmol/g). The adsorption capacity varied from 63 to 141 mg/g. The influence of different parameters, such as the effectiveness of methyl red sodium salt adsorption, was evaluated. The adsorption kinetics was well fitted using a pseudo-second-order model. The Freundlich model best represented the equilibrium data. The amount of adsorbed dye was also found to increase with the increasing temperature of the process. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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10 pages, 3795 KiB

Open AccessEditor’s ChoiceArticle

Effects of the Parent Alloy Microstructure on the Thermal Stability of Nanoporous Au

by Andrea Pinna, Giorgio Pia, Roberta Licheri and Luca Pilia

Materials 2022, 15(19), 6621; https://doi.org/10.3390/ma15196621 - 23 Sep 2022

Cited by 2 | Viewed by 1274

Abstract

Nanoporous (NP) metals represent a unique class of materials with promising properties for a wide set of applications in advanced technology, from catalysis and sensing to lightweight structural materials. However, they typically suffer from low thermal stability, which results in a coarsening behavior [...] Read more.

Nanoporous (NP) metals represent a unique class of materials with promising properties for a wide set of applications in advanced technology, from catalysis and sensing to lightweight structural materials. However, they typically suffer from low thermal stability, which results in a coarsening behavior not yet fully understood. In this work, we focused precisely on the coarsening process undergone by NP Au, starting from the analysis of data available in the literature and addressing specific issues with suitably designed experiments. We observe that annealing more easily induces densification in systems with short characteristic lengths. The NP Au structures obtained by dealloying of mechanically alloyed AuAg precursors exhibit lower thermal stability than several NP Au samples discussed in the literature. Similarly, NP Au samples prepared by annealing the precursor alloy before dealloying display enhanced resistance to coarsening. We suggest that the microstructure of the precursor alloy, and, in particular, the grain size of the metal phases, can significantly affect the thermal stability of the NP metal. Specifically, the smaller the grain size of the parent alloy, the lower the thermal stability. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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7 pages, 1991 KiB

Open AccessEditor’s ChoiceCommunication

Estimation of Nanoporous Au Young’s Modulus from Serial Block Face-SEM 3D-Characterisation

by Michele Brun, Elisa Sogne, Andrea Falqui, Federico Scaglione, Paola Rizzi, Francesco Delogu and Giorgio Pia

Materials 2022, 15(10), 3644; https://doi.org/10.3390/ma15103644 - 19 May 2022

Viewed by 1675

Abstract

Nanoporous Au has been subjected to serial block face-scanning electron microscopy (SBF-SEM) 3D-characterisation. Corresponding sections have been digitalized and used to evaluate the associated mechanical properties. Our investigation demonstrates that the sample is homogeneous and isotropic. The effective Young’s modulus estimated by an [...] Read more.

Nanoporous Au has been subjected to serial block face-scanning electron microscopy (SBF-SEM) 3D-characterisation. Corresponding sections have been digitalized and used to evaluate the associated mechanical properties. Our investigation demonstrates that the sample is homogeneous and isotropic. The effective Young’s modulus estimated by an analytical multiscale approach agrees remarkably well with the values stated in the literature. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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8 pages, 1400 KiB

Open AccessCommunication

Hardening of Nanoporous Au Induced by Exposure to Different Gaseous Environments

by Giorgio Pia, Elisa Sogne, Andrea Falqui and Francesco Delogu

Materials 2022, 15(8), 2718; https://doi.org/10.3390/ma15082718 - 7 Apr 2022

Viewed by 1424

Abstract

This work focuses on the mechanical behaviour of nanoporous Au samples alternately exposed to ozone and carbon dioxide. Nanoporous Au was fabricated by freely corroding the Ag₇₀Au₃₀ parent alloys prepared by mechanical alloying in the form of powder and subsequently [...] Read more.

This work focuses on the mechanical behaviour of nanoporous Au samples alternately exposed to ozone and carbon dioxide. Nanoporous Au was fabricated by freely corroding the Ag₇₀Au₃₀ parent alloys prepared by mechanical alloying in the form of powder and subsequently compacted by cold pressing. Dealloying was performed in acidic solution, and conditions were suitably adjusted to obtain fine nanoporous Au structures with ligaments about 15 nm thick. Nanoporous Au samples with increasingly thicker ligaments, up to about 40 nm, were fabricated by annealing the pristine nanoporous Au structure for different time intervals at 473 K. For all of the samples, the cyclic variation of gaseous atmosphere results in a macroscopic strain variation due to the occurrence of surface oxidation and reduction processes. We show that the reiterated cyclic exposure to the different gases also induces the progressive hardening of nanoporous Au, which can be ascribed to irreversible strain contributions. For nanoporous Au samples with ligaments that are 15 nm thick, after 50 exposure cycles, the yield strength increases approximately from 49 MPa to 57 MPa. A systematic investigation on coarser nanoporous Au structures indicates that, with the same exposure cycles, the degree of hardening decreases with the ligament thickness. Full article

(This article belongs to the Special Issue Recent Advances in the Mechanical Properties and Microstructural Features of Porous Materials)

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