Gradient Porous Materials Research Articles

The acoustic radiation analysis of SFGP conical shell

The shell of revolution made of sandwich functionally graded material (SFGM) has broad applications in engineering. Pores are inevitable in processing SFGM, making it complex for the vibro-acoustic characteristics of the structure. To analyze the acoustic radiation mechanism of sandwich functional gradient porous materials (SFGP) shells deeply, a theoretical model for vibro-acoustic coupling of SFGP shells based on a semi-analytical approach is proposed. The spectral boundary element approach is used to simulate the sound field while the energy method is utilized for representing the structural field. The substructure scheme is introduced, resulting in a uniform division of both the structural field and the sound field into several segments. Similarly, both the displacement and sound pressure are depicted in an identical manner, with the meridional direction expanded using the Legendre series and the circumferential direction expanded using the Fourier series. By introducing the virtual work done by the sound pressure, the structural and sound fields are coupled to form the vibro-acoustic coupling equation, which is solved using the strong coupling approach. The present method exhibits outstanding convergence and precision, showcasing a strong agreement in vibro-acoustic response results when compared to prior research. Since the conical shell is one of the most widely applicable shells of revolution, this paper takes the conical shell as the research object to study. Following the proposed methodology, we delve into the examination of the roles played by various circumferential wave number modes in influencing the vibro-acoustic response of SFGP conical shells. Building upon this groundwork, an investigation is conducted into the influence of factors such as material gradient index, porosity, and pore distribution on the vibro-acoustic characteristics of SFGP conical shells.

Two conjectures on 3D Voronoi structures: a toolkit with biomedical case studies.

3D Voronoi scaffolds are widely applied in the field of additive manufacturing as they are known for their light weight structural resilience and share many topological similarities to various natural (bone, tumours, lymph node) and synthetic environments (foam, functionally gradient porous materials). Unfortunately, the structural design features that promote these topological similarities (such as the number of vertices) are often unpredictable and require the trial and error of varying design features to achieve the desired 3D Voronoi structure. This article provides a toolkit, consisting of equations, based on over 12 000 3D Voronoi structures. These equations allow design features, such as the number of generating points (G), to be efficiently and accurately predicted based on the desired structural parameters (within ±3G). Based on these equations we are proposing, to the best of our knowledge, two new mathematical conjectures that relate the number of vertices or edges, and the average edge length to G in Voronoi structures. These equations have been validated for a wide range of parameter values and Voronoi network sizes. A design code is provided allowing any of over 12 000 structures to be selected, easily adjusted based on user requirements, and 3D printed. Biomedical case studies relevant to T-cell culturing, bone scaffolds and kidney tumours are presented to illustrate the design code.

Crafting and Analyzing Multi-Structured Aramid Materials and Their Pyrolytic Transformations: A Comprehensive Exploration.

Gradient porous materials, particularly carbon-based materials, hold immense potential in the fields of batteries, energy storage, electrocatalysis, and sensing, among others, by synergistically combining the attributes associated with each pore size within a unified structural framework. In this study, we developed a gradient porous aramid (GP-Aramid) by incorporating cellulose acetate as a porosity promoter in the polymer casting solution in different proportions. These GP-Aramids were subsequently transformed into their pyrolyzed counterparts (GP-Pyramids), retaining their original structures while displaying diverse cellular or dense microstructures inherited from the parent aramid, as confirmed via scanning electron microscopy. X-ray diffraction spectra provided evidence of the conversion of aramids into carbonaceous materials. The materials showed structural defects observed through the intensity ratio of the G and D bands (ID/IG = 1.05) in the Raman spectra, while X-ray photoelectron spectra (XPS) revealed that the carbonization process yielded pyrolyzed carbon materials unusually rich in nitrogen (6%), oxygen (20%), and carbon (72%), which is especially relevant for catalysis applications. The pyrolyzed materials showed bulk resistivities from 5.3 ± 0.3 to 34.2 ± 0.6 depending on the meta- or para-orientation of the aramid and the porous structure. This work contributes to understanding these gradient porous aromatic polyamides' broader significance and potential applications in various fields.

Fabrication of Max Phase-Based Gradient Porous Materials from Preceramic Paper

Fabrication of Max Phase-Based Gradient Porous Materials from Preceramic Paper

PLA toughening via bamboo-inspired 3D printed structural design

Bioinspired structures can attain mechanical properties unseen in conventional artificial materials. Specifically, the introduction of a cellular structure with a precisely designed distribution of cells, cell sizes, and cell walls is expected to enhance the mechanical response. Polylactic acid (PLA) is a biodegradable polymer produced from renewable resources with very interesting properties and good three-dimensional (3D) printing processability. However, its embrittlement during ageing at room temperature after a very short period of time (a few hours) significantly reduces its usability for advanced applications. Intense effort has been invested in improving its toughness via composition modification. However, this approach can worsen some other properties, make processing more difficult, and increase the carbon footprint. Therefore, fused deposition modelling (FDM) 3D printing was used to manufacture porous bamboo-inspired structures of unmodified PLA. The toughening of PLA solely by the pore gradient, which controlled the energy dissipation mechanism, was introduced for the first time. Improvement of the ductility and work at break was observed especially for notched specimens. Prevention of catastrophic failure could enable the use of gradient porous materials in structural components. The fundamental relationships and practical hints resulting from the work provide a foundation for the future design of toughened 3D printed structures.

A design method of Voronoi porous structures with graded relative elasticity distribution for functionally gradient porous materials

A design method of Voronoi porous structures with graded relative elasticity distribution for functionally gradient porous materials

On the behaviors of porous shape memory alloy beam with gradient porosity under pure bending

Abstract

Structural design and mechanical response of gradient porous Ti-6Al-4V fabricated by electron beam additive manufacturing

Gradient porous materials are gradually developed for some biomedical implants such as mandible and vertebrae to meet the varied Young's modulus due to serious bone density variation and thus to avoid serious stress shielding effect. In this study, different designs of gradient porous materials are fabricated by additive manufacturing 3D printing via the electron beam melting (EBM) method, and the mechanical properties are examined. The first attempt is to examine the size variation of porosity gradient region, with gradual transition region from 0 to 8 mm in height from the lower 70% porosity region to the higher 90% porosity region. The gradient transition has pronounced impact on the mechanical response improvement of porous EBM foams. The second attempt is to explore the effect of porosity variation and the interface discontinuity degree, or the degree of strut overlapping. The foam mechanical properties are governed mainly by the mechanical properties of the higher porosity portion and the mismatch on the interface; the latter degree of mismatch (or the degree of strut overlapping) plays a more dominant role. By re-designing to fulfill complete continuity with no mismatch of the struts on the interface, significant improvement of the mechanical properties can be achieved.

Numerical Investigation of Heat Transfer Enhancement Inside the Pipes Filled With Radial Pore-Size Gradient Porous Materials

The gradient porous materials (GPMs)-filled pipe structure has been proved to be effective in improving the heat transfer ability and reducing pressure drop of fluid. A GPMs-filled pipe structure in which radial pore-size gradient increased nonlinearly has been proposed. The field synergy theory and tradeoff analysis on the efficiency of integrated heat transfer has been accomplished based on performance evaluation criteria (PEC). It was found that the ability of heat transfer was enhanced considerably, based on the pipe structure, in which the pore-size of porous materials increased as a parabolic opening up. The flow resistance was the lowest and the integrated heat transfer performance was the highest when radial pore-size gradient increasing as a parabolic opening down.

Viscous second gradient porous materials for bones reconstructed with bio-resorbable grafts

It is well known that size effects play an important role in the mechanical behavior of bone tissues at different scales. In this paper we propose a second gradient model for accounting these effects in a visco-poro-elastic material and present some sample applications where bone is coupled with bioresorbable artificial materials of the kind used in reconstructing surgery.

Design and characterization of isothermal chambers filled with gradient-porous materials

Design and characterization of isothermal chambers filled with gradient-porous materials

Gradient-structural optimization of metal fiber porous materials for sound absorption

Metal fiber porous material with full inter-connected pore structure, is a kind of attractive sound-absorbing material sintered by powder metallurgy process. In order to improve the sound absorption performance, the stainless steel fibers with different diameters were used to fabricate porous sound-absorbing materials with gradient pore structures in this paper. Two or three layers of sintered fiber porous plats with different pore structures were superposed in a certain sequence and then sintered to gradient porous materials. The effects of gradient pore structure on the sound absorption performance were also investigated. The results show that the gradient porous structure can effectively improve the sound absorption performance, and the direction and quantity of the pore gradient interface also exhibit remarkable effects on the sound absorption performance. The sound waves repeatedly reflect in the porous media between the gradient interfaces, which contributes to sound absorption improvement.

Numerical configuration design and investigation of heat transfer enhancement in pipes filled with gradient porous materials

A novel design of a GPM-filled pipe structure was proposed to improve the heat transfer and reduce pressure drop of fluid flowing through the pipes filled with gradient porous materials. The pore-size gradient and porosity gradient were studied for both partially and fully filled configurations. The effects of GPMs on the fluid flow and heat transfer in the pipes were investigated and compared with the those under the conditions of non-porous materials and homogeneous porous materials (HPMs) serving as controls. Some typical GPM configurations were studied with Rp=0.6 and Rp=1.0, showing an enhanced heat transfer and a relatively low friction factor can be reached in comparison with the controls. An attempt was made to illustrate the mechanism of heat transfer enhancement with the field synergy theory. Velocity-based average pore-size was introduced to explain the reduction in friction factors in GPM configurations. A tradeoff analysis between pressure drop and heat transfer enhancement was made based on performance evaluation criteria (PEC).

Towards the Design of Metamaterials with Enhanced Damage Sensitivity: Second Gradient Porous Materials

Numerous computational and conceptual difficulties are often encountered when conceiving techniques which are effective in detecting damage intensity, localization, and onset. Actually, also when the semi-inverse or the material characterization problems (which are commonly formulated in this context) can be recognized to be well posed, the numerical and computational obstacles which need to be overcome can render useless the conceived methodology. In the present paper we propose to change the paradigm used up to now when addressing the problem of damage assessment in engineering materials. In fact, we propose to conceive a metamaterial the properties of which make more expedite and effective the detection of cracks onset and damage evolution via the study of reflection and transmission of waves. More particularly, porous materials with underlying heterogeneous micro-structure may magnify the effects of reflection and transmission of waves at damaged sites depending on the considered boundary conditions. Materials of this type would make easier the structural health monitoring via nondestructive evaluation of local damage and would permit to detect incipient structural failure in a more efficient way. By analyzing the characteristic patterns of the reflection and transmission properties of surfaces where damage is concentrated, we show that, in the considered metamaterials, slow incident waves can be used to detect the onset and evolution of first gradient macroscopic damage (δ e ), while fast incident waves can be used to reveal loss of contact at the microscopic level, i.e. to detect the onset of second gradient macroscopic damage (δ r ).

Gradient porous materials by emulsion centrifugation

Oil-in-water emulsions are centrifuged to generate a gradient distribution of emulsion droplets. This structure is locked by freezing or polymerization and the subsequent removal of the solvents produces gradient porous materials.

Deformation and fracture model for a multicomponent elastoplastic porous medium with continuous variation of physicomechanical characteristics

A mathematical model and a procedure of solving problems for the development of functionally gradient porous materials ensuring the desired distribution of stress-strain state parameters over the volume of the structure under explosion and impact loadings are proposed. The choice of the model is based on general theoretical concepts and is validated by comparison of the calculated results with experimental data.