Search results

The samples of nickel foam with porosity of about 88 percent were uniaxially tensioned at room temperature, and the phenomena of tensile fracture were compared with that from the fully dense plate of metal nickel. The purpose of this paper is to investigate the differences between their behaviors of tensile fracture.

The tensile test was carried out by using the tester of CMT-series microcomputer-controlled electronic universal testing machine. The difference of tensile fracture behavior between the nickel foam and the dense metal nickel was discussed by analyzing the load-displacement curve and the microscopical fracture.

The results indicated that, nickel foam also displayed the feature of macroscopic plastic-deformation during tension, but it showed a macroscopic brittleness much more than that of the fully dense body. The axial apparent strain at the maximum load for the foamed sample was markedly less than that for the dense one. In addition, an obviously gradual course exhibited for the foamed body during tensile failure and a rapidly instant course for the dense body correspondingly.

There have been some studies on the tensile behavior for metal foams, but much less than on the compression, and the relevant works are mostly for aluminum foam. The present work provides the investigations on the difference of tensile fracture behavior between the nickel foam and the dense metal nickel, as well as that of the corresponding samples in various cases with different tensile velocities. It is found that the porosity can make a remarkable decrease of the apparent strain at the maximum load and a significant increase of the macroscopical brittleness for the metallic nickel under tension.

The purpose of this paper is to introduce different methods for measuring the porosity of metal foams, and especially present a new method for conveniently measuring the open porosity that has a stronger impact on a number of physical properties of the porous product.

Metal foam is a kind of material that utilizes the function of pores inside the porous body. For such materials, the porosity is an important factor or even a key factor to determine a number of the practical parameters, such as the conductivity, acoustic properties and mechanical performances. Especially, the open porosity has a stronger impact on the sound absorption, electromagnetic shielding, heat transfer of the porous product, as well as the performances of using the internal pore surface. Therefore, it would be meaningful to find the simple and convenient to well measure the open porosity of metal foams.

In the present new method, the open porosity can be obtained directly by different volume parameters of the porous sample, while it can only by some weight indexes of the porous sample in other measuring methods.

The characteristic of this new method makes the measurement simpler and more convenient in this new method than in the other methods.

Gives a bibliographical review of the finite element analyses of sandwich structures from the theoretical as well as practical points of view. Both isotropic and composite materials are considered. Topics include: material and mechanical properties of sandwich structures; vibration, dynamic response and impact problems; heat transfer and thermomechanical responses; contact problems; fracture mechanics, fatigue and damage; stability problems; special finite elements developed for the analysis of sandwich structures; analysis of sandwich beams, plates, panels and shells; specific applications in various fields of engineering; other topics. The analysis of cellular solids is also included. The bibliography at the end of this paper contains 655 references to papers, conference proceedings and theses/dissertations dealing with presented subjects that were published between 1980 and 2001.

The purpose of this paper is to prepare a new modified activated carbon fibers (ACFs) of high specific capacitance used for electrode material of supercapacitor.

In this study, the specific capacitance of ACF was significantly increased by using the phenolic resin microspheres and melamine as modifiers to prepare modified PAN-based activated carbon fibers (MACFs) via electrospinning, pre-oxidation and carbonization. The symmetrical supercapacitor (using MACF as electrode) and hybrid supercapacitor (using MACF and activated carbon as electrodes) were tested in term of electrochemical properties by cyclic voltammetry, AC impedance and cycle stability test.

It was found that the specific capacitance value of the modified fibers were increased to 167 Fg^-1 by adding modifiers (i.e. 20 wt.% microspheres and 15 wt.% melamine) compared to that of unmodified fibers (86.17 Fg^-1). Specific capacitance of modified electrode material had little degradation over 10,000 cycles. This result can be attributed to that the modifiers embedded into the fibers changed the original morphology and enhanced the specific surface area of the fibers.

The modified ACFs in our study had high specific surface area and significantly high specific capacitance, which can be applied as efficient and environmental absorbent, and advanced electrode material of supercapacitor.

With the nickel foam made by the technique of electrodeposition on polymer foam, the purpose of this paper is to investigate the influence of several deferent processes on the surface morphology and the specific surface area of this porous product.

The surface morphologies of the nickel foam were examined by SEM. The specific surface area of the porous product was measured by gas (N₂) permeability method and also calculated by the reported formula.

The nickel foam from sintering in NH₃ decomposition atmosphere at 850°C will achieve the same specific surface area as that at 980°C, whether this porous structure after electrodeposition comes through direct sintering in NH₃ decomposition atmosphere, or through burning in air at 600°C for 4 min beforehand then the same reductive sintering.

There have been some studies on the preparation and application of nickel foam, but few works focus on the processing influence on the specific surface of this porous product. The present work provides the investigations on the difference of the product made under different producing conditions, and the influence of several deferent processes on the specific surface area of the product.

Common Aero Vehicles (CAVs) are relatively small‐size, un‐powered, self‐maneuvering vehicles equipped with a variety of weapons and launched from space. One of the major obstacles hampering a full the realization of the CAV concept is a present lack of lightweight, high‐temperature insulation materials which can be used for construction of the CAV’s thermal protection system (TPS). A computational analysis is utilized in the present work to examine the suitability of a carbon‐based, coal‐derived foam for the TPS applications in the CAVs. Toward that end, a model is developed for the high‐temperature effective thermal conductivity of foam‐like materials. In addition, an insulation sizing procedure is devised to determine the minimum insulation thickness needed for thermal protection of the vehicle structure at different sections of a CAV. It is found that the carbon‐based foam material in question can be considered as a suitable TPS insulation material at the leeward side and at selected portions of the windward side of a CAV (specifically the portions which are further away from the vehicle nose).

The purpose of the study is to present a simplified model to replace the complicated foaming simulations for investigating the liquid polyurethane behavior just before solidification.

This model is inspired from the traveling heater method of crystallization because of the low injection velocity. Besides, the heat generated during the reaction is considered as a heat source function in the energy equation.

Various distributions of the heat generation function inside the geometry have been studied to choose the most realistic one. Effect of parameters such as the soil material and porosity on the temperature distribution and flow field are examined for different values of heat flux on the boundaries. Results show an almost linear dependency of pressure drop to the velocity, a uniform velocity profile and an expected temperature distribution compared to literature, which approves the suggested model.

A new model is presented in this study for foaming which replaces a heat generation function (exponential) in the source term of the energy equation instead of the heat produced at the exit boundary (the solid–liquid interface), and the traveling method is used instead of moving the geometry; besides, the growth ratio has been neglected; therefore, this model has been validated by a foaming simulation to confirm the suggested simplified idea.

The purpose of this paper is to provide a summarization and review of the present author's main investigations on failure modes of reticular metal foams under different loadings in engineering applications.

With the octahedral structure model proposed by the present authors themselves, the fundamentally mechanical relations have been systematically studied for reticular metal foams with open cells in their previous works. On this basis, such model theory is continually used to investigate the failure mode of this kind of porous materials under compression, bending, torsion and shearing, which are common loading forms in engineering applications.

The pore-strut of metal foams under different compressive loadings will fail in the tensile breaking mode when it is brittle. While it is ductile, it will tend to the shearing failure mode when the shearing strength is half or nearly half of the tensile strength for the corresponding dense material and to the tensile breaking mode when the shearing strength is higher than half of the tensile strength to a certain value. The failure modes of such porous materials under bending, torsional and shearing loads are also similarly related to their material species.

This paper presents a distinctive method to conveniently analyze and estimate the failure mode of metal foams under different loadings in engineering applications.

The purpose of this paper is mainly to know: (1) the sound absorption coefficient of porous composite structures constituted by a new kind of lightweight ceramic foam and perforated plate; (2) the availability of an equivalent porous material model, recently proposed by the present author, to these composite structures in sound absorption.

A kind of lightweight ceramic foam with bulk density of 0.38–0.56 g·cm-3 was produced by means of molding, drying and sintering. The effect of stainless steel perforated plate on sound absorption performance of the ceramic foam was investigated by means of JTZB absorption tester.

The results indicate that the sound absorption performance could be obviously changed by adding the stainless steel perforated plate in front of the porous samples and the air gap in back of the porous samples. Adding the perforated plate to the porous sample with a relatively large pore size, the sound absorption performance could be evidently improved for the composite structure. When the air gap is added to the composite structure, the first absorption peak shifts to the lower frequency, and the sound absorption coefficient could increase in the low frequency range.

Based on the equivalent porous material model and the “perforated plate with air gap” model, the sound absorption performance of the composite structures can be simulated conveniently to a great extent by using Johnson-Champoux-Allard model.

The purpose of this paper is to demonstrate a method for modeling of cellular structures by means of Voronoi tessellation and to conduct a validation by comparison with real metal foam structures.

Heat propagation behavior of open-pore metal foams is studied for both experimental as well as computer-modeled structures showing excellent agreement. The 3D open-pore structure of the real foam is reconstructed from 2D light microscope images in-depth.

An algorithm to create synthetic open-pore foam structures has been developed.

The algorithm for modeling synthetic open-pore cellular structures allows the random distribution of the individual pores close to reality.