Relative Density Of Foam Research Articles

Compressive and shear strengths of the ductile closed-cell Kelvin and Weaire-Phelan foams along the lattice direction [100

The compressive and shear responses of the closed-cell Kelvin and Weaire-Phelan foams along the lattice direction [100] were studied using explicit dynamic analyses in this work. Expressions describing the relationship of compressive and shear strengths to relative density were developed for these two foams. The compressive and shear strengths of the Kelvin and Weaire-Phelan foams are found to increase quadratically with relative density at low relative densities and linearly at high relative densities. This is because elastic buckling followed by material yielding cause the failure of low relative density foams, while large deformation and material yielding is the main cause of failure for high relative density foams. Cell wall buckling and local material yielding only cause reduction in global stiffness. Ductile foams fail globally when a certain amount of material has yielded, forming a plastic band across the foams. Shear buckling occurs in foams with very low relative density under shear.

Aluminum foam sandwich with density-graded open-cell core: Compressive and flexural response

We created a density-graded, open-cell, aluminum foam core sandwich (AFS) by joining, alternately arranged Al sheets and three different relative density (ρ* = 7%, 29%, and, 42%) foams using a zinc filler. A defect free, lamellar, α + η microstructure was observed in the foam/facesheet joint interface. Vickers microhardness and nanoindentation of the joint revealed higher hardness in the Zn filler compared to foam struts and sheets. The density-graded AFS showed a staggered compressive stress-strain response and its energy absorption increased by up to 607% compared to as-received (7% ρ*) foam core AFS. Three-point bend testing of the density-graded AFS showed indentation, foam strut bending, core shear and interface debonding as major failure mechanisms. Our results show that density-grading of foam core by introducing different relative density foam layers is a viable method to tailor the mechanical response of AFS.

A novel route to produce structural polymer foams with a controlled solid skin-porous core structure based on gas diffusion mechanisms

A comprehensive study about a new production route of structural polymer foams is presented. This methodology is based on the one hand on a free foaming process induced by a chemical blowing agent inside a closed mold, and on the other hand on the use of a solid polymer able to absorb gas in close contact with the molten foamed polymer, establishing a competitive absorption of the blowing gas between both materials. This competitive absorption of the gas promotes the formation of a solid skin in all the areas in contact with the solid polymer. This phenomenon has been identified in-situ and evaluated in real time using a specific X-ray radioscopy set-up, being possible to relate unequivocally the apparition and thickness of the solid skin with the presence of the solid polymer and with the pressure achieved in the closed mould during the foaming process. The presented production route shows an accurate and independent control of the final foam relative density (even below 0.5) and the thickness of the solid skin, together with an excellent surface quality and a broad applicability, which allows the design and production of structural polymer foams with exceptional features.

Process comparison on the microstructure and mechanical properties of fiber-reinforced polyphenylene sulfide using MuCell technology

The MuCell process is a special injection molding process which utilizes supercritical gas (nitrogen) to create integral foam sandwiches. The advantages are lower weight, higher specific properties and shorter cycle times. In this study, a series of glass fiber-reinforced polyphenylene sulfide foam blanks are manufactured using the MuCell injection molding process. The different variations of the process (low-pressure also known as structural foam injection molding) and high-pressure foam injection molding (also known as “core back expansion,” “breathing mold,” “precision opening,” decompression molding) are used. The sandwich structure and mechanical properties (tensile strength, bending strength, and impact behavior) of the microcellular and glass fiber-reinforced polyphenylene sulfide foams are systematically investigated and compared to compact material. The results showed that the injection parameters (injection speed, foaming mechanism) played an important role in the relative density of microcellular polyphenylene sulfide foams and the mechanical properties. It could be shown that the specific tensile strength decreased while increasing the degree of foaming which can be explained by the increased number of cells and the resulting cell size. This leads to stress peaks which lower the mechanical properties. The Charpy impact strength shows a significant dependence on the fiber orientation. The specific bending modulus of the high-pressure foaming process, however, surpasses the values of the other two processes showing the potential of this manufacturing variation especially with regard to bending loads. Furthermore, a high dependence of the mechanical properties on the fiber orientation of the tested specimens can be found.

Prediction of the Stress–Strain Behavior of Open-Cell Aluminum Foam under Compressive Loading and the Effects of Various RVE Boundary Conditions

The prediction of the mechanical behavior of metallic foams with realistic microstructure and the effects of various boundary conditions on the mechanical behavior is an important and challenging issue in modeling representative volume elements (RVEs). A numerical investigation is conducted to determine the effects of various boundary conditions and cell wall cross sections on the compressive mechanical properties of aluminum foam, including the stiffness, plateau stress and onset strain of densification. The open-cell AA6101-T6 aluminum foam Duocel is used in the analyses in this study. Geometrical characteristics including the cell size, foam relative density, and cross-sectional shape and thickness of the cell walls are extracted from images of the foam. Then, the obtained foam microstructure is analyzed as a 2D model. The ligaments are modeled as shear deformable beams with elastic-plastic material behavior. To prevent interpenetration of the nodes and walls inside the cells with large deformations, self-contact-type frictionless interaction is stipulated between the internal surfaces. Sensitivity analyses are performed using several boundary conditions and cells wall cross-sectional shapes. The predicted results from the finite element analyses are compared with the experimental results. Finally, the most appropriate boundary conditions, leading to more consistent results with the experimental data, are introduced.

Compressive behavior of a rolled open-cell aluminum foam

In this paper, we investigate compressive behavior of an open-cell 6101 aluminum foam in as-cast and as-rolled conditions. The as-cast foam with a relative density of ρ* = 7% was rolled to create two distinct as-rolled conditions with relative densities of ρ* = 29% and ρ* = 42%, respectively. The quasi-static and high strain rate compressive behavior was studied over a range of strain rates 10−4 /s ≤ ε̇ ≤ 5 × 103/s. It was found that the internal structure of as-rolled foams significantly differs from as-cast foams. Rolling causes plastic bending, stretching, and buckling of individual struts and ligaments, resulting in reduced pore size and an increase in relative density. In as-rolled condition, compressive plateau strength increased with increase in ρ*; it was up to 26 times higher as compared to the as-cast condition. In the range of strain rates considered here, strain rate sensitive compressive behavior was not observed; instead, the intrinsic strain rate sensitivity of parent material governed the compressive behavior in all conditions. Our results demonstrate the feasibility of using conventional rolling as a simple way to modify internal structure and relative density of as-cast foams, thereby enabling mechanical properties more attractive for various structural applications.

Nanomechanics and Testing of Core-Shell Composite Ligaments for High Strength, Light Weight Foams

ABSTRACT Composite nanostructured foams consisting of a metallic shell deposited on a polymeric core were formed by plating copper via electroless deposition on electrospun polycaprolactone (PCL) fiber mats. The final structure consisted of 1000-nm scale PCL fibers coated with 100s of nm of copper, leading to final core-shell thicknesses on the order of 1000-3000 nm. The resulting open cell, core-shell foams had relative densities between 4 and 15 %. By controlling the composition of the adjuncts in the plating bath, particularly the composition of formaldehyde, the relative thickness of copper coating as the fiber diameter could be controlled. As-spun PCL mats had a nominal compressive modulus on the order of 0.1 MPa; adding a uniform metallic shell increased the modulus up to 2 MPa for sub-10 % relative density foams. A computational materials science analysis using density functional theory was used to explore the effects pre-treatment with Pd may have on the density of nuclei formed during electroless plating.

Preparation and characterization of paraffin/nickel foam composites as neutron-shielding materials

Traditional neutron-shielding materials usually have poor mechanical properties and secondary gamma-shielding capability. The new requirements of modern neutron-shielding materials are difficult to satisfy. A paraffin/nickel foam neutron-shielding composite was prepared and characterized in this study. Open-cell nickel foams were fabricated through electrodeposition. Subsequently, the paraffin/nickel foam composite were prepared by filling the open-cell nickel foams with melted paraffin. The intrinsic parameters of nickel foam and the content of neutron absorber (boron carbide) were controlled to optimize the composite. The mechanical properties of the composite were studied through a static compression test. The compressive strength improved to 0.4 times that of the nickel foams. The Am–Be source transmittance experiment showed that the 8 cm thick PFM presented a neutron transmittance of 56.1%, and the 6 cm thick boron carbide/paraffin/nickel foam (PFM-B) presented a neutron transmittance of 37.6%. The paraffin/nickel foam and PFM-B had approximately the same shielding efficiency as paraffin and boron carbide/paraffin, respectively. However, the second gamma ray shielding efficiency of the paraffin/nickel foam and PFM-B was significantly higher than that of paraffin and boron carbide/paraffin. The mechanical properties and secondary gamma ray-shielding capability of the composite can be improved by increasing the relative density of nickel foams.

Development of Aluminium Foam through the Sintering Dissolution Process from the Alloy AA 3104

The increasing demand for lightweight materials capable to absorb impact energy has driven the growth of scientific research in the metallic foams field. This paper aims to investigate the possibility to obtain Al foams from recycled aluminium alloy through the sintering dissolution process (SDP) with sodium chloride (NaCl) as space holder. Aluminium scraps from AA 3104 alloy were powdered by high energy ball milling. Alloy powder was mixed with variable weight fraction of NaCl. The mixtures were die-pressed at room temperature and then sintered at 680°C. In the following step sintered parts were immersed in boiling water to obtain the aluminium foam. Foam microstructure was characterized by scanning electron microscopy and chemical composition was analyzed by energy dispersive spectroscopy. In addition, the residual NaCl was quantified and the foam density was determined by hydrostatic method. Best result was obtained with 60 wt% of NaCl, given a relative foam density of 30%, which in turn justifies further studies with metallic foams from aluminium scraps.

Effect of relative density on the dynamic compressive behavior of carbon nanotube reinforced aluminum foam

Closed-cell aluminum foams represent a unique class of solid cellular light metals that are made by deliberately introducing voids or pores during fabrication. This lightweight material is able to undergo large deformation at a nearly constant stress known as Plateau Stress because of which aluminum foams are good energy absorbers under dynamic loads such as an impact. In this investigation, carbon nanotubes (CNT) reinforced closed-cell aluminum foams were fabricated using the liquid metallurgy route through the dissociation of a foaming agent within the liquid metal. Four different relative densities of CNT reinforced Al-foam were used: 0.16, 0.20, 0.26 and 0.30, to study the effect of strain rate on the mechanical properties. The compressive mechanical behavior of CNT reinforced Al-foam has been studied under quasi-static and dynamic loading conditions. The high strain rate compressive response was investigated using a Split Hopkinson Pressure Bar (SHPB) over a range of strain rates up to 2750s−1. Mechanical properties such as peak stress, plateau stress and energy absorption increased with the increase in relative density; however, the densification strain decreased with the increase in relative density. Dynamic compressive properties improved as the strain rate increased indicating that this material is strain rate dependent. Among all the foams, the 0.30 relative density exhibited the highest mechanical properties whereas the 0.20 relative density foam displayed the highest strain rate sensitivity.

Theoretical analysis of thermal shock resistance of ceramic foam coatings

Ceramic foams have a high resistance to corrosion and wear. They also have a good thermal insulation performance because of their high melting point and low thermal conductivity. The thermal shock resistance of a ceramic foam coating with an edge crack under a sudden temperature variation is investigated. The dynamic thermal stress fields in the ceramic foam coating are obtained. Using the superposition principle, the crack problem of the ceramic foam coating is reduced to the solution of a set of singular integral equations. Propagation of the edge crack is analyzed. Effects of the relative density and thermal properties of the ceramic foam and of crack length on the thermal shock resistance are identified. The results obtained can be useful in designing thermal protective ceramic materials for thermal barrier coatings.

Compressive properties and energy absorption characteristics of open-cell nickel foams

Open-cell nickel foams with different relative densities and pre-stretching degrees were subjected to room temperature quasi-static compressive tests to explore their compressive properties. The compressive properties of the nickel foams including yield strength, elastic modulus, energy absorption density and energy absorption efficiency were calculated accurately. The results show that the compressive properties of yield strength, elastic modulus and energy absorption density increase with the increase of relative density of nickel foams. The compressive properties are sensitive to the pre-stretching degree, and the values of yield strength, elastic modulus and energy absorption density decrease with the increase of pre-stretching degree. However, the energy absorption efficiency at the densification strain state exhibits the independence of relative density and pre-stretching degree. The value of energy absorption efficiency reaches its peak when the strain is at the end of the collapse plateau region.

Effect of Porosity on Structure, Young's Modulus, and Thermal Conductivity of SiC Foams by Direct Foaming and Gelcasting

The study demonstrates the aqueous processing of solid‐state‐sintered SiC foams by gelcasting technique. Aside from increasing strength of green bodies, gelcasting monomers were the source of carbon additive which helped in sintering of SiC foams. Sintered foams with the relative density (RD) between 0.44 and 0.11 were processed by direct foaming of SiC slurries followed by gelcasting and sintering. Structural analysis by X‐ray tomography showed the presence of spherical pores with bimodal pore size distribution and the proportion of large size cell and their interconnectivity increased in low RD foams. SEM study revealed that decreased RD resulted in gradual changes in the strut microstructure from the grains with faceted interface to smooth interfaced grains. The analysis of changes in Young's modulus and thermal conductivity with RD were in agreement with the Ashby model for open cell foams.

Energy absorption efficiency of open-cell pure aluminum foams

For their application as crash absorber the specific energy absorption efficiency of metal foams is of particular interest. Current literature offers limited information about the relation between the relative density of open-cell foams and their specific energy absorption efficiency. With the aid of own measurements and literature data this relation was derived. According to the developed correlation a relative density of less than 3% can be suggested for a high specific energy absorption efficiency of open-cell ductile foams. To achieve an efficiency of at least 50% a relative density of 50–60% is suggested.

Semi-rigid foams of calcium silicate (CaSiO3) embedded in natural rubber latex

Semi-rigid foams were prepared by NR latex with 0, 2, 5, 10, 20 and 30 phr CaSiO3 added in a sulphur-curing system. The main composition of eggshell is made of 96.23%wt of CaCO3 and 3.77%wt of other oxide compounds. The CaSiO3 induced a spontaneous polarisation and reinforced the NR matrix due to ionic charge contents of Ca2+, Si4+ and O2− in its structure. Furthermore, the CaSiO3 was found to enhance the mechanical, thermal and physical properties of the composite foams. The suitable condition to prepare the semi-rigid composite foams was by adding 30 phr CaSiO3 in the NR latex with the sulphur-curing system. The obtained bulk density, the relative composite foam density, the compressive strength, the contact angle with water, and acetone at the water to acetone ratio of 1:1 were found to be 1.2230 g cm−3, 0.3611, 588.10 kPa, 103.3°, 26.5° and 85.3°, respectively.

Cellulose nanofibril foams: Links between ice-templating conditions, microstructures and mechanical properties

This study aimed at investigating how ice templating conditions affected the shrinkage, the microstructure, and the mechanical properties of cellulose nanofibril (NFC) foams. Enzymatic and TEMPO-oxidized NFC foams were fabricated using two solidification techniques, i.e., quenching NFC suspensions in temperature-controlled baths, and mechanical stirring of NFC suspensions during solidification followed by quenching, prior to freeze-drying. Foams prepared by direct quenching using stabilized TEMPO-oxidized NFC suspensions exhibited higher specific mechanical properties and more regular anisotropic cells with unimodal size than enzymatic NFC foams. In addition, NFC concentration and NFC morphology severely affected the foam shrinkage and the geometry of foam cells. Controlling the solidification had also a drastic effect on the foam microstructure, e.g. foams prepared by mechanical stirring and quenching exhibited bimodal cell size and enhanced mechanical properties. The compressive behavior of foams showed successive elastic, strain-hardening and densification regimes with auxetic effects and strain localization. Both the elastic modulus and the yield stress were power-law functions of the foam relative density whose exponents reached unusual high values for enzymatic NFC foams, potentially because of their chaotic microstructures. The evolution of a typical TEMPO-oxidized NFC foam was studied under compression using X-ray microtomography, unveiling deformation mechanisms at the cell scale.

Compressive properties of green rubber foam from reclaimed rubber glove

Nowadays, green materials are of interest due to the changes of government policies in many countries towards sustainable product development. In this study, green rubber foam from reclaimed rubber glove at various sodium bicarbonate content (4, 6, 8, 10 and 12 phr) as blowing agent was prepared via melt compounding technique and expanded via two-step heat transfer foaming process. Compression testing and water absorption were performed and the results were then supported with morphological analysis. The crosslink densities determined using Flory-Rhener equation indicated the value had slightly decreased with increasing blowing agent. The 4 phr sodium bicarbonate generated the smallest cells and the highest relative density foam of 0.9. The foam exhibited the lowest water absorption rate of 1.7 × 10 g/min as well as the highest compressive strength of 105 kPa. Increasing blowing agent evidently increased the cell size and decrease the compressive strength of the foam.

EFFECT OF RELATIVE DENSITY AND VELOCITY TOWARDS DYNAMIC RESPONSE OF METAL FOAM

Dynamic response of ALPORAS aluminium foam has been investigated experimentally and numerically. The dynamic response is quantified by the force produced as the foam deforms as a function of time. Quasi-static tests are conducted to determine the quasi-static properties of the foam. In the impact test, the aluminium foams are fired towards a rigid load-cell and the force signals developed are recorded. Experimental dynamic stress is also compared with theoretical prediction using existing theory. Finite element model is constructed using LS-DYNA to simulate the impact test. Results from the experiment, finite element analysis and theoretical prediction are in acceptable agreement. Finally, parametric studies have been conducted using the verified model to investigate the effect of impact velocity and relative density towards the dynamic response of the foam projectile. It is found that the dynamic response of the foam is more sensitive towards impact velocity as compare with the foam relative density.

Embedded Eggshells as a Bio-Filler in Natural Rubber for Thermal Insulation Composite Foams

Thermal insulation composite foams were prepared from the natural rubber as a matrix phase and an eggshell powder as a calcium carbonate dispersed phase, using chlorinated polyethylene acting as a flame retardant and curing agent at the vulcanization temperature 150°C in a two-roll mill. The main composition of eggshell is calcium carbonate which is more than 96.35 wt%. The obtained composite rubber foams with 50 phr eggshell added possessed the thermal conductivity, compression set, crosslink density, bulk density, and relative foam density values equal to 0.070 W/m.K, 45.0%, 6.95 × 10−5mol/cm3, 0.58, and 0.63, respectively. The obtained composite rubber foams were of good thermal resistance, good compression set, short curing time, good crosslink density, and light weight, suitable for various applications such as automobiles, storage tank, and transport packaging. Furthermore, the scanning electron micrographs, X-ray diffraction patterns, specific heat, and physical properties (bulk density, crosslink density, and relative foam density) were taken or measured to investigate the microstructures, phase compositions, thermal properties, and characteristics of the insulating composite foams and were reported here.

Microstructural and mechanical properties of Al–SiO2 nanocomposite foams produced by an ultrasonic technique

In this study, nanocomposite foams reinforced with different weight percentages of silicon dioxide nanoparticles (0.25, 0.5, 0.75 and 1.0wt%) were fabricated using the ultrasonic and stir casting techniques. For this purpose heat treated TiH2 was used as foaming agent. Microstructural studies were done by optical microscope and scanning electron microscope. Hardness evaluation of precursor nanocomposites showed that the hardness was significantly increased by the addition of SiO2 nanoparticles and Al–0.75wt% SiO2 nanocomposite makes the highest hardness. Evaluation of compressive behavior of Al–SiO2 nanocomposite foams showed that the plateau stress increases more than 3 times as the foam relative density increases from 0.09 to 0.16. Energy absorption of Al–SiO2 nanocomposite foams has been found to be dependent on both relative density and structural properties.