Compressive Properties Of Foams Research Articles

Structure-tunable poly(butylene adipate-co-terephthalate) foams with enhanced mechanical performance derived by microcellular foaming with carbon dioxide as blowing agents

Poly(butylene adipate-co-terephthalate) (PBAT) is an advanced environment-friendly polymer that exhibits excellent biodegradability and outstanding mechanical properties. Microcellular foaming can endow PBAT with many admirable properties, which is significant for broadening its applications. Nevertheless, it is still challenging to prepare high-performance PBAT foams with tailored structures due to poor foaming ability. Moreover, the unclear relationships between foaming process, cellular structure, and mechanical properties significantly limit its development and application. In this study, microcellular foaming with carbon dioxide as blowing agents was developed to prepare structure-tunable PBAT foams with enhanced mechanical performance. Firstly, microcellular foaming experiments were conducted under various foaming pressures and temperatures to investigate the dependence of cellular morphology on foaming conditions. Under the investigated foaming conditions, the cell diameter and expansion ratio of PBAT foams can be manipulated in the ranges of 10–100 µm and 1–20, respectively. Furtherly, the dependence of tensile properties and compressive properties on cellular morphology was clarified. Compared with cell diameter, expansion ratio exhibited a much more significant effect on both the tensile and compressive properties of foams. In particular, PBAT foams with a tensile property of 5 MPa and a compressive property of 0.5 MPa were prepared, which possessed a lower density of 0.15 g/cm3. The prepared structure-tunable PBAT foams showed much lower density but obviously enhanced mechanical properties than the PBAT foams reported in literature.

Reactive sintering principle and compressive properties of porous AZ91 magnesium alloy foams produced by powder metallurgy approach

AbstractPorous magnesium alloy foams have gained tremendous interest from scientists because of their super lightweight, unique mechanical and physical properties. Despite numerous studies suggesting these advanced materials for structural and functional applications, their manufacturing processes remain poorly understood. In this paper, the porous Mg‐9 wt. %Al‐1 wt. % Zn alloy foam was prepared through the reactive sintering principle (i. e. the element metal powder reaction principle) by using the powder metallurgical method that is combined with a pore‐making agent. The chemical and phase compositions of the cell wall microstructure were investigated by X‐ray diffraction and scanning electron microscope equipped with energy dispersive spectrometer. The compressive properties of the foams were evaluated by quasi‐static compression testing. The results of the analysis reveal that low‐temperature sintering can produce qualitative magnesium alloy foams with good mechanical properties by taking advantage of the intermetallic/or intermediate compounds which are formed in the cell wall through metal elements powder diffusion and reaction. Particularly, the foam samples sintered at 380 °C for 12 h gave the best compressive properties owing to the alloy intermetallic contents and the relative density of the foams.

Synthesis and compressive behaviors of PMMA microporous foam with multi-layer cell structure

The polymeric microporous foams with multi-layer cell structure is prepared via the combination of multi-layer hot melt pressing and supercritical carbon dioxide(SCCO2) foaming method. The morphology and compression properties of such foams were detailed studied. The results show that nucleation and directional growth of the cells are promoted by the introduction of multi-layer interface into the polymer matrix. When the distance of the multi-layer interface is smaller than the critical nucleation size of the cell, the microcellular foams with uniform, continuously and directionally multi-layer cell structure can be prepared, and the unit cell shape is well controlled. In addition, the compressive properties of the foams with multi-layer cell structure are different in vertical and horizontal loading direction. The compression strength of the multi-layer foam is up to 20.27 MPa and 11.84 MPa in horizontal and vertical loading direction, respectively, which is much higher than that of the uniform foam.

The Compressive Properties of Open-Cell Zn-22Al Foams with Spheroidal Pore at Different Temperatures

Open-cell Zn-22Al foams with different porosities were fabricated by replication process using spheroidal CaCl2 particles as space holder. A series of compressive tests were carried out at different temperatures (i.e., room temperature, 100 °C and 200 °C). The effect of porosity and testing temperature on compressive property and energy absorption characteristic of Zn-22Al foams were studied. The experimental results showed that the compressive properties of the foams are dependent on porosity and testing temperature: the compressive yield stress decreases with the increasing testing temperature and the porosity; In addition, the energy absorption capacity also decreases with the increasing temperature and porosity; Moreover, Gibson-Ashby model can be used to describe the relationship between relative yield stress and relative density of the foams.

Production of high porosity Zn foams by powder metallurgy method

Open-cell Zn foams with 74–92% porosity were fabricated by space holder technique, including compacting spherical carbamide granules coated with Zn powders followed by leaching the space holder and sintering. The role of compaction and sintering parameters on pore structure, cell wall integrity and compressive properties of foams was investigated. The results show that compressive yield strength and modulus of elasticity decrease with porosity and a good compatibility with Gibson–Ashby model of cellular solids is discovered. The optimum structure and mechanical properties of Zn foams are achieved by compaction at 300 MPa and sintering for 2 h at 410°C.

A multilayer tissue engineered meniscus substitute

Various methods have been tried to treat the main meniscus problem, meniscal tears, for which we believe tissue engineering could be a viable solution. In this study, a three dimensional, collagen-based meniscus substitute was prepared by tissue engineering using human fibrochondrocytes and a collagen based-scaffold. This construct was made with 3 different collagen-based foams interspaced with two electrospun nano/microfibrous mats. The top layer was made of collagen type I-chondroitin sulfate-hyaluronic acid (Coll-CS-HA), and the middle and the bottom layers were made of only collagen type I with different porosities and thus with different mechanical properties. The mats of aligned fibers were a blend of collagen type I and poly(L-lactic acid-co-glycolic acid) (PLGA). After seeding with human fibrochondrocytes, cell attachment, proliferation, and production of extracellular matrix and glucoseaminoglycan were studied. Cell seeding had a positive effect on the compressive properties of foams and the 3D construct. The 3D construct with all its 5 layers had better mechanical properties than the individual foams.

Effect of Compression Speed on Static Compression Properties of Foams

Expandable polystyrene and expandable polyethylene foams are frequently used in packaging of products. The study on their cushioning properties is important for the design of the transport package. The effect of compression speed and multiple reloading on the cushioning properties of HDEPS, LDEPS and HDEPE was studied in this paper. The results indicate that the cushioning properties of HDEPS and LDEPS are affected obviously by the compression speed, but the change of the cushioning properties for LDEPE was unconspicuous with the compression speed. LDEPE appeared obvious fatigue after twice reloads.

Processing and mechanical properties of porous Fe–26Cr–1Mo for solid oxide fuel cell interconnects

Porous, ferritic steel was produced by blending, pressing and sintering Fe, Cr, Mo and NaCl powders. During sintering NaCl evaporated to form 40–58% interconnected open porosities, while the metal powders densified and interdiffused to create a nearly dense Fe–26Cr–1Mo matrix (E-Brite, developed for solid oxide fuel cell interconnects). The foam compressive properties at ambient temperature were in good agreement with the Gibson–Ashby scaling laws for stiffness and strength and demonstrate high mechanical energy absorption. The foam compressive creep response at 850 °C under an argon atmosphere followed the same power law stress dependence as the bulk material, suggesting similar deformation mechanisms in each case. Creep data under argon were compared with a variational composite model and a simple unit cell model taking into account thicker nodes connecting slender struts.

Production of aluminum foam by spherical carbamide space holder technique-processing parameters

Spherical carbamide has been employed to produce aluminum foams by space holder technique via powder metallurgy route. The effect of different processing parameters such as applied pressure, dissolving time of spacer, sintering temperature and time, metallic additives, on compression properties of the resultant foams has been evaluated. Aluminum foam samples with 40–85 vol.% porosity were successfully produced. Addition of 1 wt.% Sn and Mg to aluminum powder increased strength of the sintered foams. The results indicate that the appropriate compressive properties of foams are achieved under 330 MPa compacting pressure, sintering temperature and time of 640 °C and 2 h, respectively.

Simulation of Aluminium Foam Compressive Properties

In this paper, the simulation of the commpress properties of Al foam was investigated by finite element methods. The simulation results show that the compressive yield strength of Al foam is consistent with the theoretical model of Gibson and Ashby. The yield strength of Al foam decrease with the increase of porosity, and the yield strength decreases significantly with the increase of porosity. The density of Al foam is proportional to the compressive strength. At a certain porosity, the ratio of sample size and the aperture have an extremely important effects on compressive behavior of aluminum foam. When 4 ≤ D / d <8, with the increase of the ratio of D / d, the plastic deformation plateau and the compressive strength of metal foam is increasing ; on the contrary ,when the ratio> 8, with the increase of the ratio, the plastic deformation plateau is decreasing, the compressive strength keeps constant.

Properties of heat-treated aluminium foams

Aluminium foams based on the wrought alloy AA6061 were subjected to different heat treatments in order to evaluate possibilities to tailor their mechanical properties. Quenching after foaming was carried out either in air or in water. Solution heat treatment conditions were varied from ‘no treatment’ to treatments combined with different air and water quenching methods. This gave rise to different cooling rates that were measured in-situ. Full age-hardening cycles were compared to heat treatments in which a simplified programme was applied. In total, the effect of nine different heat treatments on micro-hardness and the compression properties of foams were investigated. Foams that were fully heat-treated performed best with an increase of strength by 60–75% over the untreated samples. However, age-hardening directly after foaming also caused significant improvements of strength, thus allowing to omit water quenching steps which carry the danger of damaging the foamed structure.

Influence of the Void Fraction on the Mechanical Compression Properties of Foams

Epoxy and polyurethane foams with different content of voids were tested under compression. Thereby, the epoxy foam showed a simple correlation between the fraction of the foaming agent and the density and void fraction. In contrast to this foam, the density and void fraction of the polyurethane system is additionally dependent on the position in the body of the foam. The empirical classic correlation and the mechanical modified Gent-Thomas model as models for the calculation of the compression properties of foams showed good agreement between the measured and the calculated values. The empirical model with its materials parameters showed a bigger flexibility.

Predicting the compressive properties of rigid urethane foam

The classic equation1 in use throughout the urethane industry to predict the compressive properties of rigid foams is ((1)) The value of K and a need to be determined experimentally for each foam system at a given temperature. By evaluating the compressive properties of 14 different rigid urethane foams, a was defined as 1.75 for all materials at all test temperatures. General equations for predicting the foam's compressive properties over a temperature range of −65° to 325°F (−54° to 204°C) were then developed. These general equations appear to be reasonably accurate in predicting the compressive properties of any rigid urethane at any temperature up to the foam's softening point. The equations are of the form shown above with K being a function of temperature only. Finally, the K term was defined as a function of temperature. The equations developed for predicting the compressive strength and modulus of the rigid urethane foams are: ((2)) for T equal to or greater than 77°F (25°C), and ((3)) for T equal to or greater than −65°F (−54°C), where the compressive strength and modulus are in pounds per square inch and density is pounds per cubic foot. These equations are valid up to the softening point of the foam.