Relative Density Of Foam Research Articles

Experimental Analysis of the Mechanical Properties of Carbon Foams Under Quasi-Static Compressive Loads.

This article sought to determine the response of a carbon foam material derived from polyurethane foam when subjected to a quasi-static compression load. The effects of the foam pore densities and additives (solvents) on the compression strength, compressive modulus, and surface morphology of the carbon foam were investigated. In this study, three different carbon foam pore densities (20, 40, and 60 ppi) and three solvents for the phenol-formaldehyde resins that coated the polymer foam (acetone, ethanol, and methanol) were used. Carbon foams were derived from polyurethane foams by carbonization. Quasi-static compression testing was carried out using a universal testing machine. The compressive strength, compressive modulus, and relative density of these different carbon foams were computed and compared. Two-way ANOVA analyses were performed to compare the significance of solvents and pore density. These results showed that pore density and solvents significantly affected the compressive strength, compressive modulus, and surface morphology of the fabricated polyurethane-derived carbon foam. Finally, the maximum compressive strength and maximum compressive modulus were observed in carbon foam (60 ppi) with 40% methanol as the solvent. Conversely, a minimum compressive strength was observed for a 20 ppi carbon foam with a 20% acetone solvent, and a minimum compressive modulus was observed for a 20 ppi foam with 40% methanol. Lastly, the chemical composition of the polyurethane foams was investigated, and these results indicated that the polyurethane-derived carbon foam had 96% carbon atoms after carbonization.

The mechanical characteristics of an aluminum foam winding CFRP composite structure under axial compression

To enhance the energy absorption properties of the energy-absorbing structure, carbon fiber-reinforced polymer (CFRPs) with higher specific energy absorption and porous material aluminum foam with better compressive characteristics were organically combined, and a lighter aluminum foam winding carbon fiber-reinforced polymer structure (CFRP-FA-FW) was designed. Through quasi-static compression testing, the deformation mode and energy absorption properties of CFRP-FA-FW under axial load were examined. The energy absorption and specific energy absorption of CFRP-FA-FW are both increased by 113.55 % and 60.73 %, respectively, compared to the simple composite structure CFRP-FA. Finite element simulation was used for the parametric analysis of the CFRP-FA-FW structure to assess the effects of the relative density of the aluminum foam, the fiber lay-up angle, and the thickness. The results reveal that the change in the relative density of aluminum foam has little impact on the failure deformation mode of CFRP-FA-FW under axial load; the structure has a higher energy absorption capacity and a smoother energy absorption process when the fiber lay-up angle is [0°/90°]ns and [45°]ns; the energy absorption capacity of CFRP-FA-FW is significantly improved by increasing the thickness of the carbon fiber lay-up, and the procedure is also more efficient.

Axial Crushing Behaviors of Metal Density Gradient Foam-Filled Square Taper Tubes: Analytical Model and Numerical Calculation

Abstract Metal tube is a traditional energy-absorbing structure, and metal foam is a lightweight material with advantages, i.e., high energy absorption and high specific strength. The foam-filled square tube can improve crashworthiness and has better energy absorption, which is higher than the sum of the energy absorption of the tube and foam. Axial crushing behaviors of metal density gradient foam (DGF) filled square taper tubes are studied analytically and numerically in this paper. An analytical model is presented to study the crushing behavior of DGF-filled square taper metal tube under axial loading, in which the interaction between square taper tube and DGF is considered. The numerical calculation is conducted, and the deformation mode is obtained. The analytical predictions are well consistent with the experimental and numerical results. The influences of taper angle, foam strength, maximum relative density, and minimum relative density of gradient foam on the compressive behavior of metal DGF-filled square taper tubes under axial loading are considered. It is demonstrated that when the taper angle is less than 85 deg, the average crushing force increases as the minimum density of the DGF increases. However, when the taper angle is greater than 85 deg, the average crushing force decreases with the increase of the minimum density of the gradient. This proposed analytical model can effectively predict the axial crushing behaviors of metal DGF-filled square taper tubes.

Novel design of irregular closed-cell foams structures based on spherical particle inflation and evaluation of its compressive performance

Due to the high degree of randomness in the microstructure of real closed-cell foams, many reported numerical models in the literature are not able to capture precisely the local morphological features found in solid foams geometry. This is still the main impediment that restricts the investigation of this novel material and motivates the development of a sophisticated 3D solid model, which describes properly the complex geometry of real closed-cell foams. In this regard, this paper presents an original approach to generate a realistic and accurate 3D computational model of irregular closed-cell foams with relative density control and detailed finite element analysis of their mechanical performance under quasi-static loading up to densification. The solid model is constructed based on spherical particles inflation simulation. It resembles the real foams in terms of local features such as cell walls irregularities and thickness variation. The modeling approach was successfully verified by comparing cell-morphological details of the generated models with those produced experimentally available in the literature and by the high-quality of obtained 3D printed models containing complex shapes and irregular cell wall thickness distribution. The evolution of spherical particles during the inflation process is analyzed based on finite element (FE) simulations. It was found that it can produce varying relative densities of foam due to the gradual decrease in the gap between the inflated particles, this makes the geometrical model of the foam suitable for studying the effect of local morphological characteristics on the mechanical performance of closed-cell foam material. To demonstrate that the compressive performance of the proposed closed-cell foam models can be controlled by relative density, 3D foam models were extracted from different inflation times and then subjected to quasi-static compression tests up to densification using the Abaqus software. The results confirm that the plateau stress can be expressed as a function of foam relative density, its accuracy is validated by comparing it to the closed-cell aluminum foam power law equation existing in the literature. The new design method offers suitable numerical models for AM technology, plenty of experimental works on closed-cell foam can be reduced for engineering applications.

Investigation of the effect of polymers on dermal foam properties using the QbD approach

Dermal foams are promising drug delivery systems due to their many advantages and ease of application. Foams are also considered a novelty in the field of dermatology. In particular, they are beneficial for the treatment of skin conditions where patients have highly inflamed, swollen, infected and sensitive skin, as the application of the foam to the skin surface to be treated minimizes the need for skin contact. In order to formulate foams, it is necessary to know which material and process parameters influence the quality characteristics of foams and which methods can be used to study foams; this part of the research is assisted by the QbD approach. By using the QbD concept, it contributed during the development process to ensure quality-based development. With initial risk assessment, the critical material attributes (CMAs) and the critical process parameters (CPPs) were identified to ensure the required critical quality attributes (CQAs). During the initial risk assessment, five high-risk CQAs, namely foam volume stability, foam expansion, cross point, the initial values of the number and size of bubbles, and three medium-risk CQAs, namely spreadability, relative foam density and viscosity of the liquid system were identified and investigated. In this research, different types of polymers (xanthan gum, hydroxyethylcellulose, different types of hyaluronic acids) were used to improve the properties of foam formulations. The formulations containing xanthan gum and high molecular weight hyaluronic acid had good foam properties and will be appropriate delivery systems for an active pharmaceutical ingredient. Overall, the polymer content had a great effect on the properties of the foams. Different polymers affect the properties of foams in different ways. When used in combination, the methods reinforce each other and help to select a formula for dermal application.

Investigating relative density effects on quasi-static response of high-density Rigid Polyurethane Foam (RPUF)

This study aims at characterisation of various densities of Rigid Polyurethane Foam (RPUF) under quasi-static tension and compression. The density of foam is key parameter in selection of suitability for structural applications. Various densities of RPUF are synthesised using commercial grade Polyols and Methylene diphenyl isocyanate (MDI). The ratio of mixing both constituents was maintained at 1:1.15 for polyol and MDI respectively. Free rise density of the foam was achieved at 234 kg/m3 and is considered the baseline density for comparison. The higher than baseline densities were achieved by blowing the mixture into a mould with variable pouring times and three densities in the range of 252 kg/m3, 303 kg/m3 and 353 kg/m3 were achieved. The tensile and compression specimens were prepared from the manufactured blocks. SEM images were taken from the blocks of various densities and uniform cell patterns were observed for all densities. The specimens were then tested under compressive and tensile loads. It was found that the specimen exhibit consistency in results and the density affects the mechanical properties directly. Optimum density of foam for energy absorption capability of RPUF based on specific work done is also estimated. A phenomenological model based on relative density of foam was developed to assess material behaviour which can reduce the requirement of test specimens for obtaining a set of particular material properties.

Classification of natural rubber foam grades by optimising the azodicarbonamide content

This study aimed to focus on classifying rubber foam grades according to ASTM D1056. The natural rubber foams were prepared by varying the Azodicarbonamide (ADC) content from 2 - 10 phr. The results were evaluated on their physical and mechanical properties. The relative foam density of the foams decreased, and the expansion ratio increased with the addition of ADC. This was due to the increase in the gas phase raised by ADC. In addition, adding ADC also decreased hardness and compression-deflection of the foams, whereby the values obtained were higher after oven aging due to the radical recombination caused by chain breaking. According to ASTM D1056, the compression-deflection values of the foams were 2A2 and 2A3 grades, where the ADC content at 6 – 10 phr met the basic properties required by the same standard. Furthermore, the ADC content at 6 phr is strongly suggested when considering the foam morphology.

Quasi-Static Compression Properties of Bamboo and PVC Tube Reinforced Polymer Foam Structures.

In recent years, there has been a growing interest for composite materials due to the superior capability to absorb energy and lightweight factor. These properties are compatible to be utilized in the development for transportation system as it can reduce the fuel consumption and also minimize the effect of crash to the passenger. Therefore, the aim for this project is to study the compression strength and energy absorbing capability for Polyvinyl chloride (PVC) and bamboo tubes reinforced with foam. Several parameters are being considered, these being the effect of single and multiple tube reinforced foam structure, foam density, diameter of the tube as well as effect of different crosshead speed. The results showed that increasing the relative foam density will led to an increase in the compression strength and specific energy absorption (SEA) values. Furthermore, a significant increase of compression strength can be seen when several tubes are introduced into the foam while SEA remained almost the same. Finally, the influence of crosshead below 20 mm/min did not vary significantly for both compression strength and SEA.

Tensile properties of anisotropic foamed polyethylene films with ellipsoidal closed cells

In this work, the tensile properties of high density polymer foam films with ellipsoidal closed cells are studied to determine the effect of the cell structure and orientation on the elastic modulus. As expected, not only the relative foam density (ρr) has a direct effect on the elastic modulus, but also the cell aspect ratio (AR) and cell orientation (θ). Based on the results available from our previous works, a simple model based on the Gibson and Ashby equation is proposed to predict the relative elastic modulus of foamed films. Then, a validation of the model is done using experimental data from the literature. For the range of parameters included (0.45 < ρr < 1.0, 0 < θ < 90ο, 1 < AR < 6), an average absolute deviation of 6% is obtained for all the samples tested.

Manufacturing and Characterization of Open-Cell Aluminum Foam Produced via Infiltration of Leachable Space Holder

Open-cell Al-Si foam samples were produced using infiltration casting technique. The metal infiltration process was performed in a specially designed and built setup consisting of a vertical chamber resistance furnace, a pressurization chamber connected to an Argon gas cylinder through a control manifold. To control the relative density of the produced foams, non-compacted and compacted preforms (5 MPa) were prepared from 2 or 4 mm NaCl particles. The compaction was performed using a hydraulic press in the same infiltration chamber. Argon pressure of 3 bars was applied to infiltrate the preforms with the aluminum alloy after melting at 750 °C. The produced aluminum foam specimens show no lack of filling, a high degree of preform replication, and good homogeneity of pore sizes. The preliminary physical and mechanical characterization tests, including relative density, plateau stress, densification strain, and elastic modulus of the foam, are comparable to the values reported in previous investigations, in which more complicated, time-consuming, higher energy, and costly techniques were used. Further investigations on wider ranges of particle sizes, compaction, and infiltration pressures are currently in progress.

Microstructure and mechanical behaviour of Ti-Cu foams synthesized via powder metallurgy technique

In the present study titanium based copper alloy foams were synthesized using acrawax as a space holder through powder metallurgy route. The effects of distinct pore size range and Cu content on the microstructural features, density, compressive and flexural behaviour was investigated. Results show that the amount of microporosity generated was more in case of foams with coarser pores than finer ones and also it increased with increase in Cu content. The presence of fine pores and lower amount of Cu led to generation of minimal amount of microporosity; resulting into greater relative density of Ti-Cu foams. The plastic collapse stress, plateau stress and bending strength of Ti-Cu foams decreased while densification strain increased with increase in Cu content. The maximum value of plastic collapse stress is reported for Ti-3Cu foam with fine pores. The plateau strength and bending strength of Ti-3Cu foam with fine pores was found to be higher than that of Pure Ti foams and was found to be the most optimized in terms of the characteristic features. The higher values of relative density, plateau and bending strength of Ti-3Cu foams makes them more preferable over pure Ti foams for implants applications.

Properties of Zn foam filled with cenosphere microballoons

ZnAl27 hybrid foam was synthesised with addition of CPs and TiH2 as foaming agent through melt foaming technique with relative densities ranging from 0.11 to 0.36 which have porosity up to 89 percent. SEM analysis has been carried out for the microstructural characterization in terms of actual cell and CPs distribution in the foam porosity. The foam was obtained, having closed pores and the size of the pores depends on their relative densities. Lowering the pore size gives high relative density. Compressive properties were observed in terms of plateau stress and energy absorption capacity and these properties follow power law relationship with relative density of Zn foam.

Investigation of propellant-free aqueous foams as pharmaceutical carrier systems

Due to their light consistency and good spreadability, aqueous foams are considered as convenient and highly accepted drug carrier systems that are of great importance in the field of topical drug delivery. The production of a stable, easy to dose, preferably environmentally harmless foam formulation is challenging. Therefore, foam characterisation requires a complex approach: several tests are to be performed throughout the formulation. Our study primarily aims to investigate the quality attributes of propellant-free foam-forming additives. Throughout the research, we focused on acquiring knowledge about the properties of pharmaceutical excipients suitable for foam formulations and their effect on foam characteristics. Not only were the relative foam density, actuated foam weight and the foam collapse tendencies studied, but also the initial liquid properties. Along with surface tension determination, bubble-forming experiments were carried out. The bubble size and rate of formation, standardised by using a texture analyser, were followed by image analysis. Analysing the bubble-forming properties of dilute surfactant solutions allows assumptions on the properties of foam formed from the more concentrated solutions. The size and number of bubbles in the produced foams are related to the kinetics of single bubble formation. For comparison, commercially available medicated foams were studied.

Experimental and finite element simulation of natural rubber foams using real 3D structures

Natural rubber (NR) foams were prepared via a one-step foaming process, the effect of density and morphology on micro-level and macro-level mechanical properties was studied. In particular, experimental data were used to validate different numerical models based on actual three-dimensional (3D) foam structures built using a combination of 2D scanning electron microscopy (SEM) images. Then the uniaxial compression behavior was simulated at two levels (micro-scale and macro-scale) with finite element methods (FEM). The FEM results were finally compared with experimental data and different hyper-elastic models. SEM images showed that increasing the relative foam density from 0.3 to 0.5 led to a 55% decrease in cell size and a 1000% increase in cell number. The real 3D structures showed that foams with higher density have a more homogenous structure with lower structural defects or cell connections. The results also revealed that FEM at the macroscopic level is in good agreement with experimental results, especially for high density foams. On the other hand, FEM at the microscopic level showed that the maximum stress concentration and related micro-strain substantially decreased with increasing foam density.

Additive manufacturing and characterization of brittle foams

This work focuses on the synthesis of brittle foams with controlled morphological characteristics, measurements of their crushing strength and its connection to the cellular microstructure. Tessellation-based topologies are used to generate realistic microstructures of open-cell foams that are subsequently 3D-printed by stereolithography. The brittle material behavior and fracture strength of the base photopolymer are measured using tensile tests on small dog-bone specimens with the dimensions of foam ligaments. Synthesized foams are scanned by microcomputed tomography and manufacturing-induced variations are quantified through image analysis. Characterization shows that there is a small amount of volume shrinkage of the material caused by the additive manufacturing process, but all other microstructural features are accurately reproduced. We then perform a series of experiments to measure the compressive response and strength of the 3D-printed foams and connect it to load-transferring conditions, the strength of the base solid material and the foam relative density.

High shear strength and ductile ZrC–SiC/austenitic stainless steel joints bonded with Ti/Ni foam interlayer

A transient-liquid-phase (TLP) diffusion bonding method was employed to join ZrC–SiC ceramic and austenitic stainless steel by using Ti foil and various density Ni foam as interlayer. The Ti–Ni TLP contributed to a firm bonding between ceramic and foam interlayer while avoiding liquid infiltration in foam structure. The influence of holding time on the microstructure of the TLP reaction layer was investigated. The shear tests showed the joints with foam interlayer exhibited ductile failure mode and improved fracture work in comparison with the one with dense Ni interlayer. A maximum shear strength of 117.2 MPa was reached when the relative density of Ni foam was 0.57. The fracture behaviors of the joints during shear test were in-situ observed.

Prediction of Foaming Process in the Production of Aluminium Foams

The paper deals with the physical-chemical effects of a blowing agent on production the cellular metal systems (in this case aluminium foams). Based on the isothermal concertation and pressure curves for the H-Ti system and by using the maximum gas volume obtained from equation of state, there was applied the blowing agent to 1 kg of AlSi12 aluminium alloy. Moreover, using relation to determine aluminium foam relative density (&#961; REL) from alloy AlSi12, there was done prediction to determine density of 1 kg metal foam from AlSi12 alloy at different blowing agent contents from 0.1 up to 1.5 wt% of titanium hydride TiH 2. These isothermal calculations were compared with the density of aluminium foal from alloy AlSi12, which was produced by an industrial process. Basic mechanical properties were subsequently measured on the produced foam samples.

Piezoelectric property improvement of polyethylene ferroelectrets using postprocessing thermal‐pressure treatment

In this work, biaxially stretched polymer foams with well‐defined cellular structures were prepared from polyethylene via blown‐film extrusion and subjected to corona charging to produce a piezoelectric response. The charging parameters were first optimized in terms of charging voltage and needle distance, as well as the gas type and pressure to investigate their effect on the piezoelectric coefficient (d33). The results show that samples charged under nitrogen (N2) at 100 kPa had better d33 coefficient than those charged under ambient air or N2 at 20 kPa. Moreover, 2 different thermal pressure treatments were imposed to obtain an optimized eye‐like cellular structure with different cell aspect ratios (AR). The results showed that when the cells were elongated in both the longitudinal and transverse directions (higher AR), higher d33 coefficients were achieved. From all the samples produced, the best results were obtained for a longitudinal aspect ratio (AR‐L) of 7.1, a transversal aspect ratio (AR‐T) of 4.6, and a relative foam density of 0.52 leading to a d33 coefficient of 935 pC/N. This coefficient was further increased using reverse charging and multilayered films, reaching a maximum of 2550 pC/N. This value is much higher than typical ones reported so far for any polyethylene and polypropylene ferroelectrets. These results could increase the use of polyethylene in piezoelectric applications as these materials are very attractive for the large‐scale production of electret‐based sensors and transducers due to their low cost and easy processing.

Validation of an experimental-numerical approach for the high temperature behaviour of open-cell ceramic foams

Open-cell ceramic foams are used as filters in casting processes of molten metal to reduce the amount of non-metallic inclusions. These filters are exposed to high temperatures and loadings, sometimes for a longer time. Therefore, the dimensional stability has to be considered, which suffers from inelastic deformations, in particular creep deformations.A recent work of the authors describes the creep deformation behaviour of such foam structures using an experimental-numerical approach based on bulk material creep tests. Now, the results of this prediction are validated by creep curves of real foam samples. This comparison shows a good accordance for the considered parameters (load, temperature, time, and creep phase).Moreover, the influences of different structural parameters on the elastic foam stiffness and foam creep resistance are investigated. The relative foam density has the greatest impact, followed by uniaxial pore stretching in one direction and strut shape, whereas polydispersity has only a very small effect.

Effect of strain rate and temperature on deformation behavior of closed-cell ZnAl12 hybrid foam

Stir casting technique has been applied to synthesize ZnAl12 hybrid foam to study the effect of temperature on the deformation behavior of the composite. Cenosphere particles (CPs) were used as thickening agent to increase the viscosity of melt and also used as a space holder to create microporosity into the structure. CaH2 (0.5 wt%) was used as the foaming agent. The relative density of ZnAl12 hybrid foam was found between 0.27–0.40. The synthesized hybrid foam was put under microstructural investigation and for compressive deformation behavior at high temperature. The effect of strain rate was observed at constant temperature (100 °C) varying strain rate from 0.001/s to 1/s and the effect of temperature was studied at constant strain rate (0.01/s) varying temperature in the range of 100 °C–250 °C. It is noted that higher relative density with high strain rate has higher plateau stress and energy absorption capacity at a steady temperature. The values of plateau stress and energy absorption capacity decreases as an increase in the temperature range. Densification strain has been found less effect of strain rate and temperature but it varies according to relative density.