Behavior Of Foams Research Articles

Investigating the Acoustic Behavior of Polyurethane Foam Reinforced with Clay Nanoparticles

Introduction: Disturbing noise can cause physical and mental illnesses among workers; for this reason, it is necessary to restrain it, especially in workplaces. Using sound-absorbing materials with suitable acoustic properties has been a growing trend in mitigating noise. This study aimed to improve the acoustic properties of polyurethane foam (PUF) as a sound absorber. Material and Methods: In the present study, PUF was synthesized with different percentages of clay nanoparticles (0 -1.2 wt.%), and then the Sound Absorption Coefficient (SAC) of the synthesized PUF was measured by the acoustic impedance tube in the frequency range of 63 to 6400 Hz according to the ISIRI 9803 standard. The morphology of the foam was also investigated by Scanning Electron Microscope (SEM) Results: The results showed that the addition of clay nanoparticles to PUF improved the sound absorption behavior of the samples, and the best sound absorption behavior was for PUF with 1.2% weight of nanoparticles at low frequencies (500-2600 Hz). This increase in the absorption coefficient can be due to the increase in the number and smaller size of the pores with the increase in the amount of nanoparticles in PUF. Conclusion: This study illustrates that the incorporation of clay nanoparticles into PUF at varying percentages results in an enhanced absorption coefficient. The presence of clay nanoparticles leads to a reduction in cell size and an increase in the number of pores, consequently enhancing surface friction. The absorption coefficient was observed to increase with the growing concentration of clay nanoparticles in PUF.

An Interactive Fluid–Solid Approach for Numerical Modeling of Composite Metal Foam Behavior under Compression

An Interactive Fluid–Solid Approach for Numerical Modeling of Composite Metal Foam Behavior under Compression

Mesoscopic simulation study on density gradient metallic foam sandwich panels under hypervelocity impact

The high stiffness of sandwich panel shield ensures the survival of satellites and spacecrafts, making them extensively utilized in practical aerospace engineering. Metallic foams are exceptionally appropriate for spacecraft debris shields owing to their light weight and superior energy absorption characteristics. The internal mesostructure of a metallic foam plays a crucial role in determining its protective performance. At the mesoscale, the density gradient metallic foam exhibits a greater potential for protection compared to uniform metallic foam under hypervelocity impact. Therefore, this study investigates the behavior of density-gradient foams under hypervelocity impact. By leveraging three-dimensional Voronoi tessellation in conjunction with the background mesh-mapping algorithm, this study constructed mesoscopic finite element models of the layered and continuous-density gradient metallic foam, considering the internal structure of randomness. Subsequently, the Finite Element-Smoothed Particle Hydrodynamics (FE-SPH) adaptive method in LS-DYNA was employed to conduct numerical simulations of the hypervelocity impact. First, the simulation was validated through a comparison with the experiment. Based on the results of the numerical simulations, the characteristics of the debris cloud and the damage within the foam were analyzed. It was determined that the protection mechanism of the density gradient foam sandwich panel under hypervelocity impact involved a coupling effect between the domino and microchannel effects. The different damage characteristics of layered density gradient foam sandwich panels were analyzed. According to this mechanism, foam sandwich panels with different density-gradient configurations were designed and their protective performances were compared to determine the optimal density-gradient configuration to provide valuable insights into the optimal design of protective structures.

Investigations into the foaming behavior of ABS by means of granule extrusion using expandable microspheres

The following investigations address the production of syntactic polymer foams using thermally expanding microspheres (TEM) in the extrusion process. A process model for the foaming behavior of acrylnitrile butadiene styrene (ABS) with thermally expanding microspheres as masterbatch is derived by varying the two basic process parameters extruder rotational speed and extruder temperature in a test matrix with five stages each. The investigations include the production of unfoamed and foamed strands and the measurement of process relevant properties and parameters such as extrusion mass flow, relative density of the structures, die-swelling and the characterization of the generated foam structures. The achievable density reduction is within the order of 50%. The process model resulting from the investigations allows the production of homogeneously foamed strands. These results are intended to serve as the basis for a transfer to the Large Scale Additive Manufacturing (LSAM) process.

Bead‐to‐Bead Analysis: Introducing an Innovative Methodology for Accelerated Quantitative Analysis of the Welding Behavior of Bead Foams

ABSTRACTPerformant lightweight components made of bead foams are essential for a sustainable transformation of industry in multiple areas. An in‐depth understanding of the welding process is key in reaching maximum mechanical properties. This study presents the novel methodology of Bead‐to‐Bead analysis, providing a superior way in directly and quantitatively evaluating the welding behavior of bead foams compared with current approaches. Individual beads of expanded polystyrene (EPS) and expanded thermoplastic polyurethane (ETPU) are welded in a rheometer at defined parameters. A subsequent tensile test in combination with the analysis of the welded surface allows the evaluation of shrinkage/softening of the beads during welding and their tensile strength. For EPS, softening of the amorphous material is observed at the beginning of glass transition (~95°C) in addition to an increased welding quality. Residual stresses in ETPU lead to initial shrinkage followed by softening above 140°C. Welding of ETPU starts at 100°C and reaches a maximum at 140°C. The subsequent thermal analysis of the welded beads show the importance of recrystallization processes during cooling due to the formation of new crystalline domains across the bead interfaces. In the absence of such domains, sufficient bonding between beads is not possible.

Influence of Strain Rate and Temperature on the Multiaxial Failure Stress Locus of a Polyamide Syntactic Foam

This study introduces a comprehensive experimental methodology allowing for the direct measurement of the rate dependent multiaxial response of polymer syntactic foams under combined direct-shear loading. The combined tension-torsion behaviour of a syntactic foam and its rate dependence are investigated for the first time.Dynamic tension-torsion experiments were conducted using a newly developed Tension-Torsion Hopkinson Bar (TTHB) enabling the measurement of the combined tensile-shear response of engineering materials at high rates of strain.The response and multiaxial failure envelope of a polyamide syntactic foam were experimentally measured and analysed to determine the combined influences of stress state, strain rate, and temperature. The multiaxial failure stress locus was defined in both the normal versus shear stress space and the principal stress space, providing a comprehensive characterisation of the behaviour of the material under various loading and environmental conditions.The suitability of existing pressure dependent failure criteria to represent the measured experimental data was also assessed. The Drucker-Prager pressure dependent criterion proved to be effective in capturing the measured quasi-static and dynamic multi-axial stress loci at different temperatures.The effects of temperature, loading rate and stress state on the deformation and failure modes were analysed by means of SEM micrographs of the tested samples.

An investigation into instantaneously tuning the EMI shielding characteristics of CNT-based nanocomposite biofoams in the X-band range by strain loading

The electromagnetic interference (EMI) shielding of CNT-based nanocomposite biofoams is capable of being tailored instantaneously by mechanical loading. In contrast to tuning the EMI shielding via nanofillers or by decoration process, the strain-activated EMI tailoring characteristics possess enormous potential that still await to be explored. To reveal this tailoring mechanism, a multi-scale electro-magneto-mechanically coupled homogenization model is developed to tailor the EMI characteristics of CNT-based nanocomposite biofoams in the X-band range (8.2–12.4 GHz). In this development, the elastic moduli, complex conductivity, and complex permeability are all selected as the homogenization variables. Four categories of interface effects are considered, including imperfect interface bonding, electron tunneling, Maxwell-Wagner-Sillars polarization, and electron hopping. The predicted EMI tailoring characteristics are validated by the experiment of CNT/wheat flour nanocomposite biofoam over a wide range of stain loading. The effective EMI shielding behavior decreases with the compressive loading, but it increases with the tensile loading. It is found that a CNT content higher than the percolation threshold is necessary to tailor the EMI shielding behavior of this nanocomposite foam via strain loading. This study can provide innovative insights to tune the EMI shielding characteristics of CNT-based nanocomposite biofoams in X-band instantaneously.

Coal gangue based geopolymer as an additive of warm mix asphalt: preparation and properties

Abstract In contrast to conventional hot mix asphalt technology (HMA), warm mix asphalt technology (WMA) permits the mixing and compaction of asphalt mixture at lower temperatures. This innovative approach is characterized by significant energy savings and reduced emissions, making it a sustainable choice for asphalt mixture production. This paper used coal gangue to prepare a WMA additive. By leveraging the free water in its zeolite-like structure, which evaporates upon heating, bubbles form within the bitumen. This causes bitumen to expand and lose viscosity, thereby achieving the purpose of warm mixing. Both achieve a decline in the asphalt mixture’s mixing temperature and provide an effective method for utilizing coal gangue resources. It helps mitigate the environmental hazards associated with the massive accumulation of coal gangue, including soil contamination and water resource pollution. Therefore, based on alkali activation theory, this paper aimed to develop a novel coal gangue geopolymer (CG) WMA additive. CG was characterized through microscopic testing and analysis of water storage stability. The impact of varying CG dosages on the conventional performance of bitumen was examined. The bitumen foaming test elucidated the warm mixing mechanism and foaming behavior of the CG. Additionally, the road performance of the WMA was analyzed. The findings indicate that CG has abundant pore structures, providing an effective water storage space, and CG as a WMA additive exhibits good water storage stability at ambient temperature. When the CG dosage is 5% by the mass of bitumen, the viscosity of bitumen at 130∼140 °C is appropriate, and the WMA results in good road performance. Compared with HMA, the mixing temperature is reduced by a range of 20∼50 °C.

Study on the crosslinking reaction and foaming behavior of silicone rubber in high-pressure fluids

High-pressure gas might affect the molecular chain movement, chain interaction, and crosslinking behavior of MVQ during the saturation process. In this paper, by comparing crosslinking exothermic behaviors of MVQ in air, CO2, and N2, it is found that the supercritical CO2 (scCO2) can promote crosslinking reaction of MVQ through enhancing the swelling and molecular chain's mobility. The result of rheological property shows the competitive relationship between crosslinking and plasticizing effects of MVQ in CO2. MVQ foams with different cellular structures and porosity are designed by balancing the crosslinking density and plasticization effect. MVQ foams prepared in this study have excellent compressive mechanical properties, and compressive stress can reach up to 1839 kPa at 40 % strain. This paper offers a reference for preparing thermosetting polymer foams in the aspect of crosslinking reaction and cellular structure regulation.

Evaluation of critical process parameter on the production of sustainable bead foams based on polylactic acid

A commercial grade of polylactic acid (PLA) was foamed without using modifiers to obtain expanded polylactic acid bead foams (EPLA). Typically, the foaming process is influenced by both melt properties and crystallization behavior. While factors like water temperature, die structure, and die temperature are known to have effects on bead foam processing, these aspects have not been thoroughly explored in the context of PLA bead foam production. To address this gap, a comprehensive investigation was undertaken, varying water temperature, die structure, and die temperature to discern their impact on PLA processing behavior. Results revealed that water temperature significantly influenced foaming behavior, particularly at elevated temperatures near the glass transition of PLA. Additionally, the study demonstrated that die size wielded a notable influence on all foam properties, dictating process limits. With the selection of an appropriate die size, the die temperature could be manipulated within the range of 190°C to 160°C, revealing a substantial impact on the overall process. Remarkably, the lowest densities achieved were 63 kg/m3 with an average cell size of 36 µm and a cell density of 1.1*107 cells per cm3.

Investigation of Tensile Properties and In Situ Analysis of Fracture Behavior in High-Porosity Open-Cell Nickel Foam.

Nickel foam offers excellent conductivity, a high surface area, and lightweight structure, making it ideal for applications, like battery electrodes, catalysts, and filtration systems. Its durability and corrosion resistance further enhance its performance in various industries. However, few studies focus on the tensile anisotropy of nickel foam and its tensile fracture process. In this study, the anisotropic tensile behavior of nickel foam with varying relative densities has been investigated, along with its tensile fracture behavior using in situ techniques. The tensile properties of nickel foams show strong anisotropy due to the flattening process in the production process. The results show that the tensile properties, including the yield strength, tensile strength, and elastic modulus, increase with the increasing relative density, while the elongation percentage has no relationship with the relative density. The experiment data on tensile strength are in agreement with Gibson's formula and Liu's formula. In situ tensile tests are conducted to explore the microscopic fracture mechanism of nickel foam. The results show that the struts of nickel foam are tensile fractures or shear fractures near the joints, and the fracture process of struts is clearly recorded and analyzed. This study is significant as it provides critical insights into the anisotropic tensile behavior of nickel foam and fracture mechanism, enabling the optimization of production processes and broadening its potential applications.

Shape Memory Polymer Foam Based on Nanofibrillar Composites of Polylactide/Polyamide.

This paper presents the novel development of a shape memory polymer foam based on polymer-polymer nanocomposites. Herein, polylactide (PLA)/biosourced polyamide (PA) foams are fabricated by in situ fibrillation of polymer blends and a subsequent supercritical CO2 foaming technique. In this system, PLA serves as a shape memory polymer to endow this foam with a shape memory effect (SME), and in situ generated PA nanofibers are employed to reinforce the PLA cell walls and provide an additional permanent phase. A concentration of PA, 5 wt.%, was chosen to form an entangled nanofibrillar network. Foams of PLA/PA nanoblends with the same content of constituents were fabricated to reveal the effect of minor phase morphology on the cell structure and shape memory behavior of polymer foams. Profiting from the reinforcing effect of PA nanofibers, the PLA/PA nanocomposite foam exhibits smaller foam cells, a narrower cell size distribution and a comparable cell concentration than the PLA/PA nanoblend foam. In addition, PA nanofibers, unlike PA nanodroplets, favor the shape fixation ratio and recovery ratio and shorten the shape recovery time.

Study on foaming behavior of block copolymer/inorganic particles co‐construction of toughened epoxy resin foams

AbstractLow toughness and brittleness limit its application range of thermosetting epoxy resin (EP) based foams. In current research, inorganic particles are commonly utilized as heterogeneous nucleating agents to enhance foaming quality and EP toughness. However, the increasing inorganic particle content usually leads to particle agglomeration, which negatively impacts foaming quality and reduces EP performance. Block copolymers, which appear as liquid to effectively mitigate agglomeration, are employed as toughening materials for EP. In this study, a small number of modified calcium silicate particles (MCS) were used as anchor points to induce the distribution of block copolymers (P‐F68) to improve EP toughness and effectively enhance cell nucleation, thus, EP/MCS/P‐F68 foams performance was improved. The research results showed that EP foams obtained excellent cell structure and very small foam density (0.256 g/cm3) at the P‐F68 content of 10 wt%. The continuous increase of P‐F68 content would lead to the thickening of cell wall and the increase of cell size. Simultaneously, the core‐shell structure formed by P‐F68 in EP effectively enhanced the toughness of EP foams and mitigated its brittleness, offering crucial theoretical guidance for toughening and regulating the cell structure of EP foams.

Methodological approach to characterize the interfacial and foaming properties of carbonated beverages

The adjustment and control of specific product characteristics, e.g., foaming behavior of carbonated beverages, requires an understanding of influencing factors along with reliable analytical methods. However, due to the overlay of different phenomena, i.e., release of CO2 and action of surface-active molecules contained in such beverages, it is difficult to assess their respective contribution to foam appearance and stability. This study aimed at evaluating a new methodological approach to investigate the interfacial and foaming properties of carbonated beverages. Using beer as an example, it was attempted to establish a correlation between interfacial properties and foaming behavior. To ensure a comprehensive dataset, surface tension, interfacial dilatational rheology, and foaming properties including foam structural characteristics of six different German beers of three different types (i.e., Pils, wheat beer and Koelsch), which are known to exhibit distinct foaming behavior, were measured. While foams prepared with CO2 as sparging gas did not show any differences in foam aging, use of air for foaming enabled differentiation based on beer type. Differences observed in foam structural characteristics and stability could not be related to dynamic surface tension but might be linked to interfacial dilatational properties. Overall, the presented multiscale approach can be seen as promising concept for further experimental studies on carbonated beverages.

Understanding the impact of nickel coating on the mechanical and corrosion behaviour of copper foams

ABSTRACT This study used a sponge replication technique to fabricate open-cell copper (Cu) foams with varying pore sizes. Nickel coating was applied via electrolysis to produce nickel-copper (NiCu) foams to enhance the Cu foams' energy absorption efficiency and corrosion resistance. The foams were characterized under static conditions to assess their compressive and corrosion properties. The nickel coating improved compressive strength by increasing foam strut thickness and reducing defects, as observed via scanning electron microscopy (SEM). The 10 Pores per inch (PPI) NiCu foam shows a substantial increase in compressive strength, close to 17.7%, compared to the 10 PPI Cu foam, resulting in a maximum compressive strength of 11.3 MPa. Similarly, 20PPI NiCu foam shows an increase of compressive strength of 20% when compared to 20 PPI Cu foam. NiCu foams significantly reduced corrosion current density compared to uncoated Cu foams, indicating enhanced corrosion protection from the nickel coating.

Highly efficient flame retardancy and fire spread behavior of rigid polyurethane foams with extremely low content of flame retardant

In recent years, flame-retardant rigid polyurethane foam (RPUF) has once again captured the scholars’ attention due to the growing the growing demands in the field of building energy efficiency. However, the inherent flammability of RPUF is high and the complexities of its flame-retardant mechanisms remain inadequately understood. In this study, a modified biomass material, amino starch phosphate ester was successfully synthesized which was then combined with expandable graphite (EG) and incorporated into RPUF. The research delved into the optimal ratio and minimal flame-retardant additive required to achieve the stringent UL-94 V-0 rating, while also thoroughly investigating the flame retardancy and thermal properties of the composite system. The findings revealed that with just 6 wt.% of flame retardants, the RPUF achieved the UL-94 V-0 rating, with a 41.1 % reduction in peak heat release rate (pHRR) and a 23.7 % decrease in total heat release (THR). Additionally, it diminishes the flame's size and width, leading to quicker extinction, while also lowering the internal combustion temperature of the polyurethane, thereby delaying both preheating and combustion times. The synergistic interaction between amino starch phosphate ester and EG during combustion results in the formation of a dense, continuous char layer, effectively inhibiting the pyrolysis and combustion of RPUF. This study provides a theoretical foundation for the development of efficient flame-retardant systems for RPUF.

A statistical approach towards determining the governing parameters in volume expansion behavior of polypropylene foams

This study delves into the complex relationship between molecular structures and properties within polypropylene (PP) foams, with a particular focus on how various material parameters influence foamability. Multiple linear regression was adopted to efficiently assess the impact of eleven material parameters on foam expansion behavior. A primary finding is the significant role of branching index (g'vis) in shaping the expansion profile (i.e., the foaming window, maximum expansion ratio (Φmax), and optimum foaming temperature (Toptimum)). Additionally, Z-average molecular weight (Mz) is identified as crucial factor influencing the foaming window. Furthermore, the Winter-Chambon parameter n, indicator of the relaxation behavior of a resin in the terminal zone, is distinguished as a key parameter in determining Φmax. The crystallization temperature (Tc) also plays a pivotal role, particularly in its relationship with Toptimum. The research further highlights the significance of long-chain branching (LCB) and suggests strategies for cost reduction by minimizing the degree of LCB without compromising foaming performance, achievable through the adjustment of Mz and n. This strategy was exemplified through the comparison of two LCB PP resins, PP-12 and PP-22, demonstrating the feasibility of achieving similar foamability with adjustments in material parameters. The findings offer a detailed assessment of these parameters' influence on foamability, presenting valuable guidelines for optimizing PP foam production and customizing material properties for targeted applications.

All-polymer syntactic foams: Linking large strain cyclic experiments to Quasilinear Viscoelastic modelling for materials characterisation

The time-dependent behaviour of polymeric composites is critical in a broad range of applications, including those in marine, aerospace, and automotive environments. In the present study, we assess the validity of the quasi-linear viscoelastic (QLV) model to fit the stress–strain behaviour of all-polymer syntactic foams under large cyclic compressional strain in a novel experimental configuration. These syntactic foams were manufactured by adding hollow polymer microspheres of various sizes and wall thicknesses into a polyurethane matrix. These materials are known for their relatively large initial stiffness, and strong recoverability after large strains. In the QLV model, several strain energy functions (SEFs) were employed, including neo-Hookean, Ogden type I, and type II. The bulk and shear moduli are presented in the form of a Prony series. By estimating these experimental data using optimisation, the natural viscoelastic material properties and coefficients associated with the SEF were determined. The influence of the microsphere filling fraction was also explored. We show that at the strain rate considered here of 0.013 s−1, the compressible QLV model coupled with the Ogden-I SEF is capable of providing an excellent fit to experimental data. Critically, this fit can be achieved over a range of cycles via model optimisation to the first cyclic response only.

An Interactive Fluid–Solid Approach for Numerical Modeling of Composite Metal Foam Behavior under Compression

Composite metal foams (CMF) are renowned for their high strength‐to‐density ratio, high stiffness, and energy absorption capabilities. Homogenized finite element models of CMF have been numerically solved to understand the mechanical behavior of the material under a variety of external loading conditions. This work aims to pioneer a comprehensive finite element model for steel–steel composite metal foam by incorporating the interactions between embedded stainless‐steel hollow spheres with entrapped air inside stainless‐steel matrix. The material behavior of hollow spheres, surrounding matrix, and air are modeled using Johnson–Cook (JC) plasticity, Deshpande–Fleck (D–F) foam, and linear polynomial equation of state in LS DYNA. Further, the finite element model utilizes a combination of Lagrangian solid elements and meshfree smooth particles hydrodynamics with appropriate contacts to effectively model the interaction of entrapped air within stainless‐steel hollow spheres with surrounding metallic spheres and matrix. The strain rate and the crosshead velocity of 65 s−1 and 2.4765 m s−1 are used for quasistatic compression analysis. Finally, the results obtained from the computational model are compared and validated using previously reported experimental quasistatic compression data. The numerical model corroborates stress–strain response of CMF with 5.6% error for plateau stresses average within 25% and 30% strain.

Experimental and analytical study on the compressive behavior of PMI foam with different densities and cell sizes under intermediate strain rates

Polymethacrylimide (PMI) foam materials have great potential for applications in the field of protective energy absorption owing to their superior compressive properties. Existing studies on the mechanical behavior of PMI foams are limited, particularly for loading at intermediate strain rates. This paper presents a comprehensive experimental study of PMI foam with four different densities under quasi-static and intermediate strain rate compression (0.001 s−1 to 100 s−1). Each density included three different cell sizes to determine their effects on the compressive performance. Loads parallel and perpendicular to the foam rise direction were considered to investigate the anisotropic behavior. Intermediate strain rate tests were conducted using a high-speed hydraulic servo testing machine, which achieved a stable strain rate while ensuring consistent specimen sizes in both quasi-static and dynamic tests. In all the experiments, the compression process was captured using a high-speed camera and the macroscopic deformation mode and microscopic deformation mechanism were analyzed by combining Digital Image Correlation (DIC) and Scanning Electron Microscopy (SEM). The PMI foam with finer cell sizes exhibited an enhanced compression performance. As the strain rate increased, the strain rate effect became more evident in the high-density specimens and an increase in cell size diminished this effect. A modified analytical model incorporating the cell-size correction term was developed based on Gibson and Ashby's model. The modified model exhibited an average error of 4.9 % in the predicted plateau stress of PMI foam with different cell sizes at the same density.