Compressed Foam Research Articles

Beryllium–tungsten graded density inner shells in double shell capsules for improved hydrodynamic stability

The outer surface of the high-Z inner shell in the double shell configuration of inertial confinement fusion experiments experiences Rayleigh–Taylor instability growth during the implosion process due to inverted density and pressure gradients between a highly compressed foam interstitial layer and the accelerating dense inner shell. Graded density layers have long been known to reduce instability growth rates. In this study, we employ high-fidelity radiation hydrodynamic simulations to demonstrate this improved stability when grading beryllium into tungsten. We first characterize the response to L-band preheat of these layers using a newly calibrated radiation drive. While graded layer capsules suffer reduced performance (here, measured as DD neutron yield from a CD foam fuel) in 1D simulations due to reduced kinetic energy coupling and reduced fuel compression, they suffer less of a performance drop when 2D instabilities are accounted for. With the improved stability of graded layers, we explore the performance of capsules with larger fuel radii and thinner shells as a preliminary study to find new designs in which graded layers produce the highest yields.

DEVELOPMENT OF A TEST SAMPLE OF A SYSTEM FOR GENERATING AND SUPPLYING COMPRESSED AIR FOAM

An effective fire extinguishing agent for class A fires is the compressed air foam formed in Compressed Air Foam Systems (СAFS). Such systems have become widespread in leading countries such as the USA, Germany, China, and others. It is worth noting that the technical parameters of CAFS (intensity and consumption of an aqueous solution of foaming agent/air), implemented in the practice of fire extinguishing in the form of industrial samples, are designed and manufactured in such a way as to ensure effective extinguishing of developed fires of a significant area. When using existing samples for obtaining compression foam, a problem arises, which lies in the limited possibilities of regulating the supply of compression foam (intensity and consumption of the aqueous solution of the foaming agent/air), under which it is possible to use it with modified additives when extinguishing laboratory fires of solid combustible materials, and the lack of a smooth regulation of its supply. As a result of the research, the authors proposed a compressed air foam system to study its properties with the content of modified additives when changing the composition of the liquid and air that make it up. The manufactured system has the following parameters: multiplicity of 4–20, working pressure of systems of 4–8 bar, smooth adjustment of the consumption of aqueous solution/foaming agent of 2–20 l/min, and smooth adjustment of gas fraction consumption of 8–450 l/min. In particular, it is possible to adjust the consumption of the aqueous solution of the foaming agent and air, to work in dependant and autonomous mode, to regulate the intensity of the foam supply using nozzles of different diameters, and to change the porosity of the porous body in the foam generator. Further, we developed a system for measuring the flow of aqueous solution and air, which is a hardware and software complex. The system allows saving the measurement results to a PC in the form of an Excel spreadsheet for further development of dependencies and simultaneously displaying the flow rate of the aqueous foaming agent solution and air on the display screen and PC in real-time. Keywords: compressed air foam, class A fires, compressed air foam systems, modified additives.

Lightweight and compressible PANI/Ti3C2Tx/EVA composite foam for tunable microwave absorption

Dynamic deformation and absorbing regulation are still challenging for designing lightweight and high-efficiency microwave absorbing materials, which are of great indispensability to satisfy changeable and complex electromagnetic environments. Herein, a compressible composite foam with sea-island structure was prepared by loading porous polyaniline (PANI)/Ti3C2Tx composites on ethylene/vinyl acetate (EVA) skeleton via a thermally induced phase separation strategy. The composite foam exhibits a minimum reflection loss (RLmin) of −57.84 dB and an effective absorption bandwidth (EAB, RL ≤ −10 dB) of 1.86 GHz (8.2–10.05 GHz) at 3.4 mm. Notably, the microwave absorption (MA) performance can be precisely regulated by simply adjusting the compression ratio of composite foam. The RL peaks shift towards higher frequencies with increasing compression ratios, originating from changes in the internal conductive network. Even under 30 % compression strain, the composite foam still maintains RLmin of −21.53 dB and broadens EAB up to 2.71 GHz at 2.0 mm. This combination of compression capabilities and dynamically tunable MA performance may expand a novel approach to designing multifunctional polymer-based foam.

A comparative study of constitutive models for EPS foam under combined compression and shear impact loading for helmet applications

Virtual testing of helmets using finite element (FE) analysis can be a valuable tool during product development. Still, its usefulness is limited by the quality of the constitutive model of the energy-absorbing material, usually foam. Built-in constitutive models in commercial FE software are developed for traditional linear compression loading. However, modern oblique test methods load the foam in combined compression and shear. Therefore, we aim to evaluate to what extent built-in constitutive models in commercial FE software can represent Expanded Polystyrene (EPS) foam during combined compression and shear loading (CCSL). EPS foam is tested experimentally in a newly developed test rig for CCSL (V-test). The response is compared against the simulation using three different constitutive models available in LS-DYNA (M83, M126, and M181). The models are assessed by their ability to capture the correct response, focusing on how well the continuum models can capture the phenomenological events seen in the experiments. The results show that the models perform well in compression, as expected. However, we point out limitations in the shear response and significant limitations in the unloading response, both important for oblique helmet testing. Due to these limitations, we conclude that the existing models are inadequate for accurately simulating oblique helmet impacts. There is a clear need to develop and implement new constitutive models focused on capturing CCSL including the unloading. Additionally, frictional sliding was found to substantially influence the measured response in the V-test method. Minimizing interface sliding is therefore critical for isolating the material behavior.

Effect of the heat treatment on the compression of Cu20Sn matrix syntactic foams reinforced with Fe-hollow spheres

This work analyzes the manufacturing process, phase transformations and compression behavior of un-treated and heat-treated syntactic foams consisting of a Cu20Sn alloy matrix reinforced with Fe-hollow spheres. Manufacturing process included the infiltration of the molten alloy into preforms of spheres sintered at 1000 °C during 1 h, obtaining syntactic foams with porosities near 52 %. These foams were heat-treated at 750 °C for 1 h, followed by quenching in water, which led to phase transformations from ε to β. This fact improved the compressive properties of the foams, increasing compression strengths from 195 to 243 MPa. Interfaces were not found between matrix and the Fe-hollow spheres.

СРЕДСТВА ПОЛУЧЕНИЯ И ПЕРСПЕКТИВЫ ПРИМЕНЕНИЯ КОМПРЕССИОННОЙ ПЕНЫ В ПОЖАРОТУШЕНИИ

The subject of the article is modern fire extinguishing technologies based on compression foam. The purpose of the study is to study the means of obtaining and the prospects for using compression foam in fire fighting. Methods: analysis and synthesis, modeling. The results obtained indicate that compression foam has a number of advantages compared to water and conventional air-aspirated foam, so it can be used to extinguish fires in many industries and areas. A diagram of the production of compression foam is presented (the foam concentrate acts as a foaming agent) and a diagram of an autonomous installation for the production of compression foam. It is noted that one of the significant advantages of CAFS is the ability to create a finished product that matches a specific type of fuel or a specific situation. The characteristics of the SmartCAFS product have been defined. A typology of the use of compression foam depending on the type of incident is presented. The results of fire resistance tests of various foams are presented. It is concluded that fire suppression systems using compression foam have significant advantages, such as minimizing the spread of fire, the volume of water required to cover large areas, costs and placement, and the integration of CAFS with digital technologies.

Relation between Tensile Strut and Compressive Foam Deformation Behaviour: Failure Mechanisms and the Influence of Dendritic Versus Globular Grain Structure in an AlSi7Mg0.3 (A356) Precision‐Cast Open‐Cell Foam

Open‐cell aluminum foams are gaining importance for the design of lightweight structures and as electrodes in lithium‐ion batteries. AlSi7Mg0.3 foams were produced by a modified investment‐casting process. By tuning the mold temperature, a change from the usual nearly monocrystalline dendritic to a polycrystalline globular grain structure was achieved. Tension and compression tests on single struts and foam specimens, respectively, were combined with digital image correlation, scanning electron microscopy, and phase‐contrast enhanced micro‐computed tomography in a synchrotron facility to correlate the mechanical properties and the failure mechanisms with the microstructure. The “globular” foams exhibited a lower strength and a less pronounced subsequent stress drop than the “dendritic” foams, and the deformation mechanism changed from shear‐band dominated failure to a layer‐by‐layer collapse, because of the lower strength and higher ductility of the “globular” struts. The “dendritic” struts have a more homogeneous microstructure, while the “globular” struts often contain silicon agglomerates in their central region. Accordingly, the latter struts exhibit a higher degree of scatter for the fracture strain. Thus, the arrangement of the silicon particles and the eutectic determines the mechanical properties on the strut level and thereby the failure behavior on the foam level.This article is protected by copyright. All rights reserved.

Devising technology for extinguishing oil tanks using compressed foam by sub-layer technique

Tank facilities storing various combustible substances are a potential source of danger for the environment and human life. Fires in tanks can occur for various reasons: technical malfunctions, human factors, military operations, natural phenomena. One of the effective methods for extinguishing such fires is "sublayer" extinguishing with the help of foam of low multiplicity. The possibility of "sub-layer" extinguishing with the help of compression foam, which has unique properties, has been considered. The object of this study is the processes of stopping combustion during fire extinguishing in steel tanks for the storage of petroleum products with the use of foaming agents of increased stability, which ensure the generation of compression foam in a "sub-layer" way. A mathematical model of the movement of a submerged non-free jet of foam in the medium of motor fuel is given, which adequately describes the real physical processes that occur during "sublayer" quenching of vertical steel tanks. According to the research, it was established that the use of foam with a multiplicity of 10 (K10) is 1.56 times more effective in serving time than the use of foam with a multiplicity of 5 (K5). From an economic point of view, K10 foam also has greater advantages as the costs of the foaming agent during its generation are 3.1 times lower than when using K5 foam. The simulations demonstrated that the foaming agent consumption of the K10 foam is lower than the foaming agent consumption of the K5 foam and results in a different amount of foam coming to the surface. The simulations also showed that the volume of K5 foam increases proportionally with the feeding time, while the volume of K10 foam increases disproportionally and starts to decrease after half the time. The results from the implementation of the mathematical model were fully consistent with the results from experimental studies on extinguishing a model fire of class B

New Fire-Retardant Open-Cell Composite Polyurethane Foams Based on Triphenyl Phosphate and Natural Nanoscale Additives.

Despite the mechanical and physical properties of polyurethane foams (PUF), their application is still hindered by high inflammability. The elaboration of effective, low-cost, and environmentally friendly fire retardants remains a pressing issue that must be addressed. This work aims to show the feasibility of the successful application of natural nanomaterials, such as halloysite nanotubes and nanocellulose, as promising additives to the commercial halogen-free, fire-retardant triphenyl phosphate (TPP) to enhance the flame retardance of open-cell polyurethane foams. The nanocomposite foams were synthesized by in situ polymerization. Investigation of the mechanical properties of the nanocomposite PUF revealed that the nanoscale additives led to a notable decrease in the foam's compressibility. The obtained results of the flammability tests clearly indicate that there is a prominent synergetic effect between the fire-retardant and the natural nanoscale additives. The nanocomposite foams containing a mixture of TPP (10 and 20 parts per hundred polyol by weight) and either 10 wt.% of nanocellulose or 20 wt.% of halloysite demonstrated the lowest burning rate without dripping and were rated as HB materials according to UL 94 classification.

Enhanced Air-Flow Forced Convection Through Metal Foams: Contrasting Compressed and Uncompressed Foams

Abstract The influence of complex pore architecture, its characteristic length, and the contrast between compressed and uncompressed open-cell foam structures in forced convection are explored experimentally. Air-flow (Pr ∼ 0.71; 300 < Re < 10,000) data is presented and a critical issue of the appropriate definition of the hydraulic diameter, especially with foams of different pores/inch (ppi) and compressions, is addressed. Instead of the usual characterization, fin theory is applied and for this, the foam void volume structure is precision mapped by micro-CT scans. The veracity of defining the hydraulic diameter as 4× void volume divided by wetted area is supported by forced convection heat transfer results for different uncompressed and compressed metallic (aluminum) foam cores. All foams promote higher heat transfer coefficients, albeit accompanied with greater pressure drop. While the latter increases with foam ppi and compression (decreasing porosity), the former has a more complex interplay with these factors along with surface area changes and ligament fin effects. This scales with thermally effective surface area density βe (product of area density and overall fin effectiveness), and the overall convective-conductance of the foam (product of empty-duct-based heat transfer coefficient ho and βe) increases. The consequent enhancement, when evaluated by a modified volume goodness factor figure of merit, shows that the 40 ppi compressed foam (×3-in-x) performance is the highest (∼ 15–45 times an empty duct for the same fan power) with significant reduction in the volume of a heat exchanger.

Characterization of Magnetorheological Impact Foams in Compression.

This study focuses on the development and compressive characteristics of magnetorheological elastomeric foam (MREF) as an adaptive cushioning material designed to protect payloads from a broader spectrum of impact loads. The MREF exhibits softness and flexibility under light compressive loads and low strains, yet it becomes rigid in response to higher impact loads and elevated strains. The synthesis of MREF involved suspending micron-sized carbonyl Fe particles in an uncured silicone elastomeric foam. A catalyzed addition crosslinking reaction, facilitated by platinum compounds, was employed to create the rapidly setting silicone foam at room temperature, simplifying the synthesis process. Isotropic MREF samples with varying Fe particle volume fractions (0%, 2.5%, 5%, 7.5%, and 10%) were prepared to assess the effect of particle concentrations. Quasi-static and dynamic compressive stress tests on the MREF samples placed between two multipole flexible strip magnets were conducted using an Instron servo-hydraulic test machine. The tests provided measurements of magnetic field-sensitive compressive properties, including compression stress, energy absorption capability, complex modulus, and equivalent viscous damping. Furthermore, the experimental investigation also explored the influence of magnet placement directions (0° and 90°) on the compressive properties of the MREFs.

Comparison of two ablation procedures combined with high ligation and foam sclerotherapy and compression therapy for patients with venous leg ulcers

ABSTRACT Aim To compare the ablation techniques’ efficacy of endovenous microwave ablation (EMA) combined with high ligation (HL), foam sclerotherapy (FS) and compression therapy (CT) and endovenous laser ablation (EVLA) combined with HL-FS-CT in the treatment of VLUs. Method 301 consecutive patients with VLUs from 2013 to 2022 in a 3200-bed hospital were intervened by EMA combined with HL-FS-CT and EVLA combined with HL-FS-CT were retrospectively compared. Results One hundred thirty-four patients underwent EMA+HL-FS-CT and 167 patients underwent EVLA+HL-FS-CT. The primary outcome of the ulcer healing time was 1.45(0.75–1.5) months and 1.86(0.5–2.5) months, respectively, in the two groups (HR for ulcer healing was 1.26, 95% CI [0.96–1.66], p = 0.097). Secondary outcomes included that no significant difference was found in ulcer recurrence and GSV recanalization and complications between the two groups, and the postoperative VCSS and AVVQ were significantly lower than the baseline values in the respective groups (p = 0.0001). Conclusion EMA+HL-FS-CT and EVLA+HL-FS-CT are both effective at treating VLUs. Both of the two comprehensive treatments were beneficial to the healing of ulcers, but no evidence showed which one was superior in the ulcer healing time.

The mechanical behavior of epoxy resin foams and the numerical simulation based on phenomenological strain rate‐dependent constitutive model and cellular structure

AbstractEpoxy resin foams are lightweight materials commonly utilized as core materials in shipbuilding and aerospace applications. Mechanical properties and yielding behavior were the basis of the application of epoxy resin foams. In order to reveal the yield behavior and mechanical properties of epoxy resin foams. The compression and tension behavior of epoxy resin foams were investigated. The compression modulus and the tensile modulus increased with the strain rates and foams' density. Epoxy resin foams exhibited excellent toughness and the maximum elongation at break could reach 17.2%. The mechanical properties ( < 5%) of epoxy resin foams were successfully predicted through combining phenomenological strain rate‐dependent constitutive model for epoxy resin and cell structures. The yield point was represented through the elastic strain fraction. The compressive elastic strain fraction () was 0.908, and the tensile elastic strain fraction () was 0.884.

Study on the fire extinguishing effect of compressed nitrogen foam on 280 Ah lithium iron phosphate battery

This study conducted experimental analyses on a 280 Ah single lithium iron phosphate battery using an independently constructed experimental platform to assess the efficacy of compressed nitrogen foam in extinguishing lithium-ion battery fires. Based on theoretical analysis, the fire-extinguishing effects of compressed nitrogen foam at different outlet pressures from foam mixture tanks were analyzed, examining factors such as battery surface temperature, flame temperature, and thermal weight loss. The results indicate that the compressed nitrogen foam can extinguish the open flame of the battery in 14 s at 0.7 MPa, with the battery's surface temperature dropping by approximately 11 % before and after the application of the extinguishing agent. Compared with other commonly used extinguishing agents, the compressed nitrogen foam demonstrates superior extinguishing efficiency, but its cooling efficiency is somewhat lower. At pressures ranging from 0.4 to 0.6 MPa, the foam displays prolonged drainage time and sustained cooling effects, rendering it more suitable for lithium-ion battery fire scenarios. To address the issue of reduced cooling performance during later stages of fire suppression by compressed nitrogen foam, an intermittent injection approach has been proposed to effectively preserve its cooling efficacy.

Gamma Radiation-Mediated Synthesis of Antimicrobial Polyurethane Foam/Silver Nanoparticles.

Nosocomial infections represent a major threat within healthcare systems worldwide, underscoring the critical need for materials with antimicrobial properties. This study presents the development of polyurethane foam embedded with silver nanoparticles (PUF/AgNPs) using a rapid, eco-friendly, in situ radiochemical synthesis method. The nanocomposites were characterized by UV-vis and FTIR spectroscopy, scanning electron microscopy coupled with energy dispersive X-ray technique (SEM/EDX), differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), tensile and compression strengths, antimicrobial activity, and foam toxicity tests. The resulting PUF/AgNPs demonstrated prolonged stability (over 12 months) and good dispersion of AgNPs. Also, the samples presented higher levels of hardness compared to samples without AgNPs (deformation of 1682 µm for V1 vs. 4307 µm for V0, under a 5 N force), tensile and compression strength of 1.80 MPa and 0.34 Mpa, respectively. Importantly, they exhibited potent antimicrobial activity against a broad range of bacteria (including Pseudomonas aeruginosa, Staphylococcus aureus, Escherichia coli, and Enterococcus faecalis) and a fungal mixture (no fungal growth on the sample surface was observed after 28 days of exposure). Furthermore, these materials were non-toxic to human keratinocytes, which kept their specific morphology after 24 h of incubation, highlighting their potential for safe use in biomedical applications. We envision promising applications for PUF/AgNPs in hospital bed mattresses and antimicrobial mats, offering a practical strategy to reduce nosocomial infections and enhance patient safety within healthcare facilities.

High temperature and mesostructure effect on aluminum foam compression responses

Closed-cell Al foam is widely utilized in high-temperature environments due to its high strength-to-weight ratio and considerable energy absorption capability. However, the mechanical properties depend on temperature and mesostructure. In this paper, the compressive responses of Al foams at temperatures ranging from 25 ℃ to 600 ℃ are investigated by experimental tests and two types of high-fidelity finite element simulations, including the X-ray computed tomography (CT) reconstructed model and Voronoi model. A deep learning approach is employed to remove tiny pores of CT slices, simplifying geometry features and improving the computational efficiency of the CT reconstructed model. A novel improved Voronoi model with high accuracy is proposed, considering the nonuniform distribution of cell wall thickness in actual closed-cell Al foams. A temperature-depend macro constitutive model is established and validated through the experimental and numerical results. This work reveals the influence mechanism of temperature and mesostructure on the mechanical responses of Al foams, and exhibits significant potential for the application of Al foams in high temperature environment.

Tailorable Energy Absorbing Cellular Materials via Sintering of Dry Powder Printed Hollow Glass Microspheres

This article examines amorphous glass-based foams as lightweight core materials for crash-resistant structures that offer tailorable energy absorption capabilities. Hollow glass microspheres (HGMs) of different densities are layered using dry powder print- ing (DPP), an additive manufacturing process, and subsequently sintered to consolidate these microspheres into a cellular foam structure. The tuning of energy absorption is achieved in these foams by layering hollow microspheres with different densities and different thickness ratios of the layers. The mechanical response to quasi-static uniax- ial compression of the bilayer foams is also investigated. Bilayer samples a distinctive two-step stress-strain profile that includes first and second plateau stress, as opposed to a single constant density which does not. The strain at which the second plateau occurs can be tuned by adjusting the thickness ratio of the two layers. The resulting tailorable stress-strain profile demonstrates tailorable energy absorption. Tailorability is found to be more significant if the density values of each layer differ greatly. For comparison, bilayer samples are fabricated using epoxy at the interface instead of the co-sintering process. Epoxy-bonded samples show a different mechanical response from the co-sintered sample with a different stress-strain profile. Designing the bilayer foams enables tailoring of the stress-strain profile, so that energy-absorption requirements can be met for a specific impact condition. The implementation of these materials for energy absorption, crashworthiness, and buoyancy applications will be discussed.

Metallic Wood through Deep-Cell-Wall Metallization: Synthesis and Applications.

Metallic wood combines the unique structural benefits of wood and the properties of metals and is thus promising for applications ranging from heat transfer to electromagnetic shielding to energy conversion. However, achieving metallic wood with full use of wood structural benefits such as anisotropy and multiscale porosity is challenging. A key reason is the limited mass transfer in bulk wood where fibers have closed ends. In this work, programmed removal of cell-wall components (delignification and hemicellulose extraction) was introduced to improve the accessibility of cell walls and mass diffusion in wood. Subsequent low-temperature electroless Cu plating resulted in a uniform continuous Cu coating on the cell wall, and, furthermore, Cu nanoparticles (NPs) insertion into the wood cell wall. A novel Cu NPs-embedded multilayered cell-wall structure was created. The unique structure benefits compressible metal-composite foam, appealing for stress sensors, where the multilayered cell wall contributes to the compressibility and stability. The technology developed for wood metallization here could be transferred to other functionalizations aimed at reaching fine structure in bulk wood.

Analysis of fire extinguishing performance and mechanisms in transformer oil pool fires by large-scale compressed nitrogen foam: Impact of different nozzle pressures

This article investigates the suppression of transformer oil pool fires using compressed nitrogen aqueous film-forming foam extinguishing agents with varying nozzle pressures (0.1–0.4 MPa), and a comprehensive analysis of fire extinguishing behavior and resistance to re-ignition was conducted. The research findings indicate that at a nozzle pressure of 0.4 MPa, there is a significant enhancement in fire extinguishing efficiency, with a reduction in extinguishing time by 15.0%–29.2%, and an increase in resistance to re-ignition by 32.2%–48.2%, making it the optimal choice. In comparison to the 0.1 MPa condition, the maximum instantaneous emissions of CO and SO2 at 0.4 MPa are only 66.7%. The interaction of various effects, such as atomization, results in a significant enhancement of flame intensification and fire extinguishing effects when compressed nitrogen aqueous film-forming foam is sprayed at high nozzle pressures. The study provides valuable insights for firefighters in the practical use of foam extinguishing agents.

Solid Wood Modification toward Anisotropic Elastic and Insulative Foam-Like Materials.

The methods used to date to produce compressible wood foam by top-down approaches generally involve the removal of lignin and hemicelluloses. Herein, we introduce a route to convert solid wood into a super elastic and insulative foam-like material. The process uses sequential oxidation and reduction with partial removal of lignin but high hemicellulose retention (process yield of 72.8%), revealing fibril nanostructures from the wood's cell walls. The elasticity of the material is shown to result from a lamellar structure, which provides reversible shape recovery along the transverse direction at compression strains of up to 60% with no significant axial deformation. The compressibility is readily modulated by the oxidation degree, which changes the crystallinity and mobility of the solid phase around the lumina. The performance of the highly resilient foam-like material is also ascribed to the amorphization of cellulosic fibrils, confirmed by experimental and computational (molecular dynamics) methods that highlight the role of secondary interactions. The foam-like wood is optionally hydrophobized by chemical vapor deposition of short-chained organosilanes, which also provides flame retardancy. Overall, we introduce a foam-like material derived from wood based on multifunctional nanostructures (anisotropically compressible, thermally insulative, hydrophobic, and flame retardant) that are relevant to cushioning, protection, and packaging.