Foam Density Research Articles

Analysis of energy absorption characteristics of a sinusoidal corrugated filled tube

In this paper, a sinusoidal corrugated filled tube (SCFT) is proposed by filling aluminum foam into a sinusoidal corrugated tube, the finite element model is established using the finite element software Pro/Engineer and Abaqus/Explicit, and the accuracy of the finite element model is verified. Crashworthiness studies under axial impact show that SCFT has better energy absorption (EA) performance than a circular filled tube (CFT) under the same outer tube wall thickness conditions, and the EA and specific EA of SCFT are 1.16 times and 1.12 times that of CFT, respectively; in addition, SCFT has a better interaction effect than CFT under the same outer tube wall thickness. Subsequently, a parametric study of SCFT by amplitude, wavenumber, outer tube wall thickness and aluminum foam density was systematically carried out. The structure studied in this paper can provide a reference for the innovative structural design of filled tubes.

Water-Glass-Assisted Foaming in Foamed Glass Production

The energy efficiency of buildings can be greatly improved by decreasing the energy embodied in installed materials. In this contribution, we investigated the possibility of foaming waste bottle glass in the air atmosphere with the addition of water glass, which would reduce the energy used in the production of foamed glass boards. The results show that with the increased addition of water glass, the crystallinity and the thermal conductivity decrease, however, the remaining crystal content prevents the formation of closed-porous foams. The added water glass only partly protects the carbon from premature oxidation, and the foaming mechanism in the air is different than in the argon atmosphere. The lowest obtained foam density in the air atmosphere is 123 kg m−3, while the lowest thermal conductivity is 53 mW m−1 K−1, with an open porosity of 50% for the sample obtained in the air, containing 12 wt% of water glass, 2 wt% of B2O3, 2 wt% AlPO4 and 2 wt% K3PO4.

Free vibration properties of beetle elytron plate: Composite material, stacked structure and boundary conditions

Beetle elytron plate (BEP), which is derived from the bionics of Trypoxylus dichotomus's elytra, is a typical lightweight and high-strength structure with superior and comprehensive mechanical properties. To promote the engineering application of BEPs, this paper explores the vibration characteristics of foam-filled fiber composite BEPs. Through the finite element method (FEM), structural parameters such as the length-to-width ratio, core height-to-thickness ratio, skin thickness and foam density influence the natural frequency and mode. Furthermore, the influence pattern of parameters (such as boundary conditions and the number of stacked layers) toward the first two orders of natural frequencies and modes of the BEP were investigated under controlled total height and controlled single layer height. The results indicate that 1) the ranking of structural parameters on the 1st order frequency from a strong to weak sequence is as follows: length-to-width ratio, core height-to-thickness ratio, foam density and skin thickness; for the 2nd order natural frequency: length-to-width ratio, skin thickness, foam density and core height-to-thickness ratio. 2) Generally, an increase in the length-to-width ratio will reduce the frequency of the BEP, and increases in the core height-to-thickness ratio and skin thickness will raise its frequency. Additionally, foam filling plays a decisive role in local deformation. 3) When the total height of the sandwich plate is controlled, the improvement of the boundary conditions can effectively boost its 2nd-order frequency (approximately 200%), but the 1st-order frequency can be significantly increased (approximately 140%) only when all four sides are improved. 4) In the case of controlling the height of the single layer of the sandwich plate, its frequency gradually increases with the increase in the number of stacked layers. However, when the constraints are weak or there are few stacked layers, increasing the number of stacked layers can effectively boost the vibration frequency. This paper provides references and suggestions for the design and application of sandwich structures, enriching the research on the mechanical properties of BEPs and establishing groundwork for promoting BEPs in engineering practices.

Stress wave propagation and force transmission in polymeric closed cell foams subjected to air shock loading

Polymeric foams are widely used in sandwich structures to withstand blast loadings, serving as energy dissipators and force attenuators. This study explores the mechanics involved when an air shock interacts with closed-cell polymeric foam. The authors provide a comprehensive analysis of stress wave propagation and its evolution across the foam specimen by employing ultra-high-speed imaging and digital image correlation (DIC). Measurement of elastic, plastic, and shock wave velocities inside the impacted foam was conducted. A methodology to predict elastic precursor wave velocity is proposed, that considers the foam material’s behavior at higher strain rates. The predicted values were found to be in excellent agreement with the experimentally obtained values. Furthermore, the authors investigate the force transmission through foams as a function of bulk foam density under unconfined conditions. The results reveal that under shock loading intensities where foam specimens remained in their elastic regime, a transmitted force amplification was observed relative to the input load. However, when subjected to higher-intensity shock loading, substantial foam deformation occurs during the initial propagation of the shock wave. In these cases, the transmitted force measured was found to rely on the plastic and shock waves generated within the material. Additionally, as the loading persists, the force transmissibility ratio decreases beyond the initial stress wave propagation phase, thus demonstrating the material’s suitability for blast mitigation applications.

Characteristics of Components and Density of Rigid Nanoclay-Filled Medium-Density Polyurethane Foams Produced in a Sealed Mould.

The characteristics of rigid, nanoclay-filled, medium-density NEOpolyol-380 polyurethane foams components can be estimated when two conditions are met: (1) the foam blocks are produced in a sealed mould; and (2) the mass of the reacting mixture is kept constant. It was shown that, with an increase in filler concentration, the total mass of the filled polymeric network stays constant, but the total volume reduces; the higher the ratio of density of the exfoliated nanoclay platelets and polymer, the higher the volume reduction of the polymeric network. Experimental data of polyurethane foam block mass were acquired at concentrations η = 0%, 0.25%, 0.5%, 1%, 2%, 3% and 5% from the mass of a filled reacting mixture. Foam-density dependence in the uniform zone and in the side-sections of the produced blocks on the: (1) mass of the blocks; and (2) the concentration of the filler was analysed. The study demonstrated that the correlation of the specimens' density with the foam block mass is much higher than that of the filler concentration.

Enhanced sensing performance of EVA/LDPE/MWCNT piezoresistive foam sensor for long-term pressure monitoring

Conductive polymer composites (CPCs) with piezoresistive properties are smart detecting systems with high sensitivity, fast response, and low energy consumption. To enhance their sensitivity and cope with their high filler content requirements, solid CPCs are normally transformed into blends and foams, which reduces the elastic modulus, enabling larger deformations, wider detection range, and increased sensitivity. However, providing reversible and durable sensing properties remains challenging as it depends on the phase morphology, foam cell structure, and particle dispersion. To this end, we use multi-walled carbon nanotube (MWCNT) as a conductive filler with a high aspect ratio and develop CNT-filled ethylene vinyl acetate/low-density polyethylene (EVA/LDPE) blend foams. We fix the foam structure using chemical foaming and crosslinking agents in a compression molding process. To optimize the piezoresistive behavior, we follow a step-wise tuning approach, studying the blending morphology, the foaming attributes, the particle dispersion and affinity, thereby selecting the most promising formulations for further investigations. The least mechanical and electrical hysteresis is obtained at minimum foam density, which is obtained at a compromised crystallinity and crosslinking density. The higher affinity of MWCNT to EVA and the faster crosslinking of the EVA phase results in uniformly dispersed small cells at EVA-rich formulations and 4 phr MWCNT content. The final foam sensor demonstrates an impressive response and recovery times of less than 200 ms and remarkable durability thanks to the optimized cell morphology and mechanical properties. These findings expand the application of carbon-filled polyolefin foams in pressure monitoring, particularly in wearable sensors for strain and motion sensing.

Application of titanium dioxide as a filler to regulate the properties of epoxy-novolak foams

The influence of titanium dioxide filler on the physical, mechanical and dielectric properties of epoxy-novolac foams of the PEN-I brand has been studied. The dependences of the apparent density, thermomechanical characteristics, and water absorption of structural foams depending on the filler content are analyzed. It is established that by introducing dispersed additives, it is possible to regulate the dielectric constant within specified limits and with high accuracy.

Thermal Management of Microelectronic Devices Using Nanofluid with Metal foam Heat Sink.

Microelectronic components are used in a variety of applications that range from processing units to smart devices. These components are prone to malfunctions at high temperatures exceeding 373 K in the form of heat dissipation. To resolve this issue, in microelectronic components, a cooling system is required. This issue can be better dealt with by using a combination of metal foam, heat sinks, and nanofluids. This study investigates the effect of using a rectangular-finned heat sink integrated with metal foam between the fins, and different water-based nanofluids as the working fluid for cooling purposes. A 3D numerical model of the metal foam with a BCC-unit cell structure is used. Various parameters are analyzed: temperature, pressure drop, overall heat transfer coefficient, Nusselt number, and flow rate. Fluid flows through the metal foam in a turbulent flow with a Reynold's number ranging from 2100 to 6500. The optimum fin height, thickness, spacing, and base thickness for the heat sink are analyzed, and for the metal foam, the material, porosity, and pore density are investigated. In addition, the volume fraction, nanoparticle material, and flow rate for the nanofluid is obtained. The results showed that the use of metal foam enhanced the thermal performance of the heat sink, and nanofluids provided better thermal management than pure water. For both cases, a higher Nusselt number, overall heat transfer coefficient, and better temperature reduction is achieved. CuO nanofluid and high-porosity low-pore-density metal foam provided the optimum results, namely a base temperature of 314 K, compared to 341 K, with a pressure drop of 130 Pa. A trade-off was achieved between the temperature reduction and pumping power, as higher concentrations of nanofluid provided better thermal management and resulted in a large pressure drop.

Engineering novel phenolic foams with lignin extracted from pine wood residues via a new levulinic-acid assisted process

Phenolic foams are typically produced from phenolic resins, using phenol and formaldehyde precursors. Therefore, common phenolic foams are non-sustainable, comprising growing environmental, health, and economic concerns. In this work, lignin extracted from pine wood residues using a “green” levulinic acid-based solvent, was used to partially substitute non-sustainable phenol. The novel engineered foams were systematically compared to foams composed of different types of commercially available technical lignins. Different features were analyzed, such as foam density, microstructure (electron microscopy), surface hydrophilicity (contact angle), chemical grafting (infrared spectroscopy) and mechanical and thermal features. Overall, it was observed that up to 30 wt% of phenol can be substituted by the new type of lignin, without compromising the foam properties. This work provides a new insights on the development of novel lignin-based foams as a very promising sustainable and renewable alternative to petrol-based counterparts.

Investigation of cellulose filaments as filler in rigid insulating polyurethane foam

Cellulose is a biopolymer that has broad potential applications including in building insulation, and it was studied for its potential as a filler material. A closed-cell polyurethane foam insulation formulation was developed, and cellulose filaments (CFs) were introduced at varying percentages. The viscosity and morphology of the formulations were studied, as were different foam properties, such as water vapor permeability, reaction kinetics, density, porosity, thermal conductivity, and compressive strength foams as a function of cellulose filaments content. A commercial foam was also tested as a reference. The cellulose filaments impacted the formulations’ viscosity, and all the properties of the resulting insulating material. For example, samples containing 5% of cellulose filaments were found to perform differently than samples containing 0%, 1% and 2.5% mainly due to agglomerate formation, which impacted cell size (about 0.1 mm2 at 0%, 1% and 2.5% versus a mean of over 0.4 mm2 at 5%), and differential vapor sorption (with a mass change of 2%wt at 0 parts per hundred of polyol versus 2.5%wt at 5% from 0% to 95% relative humidity). However, the required performances by the standards of polyurethane foam insulation material were always fulfilled regardless of the amount of cellulose filaments present.

Perspective: The unexplored dimensions behind the foam formation in River Yamuna, India.

For nearly two years, a persistent foam cover has been observed during the post-monsoon season in the Yamuna River beneath the barrage near Okhla in Delhi, India. This affair has been a matter of public concern now, after the gigantic appearance of foam in November 2021, as the visibility of foam has awakened people's environmental 'conscience' over the 'concealed' chemical pollution. The mechanisms of agents responsible for foaming in rivers, particularly surfactants and phosphates, have received wide attention in the dynamic community of river pollution. Many studies in the past, around the globe, have evidently provided different rationales behind the dense foam formation in rivers, yet the Concerned Govt. Authorities have highlighted the cause of foam formation in the river Yamuna is associated with the presence of detergents and phosphates as foaming agents. Despite this, an aperture with copious unaccounted factors or underlying agents still exists to rationalize the foam formation and persistence. In this article, we outline these unaccounted factors which might be responsible for the foam formation and stabilization and give indications for future research directives towards the emergence of studies regarding the dense foam formation in river Yamuna.

Conversion of Polypropylene (PP) Foams into Auxetic Metamaterials

In this work, a simple and environmentally friendly process combining low pressure (vacuum) and mechanical compression is proposed to convert recycled polypropylene (PP) foams (28 kg/m3) into low density foams (90–131 kg/m3) having negative tensile and compressive Poisson’s ratios (NPR). The main objective of the work was to determine the effect of processing conditions (vacuum time, temperature and mechanical pressure). Based on the optimized conditions, the tensile Poisson’s ratio of the resulting auxetic foams reached −1.50, while the minimum compressive Poisson’s ratio was −0.32 for the same sample. The foam structure was characterized via morphological analysis (SEM) to determine any changes related to the treatment applied. Finally, the tensile and compressive properties (Young’s modulus, strain energy, energy dissipation and damping capacity) are also presented and discussed. It was observed that the mechanical properties of the resulting auxetic foams were improved compared to the original PP foam (PP-O) for all tensile properties in terms of modulus (19.9 to 59.8 kPa), strength (0.298 to 1.43 kPa) elongation at break (28 to 77%), energy dissipation (14.4 to 56.3 mJ/cm3) and damping capacity (12 to 19%). Nevertheless, improvements were also observed under compression in terms of the energy dissipation (1.6 to 3.6 mJ/cm3) and the damping capacity (13 to 19%). These auxetic foams can find applications in sport and military protective equipment, as well as any energy mitigation system.

Nano-composite semi-flexible polyurethane foams containing montmorillonite intercalated/exfoliated in situ during the synthesis of the intermediate polyester-polyols obtained from PET wastes

Low-cost nano-composite semi-flexible polyurethane foams with improved thermal and mechanical features were obtained using a cost-saving and environmentally friendly preparation process of an intermediate composite, obtained from polyethyleneterephthalate (PET) wastes, depolymerization/chemical modification agents from renewable resources and unmodified natural montmorillonite. The process implies tailoring the polyester-polyols chemical structure/ composition and using specific catalysts, aiming to intercalate the montmorillonite layers during the synthesis reactions, while maintaining the appropriate properties of the products required for the preparation of polyurethane semi-flexible foams, thus avoiding conventional treatments of the nanofiller, involving the use of solvents, additional energy consumption by heating and stirring, as well as longer processing time. The polyester-polyols composites and the polyurethane semi-flexible foams obtained therefrom were investigated by specific analytical methods. In this regard, the foams showed an improvement of the thermal stability, and values of Young’s moduli and compression strengths about double or higher, compared to conventional semi-flexible polyurethane foams of same density. The potential applications of such foams target shock wave damping sandwich systems for marine structures.

ACOUSTIC PROPERTIES OF HIGHLY ELASTIC POLYURETHANE FOAM VAPEN HR 3744

Within this research, testing of the acoustic properties of polyurethane foam samples was conducted. The measurement of the absorption coefficient was performed using the transfer function method in an impedance tube, according to the SRPS EN ISO 10534-2:2008 standard. The tested samples represent highly elastic polyurethane foam of low density, with sample thickness ranging from 10 mm to 100 mm. The research results indicate the potential application of polyurethane foam in areas that require efficient sound insulation or noise control, particularly in the mid-frequency range. Therefore, polyurethane foam can be considered an excellent material with acoustic properties that exceed expectations within the given frequency range.

Carbon composite foams from the wasted banana leaf for EMI shielding and thermal insulation

Low-density fire-resistant materials with high EMI shielding effectiveness and low thermal conductivity are extremely important in aerospace and defence applications. Utilization of agricultural residues for achieving this reduces CO2 emission as well as produces wealth for the farmers. Herein, a fibre extracted from the wasted matured banana leaf by a simple chopping and grinding using a mixture-grinder is used for the preparation of carbon composite foams. The banana leaf fibres dispersed in sucrose solution are consolidated by filter-pressing followed by freeze drying to produce banana leaf fibre-sucrose composites. The carbon produced from sucrose during carbonization binds the carbonized banana leaf fibre to produce the carbon composite foams. The XRD pattern and Raman analysis indicated the turbostratic nature of the carbon, and XPS analysis shows the presence of oxygen-containing functional groups. The textural property measurement and TEM analysis indicated the presence of micro and meso pores in the carbon composite foams. The foam density (0.14–0.28 g cm−3), compressive strength (0.14–0.88 MPa), electrical conductivity (3.7–8.7 S m−1), and thermal conductivity (0.095–0.144 W m-1 K−1) of the carbon composite foams increases with an increase in sucrose solution concentration (300–700 g L−1). The carbon composite foams exhibit a reflection-dominated EMI shielding with high total shielding effectiveness in the range of 48.3–77.5 dB. The multiple internal reflections within a range of macropores available in the carbon composite foams, leading to enhanced absorption, are responsible for the excellent EMI shielding characteristics.

Biomechanical Performance of a Novel Implant Design in Simulated Extraction Sites and Sinuslift Procedures

With increasing experience and in an attempt to shorten overall treatment times, implant placement in combination with tooth extractions and sinus lift procedures has become popular. In both cases, primary stability has to be achieved by either engaging apical and oral regions of trabecular bone or by engaging residual host bone beneath the sinus cavity. Extraction sites were formed by pressing a root analog into homogeneous low density polyurethane foam which was used as bone surrogate while a 3 mm thick sheet of medium density foam was used for mimicking a sinus lift situation. Two types (n = 10) of bone level implants with a conventional tapered design and a cervical back taper (NobelActive; control) and a novel design characterized by a shift in core diameter and thread geometry (AlfaGate; test) were placed in these models following conventional osteotomy preparation. Insertion torque was measured using a surgical motor and primary stability was determined by resonance frequency analysis. Statistical analysis was based on Welch two sample t tests with the level of significance set at α = 0.05. In sinuslifting, NobelActive implants required significantly higher insertion torques as compared to AlfaGate (p = 0.000) but did not achieve greater implant stability (p = 0.076). In extraction sites, AlfaGate implants showed both, significantly higher insertion torques (p = 0.004) and significantly greater implant stability (p = 0.000). The novel implant design allowed for greater primary stability when being placed in simulated extraction sockets and sinuslift situations. While in extraction sockets the position of condensing threads in combination with an increase in core diameter is beneficial, the deep cervical threads of the novel implant lead to superior performance in sinuslift situations.

Study on the foaming behavior of density‐controllable epoxy resin composite foam under negative pressure environment

AbstractThe incomplete decomposition of foaming agent and tedious process during the preparation of epoxy resin composite foam (ERCF) will reduce the mechanical properties and lead to more complex production. Therefore, in this study, a new and simple negative pressure foaming method was designed innovatively to prepare ERCF under negative pressure using strong gas adsorption capacity of inorganically modified calcium silicate (MCS) particles as air carriers instead of foaming agent, and the density and expansion ratio of ERCF could be precisely controlled by adjusting the negative pressure value in a vacuum oven. The results showed that the density of ERCF could reach a very low value of 0.056 g/cm3 at 15 wt% MCS content with decreased negative pressure, but the negative pressure decreases would damage the quality of cells. At the same time, it was found that a rapid rise in the viscosity of the epoxy composite material system under negative pressure of −0.080 MPa owing to the increase in MCS content, when the MCS content was higher than 15 wt%, the MCS dispersion was reduced, leading to a decrease in the quality of the cells. In addition, the ERCF products prepared by the negative pressure foaming method in this study could be easily molded and possessed a better compressive strength among epoxy foams of similar density.

Performance of foam-filled kirigami corrugated sandwich panels as sacrificial cladding against blast loads

In this study, the blast mitigation performance of kirigami corrugated (KC) panels filled with polyurethane foam as sacrificial cladding was investigated. Firstly, the effect of filling polyurethane (PU) foam on the energy absorption capacity and deformation mode of KC units was investigated by quasi-static compression. Numerical model was then built and validated. Following this, blast simulations were conducted to investigate the protective effectiveness of the aluminum foam panel, KC panel, and foam-filled KC panel as cladding for comparison. The blast loading effects on the structure without protection were also calculated and compared with different types of cladding. The key evaluating parameters, including peak transmitted load to the protected structure, energy absorption, and the crushed depth of the front plate, were used to evaluate the mitigation performance under various blast loads. The numerical results demonstrated the superior mitigating performance of foam-filled KC sandwich structures under various blast loading scenarios. The proposed foam-filled KC panel shows a higher energy absorption capacity than aluminum foam panels. The foam-filled KC panels with various densities of PU foam under different blast loads were also conducted to investigate its influence on blast mitigation performance. It was found that the second peak in the transmitted load can be reduced for KC panels with a higher density of the foam, as it leads to higher energy absorption capacity and later densification of the core against blast loads.

An Experimental Investigation of the Mechanical Performance of EPS Foam Core Sandwich Composites Used in Surfboard Design.

Surfboard manufacturing has begun to utilise Expanded Polystyrene as a core material; however, surf literature relatively ignores this material. This manuscript investigates the mechanical behaviour of Expanded Polystyrene (EPS) sandwich composites. An epoxy resin matrix was used to manufacture ten sandwich-structured composite panels with varying fabric reinforcements (carbon fibre, glass fibre, PET) and two foam densities. The flexural, shear, fracture, and tensile properties were subsequently compared. Under common flexural loading, all composites failed via compression of the core, which is known in surfing terms as creasing. However, crack propagation tests indicated a sudden brittle failure in the E-glass and carbon fibre facings and progressive plastic deformation for the recycled polyethylene terephthalate facings. Testing showed that higher foam density increased the flex and fracture mechanical properties of composites. Overall, the plain weave carbon fibre presented the highest strength composite facing, while the single layer of E-glass was the lowest strength composite. Interestingly, the double-bias weave carbon fibre with a lower-density foam core presented similar stiffness behaviour to standard E-glass surfboard materials. The double-biased carbon also improved the flexural strength (+17%), material toughness (+107%), and fracture toughness (+156%) of the composite compared to E-glass. These findings indicate surfboard manufacturers can utilise this carbon weave pattern to produce surfboards with equal flex behaviour, lower weight and improved resistance to damage in regular loading.

Study on Preparation and Performance of Foamed Lightweight Soil Grouting Material for Goaf Treatment.

The harm goafs and other underground cavities cause to roads, which could lead to secondary geological hazards, has attracted increased attention. This study focuses on developing and evaluating the effectiveness of foamed lightweight soil grouting material for goaf treatment. The study examines the foam stability of different foaming agent dilution ratios by analyzing foam density, foaming ratio, settlement distance, and bleeding volume. The results show that there is no significant variation in foam settlement distance for different dilution ratios, and the difference in foaming ratio does not exceed 0.4 times. However, the bleeding volume is positively correlated with the dilution ratio of the foaming agent. At a dilution ratio of 60×, the bleeding volume is about 1.5 times greater than that at 40×, which reduces foam stability. Furthermore, an appropriate amount of sodium dodecyl benzene sulfonate improves both the foaming ability of the foaming agent and the stability of the foam. Additionally, this study investigates how the water-solid ratio affects the basic physical properties, water absorption, and stability of foamed lightweight soil. Foamed lightweight soil with target volumetric weights of 6.0 kN/m3 and 7.0 kN/m3 meet the flow value requirement of 170~190 mm when the water-solid ratio ranges are set at 1:1.6~1:1.9 and 1:1.9~1:2.0, respectively. With an increasing proportion of solids in the water-solid ratio, the unconfined compressive strength initially increases and then decreases after 7 and 28 days, reaching its maximum value when the water-solid ratio is between 1:1.7 and 1:1.8. The values of unconfined compressive strength at 28 days are approximately 1.5-2 times higher than those at 7 days. When the water ratio is excessively high, the water absorption rate of foamed lightweight soil increases, resulting in the formation of connected pores inside the material. Therefore, the water-solid ratio should not be set at 1:1.6. During the dry-wet cycle test, the unconfined compressive strength of foamed lightweight soil decreases, but the rate of strength loss is relatively low. The prepared foamed lightweight soil meets the durability requirements during dry-wet cycles. The outcomes of this study may aid the development of enhanced approaches for goaf treatment using foamed lightweight soil grout material.