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The primary aim of this project is to develop ultra‐high expansion and quick‐setting foams using poly (ethyl cyanoacrylate), poly (butyl cyanoacrylate), and poly (co‐ethyl‐butyl) cyanoacrylate. To achieve this, poly cyanoacrylate foams were created under various conditions, utilizing different monomers, initiators, foaming agents/solvents, and compositions. Several properties of the foams were assessed, including formation and expansion rates, mechanical strength, moisture absorption, thermal resistance, density, and morphology. The findings indicated that, under optimal conditions, the foams made from poly (ethyl cyanoacrylate), poly (butyl cyanoacrylate), and a copolymer of poly (ethyl cyanoacrylate‐co‐butyl cyanoacrylate) exhibited fast expansion times of approximately 0.9, 2, and 1.5 s, respectively. These foams demonstrated an average volume increase of about 35 times, 45 times, and 36 times compared to the raw materials. The average compressive strengths recorded were 6, 3, and 4 kg/cm2, while the average water absorption rates were 5%, 20%, and 7%, respectively. [ABSTRACT FROM AUTHOR]

Anisotropy in naturally occurring or synthetic microcellular structures is an important feature for the development of materials with high specific stiffness and strength, in addition to creating materials with unique physical properties. Polymeric foams constitute a broad class of materials that are widely used for their advantages of low density, high specific mechanical properties and high insulative properties. Traditional synthetic routes are slow, energy demanding processes that employ the use of high temperature ovens, freezers, or high‐pressure equipment. Herein we present a convenient and energy efficient method to produce anisotropic high performance polymeric foams via rapid radically induced cationic frontal polymerization coupled with chemical blowing agents. The degree of pore orientation and degree of anisotropy are a result of the propagating front working in concert with the foam volume expansion. This paper presents results into FP foam formation to illustrate how changes in boundary conditions and front initiation position affect both the microcellular structure and their resulting physical and mechanical properties. Additionally, results are presented to show how changes in resin formulation, such as the addition of nanoparticles affect both properties as well as the microcellular structure and anisotropy. [ABSTRACT FROM AUTHOR]

In conventional foams, anisotropy within the microcellular structure can only be achieved through confinement in one or more directions during the foaming process. Herein, we present a novel, versatile, and energy efficient method to create unique high‐performance foams where the anisotropy of the microcellular and the microcellular structure itself is not dictated by external confinement during the foaming process. To generate such foams, an initial crosslinked gel is first created where the crosslink density of the gel can be tuned by UV intensity and cure time. Next, the gel can be foamed while simultaneously creating a second network via radically induced cationic frontal polymerization (RICFP). In this case, the anisotropy in the foam is dictated by propagation front during the RICFP and the microcellular morphology and cell surface area are dictated by the crosslink density of the gel. These two unique qualities lead to rigid foams that can be generated from a gel without the need for confinement where the microcellular size and shape can be tuned by the crosslink density of the gel precursor. A one‐pot liquid system composed of miscible epoxies, acrylates, and chemical blowing agents (CBAs), allows for control over the foam physical, mechanical, and thermal properties with glass transition temperatures ranging from 74.7 to 125.8°C. Additionally, by patterning the crosslink density of the initial gel through controlled exposure of UV, complex microcellular structures can be formed that are not possible in conventional foaming processes. This positions gel frontal polymerization and foaming as an advanced technique to produce high performing anisotropic foams with a wide array of tunable physical, mechanical, and thermal properties. [ABSTRACT FROM AUTHOR]

The adoption of Nature‐inspired strategies to improve materials has fostered the introduction of cavities. But how to mass‐produce structures in which a complex architecture of cavities is point‐to‐point fine‐tuned to the local and global application requirements? To this aim, the use of a procedure based on topology optimization and gas foaming is herein reported. As an example case, a polymeric foamed beam whose density map is optimized in 3D for three‐point bending is designed and produced by gas foaming a purpose‐designed preform. The preform is produced with polypropylene and by a high pressure autoclave with CO2 as blowing agent. Optical and scanning electron microscopy as well as X‐ray microscopy are used to analyze the 3D optimized foamed structures and show the effectiveness of the foaming design protocol in producing the finite element method‐optimized structures. A remarkable twofold increase in the stiffness of the optimized structures is measured with respect to that of the uniformly foamed counterpart with equal overall mass. With the use of a single recyclable material in a single processing step, this method allows one to conceive the mass production of optimized, therefore more sustainable, plastic parts. [ABSTRACT FROM AUTHOR]

Polymer-based (nano)composite foams containing conductive (nano)fillers limit electromagnetic interference (EMI) pollution, and have been shown to act as good shielding materials in electronic devices. However, due to their high (micro)structural complexity, there is still a great deal to learn about the shielding mechanisms in these materials; understanding this is necessary to study the relationship between the properties of the microstructure and the porous structure, especially their EMI shielding efficiency (EMI SE). Targeting and controlling the electrical conductivity through a controlled distribution of conductive nanofillers are two of the main objectives when combining foaming with the addition of nanofillers; to achieve this, both single or combined nanofillers (nanohybrids) are used (as there is a direct relationship between electrical conductivity and EMI SE), as are the main shielding mechanisms working on the foams (which are expected to be absorption-dominated). The present review considers the most significant developments over the last three years concerning polymer-based foams containing conductive nanofillers, especially carbon-based nanofillers, as well as other porous structures created using new technologies such as 3D printing for EMI shielding applications. It starts by detailing the microcellular foaming strategy, which develops polymer foams with enhanced EMI shielding, and it particularly focuses on technologies using supercritical CO2 (sCO2). It also notes the use of polymer foams as templates to prepare carbon foams with high EMI shielding performances for high temperature applications, as well as a recent strategy which combines different functional (nano)fillers to create nanohybrids. This review also explains the control and selective distribution of the nanofillers, which favor an effective conductive network formation, which thus promotes the enhancement of the EMI SE. The recent use of computational approaches to tailor the EMI shielding properties are given, as are new possibilities for creating components with varied porous structures using the abovementioned materials and 3D printing. Finally, future perspectives are discussed. [ABSTRACT FROM AUTHOR]

Polyurethane foam (PUF)'s porous structure, light weight, flexibility, and low‐cost properties make it useful in various cutting‐edge technologies. However, time‐consuming, costly, and complicated surface modification methods severely hinder its commercial applications. Herein, an ultrafast, simple, and cost‐effective surface modification method based on the evaporation of a low boiling point solvent to prepare a multifunctional graphene nanoplatelet (GNP)‐decorated PUF (GNP@PUF) is proposed. Due to the passive heat barrier of GNP sheets, the resulting sponge exhibits excellent flame retardancy by reducing the critical fire retardancy metrics, that is, peak heat release rate, total heat release, and total smoke release by 72%, 50%, and 81%, respectively. In addition, GNP@PUF can function as a piezoresistive sensor and electromagnetic interference (EMI)‐shielding material. As a piezoresistive sensor, it exhibits a wide‐compressive pressure (2.4–112 kPa)/strain (5–70%) range and ultra‐fast response/relaxation time (48/35 ms), wide‐stretching strain (5–100%) range, and it can detect minute human motions by being attached to different parts of the human body. Meanwhile, the composite foam displays good absorption‐dominant EMI shielding performance (≈38 dB), possibly due to conductive dissipation and multiple reflections/scattering of EM waves inside the 3D conductive graphene network. This study provides a simple coating technique for developing multifunctional lightweight foam materials. [ABSTRACT FROM AUTHOR]

Abstract Polyurethane foam (PUF)’s porous structure, light weight, flexibility, and low‐cost properties make it useful in various cutting‐edge technologies. However, time‐consuming, costly, and complicated surface modification methods severely hinder its commercial applications. Herein, an ultrafast, simple, and cost‐effective surface modification method based on the evaporation of a low boiling point solvent to prepare a multifunctional graphene nanoplatelet (GNP)‐decorated PUF (GNP@PUF) is proposed. Due to the passive heat barrier of GNP sheets, the resulting sponge exhibits excellent flame retardancy by reducing the critical fire retardancy metrics, that is, peak heat release rate, total heat release, and total smoke release by 72%, 50%, and 81%, respectively. In addition, GNP@PUF can function as a piezoresistive sensor and electromagnetic interference (EMI)‐shielding material. As a piezoresistive sensor, it exhibits a wide‐compressive pressure (2.4–112 kPa)/strain (5–70%) range and ultra‐fast response/relaxation time (48/35 ms), wide‐stretching strain (5–100%) range, and it can detect minute human motions by being attached to different parts of the human body. Meanwhile, the composite foam displays good absorption‐dominant EMI shielding performance (≈38 dB), possibly due to conductive dissipation and multiple reflections/scattering of EM waves inside the 3D conductive graphene network. This study provides a simple coating technique for developing multifunctional lightweight foam materials.

Polyurethane foams (PUFs) are a significant group of polymeric foam materials. Thanks to their outstanding mechanical, chemical, and physical properties, they are implemented successfully in a wide range of applications. Conventionally, PUFs are obtained in polyaddition reactions between polyols, diisoycyanate, and water to get a CO2 foaming agent. The toxicity of isocyanate has attracted considerable attention from both scientists and industry professionals to explore cleaner synthesis routes for polyurethanes excluding the use of isocyanate. The polyaddition of cyclic carbonates (CCs) and polyfunctional amines in the presence of an external blowing agent or by self-blowing appears to be the most promising route to substitute the conventional PUFs process and to produce isocyanate-free polyurethane foams (NIPUFs). Especially for polyhydroxyurethane foams (PHUFs), the use of a blowing agent is essential to regenerate the gas responsible for the creation of the cells that are the basis of the foam. In this review, we report on the use of different blowing agents, such as Poly(methylhydrogensiloxane) (PHMS) and liquid fluorohydrocarbons for the preparation of NIPUFs. Furthermore, the preparation of NIPUFs using the self-blowing technique to produce gas without external blowing agents is assessed. Finally, various biologically derived NIPUFs are presented, including self-blown NIPUFs and NIPUFs with an external blowing agent. [ABSTRACT FROM AUTHOR]

Polymeric foams are one of the most widely used piezoelectric materials due to their high piezoelectric properties, high flexibility, excellent special mechanical properties, thermal, electrical, and acoustic insulation, and low cost. Due to the cost and time-consuming nature of the experimental research, optimization of the piezoelectric properties of the polymeric foams requires the help of a precise theoretical model to predict these properties. So far, only one theoretical model has been proposed to predict the piezoelectric properties of the polymeric foams. However, some terms of this model are obtained experimentally and there is no comprehensive research that examines the piezoelectric properties of the polymeric foams with all its effective terms in a merely theoretical way. Therefore, in this research, different models are presented to calculate the two effective terms on the piezoelectric coefficient, including the Young modulus of the polymeric foams (Yf) and the effective relative permittivity (εeff). Then, the validity of the proposed theoretical models is investigated in comparison to the experimental results. The results based on the mean absolute error (MAE) parameter show that the best combined model to predict the piezoelectric properties of the polymeric foams is when the Wang and Sessler models are used to calculate Yf and εeff, respectively. According to the results, the average error of this combined model is less than 3%. [ABSTRACT FROM AUTHOR]

The evolution of technologies applied to surfboards has shown an accelerated growth in recent years. Not only has the design of the boards changed, but the materials used in the surfboards production have also evolved greatly. In this sense, in this work an investigative and comparative study was carried out between different types of materials used for the production of composites with sandwich structures used in surfboards. It was evaluated two thermoset polymeric matrices (unsaturated polyester and epoxy), 4 types of fibers in the form of blankets (glass, carbon, polyaramid and cotton) and 3 types of cores in the form of foams (polyurethane, expanded polystyrene and cork). The composite processing was carried out on a laboratory scale, but following the same procedures used in the surfboard production, that is, manual lamination by hand lay up. For the production of the sandwich structure, the composites (epoxy) were laminated on the foam surface, using two layers of glass fabrics and different cores. The main results indicate a better efficiency of the polyurethane core. In laminated composites, among the evaluated formulations, epoxy with carbon sample showed superior mechanical properties. [ABSTRACT FROM AUTHOR]

In this review, we survey the state of the art on polymeric foams incorporating nano-scale fillers. Particular focus of the review is on foams from polyolefinic nanocomposite formulations incorporating a wide variety of fillers. The nano-scale additives can influence the foam structure and properties in two ways: Firstly, they can act as composite reinforcement to enhance the mechanical properties and functionality of the matrix polymer; and secondly, they can act as foaming-processing aids through modification of the rheological, thermal and crystallization properties of the matrix as well as serving as heterogeneous nucleation sites. Through a combination of these influences, and using advanced processing techniques it is possible to achieve nanocomposite foams that have higher cell density, and more uniform cell size or controlled cell-size distribution. Such controlled foam morphologies, in turn, can yield better specific mechanical properties resulting in more effective light-weighting solutions. Further, the nano-scale additives can impart additional desired functionality resulting in multi-functional foams. In this article, we provide an overview of the mechanical, thermal and a few other relevant functional properties – such as piezoelectric sensitivity, acoustics, and filtration efficiency – of foams prepared using nanocomposite formulations, along with the processing considerations for achieving high quality foams using such materials. [ABSTRACT FROM AUTHOR]

Cellular solid materials are progressively becoming more predominant in lightweight structural applications as more technologies realize these materials can be improved in terms of performance, quality control, repeatability and production costs, when allied with fast developing manufacturing technologies such as Additive Manufacturing. In parallel, the rapid advances in computational power and the use of new numerical methods, such as Meshless Methods, in addition to the Finite Element Method (FEM) are highly beneficial and allow for more accurate studies of a wide range of topologies associated with the architecture of cellular solid materials. Since these materials are commonly used as the cores of sandwich panels, in this work, two different topologies were designed — conventional honeycombs and re-entrant honeycombs — for 7 different values of relative density, and tested on the linear-elastic domain, in both in-plane directions, using the Natural Neighbor Radial Point Interpolation Method (NNRPIM), a newly developed meshless method, and the Finite Element Method (FEM) for comparison purposes. [ABSTRACT FROM AUTHOR]

Emerging polymeric foams exhibiting unique microstructure of microspherical shells with reinforcing dense microspheres creates a new opportunity for impact-tolerant foam paddings in sport gears applications. This paper describes the static response of reinforced microcell consisting of an outer spherical shell and uniformly distributed microspheres while quantifying the stiffening effect. The distribution of the microspheres is illustrated using the Fourier series, allowing tuning of the reinforcing strategy. Expressions of the external and internal works are derived, whereas the Ritz energy method is adopted to calculate the deformations due to a compressive load distributed over a range of areas. Emphasis is given to the effect of the geometrical attributes of the microcell and the reinforcing microspheres on the resulting deformation response and stiffening effect. The framework is used to investigate the response of several case studies to elucidate the effects of relative radii ratio, reinforcement density, microcell wall thickness, and loading configurations on the stiffness. A new normalized strain energy parameter is introduced to simplify and accelerate the analysis while providing insights on the underpinnings of the observed buckling response. The results strongly suggest the viability of the newly discovered foam microstructure in managing static loads while providing an opportunity to strategically tune the mechanical response using the analytical framework presented herein. [ABSTRACT FROM AUTHOR]

The factors determining the mechanical properties of plastic polymeric foams are systematized. A unification procedure for their deformation behavior in the range of strains not higher than the forced elasticity limit of the material is proposed. The universal character of the deformation process is described by a unified strain curve and ratios of the main mechanical characteristics of the material, which are independent of the chemical nature of the polymer, the structural parameters of the foam, and the temperature–rate deformation conditions. The deformation behavior of monolithic and foam plastics and inorganic plastic bodies is shown to be similar. [ABSTRACT FROM AUTHOR]

The loss of energy especially in industrial and residential buildings is one of the main reasons of increased energy consumption. Improving the thermal insulation properties of materials is a fundamental method for reducing the energy losses. Polymeric foams are introduced as materials with excellent thermal insulation properties for this purpose. In the present study, a deep theoretical investigation is performed on the overall thermal conductivity of low-density polyethylene (LDPE) foams. The thermal conductivity by radiation is predicted using two different methods. The most appropriate model is selected in comparison with experimental results. The results show that the theoretical model has an appropriate agreement with the experimental results. The effects of foam characteristics including foam density, cell size, and cell wall thickness on the overall thermal conductivity are investigated. The results indicate that by decreasing the cell size and increasing the cell wall thickness, the overall thermal conductivity is decreased significantly. Also, there is an optimum foam density in order to achieve the smallest thermal conductivity. The lowest overall thermal conductivity achieved in the studied ranges is 30 mW/mK at foam density of 37.5 kg.m-3, cell size of 100 μm, and cell wall thickness of 6 μm.

Polymeric foams have good capacity of absorbing energy in compression but are brittle in tension. Linear elastic fracture mechanics is successfully applied to assess the integrity of polymeric foam‐based composite structures. The fracture toughness represents an important parameter. The different approaches to estimate the fracture toughness of polymeric foams are reviewed: analytical and numerical micromechanical models and experimental investigations. Focus is given on the parameters influencing the fracture toughness of polymeric foams like specimen type, solid material, density, loading speed, size effect and temperature. Data on mixed‐mode loading and dynamic fracture toughness are also presented. The last part of the paper presents some results to increase the fracture toughness by reinforcing of polymeric foams. [ABSTRACT FROM AUTHOR]

Cellular multistable architected material has been widely studied for its promising energy absorption applications for personnel protection, protective packaging, and crash mitigation. Despite the tailorable properties enabled by their geometric features, a major issue in the actual application is their lower strengths in the elastic behavior of the multistable architected material. Herein, a novel design strategy of strain rate-dependent architected cellular composite material (FACCM) is proposed, aiming to achieve enhanced energy-absorbing properties with the proposed composite system than the single material constituent. Guided by numerical simulations and experimental tests, the compressive behaviour of FACCM at multiple strain rates and the effect of filled foam on it with specific geometric parameters are characterized. The quasi-static performances of the FACCM specimens were evaluated both at the cell level and planar array level. Our results indicate that the strength, stiffness, and snap-through behaviour of multistable architected material can be significantly improved by the filled foam at elevated loading rates regardless of quasi-static loading or impact tests. The current study offers a new strategy for developing novel packing, shock absorption, and impact protection systems. [ABSTRACT FROM AUTHOR]

• A DMA test on the PIR foam has shown very high thermal stability between 0 and 40 °C. • Shear creep behavior of PIR slightly varied in the temperature range of 20–30 °C. • A stress amplitude of 30% was enough to cause nonlinear creep in the PIR foam. • Shear creep analytical curves were successfully calibrated using Findley's power law. An experimental campaign was carried out to assess shear creep behaviour of a rigid low-density closed-cell polyisocyanurate (PIR) foam. Two service temperature values were considered, 20 °C and 30 °C, and the applied stresses ranged between 20% and 60% of the corresponding shear strength. The results showed that a stress amplitude of 30% was enough to cause nonlinear creep response. Furthermore, creep deformations were slightly smaller in the tests at 30 °C, a fact that matched the viscoelastic response of the PIR foam obtained from DMA testing. Finally, creep prediction curves were calibrated through an analytical approach based on the Findley's power law. [ABSTRACT FROM AUTHOR]

Polymeric foams are used for impact protection due to their ability to absorb large amounts of strain energy. In this work, the compressive response of an open cell polyurethane foam currently used as liner in the advanced combat helmet is examined across strain rates. A traditional load frame is used to investigate the quasi-static behavior, and two different modifications of a conventional Kolsky (split-Hopkinson) bar configuration are used to probe the dynamic response. A unique, independent method not relying on strain gage signals is presented that leverages high-speed full-field imaging to track the velocity on each side of the sample-bar interface and used to extract the dynamic stress-strain response; the results are compared against traditional strain gage measurements. X-ray tomography is used to examine the global morphological characteristics of the foam. The foam is found to be strongly rate dependent, where the characteristic properties vary logarithmically with strain rate. An analytical expression is presented to describe the rate dependency that collapses all stress-strain curves on a master curve. Full-field kinematic data from digital image correlation taken during loading is used to extract a nonlinear Poisson's ratio as a function of strain, which is found to be strain rate insensitive. A tangent Poisson function is used to explore the foam's auxetic behavior. These findings provide insight on physically-based constitutive modeling of foams, crucial to predictive brain injury simulations, as well as motivate the need to probe local heterogenous behavior across strain rates moving forward. [ABSTRACT FROM AUTHOR]

Featured Application: Mitigating vibrations of flat, large-scale structures, for example, car front wall or ceiling, as well as structural and/or cover parts for rail vehicles or noise barriers of different kinds. Furthermore adaptable compact dampers, for example, machine feet are also a promising application field for the proposed novel damping approach. Evanescent morphing in combination with an original concept of Compressible Constrained Layer Damping (CCLD) is a novel and promising approach for dynamic behaviour adaptation. The crucial component of the CCLD is a compressible intermediate layer with its thickness and material properties controlled by fluid actuation, enabling the adjustment of the damping and stiffness of the overall system. To estimate the potential of the CCLD, an analytical model was developed which describes the vibration behaviour of the overall structure, taking into account the compression-driven properties of the intermediate layer. The results confirm the principal correctness of the initial theoretical assumptions regarding the adaptive dynamic behaviour of structures with CCLD treatment. A significant vibration mitigation as well as a high adaptability of dynamic behaviour were observed, however, they show a complex dependence on the system configuration. Nevertheless, the developed analytical modelling approach can already be used for a preliminary system design. Besides the analysed polymer-based foams as the intermediate layer, nonwovens also exhibit compression-dependent shear properties and can therefore be used in CCLD. First preliminary investigations show that the damping performance is on average about ten times better than that of the polymeric foams. [ABSTRACT FROM AUTHOR]

Polymeric foams are one of the most applicable thermal-insulation materials due to their low thermal conductivity, high mechanical properties, and low cost. Optimization of thermal-insulation performance of polymeric foams needs a theoretical model in order to predict the overall thermal conductivity. So far, several theoretical approaches are presented in this regard but to the best knowledge of the authors, there is no comprehensive investigation on comparing the proposed models. Therefore, the study of validity of the theoretical models in comparison with the experimental results is one of the main goals of the present study. Low density polyethylene (LDPE) foams are selected as the case study due to the wide application range. Different models to predict the overall conductivity of the foam based on conduction through the combined gas and solid phases (λgs) as well as radiation thermal conductivity (λr) are presented. The results indicate that the best model is a model in which λgs is calculated using Gibson and Ashby model and λr is obtained using Williams and Aldao model based on the root mean square (RMS) parameter. The results show that the theoretical error of this model is smaller than 10%. [ABSTRACT FROM AUTHOR]

Carbon nanotube (CNT) foams have received an overwhelming response in research community due to their large strength to weight ratio. In this work, CNT foam was prepared using functionalized CNT. Pore size distribution in synthesized CNT foams was observed to be in the range 200-400 μm and porosity is in range 60-65%. The bulk density of foam is 0.2-0.3 g/cc. Furthermore, uniaxial compression tests at varying rates, indicates deformation behavior to be rate dependent. Cyclic compression test was also performed showing similar behavior to cellular materials; hysteresis loop is found in loading-unloading cycles, clearly indicating energy dissipation. [ABSTRACT FROM AUTHOR]

Summary: Structural anisotropy of two‐phase materials can be evaluated through global measurements, as volume orientation or mean‐intercept length methods do, or through statistics performed on a set of individual measurements. This last procedure is encouraged by recent improvements in the spatial resolution of conventional X‐ray tomography. In this paper, the above‐described approaches were compared in three case studies: a foam subjected to an in situ compression test, a second foam with a completely different cell morphology and a plastic material reinforced with short fibres. The approach based on the subdivision into distinguishable objects of the considered material phase has proved to be more sensitive in highlighting small deformations in the structure or small irregularities in an otherwise isotropic structure. On the other hand, the other approach is more general and is always usable. The two methods for calculating the fabric tensor tend to converge as the average anisotropy of individual objects in the statistical population increases. The use of Lambert's cylindrical equal‐area projection of cell/fibre directions or local volume orientations is suggested, because the density of points is preserved from the sphere to the plane surface. Finally, a quick vector method to evaluate the anisotropy of the directions distribution has been presented, by defining a coherence index of the average direction. [ABSTRACT FROM AUTHOR]

In the present study, hygro-thermal and durability related properties of a cementitious mortar containing highly porous foamed aggregates obtained from polymeric end-of-waste materials were investigated. The evaluation of capillary water absorption, thermal conductivity, water vapour permeability and sulfate attack resistance of samples where natural quartz sand was replaced by 10%, 25% and 50% in volume with foamed aggregates was carried out. Experimental investigations showed that the presence of plastic aggregates decreased mortar density (up to 36%, compared to the reference sample, for the maximum investigated natural sand volume replacement) as well as thermal conductivity (10% for the 50% volume replacement). Moreover, water vapour transmission rate increased at increasing natural sand replacement while capillary water absorption decreased. Finally, after fifteen cycles of sulfate attack test, lightweight mortars evidenced a lower mass loss compared to the reference sample. The results were related to morphological modifications in the mortars bulk porosity, demonstrating by mercury intrusion porosimetry investigations, that polymeric foamed aggregates determine a variation of the pores microstructure, resulting in an increased pores dimension. [ABSTRACT FROM AUTHOR]

• A numerical inverse analysis procedure was developed in Matlab based on a FEM based functional. • Temperature-dependent thermophysical properties of polymeric foams were calibrated. • The calibrated properties can be used to model foam-core sandwich panels in fire. • The properties and procedure were validated by successfully modelling an independent case. Polymeric foams used as core materials of sandwich panels undergo severe degradation under high temperatures, making the experimental measurement of their thermophysical properties (thermal conductivity and specific heat) possible only up to 150 °C–200 °C. However, their knowledge at higher temperatures is needed to fully understand their behaviour and to develop advanced numerical models for analysis and design of sandwich structures subjected to fire. This work presents a numerical inverse analysis procedure to determine such effective properties for rigid polyurethane (PUR) and polyethylene terephthalate (PET) foams. Firstly, the campaign used to obtain experimental results is presented and then the proposed numerical inverse analysis procedure is described. This is based on the minimization of a least squares functional and a nonlinear finite element thermal analysis. Next, the numerical results and the effective thermophysical properties obtained for both foams are presented and discussed, and are validated by extending their use to the simulation of the thermal response of a sandwich panel subjected to a standard fire. It is concluded that the numerical procedure is capable of estimating the temperature-dependent effective thermal conductivity and specific heat of PUR and PET foams for temperatures well above those corresponding to their decomposition. [ABSTRACT FROM AUTHOR]

Evanescent morphing in combination with an original concept of Compressible Constrained Layer Damping (CCLD) is a novel and promising approach for dynamic behaviour adaptation. The crucial component of the CCLD is a compressible intermediate layer with its thickness and material properties controlled by fluid actuation, enabling the adjustment of the damping and stiffness of the overall system. To estimate the potential of the CCLD, an analytical model was developed which describes the vibration behaviour of the overall structure, taking into account the compression-driven properties of the intermediate layer. The results confirm the principal correctness of the initial theoretical assumptions regarding the adaptive dynamic behaviour of structures with CCLD treatment. A significant vibration mitigation as well as a high adaptability of dynamic behaviour were observed, however, they show a complex dependence on the system configuration. Nevertheless, the developed analytical modelling approach can already be used for a preliminary system design. Besides the analysed polymer-based foams as the intermediate layer, nonwovens also exhibit compression-dependent shear properties and can therefore be used in CCLD. First preliminary investigations show that the damping performance is on average about ten times better than that of the polymeric foams.

Experimental and numerical studies of sustainable sandwich bio-composites were presented. The bio-composites were developed using plant-based materials. The laminated face sheets comprised woven hemp fabric and a tree sap–based epoxy, while the core comprised castor oil-based polyurethane foam reinforced with waste rice hulls ashes. Uniaxial compression, tension, and three-point flexural bending tests were performed. Finite element models were developed. Good agreements between experimental and numerically simulated flexural responses were found. From numerical simulation results, the sandwich bio-composites were found to be a structurally acceptable replacement for standard gypsum drywall. Further experimental works are needed to validate the applications. [ABSTRACT FROM AUTHOR]

An inverse radiation analysis is performed for identification of spectral radiative properties for a class of highly porous closed cell polymeric foams using coupled Monte Carlo-Particle Swarm Optimization method. An Open Message Passing Interface (MPI) based parallel Monte Carlo method is adopted to simulate thermal radiation within the foam. The Particle Swarm Optimization (PSO) with adaptive weighted delay velocity is employed to inversely identify the spectrally dependent transport extinction coefficient and scattering albedo of expanded polystyrene and polyethylene foams from measured spectral transmittance. The transmittance measurements were performed with a Fourier-transform infrared spectrometer across the IR wavelength range of 2.0–16.7 μm. The developed inverse model used transmittance measurements of two samples of the same foam having different thicknesses to successfully retrieve the unknown radiative parameters of the foams. Both of the foams demonstrated consistently high transport extinction coefficients at all wavelengths in a range of 6400–400 m−1. Spectral transport scattering albedos of both the foams were discovered to be in the range 0.70–1.0. The accuracy of the proposed inverse model is checked by numerically predicting the spectral transmittances for a third sample of different thickness using the retrieved radiative properties. A good agreement is observed between the experimental and the numerically predicted transmittance values for the third thickness. [ABSTRACT FROM AUTHOR]

• PUR foams are non-linear-elastic quasi-brittle with positive post-peak behavior. • Structural foam systems of XPS, EPP, and PUR reveal high anisotropy. • XPS foams are evaluated indicating adverse orientation effects (anisotropy). • EPS and PUR foams indicate positive size effects. • The G F method seems suitable to characterize the damage effects of polymeric foams. In the construction industry, materials with density advantages are becoming increasingly prevalent due to the trend toward lightweight construction. These include, above all, synthetic foams based on polyurethane and polypropylene. While they are mainly used for thermal insulation during thermal refurbishment, they are also increasingly being used for structural tasks. On the part of manufacturers, these are still dominated by standardized mechanical test methods such as compression or flexure tests. However, the major drawback of these strength tests is the need for more information about the structural failure behavior of polymer foams in the fracture zone itself, the interface. Since fracture analytical approaches provide only limited vital figures, this work presents a holistic approach that encompasses all areas of evaluation. This influences sample size, orientation (isotropy), fracture zone effects (failure patterns), and structural safety. Common synthetic polymer foam systems (open-cell and closed-cell) are used to represent the broadest possible range of evaluation. The results show that it is not the materials with the highest tensile strength that are most convincing, but those with the most extraordinary fracture energy and damage tolerance. The practical information greatly expands the selection options for decision-makers since technical data sheets from manufacturers can only be used to a limited extent. [ABSTRACT FROM AUTHOR]

Bike and ski helmets are mainly made up of two layers: the external shell and the foam liner. The foam liner, typically made of expanded polystyrene (EPS) or polypropylene (EPP), is asked to provide energy absorption in case of impacts. Standard helmet design requires the foam to maximize this energy absorption, thus achieving large deformations (up to 25% in compression) while maintaining the stress level below a threshold value. To optimize the helmet construction in terms of foam composition, structure and density, reliable numerical models are required, which in turn need to be fed with accurate experimental data. A characterisation of several foams was performed, including EPS and EPP having varying densities, under tensile and compressive stress states at varying strain rates. Typical mechanical parameters (elastic moduli and plateau stress in compression, Poisson's ratio) were compared with literature data and applicability of existing models to experimental results was discussed. A marked strain rate dependence – very important for impact applications – was accurately described using the Nagy phenomenological model. The foam microstructure was investigated using scanning electron microscopy (SEM) to assess structural changes before and after compression. The aforementioned mechanical features were then adopted in a rate-dependent constitutive law for crushable foams, to model the shock attenuation properties of helmets and validate the approach against available data. Finally, a microelectromechanical system based in-helmet wireless micro monitoring system was developed and inserted in a helmet prototype. The system is capable of acquiring impact load spectra, providing valuable information to investigate generic impacts with varying angles and energy. In particular, it can monitor the effect of repeated micro-impacts on the residual energy absorption characteristics of the foam. [ABSTRACT FROM AUTHOR]

The solubility of gases in various polymers plays an important role for the design of new polymeric materials. Quantitative structure–property relationship (QSPR) models were designed to predict the solubility of gases such as CO2and N2in polyethylene (PE), polypropylene (PP), polystyrene (PS), polyvinyl acetate (PVA) and poly (butylene succinate) (PBS) at different temperatures and pressures by using quasi-SMILES codes. The dataset of 315 systems was split randomly into training, calibration and validation sets; random split 1 led to 214 training (r2= 0.870 and RMSE = 0.019), 51 calibration (r2= 0.858 and RMSE = 0.020) and 50 validation (r2= 0.869 and RMSE = 0.017) sets. The suggested approach based on the quasi-SMILES, which are analogues of the traditional SMILES gives reasonable good predictions for solubility of CO2and N2in different polymers. The described methodology is universal for situations where the aim is to predict the response of an eclectic system upon a variety of physicochemical and/or biochemical conditions. [ABSTRACT FROM AUTHOR]

A constitutive model of polymeric foams having a four-parameter modulus function is suggested. The modulus function consists of two linear functions and a cubic polynomial of strain depending on the strain range. The parameters of the model are determined by minimizing the sum of squares of errors between the experimental data and model's predictions. Quasi-static compression tests are done for expanded polyurethane and polypropylene foams to obtain the parameters. Dynamic compression tests give stress strain data at high strain rate and the results are compared with those of the proposed model. [ABSTRACT FROM AUTHOR]

Developments in design and technology in the engineering and medical fields necessitate the use of smart and high-performance materials to meet higher engineering specifications. The general requirements of such materials include a combination of high stiffness and strength with significant weight savings, resistance to corrosion, chemical resistance, low maintenance, and reduced costs. Over the last three decades, it has been demonstrated that auxetic materials offer a huge potential for the fields of engineering, natural sciences, and biomedical engineering, and for many other industries, including the aerospace and defense industries, through their unique deformation mechanism and measured enhancements in mechanical properties. To meet future engineering challenges, auxetic materials are increasingly being recognized as integral components of smart and advanced materials. Although materials with a negative Poisson's ratio have been known since the early 1900s, they did not capture researchers' attention until the late 1980s. Since 1991, these materials have been known as auxetic materials. Since then, their benefits and applications have been expanded to all major classes of materials such as metals, ceramics, polymers, and composites, and they are also now being used in engineering applications. The goal of this review was to present the development of auxetic polymers, which were first fabricated in the form of polyurethane foam approximately three decades ago and are now used in the fabrication of non-woven nano/micropolymeric structures. This review could provide useful information for the future development of auxetic polymers. [ABSTRACT FROM AUTHOR]

Portable, water filled road safety barriers are used to provide protection and reduce the potential hazard due to errant vehicles in areas where the road conditions change frequently (e.g. near road work sites). As part of an effort to reduce excessive working widths typical of these systems, a study was conducted to assess the effectiveness of introducing polymeric foam filled panels into the design. Surrogate impact tests of a design typical of such as barrier system were conducted utilising a pneumatically powered horizontal impact testing machine up to impact energies of 7.40 kJ. Results of these tests are utilised to examine the barrier behaviour, in addition to being used to validate a couple FE/SPH model of the barrier system. Once validated, the FE/SPH model it utilised as the basis for a parametric study into the efficacy and effects of the inclusion of polymeric foam filled panels on the performance of portable water filled road safety barriers. It was found that extruded polystyrene foam functioned well, with a greater thickness of the foam panel significantly reducing the impacting body velocity as the barrier began to translate. [ABSTRACT FROM AUTHOR]

Composite sandwich panels comprising fibre reinforced polymer (FRP) skins and lightweight material cores are being increasingly used in civil engineering. In several applications, such as façades, roof structures and bridge decks, these panels may experience a wide range of in-service temperatures. This paper presents experimental and analytical investigations about the effects of elevated temperature on the shear response of polyethylene terephthalate (PET) and polyurethane (PUR) foams used in composite sandwich panels. The experimental programme included (i) DMA and DSC/TGA tests, aimed at assessing the glass transition and decomposition processes underwent by those foams; and (ii) Iosipescu tests for temperatures ranging from −20 °C to 120 °C, in order to characterise their shear response. The analytical study comprised the assessment of the accuracy of different empirical (relaxation) models in describing the shear modulus reduction with temperature of those polymeric foams. Results obtained show that with increasing temperature, the shear responses of PET and PUR foams become more markedly non-linear. In addition, the shear moduli of these foams suffer considerable reductions, particularly for the PET foam; although at ambient temperature (∼20 °C) the PET foam is 3 times stiffer than the PUR foam, at 80 °C their shear moduli become similar, being respectively 24% and 66% of those at ambient temperature. All relaxation models assessed in this study were able to simulate with good accuracy the variation of the shear modulus of both foams with temperature. [ABSTRACT FROM AUTHOR]

[Display omitted] • EPP foams take the structural lead among the set of test candidates. • Different crack-shielding effects of several polymeric foam systems are identified. • The G F principle characterizes the post-peak softening behavior of polymeric foams well. • Hybridization can enhance polymeric foam performance. Materials with density advantages are rapidly gaining ground due to the trend towards lightweight structures. These include light metals, polymeric composites, and various types of foam. A glance at the literature on polymeric foams reveals different approaches of structural safety characterization. These are still dominated by standardized mechanical testing methods, such as compression or bending test. However, from such setups no empirical statements can be made about how the post-peak softening behavior is influencing the structural safety. Thus, a holistic fracture analysis is applied to examine various polymeric foam systems from the automotive industry. Commonly used synthetic foams based on EPS, XPS, EPP, and PUR are compared and evaluated. The results provide empirical in-depth information for decision-makers enhancing their options for the selection process. [ABSTRACT FROM AUTHOR]

The application of a new family of strain energy functions to modelling the finite deformation of isotropic compressible elastomers, including polymeric foams and (hydro)gels, is presented in this paper. The proposed family of models is developed from a parent incompressible strain energy function, customised to the compressible case via an additive split of deviatoric and volumetric contributions. With a minimum of four and maximum of five parameters, the developed models are shown to be compatible with the empirical deformation kinematics of slight compressibility (or almost incompressibility) and provide favourable fits to the extant deformation datasets by simultaneous fitting to uniaxial, biaxial and/or simple shear deformations. Some intricate behaviours such as the shear-softening of polystyrene foams and the ensuing instability under simple shearing, as well as the simple tension of alginate-based hydrogels under extremely high levels of stretch are also successfully modelled. Given the versatility of the proposed family of models in terms of their relatively low number of model parameters, their capability to predict a wide range of deformation behaviours for a wide range of elastomers (from foams to gels), and the robustness of the provided fits, the advantages of the considered models over the existing models of the same class in the literature is demonstrated. • A robust three to five -parameter strain energy function W for compressible isotropic rubber-like materials. • The model is applied to a variety of extant experimental datasets. • Polymeric foams and hydrogels are considered. • The favourable correlation between the data and model predictions is shown. • Improvements compared with existing models in the literature are demonstrated. [ABSTRACT FROM AUTHOR]

Of interest, in this work, is the behavior of open-cell polymer foams under compression. In a recent work by Del Piero and Pampolini (Continuum Mech Thermodyn 24:181-199, ), a model coupling nonlinear elasticity and viscosity was introduced to describe the response of a polyurethane foam subjected to uniaxial cyclic compression. Inelastic effects were attributed to the viscous properties of the foam, while strain localization and hysteresis were attributed to the nonconvexity of the strain energy density. But the model did not reproduce the response curves after the first loading-unloading cycle. Here, the model is extended by taking into account the damage of the foam. A simple phenomenological one parameter damage law is used to describe the damage occurring during the first loading cycle. An accurate identification procedure for the material constants is also developed, and the interaction of viscosity and damage in both monotonic and cyclic deformation processes is discussed. In spite of the one dimensional formulation, the model permits a precise analysis of the main phenomena which determine the complex behavior of the foam. [ABSTRACT FROM AUTHOR]

Abstract: Heat insulating properties of polymeric foams at ambient temperature were investigated using the model of coupled heat transfer by conduction and radiation through computer-reconstructed domains. The proposed model considers absorbing and emitting gas and solid phases and partial photon reflection on phase interfaces. The P 1-approximation is used for the description of radiation. For optically thin polymeric walls, the interface conditions are adjusted to account for specular reflection and wave interference effects. The developed model was validated using experimental data and compared with other approaches, including state-of-the-art homogeneous phase approach (HPA). Contrary to HPA, our approach doesn't treat polymeric foams as homogeneous materials with effective properties and provides temperature and radiation gradient fields, which respect foam morphology. The model predicts that the radiative heat flux can account for more than one third of the total heat flux in high porosity expanded polystyrene (EPS) or polyethylene (PE) foams and that the equivalent conductivity of polymeric foam can be significantly reduced by the careful balancing of porosity, cell size, wall thickness and strut content. The presented model doesn't use any empirical correlations and can be used for the optimization of heat transfer in any type of polymeric foam. [Copyright &y& Elsevier]