Foam Density Research Articles

Energy absorption performance of steel plate-polyurethane foam composite protective structures

In recent years, accidents of vehicles (or vessels) hitting bridge piers have occurred frequently, posing serious threats to the safety of the bridge structures, vehicles, and people. Due to their energy-absorbing effects, flexible protective structures have the potential to reduce the damage of both the bridges and vehicles. Therefore, it is of great significance to develop flexible protective structures with high performance of energy absorption. In this study, a new type of steel plate-polyurethane foam composite protective structure was proposed, in which the face panels and webs were made of flat and folded steel plates, respectively, and polyurethane foam was used as the filling material. Basic mechanical behavior of the composite protective structure was studied through static compression tests; and the influences of three key variables (i.e., web form, foam density and foam-filling pattern) on the energy absorption performance of the structures were focused. The results showed that the energy absorption (EA) and crushing force efficiency (CFE) of the folded-web specimens without foam filling were higher than the straight-web counterparts by 19.6 % and 74.2 % on average, respectively; and the EA and CFE of the folded-web specimens fully-filled with a foam density of 50 kg/m3 (100 kg/m3) were 30.6 % (33.8 %) and 124.7 % (116.6 %) higher on average than the straight-web counterparts, respectively. In addition, it was found that there was a positive composite effect between steel plates and polyurethane foam; but the polyurethane foam on the outside of the protective structure was prone to bending deformation, which weakened the energy absorption performance of the structure to a certain extent. In the future, the proposed composite protective structure can be further optimized to achieve better energy absorption performance, so as to provide a better solution for the impact protection of bridge piers or other structures.

Conversion of low density polyethylene foams into auxetic metamaterials

AbstractCellular polymers, such as polyethylene foams, are commonly used in the packaging industry. These materials have short service life and generate a high volume of waste after use. In order to valorize this waste and produce added‐value applications, it is proposed to convert these materials into highly efficient energy absorption structures. This was done by modifying the original cellular morphology of the foams (spheroidal or polygonal) into a re‐entrant structure to produce auxetic materials. This work presents an optimized process combining mechanical compression and solvent vapor evaporation‐condensation leading to low density foams (77–200 kg/m3) having negative Poisson's ratios (NPR). Three series of recycled low density polyethylene (LDPE) foams with an initial density of 16, 21, and 36 kg/m3 were used to optimize the processing conditions in terms of treatment temperature, time, and pressure. From all the samples prepared, a minimum Poisson's ratio of −3.5 was obtained. To further characterize the samples, the final foam structure was analyzed to relate with mechanical properties and compare with conventional foams having positive Poisson's ratios. The results are discussed using tensile properties and energy dissipation which were shown to be highly improved for auxetic foams. Overall, the resulting foams can be used in several applications such as sport and military protection equipment.

Addition Of Chain Extender To Improve Flexible Polyurethane Foam Characteristics Of Palm Oil Polyol

The use of 100% palm oil polyol without the addition of a chain extender produced foam which initially expands and then collapses so that the resulting foam has tight pores, dense texture, and brittle (brittle). It was necessary to use a chain extender to improve the flexible properties of the foam. This study aimed to examine the ratio of palm oil polyols with a chain extender to produce flexible polyurethane foam with good characteristics. The treatment of this study was a combination of types and comparisons of palm oil polyols with chain extenders which were carried out 3 times, consisting of factor A = type of chain extender (diethylene glycol (DEG), diethanolamine (DEA), and polyethylene glycol (PEG)-400) and factor B = ratio of palm oil polyols. with a chain extender (80%:20%; 70%:30%; 60%:40%; 50%:50%). The obtained foam was observed visually, foam development, and foam density. The best sample for each type of extender was analyzed by FTIR. The results showed that 40% PEG-400 has succeeded in producing flexible polyurethane foam with higher expansion (291.22%), lower density (29 kg/m3), and visually has the best flexible properties. Based on FTIR analysis, the use of PEG-400 in the polyol system can increase the reactivity of palm oil polyols to isocyanates.

Polivinil klorür (PVC)’ün geri dönüştürülmesi: PVC köpük üretimi ve Karakterizasyonu

Plastikler hayatımızın birçok alanında yıllardır kullanılmakta olup kullanım ömrü sonunda önemli miktarda atık oluşturmaktadır. Doğada uzun yıllar bozunmadan kalan ve çevreye zarar veren bu malzemelerin geri dönüştürülüp tekrar kullanıma kazandırılması önem taşımaktadır. Termoplastik köpük malzemeler düşük yoğunluk, yüksek spesifik mukavemet, yüksek enerji absorblama özellikleri ve üstün yalıtım özelliklerinden dolayı ısı yalıtımı, otomotiv koltukları, ambalaj malzemeleri ve enerji absorblayıcı (soğurucu) malzemeler olarak yaygın bir şekilde kullanılmaktadır. Bu çalışmada, en çok kullanılan plastiklerden biri olan ve önemli miktarda atık oluşturan polivinil klorür (PVC)’ün geri dönüşüm yoluyla termoplastik köpük malzemelerin üretiminde kullanımı amaçlanmıştır. Bu amaçla kapı ve pencere profil atıklarından elde edilen atık PVC kullanılarak termoplastik köpük malzemeler üretilmiştir. PVC köpük malzemelerin bazı fiziksel, mekanik ve morfolojik özellikleri üzerine kimyasal köpük oluşturucu miktarının etkisi incelenmiştir. Üretilen PVC köpük malzemelerde kimyasal köpük oluşturucu malzeme miktarının artması ile PVC köpüklerin yoğunluk değerlerinde %40’lara kadar bir azalma sağlanmıştır. PVC köpüklerin spesifik darbe direnci değerleri kimyasal köpük oluşturucu miktarı ile doğrusal bir şekilde artış göstermiştir. Köpüklerin hücre yapısı incelendiğinde ise kimyasal köpük oluşturucu miktarının artması ile hücre birleşmelerinin meydana geldiği ve daha büyük hücrelerin oluştuğu gözlemlenmiştir.

Microcellular foaming and mechanical properties of iPP-iPPF using supercritical CO2

Isotactic polypropylene (iPP) is one of the most widely used commercial polymers in the industry. However, it is difficult to foam iPP due to its low melt strength. In this work, the foamability and mechanical properties of iPP were investigated by incorporating isotactic polypropylene fiber (iPPF), using a batch foaming method. Compared to the neat iPP foams, smaller cell size and more uniform cell size distribution were obtained for iPP–iPPF. When 30 % iPPF was added, the cell density of iPP-iPPF foam was 1.1 × 1010 cells/cm3 which was twice that of the neat iPP foam. It was attributed to the improved melt strength and heterogeneous nucleation of iPPF in the iPP matrix. In addition, the impact strength of foamed iPP-30iPPF was found to be increased by 136 % compared to its neat iPP counterpart. Furthermore, the tensile strength of the foamed samples also increased with the increasing iPPF content.

Pore-scale numerical simulation of the heat transfer and fluid flow characteristics in metal foam under high Reynolds numbers based on tetrakaidecahedron model

In this paper, the pressure drops and interfacial heat transfer coefficient in metal foam with different pore density which was constructed by tetrakaidecahedron models were numerically studied under high velocity by Computational Fluid Dynamics (CFD). The velocity fields, temperature fields and pressure fields in the computational domain of metal foam were investigated. The equation of pore density and hydraulic diameter of metal foam was obtained. Influence of flow rate on the whole porous zone was also studied and obtaining the fitting formula to predict pressure loss in porous metal which was applied to the pore density range from 10PPI(Pore Per Inch)to 40PPI at high flow rate. Comparing with the previous literatures, the maximum error of pressure drop value was 12.23%. Meanwhile, the relationship between Reynolds number and interfacial heat transfer coefficient was studied, the results shown that the values of heat transfer coefficient increase with the rising of Reynolds number, but the lifting rate decreases gradually. And according to the data points, the numerical formula of interfacial heat transfer coefficient in porous metal was obtained which had a great correctness through contrasting with other data. As a result, the fitting formula could accurately predict the convection heat transfer coefficient of the metal foam interface and provide relevant data for the Thermal Non-equilibrium Model.

B4C‐Reinforced Al–Zn Foams Having Superior Energy Absorption Efficiency

The low density of the aluminium foam and high energy absorption make them favourable for automobile, aerospace, and defence industries. However, the melt route for foam fabrication has challenges in achieving homogeneous distribution of pores. Hence, we have adopted the space holder technique using the powder metallurgy methodology to overcome such a challenge. In the current study, we fabricated Al–Zn alloy foams reinforced with varying volume fractions of B4C particles using NaCl as a space holder implemented by hot pressure‐assisted sintering and dissolution. X‐ray computed tomography revealed a homogeneous distribution of pores. The quasistatic compression studies showed that the samples containing a higher volume fraction of pores exhibited higher energy absorption efficiency in the fabricated foam. The maximum energy absorption efficiency (η) achieved was ≈93% for the pristine Al alloy foam with ≈50% porosity, which is ≈11% higher than the η value of 9 vol% B4C samples with similar porosity. Additionally, B4C particles delay the sudden collapse of cell walls and stabilize the compression behaviour. Adding B4C improves the η and strength at higher relative density. This fabrication methodology would help us develop foams with a homogenous pore distribution and regular geometry, achieving highly desirable mechanical properties.

Enhanced power density during energy charging of a shell-and-tube thermal storage unit: Comparison between the inclusion of metal fins and foams

Introducing metal fins or foams can both enhance the performance of shell-and-tube phase change thermal energy storage (TES) devices, but the heat transfer mechanisms are different, i.e., heat transfer through a micro-liquid film, named close-contact melting (CCM) mode, brought by fins and reinforced-heat-conduction is triggered by foams. In order to find a method with maximum power density boost for TES devices, an experimental study was conducted to reveal the effect of parallel fins (N = 5, 10) and foams (20 ppi, 40 ppi) attachments on the power density of a shell-and-tube TES device with a heating condition of the 30 °C superheat. Additionally, the finned cases were studied numerically to observe their melting behavior. It was shown that under the working conditions set in this work, the effective use of CCM mode allows addition of fins to win the competition with metal foams for higher power density. At a penalty of energy density loss of only 7 %, the ten-fin-attached TES device achieves a clear boost of power density over 70 % (up to 0.503 W/cm3) and a reduction in melting time of ~47 %. because the CCM mechanism dominates comparing with the two basic heat transfer modes of heat conduction and convection. Introducing metal foams causes both conduction enhancement and convection suppression, thus resulting in high initial power density at the beginning of the melting process and a gradual decrease in power density as the melting process progresses. Properly increasing pore density of metal foams is effective for thermal conductivity enhancement, but too dense structures may lead to deteriorating heat transfer. On balance, taking advantage of CCM mechanism with rational fin design in phase change TES may be a promising and cost-effective way to increase power density, which should be widely used in practice.

Thermal insulative 2D-oriented bimodal micro-foams and high strength photonic thermoplastic elastomers by assembling olefin multiblock copolymers

Hierarchical 2D-oriented micro-foams and photonic elastomers are produced by assembling the mesophase separated and crystallized superstructures of olefin multiblock copolymers (OBCs). Highly 2D-oriented monomodal and bimodal micro-foams are prepared via compression molding of as-received nascent OBC pellets, irradiation crosslinking, and a subsequent moderate-to-high-pressure supercritical CO2 foaming. Randomly short range ordered bimodal micro-foams are generated from the sheared counterparts. These micro-foams show excellent lightweight properties with foam density of 0.061–0.188 g cm−3 and outstanding thermal conductivity of 20–36 mW m−1 K−1 by laser flash analysis. Moreover, the order-disorder and order-order transitions of nascent and sheared bulk OBCs are characterized by a sequential annealing and subsequent crystallization procedure. The self-seeded nascent and sheared OBCs show hierarchical mesophase separation with domain spacings of 80–258 nm, measured by ultra-small X-ray scattering. The selective visible-light transmitted, transparent, and high-strength thermoplastic elastomers are then made via solvent-free compression molding of these OBC pellets. Meanwhile, low-temperature Sc-CO2 foaming shows that 2D lamellar crystals and 2D, 3D-growing spherulitic crystals with sharp interfaces are individually organized within 2D-oriented lamellar domains of photonic and opaque sheets, which account for their high tensile strength and low strain hardening properties, respectively. The 2D-oriented bimodal micro-foams and assembled photonic elastomers possess potential applications in lightweight sound and thermal insulation, auto-parts, shape memory light actuators, and soft sensors.

Noise attenuation inside airplane cabin: Preliminary results on combined porous/nano-fibrous materials

A series of light weight and cost-effective combined system made of poly (vinylidene fluoride-co-hexafluoropropylene) (PVdF-HFP) nanomembranes doped with carbon nanotubes and cellular materials (aerogel and melamine foams) were prepared and tested. The overall composite system acoustic behavior was affected by each of its individual constituents. The hypothesis of a Helmholtz resonator-like behavior caused by the combination of nanomembranes and cellular materials was proved experimentally and by analytical models. The proposed analytical correction of sound absorption coefficient (α) was able to capture the resonant effect “physical phenomenon”. The aerogel by itself is not an effective sound insulation component, but the nanomembrane + aerogel association can lead to sound absorption coefficients of around 0.7 with a thickness around 4.0 mm at 6000 Hz frequency. The melamine foam + nanomembrane has its sound absorption coefficient peak at ∼0.97, at 1600 Hz with a thickness of 12 mm. The changes in melamine foam (density ∼6 kg/m3) frequency from high range (5500 Hz) to mid-range (1600 Hz) with the addition of ∼60.00 µm thick nanomembrane, opened a new venue for a new class of cellular composites for acoustic insulation of commercial airplanes cabins.

Compressive Properties of Poly (Dimethylsiloxane)–Hollow Glass Microballoons Syntactic Foams

Polymer syntactic foams are lightweight polymer composites that are prepared by introducing hollow microspheres in a resin. The main endeavour is to obtain a significant reduction in the weight of the composite along with energy absorption. The present investigation aims to prepare poly (dimethylsiloxane) (PDMS)-hollow glass microballoons (HGM) (40–60% v/v) syntactic foams. Not only did HGM reduce the density of the syntactic foams but also act as a reinforcing phase and increase the compressive properties of PDMS. A ∼25% reduction in density was obtained in syntactic foam when compared to the neat elastomer. Similarly, an improvement of ∼118% in compressive strength was attained at 40% loading of HGM in PDMS. Specific compressive strength and toughness values also registered improvements of the order of ∼191 and ∼240% respectively which highlight the potential of PDMS syntactic foams in varied applications.

Energy absorption of multilayer aluminum foam-filled structures under lateral compression loading

This article proposes a biomimetic multilayer foam-filled structure (BMFS) that mimics the microstructural characteristics of biological structures such as human bone and whale baleen. The lateral compression performance of such structures is investigated using experimental and numerical analyses. The proposed structure consists of three layers of aluminum foam with different densities filled in several concentric circular aluminum tubes. The test includes a solid design (Design-1) and a hollow design (Design-2). A series of quasi-static compression tests and finite element simulations are conducted, and the results show that BMFS exhibits a more advantageous sequential collapse deformation pattern for practical use. An energy absorption analysis of each layer shows that the energy absorption ratio of the foam layer reaches 85%. Comparing Models 1–3 of the two designs shows that the energy efficiency decreases, and the work efficiency increases, as the foam density increases. In addition, the interaction between the tubes and foams enhances the energy absorption properties of the structure. The parameter study shows that the energy absorption characteristics of Design-2 are insensitive to the diameter of the tube. The SEA of Design-1 increases with the thickness of Tube-1.

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

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

Experimental Study of the Dynamic and Static Compression Mechanical Properties of Closed-Cell PVC Foams.

Closed-cell polyvinyl chloride foam (PVC) possesses many advantages, including its light weight, moisture protection, high specific strength, high specific stiffness, and low thermal conductivity, and is widely used as the core material in composite sandwich structures. It is increasingly used in fields with light weight requirements, such as shipbuilding and aerospace. Some of these structures can be affected by the action of dynamic loads during their lifespan, such as accidental or hostile blast loads as well as wind-loaded debris shocks. Examining the material properties of PVC foams under dynamic load is essential to predict the performance of foam sandwich designs. In this study, the compressive responses of a group of PVC foams with different densities were investigated under a broad range of quasi-static conditions and high strain rates using a universal testing machine and a lengthened Split Hopkinson press bar (SHPB) fabricated from titanium alloy. The results show that the mechanical properties of foam materials are related to their density and are strain rate-sensitive. The compressive strength and plateau stress of the foams were augmented with increased foam density. In the quasi-static strain rate range, the compressive strength of PVC foams at 10−1 s−1 was 27% higher than that at 10−4 s−1. With a strain rate of 1700 s−1, the strength was 107% higher than the quasi-static value at 10−4 s−1.

Impact behavior of corrugated-core infilling foam sandwich composite structure

The anti-collision device has the effect of protecting both the ship and bridge. Two forms of corrugated-core infilling foam sandwich composite structure were developed to study their impact characteristics. The influence of structural geometric parameters on the peak force, failure modes, and energy absorption were analyzed via low-speed impact tests. The results show that the impact energy was almost absorbed by all specimens under impact velocity of 4 m/s. Compared with the dislocation corrugated core specimen (DC), the peak impact force of the parallel corrugated core specimen (PC) got a maximum of a 26.54% decline on the peak value. PC effectively improved the structural uniform compression deformation ability. Little influence on the interaction between wavelength and lattice thickness was proved. The impact peak force of PC was more sensitive to the change of lattice thickness, while the impact peak force of DC was more sensitive to the change of lattice wavelength. Numerical simulation predicted the impact peak force value and stress distribution of specimens. The effect of foam density on the peak force and the impact velocity on the energy absorption were investigated using the finite element (FE).

P15. Biomechanical analysis of bone density and depth of subsidence after expandable interbody cage placement

BACKGROUND CONTEXT Expandable interbody fusion cages have been developed to improve the ability to restore disc height and segmental lordosis. However, expandable cages have been shown to be associated with increased rates of postoperative subsidence. To optimize patient outcomes, it is critical to evaluate all variables which may influence a patient's risk of subsidence following the placement of an expandable interbody cage. PURPOSE To evaluate the association between bone density and depth of subsidence due to expandable interbody cages. STUDY DESIGN/SETTING Biomechanical study. PATIENT SAMPLE No patients were included. OUTCOME MEASURES Depth of subsidence (mm). METHODS In the first stage of the study, the depth of subsidence was measured following 150 N output force exerted by an expandable interbody cage. In the second stage, subsidence depth was measured with 1 Nm of input expansion torque. Within each stage, different bone foam densities were analyzed, including 5, 10, 15, and 20 pounds per cubic foot (PCF). Five experimental trials were performed for each PCF material, and the mean subsidence depths were calculated. Trials which failed to reach 150 N output force were considered outliers and were excluded from the analysis. The Mojave PL 3D Expandable Interbody System (Stryker, Leesburg, VA, USA) was utilized for all trials. RESULTS There was an overall decrease in subsidence depth with increasing bone foam density. The subsidence depths (mean ± standard deviation) at 150 N output force were 2.0±0.3 mm for 5 PCF, 1.8±0.2 mm for 10 PCF, 1.1±0.2 mm for 15 PCF, and 1.1±0.2 mm for 20 PCF bone foam. The mean subsidence depths at 1 Nm of input torque were 2.3±0.5 mm for 5 PCF, 2.3±0.5 mm for 10 PCF, 1.2±0.2 mm for 15 PCF, and 1.1±0.1 mm for 20 PCF bone foam. CONCLUSIONS The current study demonstrates the significant correlation between bone density and depth of subsidence due to an expandable interbody cage. At the same expansion torque, an expandable interbody cage implant will subside further into lower density bone. To apply the same distraction force, an implant on lower density bone will lose more expansion height to subsidence. These findings highlight the concern for catastrophic subsidence and resultant construct failure. Notably, because tactile feedback of cage expansion into subsiding bone cannot be reliably distinguished from true expansion of disc space height, surgeons should take bone quality into account when deploying expandable cages. FDA DEVICE/DRUG STATUS Mojave PL 3D Expandable Interbody System (Stryker, Leesburg, VA, USA) (Approved for this indication) Expandable interbody fusion cages have been developed to improve the ability to restore disc height and segmental lordosis. However, expandable cages have been shown to be associated with increased rates of postoperative subsidence. To optimize patient outcomes, it is critical to evaluate all variables which may influence a patient's risk of subsidence following the placement of an expandable interbody cage. To evaluate the association between bone density and depth of subsidence due to expandable interbody cages. Biomechanical study. No patients were included. Depth of subsidence (mm). In the first stage of the study, the depth of subsidence was measured following 150 N output force exerted by an expandable interbody cage. In the second stage, subsidence depth was measured with 1 Nm of input expansion torque. Within each stage, different bone foam densities were analyzed, including 5, 10, 15, and 20 pounds per cubic foot (PCF). Five experimental trials were performed for each PCF material, and the mean subsidence depths were calculated. Trials which failed to reach 150 N output force were considered outliers and were excluded from the analysis. The Mojave PL 3D Expandable Interbody System (Stryker, Leesburg, VA, USA) was utilized for all trials. There was an overall decrease in subsidence depth with increasing bone foam density. The subsidence depths (mean ± standard deviation) at 150 N output force were 2.0±0.3 mm for 5 PCF, 1.8±0.2 mm for 10 PCF, 1.1±0.2 mm for 15 PCF, and 1.1±0.2 mm for 20 PCF bone foam. The mean subsidence depths at 1 Nm of input torque were 2.3±0.5 mm for 5 PCF, 2.3±0.5 mm for 10 PCF, 1.2±0.2 mm for 15 PCF, and 1.1±0.1 mm for 20 PCF bone foam. The current study demonstrates the significant correlation between bone density and depth of subsidence due to an expandable interbody cage. At the same expansion torque, an expandable interbody cage implant will subside further into lower density bone. To apply the same distraction force, an implant on lower density bone will lose more expansion height to subsidence. These findings highlight the concern for catastrophic subsidence and resultant construct failure. Notably, because tactile feedback of cage expansion into subsiding bone cannot be reliably distinguished from true expansion of disc space height, surgeons should take bone quality into account when deploying expandable cages.

Ultra-light polylactic acid/combination composite foam: A fully biodegradable flame retardant material

In this study, low-density polylactic acid (PLA) flame retardant foams were prepared using lignin fiber (LF), ammonium polyphosphate (APP), resorcinol bis(diphenyl phosphate) (RDP) and SiO2 aerogel. LF, RDP and SiO2 aerogel alone did not improved the flame retardancy of PLA composites; however, APP alone required a higher addition of amount to achieve a better flame retardancy. The synergistic effect between the four can improve the flame retardancy of PLA at a lower addition level. The intumescent flame retardant system composed of LF/APP/RDP/SiO2 aerogel can not only form a dense carbon layer on the surface of the material when burning to improve the flame retardant performance, but also improve the thermal stability of PLA, increase the degradation temperature and reduce the thermal weight loss rate. The final PLA flame retardant foam (density: 0.022 g/cm3) prepared by supercritical foaming can reach V-0 rating in UL-94 vertical combustion test, and the limiting oxygen index (LOI) can reach 30.5 %.

Fabrication strategy for long‐chain branched polypropylene foams with high resilience and compressive strength

AbstractA flexible and controllable is proposed for fabricating long‐chain branched polypropylene (LCBPP) foams with high resilience and strength. LCBPP was blended with thermoplastic polyester elastomer (TPEE) using polyethylene octene elastomer grafted glycidyl methacrylate (POE‐g‐GMA) as a compatibilizer at different mass ratios, and the blends were then used to prepare foams at different temperatures by the supercritical CO2 batch foaming method. The foams were then tested for their compressive permanent strain and compressive strength. The results showed that introducing TPEE and POE‐g‐GMA increased the resilience. In particular, the permanent strain of the LCBPP/TPEE/POE‐g‐GMA foam at a ratio of 90/10/7 decreased from an initial 14.5% for the original LCBPP foam to 5% after five compression cycles. However, the compressive strength decreased from 65.59 to 39.82 kPa. Therefore, the foam density (ρ) and cell size (d) were adjusted to balance the resilience and strength. Increasing ρ/d from 0.32 to 3.10 increased the compressive strength significantly from 39.82 to 91.67 kPa while the permanent strain only increased 3.5%. Thus, the proposed strategy realized LCBPP foams with high resilience and compressive strength.

Energy absorption of foam-filled corrugated core sandwich panels under quasi-static loading

The present paper tries to introduce the effect of foam-filled on a type of trapezoidal corrugated core and their structures derived from the related previous studies. The main purpose of this work is to present a novel geometry of trapezoidal cores, and their configurations are inspired by the earlier works. These absorbers have been proposed to raise the specific energy absorption (SEA) while declining the initial peak crushing force. Therefore, five corrugated core sandwich panels have been tested under quasi-static axial compressive load experimentally and then simulated by ABAQUS software. The accuracy of the numerical simulations is validated by comparing the numerical results with the corresponding experimental data. Besides, some other simulations have been carried out to investigate the effect of foam density, core type, and thickness in more detail. The comparison results show that the SEA rate of bi-core sandwich panels which has not been filled by foam is better than the single trapezoidal core sandwich panels, and this rate is roughly around 70%. The best performance is relevant to the pure foam core without any trapezoidal core structure and the next item is the single foam-filled corrugated core and the lowest performance among them is related to the bi-core corrugated core foam-filled.

Microfoamed Strands by 3D Foam Printing.

We report the design, production, and characterization of microfoamed strands by means of a green and sustainable technology that makes use of CO2 to create ad-hoc innovative bubble morphologies. 3D foam-printing technology has been recently developed; thus, the foaming mechanism in the printer nozzle is not yet fully understood and controlled. We study the effects of the operating parameters of the 3D foam-printing process to control and optimize CO2 utilization through a maximization of the foaming efficiency. The strands’ mechanical properties were measured as a function of the foam density and explained by means of an innovative model that takes into consideration the polymer’s crystallinity content. The innovative microfoamed morphologies were produced using a bio-based and compostable polymer as well as polylactic acid and were then blown with CO2. The results of the extensive experimental campaigns show insightful maps of the bubble size, density, and crystallinity as a function of the process parameters, i.e., the CO2 concentration and temperature. A CO2 content of 15 wt% enables the acquirement of an incredibly low foam density of 40 kg/m3 and porosities from the macro-scale (100–900 μm) to the micro-scale (1–10 μm), depending on the temperature. The foam crystallinity content varied from 5% (using a low concentration of CO2) to 45% (using a high concentration of CO2). Indeed, we determined that the crystallinity content changes linearly with the CO2 concentration. In turn, the foamed strand’s elastic modulus is strongly affected by the crystallinity content. Hence, a corrected Egli’s equation was proposed to fit the strand mechanical properties as a function of foam density.