Polyurethane Foam Core Research Articles

Extending the Natural Neighbour Radial Point Interpolation Meshless Method to the Multiscale Analysis of Sandwich Beams with Polyurethane Foam Core

This work investigates the mechanical behaviour of sandwich beams with cellular cores using a multiscale approach combined with a meshless method, the Natural Neighbour Radial Point Interpolation Method (NNRPIM). The analysis is divided into two steps, aiming to analyse the efficiency of NNRPIM formulation when combined with homogenisation techniques for a multiscale computational framework of large-scale sandwich beam problems. In the first step, the cellular core material undergoes a controlled modification process in which circular holes are introduced into bulk polyurethane foam (PUF) to create materials with varying volume fractions. Subsequently, a homogenisation technique is combined with NNRPIM to determine the homogenised mechanical properties of these PUF materials with different porosities. In this step, NNRPIM solutions are compared with high-order FEM simulations. While the results demonstrate that RPIM can approximate high-order FEM solutions, it is observed that the computational cost increases significantly when aiming for comparable smoothness in the approximations. The second step applies the homogenised mechanical properties obtained in the first step to analyse large-scale sandwich beam problems with both homogeneous and functionally graded cores. The results reveal the capability of NNRPIM to closely replicate the solutions obtained from FEM analyses. Furthermore, an analysis of stress distributions along the beam thickness highlights a tendency for some NNRPIM formulations to yield slightly lower stress values near the domain boundaries. However, convergence towards agreement among different formulations is observed with mesh refinement. The findings of this study show that NNRPIM can be used as an alternative numerical method to FEM for analysing sandwich structures.

Evaluation of mechanical properties and energy absorption of polyurethane foam core sandwich panels with kevlar/basalt-epoxy laminates as face sheets

Evaluation of mechanical properties and energy absorption of polyurethane foam core sandwich panels with kevlar/basalt-epoxy laminates as face sheets

Multiscale Analysis of Sandwich Beams with Polyurethane Foam Core: A Comparative Study of Finite Element Methods and Radial Point Interpolation Method.

This study presents a comprehensive multiscale analysis of sandwich beams with a polyurethane foam (PUF) core, delivering a numerical comparison between finite element methods (FEMs) and a meshless method: the radial point interpolation method (RPIM). This work aims to combine RPIM with homogenisation techniques for multiscale analysis, being divided in two phases. In the first phase, bulk PUF material was modified by incorporating circular holes to create PUFs with varying volume fractions. Then, using a homogenisation technique coupled with FEM and four versions of RPIM, the homogenised mechanical properties of distinct PUF with different volume fractions were determined. It was observed that RPIM formulations, with higher-order integration schemes, are capable of approximating the solution and field smoothness of high-order FEM formulations. However, seeking a comparable field smoothness represents prohibitive computational costs for RPIM formulations. In a second phase, the obtained homogenised mechanical properties were applied to large-scale sandwich beam problems with homogeneous and approximately functionally graded cores, showing RPIM's capability to closely approximate FEM results. The analysis of stress distributions along the thickness of the beam highlighted RPIM's tendency to yield lower stress values near domain edges, albeit with convergence towards agreement among different formulations. It was found that RPIM formulations with lower nodal connectivity are very efficient, balancing computational cost and accuracy. Overall, this study shows RPIM's viability as an alternative to FEM for addressing practical elasticity applications.

Analysis of electrothermal damage in a radome exposed to electromagnetic radiation

Abstract After nearly 9 months of electromagnetic irradiation with a power density of 10 W/cm2, the unit blocks of an A-sandwich radome in the electromagnetic beam scanning area experienced electrothermal damage. Both the inner skin and core layer foam of the A-sandwich unit blocks in that area present different levels of damage. The inner skin is wrinkled and cracked, and the core layer foam is locally charred, carbonized, and ablated. The temperature images recorded through the infrared thermal beam method show that the temperature distribution of the unit blocks in the beam irradiation area is abnormal and strongly related to the discontinuous structure distribution of the core foam and resin. The non-uniformity of core material is the main cause of the electrothermal damage to unit blocks. By process improvements, the shaping of the polyurethane foam core layer is changed from cutting, resin bonding, and splicing to one-step foaming without resin binder, and the continuity of the core layer material is ensured. The usage results of unit blocks made by the new process show that the temperature field distribution is uniform, with a maximum temperature of only 31.3°C, which is 71.62% lower than the maximum temperature of 110.3°C in the damaged block.

Multifunctional sandwich composites with optimized phase change material content for simultaneous structural and thermal performance

This work aims at developing novel multifunctional sandwich composites with optimized thermal energy storage and structural load-bearing performance by incorporating microencapsulated phase change materials (PCMs) into polyurethane (PU) foam cores. The optimized foam containing 20 wt% PCM, balancing good latent heat storage (up to 29 J/g) with low thermal conductivity (up to 0.035 W/(m·K) at 50 °C), was used to produce sandwich panels with high-performance epoxy/carbon fiber laminate skins. Microstructural characterization confirmed excellent interfacial adhesion between the core and skins. The multifunctional panels exhibited comparable flexural strengths (150 kPa) and facing stresses (25 MPa) to neat PU sandwich controls. By integrating thermal regulation from PCM phase change with structural reinforcement from the sandwich architecture in a single multifunctional material system, this work contributes to the development of lightweight, energy-efficient composite materials suitable when weight reduction and thermal management are paramount, such as in aeronautics and cold chain logistics.

Flexural behavior of singly curved GFRP sandwich panel with polyurethane foam core

Curvilinear architecture and structures are becoming a worldwide trend for its streamlined appearance and synchronicity with the surroundings. Nonetheless, the conventional construction materials might not be able to achieve the desired curvilinear geometries in an effective and economic manner. In this regard, glass fiber-reinforced polymer (GFRP) curved sandwich panel with polyurethane foam core is able to meet the requirement of the construction efficiency and economy as well as satisfy the need for a lower energy consumption. However, few studies are available on the mechanical behavior of such panels. In this regard, this work was to conduct an experimental and numerical investigation on the singly curved GFRP sandwich panels to evaluate the flexural performance. In particular, the effect of the foam density, inclined angle, core thickness and stacking sequence of face sheet on the load-carrying capacity and failure mode was addressed. Four failure modes were identified. The singly curved GFRP sandwich panel showed an improved stiffness when compared to the flat panel, but showed more complicated failure mechanism. The stiffness of the curved panel with inclined angle 30° was 250 % higher than that of the flat panel in the test results. It was shown that the strength and stiffness increased as the density and thickness of the foam core increased. In addition, a finite element analysis was conducted via MSC.Marc and validated by the experimental results. A parametric study was performed to address the design parameters. It was found that the specimens with inclined angles of 30° and 45° showed the greatest stiffness.

Effect of cellulose nanocrystals on the mechanical and free vibration behavior of hybrid glass/kenaf fiber reinforced polyurethane core-based sandwich structures

ABSTRACT Engineering applications widely use foam-core-based sandwich structures. The study incorporated cellulose nanocrystals (CNC) into a hybrid glass/kenaf fiber-based polymeric sandwich structure with a 65 kg/m3 polyurethane foam core. Four unique face sheets (S1, S2, S3, and S4) were made using glass, kenaf, and CNC. Three-point bending, Charpy impact testing, and free vibration testing were used to characterize sandwich structures. The inclusion of CNC in the matrix of face sheets improved the hybrid composite’s bending strength and impact resistance. One layer of Kenaf fabric and two layers of glass make up the hybrid composite, which is stronger in both flexural strength and impact resistance, with 14.56 MPa and 8.1 J, respectively. These improvements are 44.84% and 57.49% compared to the pure glass/epoxy composite face plate. Nevertheless, the incorporation of Computer Numerical Control (CNC) failed to result in a substantial enhancement in vibration characteristics. Both matrix modification and natural fiber (kenaf) can effectively substitute glass fabric in sandwich structures.

The Effect of Damages on Modal Frequencies of Flat Glass Fiber Reinforced Polyurethane Foam Sandwich Structures

The Effect of Damages on Modal Frequencies of Flat Glass Fiber Reinforced Polyurethane Foam Sandwich Structures

Lateral compressive behavior of multi-layer lattice-web reinforced composite cylinders

Several novel multi-layer lattice-web reinforced composite cylinders, consisting of glass fiber reinforced polymer (GFRP) face sheets and lattice webs, polyurethane (PU) foam core and clay ceramsite filler, were proposed and manufactured using a vacuum assisted resin infusion process (VARIP) method. A series of quasi-static lateral compressive experiments were carried out to investigate the feasibility of the proposed cylinders. For both the hollow composite cylinders and ceramsite filling composite cylinders, the bearing capacity and energy absorption performance can be significantly improved with the use of multi-layer lattice-web layouts. Among the proposed three types of lattice-web layouts, the double-layer dislocated lattice-web layout made the composite cylinder exhibit the greatest specific energy absorption (SEA) performance and can be chosen as an optimal configuration. Furthermore, numerical models were established using LS-‍DYNA software to simulate the large deformation of the composite cylinders with double-layer dislocated lattice-web layout. Based on the numerical models, parametric analysis was carried out to discuss the effects of various parameters on the crushing response of the composite cylinders. Generally, using thicker GFRP material or higher radial lattice web can make the composite cylinders present an increased likelihood of brittle failure. However, filling ceramsite can not only make them exhibit plastic deformation characteristics but also facilitate the full utilization of various components.

Analyzing the influences of fabrication methods on the mechanical properties of Sumberejo kenaf/epoxy sandwich composites with polyurethane foam core

Natural fiber composite sandwich structures have developed significantly to create building materials that are strong and lightweight. The purpose of this study is to compare the cold press and vacuum assisted resin infusion (VARI) methods to investigate the mechanical properties of sandwich composites made of Sumberejo kenaf fiber (KF) reinforced epoxy (EP) as the skin and polyurethane (PU) foam as the core. The kenaf fibers were alkalized by NaOH solution. The results show that manufacturing KF/EP-PU foam sandwich composites using cold press has flatwise tensile strengths that are around (0.220 ± 0.031) MPa higher than VARI, which is only about (0.170 ± 0.057) MPa. This implies that cold press creates an enhanced composite structure. The core shear strength of cold press sample was 17% higher than VARI, with a value of (0.603 ± 0.052) MPa and (0.499 ± 0.016) MPa, respectively. Also, the skin bending stress of cold press sample was (6.106 ± 1.203) MPa while VARI sample had a value of (5.405 ± 0.687) MPa. However, the VARI method exhibited higher flatwise compressive strength with a value (0.393 ± 0.004) MPa and cold press method was (0.331 ± 0.032) MPa. In conclusion, the manufacturing method substantially impacts the mechanical properties of KF/EP-PU foam sandwich composites in this study. This study is a valuable reference for natural fiber sandwich composites as a building material.

Understanding Damage Initiation and Propagation Mechanisms in Polyurethane Foam Core Sandwich Panels Using Acoustic Emission Monitoring

Understanding Damage Initiation and Propagation Mechanisms in Polyurethane Foam Core Sandwich Panels Using Acoustic Emission Monitoring

Study on low-velocity impact response of kevlar/epoxy-polyurethane sandwich panels

This study aims to investigate the maximum energy absorption of sandwich panels featuring composite facesheets and a polyurethane foam core under low-velocity impact. The research explores various impactor head geometries, fiber orientations, and the number of composite layers on the panel facesheets. Three different impactor heads with flat, hemispherical, and conical shapes were used for experimental impacts. Numerical simulations were performed using Abaqus/Explicit finite element software, with damage initiation in the composite layers determined by the three-dimensional Hashin criterion. The results revealed that the conical-head impactor caused the highest energy absorption, accompanied by the greatest displacement and velocity changes. Among specimens with different fiber orientations, the 60° fiber layers exhibited a 9.41% and 8.45% higher maximum force compared to the 30° and 45° fiber layers, respectively. Furthermore, the study investigated the influence of the number of composite layers in the facesheets. It was found that panels with more layers in the bottom facesheet demonstrated a 4.94% increase in energy absorption compared to panels with more layers in the top facesheet. This research provides valuable insights into optimizing sandwich panel designs for enhanced energy absorption during low-velocity impact scenarios.

Crushing behavior of multi-layer lattice-web reinforced double-braced composite cylinders under lateral compression and impact loading

This paper reports on the crushing behavior of several novel multi-layer lattice-web reinforced double-braced composite cylinders composed of glass fiber reinforced polymer (GFRP) face sheets, GFRP lattice webs, polyurethane (PU) foam core and steel bars. A series of quasi-static lateral compression and low-velocity impact experiments were carried out to investigate the feasibility of the proposed cylinders. All the experimental specimens were manufactured using a vacuum assisted resin infusion process (VARIP) method. The bearing capacity and energy absorption performance of the composite cylinders can be significantly improved with the enhancement of multi-layer lattice-web layout and use of bracing. Among the proposed three types of lattice-web layouts, the double-layer dislocated lattice-web layout made the composite cylinder exhibit the greatest specific energy absorption (SEA) performance and good impact resistance property and can be chosen as an optimal configuration. Furthermore, numerical models were established using LS-DYNA software to simulate the large deformation of the composite cylinders with double-layer dislocated lattice-web layout. Based on the numerical models, parametric analysis was carried out to discuss the effects of various parameters on the crushing behavior of the composite cylinders. The bearing capacity and impact resistance property can be generally improved with the increase of GFRP thickness or radial lattice-web height. Additionally, using stronger foam material or smaller inclination of bracing can increase the absorbed energy in PU foam but the GFRP material always makes an essential contribution to the energy absorption of the composite cylinders.

Dynamic plastic response of sandwich structures with graded polyurethane foam cores and metallic face sheets exposed to uniform blast loading: experimental study and numerical simulation

Dynamic plastic response of sandwich structures with graded polyurethane foam cores and metallic face sheets exposed to uniform blast loading: experimental study and numerical simulation

Recycled Ti6Al4V alloy powder reinforced polyurethane core based sandwich structures: Mechanical and modal properties

In this study, recycled Ti6Al4V alloy powder was utilized as a reinforcement to enhance the mechanical and modal properties of polyurethane foam (PUF) core-based sandwich composites. Sandwich composite having carbon fiber reinforced polymer (CFRP) composite face sheets and Ti6Al4V powder-reinforced PUF cores were manufactured. The PUF cores were reinforced with two different variants of Ti6Al4V powder based on particle sizes from 1 to 3 wt.%. The dispersion quality was investigated using scanning electron microscopy (SEM). A detailed experimental modal analysis was conducted to evaluate the modal properties in terms of the natural frequencies and damping ratios of the sandwich specimens. A comprehensive mechanical study was also conducted in terms of compression, buckling, flexural, and impact tests according to the relative ASTM standards. The experimental results demonstrated that the Ti6Al4V reinforced sandwich specimens exhibited superior mechanical and modal properties with enhanced PUF cores. Improvements in excess of 21%, 37%, and 24% were recorded in the compression, buckling, and flexural response of the reinforced specimens, respectively, compared to those of their neat counterparts. Similarly, remarkable improvements were also observed in the experimental modal and impact properties of the Ti6Al4V alloy powder-reinforced sandwich composites.

Tailoring of mechanical, thermal and vibration behaviour of hybrid fibre with core honeycomb energy-absorbing materials reinforced polymer sandwich laminates

Sandwich laminates are particularly important in the early stages of structural design due to their excellent mechanical, energy absorption, and other structural properties. High-strength carbon and glass fibre with honeycomb core sandwich laminates were fabricated by vacuum bag moulding. Three different energy-absorbing materials are used to develop sandwich structure laminates, such as cores filled with Rohacell, naturally available wheat husk and polyurethane foam (PUF). Some tests, such as flexural strength, vibrational behaviour, flammability analysis and impact tests, are carried out to assess the mechanical and dynamical properties of the sandwich laminates. According to the results, the PUF sandwich layer designed laminate exhibits good vibration with higher mechanical properties compared to the Rohacell and wheat husk laminates. Moreover, the PUF core laminate enhances the fire resistance property. PUF foam with fibres reinforced sandwich composite exhibited a higher natural frequency (825 Hz) and a higher damping value (0.059) than the wheat husk and Rohacell core sandwich laminates. This is because the PUF core dissipates energy more efficiently than other core sandwich laminates at all modes.

Numerical Studies on Flexural Behaviour of Graded Multi-Layer Puf Cored Sandwich Panels

The present numerical investigation was mainly concerned with the evaluation of flexural properties of graded multi-layered polyurethane foam cored (MLCC) sandwich panels using a novel approach through the medium of general purpose program i.e. FEM/ANSYS. Aiming to the goal, three-point bending analysis was performed on sandwich beam models assumed to be made up of composite face sheets (GFRP) and graded multi-layer polyurethane foam cores of different layer densities. Finite element models of sandwich beams were obtained successfully using nonlinear shell 91 elements for face sheets (orthotropic material) and 8-noded shell 98 elements for core (isotropic material).Various multi-layer core configurations in a stack of three layered core were studied with great care. Prior to actual task, the proposed evaluation technique was verified using bench marks. Series of multi-layered cored beam models of different core configurations and span length were analysed in order to study the influence of different graded (density) layer configuration on flexural properties. The present studies reveals that use of MLCC panels for sandwich construction can provide improved flexural properties and hence these panels could be the better choice for structures under non uniform bending and shear loads due to their higher shear stiffness values compared to soft PUF cored panels. Furthermore the MLCC-2 panels in which layers arranged in order of higher to lower density between compression face and tension face stand better among all the possible core configurations.

A Butterfly-Like Connection Proposed for Bridge Pier Composite Protective System against Vessel Collision: Experimental and Numerical Analyses

Reliable connections are crucial for a bridge anti-collision protective system. Thus, this study proposes an innovative butterfly-like connection to tightly connect all segments of the pier composite protective system. The composite protective system is composed of four large segments, made of glass fiber-reinforced polymer (GFRP) panels, GFRP lattice plates, GFRP octagonal honeycomb tubes, round steel tubes, and polyurethane (PU) foam cores. The segments are jointed as a whole protective system by using eight proposed butterfly-like connections. First, the quasi-static tensile test is carried out to study the tensile strength and failure mechanism of the proposed connection. Then, a numerical model of the connection is established to determine the optimization parameter, and the numerical results are verified by experimental data. The optimal structural parameters for the connection are determined by parameter analysis using numerical results. Finally, a case study of a cable-supported bridge under vessel collision is numerically analyzed to comprehensively evaluate the overall protective performance and the dynamic reliability of the connection. It was found that the dynamic performance of the proposed connection is so reliable that it can ensure the protection system’s excellent performance. Also, the composite protective system can effectively reduce the collision force and the damage to both bridge and vessel.

Quasi-static indentation damage mechanics of PU foam core reinforced with fly ash particulate

The fly ash (FA) particulates are used in this study to reinforce the polyurethane foam (PUF) core. The FA particles inclusion improves the mechanical performance of the PUF core under compression by increasing its modulus of elasticity. Low-velocity impacts have damage dynamics that are pretty similar to quasi-static indentation. Consequently, the indentation resistance capability of the PUF core is investigated for three types of indenter nose tips with varied FA wt. Percentages (flat-circular, hemispherical, and conical). The results reveal that the reinforced foam core’s resistance varies with reinforcement percentage under indentation. However, FA reinforcement to PUF does not necessarily improve indentation resistance. The damage mechanism of the PUF core under indentation has been evaluated for each type of indenter. The interaction of crushing, shear, and tear of the damaged surface with the change in indenter nose tip has been explained with 0–20% variation of FA particles. Scanning electron microscope (SEM) images are taken for the analysis of the damaged PUF core cross-section at the indented location. Earlier mechanical findings of the scatter in deformation behavior with the indenter nose tip geometry are substantiated by the SEM studies.

Effects of Wood Flour and Curing Temperature on Some Properties of the Polyurethane Foam Core in a Wood-Based Sandwich Panel

The objectives of this study were to examine the chemical, physical, and mechanical properties of polyurethane (PU) foam prepared with various wood flour contents and curing temperatures for use as a core layer in wood-based sandwich panels. The five alternative wood flour contents tested were 2, 4, 6, 8, 10, and 12%, and the alternative curing temperatures 100, 120, 140, and 160°C were studied with 10% wood flour content. The results showed that the cell size and density of the PU foam increased at wood contents above 6%, which reduced the compressive strength of the samples. It was also found for PU with 10% wood content that curing at 100 to 160°C caused a decrease in foam density by 50%, compared with PU foam cured under the standard conditions (i.e., at room temperature). SEM and cell size measurements show the anisotropy of PU foam and the increase of foam cell diameter when increasing the curing temperature from standard condition to 140°C. Consequently, the compressive strength and its specific value declined abruptly at elevated curing temperatures, starting from 100°C. These results suggest that elevated curing temperatures cause degradation of the properties of wood-filled PU foam, due to effects on foam cell structure.