Syntactic Foams Research Articles

SYNTACTIC FOAMS BASED ON HOLLOW CERAMIC MICROSPHERES AND POLYCARBOSILANE

Syntactic foams based on hollow ceramic microspheres and the ceramic-forming binder polycarbosilane, capable of transition to silicon carbide at elevated temperatures, are considered. The processes of heat treatment of compositions and the transition of polycarbosilane to silicon carbide are considered. The physicomechanical and thermophysical characteristics of syntactic foams are studied.

Local elastic and limit strength characteristics of epoxy compositions with hollow glass microspheres

A method is proposed for predicting local elastic characteristics and ultimate strength parameters under monoaxial compression of epoxy compositions with hollow glass microspheres. The method takes into account the composition, volume fractions of the components of syntactic foams, and the characteristic size of microspheres (the ratio of the shell thickness to the cavity radius). Model calculations are carried out, taking into account changes in these parameters. Keywords: microsphere, epoxy binder, syntactic foam, syntactic, stress concentration operator, mehanical strength, modeling. alekc_sap@mail.ru

Physicochemical, Mechanical and Electrical Properties of Epoxy-Based Syntactic Foam Under Thermal and Hydrothermal Aging Conditions

Physicochemical, Mechanical and Electrical Properties of Epoxy-Based Syntactic Foam Under Thermal and Hydrothermal Aging Conditions

Mg Alloy Matrix Syntactic Foams Filled with Mgo Coated Al2o3 Hollow Spheres: Microstructure and Mechanical Properties

Mg Alloy Matrix Syntactic Foams Filled with Mgo Coated Al2o3 Hollow Spheres: Microstructure and Mechanical Properties

Preparation and Quasi-Static Compression Properties of Hybrid Aluminum Matrix Syntactic Foam Reinforced with Glass Cenospheres and Silicon Carbide Nanowires

Preparation and Quasi-Static Compression Properties of Hybrid Aluminum Matrix Syntactic Foam Reinforced with Glass Cenospheres and Silicon Carbide Nanowires

Effects of filler and matrix materials on the properties of metal syntactic foams

Effects of filler and matrix materials on the properties of metal syntactic foams

Impact behavior of natural rubber based syntactic foam core sandwich structures

Abstract In this study, the impact behavior of sandwich panels of natural rubber-based syntactic foam cores with aluminum face sheets was investigated experimentally and with the help of finite element analysis (FEA). Syntactic foam cores were produced byadding glass bubbles (GB) to the natural rubber (NR). Natural rubber was dissolved at room temperature with chemical solvents mixed with glass bubbles at 10, 20, and 30 weight percentages. Very low density (~0.8 g × cm-3) and high compressible foams were obtained depending on the GB weight percentages. Aluminum face sheets and the NR/GB syntactic foam core developed were joined by adhesive bonding to produce sandwich beam specimens. The sandwich beams manufactured in this way were subjected to impact loading under three-point bending boundary conditions experimentally. The experimental results were compared with finite element simulation results under the same loading and boundary conditions. The damage mechanism of the sandwich panels devised were analyzed. According to the results, natural rubber containing an additive of 20 wt.-% GBs showed better impact resistance than the others.

Preparation, compression behavior and 3D damage evolution of epoxy syntactic foam with nickel hollow spheres

The nickel thin-walled hollow spheres (NHS) epoxy syntactic foam was fabricated by the infiltration method. The crystal structure and grain size of the NHS were quantitatively analyzed by FIB-TEM. The bulk compressive response of the NHS syntactic foam was determined and compared with glass bubble syntactic foam. The X-ray computed microtomography (XCT) coupling with the interrupted compression tests were conducted on a single NHS and the NHS syntactic foam to demonstrate the 3D deformation history. The bulk behaviors of the NHS syntactic foam were correlated with the XCT examinations to analyze the mechanisms of the failure process. The electrodeposited NHS shows the nanocrystalline and polycrystalline microstructure. The low air void content was achieved in the NHS syntactic foam produced by the infiltration method. Although the NHS syntactic foam's elasticity and yield strength are lower, the compressive resistance and toughness as well as the energy absorption of the NHS syntactic foam are higher than those of glass syntactic foam. The failure process of the NHS syntactic foam is dominated by the NHSs deformation and the resultant strain hardening. The damage initiates from the weak NHSs, then more crushed bands arise with the increased compressive stress. The further deformation of the damaged bands can intermittently develop owing to the strain hardening. During the deformation history, no visible macro cracks can be found in the epoxy matrix from the XCT slices.

Effects of particle size, bimodality and heat treatment on mechanical properties of pumice reinforced aluminum syntactic foams produced by cold chamber die casting

In recent years, metal matrix syntactic foams (MMSFs) have become highly attractive owing to their unique physical, microstructural and mechanical features. Due to their promising potential for different industrial areas like automotive, aviation, and defense, these advanced engineering materials can also be evaluated as serious alternatives to particle reinforced metallic composites and conventional metallic foams. Differently from previously reported laboratory scaled techniques in the literature, this experimental effort focuses on the feasibility of MMSF manufacturing via a fully automated and industrial-based cold chamber die casting technique. Accordingly, 1–2 mm, 2–4 mm, and bimodal (50vol.%) natural-based pumice filled aluminum syntactic foams were manufactured utilizing a purpose-made casting machine. Physical, macroscopic, and microscopic examinations show that all of the fabricated samples display perfect matrix/filler harmony. Average density levels of fabricated syntactic foams range between 1.50 and 1.80 g·cm−3 depending upon the pumice particles size interval. To assess mechanical responses, quasi-static compression tests were performed. Furthermore, half of the foam samples were subjected to heat treatment to explore possible influences of aging on the compressive features and damage modes. Results indicate that although the heat treatment enhances the compressive strength, plateau stress, and energy absorption properties of the fabricated foams, it changes damage mode of the samples by causing brittle dominant deformation.

Fabrication and properties of slag-based geopolymer syntactic foams containing hollow glass microspheres

High porosity and high strength slag-based geopolymer syntactic foams were achieved by a combined route consisting in both embedding hollow glass microspheres and direct foaming with H2O2 and a surfactant. The effect of the hollow glass microspheres content on the pore morphology, porosity, density, mechanical strength, and thermal conductivity was investigated. Results showed that the hollow glass microspheres were dispersed homogenously and bonded well with the geopolymer matrix.

The dependency of compressive response of epoxy syntactic foam on the strain rate and temperature under rigid confinement

Syntactic foam is being increasingly conceived for aero engine applications to enhance overall structural reliability under impact loading. Systematic compressive tests without and with lateral confinement are carried out to investigate the deformation and failure of an epoxy syntactic foam (ESF) at quasi-static 0.01/s, medium rate 10–100/s and high strain rates 500–1100/s at gradually increasing temperatures from room temperature 25 °C to 150 °C. The stress–strain response and the corresponding deformation process, complemented by Digital Image Correlation (DIC) technique, were monitored to reveal the dynamic deformation and strain localization of the foam. The elastic-brittle behavior without confinement at high strain rates can be suppressed by the lateral confinement and by elevated temperatures above 100 °C. The lateral confinement slightly increases yield stress and significantly improves the energy absorption of ESF. Both confined yield stress and energy absorption evolve nonlinearly with strain rate and temperature. The strain hardening in the elastic–plastic behavior of ESF under confinement is strain rate independent, compared to its modest temperature dependency. A nonlinear phenomenological model is found to be able to describe the unconfined and confined responses of ESF and its temperature-strain rate equivalence, and reveal the competition between strain hardening and strain softening which is influenced by temperature.

Effects of silane coupling agent modifications of hollow glass microspheres on syntactic foams with epoxy matrix

A syntactic foam was prepared from an epoxy resin matrix and modified hollow glass microsphere fillers. Modification by silane coupling agents with different molecular structures was analyzed, and the optimal content of the silane coupling agent was determined. The results demonstrated that all silane coupling agents enhanced the adhesion between the hollow glass microspheres and epoxy resin matrix, resulting in enhanced water absorption, compressive performance, tensile performance, and bending performance compared to those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end groups, the one with a sulfhydryl end group exhibited optimal modification for hollow glass microspheres. Among the silane coupling agents with different backbone structures, the one with silanol groups exhibited the optimal modification of hollow glass microspheres. Additionally, the performance of the syntactic foams was optimal when 6% of the silanol-containing coupling agent was used. The results demonstrated that syntactic foams prepared with hollow glass microspheres modified by silane coupling agents exhibited improvements in water absorption, compressive performance, tensile performance, and bending performance, compared with those prepared using unmodified hollow glass microspheres. Among silane coupling agents with different end structures, the one with a sulfhydryl group as end group showed the best modification effect on hollow glass microspheres. The water absorption was 0.35%, the compressive strength was 62.15 MPa, the tensile strength was 40.15 MPa, and the bending strength was 53.17 MPa. Among silane coupling agents with different backbone structures, the one with silanol groupsbonds showed the best results. Its compressive strength was up to 64.15 MPa, the tensile strength was 35.47 MPa, and the bending strength was 53.99 MPa.

Loading Effect of Hollow Glass Microsphere (HGM) and Foam Microstructure on the Specific Mechanical Properties and Water Absorption of Syntactic Foam Composite

AbstractEpoxy syntactic foams (SF) filled with hollow glass microspheres (HGM) were prepared by simple resin casting method and characterization in this study. The effect of varying the amount of HGM on the specific mechanical and water absorption properties of SF composites were investigated. Five different composition of SF (SFT60-0.5 to SFT60-2.5) were compared with the neat epoxy matrix. The wall thickness of the microballoons differ because of its different percentile size distribution (10th, 50th and 90th), which reflects in its density variation. The results show that the specific tensile and flexural strength increases with an increasing filler (HGM) content. The density of SF filled with HGM reduces with increasing volume fraction of filler content. Scanning electron microscopy was done on the failed samples to examine the fractured surfaces. The water absorption capacity of the SF was also investigated as it relates to the HGM volume fraction variation. All the syntactic foam composition shows a better diffusion coefficient capacity than the neat epoxy resin. This makes it applicable in structural purposes and several marine application products such as Autonomous Ultimately Vehicle (AUV).

Functionally Graded Syntactic Foams with Layers of Dissimilar Metallic Matrices

Functionally Graded Syntactic Foams with Layers of Dissimilar Metallic Matrices

Time-dependent response of thermoplastic matrix composite material under the cyclic loadings

Under the service conditions, steel pipelines coated with the thermal protection system are subjected to cyclic loadings of axial tension and hydrostatic pressure. The finite element method generally used to simulate the behavior of composite structures under these loadings allows us to estimate the stresses generated in the system and to conclude on several origins of damage. However, for the framework of displacement or deformation analyses in such multilayer systems, these calculations do not allow a better prediction of their behavior. The methods used do not take sufficiently into account the characteristics of the different coating materials to predict their response in service conditions under cyclic loading. In this paper, we consider the viscosity of the thermoplastic materials used for the five layers coating system. Finite element calculations allow us to observe the areas of highest stress concentration at the interface with the steel pipe. Simulations allowed us to observe that the applied loads lead to increases in residual deformation in the thermoplastic matrix composite material. Cyclic tensile loading causes cracks in the matrix of the syntactic foam material. The study carried out here makes it possible to justify the origin of the failure mechanism in the composite material at the time of the installation of the pipelines which could limit the duration of their use in an offshore environment. The tensile failure of the syntactic foam considered as the polypropylene matrix composite material on which cyclic loads have been applied, is due to the stress level at a given temperature.

Experimental investigation on the machinability characteristics in drilling of syntactic foams

Syntactic foams (SFs) finds its application in automobiles, aircrafts and underwater vehicles. Drilling is most frequently used machining operation for assembly of these composite structures. In the present investigation, an effort is made to analyse the effect of cutting speed (Cs ), feed rate (fr ), drill diameter (D) and filler content (F) on machinability characteristics in drilling glass microballoon (GMB) reinforced epoxy SFs. Machinability characteristics analyzed includes thrust force (Tf ) and surface roughness (Sr ). SFs are fabricated by dispersing 25, 35 and 45 vol.% of GMBs in epoxy resin. Experiments are carried out based on full factorial design (FFD) using TiAlN coated carbide drills. Experimental results show that Tf and Sr increases with increasing Cs . As fr increases, Tf increases but decreases the Sr . Increasing GMB content significantly reduces the Tf and Sr of developed SFs.

Manufacturing, Heat Treatment and Investigation of Foam-Filled Tubes

Abstract Composite metal foams are hybrid structures with the main advantages of high specific strength and mechanical energy absorption associated with low density. In the course of our research, we successfully manufactured functional metal foams of EN AC-44200 matrix filled with lightweight expanded clay aggregate particles (LECAPs) in EN AW-6060 alloy tubes with a diameter of 50 mm and a wall thickness of 5 mm. Manufacturing was performed by low-pressure infiltration directly into the aluminium tube. Six different types of samples were examined: metal matrix syntactic foam, in-situ metal foam, ex-situ metal foam, and their heat-treated pairs. In the compression tests, the heat treatment provided a visible improvement in the results of the ex-situ metal foams.

Current Status of Research on the Modification of Thermal Properties of Epoxy Resin-Based Syntactic Foam Insulation Materials.

As a lightweight and highly insulating composite material, epoxy resin syntactic foam is increasingly widely used for insulation filling in electrical equipment. To avoid core burning and cracking, which are prone to occur during the casting process, the epoxy resin-based syntactic foam insulation materials with high thermal conductivity and low coefficient of thermal expansion are required for composite insulation equipment. The review is divided into three sections concentrating on the two main aspects of modifying the thermal properties of syntactic foam. The mechanism and models, from the aspects of thermal conductivity and coefficient of thermal expansion, are presented in the first part. The second part aims to better understand the methods for modifying the thermal properties of syntactic foam by adding functional fillers, including the addition of thermally conductive particles, hollow glass microspheres, negative thermal expansion filler and fibers, etc. The third part concludes by describing the existing challenges in this research field and expanding the applicable areas of epoxy resin-based syntactic foam insulation materials, especially cross-arm composite insulation.

Compressive properties of metal matrix syntactic foams in uni- and triaxial compression

Metal matrix syntactic foams (MMSFs) with Al alloy matrix (Al99.5 and AlSi12) and pure Fe metallic hollow spheres (MHSs, 64 vol%) were produced by pressure infiltration process. The density of the produced MMSFs was between 1.18 and 1.54 g cm−3. Cylindrical samples were investigated by compressive tests in free (between rigid plates) and radially constrained (in a thick wall steel sleeve) condition. The compressive curves were generalized, and the characteristic properties were identified (structural stiffness, yield strength, plateau strength, energy absorption). The general compressive curves altered in their plateau region: in free condition the plateau was flat, in constrained condition it was increasing. The characteristic properties of the MMSFs could be described by scaling laws and were influenced by the matrix properties and by the relative density of the samples. For the implementation of MMSFs into finite element systems, their constitutive law was formalized by the implementation of the Shima-Oyane model.

Effects of hollow glass microspheres on the polybenzoxazine thermosets: Mechanical, thermal, heat insulation, and morphological properties

AbstractThe growing need for high thermal and mechanical resistant lightweight syntactic foams demands the designing of new materials. Herein, we report the successful fabrication of lightweight and high thermal resistance syntactic foams with excellent thermal and good mechanical properties. For this end, 10–50 wt% hollow glass microsphere (HGMS) containing polybenzoxazine based syntactic foams were prepared by using bisphenol‐A‐aniline (BA‐a) and phenol‐diaminodiphenylmethane (P‐ddm) benzoxazine via curing at 10 MPa compression molding. The curing behavior, tensile, flexural, compressive, and impact strength, thermal properties, and fracture morphology of the syntactic foams were studied by DSC, universal material testing machine, and drop hammer impact testing machine, TGA, and SEM, respectively. The curing temperatures of BA‐a and P‐ddm benzoxazine resins were slightly increased after blending the HGMS. The highest decline (59%) in the density and highest void contains (13.17%) was recorded for the poly(P‐ddm/HGMS50) sample. The excellent specific mechanical properties of the syntactic foams were observed on the 30 wt% HGMS loading. The thermal conductivity of the foams was gradually decreased and the lowest values of 0.106 and 0.0985 W/m.K were observed for poly(BA‐a/HMGS50) and poly(P‐ddm/HGMS50) sample, respectively. Furthermore, a gradual improvement in the thermal properties was observed as the loading of HGMS increased.