Compressive Properties Of Syntactic Foams Research Articles

Dynamic response and residual compressive characteristics of syntactic foams at high and low temperatures

The dynamic response at low and high temperatures and compression after impact of aluminum matrix syntactic foams were studied. There were many cracks in syntactic foams after dynamic compression. The failure behaviors of compression after impact were almost identical to those of quasi-static compression in the late plateau stage and densification stage. The dynamic compressive properties of syntactic foams are greatly affected by the hollow sphere size at low strain rate, but this phenomenon is not remarkable at medium and high strain rates. The compressive strength and plateau stress are insensitive to the strain rate, but the energy absorption increases when increasing the strain rate. The dynamic compressive properties of syntactic foams have low-temperature strengthening and high-temperature softening effects, but the latter no longer changes above 100 ℃. The residual energy absorption is high, which indicates syntactic foams have potential as energy absorbing materials after dynamic damage.

Finite element simulation and experimental verification of quasi-static compression properties for 3D spacer fabric/hollow microspheres reinforced three phase composites

To enhance the compressive properties of syntactic foams, a new type of ternary composite named 3D spacer fabric/hollow microspheres reinforced composite (3DSMRC) was designed by adding warp-knitted space fabric (WKSF) into traditional syntactic foam. In order deeply understand the meso-mechanical properties of 3DSMRC composites, the compression tests of 3DSMRC were carried out and the quasi-static compression finite element models were established based on COMSOL Multiphysics. The results show that the compression properties of 3DSMRC were obviously controlled by structures of WKSF. To be specific, the 3DSMRC composites with more spacer yarns per unit area could withstand higher critical load, and with denser surface layers and larger spacer yarns inclination-angle could gain better compression capacities. Meanwhile, different types of microspheres also had important impact on the compression capacities of specimens, which could be improved by using smaller radius ratio (higher strength) microspheres. In addition, the finite element model can accurately reproduce the compression process and stress-strain curves of representative 3DSMRC samples, and then accurately simulate the values of compressive modulus and yield strength. The simulation and experimental studies of 3DSMRC can help to obtain a better and deeper understanding of the compression properties of this new type of composite, and finally provide a useful theoretical reference for the optimization design of 3DSMRC.

Compressive properties of expanded glass and alumina hollow spheres hybrid reinforced aluminum matrix syntactic foams

Expanded glass (EG) and alumina hollow spheres (HS) hybrid reinforced aluminum matrix syntactic foams and syntactic foams containing only a single reinforcement were prepared using the stir casting method. The volume fraction of reinforcements in the syntactic foam reached the maximum value by this production method in the available reports, i.e. 52.24%. No significant chemical reaction occurred between matrix and reinforcements. The quasi-static compressive properties of reinforcements and syntactic foams were tested. Regardless of the reinforcement type, the compressive properties of syntactic foams containing smaller reinforcements (diameter 2–3 mm) are higher than that of foams with 3–4 mm reinforcements. The compressive strength, plateau stress, stress drop, and energy absorption of hybrid reinforced syntactic foams decrease with the increase of EG content. The density and compressive properties of hybrid reinforced syntactic foams can be predicted using the rule of mixture and are in good agreement with the measured values. The syntactic foams exhibit brittle deformation characteristics and the crack propagation path depends on the EG content.

Microstructure and Compressive Properties of Al/Al<sub>2</sub>O<sub>3</sub> Syntactic Foams

Metal matrix syntactic foams with relativity low density (2.03 g/cm3) were prepared by stir casting method. The syntactic foam is comprised of alumina hollow spheres with a diameter range of 1.0-1.5 mm as reinforcement and ZL111 aluminum alloy as matrix. Calcium particles are used to increase the viscosity of the melt to ensure that low density hollow spheres are immersed in the melt. Microstructure characteristics and quasi-static compressive properties of syntactic foams were studied. The hollow spheres were uniformly distributed in the aluminum matrix, and the interface between them was in continuous contact. Compressive stress-strain curve exhibits three distinct stages of deformation: (i) the linear elastic stage; (ii) the plateau area; (iii) final densification stage. The compression strength and plateau stress are 85 MPa and 75 MPa, respectively. The main reasons for the sample failure are the collapse of hollow spheres and the formation of multiple shear bands.

Compressive Stress of Syntactic Foam: Effect of rNBR Particles Reinforced Epoxy Macrospheres (rNBR-EM)

This research focuses on the effect of rejected nitrile butadiene rubber (rNBR) gloves particles reinforced epoxy macrospheres (EM) on the physical properties and compressive stress of syntactic foam. Adding rNBR particles on the surface of macrospheres can increase the energy absorption as a result of improving the compressive properties of syntactic foam. Three types of macrospheres have been produced for the fabrication of syntactic foam, namely EM without rNBR, 1-layer rNBR-EM and 2-layer rNBR-EM. The results showed that increased rNBR particles layer on macrospheres has increased the wall thickness, and reduced the radius ratio of macrospheres as well as increased the density of syntactic foams. The compressive strength and modulus of syntactic foam with 2-rNBR-EM increased compared to the syntactic foams of 1-rNBR-EM and EM without rNBR. In addition, the toughness of the 2-rNBR-EM increased compared to the syntactic foams of 1-rNBR-EM and EM without rNBR.

Compressive Properties of Syntactic Foam Reinforced by Warp-knitted Spacer Fabric

Syntactic foam composites are widely used as aviation, construction and marine materials because of their high specific strength, specific modulus, damage tolerance and low moisture absorption. The present work aimed to investigate the compression behaviours of syntactic foam reinforced by warp knitted spacer fabric (SF-WKSF). Eight kinds of SF-WKSF samples were produced with warp knitted spacer fabrics of various surface layer structures and parameters including inclination-angle, fineness of spacer yarns, different microballoons types as well as contents. The compression tests were carried out on aMTS material testing system and the compression properties of SF-WKSF were analyzed based on the experimental compressive stress-strain curves and modulus values. It was indicated that the SF-WKSF made with preferable spacer fabric showed higher compressive modulus and yield strength values compared to neat syntactic foam (NSF). The results also demonstrated that all the parameters had significant effects on the compression performances of SF-WKSF. The composites could gain better anti-compression capacities by selecting larger inclination-angle, coarser spacer yarn, denser surface layer structure, higher microballoon density and higher S60HS microballoon contents.

Preparation and Characteristic of Different Hollow Microspheres Filled Syntactic Foams

In this study, hollow glass microspheres (HGM) and hollow polystyrene microspheres (HPSM) have been employed as fillers in epoxy resin to prepare the syntactic foam. A kind of good performance composite was prepared. The effects of presence of various hollow microspheres on the impact and compressive properties of syntactic foams are studied. Weight fraction of HPSM and HGM for the syntactic foams varies up to 2.0 wt% and 25 wt%, respectively. The results show that the coupling agent can induce the interfacial adhesion between the HGM and the resin and help HGM uniformly disperse in the resin and hence result in better mechanical properties of composite. On the other hand, the effect of HPSM for the composite density is greater than that of HGM. The addition of a small percentage of HPSM helps produce an important improvement in the low density of syntactic foam. The syntactic foam has uniform stability component and the excellent integrative performances. Fabricated syntactic foams had compression strength of 51.96 MPa and density of 0.671 g/cm3.

Study on Compressive Properties of Syntactic Foams for Marine Applications

Study on Compressive Properties of Syntactic Foams for Marine Applications

Carbon-Nanofiber-Reinforced Syntactic Foams: Compressive Properties and Strain Rate Sensitivity

The current study is focused on exploring the possibility of reinforcing syntactic foams with carbon nanofibers (CNFs). Syntactic foams are hollow, particle-filled composites that are widely used in marine structures and are now finding applications in other modes of transportation due to their high stiffness-to-weight ratio. The compressive properties of syntactic foams reinforced with CNFs are characterized over the strain rate range of 10−4 to 3,000 s−1, which covers seven orders of magnitude. The results show that despite lower density with respect to neat epoxy, CNF/syntactic foams can have up to 7.3% and 15.5% higher quasi-static compressive strength and modulus, respectively, for the compositions that were characterized in the current study. In addition, these properties can be tailored over a wide range by means of hollow particle wall thickness and volume fraction, and CNF volume fraction. The compressive strength of CNF/syntactic foams is also shown to generally increase by up to a factor of 3.41 with increasing strain rate when quasi-static and high-strain-rate testing data are compared. Extensive microscopy of the CNF/syntactic foams is conducted to understand the failure and energy absorption mechanisms. Crack bridging by CNFs is observed in the specimens, which can delay final failure and increase the energy absorption capacity of the specimens. Deformation of CNFs is also noticed in the material microstructure. The deformation and failure mechanisms of nanofibers are related to the test strain rate and the structure of CNFs.

Compressive properties of Al-A206/SiC and Mg-AZ91/SiC syntactic foams

Abstract

Volume fraction effect on high strain rate properties of syntactic foam composites

The volume fraction effect on the high strain rate compressive properties of syntactic foams is characterized using a pulse-shaped Split-Hopkinson Pressure Bar (SHPB) technique. Eighteen different types of syntactic foams are fabricated with the same matrix resin system but six different microballoon volume fractions and three different size microballoons. The volume fractions of the microballoons in the syntactic foams are maintained at 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6. The microballoons have the same mean outer radius of 40 μm, but different internal radii leading to a difference in their density. Analysis is carried out on the effect of microballoon volume fractions on the high strain rate properties for each type of syntactic foam. This approach is helpful in understanding the effect of microballoon reinforcement at different volume fractions on the dynamic compressive properties of syntactic foams. The results at high strain rates are compared to quasi-static strain rate compressive properties of the same material. The results show that there is a decrease in both compressive strength and modulus as the microballoon volume fraction increases for the same type of syntactic foam at all strain rates. However, at strain rates of quasi-static and 450/s, the decrease tends to be gradual across all volume fractions, while for strain rates of 800/s, there is a dramatic decrease from 10 to 20% followed by a gradual decline for most specimens. The fracture mode plays a major role in the dynamic behavior of syntactic foams.

Radius ratio effect on high-strain rate properties of syntactic foam composites

The high-strain rate compressive properties of syntactic foams are characterized in this study. This study is performed using a pulse-shaped Split-Hopkinson Pressure Bar technique. Nine different types of syntactic foams are fabricated with the same matrix resin system but three different size microballoons and three different microballoon volume fractions. The microballoons have the same outer radius of 40 μm, but different internal radii leading to a difference in their densities. The volume fractions of the microballoons in the syntactic foams are maintained at 0.1, 0.3, and 0.6. Analysis is carried out on the effect of the microballoon radius ratio at each volume fraction on the high-strain rate properties. This approach is helpful in separating and categorizing the contribution of matrix and microballoons to the dynamic compressive properties of syntactic foams. The results at high-strain rates are compared to quasi-static strain rate compressive properties of the same material. The results show that there is little or no significant change in both compressive strength and modulus of syntactic foams at all radius ratios when tested at strain rates of 400–500/s compared to quasi-static rates. However, higher dynamic strength and stiffness values are obtained consistently at all radius ratios when tested at 800–1000/s compared to quasi-static values. It is observed that the radius ratio does not affect the syntactic foam properties significantly when tested at the same high-strain rate and volume fraction. Scanning electron microscopy is carried out to understand the fracture modes of the syntactic foams.

Characterization of Mechanical and Electrical Properties of Epoxy-Glass Microballoon Syntactic Composites

The density of hollow particle (microballoon) filled composites called syntactic foams can be varied by two methods. The first method is the variation in microballoon volume fraction and the second method is the variation in the microballoon wall thickness, while keeping their volume fraction the same. A comparison of compressive properties of syntactic foams having microballoons of four different wall thicknesses in five volume fraction each is presented here. It is found that the compressive strength and modulus vary linearly with respect to the foam density. Dielectric constant, dielectric loss and electrical impedance are measured for four syntactic foam compositions with respect to temperature and frequency. Dielectric constant and loss are found to decrease with increase in frequency and with decrease in temperature in the range of 40–140°C.

Effects of density and strain rate on properties of syntactic foams

Syntactic foams are characterized for high strain rate compressive properties using Split-Hopkinson Pressure Bar (SHPB) technique in this study. The results at high strain rates are compared to quasi-static strain rate compressive properties of the same material. Four different types of syntactic foams are fabricated with the same matrix resin system but different size microballoons for testing purpose. The microballoons have the same outer radius. However, their internal radius is different leading to a difference in their density and strength. The volume fraction of the microballoons in syntactic foams is maintained at 0.65. Such an approach is helpful in isolating and identifying the contribution of matrix and microballoons to the dynamic compressive properties of syntactic foams. Results demonstrate considerable increase in peak strength of syntactic foams for higher strain rates and increasing density. It is also observed that the elastic modulus increases with increasing strain rate and density. Scanning electron microscopy is carried out to understand the fracture modes of these materials and the density effect on high strain rate properties of syntactic foam.

Enhancement of Energy Absorption in Syntactic Foams by Nanoclay Incorporation for Sandwich Core Applications

Syntactic foams are closed pore foams fabricated by the mechanical mixing of hollow glass particles in a matrix resin. The present study deals with change in compressive properties of syntactic foams due to the incorporation of nano-sized clay (nanoclay) particles. A surface modified clay, Nanomer I.30E, has been used in the fabrication of specimens. Six different types of syntactic foams are fabricated and tested for compressive properties. Three types of hollow particles (microballoons) of glass having different densities are used for fabrication. Each type of microballoon is combined with 0.02 and 0.05 volume fraction of nanoclay, respectively. The combined volume fraction of microballoons and nanocparticles is 0.65 in all kinds of foams. Compressive properties of these samples are compared with those of syntactic foams without nanoclay particles. It is observed that partial intercalation of nanoclay has taken place in the specimens and remaining nanoclay particles are present in small clusters. Such microstructure leads to nearly the same strength with considerable enhancement in fracture strain. Hence, the toughness of the material, measured as the area under stress–strain curve, is found to increase by 80–200% for various kinds of foams tested in the study. Fracture features of syntactic foams with and without nanoclay are compared.

Confinement effects on the dynamic compressive properties of an epoxy syntactic foam

Dynamic compressive properties of an epoxy syntactic foam at various strain rates under lateral confinement have been investigated with a pulse-shaped split Hopkinson pressure bar (SHPB). The quasi-static responses were obtained with an MTS 810 materials test system. The quasi-static and dynamic stress–strain behavior of the foam under confinement exhibited an elastic–plastic-like response whereas an elastic–brittle behavior was observed under uniaxial stress loading conditions. The modulus of elasticity and yield strength, which had higher values than those in uniaxial stress case, were both sensitive to strain rates. However, the strain-hardening behavior under confinement was not strain-rate sensitive. A phenomenological elastic–plastic type of material model was employed to describe the strain-rate-dependent compressive properties of the syntactic foam under confinement, which agreed well with experimental results.

Effect of Absorption in Aqueous and Hygrothermal Media on the Compressive Properties of Glass Fiber Reinforced Syntactic Foam

Absorption due to immersion in aqueous media consisting of either saline or seawater or due to exposure to water vapor conditions and the attendant effect on the compressive properties of syntactic foam reinforced with E-glass fibers in the form of chopped strands were studied. Whereas the compressive strength decreased in samples exposed to water vapor, the saline or seawater immersed samples showed increase when compared to the dry sample. The decrease in strength in the vapor-exposed case is ascribed to higher absorption of water and to debonding and damaged features for interfaces. The enhancement of strength values for the samples immersed in saltish media is traced to the larger size of the chloride ion and resultant changes in the stress state around the fiber-bearing regions. Recourse to an analysis of scanning electron microscopic pictures of the compression-failed samples is taken to explain the observed trends.

Comparison of Compressive Properties of Fiber-Free and Fiber-Bearing Syntactic Foams

The comparative compressive properties of syntactic foam with and without the inclusion of E-glass fibers in the form of chopped strands are reported. The effort pointed to the fact that the fiber-free syntactic foam had a higher compressive strength than the fiber-bearing one whereas as regards the moduli values they did not differ much. The difference in strength is correlated with the amount of voids present in two foams. The scope of the work was further expanded by including scanning electron microscopy for examining the surface features of samples prior to and after compression test.