Types Of Syntactic Foams Research Articles

Water absorption in hollow glass microsphere composites under hydrostatic pressure: Mechanisms and influencing parameters

AbstractHollow glass microsphere composites, or syntactic foams, are widely used in marine environments due to their buoyancy. However, in service, loss of buoyancy occurs along time. This behavior is attributed to water absorption that leads to a mass increase of the material. This study investigates the water absorption of three types of syntactic foams under hydrostatic pressure with density ranging from 0.59 to 0.74 g. cm−3. Water absorption measurements are performed for a maximal duration of 3 years and under hydrostatic pressure up to 700 bars. Results show that water absorption is much higher than expected and attributed to the filling of microspheres that collapse over time. Based on results presented here, prediction of water absorption syntactic foams is proposed including the impact of applied hydrostatic pressure. This prediction allows estimating the buoyancy loss in hollow glass microsphere composite as a function of time, depth and sample size.

Electrical and Hydrolysis-resistance Properties of Silicone-Modified Resin/Microsphere Syntactic Foam for Composite Cross-arms Insulation Application

Herein, a type of syntactic foam, consisting of silicone-modified resin and hollow polymer microspheres, is developed and tested for the application of a composite cross-arm. The physical properties, electrical properties, and hydrolysis-resistance are tested and analyzed. Suitable microspheres can reduce the density of the syntactic foam to 46.63% of the resin. The dielectric strength of the syntactic foam decreases from 37.9 to 26.1 kV/mm with increasing microsphere content, which is still much higher than the operational requirement of 3 kV/mm. The water-absorption rate (<; 0.36% after 720 h) and leakage current (<; 24.17 μA after boiling for 300 h) show that the syntactic foams have excellent penetration resistance and hydrolysis-resistance. In summary, the syntactic foam can be used as the internal insulation material for composite cross-arms and applied to the electrical insulation field.

Fabrication and characterization of the thermoplastic and thermoset syntactic foam core‐based sandwich composites

AbstractThis study focuses on the preparation and characterization of two types of syntactic foams with the raw materials of hollow glass microspheres, polypropylene, and epoxy resin. The thermoset resin‐based and thermoplastic resin‐based syntactic foam slabs were produced and then used as the core material to fabricate thin‐layer sandwich composites. The carbon/epoxy composites were used as skins. The tensile properties and the fracture surface of the syntactic foams were observed. The bonding performance between the laminations and bending strength of the sandwich composites were investigated. The results show that both the thermoplastic resin‐based and thermosetting resin‐based syntactic foam slabs can be well bonded with the skins. The densities of the sandwich composites are 1.06 and 1.04 g/cm3, respectively. The sandwich composites have a good performance in bending resistance and the flexural strengths are 473.0 and 627.7 MPa, respectively.

Investigations on thermal energy transfer between two contrasting media and its application to protect skin burn

Thermal energy transfer between two materials with different thermal properties is due to not only the temperature difference of the two objects but also the discrepancy in thermal inertia between the two materials. In this study, composite materials, called syntactic foams, with low thermal inertia feature were introduced as a new type of thermal shield preventing skin burn. Some types of syntactic foams are designed and manufactured by varying the mixing ratio of hollow glass microsphere and epoxy resin. An experimental study on thermal properties ranging from density to specific heat is conducted to deduce the thermal inertia of the composite materials as well. In order to confirm the effect of the composite materials intended to provide prevention to skin burns, a one-dimensional transient heat transfer model with heat generation and absorption is developed to scrutinize the situation when human skin is abruptly in contact with a heat source with or without the composite materials. The numerical results show that all the syntactic foams combined with hollow glass microsphere (HGM) and epoxy resin (ER) have a considerable delay effect on thermal energy transfer to skin tissue, and the HGM80/ER20 was superior to others. Based on the results, even with the equivalent temperature for the heat source, as the thermal inertia of the syntactic foams is lowered, the heat transfer impediment effect becomes higher. It is expected that the skin damage factor (Ω) can be reduced by 34.8% within the designed syntactic foams.

Novel test method for the hydrostatic properties of syntactic foams

Hydrostatic properties are important in characterizing the syntactic foams in subsea applications. But they are rarely studied due to the lack of standard test methods and instruments. A novel method of characterizing the hydrostatic properties of syntactic foams based on the pressure build-up and the water input has been developed. A test system has been built with standard and easily accessible parts and components. A demonstration experiment has been carried out on two types of syntactic foams. The effect of the preliminary pressure cycles on the bulk modulus has been studied. The distinct hydrostatic yield and crush behaviors of the two types of syntactic foams are revealed in the test results. The Type I syntactic foam, which is composed of a lighter but weaker type of glass bubble, exhibits a hydrostatic compressive behavior dominated by the properties of the filler. The Type II syntactic foam, which is composed of a stronger but heavier type of glass bubble, exhibits a catastrophic failure mechanism involving both the crushing of the glass bubbles and the failure of the matrix material. With the developed test method, further investigations into the hydrostatic behaviors of the syntactic foams are possible.

Plane Stress/Strain Compressive Behavior of Perlite Composite Foam

Abstract The novel mechanical behavior of perlite/sodium silicate composite foam, a type of syntactic foam made of non-spherical particles, subjected to compression is studied in relation to plane stress and plane strain conditions. Plane stress and plane strain conditions were conceptualized and experimentally verified using various specimen sizes with aspect ratios ranging from 0.25 to 1.5 for compressive strength and modulus. Two distinctive sets of compression properties dependent on plane stress/strain were produced for practical characterization. The greatest compressive strength occurring under plane strain dominant condition was experimentally found to be ∼50 % greater than the lowest value occurring under plane stress dominant condition. The greatest compressive modulus occurring under plane stress dominant condition was also experimentally found to be ∼ 200 % greater than the lowest value occurring under plane strain dominant condition. A new failure mode under plane strain dominant condition for perlite foam was found to be the progressive densification of individual perlite particles.

Fatigue properties of EP/A356 aluminium matrix syntactic foams with different densities

The fatigue properties of EP/A356 aluminium matrix syntactic foams were measured. Four different type of syntactic foam were produced in order to determine the relation between the density and the fatigue properties. The density range was set to be between 0.7 – 1.1 g/cm3. The measured values indicated that, both the fatigue limit and the slope of the Wöhler curve increased with the density. However, the comparison of Globocer filled aluminium matrix syntactic foams with EP filled aluminium matrix syntactic foams suggested that this trend only applicable to foams with identical filler materials.

Research and development of compressible foam for pressure management in casing annulus of deepwater wells

Casing annulus pressure build-up owing to fluid thermal expansion in sealed annuli severely threaten the casing safety and wellbore integrity of deepwater wells. To mitigate the annular pressure with stronger effect and lower cost, a new type of syntactic foam with high compression ratio, which consists of hollow glass microspheres and a resin matrix system, was developed in this study. It can provide extra space for the annular fluid to expand when the annular pressure exceeds the specific foam crush pressure, allowing the foam to collapse and consequently, mitigate the annular pressure. The foam compression behavior is divided into three stages according to a hydrostatic compression test, and the annular pressure is mainly influenced by the microspheres volume and temperature. To optimize the parameters of the compressible foam, a novel model considering fluid thermal expansion, casing elastic deformation, and foam compression behavior in multi-annuli is established. The results indicate that the compressible foam can reduce the trapped annular pressure effectively and permanently. In a case study well, the annular pressure no longer exceeds the maximum acceptable annular pressure in each annulus with optimized design of the foam wraps and a suitable number of installed foam casing joints.

Compression Properties of Syntactic Foam Reinforced by Warp-knitted Spacer Fabric: Theoretical Compression Strength Model and Experimental Verification

In this study, a theoretical model based on the fiber buckling theory was established to predict the compression strength of a new type of syntactic foam, namely the syntactic foam reinforced by the warp-knitted spacer fabric (SF-WKSF). In order to verify the availability of this model, compression strength values of theoretical simulations were compared with the experiment results. The comparison results showed that the model can accurately simulate the compression strength values of different SF-WKSF samples with slight deviation. Finally, the causes of deviation was analyzed in detail.

Syntactic Foam Prepared with Glass Hollow Spheres of Designed Size and Wall Thickness Ratio

A new type of syntactic foam fabricated with four types of hollow microspheres (HGMs) were prepared and its compressive properties were tested following ASTM D 695-96 standard. The HGMs were designed to have specific size distribution and wall thickness. The compressive strength and modulus of the new syntactic foam were compared with those prepared with single type of HGMs. With same density, the new syntactic foam have better compressive properties.

Carbon nanofiber reinforced syntactic foams: Degradation mechanism for long term moisture exposure and residual compressive properties

Hollow particle filled polymer matrix composites, called syntactic foams, are challenging for studies related to environmental exposure and degradation mechanisms due to the possible role of matrix, particle–matrix interface, and particle material and wall thickness. In the current study, syntactic foams reinforced with 1 wt.% vapor grown carbon nanofibers (CNFs) are subjected to water immersion and characterized for residual compressive properties under quasi-static and high strain rates. The testing is conducted on four different types of syntactic foams, fabricated with glass hollow particles of two different densities: 220 and 460 kg/m3 in 30 and 50 vol.% quantities. After a period of 6 months, a maximum of 7% weight gain is observed in the worst performing syntactic foam. The exposed specimens are tested for residual compressive properties and the results are compared with the properties of dry specimens. The quasi-static compressive strength of CNF reinforced syntactic foams is found to decrease and the modulus remained unaffected due to the moisture exposure. The high strain rate compressive strength was 1.3–2.2 times higher for wet and dry specimens compared to the quasi-static strength of the same type of syntactic foams.

Development and characterization of epoxy syntactic foam filled with epoxy hollow spheres

The present study focuses on the development and characterization of epoxy syntactic foam filled with epoxy hollow spheres (ESF/EHoS). The epoxy syntactic foam (ESF) was produced by embedding epoxy hollow spheres (EHoS) into a mixture of epoxy-hardener and 3% KOH solution. An innovative approach and simple procedure was implemented in the preparation of the EHoS where expanded polystyrene (EPS) beads were used as initiation material. The EPS beads were coated with the epoxy resin and these coated EPS beads were later cured and post-cured at high temperature which will also shrink the EPS beads thus producing a hollow structure. The physical and compressive properties of the developed ESF were characterized. The progressive collapse of the syntactic foam was monitored in real-time with respect to percent- age of strain during a compression test. Results also indicated that the (ESF/EHoS) showed similar deformation pattern with other types of syntactic foams which exhibited the common three regions of deformations.

Mechanical Behavior of Syntactic Foams for Deep Sea Thermally Insulated Pipeline

Ultra Deep offshore oil exploitation (down to 3000 meters depth) presents new challenges to offshore engineering and operating companies. Flow assurance and particularly the selection of insulation materials to be applied to pipe lines are of primary importance, and are the focus of much industry interest for deepwater applications. Polymeric and composite materials, particularly syntactic foams, are now widely used for this application, so the understanding of their behavior under extreme conditions is essential. These materials, applied as a thick coating (up to 10-15 cm), are subjected in service to: - high hydrostatic compression (up to 30 MPa) - severe thermal gradients (from 4°C at the outer surface to 150°C at the inner wall), and to high bending and shear stresses during installation. Damageable behavior of syntactic foam under service conditions has been observed previously [1] and may strongly affect the long term reliability of the system (loss of thermal properties).This study is a part of a larger project aiming to model the in-service behavior of these structures. For this purpose it is important to identify the constituent mechanical properties correctly [2, 3]. A series of tests has been developed to address this point, which includes: - hydrostatic compression - shear loading using a modified Arcan fixture This paper will describe the different test methods and present results obtained for different types of syntactic foams.

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 Syntactic Foams — An Ultrasonic Approach

Syntactic foams are hollow particle filled composites that have recently emerged as attractive materials for use in advanced structural applications. The present study focuses on the effect of radius ratio and volume fraction of microballoons on the ultrasonic properties of syntactic foam composites. Twenty-four different types of syntactic foams, with different radius ratios and volume fractions, are used in this study. Foam slabs are fabricated by varying the volume fraction of microballoons from 10 to 60% for each type of microballoon. The pulse echo method is used for the ultrasonic imaging of these materials, and determines their ultrasonic attenuation behavior. Coefficient of attenuation, ultrasonic velocities, and modulus are observed to depend upon the radius ratio as well as the volume fraction of microballoon of the composites. A major finding in this research is the discovery of a non-destructive method to determine the dynamic modulus of particulate composites.

Mechanical Response of Al Matrix Syntactic Foams Produced by Pressure Infiltration Casting

Aluminum matrix syntactic foams with low-cost porous ceramic spheres of diameters between 0.25 and 4 mm have been manufactured by pressure infiltration casting. These syntactic foams were homogeneous in structure and had densities as low as half of the density of the Al matrix. The mechanical response of the four types of syntactic foams with different sphere sizes and densities under static and dynamic conditions have been investigated. The plateau strength and thus the amount of energy absorption of the syntactic foam are largely determined by the volume fraction of Al and to a lesser extent by the mechanical properties of the ceramic spheres in the foam. Compared with the Al foams with similar Al volume fractions, the syntactic foams had better energy absorption capacity, especially under impact conditions.

Dynamic Mechanical Properties of Polypropylene Syntactic Foam with Polymer Microballoons

The main objective of this study is to measure and characterize the mechanical properties of the thermoplastic syntactic foams at the intermediate and high strain rates. The syntactic foam consists of the elastically deformable microballoons in the polypropylene matrix. The four types of syntactic foams and one polypropylene bulk specimen are prepared at same manufacturing process: 0, 20, 30, 40 and 50 volume percent of microballoons. Tensile tests are conducted at nominal strain rates ranging from 10-1 to 102 (1/sec). Elastic modulus, yield stress and rupture strain are measured and the effects of microballoons on the mechanical properties are studied. In addition, fracture surfaces are observed with ESEM (Environmental Scanning Electron Microscopy). Finally, the changes of fracture mode due to microballoons are discussed.

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.