Cenosphere Volume Fraction Research Articles

Experimental and numerical investigation on the elastic properties of luffa–cenosphere‐reinforced epoxy hybrid composite

AbstractEstimating the elastic characteristics of natural fiber‐reinforced polymer composites such as luffa fiber reinforced with epoxy is challenging. The structure of luffa cylindrica is complex, like a three‐dimensional natural fibrous mat, netting‐like structure. The multiscale modeling of such structures is the challenge to be addressed. The prime objective of this work is to determine the specific elastic properties of luffa–cenosphere‐reinforced epoxy (LCE) composite, considering the effect of filler volume fractions. Furthermore, multiscale modeling techniques, such as representative volume elements (RVEs) of finite element techniques with chopped, unidirectional, plain, and twill weaving fiber arrangements, were employed. The longitudinal modulus, transverse modulus, shear modulus, and Poisson's ratio were predicted through these modeling approaches. However, experimental and analytical methodologies, including the rule of mixture and Halpin–Tsai, were considered to validate the finite element analysis results. The elastic characteristics of LCE composite were therefore shown to be enhanced by increasing filler volume fraction. However, the cenosphere's 20% volume fraction has the highest elastic properties as determined by analytical, experimental, and computational models. Analytical and finite element simulation results were compared with the experimental results, and based on the findings, the most suitable (unidirectional, chopped, plain, and twill weaving) RVE was identified for finite element modeling of LCE composite for the evaluation of elastic properties. Results from practical approaches and the RVE twill weaving model showed good agreement, with less than 1% error, compared to the other analytical and finite element methods.Highlights NFCs are gaining ground in polymer composites. Overcoming challenges in modeling of luffa fiber inside epoxy matrix. The study uses multiscale modeling with diverse fiber arrangements. Experimental and analytical methods used to confirm FEA results. Increased cenosphere volume fraction boosts LCE composite properties.

Buckling and free vibrations behaviour through differential quadrature method for foamed composites

The current work focuses on predicting the buckling and free vibration frequencies (fn) of cenosphere reinforced epoxy based syntactic foam beam under varying loads. Critical buckling loads (Ncr) and fn are predicted using the differential quadrature method (DQM). Ncr and fn have been calculated for beams of varying cenosphere volume fractions subjected to axial load under clamped-clamped (CC), clamped-simply (CS), simply-simply (SS), and clamped-free (CF) boundary conditions (BC′s). Upon increasing the cenosphere volume fraction, Ncr and fn of syntactic foam composites increases. These numerical outcomes are compared with the theoretical values evaluated through the Euler-Bernoulli hypothesis and further compared with experimental outcomes. Results are observed to be in precise agreement. The results of the DQM numerical analysis are given out for the different BC′s, aspect ratios, cenosphere volume fractions, and varying loads. It is perceived that depending on the BC′s, the type of axial varying loads and aspect ratios has a substantial effect on the Ncr and fn behaviour of the syntactic foam beams. A comparative study of the obtained results showed that the beam subjected to parabolic load under CC boundary conditions exhibited a higher buckling load.

Compressive strength modeling and validation of cenosphere-reinforced aluminum–magnesium-matrix-based syntactic foams

Al–Mg-matrix-based syntactic foams were manufactured using stir-casting methods. The concentration of Mg in the Al–Mg matrix and the matrix hardness and lattice parameters decreased with increasing cenosphere volume fraction. The lattice parameters were calculated using field-emission electron probe microanalysis (FE-EPMA) and Redlich–Kister polynomials, and high-resolution X-ray diffraction was conducted to determine the changes in the matrix mechanical properties. A prediction model was proposed to estimate the foam compressive strengths under quasistatic conditions, demonstrating better agreement with the experimental data than previous models.

Tribological Behavior of Cenosphere-Filled Epoxy Syntactic Foams in Dry Sliding Conditions

Abstract The tribological behavior of the 10%, 20%, 30%, and 40% cenosphere-filled epoxy syntactic foams in terms of the wear rate and the friction coefficient of the foams were reported using a pin on disc tribometer in the present study. The influence of the wear parameters like applied pressure, sliding speed, and the sliding distance on the tribological performance of syntactic foams was reported. Syntactic foams with 40% cenosphere volume fraction exhibit better tribological properties over the other syntactic foams. The worn surface examination shows the adhesive dominant wear mechanism and the wear debris with broken cenosphere particles.

Effect of thermal loading on syntactic foam sandwich composite

AbstractAn experimental investigation carried out on the deflection behavior of sandwich composites with a fly ash cenosphere/epoxy syntactic foam core and plain‐woven sisal fiber fabric/epoxy skin subjected to nonuniform heating is presented. The influence of cenosphere volume fraction in the syntactic foam core, three different heating cases (increase‐decrease, decrease, and decrease‐increase), and cenospheres’ surface treatment effect is analyzed. The temperature deflection is acquired with the help of a LabVIEW program. The critical buckling and snap‐initiation temperatures are found from the temperature‐deflection plots. It is observed that the sandwich beam undergoes snap‐through buckling behavior due to viscoelastic forces associated with the syntactic foam core. The critical buckling temperature increases with the filler content, and the surface treatment enhances the buckling behavior marginally. Results also demonstrate that the sandwiching of the syntactic foam core between the natural fiber skin enhances critical buckling temperatures compared to the syntactic foam core.

Effect of addition of reinforcements on the tribological behaviour of the polymer based syntactic foams

In the present study, the tribological behaviour of the syntactic foams manufactured using the fly ash cenospheres as the reinforcements and the epoxy as the matrix were studied for their tribological performance. The effect of the reinforcement concentration on the tribological properties like wear rate and the coefficient of friction were observed by using the pin on disc tribo tester. Four types of samples were prepared by varying the cenosphere volume fraction from 10% to 40% and tribological tests were conducted at constant sliding speed of 1 m/s and constant applied load of 50 N for a sliding distance of 2000 m. The increase in cenosphere volume fraction reduced wear rate and increased friction coefficient. The reduction in the wear rate may be due to the reduction in the effective contact area due to the pores created by crushed cenospheres. The increment in the coefficient of friction may be due to the increase in the cenosphere shells in the wear debris which act as obstacles. The worn surfaces of the foams were observed using the scanning electron microscope to determine the dominant wear mechanism.

Dynamic impact behavior of syntactic foam core sandwich composites

Sandwich composites and syntactic foams independently have been used in many engineering applications. However, there has been minimal effort towards taking advantage of the weight saving ability of syntactic foams in the cores of sandwich composites, especially with respect to the impact response of structures. To that end, the goal of this study is to investigate the mechanical response and damage mechanisms associated with syntactic foam core sandwich composites subjected to dynamic impact loading. In particular, this study investigates the influence of varying cenosphere volume fraction in syntactic foam core sandwich composites subjected to varying dynamic impact loading and further elucidates the extent and diversity of corresponding damage mechanisms. The syntactic foam cores are first fabricated using epoxy resin as the matrix and cenospheres as the reinforcement with four cenosphere volume fractions of 0% (pure epoxy), 20%, 40%, and 60%. The sandwich composite panels are then manufactured using the vacuum assisted resin transfer molding process with carbon fiber/vinyl ester facesheets. Dynamic impact tests are performed on the sandwich composite specimens at two energy levels of 80 J and 160 J, upon which the data are post-processed to gain a quantitative understanding of the impact response and damage mechanisms incurred by the specimens. A qualitative understanding is obtained through micro-computed tomography scanning of the impacted specimens. In addition, a finite element model is developed to investigate the causes for different damage mechanisms observed in specimens with different volume fractions.

The 3D failure process in polymeric syntactic foams with different cenosphere volume fractions

ABSTRACTThe previous work (Huang and Li, Compos. Part B, 2015) proposed the failure mechanism in syntactic foams with low and high hollow microsphere volume fractions, based on the finite element simulation of localized stresses in the foam. In this work, in situ X‐ray microtomography of uniaxial compression tests was performed to provide the direct experimental evidence to the proposed mechanism by tracking the internal three‐dimensional failure process in epoxy syntactic foams with different cenosphere volume fractions (V). It was found that for both the low and high V, microcracks initiate in the matrix in the top and bottom of crushed cenospheres where the tensile stress concentrates, and then propagate longitudinally to become macrocracks. Increasing the cenosphere volume fraction also leads to the formation of matrix microcracks in the connection zone where the stress concentrates significantly; the matrix microcracks thus propagate diagonally and longitudinally in the high V foam. © 2019 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2019, 136, 47491.

Buckling and Free Vibration Behavior of Cenosphere/Epoxy Syntactic Foams under Axial Compressive Loading

Abstract The buckling and free vibration behavior of cenosphere/epoxy syntactic foams under axial compressive loading are investigated experimentally in this work. The buckling load is obtained from the load-deflection curve based on the Double Tangent Method (DTM) and Modified Budiansky Criteria (MBC). Furthermore, the influence of an axial compression load on the natural frequencies associated with the first three transverse bending modes is analyzed. Finally, the buckling loads predicted using DTM and MBC are compared to the buckling load calculated based on the vibration correlation technique. It is observed that the buckling loads predicted through the three different methods are in close agreement. The experimental results revealed that the buckling load and natural frequency of the syntactic foams increase with the cenosphere volume fraction. It is observed that the natural frequencies reduce with increases in the axial compression load for all the modes. However, a rapid increase in the fundamental frequency is observed when the compressive load is near and beyond the critical buckling load.

Snap-through buckling of fly ash cenosphere/epoxy syntactic foams under thermal environment

Experimental investigation on deflection behaviour of fly ash cenosphere/epoxy syntactic foam at room temperature and under thermal environment (three different heating conditions) is investigated. Influence of fly ash cenosphere volume fraction and nature of temperature variation on deflection behaviour of syntactic foam beam is discussed elaborately. Results reveal that the syntactic foam beam experience snap-through buckling under thermal environment and is reflected by two bifurcation points in temperature-deflection plot. It is observed that the time duration for which the foam beam stays in the first buckled position increases with increase in cenosphere content. Thermal environment induces compressive stresses in the samples causing such snap-through buckling. However, such phenomenon is not observed when mechanical compressive loads are applied under room temperature conditions. Temperature variation across the beam strongly influences snap-through buckling in syntactic foams in addition to volume fraction of filler content.

Effect of arctic environment on flexural behavior of fly ash cenosphere reinforced epoxy syntactic foams

Abstract In this paper, the effect of arctic conditions on the flexural response of cenosphere/epoxy syntactic foams is investigated. Understanding the behavior of such foams under extreme conditions is critical for exploring their suitability for constructing lightweight platforms used in arctic explorations. Such platforms are exposed to subzero temperatures for extended periods of time potentially degrading their mechanical properties. In the research study presented here, samples of cenosphere/epoxy syntactic foams were conditioned under arctic environment at −60 °C temperature for a period of 57 days. Flexural tests were then conducted at room temperature as well as in-situ −60 °C on the conditioned samples and compared against unconditioned samples. Combinations of surface modification and cenosphere volume fractions were considered. Experimental findings showed that an increase in flexural modulus can be observed at room temperature with increasing cenosphere volume content for both untreated and treated cenosphere reinforced syntactic foams. In contrast, a decrease in flexural strength was observed as compared to neat resin. For the case of arctic exposed samples, an apparent increase in flexural modulus was recorded between 7-15% as compared to room temperature cenospheres/epoxy syntactic foams. In addition, an apparent increase of 3–80% in the flexural strength was observed under arctic environment. The conditioning of cenosphere/epoxy syntactic foams under low temperatures manifested lower strains to failure as compared to neat epoxy and they exhibit quasi-brittle behavior leading to sudden failure in the post peak regime.

Compressive behavior of cenosphere/epoxy syntactic foams in arctic conditions

Abstract In this paper, the effects of arctic condition on the compressive response of ceno-sphere/epoxy syntactic foams are investigated. Understanding the behavior of such foams under extreme conditions is critical for exploring their suitability for constructing lightweight platforms used in arctic explorations, which are exposed to subzero temperatures for extended periods of time potentially degrading their mechanical properties. In the research study presented here, samples of cenosphere/epoxy syntactic foams were conditioned under arctic environment at a temperature of −60 °C for a period of 57 days. Compression tests were then conducted at room temperature as well as in-situ −60 °C on the conditioned samples and compared against unconditioned samples tested at room temperature. Combinations of surface modification and cenosphere volume fractions were considered. For the case of unconditioned samples, compressive strength decreased with increasing cenosphere volume fraction for both surface modified and unmodified cenospheres. For the arctic conditioned samples, cenospheres/epoxy foams did not present visible signs of degradation prior to testing, but manifested a reduction in compressive modulus in a range of 47–57% and 47–65% for untreated and treated cenospheres/epoxy syntactic foams as compared to their unconditioned counterparts. On the other hand, the compressive strength increased in a range between 32–68% for untreated and 59–80% for treated cenosphere foams in arctic environment, which can be attributed to the matrix hardening introduced by frigid in-situ environment. Also, under in-situ arctic compressive loading, the post peak response for all foam types have shifted from a progressive failure to a brittle type behavior.

Microstructure and strength correlation of pure Al and Al-Mg syntactic foam composites subject to uniaxial compression

The microstructure and quasi-static compression of glass cenospheres/aluminum matrix syntactic foams (AMSFs) with three t/R ratio cenospheres (t/R=0.043, 0.052 and 0.064) and three different matrices (cp-Al, 5A03 and 5A06) were investigated. The compression strength and energy absorption of foams were found to increase with t/R ratio and Mg in matrix. The strengthening mechanisms were attributed to the nature properties of cenospheres and the thickness of high strength interfacial reaction MgAl2O4 forming. Two models were provided to predict the quasi-static properties of AMSFs considering the factors including physical properties of matrix and cenospheres, volume fraction of cenospheres, composition changing of matrix and thickness of interfacial reaction coating caused by interfacial reaction between matrix and cenopsheres. The predictions for peak stress, plateau stress, energy absorption capacity and specific energy absorption of AMSFs showed good agreement with experimental data. The Al-Mg syntactic foams in this study exhibited high specific energy absorption (56Jg−1) and specific plateau strength (94MPacm−3g−1).

Electrochemical evaluation of sintered aluminium – ceramic cenospheres composites

ABSTRACTThe corrosion behaviour of cenospheres metal matric syntactic foams of different compositions in 3.5 wt-% NaCl aqueous solution at ∼25°C was investigated. The electrochemical properties of the composites were assessed experimentally, employing potentiodynamic polarisation and electrochemical impedance spectroscopy measurements. Appropriate equivalent electrical circuits were proposed. Results showed that the corrosion rate is higher for the metal matrix syntactic foams compared to pure sintered aluminium. As the volume fraction of cenospheres increases cenospheres fragments and the presence of reaction zones seems to have a greater effect on the corrosion behaviour of the composites compared to the presence of unintended porosity.

Effect of cenosphere content on the compressive deformation behaviour of aluminum-cenosphere hybrid foam

Al-cenosphere closed cell hybrid foams (HFs) of varying relative densities were made by melt foaming method through stir casting technique. In order to investigate the effect of cenosphere content on the compressive deformation behaviour of HFs, varying amounts of cenospheres (18, 25, 30 and 35vol%) was used as thickening agent and CaH2 (0.6wt% of alloy) was used as foaming agent. Two types of pores come in this hybrid foam: (i) micropores due to the hollow cenosphere and (ii) macropores due to the entrapment of gas generated. The results showed that the cenospheres particles were uniformly distributed in the cell wall. It was noted that the addition of cenospheres improved the yield strength, the plateau stress, and the energy absorption capacity of HFs, up to a 30vol% of cenosphere. Further increase in cenosphere content leads to reduction in the plateau stress and the energy absorption capacity of HFs. It is interestingly noted that the densification strain is almost invariant to the cenosphere volume fraction. Attempts are also made to empirically correlate the deformation response with the cenosphere volume fraction and relative density.

Effect of Cenosphere Size and Volume Fraction on the Microstructure and Deformation Behavior of Ti-Cenosphere Syntactic Foam Made Through Powder Metallurgy Route

Abstract An attempt was made for making Titanium–cenosphere metal syntactic foams with varying relative densities, using different cenosphere sizes and volume fractions. Cold compaction of Ti and cenosphere powder mix was carried out at a pressure of 75 MPa, followed by sintering at 1100°C for 2 h. The sintered foam samples were characterized in terms of microstructure, primarily to observe the extent of cenosphere crushing, distribution of cenosphere, and extent of sintering. Uniform distribution of cenosphere with some extent of cenosphere crushing has been observed within the Ti matrix. XRD and EDX analysis confirms the oxidation of Ti particles to a small extent and also the entrapment of crushed cenosphere shells within the matrix, which makes the foam stronger but brittle in nature. The plateau stress, energy absorption, and modulus of these foams vary with the cenosphere size and volume fraction. Foams made with finer size cenosphere exhibits higher plateau stress and higher energy absorption for a fixed cenosphere volume fraction and at a constant foam density. Crushing of cenosphere, while compaction causes an increased density of the foam as compared to the theoretical value. As a consequence, the foam with higher cenosphere volume fraction or with coarser cenosphere size exhibited marginally higher strength and energy absorption. The variation in deformation mechanism as a function of cenosphere size and volume fraction was examined. These foams exhibited considerably higher strength and stiffness than the conventional foam and demonstrate the possibility of using them for biomedical and engineering applications.

Mechanical and thermal properties of fly ash/vinyl ester syntactic foams

Vinyl ester matrix syntactic foams filled with hollow fly ash cenospheres are evaluated for quasi-static and high strain rate compressive, flexural and thermal properties. The results are analyzed to understand the effect of cenosphere parameters such as density and wall thickness on the properties of syntactic foams. The elastic energy absorption under compression, until the peak stress, increased with increasing strain rates for all cenosphere volume fractions. The flexural strength decreased by 73% while the flexural modulus increased by 47% at 60vol.% cenospheres, in comparison to the neat resin. The coefficient of thermal expansion (CTE) was observed to decrease by 48% corresponding to an increase in cenosphere content from 30 to 60vol.%. Cenospheres are produced as a by-product of coal combustion and their structure contains numerous defects. Therefore, mechanical properties of cenospheres cannot be directly measured. An existing theoretical model was utilized to predict the cenosphere modulus using the experimental flexural modulus values and the results were confirmed with the CTE values. These results can be used to tailor the mechanical and thermal properties of syntactic foams based on the application parameters.

In situ sensing of non-linear deformation and damage in epoxy particulate composites

Damage sensing of epoxy particulate composites was investigated using multi-wall carbon nanotubes (MWCNTs) under quasi-static uniaxial tensile loading. Two types of particulates, namely (a) aluminum silicate hollow microspheres (cenospheres), and (b) liquid carboxyl-terminated butadiene acrylonitrile (CTBN) rubber were considered in this study. The influence of three different volume fractions of cenospheres (10%, 20% and 30%) and three different weight fractions of CTBN resin (10, 20 and 30 phr) on the electromechanical response was studied. A four-circumferential ring probe (FCRP) technique was employed to measure the electrical resistance of the test specimen as a function of the axial strain. The resistance–strain curve is compared with a simultaneously measured mechanical stress–strain curve. The electromechanical measurement show additional stages of material deformation not readily revealed from the mechanical stress–strain curve. The resistance change associated with the unfolding of entangled polymer chains and further straightening of the polymer chains decreased the distance between CNTs, causing improved electron hopping in all composites except 30% cenospheres composite. The U-shaped electrical response demonstrated by both 20 and 30 phr rubber composites exploited the CNT sensory network successfully by providing early warning of composite failure due to micro-crack propagation which resulted in breaking of the CNT network.

Compressive and ultrasonic properties of polyester/fly ash composites

The addition of hollow fillers having appropriate mechanical properties can decrease the density of the resulting composite, called syntactic foams, while concurrently improving its mechanical properties. In this study, hollow fly ash particles, called cenospheres, are used as fillers in polyester matrix material. Cenospheres are a waste by-product of coal combustion and, as such, are available at very low cost. In this study, the composites were synthesized by settling cenospheres in a glass tube filled with liquid polyester resin and subsequently curing the resin. This process resulted in a functionally graded structure containing a gradient in the cenosphere volume fraction along the sample height. Uniform radial sections were cut from each composite and were characterized to observe the relationship between cenosphere volume fraction and compressive properties of the composite. The composite was also tested using ultrasonic non-destructive evaluation method. Results show that the modulus of the composites increases with increasing cenosphere volume fraction. The modulus of composites containing more than 4.9 vol% cenosphere was found to be higher than the matrix resin. In general, the modulus of composites increased from 1.33 to 2.1 GPa for composites containing from 4.9–29.5 vol% cenospheres. The specific strength of the composite was found to be as high as 2.03 MPa/(kg/m3) compared to 0.96 MPa/(kg/m3) for the neat resin. Numerous defects present in fly ash particles caused a reduction in the strength of the composite. However, the reduction in the strength was found to be only up to 22%. Increase of over 110% in the specific modulus and only a slight decrease in the strength indicates the possibility of significant saving of weight in the structures using polyester/fly ash syntactic foams.

Cenosphere filled aluminum syntactic foam made through stir-casting technique

Cenospheres in the range of 30–50 vol.% were used as space holders for making syntactic aluminum foam having density 1.5–1.9 gm/cc using stir-casting technique. The synthesized syntactic foam (SF) was characterized in terms of microstructures, hardness and compressive deformation behaviour. It was noted that the SF behaves like a high strength aluminium foam under compressive deformation exhibiting flat plateau region in the stress–strain curves. The plateau stress of SF decreases with cenosphere volume fraction vis-à-vis porosity following a power law relationship. But, the densification strain increases linearly with cenosphere volume fraction.