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

• Fly ash/vinyl ester composites are studied for mechanical and thermal properties.
• Modulus of fly ash is evaluated to be 50–70 GPa from the flexural characterization.
• CTE of fly ash filled composite is up to 67% lower than that for neat resin.
• High stiffness and improved dimensional stability of fly ash composites are useful.
• Energy absorption under compression increased with strain rate for fly ash composite.

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 60 vol.% 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 60 vol.%. 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.

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