Preparation and Characterization of Carbon Fiber Reinforced Epoxy Foams with Open-Cell Structure
Sandwich structures have many practical and potential applications in various civil and aerospace fields of engineering. Cellular materials (foams) are extensively used as the sandwich cores due to excellent combination of low weight and specific mechanical properties. Epoxy resins look as attractive candidate materials to make the foam-structured cores due to low density, high specific strength and stiffness, and simple processing procedures. In this research, open-cell epoxy foams were prepared by the sacrificial template process. The template was prepared from spherical carbamide granules (3-4 mm in diameter) using polyvinyl-pyrrolidone as a binder to form necks between the contacting granules. The template was infiltrated with epoxy-diane resin (poly(bisphenol-A-co-epichlorohydrin) modified with chopped carbon fibers (diameter – 4-5 micron, length - <250 micron). The content of the carbon fibers varied within 0-7 wt.%. Polyethylene polyamine was applied as the setting catalyst (20 wt. % in all cases). After infiltration and setting, carbamide space-holder was leached away thus forming a continuous cellular network of regular spherical cells with round interconnecting windows. Porosity of the foams varied within 0.64-0.66, which corresponded to the bulk density of 0.39-0.0.41 g/cm3. Mechanical properties of the foams were studied under uniaxial compressive loading. The foam behavior under compression was similar to the same of elastic foams; the stress-strain curves contained a near-linear region of elastic deformation interrupted with a pronounced peak and followed by a rapid stress drop. The peak stress corresponded to the sample fragmentation and crushing. No evident effect of the carbon fiber content on the stress-strain curve shape was stated. At the same time, the increase in the carbon fiber content from 0 to 5 wt. % resulted in the 15% in the crushing stress increase from 6.6 to 7.6 MPa; simultaneously, 25 % increase in elastic modulus was stated as well (from 190 to 240 MPa). As a whole, the foams demonstrated low density and rather high specific strength. The study was supported by Belarusian Republican Foundation for Fundamental Research, projects T15CO-020 and T16RA-006.