Self-sensing and microfaolure mechanisms of plasma-treated single carbon fiber/CNT-phenolic nanocomposites using electrical resistance and acoustic emmission testing

Abstract

Self-sensing and microfailure mechanisms were investigated for plasma-treated single carbon fiber/neat phenolic and carbon nanotube (CNT)-phenolic nanocomposites by electromicromechanical technique and acoustic emission (AE). The degree of comparative dispersion of CNT-phenolic mixtures was indirectly correlated with the uniform percolation in solid CNTphenolic composites by measuring the volumetric electrical resistivity. Tensile and compressive properties of neat phenolic and CNT-phenolic composites were compared. Buckling and kicking single fiber breaks in neat phenolic resin due to the transverse tensile stress were observed, which were correlated to compressive interfacial shear strength (IFSS). The contact resistivity between single-carbon fiber and CNT-phenolic composite was measured using the four-point method under cyclic loadings. Surface energy and work of adhesion of CNT-phenolic composites were determined by dynamic contact angle measurements using the Wilhelmy plate method for both untreated and plasma treated single carbon fibers. Since heterogeneous domains are formed at the CNT-phenolic surface, advancing contact angle measurements indicated that it was exhibited more hydrophobic than a neat phenolic surface. The apparent modulus for CNTphenolic composite was higher than that for neat phenolic resin, as a result of better stress transferring effects. The IFSS between single-carbon fibers and CNT-phenolic composite was greater than it was for neat phenolic as a result of the added CNT. AE measurements were used to sense Micro-damage in dual matrix CNT-phenolic composites specimens. The characteristic AE signals detected as function of time could be attributed to various different sources: i.e., fiber break, brittle phenolic matrix cracking, ductile epoxy supporting matrix failure, interfacial debonding between the matrices and fibers of CNT, etc.