Interfacial properties of two SiC fiber-reinforced polycarbonate composites using the fragmentation test and acoustic emission

Interfacial shear strengths (IFSS) between the fiber and the matrix in two SiC fiber-reinforced polycarbonate (PC) composites (TFC) were investigated through the fragmentation method and the acoustic emission (AE) technique. Statistical analysis of SiC fiber tensile strength was performed mainly in terms of a Weibull distribution. The tensile strength and elongation far Si C fiber decreased with increasing gauge lengths, because of the heterogeneo us distribution of flaws on the fiber surface. Using an amino-silane coupli ng agent, the IFSS showed significant improvement, in the range of 150%, un der dry conditions. On the other hand, in the aspect of the environmental e ffect, the IFSS was improved about 170% under wet conditions (immersed in h ot water at 85 degrees C for 75 min). This is probably due to chemical and hydrogen bonds in the two different interphases in the SiC fiber/silane cou pling agent/PC matrix system. In-situ monitoring of AE during straining of microspecimens showed the sequential occurrence of two distinct groups of A E data. The first group may result from SiC fiber breakages, and the second probably results from mainly PC matrix cracking. Charateristic frequencies coming from the failures of the fiber and the PC matrix were shown via fas t Fourier transform (FFT) analysis. By setting an appropriate threshold lev el, a one-to-one correspondence between the number of AE events and fiber b reakages was established. This AE method could be correlated successfully t o the IFSS via the fragmentation technique, which can also applied to nontr ansparent specimens.