CHARACTERIZATION OF NICALON FIBERS WITH VARYING DIAMETERS - PART I - STRENGTH AND FRACTURE STUDIES

Experimental studies have been conducted to examine the strength and f racture behaviour of monofilament Nicalon SiC fibres with diameters ra nging from 8 to 22 mu m. The effects of varying fibre diameter, flaw l ocation and flaw population on the mechanical response of individual f ibres were investigated by recourse to extensive fractographic analysi s performed on fibres fractured under tensile loading. Results indicat e that variations in fibre diameter influence the apparent fibre fract ure toughness (K-1c), with higher K-1c values observed for decreasing fibre diameters. Observations also suggest that the location of the cr itical flaw may play a role in the fracture of Nicalon fibres. Tensile strength values are shown to increase as the normalized distance of t he critical flaw from the fibre centre increases, while critical flaw population appears to be strongly dependent on location. The ratio of K-1c to geometry factor (Y) is observed to remain constant with varyin g flaw location. In addition to surface flaws, three distinct internal flaw populations are seen to cause fracture in Nicalon fibres. Based on these experimental findings, a statistical characterization of the strength of Nicalon fibres with varying diameters is presented in Part II of this paper. (C) 1998 Chapman & Hall.