Coating of Carbon Fibers—The Strength of the Fibers

Abstract

The 6k carbon fiber Torayca T800H was coated with pyrolytic carbon by a CVD process. Fiber bundles were tested and evaluated. By this procedure, the whole distribution of the failure probability with respect to the fiber strength is obtained in a single experiment. The 50% strength of the fiber bundle, i.e., the strength at which 50% of the fibers in the bundle are broken, is inversely proportional to the square root of the thickness of the coating. By relating the strength to the defect size according to linear‐elastic fracture mechanics (LEFM), the probability density function of the defects was derived. It is Weibull‐shaped for the uncoated fiber and shows an increasing bimodal shape for the increasing coating thicknesses.

Cfiber/SiCfiller/Si–B–C–Nmatrix composites with extremely high thermal stability

“…Pyrocarbon coatings on the carbon fibers provide a weak fiber-matrix bonding [38]. As a result, cracks propagated mainly along the coating, and fiber pull-out (>200 lm) was observed at the surface (ambient temperature test) of the CMC, regardless of the heating condition (Fig.…”

Statistical fracture of E-glass fibres using a bundle tensile test and acoustic emission monitoring

“…The bundle tensile test technique allows us to overcome some of these problems. Hence it becomes an alternative method to obtain the strength distribution of the fibres [10][11][12][13][14][15][16][17][18][19] and has been used with successfully to study the coating effect on strength distribution changes of carbon fibres [20,21]. The only difficulty is to obtain a reliable load-strain ) ( ε − P curve of the bundle under quasi-static loading.…”

Scaling of fracture strength in disordered quasi-brittle materials

“…These multi-modal defect cluster size populations result in multi-modal strength distributions [3,4,5,6,2]. Experimentally, bimodal Weibull strength distributions were observed in various brittle ma-terials including carbon [7] and silicon carbide fibers [6], and for certain ceramics [8]. The effect of multiple flaw (defect) populations on fracture strength distribution is also examined experimentally in certain ceramic materials [9,10,11,12].…”