BS ISO 18608:2015 pdf free
BS ISO 18608:2015 pdf free.Fine ceramics (advanced ceramics, advanced technical ceramics)一Mechanical properties of ceramic composites at ambient temperature
The load versus load line displacement curve from a fracture test on a notched specimen involves a nonlinear domain induced by diffuse micro-cracking within the matrix at the notch tip. The damage zone is in the millimetre to centimetre scale (from one to several tow diameters). At maximum load, a macroscopic crack is created from the random failure of fibres within those tows located in the damage zone. Crack extension in CMC, hence, does not result from the mechanism of extension of a single macroscopic crack as observed in monolithic materials.
Because of the presence of the damage zone and ofheterogeneous microstructure, the stress distribution in the damage zone differs from the one induced ahead of the crack tip in linear elastic bodies. The K1 parameter does not describe the stress field in the region ahead of the crack tip. A critical value KIc cannot be defined.
The main difficulty in the determination of the strain energy release rate GI, as well as the J integral,results from the presence of the micro-cracked zone at the notch tip (which is not small compared with the specimen dimensions) and the jagged surface of the macroscopic crack. As a consequence an increase in crack length can neither be easily defined nor measured.
Tensile tests performed on specimens containing holes or notches have demonstrated that many CMC are relatively notch-insensitive over a range of notch sizes. The net-section stress at fracture is typically (80 to 100) % of the un-notched strength. Notch insensitivity results from a stress relaxation at the notch tip due to the development of the damage zone. As a consequence, the fibres in the damage zone are subjected to stresses that are comparable in magnitude to the remote stresses.BS ISO 18608 pdf free download.
