RESISTANCE TO CRACK GROWTH OF ASBESTOS CEMENT

The crack resistance of sheet asbestos cement has been characterized in terms of an R-curve which can accomodate effects which often influence the measurement of the critical stress intensity factor Kc. The detection and location of the acoustic emission (AE) obtained from the asbestos cement has shown that it originates from microcracks in a zone just in front of the crack. The size of this zone increases to a maximum during slow propagation of the major crack and afterwards remains of constant size during the final crack growth. The form of the R-curve has been explained in terms of the mechanisms of fracture with the aid of AE and fractography studies. An analytical study has related the experimental R-curve to a theoretical R-curve and, hence, to the volume fraction, fibre aspect ratio and the strength of the fibre-matrix interface. It has been shown that the microcracking zone can be considered as a theoretical extension, of about one third of the zone length, to the real crack length. © 1979 Chapman and Hall Ltd.