On the axial propagation of kink bands in fiber composites : Part i experiments

In many _ber composites\ longitudinal compressive failure leads to the formation of kink bands[ It has been found that these kink bands\ once formed\ can be made to propagate "broaden# in a steady!state manner at a constant stress level called the propagation stress "sP#[ This is a characteristic stress of the material which\ for the AS3:PEEK composite used in the study reported here\ is approximately 39) of its compressive strength[ This phenomenon is investigated experimentally using a special con_ning set!up that allows direct observation of the propagation process[ For the composite studied\ the kink bands have a repeatable inclination "b# of approximately 04>\ and the _bers within the bands are rotated to about 29> in the absence of a load[ When loaded to sP\ however\ they are found to rotate further to 39>\ that issubstantially greater than the 1b reported elsewhere[ The mechanism of propagation is found to be a bend! break!rotate sequence undergone by short segments of _bers at the edge of the kink band[ It is well known that polymeric matrix composites such as the one used in this study exhibit rate!dependent behavior[ Experimental results are presented which show that the kink band propagation stress is also rate dependent[