Fiber fragmentation during processing of metallic matrix composites

Fiber fragmentation is a problem frequently encountered during the processing of metallic matrix composites. In this study, we examine the fragmentation of continuous fibers during a common composite consolidation process based on hot pressing in an open-ended channel die with fibers aligned parallel to the die walls. During the latter stages of consolidation, flow of the matrix along the die cavity may occur such that the resulting load transfer to the fibers can cause their fracture even in the absence of bending. This study analyzes the combination of conditions necessary for both matrix flow along the die cavity and the shear-lag loading of the fibers to a level that causes fragmentation. In order to validate the analysis, we model the fragmentation of fibers during elevated temperature hot pressing of Ni-base composites by the room-temperature consolidation of degraded sapphire fibers in a tin matrix. The observed fiber fragmentation behavior is in good agreement with theoretical predictions. The analysis also indicates that this mode of fiber fragmentation is confined either to low volume-fraction fiber composites or to the ends of panels of high volume-fraction fiber composites.