FIBER FRACTURE DURING THE CONSOLIDATION OF METAL-MATRIX COMPOSITES

A detailed study of conditions leading to fiber fracture during the co nsolidation of Ti-14wt%Al-21wt%Nb/SiC (SCS-6) composite monotapes has been conducted. For this continuous fiber reinforced composite system, the incidence of fracture increases with consolidation rate at higher process temperatures. Increasing consolidation temperature at a fixed pressure reduces the number of breaks per unit length of fiber. Exami nation of partially densified compacts has revealed the existence of s ignificant fiber bending and ultimately fracture due to monotape surfa ce roughness (asperities) which places the fibers in three point bendi ng. A representative volume element has been defined for the consolida ting lay-up and its response analyzed to predict the fiber deflection (and hence probability of failure) when the surface asperities deform either by plasticity or by steady state creep. The relationships betwe en fiber fracture and process conditions predicted using the volume el ement are similar to those observed experimentally. The cell analysis suggests that fiber fracture is decreased by increases in fiber stiffn ess, strength, and diameter and by decreases in matrix yield and creep strength and monotape surface roughness.