THE EFFECTS OF MATRIX AND FIBER PROPERTIES ON THE MECHANICAL-BEHAVIORAND ACOUSTIC-EMISSION IN CONTINUOUS FIBER-REINFORCED METAL-MATRIX COMPOSITES

This paper examines and compares the mechanical properties and acousti c emission activity of four metal matrix composites (MMC's), The compo sites were manufactured with either 6061 Al or a high purity aluminum (HPAL) matrix. The two fibers used were the Nextel 440 and 610 fibers made by the 3M Corporation. The two fibers differed in stiffness, stre ngth, composition and geometry. The strengths of the composites were f ound to increase from the 610/6061 composite To the 440/6061 and 440/H PAL composites to the 610/HPAL composite, The high strength and low du ctility of the 6061 matrix led to a rapid propagation of failure in th ese materials. The increased ductility of the HPAL matrix slowed crack propagation and more fibers broke prior to failure of these composite s. The increased stiffness of the 610 fibers led to an increase in res idual stresses and earlier yielding of the matrix. A flat fracture sur face was observed for all the composites with little fiber pullout ind icating a strong fiber/matrix bond. The acoustic emission (AE) events could be separated into two regions for all the composites. Events in region one were attributed to dislocation motion during yielding of th e matrix. The events in this region were predominantly low amplitude. Events in region two were attributed to continued dislocation motion a nd fiber or inclusion breaking (cracking). The events were predominant ly lower amplitude with some higher amplitude events occurring. The cr acking was more extensive in the 340 fiber composites due to the incre ased number of fibers breaking prior to failure as indicated by the in crease in AE activity of the 440 composites compared with the 610 fibe r reinforced composites. (C) 1998 Elsevier Science S.A. All rights res erved.