Correlation of tensile strength with fracture modes of KAOWOOL-and-SAFFIL-reinforced 339 aluminum

摘要

The tensile strengths of composites of339 aluminum reinforced with either SAFFIL orKAOWOOL fibers are compared over the temperaturerange of 20℃ to 300℃. For this type of composite,in which the discontinuous fibers are randomlyoriented, the fibers perpendicular to the appliedstress play a critical role, which in turn createsa dependence upon the interfacial bond strength.The KAOWOOL fibers form a strong interfacial bondso that tensile failure occurs either in thematrix at 300℃ or by fiber cleavage at 20℃. Inthe T5 condition, the SAFFIL interface is weakerthan the matrix alloy so that failure occurs bydelamination of the transverse fibers. Thus,although the SAFFIL fibers are 40 pct strongerthan the KAOWOOL fibers, the T5 composites havethe same ultimate tensile strengths. A T6 heattreatment promotes an interfacial reaction withmagnesium. This strengthens the SAFFIL interfaceso that failure occurs primarily in the matrix,producing higher composite strengths. The reactionwith the KAOWOOL fibers is so extensive that thematrix, and therefore the composite strength, isdrastically decreased. When account is taken ofthe different fracture modes, together with thematrix strengths as determined by nanoindentation,the calculated values of composite strength are ingood agreement with experiment.