STRENGTH REDUCTION AND DAMAGE CHARACTERIZATION OF SCS6 TI-6AL-4V COMPOSITE EXPOSED TO FATIGUE AT ELEVATED-TEMPERATURE/

Effect of fatigue loading on the residual strength of a unidirectional titanium matrix composite, SCS6/Ti-6-4, was investigated. The composi te was fatigued isothermally at 427 degrees C under load-controlled mo de with an applied maximum stress of 900 MPa up to a certain fraction of the fatigue life, and then loaded monotonically to failure to obtai n the residual strength. Two frequencies, 1 Hz and 0.01 Hz, were used to examine the time-dependent characteristics of the fatigue loading. Substantially different failure mechanisms and fatigue lives were obse rved, but the reduction in strength as a percentage of fatigue life wa s similar for the two cases. Practically no reduction in strength occu rred until 75% of the expected fatigue life.