THE ORIENTATION DEPENDENCE OF FATIGUE-CRACK GROWTH IN 8090 AL-LI PLATE

A series of fatigue-crack growth rate (FCGR) tests was carried out on 8090 Al-Li plate to examine the effects of specimen orientation on fat igue-crack growth. The directionality of fatigue fracture behavior is found to be related to the strong {110}[112] texture in this alloy. Ba sed on A previously developed transgranular FCGR model using restricte d slip reversibility (RSR) concepts,[1] a mechanistic model is develop ed for transgranular fatigue-crack growth in highly textured materials . The model takes the form of the Paris relationship with a power law exponent of 3, and the material texture is shown to strongly influence the proportional factor. The effect of texture on FCGR is related thr ough a geometric factor cos2 phi, where phi defines the angle between the load axis and the normal of the favorable slip plane. The effect o f specimen orientation on FCGR in 8090 Al-Li alloy is shown to be rela ted to a combination of its anisotropic mechanical properties and the variation of angle phi with specimen orientation. The model further pr edicts that fatigue-crack growth rates will be slower in many textured materials than texture-free materials because phi > 0 and cos3 phi < 1.