INPLANE ANISOTROPY IN LOW-CYCLE FATIGUE PROPERTIES OF AND BILINEARITYIN COFFIN-MANSON PLOTS FOR QUATERNARY AL-LI-CU-MG 8090 ALLOY PLATE

Low cycle fatigue (LCF) behaviour as a function of test direction was studied for a quaternary Al-Li-Cu-Mg alloy. The analysis of the variat ion in fatigue life with plastic strain amplitude Delta epsilon(p)/2 o r with average stress amplitude Delta sigma/2 or with plastic strain e nergy per cycle <Delta(W)over bar (p)> revealed bilinear power law rel ationships in all the test directions. The transition strain values in the Coffin-Manson plots were seen to match closely with those obtaine d in the cyclic str ess response as well as with the cyclic stress-str ain relationships of the alloy. The observed bilinear behaviour in the se LCF properties was attributable to a change in deformation as well as to the deformation assisted fracture mode. The allay revealed signi ficant in plane anisotropy in the LCF properties. The observed anisotr opy was found to result from the combined effects of strong crystallog raphic texture and grain fibering. (C) 1996 The Institute of Materials .