Understanding the contributions of normal-fatigue and static loading to the dwell fatigue in a near-alpha titanium alloy

Abstract

This article presents the results of a recent study of the response of an ␣/␤-forged Ti-6Al-2Sn-4Zr-2Mo alloy during static, normal-fatigue, and dwell-fatigue loading. The plastic-strain accumulation under different loading conditions is reported. The failure modes and associated fractographic features under static, normal-fatigue, and dwell-fatigue loading conditions are also discussed. These results are used to obtain a better understanding of the relative contributions of the cyclic and creep processes to the overall damage under dwell-fatigue conditions.

Effect of Volume Fraction of Primary α Phase on Dwell and Normal Cyclic Fatigue Behavior of Ti60 Alloy

“…Under normal cyclic fatigue mode, cracks initiated in the surface region while interior crack initiation was found under dwell fatigue mode at V p of about 35%, see Figure 4. Similar observations were found in other investigations [2,[19][20][21][22][23][24][25][26][27] . At 10% of V p , cracks initiated at the subsurface region under normal cyclic loading while at the interior under dwell loading, see Figure 5.…”

Effects of crystallographic orientation and grain morphology on crack tip stress state and plasticity

“…Cold dwell fatigue [1,[4][5][6][7][8][9][10] refers to a failure mode observed in titanium alloy components due to a stress hold (dwell) at peak stress during cyclic loading at ambient temperatures. This issue, first recognised in the early 1970s after the uncontained failure of two titanium alloy aero-engine fan discs [1], remains a serious concern for all engine manufacturers [4].…”

Dwell-fatigue life dispersion of a near alpha titanium alloy

“…However, engine components machined from large forged discs have a fatigue life over an order of magnitude smaller when a dwell period at high stress levels is added to the cold fatigue cycle. Thus, the dwell (cold creep) coupled with fatigue increases the initiation rate of damage in these alloys [1][2][3][4][5][6][7][8]. Experiments showed that some regions of the part are subject to early fatigue damage.…”