Low‐cycle fatigue/high‐cycle fatigue interactions in notched Ti‐6Al‐4V*

Abstract

Combined low‐cycle fatigue/high‐cycle fatigue (LCF/HCF) loadings were investigated for smooth and circumferentially V‐notched cylindrical Ti–6Al–4V fatigue specimens. Smooth specimens were first cycled under LCF loading conditions for a fraction of the previously established fatigue life. The HCF 107 cycle fatigue limit stress after LCF cycling was established using a step loading technique. Specimens with two notch sizes, both having elastic stress concentration factors of Kt = 2.7, were cycled under LCF loading conditions at a nominal stress ratio of R = 0.1. The subsequent 106 cycle HCF fatigue limit stress at both R = 0.1 and 0.8 was determined. The combined loading LCF/HCF fatigue limit stresses for all specimens were compared to the baseline HCF fatigue limit stresses. After LCF cycling and prior to HCF cycling, the notched specimens were heat tinted, and final fracture surfaces examined for cracks formed during the initial LCF loading. Fatigue test results indicate that the LCF loading, applied for 75% of total LCF life for the smooth specimens and 25% for the notched specimens, resulted in only small reductions in the subsequent HCF fatigue limit stress. Under certain loading conditions, plasticity‐induced stress redistribution at the notch root during LCF cycling appears responsible for an observed increase in HCF fatigue limit stress, in terms of net section stress.

Fatigue strength of severely notched specimens made of Ti–6Al–4V under multiaxial loading

“…The fatigue behaviour of Ti–6Al–4V in the presence of notch effects has been extensively investigated by Nicholas et al ., also with reference to the fretting fatigue performance of this titanium alloy . In particular, the notch effect on HCF with different nominal load ratios R has been investigated considering, respectively, cylindrical V‐notched and notched flat dog‐bone specimens characterized by an opening angle equal to 60° and by a notch‐tip radius ranging between 0.127 and 0.432 mm.…”

“…Considering the same specimen geometry and nominal load ratios R of the previous works, the effects of combined low‐cycle fatigue (LCF) and HCF loading have also been investigated . In particular, the fatigue limit at 10 7 cycles after LCF loading was established using a step loading technique.…”

Aeromechanical Modeling of Rotating Fan Blades to Investigate High-Cycle and Low-Cycle Fatigue Interaction

“…Although recent studies have investigated the HCF/LCF inter action using experiments on specimens [4,5,[7][8][9], there is a visible lack of numerical studies that are able to observe HCF/LCF inter action (either on a fatigue specimen or a highly loaded blade). One of the major advantages of using a numerical approach is investigating highly complex problems at a fraction of the cost of experimental approaches, especially in the case of unsteady turbomachinery aeroelasticity.…”

Low‐cycle fatigue behaviour of polyamides

“…Low‐cycle fatigue (LCF) tests were developed for investigating the fatigue behaviour of metals at relative high strain/stress levels as a way to replicate the in‐service loading patterns of some components . The cycle strain/stress ratio R of LCF tests on metals can vary from negative values to positive values, and the tests are usually performed at low frequencies (<1 Hz) .…”

“…19 Low-cycle fatigue (LCF) tests were developed for investigating the fatigue behaviour of metals at relative high strain/stress levels as a way to replicate the in-service loading patterns of some components. 20 The cycle strain/stress ratio R of LCF tests on metals can vary from negative values 21 to positive values, 22 and the tests are usually performed at low frequencies (<1 Hz). 22,23 The behaviour of fibre-reinforced composites is also investigated under LCF [24][25][26][27] and similarly, tests on polymers mostly demonstrate the Mullin's effect, and procedures rarely exceed 10 2 cycles.…”