Characterization of crack nucleation in TA6V under fretting–fatigue loading using the potential drop technique

Abstract

In this work, the crack nucleation under fretting and fretting fatigue loading was investigated experimentally on a Ti-6Al-4V alloy. The geometry considered is a cylinder on flat contact in stick slip conditions. A new dual actuator fretting fatigue device was presented and an original interrupted test expertise methodology was proposed. In order to quantify the crack nucleation, the fretting fatigue set-up was equipped with a potential drop technique device. A proper calibration, presented in this paper, allowed a crack nucleation detection threshold of 50 µm with an error threshold of 10% at the maximum. Three parallel studies have been carried out: fretting loading tests (optical expertise), fretting fatigue test for a lifetime of 100 000 (optical expertise) and fretting fatigue interrupted tests (potential drop technique).These tests have shown that the addition of a fatigue load can provide a fall of 45% of the tangential threshold of crack nucleation compared to simple fretting loading. It has been identified that the crack nucleation is influenced by the fretting and the fatigue forces in two ways: increasing the fatigue load leads to a decrease of the tangential force nucleation threshold whereas raising the fretting load leads to a decrease of the nucleation and fracture fatigue lifetime. All tests curried out with the potential drop technique system have shown that this technique is very efficient in the case of a fretting fatigue test.

Effect of contact pressure on fretting fatigue behavior of Ti-1023

“…The delamination theory provided the theoretical foundation for fatigue crack nucleation. According to literature, a large fraction of the life, approximately 80-90% of total life, is generally spent in crack nucleation and only a very small fraction of the life is spent in crack propagation to a critical size under high cycle fatigue [40,41]. Thus, we will pay much attention to the fatigue crack initiation area.…”

FEM modeling of crack nucleation and crack propagation fretting fatigue maps: Plasticity effect

“…The cylinder pad consisted of tempered 35NCD16 steel with a cylinder radius of R ¼19 mm and a lateral width of L¼10 mm (E ¼200 GPa, v¼ 0.3). It is applied on the plane with a high static normal force P. The contact was tested in plain fretting, plain fatigue and fretting-fatigue [13,14]. Scheme and photos of the fretting tests are illustrated in Fig.…”

“…The idea of applying the PDT to a fretting fatigue device was first introduced by Kondo et al [16] and transposed by Mériaux and al. [13] for double actuator fretting fatigue experiments. The technique relies on the fact that, for a given DC current, the distribution of the electrical potential in the vicinity of a crack changes with crack growth.…”

Fretting fatigue crack propagation rate under variable loading conditions

“…he calibration curve of the studied contact was established following an empirical method like Meriaux et al [10].…”