A new approach to estimating the fatigue notch factor of Ti-6Al-4V components

Abstract

Titanium alloy is used for airframe components and compressor blades application because of its high strength and fracture toughness at low temperatures and high strength and creep resistance at elevated temperature. This paper extends a recently developed probabilistic mesomechaniccs based model to notched titanium alloy components using simulation strategies that capture both the essence of notch root stress gradient and the complexity of realistic microstructures. The notch size effects and notch root and inelastic behavior are combined with probability distributions of microscale stress and small crack initiation to inform minimum life design methods. A new approach which can be applied using crystal plasticity finite element or closed form solution is also proposed as a more robust method for determining the fatigue notch factor than the existing classical methods. The fatigue notch factors predicted using the new probabilistic mesomechanics based model are in good agreements with experimental for notched titanium alloy specimens subjected to cyclic loads with various stress ratios.

Quantifying lamellar microstructural effect on the fatigue performance of bimodal Ti-6Al-4V with microdefect

“…They are tabulated in Table 1. In RVE modeling, microstructural features such as average grain size and α and β phase proportion are based upon corresponding experiments and statistics [27,49,58].…”

“…Thermal interface grooving and anisotropic deformation of titanium alloy with lamellar colony is also discussed within a modified CPFEM framework in [45]. Though considerable efforts are being devoted to the influence of microdefect on fatigue behaviors in metal alloys, such as varied microdefects in 316L stainless steel [46], notched specimen for aluminum alloy 7075 [47], inclusions in nickel-based superalloys [48], notches in Ti-6Al-4V [49]. Even more elaborated is the effect of defect size and shape on HCF behavior of 316L austenitic steel in [50].…”

Fatigue Behavior of Medium Entropy Alloys AlCrFe₂Ni₂ and AlCrFe₂Ni₂Mo_0.1- A Comparison with Super Duplex Steel 1.4517

“…A similar mechanism was reported to exist in ultra-fined grained steels [55,56], showing a decrease in fatigue notch sensitivity with increasing grain size, up to a certain limit in the high cycle fatigue regime. Moreover, Owolabi et al [57][58][59] worked on a probabilistic framework for a microstructure-sensitive fatigue notch factor estimation [57] and used computational micromechanics to clarify and distinguish the process zone for crack formation and microstructurally small crack growth, relative to the scale of the notch root radius as well as the spatial extent of stress concentrations at the notch root [58]. In a further study, [59] found that the probability of failure as well as the fatigue notch factor increase with increasing notch root radius, and that the grain orientation plays an important role in determining or predicting the fatigue strength of a material.…”

Development of a non-local approach for life prediction of notched specimen considering stress/strain gradient and elastic-plastic fatigue damage

“…Currently, a number of non-local approaches (Ferré et al., 2013; Gerin et al., 2018; Li et al., 2018; Livieri and Tovo, 2021; Saintier et al., 2013) are proposed to take into account the effects of stress/strain fields of local area by introducing the parameters of stress/strain gradient. For the notch fatigue analysis, there are two kinds of commonly-used non-local approaches, including the critical distance theory based method (Araújo et al., 2017; Braun et al., 2020; Liao et al., 2019; Santus et al., 2018; Taylor, 2017) and the weakest-link method (Klawonn et al., 2020; Liu et al., 2020a; Owolabi et al., 2016; Qvale and Härkegård, 2017). In the non-local approaches, the stress/strain gradient parameters are usually introduced into constitutive models, and the fatigue life is often predicted based on the averaged parameters in a local area.…”