## 1 Introduction  
Inconel 718 has good mechanical properties such as high yield and high ultimate tensile strength, fatigue resistance as well as good corrosion resistance at a high temperature of 650 \({}^{\circ}\)C. Thus, it has been widely employed in the aerospace industry for parts in turbine engines such as turbine disks, turbine shafts, and high-pressure compressor blades [1]. Turbine engines work with maximum speed in a harsh environment with high pressure, high load, and high temperature. Once a failure is caused by a fatigue fracture occurring on the turbine disk, turbine shaft, or compressor blade, a larger amount of high-energy debris will be generated. These debris will break through the turbine casing to threaten the aircraft safety and may cause catastrophic failure of the turbine. The surface integrity factors including surface roughness, residual stress, micro-hardness, and microstructure are considered the most relevant factors that will result in a failure of the turbine disk or shaft according to statistics [2]. It is noteworthy that, among the surface integrity factors, residual stress plays a key role in affecting the fatigue performance of components [3; 4; 5; 6]. Compressive residual stress (CRS) is beneficial to improving fatigue performance [7; 8; 9], whereas induced tensile residual stress is usually detrimental to the fatigue life of components [10; 11]. Several researchers have undertaken to study the influence of residual stress on the fatigue performance of Inconel 718. [PERSON] et al. [12] investigated the influence of the broaching process on the bending fatigue behavior of Inconel 718. They pointed out that the CRS in a longitudinal direction at the surface induced by broaching could extend the bending fatigue life of Inconel 718. [PERSON] et al. [13] analyzed the effect of CRS produced by ultrasonic nanocrystal surface modification on the fatigue behavior of Inconel 718 plus superalloy. The experimental results showed that the presence of CRS in longitudinal direction and transverse direction improved fatigue life. They explained that the CRS at the surface layer could inhibit the crack initiation and propagation. [PERSON] et al. [14] evaluated the influence of residual stress in a longitudinal direction on the fatigue life of machined nickel-based superalloy. They found that higher fatigue life could be obtained due to the presence of CRS. The negative effect of notch on fatigue life could be canceled by the positive effect of CRS. [PERSON] et al. [15] carried out machining and fatigue experiments to correlate residual stress with the fatigue life of Inconel 718 at high temperature. They suggested that the maximum residual stress at the machined surface and the area of CRS were related to fatigue life. Similar work on titanium alloy Ti6 Al4V was performed by [PERSON] et al. [16; 17]; they assumed that the maximum residual stress in a longitudinal direction on the machined surface could be a good indicator for evaluating fatigue life. There is extensive literature focusing on the residual stresses in longitudinal or transverse directions on a machined surface. However, the residual stresses in these two directions are residual normal stresses, and the residual shear stress produced during machining has not been taken into account. Indeed, both the residual normal and shear stresses were induced during the machining process. The residual shear stress induced by machining should be taken into account to obtain the equivalent stress that can determine the fatigue life of a component. Hence, the induced residual shear stress is not negligible, and it is necessary to study its effect on fatigue performance of Inconel 718. In addition, the effect of residual stress on the stress intensity factor (SIF) has not been entirely explored and reported in the literature. Therefore, the purpose of this paper was to determine the residual shear and normal stresses simultaneously and to establish the correlation between the residual stress and the SIF of Inconel 718.