PSI - Issue 48

V.M.G. Gomes et al. / Procedia Structural Integrity 48 (2023) 142–148 Gomes et al/ Structural Integrity Procedia 00 (2023) 000–000

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Gaussian with a fitting of 75.00 %. The elastic plane stress method is considered to convert and plot the measured average strain into average stress (Noyan and Cohen, 1987).

Fig. 4. X-ray diffraction analysis: A) Portable diffractometer used for analysis, B) Sample surface for residual stress analysis in depth.

3. Results Two locations on the master leaf were considered for the analysis of assembly stresses and residual stresses due to stress shot peening. Point 1 is located at a distance of 490 mm while point 2 is located at a distance of 285 mm from the geometric center as illustrated in Figure 1. 3.1. Assembling Stresses Points 1 and 2 were monitored during the stress relief test on the leaf spring. Figure 5 presents the variation of the stress recorded during the stress relief testing for points 1 and 2 over the test time. Each time increment,   , was normalized by the total trial time,   . Note that the magnitude of the stresses has been inverted since in the assembly stress relief process, we are performing an inverse experimental test to the real procedure. The acquisition system recorded a compressive stress value of 2.5%   for point 1, while for point 2, the system recorded a value of 13%   , with   denoting the ultimate strength of the material. 3.2. Residual Stresses by Stress Shot Peening Regarding the residual stress test by stress shot peening using X-ray diffraction technology along the thickness, variations in the magnitude of residual stresses on the surface and in the sub-surface region were also verified. Figure 6 illustrates the residual stress profile obtained by X-ray diffraction analysis. The profile was obtained using the sinusoidal decay function model (Ulutan, et al . 2014 and Tan et al . 2018), with the parameters obtained from the least-squares method according to Levenberg-Marquardt’s algorithm (Marquardt, 1963, Kutner, et. al ., 2004, and Hansen, et al ., 2013). According to the sinusoidal decay function model, the residual stress profile can be expressed in the form:  ݁  () = ݁ ݌ − cos (+) (1) where  is the coordinate along depth,  denotes the amplitude of under-damped oscillation,  is the damping coefficient,  is the damped frequency, and  denotes the phase angle. According to the results presented in Figure 6, differences are verified both in the magnitude of the maximum residual stress and in the profile of residual stresses.