Fatigue analysis of SAE8620: Synergistic effect of thermal treatments and surface roughness

Abstract

ABSTRACT In the present paper, the influence of machining parameters and thermal treatment cycles on the fatigue life of SAE8620 has been investigated. Experiments were designed as per L9 array and a set of nine fatigue test samples were prepared using CNC machine. Spindle speed (1900, 2100, and 2300 rpm), feed rate (0.15, 0.175, and 0.2 mm/min), and depth of cut (0.2, 0.4, and 0.6 mm) were the three machining parameters that were included for the analysis. The three different cooling rates were annealing (0.8℃/min), normalising (13℃/min), and water quenching (421℃/min). Surface roughness testing were carried out first, followed by fatigue tests. The Taguchi method was used to optimise the machining settings (spindle speed − 2100 rpm, feed rate − 0.175 mm/min and depth of cut − 0.4 mm). To determine the missing output values, the ANFIS modelling tool was employed and the predicted value was 1.07 µm. The optimal surface roughness (1.261 µm) and fatigue cycle (41149 cycles) were obtained by grey relation analysis for input parameters (spindle speed − 2300 rpm, feed rate − 0.175 mm/min and depth of cut − 0.4 mm). The so obtained optimised surface roughness values found to be close by 15.14%. It was found that fatigue life get enhanced due to synergistic effect of heat treatment (average 56%) and surface roughness (25%), respectively. Therefore, inference can be made that the fatigue life can be significantly influenced by the heat treatment and surface roughness.