## 1 Introduction
[PERSON] et al. analyzed the effect of internal and external machining applied to a compound tube after autofrettage on residual stress loss analytically and numerically. The analysis revealed that the sequence of operations led to different results in residual stress loss when both internal and external machining were applied together [15]. Despite the extensive research on autofrettage and its effects on residual stress, there is a notable gap in the literature regarding the quantitative impact of material parameters on the safety factor of autofretaged cylinders, especially when different machining processes are applied post-autofrettage. This study advances the field by providing a detailed analysis of how yield strength, Young's modulus, and tangent modulus influence the safety factor under various scenarios. By integrating the Taguchi experimental design, finite element simulations, ANOVA, and regression analysis, this research offers a comprehensive approach to understanding and predicting the behavior of autofretaged cylinders. The novel contribution lies in quantifying the effects of these material parameters and validating the findings with both numerical and analytical methods, filling a critical gap in the existing research. In this study, the effect of material parameters such as yield strength, Young's modulus, and tangent modulus on the safety factor for the working pressure of autofrettagged cylinders has been investigated for the following three scenarios: with no machining, only internal machining, and only external machining. The working pressure was chosen as 400 MPa, which is a pressure value commonly experienced in pressure vessels and artillery guns [9; 16; 17]. Initially, a series of finite element (FE) simulations were conducted based on the Taguchi experimental design, where three levels were set for each of the three selected material parameters, creating a standard orthogonal array \(L_{9}\). The machining simulation after autoftrettage simulation was performed using the element birth and death method available in the ANSYS 2023 R1. The results of nine FE simulations, conducted according to the Taguchi experimental design, were transformed into signal-to-noise (S/N) ratios to determine the best settings. Analysis of variance (ANOVA) was used to understand how much each factor contributed and how significant they were. To ensure the accuracy of the FE model, its outcomes were compared with an analytical method based on the deformation theory of plasticity, showing close agreement. Finally, a regression analysis predicted responses for different parameter values, with confirmation simulations confirming the accuracy of the regression model. The analysis indicated that among autoftretaged cylinders across three scenarios--without machining, with only internal machining, and with only external machining--the parameter most significantly affecting the safety factor is \(S_{y}\). [PERSON] et al. also highlighted the crucial role of yield strength in residual strain outcomes, noting that materials with higher yield strength exhibit better performance in terms of residual strain upon pressure removal, which aligns with our findings [14]. In all three scenarios, the influence of \(E\) and \(T\) on the safety factor is relatively minimal. However, \(T\) exhibits a greater impact than \(E\). As \(E\) decreases and \(T\) increases, there is a slight tendency for the safety factor to increase. A strong agreement is noted between the numerical and analytical findings. Generally, the safety factor tends to show lower values in the analytical approach compared to the numerical approach across all scenarios. The numerical analysis results suggest that internal machining results in a higher loss of residual stress compared to external machining.