<![CDATA[A failure originating from a crack that propagated into a fracture occurred in the middle section of a shaft delumper at PT Pupuk Iskandar Muda specifically near the center bearing seat resulting in a production stoppage. This study was conducted in two stages: identifying the root cause of the failure through visual inspection and fractography of the fracture surface, followed by evaluating the suitability of AISI 1045 and AISI 4140 steels as replacement candidates for Carbon 1114 using Finite Element Method (FEM) simulation in SolidWorks Simulation software, with standardized geometry and loading to ensure result comparability. Analysis results indicate that the critical peak stress point was located on the shaft near the center bearing seat, triggering stress concentrations exacerbated by cyclic tensile-compressive loading, micro-friction at the shaft-bearing interface, and the low fatigue resistance of the Carbon 1114 material due to the presence of manganese sulfide inclusions; all these factors point to fatigue failure. Under a torsional load of 4,726 N·m, Carbon 1114 exhibited a von Mises stress of 206.31 MPa, a deformation of 4.58 mm, a safety factor of 1.939, and Kerusakan lelah of 14.152%. AISI 1045 recorded the lowest stress and deformation values (204.70 MPa; 4.53 mm) with a safety factor of 2.589 and a damage level of 5.195%, whereas AISI 4140 showed the highest stress and deformation (209.03 MPa; 4.65 mm) due to variations in its modulus of elasticity; however, this material outperformed the others in terms of safety factor (3.542) and fatigue resistance (4.440% damage) thanks to its significantly higher yield strength. These findings confirm that material reliability is determined more by yield strength and fatigue resistance than by the magnitude of nominal stress, thereby establishing AISI 4140 as the optimal replacement material. The study demonstrates that a root cause analysis combined with finite element simulation for various materials is an effective approach to addressing the failure of the shaft delumperKeywords— Failure Analysis, Shaft delumper, Finite Element Method, Fatigue, AISI 4140.]]>
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