Finite element analysis of automotive crankshaft vibrations

• Main Author: Lim, Tee Yong
• Other Authors: Sellakkutti Rajendran
• Format: Final Year Project
• Language: English
• Published: Nanyang Technological University 2021
• Subjects: Engineering::Mechanical engineering
• Online Access: https://hdl.handle.net/10356/149207
• Institution: Nanyang Technological University

This Final Year Project (FYP) studies the free vibration of reciprocating crankshafts. Crankshafts are susceptible to fatigue failure when the natural frequency of the crankshaft is close to the frequency of the system. Free vibration analysis of crankshafts is beneficial in enhancing the knowledge vibrations in crankshaft to prevent vibration induced mechanical failure during operation. Numerical method such as finite element method serves as a powerful tool for the determination of the natural frequencies and mode shapes of crankshafts. For this FYP, the free vibration analysis is carried out using the finite element software ANSYS Parametric Design Language (APDL) which enables Computer-Aided Design (CAD) files to be constructed in external platforms such as Solidworks and subsequently imported into APDL for vibration analysis. The free vibration modes of crankshafts can be classified primarily into two groups, torsional mode and bending mode. In torsional mode, the crankshaft undergoes angular deformations about its axis. In bending mode, the deformations exist along the axial directions. The natural frequencies and mode shapes of crankshaft are first analysed under “free-free” boundary conditions. In other words, the crankshaft is treated as a “floating” structure with no boundary/constraint conditions. In the absence of external forces, oscillations are results of purely internal forces of the crankshaft. Under such conditions, the first six modes of vibrations of crankshaft correspond to rigid body modes and the corresponding natural frequencies will be zeros. Following the free vibration analysis of the crankshaft, the piston and connecting rod are then assembled to the crankshaft. Boundary conditions are applied to the components to simulate the motion constraints of the three components in actual application before being analysed for natural frequencies and mode shapes. The computed mode shapes and natural frequencies are compiled in both cases and the relationship between the various mode shapes are analysed.