# Topology Optimization and Testing of Connecting Rod Based on Static and Dynamic Analyses
## 1 Introduction  
The connecting rod is the most crucial and highly dynamic component of internal combustion engines, which helps in converting the reciprocating motion of the piston into the rotational motion of the crankshaft [1]. The connecting rod consists of a small end, shank, and big end, where the small end is connected to the piston using a piston pin, and the big end is attached to the crankshaft [2]. Irregular motion loads and moments due to crankshaft rotation combined with the combustion forces from the piston acting on the connecting rod play a vital role in optimizing this structure without affecting its longevity. Frictional energy loss plays an important role in mechanical efficiency and accounts for between 10% and 15% of the energy produced by internal combustion engines. Components of the engine and drivetrain, such as the piston rings, valve guides, cam followers, fuel injector pistons, shims, transmission gears, and front seals, are to varying degrees affected by friction. The selection of appropriate materials and lubricants and the proper design and size of an engine's functional parts are not only necessary to minimize friction and wear on operational components but also to reduce friction and wear on enginecomponents. The proper size of an engine can reduce fuel consumption by about 9% [3]. Finite element method (FEM) strength analysis is used to determine the cause of damage, evaluate structural integrity, and optimize design to prevent failure by simulating the distribution of stress and material behavior under different loading conditions [4]. In the past few years, computer-aided design (CAD) tools like SolidWorks 2024 and Autodesk Inventor 2025, and FEM tools like ABAQUS 2023 HF2, NASTRAN 2023.4, etc., have evolved, and the TO process plays a major role in product improvement. The storage and reuse of the data from the CAD model for future improvement, adaptation, or use in different applications is widely implemented by many product developers [5]. CAD models are simulated with structural analysis to understand their deformation, displacement, etc. Structural analysis is a method used to study behavior under static loading conditions depending on material properties, mesh, and boundary conditions [6]. According to the Kisaru Shveli method, the FOS at the connecting rod body should be above 1.5, and at the big end and small end, it should be above 2.5 [7]. Dynamic analysis is a method used to evaluate the kinematics of assembly by studying motion while a system is kept rigid from deformation [8]. The application of the TO process has a large scope depending on the requirement of structural enhancements in fields like the automotive industry [9], robotics [10], aerospace [11], and industrial machinery [12]. There are several methods used to achieve TO, such as the density-based method, level-set method, evolutionary structural optimization, etc. [13]. The TO process is a computational method used to reduce the mass and the maximum von Mises stress of a defined boundary condition, while ensuring structural integrity, optimizing material distribution, and maintaining a suitable factor of safety for reliable performance under applied loads [13,14]. However, despite its application, limited research has addressed the TO of highly dynamic components like connecting rods, crankshafts, etc. The main objective of this research was to perform TO on a connecting rod using the finite element method and multibody dynamics by reducing the mass and maximum von Mises stress during static structural analysis. Unlike conventional topology optimization studies that focused exclusively on mass reduction, this research simultaneously optimized the distribution of stress and ensured structural integrity by maintaining a safety factor (FOS) above 2.5. The current study also incorporated static structural analysis, dynamic analysis, and fatigue life analysis (Goodman criteria) to fully evaluate the long-term durability of optimizing designs.