# Topology Optimization and Testing of Connecting Rod Based on Static and Dynamic Analyses
## 3 Computational Analysis
### Motion Loads  
Motion loads are the loads that are obtained from the motion of a mechanical system with certain allowable DOFs, such as inertial loads due to the mass of moving parts, impact loads due to sudden collisions, and dynamic loads from cyclic motion or vibrations, etc. In this study, motion loads were important since the engine underwent rapid tensile and compressive forces during cyclic motion along with inertial forces due to the motion of the crankshaft and connecting rod.  
The obtained motion load from the rigid body dynamics was applied to a new static structural study, where the connecting rod was subjected to two reaction forces, and two tensile forces were applied simultaneously along with two reaction moments while moving toward the top dead center (TDC), as shown in Figure 9a,b.  
These reaction force values as shown in Figure 9a explains When the connecting rod moved toward the TDC, there were remote forces of 609.61 N and 293.51 N acting as tensile forces, along with moments of 1.4517 \(\times\) 10\({}^{-6}\) Nm and 3.7434 \(\times\) 10\({}^{-8}\) Nm acting on the initial design of the connecting rod.  
Figure 9b shows that when the connecting rod moved toward the TDC, there were remote forces of 858.13 N and 1156.1 N acting as tensile forces, along with moments of 2.3238 \(\times\) 10\({}^{-5}\) Nm and 1.0394 \(\times\) 10\({}^{-8}\) Nm acting on the optimized topology of the connecting rod with a mass reduction of 5.66%.  
The forces obtained from the rigid body dynamics were applied to a new static structural study where the connecting rod was exposed to two compression forces at the  
Figure 9: (**a**) Maximum unknown reaction forces applied during static structural analysis on the initial design while at the TDC. (**b**) Maximum unknown reaction forces applied during static structural analysis on the optimized topology with a mass reduction of 5.66% while at the TDC.  
same time as two reaction moments while it moved toward the bottom dead center (BDC), as shown in Figure 10a,b.  
These reaction force values as shown in Figure 10a explains When the connecting rod moved toward the BDC, there were remote forces of 428.47 N and 171.96 N acting as compressive forces, along with moments of 8.0576 \(\times\) 10\({}^{-7}\) Nm and 1.4539 \(\times\) 10\({}^{-8}\) Nm acting on the initial design of the connecting rod.  
Figure 10b shows that when the connecting rod moved toward the BDC, there were remote forces of 503.54 N and 746.81 N acting as compressive forces along with moments of 1.7722 \(\times\) 10\({}^{-6}\) Nm and 8.7817 \(\times\) 10\({}^{-4}\) Nm acting on the optimized topology of the connecting rod with a mass reduction of 5.66%.  
These reaction force values show how the engine balance varied between the initial design of the connecting and optimized topology for 5.66% weight reduction. When the mass of the connecting rod was reduced by more than 7%, that may have caused a total imbalance between the counterweight of the crankshaft and the connecting rod, making the engine unstable by causing high vibrations. To avoid this problem, the ratio between the crankshaft counterweight and connecting rod should always be maintained.