SASTECH Journal 1 Volume 10, Issue 1, May 2011 DESIGN OF CONNECTING ROD FOR HEAVY DUTY APPLICATIONS PRODUCED BY DIFFERENT PROCESSES FOR ENHANCED FATIGUE LIFE Tony George Thomas 1 , S. Srikari 2 , M. L. J Suman 3 1-M.Sc.[Engg.] Student, 2-Professor, Department of AAE, 3-Senior Lecturer, Department of MME M.S.Ramaiah School of Advanced Studies, Bangalore 560 058 Abstract The connecting rod forms an integral part of an internal combustion engine. The connecting rod is acted upon by different types of loads while undergoing its operation. One of the main reasons contributing to its failure is fatigue. The aim of this study is to redesign the connecting rod by incorporating the manufacturing process effects into the analysis and obtain a better fatigue performance. The redesign is aimed at reducing the weight of the component. Heavy duty application’s connecting rod was selected for the study. The analytically calculated loads acting on the small end of connecting rod were used to carry out the static analysis using ANSYS. A stress concentration was observed near the transition between small end and shank. A piston-crank-connecting rod assembly was simulated for one complete cycle (0.02 seconds) using ADAMS to obtain the loads acting on small end of connecting rod. This force vs. time graph was converted into an equivalent stress vs. time graph. This stress vs. time graph was used as loading graph for fe-safe. The fatigue life calculated using fe-safe is 6.94×10 6 cycles and these results are validated with the help of Palmgren-Miner linear damage rule. The fatigue life of connecting rod can be further enhanced by incorporating manufacturing process effects in the analysis stage. Fatigue life was estimated by incorporating the shot peening process effects. An in-plane residual stress for the selected surface elements were applied for obtaining the beneficial effect of shot peening. There was an increment of 72% in fatigue life cycles). We concude that shot peening can significantly increase the fatigue life of a connecting rod component Keywords: Fatigue Analysis, Compressive Residual Stress, Shot Peening, Surface Cracks Nomenclature AISI American Institute of Iron and Steel CAD Computer Aided Design CG Center of Gravity FOS Factor of Safety K f Fatigue Strength Reduction Factor K t Stress Concentration Factor LS Load Step q Notch Sensitivity Index S a Alternating Stress S m Mean Stress S max Maximum Stress S min Minimum Stress TDC Top Dead Centre UTS Ultimate Tensile Strength 2D 2-Dimensional 3D 3-Dimensional 1. INTRODUCTION Connecting rod is an integral component of internal combustion engine and it is classified under functional component [1]. It acts as a linkage between piston and crank shaft. The main function of connecting rod is to transmit the translational motion of piston to rotational motion of crank shaft. The function of the connecting rod also involves transmitting the thrust of the piston to the connecting rod. Connecting rod has three main zones. The piston pin end, the center shank and the big end. The piston pin end is the small end, the crank end is the big end and the center shank is of I- cross section. Connecting rod is a pin jointed strut in which more weight is concentrated towards the big end. In that point of view the location of the CG point of connecting rod lies more towards the big end. 1.1 Fatigue design requirement Connecting rod is acted upon by gas loads and inertial loads during its operation. The forces include gas forces due to combustion and inertia forces due to its own weight. In that point of view fatigue is an important parameter to be considered for estimating the life of the component. The magnitudes of inertia forces are constant but gas forces are varying in nature. Due to fluctuating nature of these forces the chances of component failure due to fatigue is very high. Thus fatigue is one of the significant factors to be taken into account while optimising an existing design. Fatigue in a component arises due to the following reasons [2]:  Material defect  Manufacturing defects  Poor detailing of dimensions while designing  Error in load calculation The possible zones of stress concentrations are the change in cross-section from center shank to small end, change in cross-section from big end to center shank and the center shank itself. The connecting rod is subjected to higher duty cycles and the forces acting on the connecting rod is also tremendously high. Connecting rod is being categorised as a functional component and the failure rate is very high during the