Static analysis of two wheeler connecting rod by FEA and experimentation for geometry optimization

Transcription

1 ISSN Static analysis of two wheeler connecting rod by FEA and experimentation for geometry optimization #1 Mr. Aniket B.Phatangare, #2 Mr. M. S.Mhaske 1 aniphatangare@gmail.com, 2 msmhaske2002@yahoo.co.in #1 PG Student, Department of mechanical engineering P. R. E. C. Loni, MH, India. #2 Associate Professor, Department of mechanical engineering P. R. E. C. Loni, MH, India ABSTRACT In this paper deformation, stresses and fatigue life are carried out by FEA and validated experimentally. Forces acting on connecting rod are calculated analytically and 3-D finite element analysis is carried out by using commercial software to study FE results. Analytical calculations and FE analysis is done at the TDC position at the rated power operating condition. The calculated force considering gas force and inertia forces is applied at the top side of piston pin to find out the stresses. The damage location and critical stress location are observed. The Fatigue life method is based on modified Goodman theory and strain based theory. A proper Finite Element Model is developed using Cad software CATIA. Then computational model using HyperWorks, static analysis is done to determine the Von-Misses stress, total deformation in the present design connecting rod for the given loading conditions using Finite Element Analysis Software. In the first part of the study, the static loads acting on the connecting rod. Further the work is carried out for safe design. The results determine stress and the fatigue model would be used for analyzing the fatigue life. Further, results of present model in the solver are compared with the results of existing design. The result is discussed and suggestions regarding optimization geometry are discussed. ARTICLE INFO Article History Received :18 th November 2015 Received in revised form : 19 th November 2015 Accepted : 21 st November, 2015 Published online : 22 nd November 2015 Keywords Connecting Rod, Finite Element Analysis, Hypermesh, CATIA I. INTRODUCTION The connecting rod or con rod connects the piston to the crank or crank shaft. Together with the crank, they form a simple mechanism that converts reciprocating motion into rotating motion. The big end of the connecting rod connects to the crankpin journal to provide a pivot point on the crankshaft. The automobile engine connecting rod is a high volume production critical component. Every vehicle that uses an internal combustion engine requires at least one connecting rod. From the viewpoint of functionality, connecting rods must have the highest possible rigidity at the lowest weight. The major stress induced in the connecting rod is a combination of axial and bending stresses in operation. The axial stresses are produced due to cylinder gas pressure (compressive only) and the inertia force arising in account of reciprocating action (both tensile as well as compressive), where as bending stresses are caused due to the centrifugal effects. The result of which is, the maximum stresses are developed at the fillet section of the big and the small end. For the current study, it was necessary to investigate finite element modeling techniques, optimization techniques, deformation and stress analysis. P S Shenoy et.al the study shows the stress distribution and fatigue life of Connecting Rod in light vehicle engine were analyzed using the commercial 3D finite element software, ANSYS [1]. Adila Afzal et.al study investigates and compares fatigue behavior of forged steel and powder metal connecting rods [2]. S.B. Chikalthankar et.al shows the complete connecting rod Finite Element Analysis (FEA) methodology. It also performed a fatigue study based on Stress Life (SxN) 2015, IERJ All Rights Reserved Page 1

2 theory, considering the Modified Goodman diagram [3]. Vivek. C. Pathade et.al says that, the automobile engine connecting rod is a high volume production critical component [4]. R. Luri et.al this work deals with the design of a set of dies employed to manufacture a connecting rod by forging a billet of nanostructured aluminum alloy [6]. Mr. H.B. Ramani et.al in this study, detailed load analysis was performed on connecting rod, followed by finite element method in Ansys-13 medium [7]. Bin Zheng et.al studies, stress distribution and fatigue life of CR in light vehicle engine were analyzed using the commercial 3D finite element software, ANSYSTM. The results showed that the medial surface of small end will be the critical surface whereby damage will initiate at the maximum stretch condition [8]. Tony George Thomas et.al 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. They conclude that shot peening can significantly increase the fatigue life of a connecting rod component [9]. Om Parkash et.al the main objective of this work is to reoptimize the existing design of connecting rod of universal tractor (U650) by changing some of the design variables. The existing design performs modeling and evaluates critical regions in the connecting rod under fatigue loading. The connecting rod is modeled and optimized for the reduced weight, improved life and manufacturability [11]. Christy V Vazhappilly et.al the main objective of this study is to explore weight and cost reduction opportunities in the design and production of a connecting rod. This is achieved by performing a detailed load analysis [12]. A. Objectives Identify the problem areas by studying the existing system of linkages Document the challenges to be addressed for uniformity in load distribution for connecting rod Consider feasibility for redesign of the connecting rod Analyze the alternative geometry for connecting rod using FEA Recommend the best alternative design for the connecting rod through experimentation and validation. ENGINE SPECIFICATIONS Type of Engine Air cooled, 4-Stroke Single Cylinder Bore (mm) Stroke (mm) Bore to stroke ratio Compression ratio 9.0:1 Engine Capacity 1.2 L Max. Power ( kw) 5.5kW@8000rpm Max. Torque (N-m) 7.95Nm@5000rpm Displacement(cc) 97.2CC Table1. Engine Specifications I. MATERIAL PROPERTIES Connecting rod is subjected to shock and fatigue loads. Thus material of connecting rod should be tough and fatigue resistant. The connecting rods are generally made of carbon steel, special steel, aluminum or special cast iron [8]. In industrial engines, the connecting rods are commonly made of carbon steel and manganese steel such as 42CrMo4 are generally used for making of the connecting rod. Material specification for 42CrMo4 equivalent grade steel 4140, Q&T, BHN= 293 Material specification AISI 4130 (Material Reference SAE J1099- June 1998) [15]. PROPERTIES QUANTITY UNIT Brinell Hardness Number 293 (BHN) Elastic Modulus (E) Mpa Ultimate Strength (Su) 827 Mpa Fatigue Strength Coefficient (a) Fatigue Strength Exponent (b) 1163 Mpa Cyclic Strain Hardening Coefficient (n) Density (ρ) 7840 Kg/m 3 Poisson s Ratio 0.3 Yield Strength (Ys) 625 N/mm 2 Fatigue Strength (Se) N/mm 2 Table2. Material Specification for Connecting Rod I. ANALYTICAL CALCULATIONS OF FORCES Pressure Calculation. (MSD by Shigley) Density of Petrol (C8H18), ρ = 750 Kg/m 3 = 750 x 10-9 Kg/mm 3 Operating Temperature, T = K Mass = Density x Volume m = 750x10-9 x97.2x10 3 = 72.9x10-3 Kg Molecular weight of petrol, M = x10-3 Kg/mole Gas constant for petrol, R=8314.3/ x10-3 = 72.79x10 3 J/Kg.mol.K From Gas law equation, PV = mrt P = mrt/v = 72.9x10-3 x72.79x10 3 x293.15/ (97.2x10 3 ) P = 16 MPa Design Calculation. (MSD by Shigley) 1. Gas Force = Pressure x Cross section area of piston, Fg = P x π/4 x D 2 = 16xπ/4x50 2 Fg = N 2. Inertia Force From connecting rod drawing Stroke length, l = 123mm 2015, IERJ All Rights Reserved Page 2

3 Max. Angular speed, ω = 2πNmax/60= 2xπx8000/60 ω = rad/s Crank radius, r = 49.5/2 = mm n = l/ r = 123/24.75 = 4.97 Inertia force, Fi = mω 2 r (cosθ+cos2θ/n) Fi = 72.9x10-3 x x24.75x10-3 x (1+1/4.97) Fi = N bending analysis is done for maximum gas load condition i.e. when piston is at TDC. Displacement Plot for Benchmark Geometry In this case maximum gas force is applied on top of piston pin. The figure shows load displacement plot. II. FEM ANALYSIS Sketcher: Creation of skeleton for Connecting Rod Part Mode: Creation of solid part based on skeleton which includes forging and machining considerations etc. Fig.3 Displacement Plot The displacement of the connecting rod is observed in the range of mm. Stress Plot for Benchmark Geometry Fig.1 Model of connecting rod using CATIA For the analysis of connecting rod mesh generation on the geometry of connecting rod is performed in Hypermesh 11. Fig.4 Stress Plot Fig.2 Connecting Rod meshing using Hypermesh When loads are applied to a body, the body deforms and the effect of loads is transmitted throughout the body. The external loads induce internal forces and reactions to render the body into a state of equilibrium. Linear static analysis calculates displacements, strains, stresses, and reaction forces under the effect of applied loads. Linear static The von misses stresses observed in the connecting rod are observed in the range of 0.28 N/mm 2 to N/mm 2. As the maximum stress value observed by FEA analysis is N/mm 2 which is well below than the Yield Strength (625 N/mm 2 ) of material hence original design is itself safe for operating, so the parameter selected for modification of original design of connecting rod is to go for the weight reduction, so as to reduce the material required for connecting rod. The weight optimization should be done within 5% of the original weight of specimen to avoid major changes in the operating condition as well as to avoid further design and operating complications. Fatigue Plot for Benchmark Geometry 2015, IERJ All Rights Reserved Page 3

4 Fig.5 Fatigue plot for Benchmark Geometry Maximum fatigue life of Connecting rod is 1*10 20 cycles, Minimum fatigue life is 8.933*10 7 cycles. Fig.8 Stress Plot for Optimized Geometry The von misses stresses observed in the connecting rod are observed in the range of 0.15 N/mm 2 to N/mm 2. Fatigue Plot OPTIMIZED CONNECTING ROD GEOMETRY The mass of benchmark geometry is kg and the reduced mass for optimized geometry selected is kg which is within 5% change in original mass. For reduction of this kg of mass the material is removed from both the fillet ends of the shank of connecting rod which can be done without making major changes in the remaining geometry so that the stress distribution will be uniform over cross-section. Fig.9 Fatigue plot for Optimized Geometry Maximum fatigue life of Connecting rod is 1*10 20 cycles. Minimum fatigue life is 1.608*10 7 cycles. I. EXPERIMENTAL METHODOLOGY Fig.6 CATIA model for Optimized Geometry Displacement Plot In this case maximum gas force is applied on top of piston pin. The figure shows load displacement plot. Experimental testing is carried for static loading condition on Universal Testing Machine; gas force is applied on the standard specimen for TDC position. Static analysis of the connecting rod is performed to calculate stress, displacement to optimize the weight of Connecting Rod. Fig.7 Displacement Plot for Optimized Geometry The displacement of the connecting rod is observed in the range of mm. Stress Plot 2015, IERJ All Rights Reserved Page 4

5 ACKNOWLEDGEMENT I would like to take this opportunity to express our gratitude towards all those who helped me in completing this project work. I am very thankful to my guide Prof. M.S.Mhaske for his continuous guidance. I would like to express my deepest gratitude towards him. A work of such comprehensive converge could not have been materialized without systematic guidance of Prof. R.R. Kharde (Head, Department of Mechanical Engineering) my sincere thanks and appreciation to him for guiding me to make this work a reality. I am also thankful to my friends for their help. I am also grateful to all staff members of P.R.E.C. works for their constant support in my work. REFERENCES 1) P S Shenoy and A Fatemi, Dynamic analysis of loads and stresses in connecting rods, Proc.IMechE Vol. 220 Part C: J. Mechanical Engineering Science. 2) Adila Afzal, Fatigue Behavior and Life Predictions of Forged Steel and Powder Metal Connecting Rods The University of Toledo May Fig.10 Experimental Setup II. RESULTS AND DISCUSSION Static analysis of the connecting rod is performed by FEA to calculate stress, displacement to optimize the weight of Connecting Rod. Connecting Benchmark Rod Geometry FEA Exper iment al Optimized Geometry FEA % Variation in mass Displacement (mm) Stress (Mpa) Mass (Kg) CONCLUSION Fatigue strength is the most significant factor (i.e. design driving factor) in the design and optimization of the connecting rod. The variations in FEA and experimental results are less than 10% for standard geometry. The section modulus of the connecting rod should be high enough to prevent high bending stresses due to inertia forces, eccentricities, as well as crankshaft and case wall deformations. The shank region of the connecting rod offered the greatest potential for weight reduction. The optimized geometry is 2.4% lighter than the current connecting rod for the same fatigue strength respectively. Weight reduction in the shank region is, however, limited by manufacturing constraints. 3) S.B. Chikalthankar, V.M. Nandedkar, S.P. Baratam, Fatigue Numerical Analysis for Connecting Rod International Journal of Engineering Research and Applications (IJERA) ISSN: Vol. 2, Issue 6, November- December 2012, pp ) Vivek. C. Pathade, Bhumeshwar Patle, Ajay N. Ingale, Stress Analysis of I.C.Engine Connecting Rod by FEM ISSN: , International Journal of Engineering and Innovative Technology (IJEIT), Volume 1, Issue 3, March ) M.N. Mohammed, M.Z. Omar, Zainuddin Sajuri, A. Salah, M.A. Abdelgnei, M.S. Salleh, Failure Analysis of Fractured Connecting Rod Journal of Asian Scientific Research 2(11): ) R. Luri, C.J. Luis, D. Salcedo, J. León, J.P. Fuertes, I. Puertas, FEM analysis of the isothermal forging of a connecting rod from material previously deformed by ECAE ScienceDirect Procedia Engineering 63 ( 2013 ) ) Mr. H.B. Ramani, Mr. Neeraj Kumar, Mr. P.M. Kasundra, Analysis of Connecting Rod under Different Loading Condition Using Ansys Software, International Journal of Engineering Research & Technology (IJERT) Vol. 1 Issue 9, November ISSN: ) Bin Zheng, Yongqi Liu and Ruixiang Liu, Stress and Fatigue of Connecting Rod in Light Vehicle Engine The Open Mechanical Engineering Journal, 2013, 7, ) Tony George Thomas, S. Srikari and M. L. J Suman, Design of connecting rod for heavy duty applications produced by different processes for enhanced fatigue life SASTECH Journal, Volume 10, Issue 1, May ) Moon Kyu Lee, Hyungyil Lee, Tae Soo Lee and Hoon Jang, Buckling sensitivity of a connecting rod to the shank sectional area reduction Materials and Design 31 (2010) , IERJ All Rights Reserved Page 5