National Conference in Mechanical Engineering Research and Postgraduate Studies (2 nd NCMER 2010) 3-4 December 2010, Faculty of Mechanical Engineering, UMP Pekan, Kuantan, Pahang, Malaysia; pp. 100-116 ISBN: 978-967-0120-04-1; Editors: M.M. Rahman, M.Y. Taib, A.R. Ismail, A.R. Yusoff, and M.A.M. Romlay ©Universiti Malaysia Pahang 100 PREDICTION OF FATIGUE LIFE ON LOWER SUSPENSION ARM SUBJECTED TO VARIABLE AMPLITUDE LOADING Z. Husin, M.M. Rahman, K. Kadirgama, M.M. Noor and Rosli A. Bakar Faculty of Mechanical Engineering, Universiti Malaysia Pahang Tun Abdul Razak Highway, 26600 Pekan, Kuantan, Pahang, Malaysia Email: mustafizur@ump.edu.my ABSTRACT This paper focuses on the finite element based fatigue life prediction of lower suspension arm, subjected to variable amplitude loading. The objectives of this study are to predict fatigue life of the lower suspension arm using stress-life and strain-life methods, to investigate the effect of the mean stress. The lower suspension arm was developed using computer aided design software. The finite element modeling and analysis were performed utilizing the finite element analysis code. Mesh was created using tetrahedral 10 nodes element. The finite element analysis then was performed using MSC.NATRAN code using the linear elastic approach. In addition, the fatigue life was predicted using the stress-life and strain-life approach subjected to variable amplitude loading. The three types of variable amplitude are considered in this study. The TET10 and maximum principal stress were considered in the linear static stress analysis and the critical location. From the fatigue analysis, Goodman method is conservative method when subjected to SAETRN and SAESUS loading histories while SWT method is more conservative in SAEBKT loading histories. Stress-life method is capable to give higher fatigue life when subjected to bracket mean loading (SAEBKT) while strain-life method is capable to give higher fatigue life when subjected to positive mean loading (SAETRN) and negative mean loading (SAESUS). From the material optimization, 7175-T73 aluminum alloy is suitable material of the suspension arm. Keywords: Lower Suspension arm, aluminum alloy, FEM, variable amplitude loading, stress-life, strain-life, INTRODUCTION Suspension is the system of linkages and springs or shocks that allows the wheels to move up and down independent of the body. This is important for absorbing bumps in rough terrain, gracefully landing jumps, and getting the right amount of body lean and weight transfer in turns. Both end of this component are fixed to the wheel and the chassis. Suspension components, along with wheel rims and brake components are un- sprung masses, which make weight reduction important for ride quality and response as well as for reducing the total vehicle weight. Every automotive suspension has two goals, passenger comfort and vehicle control. Comfort is provided by isolating the vehicle's passengers from road disturbances like bumps or potholes. Control is achieved by keeping the car body from rolling and pitching excessively, and maintaining good contact between the tire and the road. This fatigue analysis needs the method that related to the analysis about the stress, strain, and fracture mechanics of background study, by using the variable amplitude loading. These are important subject the safety of the lower suspension arm can be analyzed due to the result obtained from the finite element