Steering module is a part of automotive suspension system which provides a means for an accurate vehicle placement and stability control. Components such as steering knuckle are subjected to fatigue failures due to cyclic loads arising from various driving conditions. This paper intends to give a description of a method used in the fatigue life reliability evaluation of the knuckle used in a passenger car steering system. An accurate representation of Belgian pave service loads in terms of response-time history signal was obtained from accredited test track using road load data acquisition. The acquired service load data was replicated on durability test rig and the SN method was used to estimate the fatigue life. A Pearson system was developed to evaluate the predicted fatigue life reliability by considering the variations in material properties. Considering random loads experiences by the steering knuckle, it is found that shortest life appears to be in the vertical load direction with the lowest fatigue life reliability between 14000–16000 cycles. Taking into account the inconsistency of the material properties, the proposed method is capable of providing the probability of failure of mass-produced parts. 1. Introduction The steering knuckle is a part of the vehicle’s steering and suspension system which undergoes time-varying loading during its service life. This system provides a means whereby driver can place his vehicle accurately where he wants it to be on the road. This system also means in keeping the vehicle stable on course regardless of irregularities in the surface over which the vehicle is travelling. Any failure in these components results immediately in loss of the orientation of the vehicle [1]. This paper will focus on McPherson strut steering knuckle which is mainly used in the steering system of the front-wheel drive vehicles. This McPherson strut steering knuckle system consist of a strut mount at the top, ball joint at the bottom, and a steering arm on the side as illustrated in Figure 1. The wheel spindle fits through a hole in the centre. Since it is connected to the steering parts and strut assembly from one side and the wheel hub assembly from the other, the component has complex restraint and constraint conditions and tolerates a combination of loads [2]. In this study, driving a vehicle over Belgian pave applies cyclic loads to the steering knuckle through the strut mount, ball joint and steering tie rod. Figure 1: Steering knuckle system. In general, fatigue life assessment of the component could be obtained using four
References
[1]
G. K. Triantafyllidis, A. Antonopoulos, A. Spiliotis, S. Fedonos, and D. Repanis, “Fracture characteristics of fatigue failure of a vehicle's ductile iron steering knuckle,” Journal of Failure Analysis and Prevention, vol. 9, no. 4, pp. 323–328, 2009.
[2]
R. L. Jhala, K. D. Kothari, and S. S. Khandare, “Component fatigue behaviors and life predictions of a steering knuckle using finite element analysis,” in Proceedings of the International MultiConference of Engineers and Computer Scientists, Hong Kong, March 2009.
[3]
J. Devlukia, H. Bargmann, and I. Rüstenberg, “Fatigue assessment of an automotive suspension component using deterministic and probabilistic approaches,” European Structural Integrity Society, vol. 22, pp. 1–16, 1997.
[4]
N. W. M. Bishop and F. Sherratt, Finite Element Based Fatigue Calculations, NAFEMS Ltd., October 2000.
[5]
M. Zoroufi and A. Fatemi, “Experimental durability assessment and life prediction of vehicle suspension components: a case study of steering knuckles,” Proceedings of the Institution of Mechanical Engineers Part D, vol. 220, no. 11, pp. 1565–1579, 2006.
[6]
R. I. Stephens, A. Fatemi, R. R. Stephens, and H. O. Fuchs, Metal Fatigue in Engineering, Wiley Interscience, New York, NY, USA, 2nd edition, 2001.
[7]
A guide for fatigue testing and statistical analysis of fatigue data, American Society for Testing and Materials, Philadelphia, Pa, USA, 1963, ASTM STP No. 91-A.
[8]
J. D. Booker, M. Raines, and K. G. Swift, Designing Capable and Reliable Products, Butterworth-Heinemann, Oxford, UK, 2001.
[9]
P. W. Hovey, A. P. Berens, and D. A. Skinn, “Risk analysis for aging aircraft,” in Flight Dynamic Directorate, vol. 1, Wright Laboratory, Dayton, Ohio, USA, October 1991.
[10]
R. E. Melchers, Structural Reliability Analysis and Prediction, John Wiley & Sons, Chichester, UK, 2nd edition, 1999.
[11]
J. Schijve, “Statistical distribution functions and fatigue of structures,” International Journal of Fatigue, vol. 27, no. 9, pp. 1031–1039, 2005.
[12]
J. D. Kim and J. K. Ji, “Effect of super-rapid induction quenching on fatigue fracture behavior of spherical graphite cast iron FCD500,” Journal of Materials Processing Technology, vol. 176, no. 1–3, pp. 19–23, 2006.
[13]
K. J. Jun, T. W. Park, S. H. Lee, S. P. Jung, and J. W. Yoon, “Prediction of fatigue life and estimation of its reliability on the parts of an air suspension system,” International Journal of Automotive Technology, vol. 9, no. 6, pp. 741–747, 2008.
[14]
J. A. Bannantine, J. J. Comer, and J. L. Handrock, Fundamentals of Metal Fatigue Analysis, Prentice Hall, Upper Saddle River, NJ, USA, 1989.
[15]
B. Sudret, Z. Guede, P. Hornet, J. Stephan, and M. Lemaire, “Probabilistic assessment of fatigue life including statistical uncertainties in the SN curve,” in Proceedings of the 17th International Conference on Structural Mechanics in Reactor Technology, Prague, Czech Republic, August 2003.
[16]
G. Genet, A Statistical Approach to Multi-Input Equivalent Fatigue Loads for the Durability of Automotive Structures, Chalmers University of Technology and Goteborg University, Goteborg, Sweden, 2006.
[17]
G. J. Hahn and S. S. Shapiro, Statistical Models in Engineering, John Wiley & Sons, New York, NY, USA, 1967.
