Experimental and probabilistic approach for assessing fatigue life of automotive steering knuckle

In the present research. fatigue life assessment of a steering knuckle. manufactured of cast iron ASTM A536-grade 65- 45-12 was performed through experimental andprobabilistic approach. Finite element stress analyses were also conducted to assist in the critical region detennination. The results showed that the root of the arm joining the knuckle to the steering linkage is the most critical region. The time histories of the 3D stress components are extracted in the critical elements by performing transient stress analysis. The different types of equivalent stresses are calculated by using some well- known fatigue criteria For non-proportional loadings. These time histories of equivalent stresses are used as stress probability density function for fatigue life detennination by utilizing polynomial curve fitting and probabilistic approach. Finally, the predicted lives were compared with experimental results to compare accuracies of different fatigue life assessment categories. The obtained results show that Von Misses, MacDiannid, Carpintcri—Spagnoli, Findley and Dang Van criteria are not reliable in the very complicated situations. Furthermore, the Energy approach by Shariyat and Liu-Zenner criteria lead to the highest accuracies with a percentage error of 9.5% and 10% compared to test results, respectively.

Keywords:

steering knuckle , Variable amplitude loading.full-scale fatigue test , Equivalent stress. Probabilistic approach