Fretting fatigue strength of 12% Cr steel under high local contact pressure and its fracture mechanics analysis

Fretting fatigue fractures of industrial machines often occur at the point where high contact pressure occurs due to uneven contact. In this study, fretting fatigue tests were performed under high contact pressure applied in line-contact conditions using 12% Cr steel with parameters of the mean stress, contact pressure, and material strength. The fretting fatigue strength was shown to decrease as contact pressure increased, and minimized when Hertz's average contact pressure was about 1.5 times 0.2% proof stress sigma(0.2), and increased again at higher contact pressure. Crack propagation behavior was examined using fracture mechanics by observing the detailed crack propagation profile of non-propagating cracks and performing finite element analysis with an inclined elliptical surface crack. Cracks were found to propagate in stage II at the angle where the maximum stress intensity factor range Delta K-theta max occurred. Also, test results concerning the fretting fatigue strength could be successfully explained by the micro-crack propagation model in which a micro-crack can propagate when its stress intensity factor range Delta K is greater than the threshold value Delta K-th when considering small crack effects and mean stress effects. This model also confirmed the experimental results that showed the length of non-propagating cracks decreased as the mean stress and the material strength increased. (C) 2010 Published by Elsevier Ltd.