On a Predictive Fatigue Crack Initiation Reliability for Large Steel Castings

Abstract

For over a century, large steel and cast iron castings have been and are being successfully produced and operated in fatigue loading situations. More recently, however, customer requirements as to the power transmitted and reliability of heavy machinery have increased along with a corresponding increase in both component size and the effect of inherent casting defects. The long-term objectives of the research whose current status is reported in this paper are therefore twofold. The first is to establish a reliability and decision making algorithm based on probabilistic concepts which takes into consideration the nature, geometry and location of casting defects, their severity, the local fatigue material properties of metals commonly used in cast form and the variety of fatigue loading situations. The second is to accumulate an expanding data bank to aid in the formulation of future design decisions in an ever increasing number of situations which involve large cast steel components. Although this predictive technique applies in general to any large casting situation, the research effort reported here is directed toward establishing crack initiation reliability estimates for 6 to 12 m diameter ring gears used to drive ore grinding mills.