Bearing stress between a circumferential key and its keyway
Allowable bearing stress was defined as the normal stress required to initiate engraving between surfaces in direct contact. This concept was then used to evaluate the allowable bearing stress between a key and its keyway by applying the slip-line field theory of plasticity. It was found in analyzing the key that the force associated with the suggested concept of bearing stress exceeds the force permitted by conventional engineering theory. The relative strength of the key and the keyway shoulder were then discussed in detail. The strength of a rectangular key assembly was examined for three different modes of failure: (1) the bearing stress of the key; (2) the bearing stress of the keyway shoulder; and (3) the transverse shear of the key. Conditions under which each of these modes of failure dominates were expressed in terms of two dimensionless ratios: the ratio of the yield stress of the shoulder material to the yield stress of the key material and the effective aspect ratio of the rectangular key.