On the effect of key edge shape on keyway edge stresses in shafts in torsion

Two-dimensional, photoelastic tests of cross-sections of two keyed shafts with 13 different shapes of keys showed that rounded edges of keys give lower stress concentrations in the shaft than chamfered edges. Stress concentrations are reduced by making both rounding radii and chamfers larger than the key way fillet radius. Making the key a sliding fit in the keyway allows significant relative movement and produces lower stress concentrations than the usual interference fits. Boussinesq's theoretical solution for stresses near a concentrated edge load has been successfully used for direct calibration of small photoelastic models.