MAXIMUM PRINCIPAL TENSILE-STRESS AND FATIGUE-CRACK ORIGIN FOR COMPRESSION SPRINGS

Contrary to the traditional concepts, for helical compression springs with a large coil radius to wire radius ratio, the most highly stresse d region is at the outer surface of the helix rather than inside. The likely fatigue crack origin is also located on the outer surface of th e helix where the maximum amplitude of the principal tensile stress wa s calculated during cyclic loading. An equation is proposed for the ma ximum tensile stress from loading of a helical spring, and a method is presented to calculate the likely fatigue crack origin. It is demonst rated that for high-stressed springs, fatigue design should be based o n the range of the maximum principal tensile stress. The influence of the shot peening on the location of the fatigue crack origin is also i nvestigated. (C) 1998 Elsevier Science Ltd. All rights reserved.