The piston rod of a steering damper on a single decker bus fractured after 100,000 miles of service in the fully-extended left full-lock position. The steering damper, which is similar in shape and operation to a telescopic shock absorber, was secured by ball joints locked with slotted nuts. The steel piston rod fractured at the axle end leaving approximately 5 mm of rod welded to a securing ferrule. The failure was caused by a fatigue mechanism. Small surface cracks formed during welding in the heat-affected zone close to an unradiused shoulder in the piston. Under alternating stresses in normal...