Crack resistance enhancement of joint bar holes by slide diamond burnishing using new tool equipment

The article presents a new technology for joint bar holes processing. Joint bars are components of rail bolted joints, which are a critical place for nucleation and propagation of fatigue cracks caused by cyclic loading due to passing trains. The probability of corner cracks arising, starting from the internal edges of the joint bar holes, is proven using the finite element method (FEM). On this basis, the necessity for a new technology for the enhancement of crack resistance of joint bar holes is grounded. The technology comprises slide diamond burnishing (SDB) as finishing of these holes. New tool equipment is developed including a combined cutting tool and an SDB device with elastic beam in order to set the necessary burnishing force. The equipment is intended for milling machine tools and machining centers. The optimal parameters of both cutting and SDB processes are obtained through planned experiments, regression analyses, genetic algorithm, and FE analyses. The distribution of the introduced beneficial residual hoop stresses is found by conducting a FE analysis of the SDB process. These stresses delay the nucleation and growth of fatigue cracks initiating in the hole surface. Both microscope analysis and fatigue tests prove this technology's advantage, expressed in the increased crack resistance of joint bar holes.