Fatigue assessment of piston rod threaded end

The present paper deals with the research on the influence of different thread type on the piston rod fatigue life. Research was done on hydraulic cylinder piston rod, which becomes subjected to fatigue failures after change of its design. Previously used piston rods used M74 × 3 threads, but redesigned rods are compromising M76 × 2. Due to changes in thread type the supplier was convinced that changes will affect lowering stresses in thread core which is true, but they have overlooked the fact that lowering the pitch will also lead to lowering the thread root radius which leads to the significant rise of stress concentration and therefore lower the fatigue life.