Mechanism of Shot Peening on Improved Fatigue Life of Rail Clips
Q1: Why can shot peening improve the fatigue life of clips?
A1: Shot peening forms a uniform residual compressive stress layer on the clip surface, offsets part of the alternating tensile stress, and inhibits the initiation of fatigue cracks on the surface. At the same time, it refines surface grains and improves surface defects, greatly increasing fatigue life.
Q2: Where does residual compressive stress mainly act on key parts of clips?
A2: It mainly acts on the arc transition zone, clip arm root and arc surface in contact with the rail, where stress concentration is the most serious. These parts are most prone to cracks, and compressive stress can directly block crack sources and protect core stress areas.
Q3: What problems will be caused by insufficient or excessive shot peening strength?
A3: Insufficient strength results in a shallow residual compressive stress layer with limited strengthening effect; excessive shot peening will cause rough surface, local over-pressure and even micro-cracks, reducing fatigue performance instead. It must be controlled within the process window.
Q4: Do shot-peened clips perform better in corrosive environments?
A4: Yes. The compressive stress layer can delay the intrusion of corrosive media, reduce the formation of corrosion pits, and inhibit the coupling effect of corrosion and fatigue. The life improvement effect is more obvious in humid, coastal and other corrosive environments.
Q5: Can shot peening replace the role of material and heat treatment?
A5: No. Shot peening is a surface strengthening method that cannot change matrix strength and toughness. Only on the basis of high-quality materials and reasonable heat treatment combined with shot peening can the best fatigue performance be achieved, which is indispensable.