Page 97 - PCMI December 2017 Journal

Material Proper es Of High Performance Precision Strip Steel Jonas Nilsson |R&D Mgr. Precision Strip | Sandvik Materials Technology | SE
11/26/17
TYPES OF FATIGUE
• Bending Fatigue – ability to withstand bending back and forth multiple times – common in many spring applications, for example hinges on a cupboard door. The spring material is tested for 100k cycles in order to last 20 years on an average kitchen usage. Could be 10B cycles for a spring in a stirling engine.
• Impact Fatigue – is the material’s ability to withstand repeated blows. This is very critical on e.g. flapper valve steels where the valve is hitting the valve seat every time it closes – this eventually can make the valve crack or break
FATIGUE
CONTROLLING FACTORS
• Stresses from load
• Residual stresses
• Local stresses (notches)
− From defects (surface, edges) − From inclusions
PARAMETERS TO OPTIMIZE
• Static strength
• Heat treatment
• Metallurgical cleanness • Surface standard
• Stress conditions
• Compressive stresses • Design
• Corrosion resistance
Issue 130 December 2017 PCMI Journal Page 96
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