The Role of Crack Closure on Fatigue Threshold at Elevated Temperatures

Abstract

Near threshold fatigue crack growth and crack closure were investigated in SS 41, SM 41 A, SUS 304 steels and A 2218-T 6 Aluminum alloy at elevated temperatures up to 500°C. Emphasis was placed on examining the role of crack closure on fatigue threshold at elevated temperatures. The fatigue threshold, Δ K_th, was found to increase with increasing test temperature in all the steels tested, while it was found to decrease in A 2218-T 6 Aluminum alloy. Oxide-induced crack closure was found to play an important role in the in crease of ΔK_th at elevated temperatures in SM 41 A, while it was found to play a less important role in SS 41 and SUS 304. It was concluded that oxide products on the fracture surface enhance crack closure only when the CTOD at threshold remains small at elevated temperatures.