Effects of R-ratio on high-temperature fatigue crack growth behavior of a precipitation-hardening stainless steel

✍ Scribed by Kuei-Chang Hsu; Chih-Kuang Lin

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 486 KB
• Volume: 30
• Category: Article
• ISSN: 0142-1123
• DOI: 10.1016/j.ijfatigue.2008.05.029

✦ Synopsis

The high-temperature fatigue crack growth (FCG) behavior was investigated for a precipitation-hardening stainless steel, 17-4 PH, in three differently aged conditions. FCG tests were conducted at 400 and 500 °C under various load ratios (R-ratios) ranging from R = 0.1 to 0.7. Results indicated the fatigue crack growth rates (FCGRs) increased with R-ratio at the lower DK regime and merged together at the higher DK regime for all the given heat-treated conditions tested at 400 °C, except for Condition H900, in which the FCGRs increased with R-ratio for the entire DK range. At 500 °C, the FCGRs for a given heat-treated condition increased with R-ratio at lower R-ratios and became comparable at higher R-ratios for the entire DK range. The variations of FCGR with R-ratio could be described as an intrinsic behavior of FCG based on a Unified Approach. Accordingly, the dominating crack growth mechanism was similar to a general plastic blunting process except for Conditions A and H900 at 400 °C at the high R-ratio regime, in which the primary crack growth mechanism was associated with a crystallographic-faceted fracture mode. The variations of FCGR with R-ratio for all the given testing conditions were well correlated with a modified FCG driving force parameter, M * DK.