FRACTURE TOUGHNESS AND CRACK PROPAGATION OF 300 M STEEL
LOCKHEED-CALIFORNIA CO BURBANK
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Fracture toughness and crack propagation behavior was investigated for 300 M steel in sheet, plate and forging products. Variables included material thickness of 18, 38, and 34 inch and material strength levels of 220 KSI, 270 KSI, and 290 KSI. Both surface-crack and through-crack specimens were evaluated in moist air and walt water spray environments for cyclic stress ratios of 0.1, 0.2, and 0.5. It was concluded that stress intensity methods showed promise for correlating both fracture toughness and cracking rate behaviors. There appears to be an inverse relationship between fracture toughness and cracking rate although a quantitative mathematical relationship between the two was not found. Variation in fracture toughness with heat chemistry was relatively large with respect to other metallurgical variables. Geometric variables included variations in fracture toughness with at ratio and variation of cracking rate with thickness. The influence of stress ratio on cracking rate was found to be accountable through available theory. Several approaches to MIL-HDBK-5 presentation of crack growth data are discussed.
- Metallurgy and Metallography