Near-threshold fatigue crack propagation in ultra-high strength steel: influence of load ratio and cyclic strength

Journal Article · Fri Jul 01 00:00:00 EDT 1977 · J. Eng. Mater. Technol.; (United States)

DOI:https://doi.org/10.1115/1.3443519· OSTI ID:5307658

Ritchie, R O

Fatigue crack propagation behavior of an ultra-high strength steel (300-M) has been investigated in humid air over a very wide spectrum of growth rates from 10/sup -8/ to 10/sup -1/ mm/cycle. Particular emphasis has been devoted to the influence of mean stress (or load ratio R = K/sub min//K/sub max/) and microstructure on fatigue crack growth near the threshold stress intensity for crack propagation, ..delta..K/sub 0/. Increasing the load ratio from R = 0.05 to 0.70 was found to lead to increased near-threshold growth rates, and a decrease in the threshold stress intensity. Similarly, increasing material strength, by varying the microstructure through quench and tempering and isothermal transformation, resulted in higher near-threshold growth rates, and a marked reduction of ..delta..K/sub 0/. These effects are contrasted with behavior at higher growth rates. The infuence of strength on ..delta..K/sub 0/ is rationalized in terms of the cyclic hardening or softening response of the material, and hence it is shown that cyclic softening can be beneficial to fatigue crack propagation resistance at very low growth rates. The results are discussed in the light of crack closure and environmental contributions to fatigue crack growth at low stress intensities.

• Research Organization: Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
• OSTI ID: 5307658
• Journal Information: J. Eng. Mater. Technol.; (United States), Vol. 99:3
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
NICKEL ALLOYS
CRACKS
FATIGUE
SILICON ALLOYS
STEELS
CARBON ADDITIONS
CHROMIUM ADDITIONS
HEAT TREATMENTS
MANGANESE ADDITIONS
MICROSTRUCTURE
ALLOYS
CHROMIUM ALLOYS
CRYSTAL STRUCTURE
IRON ALLOYS
IRON BASE ALLOYS
MANGANESE ALLOYS
MECHANICAL PROPERTIES
360103* - Metals & Alloys- Mechanical Properties