Mixed-mode I and II fatigue threshold and crack closure in dual-phase steels

Journal Article · Mon Aug 01 04:00:00 EDT 1994 · Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States)

DOI:https://doi.org/10.1007/BF02668536· OSTI ID:7244345

Zheng, Y S ^[1]; Wang, Z G; Ai, S H ^[2]

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1. Chinese Academy of Sciences, Shanghai (China). State Key Lab. on High Performance Ceramics and Superfine Microstructure
2. Academia Sinica, Shenyang (China). State Key Laboratory for Fatigue and Fracture of Materials

Fatigue threshold under mixed-mode 1 (tensile) and 2 (shearing) loading and elastic plane-strain conditions has been studies in dual-phase steels (DPS) of two types fraction of martensite (V[sub m]) in laboratory air at room temperature. Near-threshold mixed-mode (1 and 2) fatigue crack growth occurs mainly by two mechanisms; shear mode, and tensile mode. Particular emphasis was placed on the influence of the mode 2 component. Apparent- and effective-bound curves are obtained for the threshold condition and discussed in terms of the shape and size of the plastic region of crack tip; crack surface rubbing; and especially, roughness-induced closure and shear resistance of crack surface that resulted in an extremely high extrinsic-toughening contribution to the mixed-mode fatigue threshold values. The ratio of the threshold value of pure mode 2 to that of pure mode 1 ([Delta]K[sub th,2]/[Delta]K[sub th,1]) attained highly to 1.9 times; the maximum hoop direction stress-intensity factor range of pure mode 2 branch crack tip is 2.2 times that of pure mode 1. Obviously, the resistance of pure mode 2 crack growth here is far larger than that of pure mode 1; the former is just to introduce the shear resistance of crack surface, the latter, to reduce the driving force of crack tip for crack closure. It is proposed that the apparent- and effective-bound curves are nonconservative risky and too conservative for design purposes, respectively. So, the threshold data should be obtained under the specific conditions found by concrete mechanical, microstructural, and environmental factors.

• OSTI ID: 7244345
• Journal Information: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States), Journal Name: Metallurgical Transactions, A (Physical Metallurgy and Materials Science); (United States) Vol. 25:8; ISSN 0360-2133; ISSN MTTABN
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360103* -- Metals & Alloys-- Mechanical Properties
ALLOYS
CRACK PROPAGATION
FATIGUE
IRON ALLOYS
IRON BASE ALLOYS
MARTENSITIC STEELS
MECHANICAL PROPERTIES
STEELS
STRAINS
STRESS INTENSITY FACTORS