Effect of small loads on crack growth rate and crack tip deformation in the fatigue process of A537 steel
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Effect of Small Loads on Crack Growth Rate and Crack Tip Deformation in the Fatigue Process of A537 Steel XUEJUN WEI, JIN LI, JINGWEI CHEN, and WEI KE
Fig. 6—Fractographs of the W-Cr-Co-Ni steel tested at room temperature: (a) 425 7C and (b) 475 7C, showing a large amount of intergranular area; and (c) 510 7C, showing the mostly transgranular dimples. 2. R. Ayer and P.M. Machmeier: Metall. Trans. A, 1993, vol. 24A, pp. 1943-55. 3. G.R. Speich, D.S. Dabkowski, and L.F. Porter: Metall. Trans., 1973, vol. 4, pp. 303-15. 4. G.R. Speich: Innovations in Ultrahigh Strength Steel Technology, Proc. 34th Sagamore Army Materials Research Conf., G.B. Olson, M. Azrin, and E.S. Wright, eds., U.S. Army Materials Technology Laboratory, Watertown, MA, 1990, pp. 89-110. 5. E.C. Bain and H.W. Paxton: Alloying Elements in Steels, ASM, Cleveland, OH, 1966, pp. 197-222. 6. F.B. Pickering: Physical Metallurgy and the Design of Steels, Applied Science Publishers Ltd., London, 1978, pp. 133-40. METALLURGICAL AND MATERIALS TRANSACTIONS A
Omission of small cycles is a very cost-effective option when testing materials under long-term random loading histories. Researchers[1,2] have proposed several criteria to identify ‘‘damaging’’ and ‘‘nondamaging’’ cycles. However, most proposals have been empirical and have lacked rational analysis based on physical mechanisms. In this article, crack tip stress-strain behavior and the effect of small loads superposed upon the major cycle DP on the crack growth rate da/dN were studied for A537 steel in the fatigue process. The chemical composition of A537 steel in weight percent is as follows: C0.13, Mn1.48, P0.012, S0.005, Si0.46,
XUEJUN WEI and JINGWEI CHEN, Assistant Professors, and JIN LI and WEI KE, Professors, are with the Institute of Corrosion and Protection of Metals, The Chinese Academy of Sciences, Shenyang 110015, China. Manuscript submitted January 3, 1996. VOLUME 29A, JANUARY 1998—401
Fig. 1—Schematic of complex loading waveforms: (a) constant amplitude load, (b) small loads superposed on the bottom of the major load, and (c) small loads superposed on the top of the major load.
Fig. 2—Crack growth rates under two groups of complex cycles in which subcycles are superposed on the top and the bottom of the major cycle, respectively, in air: (a) with amplitude of 30 pct DP and (b) with amplitude of 70 pct DP.
Fig. 4—Crack tip strain distributions under various loads in one fatigue cycle: (a) P 5 0.5 Pmax, loading process; (b) P 5 0.75 Pmax, loading process; (c) P 5 Pmax, (d ) P 5 0.75 Pmax, unloading process; and (e) P 5 0.5 Pmax, unloading process.
Fig. 3—Crack opening displacements in various loads in one fatigue cycle.
Mo0.016, Cr0.004, Ni0.18, Cu0.17, and V0.05. It has a yield strength of 380 MPa, tensile strength of 555 MPa, and elongation of 32 pct. The single-edge notched plate specimens (length 5 260 mm, width 5 36 mm, and thickness 5 5 mm) were used for fatigue tests. At first, da/dN was measured at a frequency of 20 Hz under constant triangular loading waveforms (Figure 1(a)), w
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