Application of a strip-yield model to predict crack growth under variable-amplitude and spectrum loading - Part 2: Middle-crack-tension specimens

作者：Ziegler B; Yamada Y; Newman J C Jr^*

来源：Engineering Fracture Mechanics, 2011, 78(14): 2609-2619.

DOI：10.1016/j.engfracmech.2011.06.018

• Cracks
• Fatigue-crack growth
• Aluminum alloy
• Crack closure
• Stress-intensity factor
• Plasticity

In previous work, fatigue-crack-growth tests were conducted on middle-crack tension. M(T), and compact, C(T), specimens made from the same D16Cz (clad) aluminum alloy sheet. These tests were conducted over a wide range of stress ratios (R = P(min)/P(max) = -0.5 to 0.75) to generate crack-growth-rate data from threshold to near fracture. These tests were used to generate the effective stress-intensity factor range (Delta K(eff)) against rate curve using a crack-closure model. The analyses collapsed the rate data from both specimen types into a fairly narrow band over many orders of magnitude in rates using proper constraint factors. Constraint factors were established from single-spike overload and the constant-amplitude tests. Herein, the life-prediction code. FASTRAN, which is based on the strip-yield model concept, was used to calculate the crack-length-against-cycles under constant-amplitude (CA) loading and the single-spike overload (OL) tests; and to predict crack growth under variable-amplitude (VA) loading and simulated aircraft loading spectrum tests on the M(T) specimens. The calculated crack-growth lives under CA and an OL tests were generally within +/- 20% of the test results, but slower crack growth under the double-shear fatigue mode, rather than single shear, may be the reason for some of the larger differences. The predicted crack-growth lives for the VA and Mini-Falstaff spectrum tests were also short by 25-45%. A modified model with some assumed notch constraint effects matched the spectrum tests quite well. Issues on the crack-starter-notch effects under spectrum loading are discussed, and recommendations are suggested on avoiding these notch effects.

• 出版日期2011-9