The stress-level effect on fatigue-crack growth under constant-amplitude loading |
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| Affiliation: | 1. Department of Aerospace Engineering, Mississippi State University, Mississippi State, MS 39762, USA;2. Materials Engineering Department, University of Dayton Research Institute, Dayton, OH 45469, USA;1. US Naval Research Laboratory, Materials Science and Technology Division, Washington, DC, USA;2. Air Force Institute of Technology, Wright-Patterson AFB, OH, USA;3. Materials Research Centre, University of Wales Swansea, UK;1. Wuhan National Laboratory for Optoelectronics (WNLO), Huazhong University of Science and Technology, Wuhan 430074, PR China;2. Joining and Welding Research Institute (JWRI), Osaka University, Osaka 5600043, Japan;1. DSTO Centre of Expertise for Structural Mechanics, Department of Mechanical and Aerospace Engineering, Monash University, Victoria 3800, Australia;2. Air Vehicles Division, Defence Science and Technology Organisation, 506 Lorimer Street, Fishermans Bend, Victoria 3207, Australia;1. Department of Engineering Science, University of Oxford, Parks Road, Oxford, OX13PJ, United Kingdom;2. SIMTech - Singapore Institute of Manufacturing Technology, 71 Nanyang Dr, Singapore 638075, Singapore |
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| Abstract: | The fatigue-crack-closure concept has been successfully used with stress-intensity factors to predict the growth of cracks under a wide variety of load histories and in complex crack configurations. Both test and crack-closure analyses have shown that the stress-intensity-factor-range-against-rate curves are affected by the stress ratio (R), the applied stress or load level (Smax or Pmax), and the crack-front constraint (plane-stress or plane-strain behavior). However, most life-prediction codes use only linear-elastic fracture mechanics (LEFM) concepts, which neglect stress-level effects, to make life predictions. Thus, under some loading conditions, such as negative R ratios or high-applied stress levels, non-conservative life predictions are made using only LEFM procedures.Fatigue-crack-growth tests have been conducted on middle-crack tension M(T) specimens made of 2024-T3 thin-sheet (B = 2.3 mm) aluminum alloy over a wide range in applied stress levels (0.1–0.5 times the flow stress of the material) and for two stress ratios (R = 0.05 and ?1). The FASTRAN life-prediction code, using either the crack-closure model or LEFM procedures, and the AFGROW code, which uses only LEFM procedures, were used to make crack-growth predictions from an initial crack size to failure in the M(T) specimens. The results from AFGROW and FASTRAN, using LEFM procedures, agreed very well with each other. The crack-closure model predicted all results with ±20%, whereas, the codes using LEFM procedures (neglecting stress-level effects) resulted in non-conservative life predictions as large as a factor-of-3 from the test results. |
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