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Abstract:
electrical potential techniques are uniquely suited for quantitative monitoring of the initiation and growth of small (0.1 to 3 mm) cracks emanating from surface defects, as reviewed in this chapter. the results of over two hundred experiments, including small surface and through-thickness edge cracks in seven alloys, confirm the accuracy of an analysis developed to transform measured potentials into crack sizes. the complicating influences of crack tunnelling and surface electrical contact are discussed. applications of potential monitoring are examined for small fatigue cracks in nickel-based superalloys at elevated temperatures, and high strength steel in hydrogen producing environments. data indicate that crack initiation is resolvable experimentally, and correlated with a fracture mechanics estimate of defect root strain. crack propagation kinetics are determinable from electrical potential monitoring, and for high strength alloys, are equivalent to the results of conventional, long crack experiments. techniques described herein are applicable to studies of 'mechanical' short crack effects prevalent in low strength alloys. furthermore, the monitoring of small cracks provides growth rate data in significantly reduced test times, and facilitates evaluations of metallurgical and environmental effects on fatigue. specific data are presented to illustrate each consideration. electrical potential monitoring is well suited for studies of novel small crack-environment interactions. data for 4130 steel in 3% nacl solution demonstrate that small cracks grow up to two orders of magnitude faster than predicted for constant stress intensity. it is suggested that electrical potential techniques will play an important role in future studies of the small crack problem. (author)
| Pages: |
55 |
| Report Date: |
SEP 82 |
| Report Number: |
D376613 |
Report Unavailable |
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