ISSN:
1460-2695
Source:
Blackwell Publishing Journal Backfiles 1879-2005
Topics:
Mechanical Engineering, Materials Science, Production Engineering, Mining and Metallurgy, Traffic Engineering, Precision Mechanics
Notes:
Manufacturing defects in the near-surface region of 2¼% Cr 1% Mo castings were investigated in a joint research programme. After ultrasonic testing and X-ray inspection, large push-pull specimens (cross section 1000 mm2) were taken from castings in regions with indications of defects and tested under fully reversed loading in the elastic and elastic plastic region up to predetermined levels of defect growth. The defects are micropores, pin holes, slag and oxide layers or inclusions, hot tears and small micro cracks in welds.The initiation of crack growth was analysed by two methods, namely (a) the local strain concept with idealization of defects as three-dimensional elliptical notches and (b) by the fracture mechanics concept with idealization of defects as two-dimensional elliptical cracks. The main results can be summarized as follows:1. The local strain concept describes the crack initiation potential of the defects more accurately than the fracture mechanics concept.2. Interpretation of casting defects as cracks produces very conservative estimates in many cases.3. Analytical evaluation of crack growth behaviour using the fracture mechanics approach for defects experiencing crack growth of at least 1 mm is much more accurate than when defects having a smaller extent of crack growth are included in the analysis.Additional evaluations of crack growth behaviour of hot tears by fracture mechanics show that crack growth starting from open and partially closed hot tears must be subjected to a larger number of cycles than normal fatigue cracks of sound material. Partially closed hot tears in the vicinity of the crack front additionally delay crack propagation.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1111/j.1460-2695.1993.tb00074.x
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