Fitness-for-Service codes require the evaluation of non-aligned multiple cracks in various practical applications. For on-site inspection, decision needs to be made on whether the cracks should be treated as coalesced or separate multiple cracks in case of non-aligned parallel cracks. In the existing literature, criteria and standards for the adjustment of multiple nonaligned cracks are very source dependent, and those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the authors previously reported on the effect between an edge and an embedded parallel crack in 2-D scenarios as well as in 3-D scenarios subject to tensile loading. Since realistic crack configurations detected using non-destructive methods are generally 3-D in nature, the study of 3-D effect of non-aligned cracks with different shapes and under different loading types is deemed necessary in order to obtain more practical guidance in the usage of rules speculated in Fitness-for-Service codes. In this study, we investigate stress intensity factors (SIFs) along the crack front of a quarter-circle corner crack when interacted by a semi-elliptic surface crack in an infinitely large plate under pure bending. Different criteria and standards found in the literature are then used to correlate the present results in order to recommend their usage in Fitness-for-Service calculations and to classify the standards as either conservative or non-conservative.  If H and S, a~2~, and b~1~/a~1~ represent the vertical gap and horizontal separation distance between the cracks, the radius of the corner circular crack, and the embedded semi-elliptic surface crack ellipticity, respectively, a parametric study of parallel crack separation distance and gap as well as the embedded surface crack ellipticity on the quarter-circle corner crack stress intensity factor has been undertaken.  The SIFs along the crack front of the quarter-circle corner crack are studied for a wide range of geometrical configurations of the semi-elliptical surface crack by varying the crack ellipticity b~1~/a~1~=0.1\~1; the relative crack size of the two parallel cracks a~1~/a~2~=1/3\~2; the normalized gap, H/a~2~ = 0.4\~2; and the normalized separation distance, S/a~2~ = -0.5\~2 between cracks on parallel planes, based on linear elastic fracture mechanics (LEFM). Our investigation indicates that both Mode I and Mode II effects exist in many of the cases studied.  Also, certain existing standards/criteria provide results that are much more conservative than others while certain ones do not provide adequate information for application irrespective of the mode type SIF configurations that are encountered. The results from this study are collectively significant to the understanding of the correlation between the criteria and standards in Fitness-for-Service community and the consequence of their usage in engineering practice. 


The Influence of a Non-Aligned Semi-Elliptical Embedded Crack on the Stress Intensity Factor Distribution Along the Front of a Quarter-Circle Corner Crack in a Semi-Infinite Plate Under Pure Bending

Division / Sponsors: 
Aerospace, Bioengineering, Applied Mechanics, Design Engineering Division, Advanced Energy Systems, Manufacturing Engineering Division, Noise Control and Acoustics, Nondestructive Evaluation, Diagnosis, and Prognosis (NDPD), Nuclear Engineering Division, Process Industries Division, Fluids Engineering, Heat Transfer, Materials, Microelectromechanical Systems, Safety Engineering and Risk Analysis, Computers & Information in Engineering


Paper Proceedings: https://asmedigitalcollection.asme.org/IMECE/IMECE2020/volume/84478

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