Non-destructive tests have found, in many cases, non-aligned parallel cracks in various inservice mechanical components. In such situations, any on-site evaluation requires an assessment of whether
the cracks can be assumed coalesced or separate multiple cracks, for the application of Fitness-for-Service
criteria. How to apply the criteria to non-aligned cracks is different depending on the source used. These
standards are normally not determined in a rigorous and systematic way, and so can result in different
outcomes. This observation is the reason for this study, namely, to investigate the stress intensity factor (SIF) of
an edge crack in a 2-D finite sheet under pure bending, in the presence of a nearby parallel crack. The various
crack alignment criteria found in the literature will be used to compare the results of the multiple aligned crack
simulation for the purpose of recommending the conservativeness or non-conservativeness of the criteria as
applied to the Fitness-for-Service situation. A 2-D linear elastic fracture mechanics (LEFM) analysis is
undertaken of to characterize the interplay characteristic of the internal crack on the SIFs of the edge crack.
The SIFs are evaluated as a function of the vertical and horizontal separation distances between the cracks, S
and H, respectively; and as a function of the crack lengths of the edge crack and the internal crack given by a2
and a1, as well. The parallel cracks are assumed to be located in the region where the bending stresses are
positive only. The SIFs have been obtained for dimensionless horizontal distances of S/a2 =0.4 to 2.0, and
dimensionless vertical distances of H/a2 = -0.5 to 2.0. The investigation shows that certain crack alignment
criteria are conservative compared to others, while certain crack alignment criteria provide inadequate
information to be useful.
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