The Interaction between an Edge and an Embedded Parallel Crack in a Structural Component

Parallel cracks are often detected in various structural components using non-destructive methods. In the case of non-aligned parallel cracks, on-site service needs to decide whether they should be treated as coalesced or separate multiple cracks for Fitness-for-Service. Criteria and standards for the adjustment of multiple nonaligned cracks are very different from one another in existing resources. Furthermore, those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, the interaction between an edge and an embedded parallel crack is investigated to correlate criteria and standards from various resources in order to recommend the usage of those standards for the purpose of Fitness-for-Service. In this study, depending on the crack ratio a1/a2, what may be deemed conservative by one standard, leading to aligned cracks for a given separation distance, H/a2 and S/a2, may be deemed non-conservative, or non-aligned, by another standard. Examples are given to show this phenomenon.

Stress Intensity Factors for an Edge Crack Interacting With an Embedded Parallel Crack for a Finite Plate Under Pure Bending

Parallel cracks are often detected in components under various pressurized applications using non-destructive methods. For non-aligned parallel cracks, on-site service needs to decide whether they should be treated as coalesced cracks or separate multiple cracks for Fitness-for-Service Criteria. Such standards are very different from one another for the adjustment of multiple nonaligned cracks in existing sources. Furthermore, those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, in this study, we investigate stress intensity factors of an edge crack in a finite plate under pure bending when interacted by an imbedded parallel crack. Different criteria and standards are then used to correlate the present results in order to recommend the usage of those standards for the purpose of Fitness-for-Service and to classify the standards as either conservative or non-conservative. If H and S represent the vertical gap and horizontal separation distance between the cracks, respectively, and a2 is the length of the crack, a parametric study of parallel crack separation distance and gap on the crack stress intensity factor has been undertaken. The parallel cracks are practically located within the tensile bending stress regime only. Stress intensity factors (SIFs) have been acquired for a wide range of the normalized horizontal gap of S/a2 = 0.4∼2.0 and the normalized separation distance of H/a2 = −0.5∼2.0 between the two parallel cracks based on the principle of linear elastic fracture mechanics (LEFM). Our study indicates that certain existing standards/criteria provide results that are much more conservative than others while certain ones do not provide adequate information for application.

A LEFM Based Study on the Interaction Between an Edge and an Embedded Parallel Crack

Parallel cracks are often detected in components of various pressurized applications using non-destructive methods. For non-aligned parallel cracks, on-site service needs to decide whether they should be treated as coalesced or separate multiple cracks for Fitness-for-Service. Criteria and standards for the adjustment of multiple nonaligned cracks are very different from one another in existing resources. And those criteria and standards are often derived from on-site service experience without rigorous and systematic verification. Based on this observation, in this study the interaction between an edge and an embedded parallel crack is investigated to correlate criteria and standards from various resources in order to recommend the usage of those standards for the purpose of Fitness-for-service and to classify them as either conservative or non-conservative. If H and S represent the horizontal gap and vertical separation distance, respectively, between the cracks, and a2 is the length of the dominant crack, a parametric study of parallel crack separation distance and gap on the crack stress intensity factor has been undertaken. Stress intensity factors (SIFs) have been acquired for a wide range of the normalized gap of H/a2 = 0.4∼2 and the normalized separation distance of S/a2 = −0.5∼2 between the two parallel cracks based on the principle of linear elastic fracture mechanics (LEFM). This study indicates that certain existing standards/criteria provide results that are much more conservative than others while certain ones do not provide adequate information for application.