Session: DA-12-02 Fracture 2-Fracture Prediction and Evaluation

Paper Number: 122218

122218 - Mode I and Mode Ii Stress Intensity Factors for a Slanted-Edge-Crack Affected by an Adjacent Horizontal Crack Under Remote Tension 

Fracture mechanics-based failure theory has been used for analyzing structural integrity in Fitness-for-Service assessments of structures containing cracks. The stress intensity factors (SIFs) along the crack front are the key information in order to assess the remaining service life of a cracked component.  In the case of a multiply cracked component, according to Fitness-for-Service (FFS) standards, these cracks must be first identified as to whether they are on the same cross-sectional plane, to be considered aligned cracks, or whether they are on parallel planes and thus be considered non-aligned parallel cracks. Extensive studies have been carried out on the mutual influence of adjacent parallel cracks. However, to date no solutions are available for non-parallel cracks. The present analysis addresses this problem by evaluating the mode I SIFs of a slanted-edge-crack of length a2 affected by an adjacent nonaligned horizontal surface crack of length 2a1. A comprehensive parametric study of the effect on the SIF of the slanted-edge-crack as a function of its slant angle (b), the horizontal separation (S) and vertical gap (H) distances between the two cracks and the crack ratio a₂/a₁ is conducted. Mode I SIFs are evaluated for a wide range of the slanted angles b=0°~75°of the edge crack, the normalized crack gaps of H/a₂ = 0.4~2, and normalized crack separation distances S/a₂ = -0.5~2.

The cracks are modelled numerically using ANSYS MECHANICAL APDL finite element program.  Mode I and Mode II SIFs for the slanted-edge-crack tip are calculated using the KCALC command under plane strain conditions. The FE model is validated against existing solutions in the literature for a solitary slanted-edge-crack. It is found that the present model results agree well with the existing models for a single slanted-edge-crack. Both Mode I and Mode II SIFs are evaluated in analysis, and their role is discussed.  As expected, mode I SIFs decrease gradually with an increase in the slanted angle, while keeping all the other parameters constant, namely, the horizontal separation distance S/a2, the vertical separation distance H/a2 as well as the relative crack size a1/a2. While the role of mode I SIFs still dominates for the purpose of Fitness-for-Service analysis, the role of mode II SIFs becomes significantly important with the increase of the slant-edge-crack angle.

Presenting Author: Qin Ma Walla Walla University

Presenting Author Biography: Dr. Qin Ma is a faculty member at Edward F. Cross School of Engineering, Walla Walla University, WA, USA. He has a sustained record of research and engineering practice. He has used finite element methods extensively for more than twenty years to solve practical engineering problems while pursuing his Masters, Ph.D. as well as his postdoctoral work in the United States. Dr. Ma has been working in the area of fracture mechanics and structural integrity, and has authored and coauthored multiple journal papers and many conference papers and presentations in this area of endeavor.

Authors:

Cesar Levy Florida International University
Mordechai Perl Ben Gurion University of the Negev
Qin Ma Walla Walla University