A MIXED-MODE ANALYSIS OF TWO PARALLEL NON-ALIGNED CRACKS IN A LARGE FLAT PLATE SUBJECTED TO REMOTE TENSION

The interaction of multiple cracks plays an important role in cracking behavior resulting from plant degradation, especially in the case of stress corrosion cracking (SCC) and fatigue. The Fitness-for-Service (FFS) standards require the characterization of multiple cracks to determine the structural integrity of cracked components using fracture mechanics concepts. Multiple cracks must first be classified as to whether they are located on the same cross-section plane for alignment purposes. Various codes and standards have been found to have differing crack alignment rules. Using these rules and standards, two parallel, non-aligned cracks have been previously simulated by various investigators in Fitness-for-Service evaluations based on Linear Elastic Fracture Mechanics (LEFM). However, all these studies focused on mode I fracture of cracks. The present study focuses on mixed-mode interaction between two parallel, non-aligned cracks subject to remote uniform tension. A parametric study of the dependence of the mixed-mode Stress Intensity Factors (SIFs), and the energy release rates (ERRs) of two parallel cracks on the intra-horizontal and vertical separation distances is conducted. The evaluation of the SIFs and ERRs was accomplished for a wide range of the normalized intra-vertical separation distances of H/2a1 = 0.4~2, and normalized intra-horizontal separation distances of S/2a₁ = - 0.4~2. It is found that for certain crack configurations mixed-mode analysis might be significant and should be carefully considered in the application of Fitness-for-Service rules.