Issue 36

L. C. H. Ricardo et alii, Frattura ed Integrità Strutturale, 36 (2016) 201-215; DOI: 10.3221/IGF-ESIS.36.20 211 Figure 11 : Crack Opening Stress (σ yy+ ) model SAE0.50 [57]. Figure 12 : Crack Closing Stress (σ yy- ) model SAE0.50 [57]. D ISCUSSION OF RESULTS n the present work was identified how difficult is to determine with proper precision the crack opening or closure. It was necessary to use the iterative process in the crack surface step by step during loading and unloading to find the crack opening or closing as shown in details in Ricardo [65]. The retard effect is present in some cycles in special cases where there are overloads. In constant amplitude loading, the effective plastic zone increases with the extension of the crack length; the crack propagation rate has no influence in the quality of results, assuming that it is in respect to the Newman [23] recommendation with four elements yielded in the reverse plastic zone. In variable amplitude loading the crack length cannot progress until a new overload occurs or the energy spent during cyclic process creates a new plastic I Crack Tip  y= - 85 MPa Surface Crack Surface Crack Crack Tip  y= 103 MPa