Issue 43

F.Z. Seriari et alii, Frattura ed Integrità Strutturale, 43 (2018) 43-56; DOI: 10.3221/IGF-ESIS.43.03 50 Figure 5: Overload ratio effect on fatigue life for repaired 2024 T351 Al-alloy plate. Figure 6: Overload ratio effect on crack growth rates for repaired 2024 T351 Al-alloy plate. The relationships between retard ratio “ D CAL N N ” and overload ratio “ORL” for repaired and unrepaired plate are plotted on a log-log graph in Fig. 9. It is seen from the plot that all the points seem to lie on a straight line on the log-log scale for unrepaired plate given by power function [42]. On the others hand, the plot in repaired plate case is given by logarithmic function. The developed equations for the both cases (repaired and unrepaired) are given below:                  3.483 4 16.9 10 3.305 1.31 Re D CAL D CAL N ORL Unrepaired N N Ln ORL paired N (12) Influence of band overloading parameter on patch repair A few investigators have studied the effect of multi overload and band overloading cycles on crack growth retardation. However no attempt has been made to predict fatigue life and fatigue crack growth in multi band overloading case. In the present attempt interaction of multi band overload is investigated. The spectrum of band overloading given by figure 2b is applied and the overload band is characterized by the parameter “q”.