w. Lee et aL. / Composites Science and Technology 66(2006)435-443 0004000 all the rs considered L,,,1,,,1,,,⊥,,,王,,,,,,,A,,,L -0.8-0.6-040. 0.0 04 0.8 Fig. 6. Change in phase angle of the deflected crack, Y, plotted as a function of a for various residual stress magnitude parameter I. imary Crack Penetrating the Compressive Residual Stress (a≤G;r<0 and R/Rm>s) Tensile Residual Stress Layer A(stiff) Layer B (compliant) Primary Crack Deflected at the Compressive Residual Stress (a>0: T>0; and R/Rm< ga/gp) Tensile Residual stress Layer A(stiff) Layer B(compliant) Fig. 7. Conceptual illustration of the laminate design utilising beneficial role of residual stress in achieving crack deflection laminates, then EL s E2(Eq (7)and from Eq( 8), it is Further, from the narrowing gap between Sa/sp ra expected that EIr A Er. In this case, unless Er is lower than tio curves with increasing I in Fig. 5, it is inferred that the failure strain of layer #l, the laminate will fail dur- the Sa/p ratio converges to a certain value with ing the fabrication process increasing T for a given a. To visualise this, Sa/ ratioslaminates, then EL  E2 (Eq. (7)) and from Eq. (8), it is expected that e1r  er. In this case, unless er is lower than the failure strain of layer #1, the laminate will fail dur￾ing the fabrication process. Further, from the narrowing gap between Gd=Gp ra￾tio curves with increasing C in Fig. 5, it is inferred that the Gd=Gp ratio converges to a certain value with increasing C for a given a. To visualise this, Gd=Gp ratios -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 10 20 30 40 50 60 70 80 90 Phase Angle of the Deflected Crack α all the Γs considered Fig. 6. Change in phase angle of the deflected crack, W, plotted as a function of a for various residual stress magnitude parameter C. Layer A (stiff) Compressive Residual Stress Layer B (compliant) Tensile Residual Stress i m d p Layer A (stiff) Compressive Residual Stress Layer B (compliant) Tensile Residual Stress i m d p Fig. 7. Conceptual illustration of the laminate design utilising beneficial role of residual stress in achieving crack deflection. W. Lee et al. / Composites Science and Technology 66 (2006) 435–443 441