20. The bending stiffness coefficients for T300/5208 unidirectional laminate of 5.0 mil ply thickness (0.125 mm) are given below [33]. Other relevant data for this laminate are given in Problem 19. (a) Using this date, calculate the critical feed force at the onset of delamination using (5.35)-(5.37). (b) Calculate the critical force at the onset of delamination using (5.28) assum- ing isotropic laminate and circular crack. Compare the results for the two approaches. Ply no. from bottom D11 D22 D12 D66 D 1 1.00 x 10-1 5.67 x 10 1.59 x 10 3.95 10-3 0.390 2 8.00 x 10-1 4.56 x 10-2 1.27 x 10-2 3.15 x 10-2 3.316 3 2.70 1.54 10-1 4.29 x 10- 1.06 x 10-1 10.584 4 6.38 3.65 10-1 1.02 x 10-1 2.52 x 10-1 25.088