Residual Strength and Fatigue Lifetime of ... - Solid Mechanics

insensitivity of the mode-mixity to the debond diameter. The low mode-mixity phase angle
illustrates the mode I dominant loading at the crack tip.
The fatigue crack propagation simulation was carried out on the sandwich panels for 100000
cycles. Because of similar material and interface properties the crack growth rates vs. the energy
release rate relations determined in the previous section were used for the simulations. To choose
the appropriate and most effective control parameter values in the cycle jump routine,
simulations with different control parameters were carried out. Figure 5.47 shows the debond
diameter vs. cycles for five different control parameters qG=q=0.4, 0.45, 0.5, 0.75 and 1. It is
seen that the results of the simulations with the control parameters qG=q= 1 and 0.75 are very
different due to large and inaccurate jumps, but decreasing the control parameter to 0.5 and 0.4
leads to converging results and the deviation becomes smaller. Based on the results presented in
Figure 5.47 the control parameter qG=q=0.4 was chosen for the simulation of debond growth in
the tested sandwich panels.
Diameter (mm)
150
140
130
120
110
q=qG=0.75 q=qG=1
100
q=qG=0.5
q=qG=0.4
q=qG=0.45
0 20000 40000 60000 80000 100000
Cycle
Figure 5.47: The effect of the control parameter on the simulation of the debonded panels.
Simulation results for the debond diameter vs. cycles using the control parameters qG=q=0.4 are
shown together with the experimental results in Figure 5.48. The accuracy of the simulation is
less compared to that of the STT specimen simulations presented in the previous sections in this
chapter. Nevertheless, the deviation in the final debond diameter after 100000 cycles between the
simulation and the experiments is less than 5 mm. The maximum deviation of approximately 7
mm occurs around 70000 cycles. This inaccuracy can be attributed to the uncertainties in the
debond diameter measurement using the DIC system during the experiments, as well as the
observed scatter in the input crack growth rates data.
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