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

panels were determined for different debond diameters for the maximum applied fatigue load. It
was shown that the mode-mixity phase angle is not sensitive to the debond diameter and is
around -5. Since no strong dependency between the mode-mixity and crack growth rate is
expected at low manitudes of mode-mixity phase angles and the loading is predominantly mode
I, the crack growth rate relations for the mode-mixity phase angle -20, measured using the
MMB specimen, were used for the simulation of the debonded panels. To accelerate the
simulation the cycle jump method outlined in Chapter 4 was exploited. A convergence analysis
was carried out for different control parameter values to choose appropriate control parameters.
Simulations of the debonded sandwich panels showed fair accuracy compared to the fatigue
experiments with a maximum deviation of 7 mm in debond diameter estimations. The observed
deviation can be attributed to the crude crack length measurement technique using the DIC
technique, which was based on out-of-plane deflections of the debond and scatter of the input
crack growth rate data.
The presented 2D and 3D fatigue crack growth schemes and the cycle jump method proved to be
reliable tools for simulation of stable fatigue crack growth, but in highly non-linear cases the
presented method should be used carefully. To mitigate inaccuracies and uncertainties
concerning simulation of highly non-linear problems, a convergence sensitivity analysis must be
carried out due to strong dependency of the accuracy of the cycle jump method on the control
parameters. However, for complete validation of the developed numerical scheme, simulations
should be compared with fatigue tests on more complicated loading scenarios and debond
geometries.
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