A converged solution is obtained with the help of the nonlinear stabilization technique.

The energy dissipation ratio is carefully chosen to avoid excessive artificial stabilization energy. As shown in Figure 5.8: Time History Plot of Strain and Stabilization Energies, the level of stabilization energy (STEN) is low compared to the total strain energy (SENE) throughout the simulation; therefore, the validity of the simulation results can be guaranteed. The figure also shows that the solution becomes increasingly unstable toward the end of simulation. If you encounter a convergence difficulty, you can increase the energy dissipation ratio to an adequate level; however, validation of the new energy dissipation ratio is required.

Figure 5.8: Time History Plot of Strain and Stabilization Energies

The buckling of the stiffener and the separation of the skin-flange connection are clearly indicated by the final deformed shape, shown below.

Figure 5.9: Global Deformed Shape (Last Substep)

This highly nonlinear deformation leads to complex overall stress distributions and a number of significant stress concentrations, as shown below.

Figure 5.10: Equivalent Stress (Last Substep)

The following two figures show the final contact status on the skin and the flange. As expected, debonding of the skin-flange interface starts at the edges of the imperfection and propagates further into the bonded areas as the load increases.

Figure 5.11: Contact Status at Final Substep

Figure 5.12: Contact Status for the Initial Bonded Contact Region

The figure above shows that the initial sticking status of the large skin-flange interface areas has changed to open or near-contact status at the final converged stage. The structure may undergo catastrophic failure and fail to withstand any further load as debonding progresses. In this case, a transient simulation would be more suitable.