Dynamic Analysis of Substructures with Account of Altered Restraint When Tested in Isolation

Abstract

The objective of this research is to simulate the response of an isolated substructure such that the response of the substructure in isolation would be the same as the substructure within the structure. Generally, the behaviour of an isolated subsystem (substructure) subjected to dynamic loading is different than the behaviour of the same substructure within a system (structure). This is primarily caused by the boundary conditions that are imposed on the substructure from the surrounding subsystem in the entire structure. A new systematic approach (methodology) is developed for performing impact analysis on the isolated substructure. The developed technique is fundamentally based on enforcing the mode shapes around the boundary of the substructure in the full structure to be similar to the mode shapes of the isolated substructure. This is achieved by providing a consistent adjustment to the loading conditions (impact velocity and mass) to account for the loss of restraint at the interface with the full structure. Another important aspect of this research is experimental validation of proposed method. This method allows the experimental testing of an isolated substructure since the testing is performed by impacting the isolated substructure with an appropriate mass and velocity. In the finite element analysis, the structure is analyzed, and then the isolated substructure simulation is performed using the developed technique. The results obtained from the numerical simulations, for both the substructure in situ and the substructure in isolation, are compared and found to be in good agreement. For instance, the effective plastic strains, kinetic and internal energies for the substructure within the structure and the substructure in isolation range from 7% to 12% discrepancies between two analyses. The numerical simulations of a full structure are verified by performing a series of experimental impact tests on the full structure. Finally, the experimental applicability of the technique is studied and its results are validated with FE simulation of substructure in isolation. This problem of experimentally testing an isolated substructure had previously not been addressed. The comparisons of FE simulation and experimental testing are made based on the deformed geometries, out-of-plane deflections and accelerometer readings. For example, the out-of-plane deformations from the FE analysis and the experimental test were determined to be within 7% to 9%. The experimental validation and numerical simulations indicates the technique is reliable, repeatable and can predict dynamic response of the substructures when tested in isolation.