Implementation of a modified residual flexibility modal testing methodology to a constrained structure

This dissertation presents the development of a modified residual flexibility modal testing methodology. Until now, a structure with different sets of interfaces that are exercised independently during its life cycles have been verified (tested) independently in a constrained environment. The construction of test stands to test the different sets of interfaces is costly and time consuming. The goal of this research is to develop a testing methodology to indirectly reduce the number of required test stands for interface verification.; The residual flexibility modal test method, from which a residual function is generated, is a procedure for modal testing large structures in an unconstrained (free-free) environment to predict constrained modes. The residual function quantifies the effects that the unmeasured higher order natural frequencies and mode shapes have on the lower frequency measurements. The residual function, from which the residual terms (flexibility, mass and damping) can be extracted, aids in the prediction of constrained natural frequencies and mode shapes. The proposed modifications of the residual flexibility modal testing methodology allow for the methodology to be implemented in a free-fixed (one set of interfaces constrained) environment, saving cost and development schedule.; In the situation where a structure is not in a free-free environment during a residual flexibility modal test, the effects of these constraints on the residual measurements of a different set of interfaces need to be evaluated. A simple uniform rectangular cross-section beam with trunnion type appendages at each end to simulate distinct interfaces with different stiffness characteristics is used to examine the effects that different constrained interfaces have on the residual measurements. A finite element model was constructed and correlated to the theoretical solution, producing a mathematical model bases for the modified residual flexibility modal testing methodology evaluation. The combination of modal testing and finite element analysis show excellent correlation of free-fixed vs free-free residual measurement.