An Introduction of a Modal Scaling Technique: An Alternative and Supplement to Quasi-Static G Loading Technique with Application in Structural Analysis

The modal-scaling technique is just a treatment of normal mode results to find stresses in an object responding in its global modes under given boundary and input environment. It takes the stresses from a normal mode run and scales them according to reaction forces either measured in testing or obtained otherwise at the boundaries. This technique is a better alternative and supplement to the traditional quasi-static g loading technique in two aspects. It finds stresses in actual global response modes, while the quasi-static g loading technique finds stresses in approximated global response modes simulated by applying a uniform g loading throughout the object. Additionally, it can find stresses beyond the three principal global response modes (roll, pitch, and bounce) that the quasi-static g loading technique is typically not capable of. The application of this technique has yielded better correlation with tests in terms of location and magnitude of stresses in our experience on both present and future products, and is routinely used. The successful application of the technique requires knowledge and test data of the modal response characteristics and boundary reaction forces of the subject. In absence of measured reaction data, it can still be used by cross-referencing reaction forces from quasi-static g loading runs. The simplicity of its use and application makes it a viable tool for quick and first-pass structural evaluation and analysis.