Date of Award
Doctor of Philosophy (PhD)
Professor J. Tlusty
One important field of "Structural Dynamics" is "Modal Analysis Testing". This field, concerns the modes of vibration which constitute the link between experimental and analytical methods, like Finite Elements.
The present work deals with the use of the experimental data obtained from Modal Analysis Testing in building a mathematical model of the structure, identifying its parameters and predicting the effects of possible design changes on its dynamics. It also deals with the use of these experimental data in predicting the behaviour of the structure according to a certain criterion. In this work, in particular, machine tool structures are considered.
A systematic formulation of identifying the structural parameters from the Modal Analysis Testing is presented. It depends basically on the accessibility of the relevant coordinates for measurement. If all these coordinates are accessible then the formulation based on the equation of motion of the system and on the orthogonality relationships leads to linear equations. On the other hand if some of the relevant coordinates are missing, like coordinates on the bearings inside a headstock, then nonlinear optimization is used to minimize the errors between experimental and estimated modal parameters. These identification formulations are applied here to theoretical structures as well as actual machine tools.
As a special exercise a procedure is suggested to be used in predicting the dynamics of a lathe with different workpieces using the modal data measured on a single workpiece. Such a procedure can help estimate the limit of stability against machining chatter beforehand and consequently could be implemented in the postprocessors of Numerically Controlled Turning Centers.
The thesis deals also with further development of the theory of machining chatter. For the first time digital simulation in the time domain of the cutting process including chatter is carried out using mathematical models of machine tools established through Modal Analysis Testing. Cutting tests carried out in this work have shown that the digital simulation approach to machining chatter represents the reality very closely. Thus it could be used in formulating acceptance test procedures of machine tools as well as in designing the cutters to achieve higher metal removal rates.
Ismail, Fathy Mohamed M., "Identification, Modelling and Modification of Mechanical Structures from Modal Analysis Testing" (1982). Open Access Dissertations and Theses. Paper 1511.