Modal Test

In real life applications, machine parts and mechanical systems are rarely under static loading. Most of the time they are excited by dynamic loads. The structure responds to these dynamic loads according to its dynamic parameters such as natural frequencies and mode shapes. Therefore, an engineer has to have a solid insight about the dynamic behavior of the structure which has been designed. The process of finding the dynamic behavior of a structure is called structural system identification.


Structural system identification consists of finding transfer function of the system which is established by finding the modal parameters of the structure such as, natural frequencies, damping, modal vectors and residues.


The transfer functions of a structure can be obtained by mathematical modeling or by experimental methods. The experimental way to obtain the transfer function of a structure is achieved by measuring the response of the structure to a measured input. The responses are generally acceleration and the inputs or excitations are generally impulse or random/sine signals.


The impulse signal is easily generated by a modal hammer with a force transducer attached at its tip. The random or sine signal excitation requires modal shakers. Moreover, if high frequency excitation content or signal controlled testing is desired, then modal shakers are the only excitation solution. Dynalabs modal shakers are lightweight and powerful modal shakers which can go up to 15,000 Hz and provide force levels up to 440N with a maximum 25mm stroke.


The modal shaker is attached to the structure and the desired excitation signal is applied to the structure via a signal generator. In the meantime, the responses of the structure are measured and Frequency Response Functions are calculated which are used in the Modal Analysis calculations.