Publications Details
Using work and energy to characterize mechanical shock
By far the most widely used tool in shock data analysis is the shock response spectrum (SRS). The SRS has gained popularity because of several primary considerations. It has physical significance, it is simple to understand and it is believed to indicate shock severity. Despite its popularity, the SRS has limitations. Foremost among them is the underlying assumption that shock severity is proportional to a time derivative of position, which does not agree with accepted material failure models. Also, the SRS cannot distinguish between naturally occurring, complex shocks and the chirps sometimes used to achieve a desired SRS using electrodynamic shakers with inadequate force capabilities. Thirdly, SODF models used in the computation of the SRS do not accurately predict accelerations in MDOF structures. A relatively new concept has been introduced whereby an analysis is made on the work done on structures by the excitation force. Since work is equal to the change in the energy of a system, this quantity is closely related to failure models based on strain energy such as the Von Mesis criterion. This paper is the first in a series exploring the use of energy-based description of shock motion and structural response. The input energy spectrum has attractive properties which include intuitive physical significance, insensitivity to system parameters such as viscous damping or hysteretic loss, the ability to distinguish between realistic shocks and chirps, and a close relation to accepted material failure models. Input energy spectra can be calculated using SDOF models and, in many cases, accurately predict the energy input to MDOF structures. Finally, this paper gives an introduction to these methods, derives the equations for relevant energy measures and presents relationships to several other shock analysis tools.