Estimation of operational strains from vibration measurements: An application to lead wires of chips on printed circuit board

Abstract

Dynamic strain in structures is normally measured using strain gauges. When direct strain measurement is not possible, vibration measurement can be an indirect practical alternative. That is, vibrations are measured, typically using acceleration pick-ups, on the underlying system under operational conditions and a certain relationship between strains and accelerations is imposed on the measured accelerations to estimate the strains. Therefore, this relationship or transformation matrix between the strain and vibration is very critical for the indirect estimation to be successful. The transformation matrix is often inevitably derived not under the real operational conditions, but under the idealized laboratory conditions or using computer simulations. This means that boundary conditions under which this transformation matrix is obtained are extremely important. In this study, this problem is discussed in detail and an application to the estimation of strains in lead wires connecting chips to a printed circuit board subject to loading by a cooling fan is illustrated. (C) 1998 Academic Press Limited.