ESTIMATION OF OPERATIONAL STRAINS FROM VIBRATION MEASUREMENTS - AN APPLICATION TO LEAD WIRES OF CHIPS ON PRINTED-CIRCUIT BOARD

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 mea sured, typically using acceleration pick-ups, on the underlying system under operational conditions and a certain relationship between strai ns and accelerations is imposed on the measured accelerations to estim ate the strains. Therefore, this relationship or transformation matrix between the strain and vibration is very critical for the indirect es timation to be successful. The transformation matrix is often inevitab ly derived not under the real operational conditions, but under the id ealized laboratory conditions or using computer simulations. This mean s that boundary conditions under which this transformation matrix is o btained are extremely important. In this study, this problem is discus sed in detail and an application to the estimation of strains in lead wires connecting chips to a printed circuit board subject to loading b y a cooling fan is illustrated. (C) 1998 Academic Press Limited.