On the comparison between displacement modal testing and strain modal testing

The conventional modal testing (referred to as displacement modal testing (DMT)) is based on measurement of displacement, velocity or acceleration as well as excitation force. Though there exits an enormous literature with regard to DMT, on the contrary, a few papers address modal testing based on strain gauges or strain sensor (referred to as strain modal testing (SMT)). The main reason for this scenario is due to practical problems in the use of strain gauges as calibration procedure, ground loop sensitivity are not adequate at high frequency, bonding quality. In this work, a novel piezoelectric strain sensor is used for SMT. In this study it is demonstrated that this sensor overcomes the practical drawbacks related to the use of strain gauges. Thus, SMT based on piezoelectric strain sensors can be a valid alternative to DMT which is usually based on accelerometers. Comparisons between the modal testing results concerning brackets with different constraint conditions using both accelerometers and strain sensors are given in terms of modal parameters, highlighting their pros and cons.