A spectral finite element model (SFEM) for a laminated composite beam with a transverse crack is developed and employed in wave-based diagnostic simulations. Although many simplified models of damage in beams for dynamic analysis have been reported in the literature, their utility in the context of damage severity estimation and related structural health monitoring (SHM) applications is not well addressed. The performance of the present simplified model is compared with detailed 2D finite element model (FEM). To estimate the damage severity, two quantities, namely the strain energy release rate (SERR) and a damage force indicator (DFI) are considered. SERR is a localized damage parameter, which can be employed to predict the possibility of damage growth in real time. On the other hand, the DFI is a frequency domain estimate of the load transmission capacity of the damaged structure. To estimate the SERR using SFEM, the continuum dynamic J-integral is discretized in terms of the element nodal variables. One of the main objectives in this article is to study the correlation between the SERR and DFI. Numerical simulations show that the DFI can be estimated efficiently using the proposed SFEM, whereas the dynamic SERR can be estimated with moderate accuracy using SFEM. The numerical results also show that the DFI-SERR correlation curves for various damage configurations and loading can be used. The article is concluded by establishing a preliminary experimental demonstration of the on-line estimation of DFI using cantilever beam with slotted cracks, PZT actuators, and accelerometer array.
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