Estimation of Dynamic Fracture Parameters in a Transverse Cracked Composite Beam using a Simplified Diagnostic Wave Propagation Model

Abstract

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.

Composite Delamination Detection Using Wavelet Spectral Finite Element and Damage Force Indicator Method

“…Spectral amplitude of global displacement vector for the damaged plate structure consists of axial displacements and , transverse displacement and rotation at each node. Now, the damage force vector is defined as (Kumar et al, 2006)…”

“…The concept of damage force has been used by Schulz et al (1998) to derive a damage indicator. This method was later extended to work under spectral element environment by Gopalakrishnan and his group for delamination detection in composites (Nag et al, 2002) and for fiber breakages (Kumar et al, 2006) using the spectral finite element damaged models. This paper reports the detection of delamination in composite plates by combining the DFI method with wavelet based spectral finite element (WSFE) and experimental measurements.…”

Wavelet spectral finite element method for modeling wave propagation in stiffened composite laminates

“…(34) with measured incomplete field data by deleting the rows and columns corresponding to rest of the DOFs. In order to remove the effect of excitation forces, a normalization procedure is followed according to the equation below [19], Fig. 10 shows the velocity response of the structure with the debonding compared with that of healthy structure at the tip and back of skin as well as top end of stiffener (n 11 , right middle between n 2 -n 3 , and n 6 in Fig.…”

Integration of Non-Destructive Evaluation-based Ultrasonic Simulation: A means for simulation in structural health monitoring

“…Apart from ray tracing, SFEM is also an alternative to FEM techniques especially at very high frequencies. The time-domain SFEM has been extensively studied by Gopalakrishnan and colleagues, 39,44 Ostachowicz et al, 38 and Mahapatra et al [45][46][47][48] for analyzing the elastic wave propagation (Lamb waves) in 2D and 3D thin-walled structures. This method combines the two different numerical techniques of spectral methods and the FEMs, respectively.…”