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.
Forming Limit Diagram (FLD) is a resourceful tool to study the formability of sheet metals. Research on the formability of Perforated Sheet Metal is growing over the years as perforated sheet metal finds its applications in various fields. But finding FLD of perforated sheet metals is complex due to the presence of holes. Also, the hole size, shape and pattern, ligament ratio, thickness of the blank, percentage of open area influence the formability of a perforated sheet metal.In the present scenario, various simulation softwares have made the process of plotting FLD much easier, saving time and money. This paper is an attempt to predict the formability of mild steel perforated sheet metal through simulation software package LS Dyna. Also, Parametric analysis is performed to determine the influence of geometric parameters on the drawability of the perforated sheet metal.
As the study of formability of perforated sheet metals using conventional approach is exhaustive and time consuming, Finite Element Analysis is used to carry out the same. This paper attempts to study the effects of perforation parameters (viz. hole size, open area and thickness) on the formability of square hole Perforated Mild Steel Sheet Metal. Finite element analysis is done using commercial Finite Element Analysis software LS-DYNA. Parametric analysis is carried out to optimize process parameters using Taguchi’s L9 orthogonal array. From the results obtained through simulation, the analysis of variance (ANOVA) is carried out to determine which group has best condition for drawing and regression equation is obtained to know, how a single response variable (Major or Minor strain) is related to a variety of predictor variables (percentage open area, hole size and thickness) and the graphs are plotted between them using MINITAB software.
One of the most important features of a material to know before using it is the maximum limit of the load at which it fails. This paper presents a micromechanical strength theory to estimate the tensile strength of the unidirectional fiber reinforced composite. The fibers used can be considered transversely isotropic and elastic till failure, but the matrix material is considered to be Elastic-plastic. The mathematical formulation used is the Variational-Asymptotic Method (VAM), which is used to construct the asymptotically-correct a reduced-dimensional model that is free of a priori assumption regarding the kinematics. The 3-D strain generated in each constituent material is explicitly expressed in 1-D strains and initial curvatures. The advantage of using VAM is that the stress state correlation of constituent materials is taken care of while applying warping constraints. Prandtl-Reuss plasticity theory has been implemented for the plastic region constitutive relationship. The other advantage of this work is that the load-bearing capacity of the composite beyond the elastic region has been considered. Good agreement has been found between experimental data and VAM analysis.
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