Abstract
This paper deals with detection of macro-level crack type damage in rectangular E-Glass fiber/Epoxy resin (LY556) laminated composite plates using modal analysis. Composite plate-like structures are widely found in aerospace and automotive structural applications which are susceptible to damages. The formation of cracks in a structure that undergoes vibration may lead to catastrophic events such as structural failure, thus detection of such occurrences is considered necessary. In this research, a novel technique called as node-releasing technique in Finite Element Analysis (FEA), which was not attempted by the earlier researchers, is used to model the perpendicular cracks (the type of damage mostly considered in all the pioneering research works) and also slant cracks (a new type of damage considered in the present work) of various depths and lengths for Unidirectional Laminate (UDL) ([0]S and [45]S) composite layered configurations using commercial FE code Ansys, thus simulating the actual damage scenario. Another novelty of the present work is that the crack is modeled with partial depth along the thickness of the plate, instead of the through the thickness crack which has been of major focus in the literature so far, in order to include the possibility of existence of the crack up to certain layers in the laminated composite structures. The experimental modal analysis is carried out to validate the numerical model. Using central difference approximation method, the modal curvature is determined from the displacement mode shapes which are obtained via finite element analysis. The damage indicators investigated in this paper are Normalized Curvature Damage Factor (NCDF) and modal strain energy-based methods such as Strain Energy Difference (SED) and Damage Index (DI). It is concluded that, all the three damage detection algorithms detect the transverse crack clearly. In addition, the damage indicator NCDF seems to be more effective than the other two, particularly when the detection is for damage inclined to the longitudinal axis of the plate. The proposed method will provide the base data for implementing online structural health monitoring of structures using technologies such as Machine Learning, Artificial Intelligence, etc.
Highlights
In high-speed mechanical applications such as turbomachinery and aerospace structures, there is a pressing need for high strength lightweight materials
The displacement shapes obtained through Finite Element Analysis (FEA) and Ex1p4e.0r4iment0a.0l8Modal Analysis (EMA) are comparable with slight changes in the natural frequency since the fabricated plate is not exactly rectangular and error in measurement at certain impact points
The main objectives of this investigation are to ascertain the effectiveness of existing damage detection algorithms for laminated composite plate structures and observe their relative merits
Summary
In high-speed mechanical applications such as turbomachinery and aerospace structures, there is a pressing need for high strength lightweight materials. Researchers studied various local non-destructive techniques for damage detection in composites like X-Ray [3], microwave [4], acoustic emission [5], infrared thermography [6], ultrasonic [7] and magnetic-field methods [8]. These techniques hold some merits, it was reported that they were found to be somewhat difficult for applying in in the stuructures where the accessibility is very difficult like offshore oil platforms and the flying machines like aerospace vehicles as it require disassembly of parts and the locality of the damage is known prior to the testing which may be difficult in complex structures. Damage detection technique which is global in nature such as vibration-based methods may be found more useful, individually or in combination with other local methods, for successful non-destructive evaluation of laminated composite structures
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