Damage detection in laminated composite structures using dynamic analysis

Laminated composite materials are used in different applications, for example mechanical, civil and aerospace structures, due to their light weight and excellent mechanical properties. However, fibre breakage and delamination are among the more serious damage that often initiate and propagate due to a number of mechanical and, specifically, dynamic loads during the operational life. Also, these damages destroy design functionality of these structures. To address this issue, damage detection is required in time to provide a good understanding of structure state in advance of any potential failure. There are a number of damage detection approaches reported in the literature and reviewed herein. Some of these are base-line free, whilst others use the intact data as a reference for the detection of damaged sections. However, currently there are a very limited number of experimental studies in the literature that use vibration-based damage detection to detect the delaminated areas, and are almost non-existent for fibre breakage; the majority of simulated studies consider delamination only. Defects in laminated structures are quite complicated and in most cases are hidden. Frequency-based damage detection is considered to be a global approach and is not useful when dealing with complex structures. There has been extensive research to develop the curvature mode shape as a reference for damage detection because it is highly sensitive at show the effects of damage. This sensitivity is tested in this research, as it is extremely difficult to detect damaged sections within composite materials, even with an active approach. Hence, the main objective of this research is to develop the curvature damage index by calculating the irregularity curvature index, and the proposal of a novel index, called the Haar index, to support the damage detection process. Both these indexes are used to detect delamination and fibre breakage on high modulus CFRP plate structures under condition of free vibration. Using these indexes gives an efficient method by which to quantify and localize damaged areas in both theoretical and experimental considerations of different lay-ups. In the modelling section, two finite element software programs, COMSOL Multiphysics 5.1 (Licence No. 7074366) and ABAQUS 6.14-1 (Licence No. 200000000008515), are used. This thesis includes development procedure of the curvature index, calculates the Haar index, gives details of the theoretical and experimental analysis, and reports the consequent results and discussion.