Analysis of the Response of Modal Parameters to Damage in CFRP Laminates Using a Novel Modal Identification Method

Nowadays, composite materials are widely used in several industries, e.g. the aeronautical, automotive, and marine, due to their excellent properties, such as stiffness and strength to weight ratios and high resistance to corrosion. However, they are prone to develop Barely Visible Impact Damage (BVID) from low to medium energy impacts (i.e. 1 – 10 m/s and 11 – 30 m/s respectively) that are reported to occur during both service and maintenance, such as bird strike; hailstones and tool drops. Therefore, Structural Health Monitoring (SHM) techniques have been developed to allow identifying damage at an early stage, in an attempt to avoid catastrophic consequences. Vibration measurement was conducted on healthy and damaged Carbon Fibre Reinforced Polymers (CFRPs) specimens. Damage is introduced to the specimen through a static indentation and the work done by the hemispherical indenter measured. This test was mainly for the purpose of damage introduction in the test samples. In this work, the effects of damage on the individual mode were studied to understand the response pattern of the modal parameters. It is intended that the current study will inform the development of a new damage identification method based on the variations between healthy and damaged specimen’s dynamic results. A new modal identification method (“Elliptical Plane”) that uses an alternative plot of the receptance has been developed in this work. The Elliptical Plane method used the energy dissipated per cycle of vibration as a starting point, to identify modal constants from Frequency Response Functions (FRFs). In comparison with the method of inverse, this new method produces accurate results, for systems that are lightly damped with its modes well-spaced. The sine of the phase of the receptance is plotted against the amplitude of the receptance, through which damping was calculated from the slope of a linear fit to the resulting plot. The results show that, there are other relevant properties of the plot that were not yet delve into by researchers. The shape of the plot is elliptical, near the resonant frequencies, whereby both parts of the modal constants (real and imaginary) can be determined from numerical curve-fitting. The method offers a new perspective on the way the receptance may be represented, in the Elliptical Plane, which may bring valuable insights for other researchers in the field. The novel method is discussed through both numerical and experimental examples. It is a simple method and easy to use. Interestingly, as the energy level increases, the percentage changes in both the modal frequency and damping increases. The linear equations reveal that there is a correlation between the increase in energy and the percentage variation in modal frequency and damping, especially from a threshold energy level determined to be between 15J and 20J for the analysed cases. Finally, modal identification is conducted on the healthy and damaged specimens, and the results were analysed with BETAlab software and the Elliptical Modal identification method. It was observed that the Elliptical Modal identification method provides some interesting results. For instance, a comparison between the modal damping from the ellipse and BETAlab methods revealed that, the level of reduction in the modal damping from the ellipse method is higher than that of the BETAlab. This behaviour offers a promising future in the area of damage identification in structures

Proceedings of Abstracts Engineering and Computer Science Research Conference 2019

© 2019 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Note: Keynote: Fluorescence visualisation to evaluate effectiveness of personal protective equipment for infection control is © 2019 Crown copyright and so is licensed under the Open Government Licence v3.0. Under this licence users are permitted to copy, publish, distribute and transmit the Information; adapt the Information; exploit the Information commercially and non-commercially for example, by combining it with other Information, or by including it in your own product or application. Where you do any of the above you must acknowledge the source of the Information in your product or application by including or linking to any attribution statement specified by the Information Provider(s) and, where possible, provide a link to this licence: http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3/This book is the record of abstracts submitted and accepted for presentation at the Inaugural Engineering and Computer Science Research Conference held 17th April 2019 at the University of Hertfordshire, Hatfield, UK. This conference is a local event aiming at bringing together the research students, staff and eminent external guests to celebrate Engineering and Computer Science Research at the University of Hertfordshire. The ECS Research Conference aims to showcase the broad landscape of research taking place in the School of Engineering and Computer Science. The 2019 conference was articulated around three topical cross-disciplinary themes: Make and Preserve the Future; Connect the People and Cities; and Protect and Care

Proceedings of Abstracts, School of Physics, Engineering and Computer Science Research Conference 2022

© 2022 The Author(s). This is an open-access work distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited. For further details please see https://creativecommons.org/licenses/by/4.0/. Plenary by Prof. Timothy Foat, ‘Indoor dispersion at Dstl and its recent application to COVID-19 transmission’ is © Crown copyright (2022), Dstl. This material is licensed under the terms of the Open Government Licence except where otherwise stated. To view this licence, visit http://www.nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: [email protected] present proceedings record the abstracts submitted and accepted for presentation at SPECS 2022, the second edition of the School of Physics, Engineering and Computer Science Research Conference that took place online, the 12th April 2022