Simone Boccardi

Monitoring impact damaging of thermoplastic composites

Thermoplastic composites are becoming ever more attractive also to the aeronautical sector. The main advantage lies in the possibility to modify the interface strength of polypropylene based laminates by adjusting the composition of the matrix. Understanding these aspects is of great importance to establish a possible link between the material toughness and the matrix ingredients. The aim of the present work is to ascertain the ability of an infrared imaging device to visualize any change, in the material behaviour to low energy impact, induced by changes in the matrix composition. Attention is given to image processing algorithms; in particular, an original procedure to measure the extension of the impact-affected area is proposed.

Evaluation of impact-affected areas of glass fibre thermoplastic composites from thermographic images

The usefulness of an infrared imaging device, in terms of both acting as a mechanism for surface thermal monitoring when a specimen is being impacted and as a non-destructive evaluation technique, has already been proved. Nevertheless, past investigation has focused on mainly thermoset-matrix composites with little attention towards thermoplastic ones. Conversely, these thermoplastic composites are becoming ever more attractive to the aeronautical sector. Their main advantage lies in the possibility of modifying their interface strength by adjusting the composition of the matrix. However, for a proper exploitation of new materials it is necessary to detail their characterization. The purpose of the present paper is to focus on the use of infrared thermography (IRT) to gain information on the behaviour of thermoplastic composites under impact. In addition, attention is given to image processing algorithms with the aim of more effectively measuring the extension of the impact-affected area.4

Nondestructive Testing With Infrared Thermography

This chapter is intended to give an overview on how an infrared imaging device can be used to get information about the conditions of a given material or structure. The main nondestructive thermographic techniques are described with highlighting of testing procedures, testing parameters and image processing. Some examples of defects detection are also presented and discussed to bear witness to the effectiveness of infrared thermography as a nondestructive evaluation technique.

Basic temperature correction of QWIP cameras in thermoelastic/plastic tests of composite materials

The present work is concerned with the use of a quantum well infrared photodetector (QWIP) infrared camera to measure very small temperature variations, which are related to thermoelastic/plastic effects, developing on composites under relatively low loads, either periodic or due to impact. As is evident from previous work, some temperature variations are difficult to measure, being at the edge of the IR camera resolution and/or affected by the instrument noise. Conversely, they may be valuable to get either information about the material characteristics and its behavior under periodic load (thermoelastic), or to assess the overall extension of delaminations due to impact (thermo-plastic). An image post-processing procedure is herein described that, with the help of a reference signal, allows for suppression of the instrument noise and better discrimination of thermal signatures induced by the two different loads.

Composite Materials in the Aeronautical Industry

This chapter reports on information about composites, which are mainly used in the construction of aircraft. In particular, the main types of composites regarding both types of matrix and of reinforcement are described with some mention of the fabrication processes. A section is also devoted to the main types of defects arising during manufacturing and in service. Finally, some information on future developments is also provided.

Graphene–polymer coating for the realization of strain sensors

In this work we present a novel route to produce a graphene-based film on a polymer substrate. A transparent graphite colloidal suspension was applied to a slat of poly(methyl methacrylate) (PMMA). The good adhesion to the PMMA surface, combined with the shear stress, allows a uniform and continuous spreading of the graphite nanocrystals, resulting in a very uniform graphene multilayer coating on the substrate surface. The fabrication process is simple and yields thin coatings characterized by high optical transparency and large electrical piezoresitivity. Such properties envisage potential applications of this polymer-supported coating for use in strain sensing. The electrical and mechanical properties of these PMMA/graphene coatings were characterized by bending tests. The electrical transport was investigated as a function of the applied stress. The structural and strain properties of the polymer composite material were studied under stress by infrared thermography and micro-Raman spectroscopy.

An excursus on infrared thermography imaging

This work represents an overview of some of the applications of infrared thermography that have been carried out at the University of Naples Federico II over the years. The focus is on four topics: thermo-fluid-dynamics, materials inspection, cultural heritage and preventative maintenance. For each topic, some results are presented as thermal, and/or phase, images with the attention being essentially devoted to the capacity of these images to communicate information. For more details on test apparatuses, procedures and data analyses, the reader is referred to the previous published work, available in the literature.

Composite material overview and its testing for aerospace components

Abstract This chapter is concerned with the application of infrared thermography to investigate composite materials, which are used for the fabrication of aerospace components, and is organized into several sections. In particular, it starts with a brief introduction to composite materials, discussing also their main weaknesses. Then, an overview on the most used methods of nondestructive evaluation is given, highlighting some crucial aspects. The core of the chapter regards the description of the basics of infrared thermography, and the advantages of introducing it in an industrial enterprise; some key examples concerning on-line monitoring of loading tests and nondestructive evaluation of either final parts, or impact damaged parts, are also illustrated. In addition, some critical features, such as noise effects, are addressed with a proposed likely solution. The most important emphasized result regards the possibility to monitor impact tests with an infrared imaging device to get information about initiation and damage propagation directly on-line during the impact event, as well as damage extension evaluation through subsequent postprocessing of the acquired thermal images.

Chapter 2 – Nondestructive Evaluation

This chapter is concerned with nondestructive evaluation of composites. First, a brief discussion on the semantics to be used when dealing with a nondestructive approach is presented, which is followed by some information on the type of defects to be discovered. Then, the available techniques are illustrated. In particular, a brief description, with the basic principles, of the most used techniques is given. A comparison between techniques is also made with the aim to highlight advantages and disadvantages in terms of performance, costs and safety concerns at work.

Monitoring thermoplastic composites under cyclic bending tests

This work is concerned with the use of infrared thermography to visualize temperature variations linked to thermo-elastic effects developing over the surface of a specimen undergoing deflection under bending tests. Several specimens are herein considered, which involve change of matrix and/or reinforcement. More specifically, the matrix is either a pure polypropylene, or a polypropylene added with a certain percentage of compatibilizing agent; the reinforcement is made of glass, or jute. Cyclic bending tests are carried out by the aid of an electromechanical actuator. Each specimen is viewed, during deflection, from one surface by an infrared imaging device. As main finding the different specimens display surface temperature variations which depend on the type of material in terms of both matrix and reinforcement.