On the use of lock-in thermography to monitor delamination growth in composite panels under compression

Abstract The success of composites in automotive, aerospace, and naval applications is mainly related to their aptitude to be tailored to obtain a final product that perfectly fulfills the design requirements. However, during both manufacturing processes and maintenance, some flaws, like delaminations (which may escape simple visual inspection), may be induced in composite structures. The presence of delaminations is of major concern for the load-carrying capability of carbon fiber-reinforced polymer panels. Indeed, delaminations can strongly affect the structural strength and may grow under in-service loads, leading sometimes to catastrophic failures. The aim of this work is to explore the use of lock-in thermography for the monitoring of delamination propagation in composite structures when subjected to generic multiaxial loading conditions. A stiffened composite panel with an embedded skin delamination subjected to compressive loading was taken as a benchmark to assess experimentally the effectiveness of lock-in thermography for monitoring the delamination propagation in situ during the compressive mechanical test. The delamination size as a function of the applied load, observed by lock-in thermography during the execution of the compressive test, was used to validate the results of preliminary numerical computations

Porosity Distribution in Composite Structures with Infrared Thermography

Composite structures are increasingly used in the transport industry especially in the aeronautical sector thanks to their favorable strength-to-weight ratio with respect to metals. However, this is true if the final part is defects free and complies with quality requirements. A main weakness in composites is porosity, which is likely to be introduced during manufacturing processes and which may knock down the material characteristics affecting its performance in service. Porosity plays a key role in sandwich structures, which involve novel metal foams as core, since the foam performance strongly depends on size and distribution of pores. The determination of porosity is mostly attained by destructive methods, which supply only a general indication linked to the production part number. Conversely, composites may entail local significant variation of porosity, which may be discovered only with effective nondestructive techniques. The attention of the present work is focused on the possibility to use infrared thermography to get information about the amount and distribution of porosity. In particular, two techniques: flash thermography and lock-in thermography are used to comply with requirements of both monolithic composites and metal foams

Monitoring Composites under Bending Tests with Infrared Thermography

The attention of the present paper is focused on the use of an infrared imaging device to monitor the thermal response of composite materials under cyclic bending. Three types of composites are considered including an epoxy matrix reinforced with either carbon fibres (CFRP) or glass fibres (GFRP) and a hybrid composite involving glass fibres and aluminium layers (FRML). The specimen surface, under bending, displays temperature variations pursuing the load variations with cooling down under tension and warming up under compression; such temperature variations are in agreement with the bending moment. It has been observed that the amplitude of temperature variations over the specimen surface depends on the material characteristics. In particular, the presence of a defect inside the material affects the temperature distribution with deviation from the usual bending moment trend

Visualization of Thermal Effects in Polypropylene-based Composites under Cyclic Bending Tests☆

Abstract The attention of this paper is focused on surface temperature changes which are experienced by thermoplastic composite materials under cyclic bending tests. Such changes are visualized and measured with an infrared imaging device and later analyzed to gain information which, coupled with other mechanical and/or chemical properties, may be exploited for the material characterization. In particular, thermoplastic composites based on a polypropylene matrix, which may be neat, or modified by the addition of a relatively low amount of a specific compatibilizing agent, and reinforced with glass or jute woven fibres are investigated

Infrared Thermography in the Architectural Field

Infrared thermography is becoming ever more popular in civil engineering/architecture mainly due to its noncontact character which includes two great advantages. On one side, it prevents the object, under inspection, from any alteration and this is worthwhile especially in the presence of precious works of art. On the other side, the personnel operate in a remote manner far away from any hazard and this complies well with safety at work regulations. What is more, it offers the possibility to quickly inspect large surfaces such as the entire facade of a building. This paper would be an overview of the use of infrared thermography in the architectural and civil engineering field. First, some basic testing procedures are described, and then some key examples are presented owing to both laboratory tests and applications in situ spanning from civil habitations to works of art and archaeological sites

The Contribution of Infrared Thermography to Impact Testing of Composite Materials†

This work wants to give an overview on information gathered at the University of Naples Federico II in the last ten years by monitoring the impact tests of composite materials with infrared thermography. Many tests have been carried out involving several different types of composites and different infrared cameras. The obtained results show that IRT can be advantageously used to both validate previously obtained data and to get new data that can be exploited for understanding more on the impact damaging of composite materials. This bears witness for the advantages of having an infrared imaging device within the testing instrumentation