ECCM16 - 16 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Seville, Spain, 22-26 June 2014 1 MEASURE OF FRACTURE TOUGHNESS IN COMPOSITE STRUCTURES USING INFRARED THERMOGRAPHY Teddy LISLE 1 , Natthawat HONGKARNJANAKUL 1 , Christophe BOUVET 1 , Marie-Laetitia PASTOR 1 , Philippe MARGUERES 1 , Samuel RIVALLANT 1 1 : Université de Toulouse ; INSA, UPS, Mines Albi, ISAE ; ICA (Institut Clément Ader) ISAE (Institut Supérieur de l’Aéronautique et de l’Espace) 10, avenue Edouard Belin, -BP 54032- 31055 Toulouse cedex 4 e-mail : christophe.bouvet@isae.fr Keywords: infrared thermography, fracture toughness, composite fracture Abstract Fracture toughness is one of the most important properties of any material for a lot of design applications involving damage and crack growth. Unfortunately its value can be difficult to evaluate with standard methods such as “compliance” method. In this work, two special cases have been studied and infrared thermography has been used to overcome the limitations of conventional methods. Damage of compressive fiber failure in unidirectional composite laminate has been chosen due to its difficulty to evaluate toughness. The infrared thermography has been used to follow compressive failure mode developing during an indentation test and a compression after impact test, and to evaluate the fracture toughness of compressive fiber failure. 1. Introduction The studied cases deal with the compressive fiber failure mode in laminated composites [1]. This failure mode is known as a very complex mode occurring as a result of the kinking process. Currently, no standard tests are available to determine the fracture toughness of this phenomenon. Infrared thermography has been used to follow compressive failure mode developing during an indentation test and a compression after impact test, and to evaluate the fracture toughness of compressive fiber failure. From the past 20 years, infrared thermography has been widely used to study the dissipative phenomena in materials, such as plasticity in metals [2-3] or damage in polymers [4]. Using the framework of irreversible thermodynamics, Chrysochoos et al. [5] have presented a methodology to estimate the internal heat sources associated with the dissipative phenomenon from temperature measurement on the sample surface. Nevertheless, the use of infrared thermography to study dissipated thermal energy is quite recent in composite materials and is essentially applied to fatigue loading. For example, Naderi et al. [6] used infrared thermography to characterize damage stage evolution by calculating the dissipated heat during fatigue loading of thin woven laminates. Nevertheless, using crack tip contour integral analysis [7], Freund and Hutchinson [8] and Soumahoro [9] have shown that the fracture toughness is linked to dissipative work. In addition, since the early work of Taylor and