ECCM15 - 15 TH EUROPEAN CONFERENCE ON COMPOSITE MATERIALS, Venice, Italy, 24-28 June 2012 1 DISCRETE PLY MODELLING OF LOW VELOCITY IMPACT AND COMPRESSION AFTER IMPACT IN UNIDIRECTIONAL LAMINATED COMPOSITES C. Bouvet 1* , N. Hongkarnjanakul 1 , S. Rivallant 1 1 Université de Toulouse; INSA, UPS, Mines Albi, ISAE; ICA (Institut Clément Ader) – ISAE, 10 avenue Edouard Belin, 31055 Toulouse Cedex 4, France *christophe.bouvet@isae.fr Keywords: composite, impact damage, CAI, damage tolerance Abstract This paper deals with impact damage, permanent indentation and compression after impact (CAI) modelling. A model enabling the formation of damage developing during low velocity / low energy impact test and CAI test in laminated composite panels has been elaborated. The different impact and CAI damage types, i.e. matrix cracking, fibres failure and interfaces delamination, are simulated. This model is compared to experimental tests and is used to highlight the failure scenario of laminate during residual compression test. Finally the impact energy effect on the residual strength is evaluated and compared to experimental results. 1. Introduction Composite materials have been increasingly introduced in airframe and space applications in the last decades because of their interesting characteristics, like their low specific weight, enhanced mechanical strength, high stiffness... Nevertheless, during the structure’s life, damage induced in these materials by impacts of minor and major objects, like hail stones, runway debris or dropping tools, can drastically decrease the structure’s life. Low velocity impact is one of the most critical loading for composite laminates. Indeed, for structures submitted to low energy impacts or minor objects drops, like tools during assembly or maintenance operations, composite laminates reveal a brittle behaviour and can undergo significant damage in terms of matrix cracks, fibres breakages or delaminations. This damage is particularly dangerous because it drastically reduces the residual mechanical characteristics of the structure, and at the same time can leave a very little visible mark onto the impacted surface [1]. Consequently, it is essential to define a damage tolerance demonstration to design this type of structure in order to take into account the possible damage. In the field of aeronautics, the damage tolerance, for damage corresponding to impact loading, drives to dimension the structure depending on the impact detectability [2]. If the damage is not detectable, in fact when the impact indentation is less than barely visible impact damage (BVID), the structure must support the extreme loads and if the damage is detectable, in fact when the impact indentation is bigger than BVID, another criterion must be considered, like repair or change of the structure [3, 4]. Then, in order to be able to numerically optimize a composite structure with impact damage tolerance concept, it is necessary to simulate, with the same model, the impact damage, and in particular the permanent indentation, and the CAI test to evaluate the residual strength versus impact energy and permanent indentation. This is the scope of the proposed model which is able to simulate the impact and the residual strength test.