Finite element simulation of low velocity impact on shape memory alloy composite plates M. Meo a, * , E. Antonucci b , P. Duclaux a , M. Giordano b a Crashworthiness, Impact and Structural Mechanics Group, School of Engineering Cranfield University, Cranfield, Bedford MK43 0AL, UK b Institute for Composite and Biomedical Materials Technology, CNR, 80-80124 Naples, Italy Abstract Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically. Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly. This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape mem- ory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures. Ó 2005 Elsevier Ltd. All rights reserved. Keywords: Delamination; Shape memory alloys; Impact damage 1. Introduction The need for improved materials with better strength, and lower weight leads to the use of composite materials in the aerospace industries. Composite structures in general are susceptible to a wide range of damage and defects due to manufacture and in-service loads. Owing to their weak impact resistance properties, laminated composite plates are very susceptible to damage when impacted by a foreign object. There is a need improve impact damage properties of composite structures so as that the integrity of the struc- ture is not compromised. One possible way to increase impact damage resistance of composite structure is by embedding SMA wires into composite structures. Super- elastic shape memory alloy has a remarkably high strain- to-failure. This superelastic alloy has a recoverable elastic strain up to 15%. The high strain capability of SMA fibers is primarily due to a stress-induced martensitic phase trans- formation creating a plateau region in the stress–strain curve. This property enables superelastic shape memory alloy fibers to absorb much more strain energy than other fibers before their failure. Thus, embedding superelastic shape memory alloy fibers in the composites could make the composites tougher and increase the damage impact resistance of composite structures. Birman [1] has given a comprehensive review of the mechanics, material and mechanical properties and applications of SMA materials. Tsoi et al. [2] results showed that for low velocity impact, 0263-8223/$ - see front matter Ó 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.compstruct.2005.09.029 * Corresponding author. Tel.: +44 1234 750111x5220; fax: +44 1234 752149. E-mail address: m.meo@cranfield.ac.uk (M. Meo). www.elsevier.com/locate/compstruct Composite Structures 71 (2005) 337–342