Shape Memory Alloys (SMAs) are characterized by their capability of sensing and reacting to the changes in its surrounding environment. They can sense thermal or stress stimulus and exhibit actuation or some pre-determined response, thus enabling the control of some technical parameters such as shape, strain, stiffness, natural frequency, damping and so on. By combining SMAs with other advanced materials, intelligent or smart composites can be fabricated, which can utilize the unique properties of the individual bulk materials and exhibit multiple responses. SMA fibers are used to strengthen some composites, to absorb strain energy and relieve residual stresses by stress-induced martensitic transformations. Ni-Ti alloy fiber impregnated composites show good damping and actuation behavior because of the shape recovery that takes place at and above the martensite-austenite transformation temperature. Embedded SMA fibers may be electrically heated to induce the martensite-austenite transformation, giving rise to changes in stiffness, vibration frequency and amplitude, acoustic transmission or shape of the composite. The main aim of the project will be to obtain composite materials with optimized mechanical properties, “tailored” thermal expansion, “tunable” stiffness and self-healing characteristics.
Partners: FFCT/UNL, CENIMAT, UNIDEMI, UNIC, UM
Funding organization: Science and Technology Foundation (PT)
Main achievements: - Improvement of processing techniques (thermal and mechanical), including the ability to severe plastic deformation of SMAs; - A detailed analysis of the mechanical behaviour of SMAs was carried out, which was supported by a structural characterization and by determining the characteristics of transformation through DSC and electrical resistivity; - The mechanical behaviour of reinforced composites with shape memory alloys was studied through the implementation of numerical models; - Techniques for producing smart composites with mortar matrix and SMAs fibres were developed and civil engineering applications were fabricated and tested.