Interfacial behaviours of smart composites

The success of conventional fiber reinforced composites (FRC) relies on the quality of bonding between fibers and matrix. A review of literatures shows that there is a lack of theoretical models and experimental findings on the interfacial behaviours of the SMA-composites. In the past, the operation limit as well as the ideal actuation condition of SMA inclusions could not be predicted accurately during the design stage and the SMA-composite structures may therefore suffer a potential risk of sudden failure due to overloading or over-actuation.; The theoretical models developed in this research provide a study basis for the prediction of internal stresses and interfacial strength of the SMA-composites. Martensite volume fraction is considered as a critical parameter which determines the material properties and shape memory effect (SME) of the SMA inclusions. The proposed model reproduce the SMA behaviour inside a substrate, evolutions of martensite volume fraction and elastic modulus of SMA, and the internal stresses along the embedded length in different loading and actuation scenarios. The concepts of 'constant martensite volume fraction region (CMR)' and 'constant axial stress region (CASR)' are proposed to justify the desired SMA actuation. In addition, substantial improvement of the initial debond stress is predicted with the increase of the actuation temperature.; The 'Optimum Actuation Condition (OAC)' that ensures the reinforcement of SMA composite but avoids the failure of composite interface due to over-actuation is also defined to optimize the application of SME in the composite structure within a safety actuation limit. A simplified OAC (SOAC) is also developed to provide an analytical solution of OAC and thus the ideal actuation temperature for achieving such specific actuation condition can be estimated more easily.; Single fiber pullout test and finite element analysis (FEA) are employed to evaluate the interfacial behaviours and analyze the stress distributions inside the partially debonded two-cylinder models. Buckling control of composites with embedded SMA wires is also employed as application examples. The results agree fairly well with the theoretical predictions and hence convince the applications of such theoretical model for the estimation of buckling resistance in the design stage of the SMA-composites.; Based on the overall developments, it appears that the proposed theoretical models and the approach of experimental study are the viable basis for the development of the SMA-composites as a new class of reliable materials for satisfying wide variety of engineering requirements. The concept of evolution of martensite volume fraction along the embedded SMA materials is particularly important for the predictions of mechanical response as well as material status of the SMA-composites.