Bykiv N. Increasing the deformability of structural elements under cyclic loads by using shape memory alloys

This work is dedicated to increasing the deformability of structural elements under cyclic loads by using shape memory alloys (SMA). Methods were developed to study the impact of load cycle asymmetry on SMA properties, utilizing force, deformation, and energy parameters. Experimental studies showed that beams with SMA inserts exhibit increased deformability compared to conventional reinforced concrete beams under low-cycle loads. During the manufacturing process of beams with SMA inserts, the problem of connecting the SMA element to the working reinforcement was resolved. Using ANSYS, the behaviour of beams with SMA inserts under cyclic loading was modelled, confirming increased deformability and durability of structures. The dissertation consists of five chapters. The introduction substantiates the relevance, goals, objectives, research methods, scientific novelty, practical significance, and personal contribution of the researcher. Chapter one describes the crystal structure of SMA and provides a literature review on their applications. The research purpose and objectives are formulated. Chapter two outlines the methods for studying the mechanical and functional properties of SMA. The methodology for modelling the mechanical behaviour and damping properties of beams in ANSYS is described. Chapter three presents the results of determining the physical-mechanical and functional properties of SMA, as well as studies on the effect of cyclic loading on the mechanical behaviour and properties of pseudoelastic NiTi. The results showed that increasing the load cycle asymmetry worsens the material's functional properties. The dissipation energy at Rσ = 0.1 is significantly higher than at Rσ = 0.5. Fractographic analysis revealed the impact of asymmetry on crack formation and fracture relief. It was established that increasing Rσ from 0.1 to 0.5 significantly enhances the fatigue life of NiTi. Chapter four describes the manufacturing of a reinforced concrete beam with and without an SMA insert based on parameters determined in chapter three. Experimental studies indicated that the destruction of beams with SMA occurs at a deflection of 20.3 mm, 2.8 times higher than that of conventional beams. The use of SMA changes the fracture behaviour to a more plastic nature. In chapter five, a nitinol model specimen was developed and verified against experimental results. The modelling error was 3.25%. Modelling confirmed increased deformability of structures under cyclic loads. Recommendations for implementing SMA in structures to enhance deformability were developed.