Shape memory alloys are increasingly used in numerous smart engineering structures. This study experimentally investigates static flexural and free vibration characteristics of composite beams reinforced with shape memory alloy wires. The key to this study is using shape memory alloy fibers as a means for influencing and tuning the static and dynamic responses of structures. A series of static three-point bending and modal experiments is performed to capture the capability of shape memory alloy wires in controlling the static and dynamic responses of a reinforced beam. Static and dynamic behaviors of the fiber-reinforced beam with different volumetric fiber fractions are examined. Before heat excitation, increasing the number of shape memory alloy wires leads to higher beam stiffness and lower beam deflection. However, with both heat activation and the higher number of shape memory alloy wires, beam deflection is significantly reduced. The modal vibration tests demonstrated that when shape memory alloy wires are not activated, the magnitude of natural frequencies slightly decreases by increasing the number of shape memory alloy wires. However, with heat excitation, the higher number of shape memory alloy wires, in contrast, increases the magnitude of natural frequencies. Furthermore, the higher number of activated shape memory alloy wires shows to predominantly increase the magnitude of higher modes of vibration rather than lower modes.

Ratcheting failure of materials and structures subjected to low cycle fatigue in the presence of significant mean stress is of great interest to researchers. In this experimental and numerical study, the response of 316L stainless steel samples was observed in symmetric strain control uniaxial test followed by post-stabilized monotonic test, uniaxial and biaxial ratcheting tests, in order to determine the Chaboche model parameters and to evaluate ratcheting prediction using finite element analysis. The critical elastic limit was initially obtained from incremental uniaxial cyclic tests. The Chaboche parameters were subsequently extracted from experimental hysteresis and post-stabilized monotonic stress plastic-strain curves using two optimization technics, namely, the Particle Swarm Optimization (PSO) and Genetic Algorithm (GA). The two optimization methods were compared for efficiency, in terms of time and accuracy. The PSO method presented higher efficient results and was subsequently used to derive the parameters from hysteresis and post-stabilized monotonic curves. Different values (by definition) of elastic limit were also used. The Finite Element commercial software ANSYS was utilized with the Chaboche model to predict the uniaxial and biaxial ratcheting behavior of 316L stainless steel pipe. The comparison between experimental and the numerical simulation demonstrates that adopting post-stabilized monotonic curve rather than hysteresis curve and with accurate elastic limit obtained from incremental loading test improves ratcheting prediction significantly.

The knee plays a significant role in locomotion and stability of the entire body through supporting the body weight and assisting the lower body kinematics during walking. However, the knee is at constant risk of becoming weakened due to disease, age, and accidents. One approach to treating weakened knee is wearing an assistive knee brace. To design a clinical knee brace, many factors such as weight and compliant mechanism should be considered. In this study, a novel smart assistive knee brace mechanism incorporated with wire actuators made of shape memory alloys is proposed to ameliorate the issues associated with weight and flexibility of existing brace designs. Unlike earlier studies, the proposed orthosis includes pressure sensor, shape memory actuator, and smart linkage. Furthermore, two distinct shape memory alloy actuator design concepts with improved stiffness are developed, and the best option is chosen systematically and prototyped. The novel mechanism proposed in this research overcomes the weight of the lower limb during swing phase using the combined shape memory alloy actuation and feed-forward controller design. As such, it can be used as a potential replacement to its conventional counterparts when the higher weight reduction as well as a flexible and controllable mechanism are simultaneously sought.