The continuous implementation of shape memory alloys’ (SMAs’) actuation capabilities in various applications from aerospace to biomedical tools has attracted researchers’ interests into design optimization of active systems. Traditional methods of optimization have mostly relied on several iterations of altering and testing different possible design of prototypes seeking the best configuration. This trial and error experimentation method is usually expensive and time consuming. In the recent years the availability of computational analysis has facilitated the optimization process by avoiding the developments of many prototypes in the whole design space. In this work an automated design optimization frameworks is presented especially for the systems including active components. Design exploration of a recently proposed medical device was considered as a case study to elaborate this iterative technique. SMA activated needle is an innovative medical tool to be used in needle-based surgeries aiming the enhancement of the needle tip placement inside the tissue. Different configurations have been assessed by altering the design variables in the assigned domain seeking the maximum needle tip deflection to assure the maximum flexibility of the structure where all the analyses were constrained to the stress level of SMAs to be in the safe range preventing plasticity. A commercially available finite element package was used for the iterative assessments in the optimization approach. The challenging part in any analysis of active components is the incorporation of a suitable material model. For this purpose three experimental setups were developed to get the material properties of SMAs through different responses of the wires. These material properties along with the implementation of Brinson model led to the generation of the isothermal stress strain curves which were defined as material model of the active components in the FE analyses. The FE model was then linked to the iterative engine of direct optimization to iterate through the whole domain and determine the best configuration. The Design of Experiments (DOE) and the Multi-Objective Genetic Algorithm (MOGA) were used for the case study optimization. Both the design optimization and the design sensitivity studies were described. The results showed the length of the needle and the offset between the neutral axis of needle and the actuator were the most sensitive variables. The best five configurations with the maximum tip deflection was also presented.

Evolution of the domain structure in bulk polycrystalline PZT during poling was studied using Piezoresponse Force Microscopy (PFM). For the study, two different experimental methods were employed. First, a trapezoidal PZT specimen was subjected to electric field so as to produce a wide variation of electric field intensity in the specimen. PFM images were then acquired from several different areas that have experienced different field strengths. Histograms of pixel intensity show a distinct difference in the pattern of piezoresponse signal between poled and unpoled areas. The presence of non-180° domain structure in the scanned area significantly affects the histogram pattern. At high levels of electric field the presence of mainly 180° domain structures leads to a bi-modal M-shaped histogram. To illustrate the evolution of the non-180° domain structure, in-plane poling was conducted with the electric field level increased in steps, and the domain evolution process was observed by PFM after each step. The resulting images demonstrate that non-180° domain structures gradually disappear from the specimen surface during the poling process. The PFM data can be exploited to study domain evolution in bulk ferroelectric materials via both qualitative observation and statistical analysis.

Flexible multi-beam structures are significant components of large space station, architecture engineering and other structural systems. The understanding of the dynamic characteristics of these structures is essential for their design and control of vibrations. In this paper, the planar nonlinear vibrations and chaotic dynamics of an L-shape flexible beam structure will be investigated using theoretical and experimental methods. The L-shape beam structure considered here is composed of two flexible beams with right-angle. The governing equations of motion for the L-shape beam structure are established firstly. Then, the method of multiple scales is utilized to obtain a four-dimensional averaged equation. Numerical method is used to analyze the nonlinear dynamic responses and chaotic motions. Finally, The experimental apparatus and schemes for measuring the amplitude of nonlinear vibrations for the L-shape beam structure are introduced briefly. Then, the detailed analysis for experimental data and signals which represent the nonlinear responses of the beam structure are given.