Finite Element Martensite Ratio Derivation on NiTi via Measurable Criteria of Strain Rate

The shape memory alloys (SMAs) and smart composites have a large use in high and low level industry, while a lot of research is being done in this field. The existence of smart composite structures is because of the advance mechanical benefits of the above materials. This work refers to dynamic and quasi static nonlinear explanation of these materials. After mathematical model consideration on the rate of strain, a model which is about martensite ratio of NiTi has been presented. This work has been done because of the high sensitivity of these materials to strain rate and use of visual and measurable engineering criteria to access other variables. As the martensite ratio is not engineering measurable amount, it needs to have macro scale property to measure this important nano scale criteria. Relative experiments are done to show the rate dependency of NiTi.

Effect of Segmented Electrodes on Piezo-Elastic and Piezo-Aero-Elastic Responses of Generator Plates

In this paper, the use of segmented electrodes is investigated to avoid cancellation of the electrical outputs of the torsional modes in energy harvesting from piezo-elastic and piezo-aero-elastic systems. The piezo-elastic behavior of a cantilevered plate with an asymmetric tip mass under base excitation is investigated using an electromechanically coupled finite element (FE) model. Electromechanical frequency response functions (FRFs) are obtained using the coupled FE model both for the continuous and segmented electrodes configurations. When segmented electrodes are considered torsional modes also become significant in the resulting electrical FRFs, improving broadband (or varying-frequency excitation) performance of the generator plate. The FE model is also combined with an unsteady aerodynamic model to obtain the piezo-aero-elastic model. The use of segmented electrodes to improve the electrical power generation from aeroelastic vibrations of plate-like wings is investigated. Although the main goal here is to obtain the maximum electrical power output for each airflow speed (both for the continuous and segmented electrode cases), piezoelectric shunt damping effect on the aeroelastic response of the generator wing is also investigated.

Modeling Smart Materials Using Hysteretic Recurrent Neural Networks

This paper describes a novel approach to modeling hysteresis using a Hysteretic Recurrent Neural Network (HRNN). The HRNN utilizes weighted recurrent neurons, each composed of conjoined sigmoid activation functions to capture the directional dependencies typical of hysteretic smart materials (piezoelectrics, ferromagnetic, shape memory alloys, etc.) Network weights are included on the output layer to facilitate training and provide statistical model information such as phase fraction probabilities. This paper demonstrates HRNN-based modeling of two- and three-phase transformations in hysteretic materials (shape memory alloys) with experimental validation. A two-phase network is constructed to model the displacement characteristics of a shape memory alloy (SMA) wire under constant stress. To capture the more general thermo-mechanical behavior of SMAs, a three-phase HRNN model (which accounts for detwinned Martensite, twinned Martensite, and Austensite phases) is developed and experimentally validated. The HRNN modeling approach described in this paper readily lends itself to other hysteretic materials and may be used for developing real-time control algorithms.

Experimental Implementation of Negative Impedance Shunts on Periodic Structures

Shunt damping of structures has been heavily researched, both passively and actively. Negative capacitance shunts actively control vibration on a structure and have been shown to obtain significant broadband suppression. The use of smaller piezoelectric patches, implemented in a periodic array, can alter the behavior of the control. Assorted shunt arrangements as well as circuit configurations will be investigated. Experimental results will be compared to theoretical predictions of shunt performance.

Using Multiscale Modeling to Predict Material Response of Polymeric Materials

Presented is a multiscale modeling method applied to light activated shape memory polymers (LASMP). LASMP are a new class of shape memory polymer (SMP) being developed for applications where a thermal stimulus is undesired. Rotational Isomeric State (RIS) theory is used to build a molecular scale model of the polymer chain yielding a list of distances between the predicted cross-link locations, or r-values. The r-values are then fit with Johnson probability density functions and used with Boltzmann statistical mechanics to predict stress as a function of strain of the phantom network. Junction constraint theory is then used to calculate the stress contribution due to interactions with neighboring chains, resulting in previously unattainable numerically accurate Young’s modulus predictions based on the molecular formula of the polymer. The system is modular in nature and thus lends itself well to being adapted for specific applications. The results of the model are presented with experimental data for confirmation of correctness along with discussion of the potential of the model to be used to computationally adjust the chemical composition of LASMP to achieve specified material characteristics, greatly reducing the time and resources required for formula development.

Topology Optimization of Mechanical Structures Using Level Set Method

This article introduces a novel algorithm in topology optimization of mechanical structures to achieve a desired compliance using the level set method. In contrast with the literature in this area that attempts to minimize the compliance of a structure, the present study concerns with an innovative formulation to reach a desired compliance. It is shown that a more comprehensive technique is required to achieve this goal.

The Calculation of Stiffness for Semiconductor Components

In this study, the correlation between macroscopic and microscopic properties of the II-IV semiconductor compounds CdX (X = S, Se, Te) is investigated. Based on constructing orthonormal tensor basis elements using the form-invariant expressions, the elastic stiffness for cubic system materials is decomposed into two parts; isotropic (two terms) and anisotropic parts. A new scale for measuring the overall elastic stiffness of these compounds is introduced and its correlation with the calculated bulk modulus and lattice constants is analyzed. The overall elastic stiffness is calculated and found to be directly proportional to bulk modulus and inversely proportional to lattice constants. A scale quantitative comparison of the contribution of the anisotropy to the elastic stiffness and to measure the anisotropy degree in an anisotropic material is proposed using the Norm Ratio Criteria (NRC). It is found that CdS is the nearest to isotropy (or least anisotropic) while CdTe is the least near to isotropy (or nearest to anisotropic) among these compounds. The norm and norm ratios are found to be very useful for selecting suitable materials for electro-optic devices, transducers, modulators, acousto-optic devices.

Comparison of Novel Conductive Open- and Closed-Porous PPy-PLA Composites

This study compared the fabrication techniques and characterization of novel open- and closed-porous structures in PPy-PLA conductive composites. For the open-porous composites, PLA samples were fabricated using compression molding and salt leaching with varying salt-to-polymer mass ratios, which were subsequently coated with PPy by in situ polymerization of pyrrole and iron (III) chloride. For the closed-porous composites, a patterned structure of PPy within PLA was created using compression molding of PPy-coated PLA pellets, followed by gas saturation and foaming techniques in order to create the closed pores. Characterization of both porous composites included their physical, mechanical, and electrical properties. Results showed that the modulus increased with increasing relative density and decreasing open porosity. The open-porous composites had lower relative density values but higher open porosities compared to the closed-porous composites. The average size of the closed pores was approximately an order of magnitude larger than the open pores. Lastly, the open-porous composites had higher conductivity values than the closed-porous composites due to the greater surface area of the continuous conductive pathway. The comparisons between open- and closed-porous composites established their characteristic properties for their future development in applications.

µ-Synthesis Control of Flexible Modes of AMB Rotor

In the paper the optimal robust vibrations control of flexible rotor supported in active magnetic bearings (AMBs) is presented. The purpose of the research is to stabilize the rotate rotor and effective control of rotor vibrations. The noncollocation effect which produce no interlaced of zeros and poles of AMBs system problem stability is investigated. The frequency mode analysis of collocation and noncollocation cases is presented. The μ-Synthesis Control is applied to stabilize the rigid and flexible critical frequency modes of the rotor AMBs. The singular value analysis is used to obtain the robust performances of closed-loop system. The dynamical behaviour of AMBs system in wide range of rotation speed (up 21000 rpm) is investigated. The goal of this paper is also the experimental evaluation of the robust performance. The stable operation, good stiffness of the rotor and robust performances of the closed-loop AMBs systems is reached. Finally, the success of the robust control is demonstrated through results of computer simulations and experimental results.

Size Effect on the Phase Transformation of In-21at%Tl Nanowires

In this work, the interaction between the size effect and the thermomechanically induced phase transformation for SMAs composed of Indium-Thallium (InTl) is analyzed. An In-21at%Tl alloy is first fabricated, from which In-21at%Tl nanowires are subsequently produced. Using the mechanical pressure injection system, the bulk alloy is pressed into pores of an Anodized Aluminum Oxide (AAO) template to fabricate the nanowires. The diameter of these nanowires can be altered by changing the anodization parameters of the AAO templates (≈20nm–750nm). The critical diameter for which nanowires show a similar phase transformation behavior to the bulk alloy is experimentally determined to lie between 280nm and 750nm.