Advanced Materials Research Vol. 445

Abstract: In this paper, the static pull-in instability of torsional nanoelectromechanical systems (NEMS) with coupling effect between torsion and bending is investigated considering the effect of translation elastic boundary condition. A set of normalized equations governing the static actuation properties of the torsional actuator is derived to demonstrate the relationships between the parameters of static characteristics, such as torsion angle, vertical displacement, and applied voltage. The results from this model demonstrated that the real model of boundary condition (elastic boundary condition) is very important issue which must be considered in manufacturing process.

Abstract: The main deformation mechanism of shape memory alloys (SMA) is martensitic phase transformation (PT). To model martensitic phase transformations in such materials, several models have been developed. In the micromechanical model developed by Levitas and Ozsoy (2009), complete system of equations that describes evolution of stresses in phases and crystallographic parameters, as well as macroscopic stress–strain response for martensitic phase transformations under complex multiaxial loadings have been formulated. However, the experimental verification is incomplete. The objective of this study is to compare the experimental results in the literature for CuAlNi SMA with the results obtained from this micromechanical model. In the experiment used for comparison (Shield, 1995), a single crystal CuAlNi specimen is subjected to uniaxial load in several directions at different temperatures. According to the results obtained by using the constitutive equations of the model, the model describes the stress induced phase transformations very well when compared with these experiments. The uniaxial loading-unloading hysteresis loop shows good agreement with the experiments.

Abstract: This paper is concerned with investigation of the dynamic behaviors of cranes under seismic effects. For this purpose, firstly we have performed experiment on a 1/20 scale crane model on the shake table with real earthquake data, then a multi degree-of-freedom non-linear mathematical model is developed including behavior of the container cranes under earthquakes and simulated. The simulation system has a five degrees-of-freedom and modeled system was simulated for the ground motion of the El Centro earthquake in USA, 1940. Finally, the time history of the crane bridge displacement and acceleration responses of the both theoretical and experimental cases are presented. Theoretical and experimental results exhibit that the mathematical model is accurate. This study also shows the destructive effects of high accelerations which occur during the earthquake. These effects cannot be omitted in the design of cranes. The result of this study which is an accurate mathematical model can be inspiring for the engineers in terms of design parameters.

Abstract: The dynamic behavior of plates with mixed boundary conditions has been the subject of intensive study for many years due to its great importance in many engineering applications. On-trend approach in dynamic response analysis is to combine mathematical model, test results and computer simulation. Classical techniques of mathematical modeling of intricate structural systems for response analysis in frequency or time domain are tiresome and time consuming. In this study, a point supported rectangular plate considered and extraction of its system model from FE model, validated by the test results, by using commercially available computer programs such as Ansys and Matlab is demonstrated. State space mathematical model in principal coordinates obtained in Matlab from the modal analysis results of its FE model. Its modes sorted with respect to peak gain values, and the modes with the less contributions to the response truncated. To validate the accuracy of this method and truncation, transient responses from the full model with no reduction, truncated model, and Ansys are compared and found to be in accord with each other. Its demonstrated by plotting the indicated results of analyses, and emphasized the significant processing times between the conventional approach and stated method. It is concluded obvious that this study will make a good understanding in simplifying the dynamic analysis of vibration problems of plates.

Abstract: This paper studies torsional wave dispersion in a three-layered (sandwich) hollow cylinder with pre-strained face (core) layers (layer) made from high elastic materials the mechanical relations of which are described through the harmonic potential. The investigations are carried out within the scope of the piecewise homogeneous body model with the use of the three-dimensional linearized theory of elastic waves in initially stressed bodies. The analytical expression is obtained for the low wave number limit values of the torsional wave propagation velocity. The numerical results on the influence of the initial strains of the face (core) layers (layer) of the cylinder on the torsional wave propagation velocity are presented and discussed.