Magnetostrictive materials such as Terfenol-D are increasingly being considered for demanding applications such as active noise damping, sonar devices and reactive structures, due to their large strain capability. A limiting factor for the use of magnetostrictive material slies in their inherent susceptibility to brittle fracture. The present study applies finite element technology in support of experimental investigations to assess the mode II fracure toughness of magnetostrictive materials. In this exploratory effort, the fully coupled non-linear behavior of the material is not considered. Rather, a methodology for converting the applied magnetic field to an equivalent mechanical load, based on the material's magnetostrictive properties, is devised and applied. The DSA-VAST finite elemtn software is emlpoyed to model the cylindrical, pre-cracked test specimen using both conventional solid elements and enriched twenty-noded solid fracture elements. Two load cases are investigated, namely one in which a mechanical load is applied to the specimen in the absence of a magnetic field, and a second case in which both a magnetic field and a mechanical load are applied to the specimen. In the absence of an applied magnetic field, the mode II fracture toughenss is found to be approximately 4.497 MPa√m, a value comparable to that reported for ceramic-like materials. On the other hand, in the presence of an applied magnetic field (simulated by an equivalent compressive prestress), the mode II fracture toughness is reduced to 2.768 MPa√m, a significant reduction from the 'zero-field' value. FE results indicate significant specimen bending and an appreciable mode III component to the fracture behavior, both of which are consistent with observed crack growth patterns in laboratory specimens.
A fuzzy finite element based approach is developed for modelling smart structures with vague or imprecise uncertainties. Fuzzy sets are used to represent the uncertainties present in the piezoelectric, mechanical, thermal, and physical properties of the smart structure. In order to facilitate efficient computation, a sensitivity analysis procedure is used to streamline the number of input fuzzy variables, and the vertex fuzzy analysis technique is then used to compute the possibility distributions of the responses of the smart structural system. The methodology has been developed within the framework of the SMARTCOM computational tool for the design/analysis of smart composite structures. The methodology developed is found to be accurate and computationally efficient for solution of practical problems.
KEYWORDS: Sensors, Actuators, Chemical elements, Smart structures, Active vibration control, Composites, Control systems, Modeling, Systems modeling, Algorithm development
In this paper, the integrated finite element methodology developed in our earlier work for designing active vibration control strategies in smart structures, is extended to compute the stresses and strains in the structure, due to combined thermal, mechanical and electrical excitations. A layered composite brick elements with linear strain-displacement and linear thermopiezoelectric constitutive relations is used to model the structure. The method, which has been encoded into a software called SMARTCOM provides a design and analysis capability that simultaneously accounts for the coupled thermopiezoelectric and control capabilities of the smart structural systems. Numerical examples are provided for structures with surface bonded piezoelectric sensors and actuators, under various types of mechanical, thermal and electrical load. Comparisons are made to other available solutions to verify the accuracy of the SMARTCOM simulations. The method provides accurate results and is seen as a valuable tool for the design and analysis of these smart structures.
KEYWORDS: Chemical elements, Composites, Smart structures, Control systems, Fuzzy logic, Optimization (mathematics), Systems modeling, Actuators, Integration, Computing systems
This paper presents a novel integrated formulation and robust computational tool that can be efficiently employed for the design and analysis of actively controlled smart composite structural systems. The modeling simulation capabilities account for the coupling between thermal, mechanical and electric fields within the framework of an integrated structure/control strategy. The paper also reports the formulation and implementation of an optimization capability for the design and tailoring of smart structural systems. Finally, probabilistic and fuzzy models for rationally and systematically accounting for the uncertainties in structural, control, material, and load parameters are presented. The capabilities are packaged in a comprehensive and user- friendly software system (SMARTCOM) that can be readily applied for cost-effective design or response characterization of actively controlled smart structures.
KEYWORDS: Sensors, Composites, Actuators, Distortion, Active vibration control, Smart structures, Control systems, Modeling, Thermal effects, Chemical elements
This paper presents an integrated finite element based computational methodology for analyzing smart composite structures with piezoelectric sensors and actuators. The method accounts for the coupling of the mechanical, electrical and thermal fields, which these structural systems will be subjected to in practical applications. 3D thermopiezoelectric composite finite elements are used to model the host structure and the piezoelectric sensors and actuators. The finite element equations are integrated with control algorithms based on the linear quadratic regulator, independent modal space control and the modified independent modal space control, to provide active vibration control capabilities. The capabilities have been incorporated into a computer program called SMARTCOM. Numerical examples illustrating the computation and/or control of deformations due to thermal excitations are presented and comparisons are made to other methods where possible. The present method provides accurate modeling of the smart structures and is seen as a convenient methodology, in that it permits modeling of the complex behavior of the smart structure in one integrated package.
KEYWORDS: Chemical elements, Composites, Sensors, Control systems, Actuators, Algorithm development, Structural design, Matrices, Optimization (mathematics), Active vibration control
This paper presents an integrated finite element-control methodology for the design/analysis of smart composite structures. The method forms part of an effort to develop an integrated computational tool that includes finite element modeling; control algorithms; and deterministic, fuzzy and probabilistic optimization and integrity assessment of the structures and control systems. The finite element analysis is based on a 20 node thermopiezoelectric composite element for modeling the composite structure with surface bonded piezoelectric sensors and actuators; and control is based on the linear quadratic regulator and the independent modal space control methods. The method has been implemented in a computer code called SMARTCOM. Several example problems have been used to verify various aspects of the formulations and the analysis results from the present study compare well against other numerical or experimental results. Being based on the finite element method, the present formation can be conveniently used for the analysis and design of smart composite structures with complex geometrical configurations and loadings.
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