Active control in flexible plates with piezoelectric actuators using linear matrix inequalities

The study of algorithms for active vibrations control in flexible structures became an area of enormous interest, mainly due to the countless demands of an optimal performance of mechanical systems as aircraft, aerospace and automotive structures. Smart structures, formed by a structure base, coupled with piezoelectric actuators and sensor are capable to guarantee the conditions demanded through the application of several types of controllers. The actuator/sensor materials are composed by piezoelectric ceramic (PZT - Lead Zirconate Titanate), commonly used as distributed actuators, and piezoelectric plastic films (PVDF-PolyVinyliDeno Floride), highly indicated for distributed sensors. The design process of such system encompasses three main phases: structural design; optimal placement of sensor/actuator (PVDF and PZT); and controller design. Consequently, for optimal design purposes, the structure, the sensor/actuator placement and the controller have to be considered simultaneously. This article addresses the optimal placement of actuators and sensors for design of controller for vibration attenuation in a flexible plate. Techniques involving linear matrix inequalities (LMI) to solve the Riccati's equation are used. The controller's gain is calculated using the linear quadratic regulator (LQR). The major advantage of LMI design is to enable specifications such as stability degree requirements, decay rate, input force limitation in the actuators and output peak bounder. It is also possible to assume that the model parameters involve uncertainties. LMI is a very useful tool for problems with constraints, where the parameters vary in a range of values. Once formulated in terms of LMI a problem can be solved efficiently by convex optimization algorithms.

Morphotropic phase boundary and electrical properties of 1-x[Bi 0.5Na0.5]TiO3 -xBa[Zr0.25Ti 0.75]O3 lead-free piezoelectric ceramics

Lead-free solid solutions (1-x)Bi0.5Na0.5TiO 3 (BNT)-xBaZr0.25Ti0.75O3 (BZT) (x=0, 0.01, 0.03, 0.05, and 0.07) were prepared by the solid state reaction method. X-ray diffraction (XRD) and Rietveld refinement analyses of 1-x(BNT)-x(BZT) solid solution ceramic were employed to study the structure of these systems. A morphotropic phase boundary (MPB) between rhombohedral and cubic structures occured at the composition x=0.05. Raman spectroscopy exhibited a splitting of the (TO3) mode at x=0.05 and confirmed the presence of MPB region. Scanning electron microcopy (SEM) images showed a change in the grain shape with the increase of BZT into the BNT matrix lattice. The temperature dependent dielectric study showed a gradual increase in dielectric constant up to x=0.05 and then decrease with further increase in BZT content. Maximum coercive field, remanent polarization and high piezoelectric constant were observed at x=0.05. Both the structural and electrical properties show that the solid solution has an MPB around x=0.05. © 2012 Elsevier Ltd and Techna Group S.r.l.

Active modal damping control of a smart truss structure using a self-organizing fuzzy controller

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Análise e implementação de técnicas de medição de microvibrações utilizando interferometria óptica e processadores digitais de sinais

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Effect of Metal-Ceramic or All-Ceramic Superstructure Materials on Stress Distribution in a Single Implant-Supported Prosthesis: Three-Dimensional Finite Element Analysis

Purpose: This three-dimensional finite element analysis study evaluated the effect of different material combinations on stress distribution within metal-ceramic and all-ceramic single implant-supported prostheses. Materials and Methods: Three-dimensional finite element models reproducing a segment of the maxilla with a missing left first premolar were created. Five groups were established to represent different superstructure materials: GP, porcelain fused to gold alloy; GR, modified composite resin fused to gold alloy; TP, porcelain fused to titanium; TR, modified composite resin fused to titanium; and ZP, porcelain fused to zirconia. A 100-N vertical force was applied to the contact points of the crowns. All models were fixed in the superior region of bone tissue and in the mesial and distal faces of the maxilla section. Stress maps were generated by processing with finite element software. Results: Stress distribution and stress values of supporting bone were similar for the GP, GR, TP, and ZP models (1,574.3 MPa, 1,574.3 MPa, 1,574.3 MPa, and 1,574.2 MPa, respectively) and different for the TR model (1,838.3 MPa). The ZP model transferred less stress to the retention screw (785 MPa) than the other groups (939 MPa for GP, 961 MPa for GR, 1,010 MPa for TP, and 1,037 MPa for TR). Conclusion: The use of different materials to fabricate a superstructure for a single implant-supported prosthesis did not affect the stress distribution in the supporting bone. The retention screw received less stress when a combination of porcelain and zirconia was used. Int J Oral Maxillofac Implants 2011;26:1202-1209

Mechanical behavior of ceramic veneer in zirconia-based restorations: a 3-dimensional finite element analysis using microcomputed tomography data

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

In Vitro Study of Fracture Load and Fracture Pattern of Ceramic Crowns: A Finite Element and Fractography Analysis

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Stress distribution in ceramic restorations over natural tooth using finite element analysis. lithium disilicate x aluminum oxide material

Background: Data on stress distribution in tooth-restoration interface with different ceramic restorative materials are limited. The aim of this chapter was to assess the stress distribution in the interface of ceramic restorations with laminate veneer or full-coverage crown with two different materials (lithium dissilicate and densely sintered aluminum oxide) under different loading areas through finite element analysis. Materials and Methods: Six two-dimensional finite element models were fabricated with different restorations on natural tooth: laminate veneer (IPS Empress, IPS Empress Esthetic and Procera AllCeram) or full-coverage crown (IPS e.max Press and Procera AllCeram). Two different loading areas (L) (50N) were also determined: palatal surface at 45° in relation to the long axis of tooth (L1) and perpendicular to the incisal edge (L2). A model with higid natural tooth was used as control. von Mises equivalent stress (σ vM) and maximum principal stress (σ max) were obtained on Ansys software. Results: The presence of ceramic restoration increased σ vM and σ max in the adhesive interface, mainly for the aluminum oxide (Procera AllCeram system) restorations. The full-coverage crowns generated higher stress in the adhesive interface under L1 while the same result was observed for the laminate veneers under L2. Conclusions: Lithium dissilicate and densely sintered aluminum oxide restorations exhibit different behavior due to different mechanical properties and loading conditions. © 2011 Nova Science Publishers, Inc.

INFLUENCE OF THE VENEER-FRAMEWORK INTERFACE ON THE MECHANICAL BEHAVIOR OF CERAMIC VENEERS: A NONLINEAR FINITE ELEMENT ANALYSIS

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Survival rate, load to fracture, and finite element analysis of incisors and canines restored with ceramic veneers having varied preparation design

Purpose: To evaluate the survival rate, success rate, load to fracture, and finite element analysis (FEA) of maxillary central incisors and canines restored using ceramic veneers and varying preparation designs.Methods and Materials: Thirty human maxillary central incisors and 30 canines were allocated to the following four groups (n=15) based on the preparation design and type of tooth: Gr1 = central incisor with a conservative preparation; Gr2 = central incisor with a conventional preparation with palatal chamfer; Gr3 = canine with a conservative preparation; Gr4 = canine with a conventional preparation with palatal chamfer. Ceramic veneers (lithium disilicate) were fabricated and adhesively cemented (Variolink Veneer). The specimens were subjected to 4 x 106 mechanical cycles and evaluated at every 500,000 cycles to detect failures. Specimens that survived were subjected to a load to fracture test. Bidimensional models were modeled (Rhinoceros 4.0) and evaluated (MSC.Patrans 2005r2 and MSC.Marc 2005r2) on the basis of their maximum principal stress (MPS) values. Survival rate values were analyzed using the Kaplan-Meier test (alpha = 0.05) and load to fracture values were analyzed using the Student t-test (alpha = 0.05).Results: All groups showed 100% survival rates. The Student t-test did not show any difference between the groups for load to fracture. FEA showed higher MPS values in the specimens restored using veneers with conventional preparation design with palatal chamfer.Conclusion: Preparation design did not affect the fracture load of canines and central incisors, but the veneers with conventional preparation design with palatal chamfer exhibited a tendency to generate higher MPS values.

Vibrational spectroscopy applied to the study of archeological ceramic artifacts from Guarani culture in Brazil

An archeological artifact can be seen as a chronological element, which helps to determine the age of certain society and to understand the thinking, values and the way of life of this society. Thus, the classification of archeological artifacts is one of the approaches used to study the cultural system of antique societies trying to reconstruct their history. The "Centro de Museologia, Antropologia e Argueologia (CEMAARQ)" of the "Unesp Univ Estadual Paulista" in Presidente Prudente, São Paulo state, Brazil, develops projects within this context (identification and preservation). This is the case of the archeological site named "Lagoa São Paulo-02" discovered in 1993 at the margins of the Parana river in the region of Presidente Epitacio city, São Paulo state, Brazil. This site has ceramic fragments of different shapes and sizes that have a strong influence of traces of the Guarani culture, which is one of the Brazilian native populations. These samples were basically characterized via micro-Raman scattering and Fourier transform infrared absorption (FTIR) spectroscopies. The main objective was to identify the pigments used in the manufacture of the ceramic artifacts and to analyze the composition of the ceramic body to understand how the artifacts were made. Three pigments were found: red, black and white. For the red pigment were identified characteristic bands of hematite, an iron oxide found in the red rocks of the river banks that were eroded by water. The black pigment, probably, is due to the use of vegetal charcoal, which is found in nature as the product of burning organic material such as wood. For the white pigment, the FTIR spectra suggested the use of kaolin, either in the ceramic body or in the proper white pigment, due to the presence of the characteristic bands of the kaolinite. Complementary, the additives applied as anti-plastics were identified as charcoal and quartz, being the latter found in the rocks present in the archeological site. (C) 2010 Elsevier B.V. All rights reserved.

Structural phase transitions of PbZr0.52Ti0.48O3 ceramic: An infrared spectroscopy study

The recent discovery of a ferroelectric monoclinic phase in the PbZr1-xTixO3 (PZT) system attained the attention of several researchers due to the possibility of understanding the relationships between structural features and piezoelectric properties. The nature of the monoclinic phase in some PZT compositions remains controversial and unclear. In this work, structural phase transitions of PbZr0.52Ti0.48O3 ceramic were investigated by infrared spectroscopy as a function of temperature. Studies were centered on nu(1)-stretching modes and corresponding half width Wi as a function of temperature. The occurrence of the anomalies in the infrared spectra as a function of temperature suggests the following monoclinic ( LT) -> monoclinic ( HT) -> tetragonal phase transition were observed at 183 K and at 263 K.

Piezoelectric effect in composite polyurethane - Ferroelectric ceramics

Flexible and free-standing films of piezoelectric composites made up of lead zirconate titanate (PZT) ceramic powder dispersed in a castor oil-based polyurethane (PU) matrix were obtained by spin coating and characterised as materials for sensor applications. The piezoelectric coefficients d(31) and d(33) were measured with the usual technique. The piezoelectric charge constant d(33) yields values up to less than or equal to 24 pC/N, even at lower PZT content (33 vol%). Some desirable properties like piezoelectricity, flexibility and good mechanical resistance show this new material to be a good alternative for use as sensors and actuators.

Influence of Cusp Inclination on Stress Distribution in Implant-Supported Prostheses. A Three-Dimensional Finite Element Analysis

Purpose: The aim of this study was to assess the influence of cusp inclination on stress distribution in implant-supported prostheses by 3D finite element method.Materials and Methods: Three-dimensional models were created to simulate a mandibular bone section with an implant (3.75 mm diameter x 10 mm length) and crown by means of a 3D scanner and 3D CAD software. A screw-retained single crown was simulated using three cusp inclinations (10 degrees, 20 degrees, 30 degrees). The 3D models (model 10d, model 20d, and model 30d) were transferred to the finite element program NeiNastran 9.0 to generate a mesh and perform the stress analysis. An oblique load of 200 N was applied on the internal vestibular face of the metal ceramic crown.Results: The results were visualized by means of von Mises stress maps. Maximum stress concentration was located at the point of application. The implant showed higher stress values in model 30d (160.68 MPa). Cortical bone showed higher stress values in model 10d (28.23 MPa).Conclusion: Stresses on the implant and implant/abutment interface increased with increasing cusp inclination, and stresses on the cortical bone decreased with increasing cusp inclination.

Passivity Versus Unilateral Angular Misfit: Evaluation of Stress Distribution on Implant-Supported Single Crowns: Three-Dimensional Finite Element Analysis

The aim of this study was to evaluate the effect of unilateral angular misfit of 100 Km on stress distribution of implant-supported single crowns with ceramic veneering and gold framework by three-dimensional finite element analysis. Two three-dimensional models representing a maxillary section of premolar region were constructed: group 1 (control)-crown completely adapted to the implant and group 2-crown with unilateral angular misfit of 100 Km. A vertical force of 100 N was applied on 2 centric points of the crown. The von Mises stress was used as an analysis criterion. The stress values and distribution in the main maps (204.4 MPa for group 1 and 205.0 MPa for group 2) and in the other structures (aesthetic veneering, framework, retention screw, implant, and bone tissue) were similar for both groups. The highest stress values were observed between the first and second threads of the retention screw. Considering the bone tissue, the highest stress values were exhibited in the peri-implant cortical bone. The unilateral angular misfit of 100 Km did not influence the stress distribution on the implant-supported prosthesis under static loading.