Electromechanical Impedance Response of a Cracked Timoshenko Beam

Typically, the Electromechanical Impedance (EMI) technique does not use an analytical model for basic damage identification. However, an accurate model is necessary for getting more information about any damage. In this paper, an EMI model is presented for predicting the electromechanical impedance of a cracked beam structure quantitatively. A coupled system of a cracked Timoshenko beam with a pair of PZT patches bonded on the top and bottom surfaces has been considered, where the bonding layers are assumed as a Kelvin-Voigt material. The shear lag model is introduced to describe the load transfer between the PZT patches and the beam structure. The beam crack is simulated as a massless torsional spring; the dynamic equations of the coupled system are derived, which include the crack information and the inertial forces of both PZT patches and adhesive layers. According to the boundary conditions and continuity conditions, the analytical expression of the admittance of PZT patch is obtained. In the case study, the influences of crack and the inertial forces of PZT patches are analyzed. The results show that: (1) the inertial forces affects significantly in high frequency band; and (2) the use of appropriate frequency range can improve the accuracy of damage identification

Fibre optic sensors for load-displacement measurements and comparisons to piezo sensor based electromechanical admittance signatures

Structural health monitoring techniques using smart materials are on rise to meet the ever ending demand due to increased construction and manufacturing activities worldwide. The civil-structural components such as slabs, beams and columns and aero-components such as wings are constantly subjected to some or the other forms of external loading. This article thus focuses on condition monitoring due to loading/unloading cycle for a simply supported aluminum beam using multiple smart materials. On the specimen, fibre optic polarimetric sensor (FOPS) and fibre Bragg grating (FBG) sensors were glued. Piezoelectric wafer active sensor (PWAS) was also bonded at the centre of the specimen. FOPS and FBG provided the global and local strain measurements respectively whereas, PWAS predicted boundary condition variations by electromechanical admittance signatures. Thus these multiple smart materials together successfully assessed the condition of structure for loading and unloading tests.Published versio

Evidence Based Uncertainty Models and Particles Swarm Optimization for Multiobjective Optimization of Engineering Systems

The present work develops several methodologies for solving engineering analysis and design problems involving uncertainties and evidences from multiple sources. The influence of uncertainties on the safety/failure of the system and on the warranty costs (to the manufacturer) are also investigated. Both single and multiple objective optimization problems are considered. A methodology is developed to combine the evidences available from single or multiple sources in the presence (or absence) of credibility information of the sources using modified Dempster Shafer Theory (DST) and Fuzzy Theory in the design of uncertain engineering systems. To optimally design a system, multiple objectives, such as to maximize the belief for the overall safety of the system, minimize the deflection, maximize the natural frequency and minimize the weight of an engineering structure under both deterministic and uncertain parameters, and subjected to multiple constraints are considered. We also study the various combination rules like Dempster\u27s rule, Yager\u27s rule, Inagaki\u27s extreme rule, Zhang\u27s center combination rule and Murphy\u27s average combination rule for combining evidences from multiple sources. These rules are compared and a selection procedure was developed to assist the analyst in selecting the most suitable combination rule to combine various evidences obtained from multiple sources based on the nature of evidence sets. A weighted Dempster Shafer theory for interval-valued data (WDSTI) and weighted fuzzy theory for intervals (WFTI) were proposed for combining evidence when different credibilities are associated with the various sources of evidence. For solving optimization problems which cannot be solved using traditional gradient-based methods (such as those involving nonconvex functions and discontinuities), a modified Particle Swarm Optimization (PSO) algorithm is developed to include dynamic maximum velocity function and bounce method to solve both deterministic multi-objective problems and uncertain multi-objective problems (vertex method is used in addition to the modified PSO algorithm for uncertain parameters). A modified game theory approach (MGT) is coupled with the modified PSO algorithm to solve multi-objective optimization problems. In case of problems with multiple evidences, belief is calculated for a safe design (satisfying all constraints) using the vertex method and the modified PSO algorithm is used to solve the multi-objective optimization problems. The multiobjective problem related to the design of a composite laminate simply supported beam with center load is also considered to minimize the weight and maximize buckling load using modified game theory. A comparison of different warranty policies for both repairable and non repairable products and an automobile warranty optimization problem is considered to minimize the total warranty cost of the automobile with a constraint on the total failure probability of the system. To illustrate the methodologies presented in this work, several numerical design examples are solved. We finally present the conclusions along with a brief discussion of the future scope of the research

Characterization of smart PZT transducer and admittance signatures using PZT-structure interaction models for structural health monitoring

The monitoring of existing aero, civil and mechanical (ACM) structures has become a regular feature after the world witnessed the various recent deadly failures and damages, due to natural calamities or continuous usage of structures causing wear and tear. The last few years have witnessed rapid development in the areas of nondestructive evaluation (NDE) based Structural health monitoring (SHM) by the emergence of the electromechanical impedance (EMI) technique. This technique employs piezoelectric-ceramic (PZT) transducers for the prediction of structural response known as electromechanical (EM) admittance. Engineering structures can be classified into two categories based on their stiffness, those which are more stiffer and those which are less stiff than the PZT material. Surface bonded and Embedded PZT transducers are more efficient when they are more stiffer and less stiff than the host structure respectively. Both types of PZT transducers are important in the EMI based NDE of the two categories of engineering structures. However, surface bonded PZT transducers have seen more prominent applications in the recent past in SHM. This research developed both surface bonded and embedded PZT- structure interaction models for SHM of existing and future ACM structures.Doctor of Philosophy (CEE

Practical implementation of piezo-impedance sensors in monitoring of excavation support structures

In the last decade, electromechanical impedance (EMI)-based monitoring technique using piezoceramic (PZT) sensors have been successfully implemented in health monitoring of lab-sized engineering structures. However, its implementation in real life application, such as monitoring underground support structures, has not been done before. In general, the EMI technique utilizes the unique EMI signature where any changes in the signature during the period of monitoring indicate possible damage in the host structure. This paper presents a part of monitoring results of the soil excavation carried out for the construction of new mass road transport (MRT) station in the southern part of Singapore using a PZT-based EMI technique. The MRT site consists of typical clayed soil of varying properties along the depth of excavation. To prevent the soil collapse during excavation, temporary support structures were laid with suitable monitoring systems. The paper presents the results obtained from the PZT sensors and the comparisons with conventional measurement devices. However, there were no damages reported in the structure, and hence the PZT sensors, which were initially aimed to capture possible damages, were used later to capture load variations on the struts due to the surrounding soil