Strain Transfer Mechanism Research Articles

The Effect of Adhesive Layers on the Dynamic Behavior of Surface-bonded Piezoelectric Sensors with Debonding

The behavior of a piezoelectric sensor is strongly affected by the bonding condition along the interface between the sensor and the host structure. This article presents an analytical study of the effect of the mechanical and geometrical properties of the adhesive layer on the coupled dynamic electromechanical behavior of a thin piezoceramic sensor bonded to an elastic medium. A sensor model with an imperfect adhesive bonding layer is proposed to simulate the two dimensional electromechanical behavior of the integrated system. The analytical solution of the problem is provided by solving the resulting integral equations in terms of the interfacial stress. Numerical simulation is conducted to study the effect of the bonding layer upon the dynamic response of the sensor under different loading frequencies. The interfacial debonding and its effect on the interlaminar strain and stress transfer mechanisms are discussed in detail.

Nonlinear finite element analysis of effective CFRP bonding length and strain distribution along concrete-CFRP interface

CFRP has been widely used for strengthening reinforced concrete members in last decade. The strain transfer mechanism from concrete face to CFRP is a key factor for rigidity, ductility, energy dissipation and failure modes of concrete members. For these reasons, determination of the effective CFRP bonding length is the most crucial step to achieve effective and economical strengthening. In this paper, generalizations are made on effective bonding length by increasing the amount of test data. For this purpose, ANSYS software is employed, and an experimentally verified nonlinear finite element model is prepared. Special contact elements are utilized along the concrete-CFRP strip interface for investigating stress distribution, load-displacement behavior, and effective bonding length. Then results are compared with the experimental results. The finite element model found consistent results with the experimental findings.

The dynamic behaviour of surface-bonded piezoelectric actuators with debonded adhesive layers

The performance of smart structures depends on the electromechanical behaviour of piezoelectric actuators and the bonding condition along the interface, which connects the actuators and the host structures. This paper provides a theoretical study of the effect of partially debonded adhesive layers on the coupled electromechanical behaviour of piezoelectric actuators subjected to high-frequency electric loads. An actuator model with an imperfect adhesive bonding layer, which undergoes a shear deformation, is proposed to simulate the two-dimensional electromechanical behaviour of the integrated system. An analytical solution of the problem is provided by solving the resulting integral equations in terms of the interfacial stress. Numerical simulation is conducted to study the effect of the bonding layer upon the actuation process. The effect of interfacial debonding on the dynamic response of the layered structure and on the interlaminar strain and stress transfer mechanisms is discussed.

Structural health monitoring with fiber optic sensors

Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity and heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors.

Practical Implementation of Optical Fiber Sensors in Civil Structural Health Monitoring

Implementation of successful civil structural health monitoring strategies requires selection and placement of sensors suitable for measurement of key parameters that influence the performance and health of the structural system. Optical fiber sensors have been successfully implemented in aeronautics, mechanical systems, and medical applications. Civil structures pose further challenges in monitoring mainly due to their large dimensions, diversity as well as heterogeneity of materials involved, and hostile construction environment. This article provides a summary of basic principles pertaining to practical health monitoring of civil engineering structures with optical fiber sensors. The issues discussed include basic sensor principles, strain transfer mechanism, sensor packaging, sensor placement in construction environment, and reliability and survivability of the sensors.

Embedded fibre Bragg grating sensors for non-uniform strain sensing in composite structures

A methodology for evaluating the response of embedded fibre Bragg grating (FBG) sensors in composite structures based on the strain in a host material is introduced. In applications of embedded FBG sensors as strain sensing devices, it is generally assumed that the strain experienced in a fibre core is the same as the one measured in the host material. The FBG sensor is usually calibrated by a strain gauge through a tensile test, centred on obtaining the relationship between the surface strain in the host material and the corresponding Bragg wavelength shift obtained from the FBG sensor. However, such a calibration result can only be valid for uniform strain measurement. When the strain distribution along a grating is non-uniform, average strain measured by the strain gauge cannot truly reflect the in-fibre strain of the FBG sensor. Indeed, the peak in the reflection spectrum becomes broad, may even split into multiple peaks, in sharp contrast with a single sharp peak found in the case of the uniform strain measurement. In this paper, a strain transfer mechanism of optical fibre embedded composite structure is employed to estimate the non-uniform strain distribution in the fibre core. This in-fibre strain distribution is then utilized to simulate the response of the FBG sensor based on a transfer-matrix formulation. Validation of the proposed method is preceded by comparing the reflection spectra obtained from the simulations with those obtained from experiments.

Adhesive Layer Effects in Surface-Mounted Piezoelectric Actuators

The role of the adhesive layers in active panels with surface-mounted (bonded) piezoelectric layers is studied. The investigation focuses on the strain transfer mechanism between the active layers and the host structure, the stress concentrations involved, and the influence of the geometrical and mechanical properties of the adhesive layers on the static response of the panel. The analysis is based on the High-Order approach and uses 2D elasticity to model the adhesive layers. The mathematical formulation is derived using variational principles, compatibility requirements, and the piezoelectric constitutive equations. Confirmation of the analytical model is achieved through an experimental study that reveals good agreement between the theoretical predictions and the behavior of the active structure. Numerical results are presented for a typical piezoelectric active panel and compared to detailed 2D finite element analysis. The results reveal the high-order effects and the stress concentrations in the transition zone near the edge of the panel and indicate that a careful selection of the adhesive's properties can improve the behavior of the structure and reduce the severity of the stress concentrations involved. The paper concludes with a summary and recommendations for the analysis, design, and use of smart structures with bonded actuators.