Quantian Luo

Exact static solutions to piezoelectric smart beams including peel stresses: I: Theoretical formulation

This paper presents exact static solutions to smart beams with perfectly bonded or partially debonded piezoelectric (PZT) actuators and sensors including peel stresses. When a PZT patch is bonded on the surface of a beam, both shear and peel stresses exist in the adhesive between the PZT patch and the host beam. In Part I, non-dimensional differential governing equations for infinitesimal elements of the PZT patch and the host beam are formulated firstly, and then the ordinary differential equation (ODE) of the coupled shear and peel stresses are completely solved analytically. The exact solutions are applicable to smart beams with PZT actuators and sensors. When the PZT patches are used as actuators, the solutions give the formulations for the energy transferring shear and peel stresses in the adhesive actuated by the applied voltages, and for the actuated stress resultants and displacements in the host beam. When the PZT patches are used as sensors, the solutions give the shear and peel stresses in the adhesive caused by the loadings, and also the sensing electric charges. When PZT patches are not perfectly bonded to the host beam, i.e., partially debonded, the developed solutions can be tailored to the case of edge debondings, i.e., PZTs with the shortened length.

Exact dynamic solutions to piezoelectric smart beams including peel stresses I: Theory and application

This work presents exact dynamic solutions to piezoelectric (PZT) smart beams including peel stresses. The governing equations of partial differential forms are firstly derived for a PZT smart beam made of the identical adherends, and then general solutions of the governing equations are studied. The analytical solutions are applied to a cantilever beam with a partially bonded PZT patch to the fixed end. For the given boundary conditions, exact solutions of the steady state motions are obtained. Based on the exact solutions, frequency spectra, natural frequencies, normal mode shapes, harmonic responses of the shear and peel stresses are discussed for the PZT actuator. The details of the numerical results and sensing electric charges will be presented in Part II of this work. The exact dynamic solutions can be directly applied to a PZT bimorph bender. To compare with the classic shear lag model whose numerical demonstrations will be given in Part II, the related equations are also derived for the shear lag rod model and shear lag beam model.

Constitutive Modeling of Photostrictive Materials and Design Optimization of Microcantilevers

This article presents constitutive models for photo-induced strains in photostrictive materials and an optimal design of microcantilevers driven by light illumination. Behaviors of photo-induced strains in semiconductors and polymeric materials are reviewed first, and then new phenomenological constitutive models are developed that depict two distinctive features of photo-induced strain profile: (a) dependence on variation of light intensity which decreases with the depth measured from the illuminated surface due to light attenuation and energy absorption; and (b) anisotropy or dependence on direction of light polarization. On the basis of the constitutive modeling of photo-induced strain in wafers, design optimization of microcantilevers is then investigated for both geometrically linear and non-linear deformations.This article presents constitutive models for photo-induced strains in photostrictive materials and an optimal design of microcantilevers driven by light illumination. Behaviors of photo-induced strains in semiconductors and polymeric materials are reviewed first, and then new phenomenological constitutive models are developed that depict two distinctive features of photo-induced strain profile: (a) dependence on variation of light intensity which decreases with the depth measured from the illuminated surface due to light attenuation and energy absorption; and (b) anisotropy or dependence on direction of light polarization. On the basis of the constitutive modeling of photo-induced strain in wafers, design optimization of microcantilevers is then investigated for both geometrically linear and non-linear deformations.

A New ENF Test Specimen for the Mode II Delamination Toughness Testing of Stitched Woven CFRP Laminates

This paper presents an experimental and numerical investigation on the effects of stitching distribution on the interlaminar fracture toughness of carbon fiber reinforced polymers (CFRPs) using an end notch flexure (ENF) specimen. To avoid premature failure in bending, reinforcing tabs were bonded to either side of the ENF specimens to create a tabbed ENF (TENF) specimen. The effect of stitch distribution on mode II delamination toughness is investigated by considering several stitch distribution patterns. The experimental results indicate that the mode II delamination toughness of stitched TENF specimens can be effectively measured and that stitch distribution does not play a significant role in improving the steady-state mode II delamination toughness of stitched CFRPs. Numerical results are also obtained using both MSC/NASTRAN and an in-house software for the tested specimens. A reasonable correlation exists between the numerical and experimental results.

Failure of stitched composite L-joints under tensile loading: experiment and simulation

This article presents an experimental and numerical investigation into the influence of transverse stitching on failure of composite L-joints under tensile loading. Six unstitched and six stitched L-joint specimens were manufactured and tested under quasi static tensile loading. It was observed that the average measured failure load and the associated crosshead displacement for the stitched L-joint specimens are increased significantly compared to those for the unstitched specimens. Full 3D and 2D plane strain finite element (FE) models were developed to simulate both stitched and unstitched L-joints with an implemented stitch element. The load—displacement curves and results predicted via FE models compare favorably with the experimental results. For the stitched L-joints, it is shown that the observed delamination in the elbow region of the flange can be modeled by using a softening model for epoxy layer.

Adaptive pressure-controlled cellular structures for shape morphing I: design and analysis

This work investigates adaptive bio-inspired pressure cellular structures for shape morphing. Optimum designs for cellular structures with void and pressure cells are proposed and then structural analyses are conducted. In the present design, a unit cell is comprised of straight and curved walls. When compressed air is pumped into a pressure cell, the curved walls deform in bending due to the pressure difference in two adjacent cells that leads to overall structural deformation in extension. One-dimensional actuation strain up to 35% can be theoretically achieved. In part I, we present basic design concepts and cellular mechanics. Unlike conventional structural analysis for cellular structures, a statically indeterminate unit cell is considered and novel analytical formulations are derived for the present pressurized cellular structures in linear and nonlinear analyses. In part II, we will present experimental testing and finite element analysis to demonstrate the feasibility of the present pressurized cellular actuators for morphing wings and to validate the present cellular mechanics formulations.

Exact static solutions to piezoelectric smart beams including peel stresses. II. Numerical results, comparison and discussion

Abstract This part presents the numerical results, comparisons and discussion for the exact static solutions of smart beams with piezoelectric (PZT) actuators and sensors including peel stresses presented in Part I. (International Journal of Solids and Structures, 39, 4677–4695) The actuated stress distributions in the adhesive and the adhesive edge stresses varying with the thickness ratios are firstly obtained and presented. The actuated internal stress resultants and displacements in the host beam are then calculated and compared with those predicted by using the shear lag model. The stresses in the adhesive caused by an applied axial force, bending moment and shear force are calculated, and then used to compute the sensing electric charges for comparison with those predicted using the shear lag model. The numerical results are given for the smart beam with (a) one bonded PZT and (b) two symmetrically bonded PZTs, with a comparison to those predicted using the shear lag model. Novel, simple and more accurate formulas for the equivalent force and bending moment induced by applied electric field are also derived for the host beam with one PZT or two symmetrically bonded PZTs. The symmetric shear stress and the anti-symmetric peel stress components caused by a shear force are discussed. In addition, in the case of PZT edge debonding, the stress redistribution in the adhesive and the self-arresting mechanism are also investigated.

Multifunctional behaviors of an indium tin oxide/PbLa(ZrTi)O3/indium tin oxide wafer illuminated by ultraviolet light

This article presents multifunctional behaviors of a Pb0.97La0.03(Zr0.52Ti0.48)O3 (3/52/48) wafer subjected to ultraviolet light illumination with a focus on its photoresistive effects. When this PLZT wafer that is spurted with indium tin oxide electrodes and then polarized through thickness is illuminated by ultraviolet light, its resistance increases rather than decreases as observed in conventional photoresistors made of semiconductors. Giant negative voltage and resistance are detected when light is switched off. The bending deformation caused by the photovoltaic and converse piezoelectric effects is examined and the photoinduced electrical field strength is further investigated. The electrical fields in light on–off states are studied. Hysteresis and memristive features of the indium tin oxide/PbLa(ZrTi)O3/indium tin oxide (ITO/PLZT/ITO) sample under repetitive light on–off operations are investigated.

3D Model of Coupled Multi-physics Fields for PLZT Ceramics and Its Applications to Photostrictive Plates

This article investigates an extended 3D model for coupled opto-electro-thermo-mechanical fields in PbLaZrTi (PLZT) ceramics by incorporating the photovoltaic, optothermic, and pyroelectric effects into the existing thermopiezoelectic model. The 3D model is then used to establish novel governing equations for 0-3 polarized orthotropic PLZT plates. Actuating and sensing behaviors of 0-3 polarized PLZT plates subjected to light illumination and mechanical loading are then studied. Stress analysis is conducted for a 0-3 polarized PLZT plate with free boundary conditions. Analytical solution for a simply supported photostrictive plate partially subjected to light illumination is derived. Numerical results for free and simply supported photostrictive plates illuminated by light are calculated using the present formulations and finite element analysis.

Calculation of Energy Release Rates for Cohesive and Interlaminar Delamination Based on the Classical Beam-adhesive Model

This article presents analytical formulas for determining mode I and II energy release rates for two cases: (a) cohesive fracture of adhesive joints and; (b) interlaminar delamination of layered beams. The formulas are firstly derived for calculating energy release rates GI and GII for a crack propagating in adhesive layer from one crack tip by using a classical beam-adhesive model. Then novel and simple closed-form formulas of G I and GII for an interface crack in layered beams are obtained by letting the adhesive thickness approach zero. In the present formulas, the effects of the asymmetry and each force component are clearly identified.This article presents analytical formulas for determining mode I and II energy release rates for two cases: (a) cohesive fracture of adhesive joints and; (b) interlaminar delamination of layered beams. The formulas are firstly derived for calculating energy release rates GI and GII for a crack propagating in adhesive layer from one crack tip by using a classical beam-adhesive model. Then novel and simple closed-form formulas of G I and GII for an interface crack in layered beams are obtained by letting the adhesive thickness approach zero. In the present formulas, the effects of the asymmetry and each force component are clearly identified.