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L. Tong - One of the best experts on this subject based on the ideXlab platform.
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An adhesively laminated plate element for PZT smart plates
Computational Mechanics, 2004Co-Authors: Q. Luo, L. TongAbstract:An adhesively laminated element taking into consideration Peel Stress is developed for a piezoelectric smart plate. In this novel finite element analysis formulation, a four node piezoelectric element is firstly derived, and an adhesive element of finite thickness with both shear and Peel stiffness is sandwiched between two collocated four node plate elements to form an adhesively laminated element for a piezoelectric smart plate. In this framework of finite element analysis, because the displacement filed in this adhesively laminated element is continuous and a plate element is derived based on the Reissner–Mindlin plate theory, and thus it can be accurately applied to a thin or moderately thick host plate with bonded or debonded piezoelectric actuators and sensors. The formulation is performed for an isotropic host plate and a fiber reinforced laminate plate. Numerical results are presented to compare with those of the exact solutions for smart beams, and validate with the experimental results of the isotropic and composite host plates available in the literature. Using the present finite element analysis formulation, energy transfer Stresses in the adhesive and equivalent forces induced in the host plate are investigated. The present formulation is demonstrated to allow debondings of piezoelectric patches and the debonding detection.
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An accurate laminated element for piezoelectric smart beams including Peel Stress
Computational Mechanics, 2004Co-Authors: Q. Luo, L. TongAbstract:This paper presents a laminated element for piezoelectric (PZT) smart beams in taking into account Peel Stresses. In the finite element analysis (FEA) formulation, a coupled electrical and mechanical beam element is used to model PZT patches, and a conventional structural element is used to model a host beam. A continuous adhesive element with shear and Peel stiffness is derived to form a PZT laminated element. For a smart beam with a partially bonded PZT patch or distributed PZTs, the laminated element is applied to an area of the host beam with PZTs and the conventional element is used in the host beam where no PZT is bonded. A novel PZT laminated element is firstly derived based on the Timoshenko beam theory, in which the FEA formulation based on the Euler-Bernoulli beam theory can be considered as its special case. FEA numerical results of static and dynamic analyses based on the Euler-Bernoulli beam theory are compared with the exact static and dynamic solutions to validate the present FEA formulation. The present FEA framework based on the Timoshenko beam theory is then used to investigate the effects of PZT debondings on static behaviors and dynamic responses, and an original and effective procedure for detecting debondings in PZT actuators or sensors is proposed.
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Holographic measurement of the relative out-of-plane surface displacement in an adhesively bonded doubler
Journal of Adhesion Science and Technology, 1997Co-Authors: L. Tong, W.z.l. ZhuangAbstract:It is relatively easy to demonstrate analytically the high gradient of Peel Stresses in an adhesive layer near the overlap ends of an adhesively bonded lap joint. However, experimental validation of such a high Peel Stress gradient becomes quite difficult. One of the experimental methods is to measure the relative normal displacement between the two adherends bonded together by an adhesive layer and then to calculate the Stresses in the adhesive layer. In this study, a simple doubler specimen was used to obtain an accurate measurement of the relative out-of-plane surface displacement using a holographic interferometry technique. Unlike a full doubler specimen, the global rotation that occurred in the overlap was removed and the effects of the end misalignment were therefore reduced. It is shown that there is a good correlation between the relative out-of-plane surface displacement measured and that predicted using finite element analysis of the misaligned specimens.
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Analysis of adhesive bonded composite lap joints with transverse stitching
Applied Composite Materials, 1996Co-Authors: L. Tong, L. K. JainAbstract:The effect of transverse stitching on the Stresses in the adhesive is investigated using an adhesive sandwich model with nonlinear adhesive properties and a transverse stitching model for adhesive bonded composite single-lap and double-lap joints. Numerical results indicate that, among all stitching parameters, thread pretension and stitch density have significant effect on the Peel Stresses in the adhesive; increase in the thread pretension and the stitch density leads to a decrease in Peel Stress in the adhesive, while an increase in other parameters generally results in a negligible reduction in Peel Stress. The effect of stitching was found to be negligible on the shear Stresses in the adhesive. Thus it is concluded that stitching is effective for the joints where Peel Stresses are critical and ineffective for those where shear Stresses are critical.
Q. Luo - One of the best experts on this subject based on the ideXlab platform.
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An adhesively laminated plate element for PZT smart plates
Computational Mechanics, 2004Co-Authors: Q. Luo, L. TongAbstract:An adhesively laminated element taking into consideration Peel Stress is developed for a piezoelectric smart plate. In this novel finite element analysis formulation, a four node piezoelectric element is firstly derived, and an adhesive element of finite thickness with both shear and Peel stiffness is sandwiched between two collocated four node plate elements to form an adhesively laminated element for a piezoelectric smart plate. In this framework of finite element analysis, because the displacement filed in this adhesively laminated element is continuous and a plate element is derived based on the Reissner–Mindlin plate theory, and thus it can be accurately applied to a thin or moderately thick host plate with bonded or debonded piezoelectric actuators and sensors. The formulation is performed for an isotropic host plate and a fiber reinforced laminate plate. Numerical results are presented to compare with those of the exact solutions for smart beams, and validate with the experimental results of the isotropic and composite host plates available in the literature. Using the present finite element analysis formulation, energy transfer Stresses in the adhesive and equivalent forces induced in the host plate are investigated. The present formulation is demonstrated to allow debondings of piezoelectric patches and the debonding detection.
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An accurate laminated element for piezoelectric smart beams including Peel Stress
Computational Mechanics, 2004Co-Authors: Q. Luo, L. TongAbstract:This paper presents a laminated element for piezoelectric (PZT) smart beams in taking into account Peel Stresses. In the finite element analysis (FEA) formulation, a coupled electrical and mechanical beam element is used to model PZT patches, and a conventional structural element is used to model a host beam. A continuous adhesive element with shear and Peel stiffness is derived to form a PZT laminated element. For a smart beam with a partially bonded PZT patch or distributed PZTs, the laminated element is applied to an area of the host beam with PZTs and the conventional element is used in the host beam where no PZT is bonded. A novel PZT laminated element is firstly derived based on the Timoshenko beam theory, in which the FEA formulation based on the Euler-Bernoulli beam theory can be considered as its special case. FEA numerical results of static and dynamic analyses based on the Euler-Bernoulli beam theory are compared with the exact static and dynamic solutions to validate the present FEA formulation. The present FEA framework based on the Timoshenko beam theory is then used to investigate the effects of PZT debondings on static behaviors and dynamic responses, and an original and effective procedure for detecting debondings in PZT actuators or sensors is proposed.
Brian L. Wardle - One of the best experts on this subject based on the ideXlab platform.
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Strength and Performance Enhancement of Multilayers by Spatial Tailoring of Adherend Compliance and Morphology via Multimaterial Jetting Additive Manufacturing
Scientific Reports, 2018Co-Authors: Jabir Ubaid, Brian L. WardleAbstract:Material tailoring of bondlayer compliance is a known effective route to enhance performance of multilayers, and here spatial material-tailoring of compliance and morphology of the adherends is examined. Multimaterial jetting additive manufacturing (AM) allows us to realize for the first time compliance- and morphology-tailored adherends, and evaluate directly the mechanical performance, including failure, of the tensile-loaded multilayers. Adherend compliance-tailoring, unlike bondlayer tailoring, requires additional consideration due to adherend bending stiffness and moment influences on bondlayer Stresses. We introduce anisotropic as well as layered/sandwich adherend tailoring to address this dependence. Numerical models show that for both sub-critical and critical bondlengths (at which shear-dominated load transfer occurs through the bondlayer), adherend tailoring reduces peak Stresses significantly, particularly Peel Stress (reductions of 47–80%) that typically controls failure in such systems. At sub-critical bondlengths, the AM-enabled layered/sandwich adherend tailoring shows significantly increased experimental performance over the baseline multilayer: strength is increased by 20%, toughness by 48%, and strain-to-break by 18%, while retaining multilayer stiffness. The adherend tailoring demonstrated here adds to the techniques available to increase the performance of bonded multilayers, suggesting that adherend tailoring is particularly well-suited to additively manufactured multilayers, but can also have application in other areas such as layered electronics and advanced structural composite laminates.
Liyong Tong - One of the best experts on this subject based on the ideXlab platform.
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Analytical solutions for adhesive composite joints considering large deflection and transverse shear deformation in adherends
International Journal of Solids and Structures, 2008Co-Authors: Quantian Luo, Liyong TongAbstract:AbstractThis paper presents a novel formulation and analytical solutions for adhesively bonded composite single lap joints by taking into account the transverse shear deformation and large deflection in adherends. On the basis of geometrically nonlinear analysis for infinitesimal elements of adherends and adhesive, the equilibrium equations of adherends are formulated. By using the Timoshenko beam theory, the governing differential equations are expressed in terms of the adherend displacements and then analytically solved for the force boundary conditions prescribed at both overlap ends. The obtained solutions are applied to single lap joints, whose adherends can be isotropic adherends or composite laminates with symmetrical lay-ups. A new formula for adhesive Peel Stress is obtained, and it can accurately predict Peel Stress in the bondline. The closed-form analytical solutions are then simplified for the purpose of practical applications, and a new simple expression for the edge moment factor is developed. The numerical results predicted by the present full and simplified solutions are compared with those calculated by geometrically nonlinear finite element analysis using MSC/NASTRAN. The agreement noted validates the present novel formulation and solutions for adhesively bonded composite joints. The simplified shear and Peel Stresses at the overlap ends are used to derive energy release rates. The present predictions for the failure load of single lap joints are compared with those available in the literature
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Exact static solutions to piezoelectric smart beams including Peel Stresses. II. Numerical results, comparison and discussion
International Journal of Solids and Structures, 2002Co-Authors: Liyong TongAbstract: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.
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Fatigue crack growth in adhesively bonded composite-metal double-lap joints
Composite Structures, 2002Co-Authors: P.t Cheuk, Liyong Tong, Chun H. Wang, Alan Baker, Peter ChalkleyAbstract:Abstract This paper presents experimental and numerical investigations of the fatigue crack initiation and growth mechanism in metal-to-composite bonded double-lap joints. Fatigue tests were conducted under tension dominated loading, with crack lengths being measured optically. Examination of the fracture surface using scanning electron microscope revealed that fatigue cracks were near the interface between the co-cured adhesive and the first ply of the composite adherend. The finite element method has been used to determine the strain-energy release rate of a fatigue crack growing along the first ply of the composite. The effects of spew fillet size and crack initiation modes have also been studied by the finite element method. Comparison of the present experimental crack growth results with those measured using double-overlap joints, where the fatigue cracks were driven by pure mode II loading, indicate that the tensile mode loading has a overwhelming effect on the fatigue crack growth rates. The present results suggest that fatigue failure of metal-composite double-lap joints is mainly driven by tensile mode loading due to the Peel Stress.
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The effect of adherend alignment on the behaviour of adhesively bonded double lap joints
International Journal of Adhesion and Adhesives, 1996Co-Authors: Liyong Tong, Andy W. Sheppard, Don KellyAbstract:For an adhesively bonded double lap joint, end mismatch between the two outer adherends can not be removed completely although it can be controlled within a manufacturing tolerance. This paper shows that the end mismatch introduces local bending and, consequently, results in a significant effect on the surface normal displacement. Furthermore, the end mismatch also affects the shear and Peel Stresses in the adhesive. To include the end mismatch effect, a modified equation is developed to characterise the Peel Stress in the adhesive layer in terms of the surface normal displacement measured using the holographic interferometry technique. The surface normal displacement predicted by the FEM is validated experimentally. A good correlation is also noted between the adhesive Peel Stress computed using the FEM and that calculated using the modified equation and the measured surface normal displacement.
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Relationship between surface displacement and adhesive Peel Stress in bonded double lap joints
International Journal of Adhesion and Adhesives, 1995Co-Authors: Liyong Tong, Andy W. Sheppard, Don KellyAbstract:Abstract For adhesively bonded double lap joints, a simple formula is developed to express the adhesive Peel Stress in terms of the surface out-of-plane displacement that can be measured to the order of
Eric Paroissien - One of the best experts on this subject based on the ideXlab platform.
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Mode I cohesive zone model parameters identification and comparison of measurement techniques based on uncertainty estimation
International Journal of Solids and Structures, 2020Co-Authors: Agathe Jaillon, Julien Jumel, Frederic Lachaud, Eric ParoissienAbstract:Adhesive bondline mechanical behaviour is frequently described with cohesive zone models (CZM). For mode I loading condition these phenomenological laws simply represent the evolution of the Peel Stress as a function of the two adherends relative displacement normal to the joint. Generally, these laws are identified rather than really measured using experimental data obtained from crack initiation and propagation experiments such as the Double Cantilever Beam Test (DCB). The uncertainty on parameter estimation are generally not indicated, as for a DCB test it is only the critical energy release rate that has the most influence on the results. However, the uncertainties on the other parameters prevent the use of the identified TSL for other mechanical tests where mode I solicitations are predominant. In this article, the purpose is to evaluate the methodologies reliability for the assessment of mode I CZM. To do so, several methods used to evaluate CZM parameters are compared in terms parameter estimation reliability. Synthetic noisy data are considered for a χ² function minimisation. Then, sensitivity calculations are performed to determine the estimated parameters standard deviation. By applying this procedure on different type of synthetic measurements (respectively P(), J(,), backface strain and DIC) the ability of these different techniques to capture the best parameters for a chosen CZM shape can be rigorously evaluated.
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Cohesive zone model identification on mode I bonded assembly: sensitivity analysis
2019Co-Authors: Agathe Jaillon, Julien Jumel, Eric Paroissien, Frederic LachaudAbstract:Adhesive bonding is usually modelled using cohesive zone models (CZM) which are defined by traction-separation (TS) law. For mode I loading condition these phenomenological laws simply represent the evolution of the Peel Stress as a function of the two adherends relative displacement normal to the joint. However, TS law shape is often empirically chosen rather than being measured. The uncertainty on parameter estimation is generally not indicated even though it strongly influences the reliability of the bonded joint strength prediction. Moreover there are several mechanical data that can be obtained experimentally from crack initiation and propagation experiments on a Double Cantilever Beam Test (DCB). In general, TS parameters are chosen from load-displacement curves, which is the most straightforward mechanical response to obtain. However, the development of digital image correlation has enabled to access more numerous data, such as adherends’ deflection and rotation along the overlap and at loading point. The latter can be directly used to obtain the J integral. Adherends’ deformation can also be measured through the use of resistive strain gauges. Therefore, these different identification methods need to be compared in terms of parameter estimation confidence intervals. To do so, a numerical test campaign has been carried out for each mechanical response (i.e. load-displacement, J integral, and strain measurement) a synthetic noise is added to the nominal response in order to artificially represent measurement data. The noisy response is then used for the identification of the parameters using a nonlinear least square minimization. Once the data are fitted, the parameters sensitivity and confidence intervals can then be established enabling the rigorous evaluation of these different techniques to capture the best parameters for a chosen CZM shape.