Adhesive thickness influence on a structural methacrylate adhesive behavior

Structural adhesive bonding importance has been growing steadily in the last decades as transport sector’s current problematic is to there products’ reduce mass. In addition, compared to riveting and welding, adhesive bonding offers better properties when joining dissimilar materials such as metals and composites which are a pair used more and more frequently. However, adhesive bonding suffers great-ly from a lack of confidence from industries as validating the bond quality need either destructive testing or long and costly nondestructive testing. Both these solutions can hardly be implemented at an industrial level. Nevertheless, with the implementation of robotics it is possible to auto-mate and control the entire bonding processes. In this con-text a collaborative project called S3PAC (Système de Supervision et de Simulation de la Production d’Assemblage par Collage) has been launched in order to offer a fully supervised and automated industrial bonding process

Mode I cohesive zone model parameters identification and comparison of measurement techniques for robustness to the law shape evaluation

Adhesive bonding modelling is often realised using cohesive zone models (CZM). For pure mode I loading, these laws represent the cohesive stress versus the interface displacement evolution designated as traction-separation laws (TSL). They enable the description of the interface irreversible phenomena such as damage and/or plasticity, while permitting a refined evaluation of the cohesive stress along the overlap. However, these laws are usually chosen a priori. For brittle and ductile adhesives the TSL shapes usually chosen are respectively bilinear softening and elasto-plastic. But the development of direct CZM measurements has highlighted that the law shapes can be more complex. The wrong initial choice of the TSL shape can then have an impact on the simulation results reliability. In this article, several methods used to evaluate CZM parameters are compared in terms of TSL shape robustness. Synthetic noisy data generated from a trapezoidal CZM are used for the inverse identification of a bilinear softening TSL. By applying this procedure on different type of synthetic measurements (respectively Force-displacement, J-integral, backface strain and DIC) the ability of these techniques to capture parameters for a chosen CZM shape that is not the right one enables a rigorous evaluation the robustness to the law shape

Thickness influence on a structural methacrylate adhesive behavior

Thickness influence on a structural methacrylate adhesive behavior

Experimental and numerical investigation of the adhesive bond thickness variability on bonded joints failure behaviour

Afin de réduire l’impact écologique de leurs produits, les secteurs du transport cherchententre autres à en minimiser la masse. Dans ce contexte, le collage structural apparaîtalors comme un concurrent direct des assemblages traditionnels. Cependant, le manquede confiance des industriels dans les propriétés réelles de l’assemblage une fois fabriquénécessite de repenser la totalité de la chaîne de fabrication. Pour cela, le projet S3PACsignifiant « Système de Supervision et de Simulation de la Production d’Assemblage parCollage » propose le développement d’une chaîne de fabrication entièrement contrôlée etsupervisée. Cela inclut notamment la mise en place d’un jumeau numérique prenant encompte les paramètres de fabrication effectifs de la pièce. La réalisation de simulationsnumériques simplifiées permet dès lors la prédiction du comportement à rupture. Il estdonc nécessaire de développer des modèles de comportement prédictifs et rapides de cesassemblages collés.L’objectif de cette étude est de développer les modèles de comportement en incluant laprise en compte d’une variation d’épaisseur de la couche adhésive. L’étude est réalisée avecun système adhésif thermoplastique méthacrylate structural dont le comportement mécaniqueet thermomécanique est caractérisé expérimentalement. Dans un premier temps,il est étudié sous sa forme massique ce qui permet de mettre en évidence un comportementcomplexe de type viscoélastoplastique. Dans un second temps, son comportementest analysé au sein d’un assemblage pour des sollicitations à champ homogène avec deuxépaisseurs de couche adhésive. Par la suite, une étude analytique de l’essai DCB est réaliséeafin de de réaliser une évaluation de la validité de l’identification inverse pour ladétermination d’une loi de traction séparation. Une étude expérimentale de la fissurationen mode I est réalisée pour des conditions de confinement variables. Elle permet demettre en évidence une amélioration de la tenue mécanique avec l’épaisseur, ainsi que ledéveloppement d’une zone plastique pour les couches adhésives les plus épaisses. Enfin,une approche numérique par éléments finis est mise en place afin de mettre en évidenceles effets d’épaisseur dans la répartition des contraintes et des déformations au sein dela couche adhésive. Une démarche d’identification d’une modélisation par des élémentscohésifs couplés à des éléments massiques est proposée et discutée.One of transport sector’s current problematic is to reduce their products’ mass. Todo so, weight to mass ratio is optimized for both materials and joining technic. Adhesivebonding then appears as a viable competitor to more traditional joining technic such asbolting and riveting. However, adhesive bonding suffers greatly from a lack of confidencefrom industries, as ensuring and validating the bond quality is quite challenging. TheS3PAC project suggests addressing it by redesigning the joining process. The implementationof an entirely supervised process would enable the use of a numerical twin, whichwould compute the failure behavior of the manufactured structure. The goal of this studyis to develop those models and to include the influence of the bond thickness variability.Throughout this work, the adhesive used is a thermoplastic methacrylate adhesive.Its mechanical and thermomechanical behavior has been studied experimentally. Firstly,it is carried out on its bulk form and in a bonded assembly subjected to a homogenousstress distribution. It shows that this adhesive has a complex viscoelastoplastic behavior.Secondly, an analytical analysis of the DCB test has been carried out in order to evaluatethe cohesive zone model inverse identification approach validity. Then, the influence ofthe adhesive thickness on mode I failure is studied experimentally. It appears that bondthickness increases the mechanical strength of the assembly and that the enlargement ofa plastic area can be monitored during crack propagation. Finally, the development of anumerical model highlights the stress and strain inhomogeneity in the adhesive thickness.The identification method of a model containing both cohesive and bulk elements is thensuggested and analyzed

Cohesive zone model identification on mode I bonded assembly: sensitivity analysis

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

Cohesive zone model identification in mode I for bonded composites: identification methods’ review and sensitivity analysis

l existe de nombreuses méthodes pour déterminer les modèles de zone cohésives en mode I. Une de ces méthodes consiste à réaliser une optimisation inverse sur les données d’essais mesurées en présupposant une forme de loi de traction-séparation. Classiquement, elle est choisie de forme bilinéaire. Cependant, en raison du développement des techniques de mesure avec notamment la corrélation d’image numérique ou le placement de jauges de mesures résistives, différents types de réponses mécaniques peuvent être obtenus.Il apparait alors possible que l’estimation des paramètres dépende de la réponse mécanique choisie.Une revue des différentes méthodes de mesures utilisées lors d’essais DCB en mode I a donc été réalisée.Cette étude a permis de mettre en évidence que les plus utilisées sont la courbe force-déplacement, l’intégrale J, les jauges (backface strain) et l’analyse de la flèche et rotation des substrats.Un modèle analytique a ensuite été mis en place afin de simulerleurs sensibilités aux paramètres du modèle de zone cohésive. Cette étude permet de mettre en évidence l’influence des paramètres de la loi de traction-séparation. Ces résultats sont ensuite nuancés par une analyse des contraintes expérimentales et théoriques de ces méthodesAdhesive bonding is most of the time modelled using cohesive zone models, whichare defined by traction-separationlaw shapes. However, the fact that TS law shape is empirically chosen rather than being measured can lead to erroneous behavior predictionwhen using inverse minimization. Moreover, it can be assumed that the mechanical response chosen to identify the TS law parameters might have an influence. A review of the existing measuring methods shows that most of the time, TS parameters are chosen from load-displacement curves, which is the most straightforward mechanical response to obtain.However, the development of digital image correlation (DIC) has enabled the access to more data, such as adherends’ deflection and rotation along the overlap and at loading point. The latter can be directly used to obtain the integral J, which once differentiated can directly give the TS law. Adherends’ deformation can also be measured usingresistive strain gauges. Therefore, the different identification methods need to be sorted according to their sensitivity to the parameters. To do so, a numerical testcampaign has been carried out, using an analytical modelin order to evaluate the mechanical responses’ sensibility to the chosen law shape parameter

Identification des modèles de zones cohésives en mode I pour des assemblages composites collés : état de l’art et analyse de sensibilité

Il existe de nombreuses méthodes pour déterminer les modèles de zone cohésives en mode I. Une de ces méthodes consiste à réaliser une optimisation inverse sur les données d’essais mesurées en présupposant une forme de loi de traction-séparation. Classiquement, elle est choisie de forme bilinéaire. Cependant, en raison du développement des techniques de mesure avec notamment la corrélation d’image numérique ou le placement de jauges de mesures résistives, différents types de réponses mécaniques peuvent être obtenus. Il apparait alors possible que l’estimation des paramètres dépende de la réponse mécanique choisie. Une revue des différentes méthodes de mesures utilisées lors d’essais DCB en mode I a donc été réalisée. Cette étude a permis de mettre en évidence que les plus utilisées sont la courbe force-déplacement, l’intégrale J, les jauges (backface strain) et l’analyse de la flèche et rotation des substrats. Un modèle analytique a ensuite été mis en place afin de simuler leurs sensibilités aux paramètres du modèle de zone cohésive. Cette étude permet de mettre en évidence l’influence des paramètres de la loi de traction-séparation. Ces résultats sont ensuite nuancés par une analyse des contraintes expérimentales et théoriques de ces méthodes

Mode I cohesive zone model parameters identification and comparison of measurement techniques based on uncertainty estimation

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

Adhesive thickness influence on a structural methacrylate adhesive behavior

Structural adhesive bonding importance has been growing steadily in the last decades as transport sector’s current problematic is to there products’ reduce mass. In addition, compared to riveting and welding, adhesive bonding offers better properties when joining dissimilar materials such as metals and composites which are a pair used more and more frequently. However, adhesive bonding suffers great-ly from a lack of confidence from industries as validating the bond quality need either destructive testing or long and costly nondestructive testing. Both these solutions can hardly be implemented at an industrial level. Nevertheless, with the implementation of robotics it is possible to auto-mate and control the entire bonding processes. In this con-text a collaborative project called S3PAC (Système de Supervision et de Simulation de la Production d’Assemblage par Collage) has been launched in order to offer a fully supervised and automated industrial bonding process

Viscoelastic behavior of an epoxy resin during cure below the glass transition temperature: Characterization and modeling

International audienceThis paper presents a viscoelastic temperature- and degree-of-cure-dependent constitutive model for an epoxy resin. Multi-temperature relaxation tests on fully and partially cured rectangular epoxy specimens were conducted in a dynamic mechanical analysis apparatus with a three-point bending clamp. Master curves were constructed from the relaxation test results based on the time–temperature superposition hypothesis. The influence of the degree of cure was included through the cure-dependent glass transition temperature which was used as reference temperature for the shift factors. The model parameters were optimized by minimization of the differences between the model predictions and the experimental data. The model predictions were successfully validated against an independent creep-like strain history over which the temperature varied