Identification of damaged zone in composite materials using displacement field measurements

This work presents an identification strategy of local elastic properties of orthotropic carbon-epoxy laminates for aviation industry. Based on global and local stages of study, this methodology uses the Finite Element Model Updating (FEMU) method as identification technique with simulated kinematic fields corresponding to tensile test response. The aim of this paper is to predict the spatial variation of elastic plane properties and to deduce the localization of damaged zones

Global and local identification on composte material

One of the main challenges in composite design and development is to be able to compute the damage state at any point of a composite structure during a complex loading. In this context, knowledge of the spatial distribution of the material elastic properties provides a quantitative estimation of the damage level and localization. The work presented here intends to access to such distribution through the association of kinematic fields and finite element model updating method. Such iterative technique has many interesting advantages for structural analysis and industrial requirements, including the numerical framework, the ability to explore complex shapes and loads and a treatment based on surface measurement without any assumption on volume distribution

Non destructive investigation of defects in composite structures by three infrared thermographic techniques

This paper investigates full-field measurement techniques based on Infrared Thermography for Non Destructive Testing (NDT) applications on composite materials. Three methods have been implemented and the paper intends to characterize and compare their defect detection limit and related specific application fields. Various composites have been considered in this study, namely laminates and sandwich structures, in order to address many important issues of performance assessment for the aviation industry

Identification of orthotropic material properties using displacement field measurements

One of the main challenges in composite design and development is to be able to compute the damage state at any point of a composite structure during a complex loading, especially to predict their in-service global mechanical behavior. In this context, knowledge of the spatial distribution of the material elastic properties provides a quantitative estimation of the damage level and localization. The association of kinematic fields and finite element model updating method (FEMU) constitutes an interesting way for such identification, especially in view of structural analysis and industrial requirements. Indeed, such iterative technique relies on a numerical framework, is able to explore complex shapes and loads and is based on kinematic fields surface measurement without any assumption on volume distribution [1,2]. If many studies have been devoted to the context of isotropic materials [3], the paper aims to extend the method to the determination of the macroscopic anisotropic elastic properties of composite materials. Compared to existing works, the approach is characterized by an important number of comparison points, which confers a great spatial precision and allows in the future the extension of such methodology to heterogeneous materials. To implement the FEMU technique, a specific algorithm in Python language following the flowchart in Fig.1 has been established. A particular attention has been paid to the matching of the kinematic fields grid and numerical one through the determination of neighboring points and interpolation functions. The cost function minimization is based on the Levenberg-Marquardt algorithm. The procedure have been applied for the identification of orthotropic carbon-epoxy laminated composites (four elastic properties and orthotropic principal angle) for aviation industry by means of kinematic fields obtained under tensile tests. An open-hole geometry is used to generate an heterogeneous strain field localized near the hole that allows to stimulate the whole strain components [4]. The displacement field measurements on the specimen surface are simulated with Abaqus finite element code as by experimental stereo-image correlation measurements. The capability of the procedure is validated for different configurations of the laminated composite (plies stacking and orientation, components properties) through a comparison with the Kirchhoff-Love theory. Stability and convergence of the algorithm are checked for each considered parameters

Caractérisation et comparaison des limites de détection de techniques de contrôle non destructif : méthodes ultrasonores et méthodes optiques

Le contexte de ce travail concerne le process d’Infusion de Résine Liquide (LRI) développé dans le cadre du projet « FUSelage COMPosite » par DAHER SOCATA. Ce process de fabrication permet de réaliser des pièces de formes complexes et des panneaux entiers de fuselage composite ce qui réduit considérablement les étapes d’assemblages et donc les temps de production. Ce travail porte sur l’inventaire de toutes les méthodes de contrôle non destructif pouvant être appliquées aux structures composites fabriquées en LRI dans le but de définir leurs limites de détection des défauts et leurs champs d’applications spécifiques. Dans l’aéronautique, les standards AITM imposent les ultrasons comme méthodes de contrôle non destructif sur les structures composites. Par conséquent, le but de ce travail est de caractériser et comparer plusieurs méthodes de contrôle sans contact telles que les méthodes ultrasonores disponibles au laboratoire IUT-ICA et les méthodes optiques disponibles au laboratoire ENIT-LGP afin de déterminer leurs limites de détection, leurs complémentarités et leurs champs d’applications spécifiques. Les différents tests sont réalisés sur des éprouvettes composites monolithiques et sandwichs, en LRI et préimprégné, avec différents types de défauts

Non destructive investigation of defects in composite structures by fullfield measurement methods

This paper presents different interests of non destructive full-field measurement. More precisely, it focuses on the characterization and the comparison of the X-ray tomography and two methods of infrared thermography in order to define the defect detection limits and to precise the specific application fields for each technique on multi-layered and sandwich composite structures. The obtained results are qualitatively and quantitatively analyzed

Non destructive testing of artificial defects in composite structures by thermal full field measurement methods

In order to achieve outstanding performance, it now seeks to optimize more and more the design and process of composite structures. Many applications require specific technical inspections at various steps of the product lifetime to assess their structural health. In such a context, non destructive techniques (NDT) offer an interesting and appropriated tool for the analysis of structural parts. For aviation industry, the AITM standards are precisely based on the NDT ultrasonic testing for the validation of composite structures. Since recent years, the use of full-field measurement NDT as infrared (IR) thermography is developing for their fast execution and analysis (defect mapping in one shot) and for the global inspection aspect. This work consists in characterizing and in comparing three thermal full-field measurement NDT in order to define the defect detection limits, the advantages and the limitations for each technique on multi-layered and sandwich composite structures

Characterization and comparison of defects detection limits of ultrasonic non destructive techniques

This work deals with the Liquid Resin Infusion (LRI) process developed within the research program “FUSelage COMPosite” of DAHER SOCATA. This manufacturing process enables the realization of complex composite structures or fuselage elements in a single phase (mono-material), which considerably reduce connections and relative difficulties. The concern here is the investigation of non destructive testing (NDT) methods that can be applied to LRI-structures in order to define their capacities for defect detection, and especially their associated critical defect size. In aviation industry, the AITM standards require the ultrasonic testing as NDT for composite materials. Therefore the aim of this work is to characterize and compare three different and complementary ultrasonic techniques on composite specimens. Such analysis allows to define the NDT application field of each method in term of defect detection

Damage investigation in CFRP composites using full-field measurement techniques: combination of digital image stereo-correlation, infrared thermography and X-ray tomography

The present work is devoted to damaging process in carbon–fiber reinforced laminated composites. An original experimental approach combining three optical measurement techniques is presented. Image stereo-correlation and infrared thermography, that respectively provide the kinematic and thermal fields on the surface of the composites, are used in live recording during axis and off-axis tensile tests. Special attention is paid to simultaneously conduct these two techniques while avoiding their respective influence. On the other hand, X-ray tomography allows a post-failure analysis of the degradation patterns within the laminates volume. All these techniques are non-destructive (without contact) and offer an interesting full-field investigation of the material response. Their combination allows a coupled analysis of different demonstrations of same degradation mechanisms. For instance, thermal events and densimetric fields show a random location of damage in the early stages of testing. The influence of the material initial anisotropy on damage growth, localization and failure mode can also be clearly put in evidence through various data. In addition to such characterization, this study illustrates at the same time the capabilities of the different full-field techniques and the damage features they can best capture respectively

Non destructive testing of artificial defects in composite structures by thermal full field measurement methods

International audienceIn order to achieve outstanding performance, it now seeks to optimize more and more the design and process of composite structures. Many applications require specific technical inspections at various steps of the product lifetime to assess their structural health. In such a context, non destructive techniques (NDT) offer an interesting and appropriated tool for the analysis of structural parts. For aviation industry, the AITM standards are precisely based on the NDT ultrasonic testing for the validation of composite structures. Since recent years, the use of full-field measurement NDT as infrared (IR) thermography is developing for their fast execution and analysis (defect mapping in one shot) and for the global inspection aspect. This work consists in characterizing and in comparing three thermal full-field measurement NDT in order to define the defect detection limits, the advantages and the limitations for each technique on multi-layered and sandwich composite structures