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

The detection of aeronautical defects in-situ on composite structures using Non Destructive Testing

A study of three Non Destructive Testing methods (Ultrasonic Testing, InfraRed Thermography and Speckle Shearing Interferometry, known as Shearography) was carried out on different specific types of composite specimens having a variety of defects. The aim of this study is to evaluate the efficiency of these NDT methods in the detection of in-situ defects resulting from Barely Visible Impact Damages (BVID) or in-service damages to complex surfaces such as wings or rods. The size and position of all the defects were determined by GVI (General Visual Inspection): GVI being the reference. The evaluation of the three NDT techniques enabled conclusions to be drawn regarding defect detection and size. The first part of the study deals with determining and measuring defects. It appears that only the ultrasonic method enables the depth of a defect to be determined. In the second part of the study, the results obtained by the three NDT methods are compared. Finally, the feasibility and the time taken to set up the experimental protocol are analyzed. The study shows that all the defects were revealed by, at least, one of the three NDT methods. Nevertheless it appears that InfraRed Thermography and Shearography produced results very quickly (in about 10 s) compared to Ultrasonic Testing

Manufacturing and quasi-static bending behavior of wood-based sandwich structures.

The quasi-static behavior of innovative wood based sandwich structures with plywood core and skins made either of aluminum or of fiber reinforced polymer (carbon, glass or flax composite skins) was investigated. The wood based sandwich structures were subjected to three point static bending tests to determine their strength and failure mechanisms. Two different manufacturing processes, namely vacuum bag molding and thermo-compression, were used to manufacture the structures. The influence of some aspects of the different manufacturing processes on the flexural behavior of wood based sandwich structures are discussed. It is shown that manufacturing processes influence strongly the static responses. Failure modes and strengths are investigated during quasi-static bending tests. Bending tests showed that the mechanical characteristics were very high compared to those of a reference sandwich that is currently used for civil aircraft floors. This new kind of structure is environmentally friendly and very cheap, and seems promising for the transportation industry in general

Experimental investigation of impact behavior of wood-based sandwich structures

Low carbon emission and sustainable development are shared goals throughout the transportation industry. One way to meet such expectations is to introduce lightweight materials based on renewable sources. Sandwich panels with plywood core and fiber reinforced composite skins appear to be good candidates. Additional properties of wood such as fire resistance or thermal and acoustic insulation are also essential for many ap- plications and could lead to a new interest for this old material. In this paper, Sandwich panels with two different types of plywood and four different skins (aluminum and glass, CFRP, or flax reinforced polymer) are tested under low-velocity/low energy impacts and their behavior is discussed

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

Comparative study of tools in drilling composites T700-M21 and T800-M21

The drilling of composite materials can produce, around the hole, defects and damages which decrease the mechanical resistance of the drilled workpiece. This study shows the influence of several tools (drill, mill and reamer) on the hole quality obtained, in the context of reference parts where surface integrity is a priority. An experimental study is suggested and the criteria used to assess the hole quality are defined. Results show the behavior of each type of cutting tool and their influence on the defects generated. Finally, this study helps creating a scale of recommended cutting conditions to reduce the tool wear and improve the hole quality

Numerical modeling of impact on wood-based sandwich structures

The impact behavior of innovative wood based sandwich structures with plywood core and skins made either of aluminum or of fiber reinforced polymer (carbon, glass, or flax composite skins) was investigated numerically. The wood based sandwich structures were subjected to low-velocity/low-energy impacts. An explicit nonlinear numerical model based on volume elements with a cohesive layer was developed. A plastic wood law already implemented in LS-DYNA was used in association with composite type damage criteria. Comparisons with experiments in terms of layer deformations and overall contact laws during impact showed satisfactory results

Dynamic crushing of wood-based sandwich composite tubes

The article presents the results of dynamic crushing of sandwich tubes that had skins made of carbon or glass fibers – with epoxy resin – and an I214 poplar ply core. By increasing the number of poplar plies from two to six, the absorbed energy is doubled, showing the significant contribution of the wood. The Specific Energy Absorption of sandwiches with carbon fiber skins oscillated between 49.4 J/g and 60 J/g while that with glass fiber skins varied from 35.4 to 43.3 J/g

Wood peeling process monitoring: a comparison of signal processing methods to estimate veneer average lathe check frequency

Experienced peeling operators are able to adjust the settings of their device by hearing the sound coming from the process. Based on this idea, a research program was undertaken to evaluate the possibility of using acoustic or vibration measurements supplying a support decision system to assist untrained operators. The present paper deals with lathe check phenomenon which is one of the most critical defects of veneer (leading to handling difficulties, excess of glue consumption, poor veneer surface quality, etc.). Several signal processing techniques giving a spectral representation of sensors measurements are compared. Finally, an original procedure based on Power Spectral Density ratio is proposed to measure the average lathe check frequency of the veneer during the process