Time-resolved full-field imaging of ultrasonic Lamb waves using deflectometry

This pioneering experimental work is a proof of concept in which ultrasonic flexural waves have been imaged in a spatially and temporally resolved manner. Thin vibrating plates made of mirror glass and carbon/epoxy composite have been used in the experiments. Results obtained via a standard approach (scanning laser Doppler vibrometry) and the novel methodology based on deflectometry have been compared with a multi-physics finite element simulation. There is a very good correlation between the two experimental techniques. The numerical model provides insight into the experiments, but differs in its detailed structure due to uncertainties over material properties. The extreme slope resolution of deflectometry allows the measurement of peak-to-peak deflections of a few tens of nanometres in one shot. The use of an ultra-high speed camera allows for both space and time resolved measurements of Lamb waves which, to the best knowledge of the authors, has never been reported before. The limitations of the technique arise from the need for a flat specularly reflective surface. However, coating is possible for non-reflective materials and extension to moderately curved surfaces is possible in the future

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

IDENTIFICATION D'ENDOMMAGEMENTS AU SEIN DE PLAQUES COMPOSITES STRATIFIÉES À L'AIDE DE MESURES DE CHAMPS CINÉMATIQUES

This work focuses on the development of an experimental technique which can help to define the key parameters for post-impact behaviour of laminated composite panels. To address this issue, finite element models were built to represent delaminations based on the observations of CT-scans of impacted samples. The results of these models have been correlated to experimental data obtained using a slope full-field measurement technique: deflectometry. This work also develops a new damage indicator based on the application of the virtual fields method to compute a local equilibrium gap. The procedure is first presened and then applied to beam and plate samples. The experimental results illustrate the remarkable sensitivity of this measurement method as it captures the effect of very small amount of damage and shows that the simple numerical models need to be refined to present a better correlation to experimental results. The damage indicator successfully detects contours of damaged areas when sufficient spatial information is available. It is believed that pursuing the present work could lead to an invaluable tool to help design engineers.Ce travail porte sur le développement d'une technique expérimentale qui peut aider à définir les paramètres clefs du comportement après impact de panneaux composites stratifiés. Pour cela, des modèles éléments finis ont été construits pour inclure des délaminages à partir d'observations de CT-scans d'échantillons impactés. Les résultats de ces modèles ont été comparés à des mesures expérimentales obtenues par une technique de mesure de champs de pentes: la déflectométrie. Ce travail aussi présente un nouvel indicateur d'endommagements basé sur l'application de la méthode des champs virtuels à l'évaluation d'écarts locaux à l'équilibre. Cette procédure d'abord détaillée est ensuite appliquée à des échantillons de types poutres et plaques. Les résultats expérimentaux illustrent la remarquable sensibilité de cette technique de mesure : elle permet de capturer les effets de très faibles endommagements. Aussi, cette technique montre que les simples modèles numériques présentés dans ce travail nécessitent des améliorations pour se rapprocher des données expérimentales. L'indicateur d'écart à l'équilibre a détecté correctement le contour des zones endommagées quand suffisamment d'information spatiale était disponible. Poursuivre ce travail permettrait de créer un outil précieux aidant la conception de pièces en composites

Identification d'endommagements au sein de plaques composites stratifiées à l'aide de mesures de champs cinématiques

This work focuses on the development of an experimental technique which can help to define the key parameters for post-impact behaviour of laminated composite panels. To address this issue, finite element models were built to represent delaminations based on the observations of CT-scans of impacted samples. The results of these models have been correlated to experimental data obtained using a slope fullfield measurement technique: deflectometry. This work also develops a new damage indicator based on the application of the virtual fields method to compute a local equilibrium gap. The procedure is first presened and then applied to beam and plate samples. The experimental results illustrate the remarkable sensitivity of this measurement method as it captures the effect of very small amount of damage and shows that the simple numerical models need to be refined to present a better correlation to experimental results. The damage indicator successfully detects contours of damaged areas when sufficient spatial information is available. It is believed that pursuing the present work could lead to an invaluable tool to help design engineersCe travail porte sur le développement d'une technique expérimentale qui peut aider à définir les paramètres clefs du comportement après impact de panneaux composites stratifiés. Pour cela, des modèles éléments finis ont été construits pour inclure des délaminages à partir d'observations de CT-scans d'échantillons impactés. Les résultats de ces modèles ont été comparés à des mesures expérimentales obtenues par une technique de mesure de champs de pentes : la déflectométrie. Ce travail présente aussi un nouvel indicateur d'endommagement basé sur l'application de la méthode des champs virtuels à l'évaluation d'écarts locaux à l'équilibre. Cette procédure d'abord détaillée est ensuite appliquée à des échantillons de types poutres et plaques. Les résultats expérimentaux illustrent la remarquable sensibilité de cette technique de mesure : elle permet de capturer les effets de très faibles endommagements. Aussi, cette technique montre que les modèles numériques assez simples présentés dans ce travail nécessitent des améliorations pour se rapprocher des données expérimentales. L'indicateur d'écart à l'équilibre a détecté correctement le contour des zones endommagées quand suffisamment d'information spatiale était disponible. Poursuivre ce travail permettrait de créer un outil précieux aidant la conception de pièces en compositesTROYES-SCD-UTT (103872102) / SudocSudocFranceF

Título: Exposición razonada de los fundamentos de la fe

Contiene: T. I La religión cristiana. -- 521

Influence of ripening on pHstat leaching of heavy metals from dredged sediments

The influence of oxidation and ripening on the kinetics of heavy metal release from anoxic sediments was investigated by means of porewater analysis and pHstat leaching tests. During simulated land disposal of an anoxic river sediment, a considerable heavy metal (Cd, Zn and Ni) release into the porewater was observed after 25 days of exposure of the sediment to the air. The release kinetics of Cd and Zn during pHstat leaching indicated that their release was related to the oxidation of Cd- and Zn-sulfides. It was not completely clear whether the release of Ni was due to the oxidation of Ni-sulfides or to the introduction of H+(generated by the oxidation of sulfides or introduced by titration). The release of Cu seemed to be explained by the oxidation of both Fe-sulfides and Cu-sulfides. As such, pHstat experiments provided an indirect way to assess the mineralogy of the anoxic sediment. During ripening of the sediment, the release rate of Zn and Cd in pHstat leaching tests increased. For Ni, however, a similar release pattern was observed in the anoxic sediment and in the ripened sediments. Two weeks drying at 100 °C resulted in an increase in the leachability of Cu. Nevertheless, at pH 4 and 6, the thermally treated sediment displayed a slower leaching of Cd and Zn than the ripened sediment. Although thermal treatment is often used to simulate ageing in soils, it cannot be used to simulate ripening of anoxic sedimentsstatus: publishe

Impact damage detection in composite plates using deflectometry and the Virtual Fields Method

This paper presents a new method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a “signature” from the measured surface slopes. Firstly, this method is applied to plate specimens using numerical and experimental data. Secondly, damage indicator based on a new application of the virtual fields method to compute local apparent gaps in equilibrium is presented and used to process the measurements on plates. It is shown that the damage indicator is very sensitive, allowing detection of damage that is difficult to identify directly from the strain maps

Damage detection in composite materials using full-field slope measurements

This paper presents a method for detecting damage in layered composite materials using a simple measurement technique, deflectometry. The aim is to locate the damage in a specimen and provide a ‘‘signature’’ in the form of surface slopes. The first part of the paper presents the experimental procedure: material, lay-up and sample types, then the set-up and data extraction are detailed followed by the finite element (FE) models. Finally the results are presented and commented

Contaminated river sediments: potential chemical time bombs ? A case study

status: publishe