Hybrid Stereocorrelation Using Infrared and Visible Light Cameras

International audience3D kinematic fields are measured using an original stereovision system composed of one infrared (IR) and one visible light camera. Global stereocorrelation (SC) is proposed to register pictures shot by both imaging systems. The stereo rig is calibrated by using a NURBS representation of the 3D target. The projection matrices are determined by an integrated approach. The effect of gray level and distortion corrections is assessed on the projection matrices. SC is performed once the matrices are calibrated to measure 3D displacements. Amplitudes varying from 0 to 800 µm are well captured for in-plane and out-of-plane motions. It is shown that when known rigid body translations are applied to the target, the calibration can be improved when its actual metrology is approximate. Applications are shown for two different setups for which the resolution of the IR camera has been modified

Regularized InfraRed Image Correlation Applied to Laser-Induced Thermal Shocks

International audienceThe thermomechanical behavior of a stainless steel undergoing thermal shocks is investigated with an infrared (IR) camera. The temperature and kinematic fields are determined simultaneously exploiting only IR frames. The thermal loading is imposed with a laser, which gives rise to very high local digital level variations. This effect is addressed thanks to a regularized infrared image correlation (R-IRIC) technique, which accounts for brightness and contrast variations. The resulting digital level residuals are reduced from 54% down to less than 1% of the dynamic range

Nouveau dispositif experimental pour la realisation d'essais de fatigue thermique a grand nombre de cycles

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Hybrid multiview correlation for measuring and monitoring thermomechanical fatigue test

International audienceThis paper focuses on the development of fully-coupled 3D thermomechanical field measurement techniques applied for monitoring thermal fatigue tests. First, an original hybrid and multiview system composed of one infrared (IR) camera and two visible light cameras is introduced. The spatial registration of multimodal imaging devices is solved successfully using global Hybrid Multiview Correlation (HMC) based on the NURBS representation of the 3D calibration target and the surface of interest. The measurement uncertainties are estimated with an initial heating up phase prior to the fatigue test. Then, HMC is performed to measure the 3D surface displacement and temperature fields during laser shocks onto an austenitic stainless steel plate. Last, the HMC measurements are validated in comparison with finite element simulations of the test

Thermomechanical field measurements by hybrid stereocorrelation

International audienceIn order to investigate the thermal fatigue occurring in the cooling system of nuclear power plants, an experimental setup, the so-called FLASH (THErmal Fatigue by LASer or Helium pulses) setup is designed to perform high cycle (about several 10$^6$) thermal fluxes onto the surface of austenitic stainless steel with excellent stability of thermal loading. With the prediction of finite element analyses, it is deduced that the largest strain variations during cyclic loading are in the out-of-plane direction resulting in several micrometer out-of-plane displacements. In the present work, it is shown that 3D displacement fields and 2D Lagrangian temperature fields can be measured thanks to a hybrid stereovision setup via global stereocorrelation. The stereovision system is composed of one infrared camera and one visible light camer

Essai de fatigue thermique par chocs laser

National audienceA new experimental setting is used to study thermal fatigue phenomenon occurring in structures ofnuclear power plants. The cyclic thermal shocks are performed by a laser. A thermal fatigue test ispresented on an A316L(N) stainless steel. The initial temperature is 380°C and the thermal loading isof 200°C imposed at a frequency of 1.5 Hz. The thermal fatigue test is performed till a crack is formed(of 800µm). The thermal and kinematic fields are measured owing to an infrared and a visiblecamera. Thanks to the synchronization of both cameras and to the digital image correlation methodused, the initiation and propagation of the crack can be approximated.Un nouveau dispositif expérimental est utilisé pour étudier les phénomènes de fatigue thermique dansles matériaux de structures de centrales nucléaires au travers de chocs thermiques cycliques par unlaser de puissance. Un essai de fatigue, sur un acier AISI 316 L(N), est mené jusqu’à apparition defissure (800µm) avec une température initiale de l’échantillon de 380°C et une variation cyclique detempérature de 200°C à une fréquence de 1.5 Hz. Les champs de température et de déformation dansla zone d’impact sont mesurés expérimentalement sans contact. Grâce à la synchronisation descaméras et à la méthode de corrélation d’image numérique, les premiers stades d’amorçage et depropagation peuvent être estimés

Hybrid Stereocorrelation for 3D Thermomechanical Field Measurements

Proceedings of the 2016 Annual Conference on Experimental and Applied MechanicsInternational audienceThree dimensional displacement fields are measured thanks to an original stereo system made of InfraRed (IR) and visible light cameras. This configuration provides the thermal fields which drive the thermomechanical loading and the 3D surface displacement fields, i.e. the response of the studied material. The calibration of the stereo rig is performed by using a 3D target of known geometry and the large gray level variations that occur on the IR images are accounted for by applying a low-pass filter. Because of a slight disorientation of the target, a further calibration correction step revealed necessary. After correction of the target orientation, the measured displacement fields display a good qualitative agreement (no quantitative comparison has been performed yet) with the expected fields

Stereo-DIC using high magnification infrared and visible cameras

International audienceMeasurements of kinematic fields are performed with an original combination of two different imaging modalities, (i.e. one IR and one visible camera). Stereo Digital Image Correlation (SDIC) procedures are performed with a global approach [1]. The stereovision system is first calibrated by performing lens distortion corrections [2]. Then the projection model parameters are determined thanks to the CAD (NURBS) representation of the 3D sample surface using an integrated approach. This CAD-based SDIC, offers the possibility to determine the specimen deformation. The simple case of3D rigid translational motions is experimentally tested and validated.Des mesures de champs cinématiques 3D sont réalisées en utilisant une combinaison originalebimodale de deux caméras (l’une infra-rouge(IR) avec un objectif G1 et l’autre visible).L’appariement des images acquises par les deux imageurs est mené par une méthode globale deStéréo Corrélation d’Images Numériques (SCIN) [1]. Le système de stéréovision est étalonné, d’unepart en corrigeant les distorsions provoquées par les optiques [2] et d’autre part en déterminant lesparamètres du modèle projectif. A l’aide d’une représentation CAO (NURBS) de la surface de l’objetobservé ces paramètres sont déterminés en utilisant une approche intégrée de SCIN. Cette techniquepermet la mesure de la cinématique de la pièce étudiée. Le cas de translations de corps rigides estétudié expérimentalement pour illustrer la méthode et la valide