John-Eric Dufour

Characterization of temperature and strain fields during cyclic laser shocks

Thermal shocks are applied to a 304L austenitic stainless steel plate with a pulsed laser. A stroboscopic reconstruction is used for infrared (IR) and visible light camera measurements. The displacement fields are measured with a digital image correlation (DIC) technique. Different IR devices are used to measure the temperature variations (i.e. medium wave camera and short wave pyrometry). Several ways of determining the emissivity or absorptivity are discussed. The complete 3D thermal loading is numerically determined by minimising the difference between experimental measurements and finite element analyses of thermal fields. An elastoplastic model is then used to compute mechanical fields that are compared with DIC measurements.

Shape Measurement Using CAD-Based Stereo-DIC

The aim of this study is to measure the (complex) shape of an object by using a priori information given by its CAD representation in a 3D-DIC framework. In order to follow a 3D object during its deformation and to determine 3D surface displacement fields, a first measurement of the object shape is necessary. The main goal of the present method is to obtain a CAD representation of this measurement by updating the CAD reference via a global approach to 3D-DIC. Although in the majority of the shape measurement methods a cloud of points is obtained and subsequently interpolated to create a continuous description of the surface, CAD-based stereoDIC is devised to directly measure a 3D shape described by NURBS. This approach allows a direct link to be established between the theoretical CAD model and its true geometry thereby yielding the metrology of the measured surface in the CAD language.

IGMU: A Geometrically Consistent Framework for Identification from Full Field Measurement

DIC can be coupled with computational tools in order to characterize materials by using identification techniques such as finite element model updating or integrated approaches. In this study a framework using CAD-based stereo-DIC coupled with Isogeometric Analyses is followed to implement such identification procedures. Using both techniques allows us to be consistent with the designed geometry and its kinematics as the NURBS formalism is kept during the whole process and fewer degrees of freedom are needed (for the displacement field and the geometric representation of the surfaces) than in classical (finite element) approaches. This technique can be adapted to be written within an integrated framework (whose sensitivity fields are given by an isogeometric code).

Displacement Measurements Using CAD-Based Stereo-DIC

The aim of this study is to measure displacement fields during an experiment on a structure by using a priori information about its surface representation in a stereoDIC framework. The main goal of the present method is to measure the displacement and strain fields in formalisms completely consistent with the surface description via global stereoDIC. Although the majority of stereoDIC methods provide clouds of 3D displacement vectors associated with clouds of 3D points, which are subsequently interpolated to get continuous fields, the proposed CAD-based stereoDIC allows continuous 3D displacement fields to be measured directly. Therefore, there is a direct link between the measured fields and computational results since common shape and kinematic bases are considered. No additional interpolation or data manipulation is needed with such approaches. One practical example will illustrate the use of this novel technique.