Jean-Charles Passieux

An adaptive model reduction strategy for post-buckling analysis of stiffened structures

The finite element simulation of structures subjected to post-buckling still faces computational limits, especially for large stiffened structures. Several solving strategies have already been proposed in response to this issue. Among them are the adaptive model reduction solving techniques which demonstrated their ability to drastically reduce the number of unknowns as well as to control the approximation error of solving non-linear problems like post-buckling. The challenges regarding these techniques are the computation of a reduced basis at lower cost, the use of an efficient adaptive procedure and the limitation of the number of call to the adaptive procedure. This paper proposes a Post-Buckling Adaptive Model Reduction (PBAMR) strategy, which requires only two initial Ritz vectors without compromising the accuracy of the simulation. This solving method is tested in the case of shear of a stiffened panel.

Multiscale analysis of complex aeronautical structures using robust non-intrusive coupling

The multiscale analysis of large composite aeronautical structures involves the development of robust coupling strategies. Among the latter, non-intrusive coupling is attractive, since it is able to consistently connect a global simplified linear model to a local detailed one, using features available in commercial software. Up to now, such coupling methods were still limited to academic situations where global and local meshes are geometrically and/or topologically conforming and of low geometric complexity. To meet the goal of merging a complex non-planar global shell to a local detailed 3D model, an extension of these techniques is proposed to handle meshes of complex shapes that are not only non-matching but also geometrically and topologically non-conforming. The implemented strategy is original and robust: the innovative nature of the approach is to expand the initial local solid model by generating transitional shell meshing. The generated model incorporates two distinct coupling interfaces: (i) non-intrusive global–local coupling and (ii) shell–solid coupling. The multiscale strategy was successfully validated through different numerical experiments using standard Input/Output of a commercial finite element software. In particular, a representative use-case involving a realistic fuselage section of an aircraft was computed.

Finite Element Stereo Digital Image Correlation Measurement for Plate Model

The aim of this study is to measure accurately the boundary conditions, namely the displacements and rotations, along the edges of a large part of a composite panel subjected to complex loadings. With classical Stereo Digital Image Correlation techniques (Stereo DIC), the displacement field can only be measured on the upper skin. The rotations are usually estimated a posteriori by numerical differentiation and smoothing. Unfortunately additional uncertainties may arise with these steps. Conversely, the use of a Finite Element plate model is proposed here to regularize a Stereo Finite Element-DIC measurement (Stereo FE-DIC). The idea is to use the 3D displacement as the primary unknown of the correlation problem. This approach thus requires projection operators (here based on a pinhole camera model). It allows taking into account distortions directly.

DD-DIC: A Parallel Finite Element Based Digital Image Correlation Solver

The computational burden associated to finite element based digital image correlation methods (FE-DIC) is mostly due to the inversion of global FE systems and to global image interpolations. On the contrary, subset based approaches require only subimages, and allow solving small independent systems in parallel. A variable separation technique was recently proposed that alleviate mesh constraints in FE-DIC. However, in digital volume correlation, the question of the interpolation of the images becomes a real issue. For that reason, a non-overlapping dual domain decomposition method is proposed to rationalize the computational cost of high resolution FE-DIC measurements when dealing with large datasets. It consists in splitting the global mesh into submeshes and the images into subimages. The displacement continuity at the interfaces between subdomains is obtained iteratively by using a preconditioned conjugate gradient. It will be shown that the method combines the metrological performances of finite element based DIC and the parallelization ability of subset based DIC methods.

3D Digital Image Correlation Applied to Birdstrike Tests

The development of new bird strike shielding materials for commercial aircrafts requires test campaigns. During these tests, measurement of the high speed deformation is needed to characterize and compare the mechanical response of the shielding samples and to correlate numerical simulations with experiments. In this work, 3D digital image correlation method is used with high speed (HSP) cameras to compute the displacement and strain fields on a large area (approximately 400 mm wide) of the back side of impacted samples. Compromise on spatial resolution, frame rate of HSP camera and measurement error is discussed.

Multiscale FE-Based DIC for Enhanced Measurements and Constitutive Parameter Identification

Since they provide a large amount of information, full-field measurement techniques like Digital Image Correlation (DIC) allow the identification of several material parameters from a single non-homogeneous test. However the level of uncertainty associated with the identified parameters depends on the displacement measurement uncertainties, which are related to the spatial resolution of the measurement. To overcome the well-known compromise between spatial resolution and uncertainty, a multiscale approach to Finite Element DIC (FE-DIC) is proposed by considering additional nearfield images to improve locally the resolution of the measurement. An accurate estimation of the nearfield/farfield transformation is obtained by a dedicated global DIC method to bridge precisely the measurements at both scales. This multiscale FE-DIC measurement is then associated to a multiscale Finite Element Model Updating (FEMU) identification technique. After being validated on synthetic test cases, the method is applied to a tensile test carried out on an open-hole specimen made of glass/epoxy laminate. The four in-plane orthotropic elastic parameters are identified. Results show that the multiscale approach greatly improves the uncertainties of both the measured displacements and the identified material parameters.