Generalizing the advancing front method to composite surfaces in the context of meshing constraints topology

International audienceBeing able to automatically mesh composite geometry is an important issue in the context of CAD-FEA integration. In some specific contexts of this integration, such as using virtual topology or meshing constraints topology (MCT), it is even a key requirement. In this paper, we present a new approach to automatic mesh generation over composite geometry. The proposed mesh generation approach is based on a generalization of the advancing front method (AFM) over curved surfaces. The adaptation of the AFM to composite faces (composed of multiple boundary representation (B-Rep) faces) involves the computation of complex paths along these B-Rep faces, on which progression of the advancing front is based. Each mesh segment or mesh triangle generated through this progression on composite geometry is likely to lie on multiple B-Rep faces and consequently, it is likely to be associated with a composite definition across multiple parametric spaces. Collision tests between new front segments and existing mesh elements also require specific and significant adaptations of the AFM, since a given front segment is also likely to lie on multiple B-Rep faces. This new mesh generation approach is presented in the context of MCT, which requires being able to handle composite geometry along with non-manifold boundary configurations, such as edges and vertices lying in the interior domain of B-Rep faces

A new approach to automatic and a priori mesh adaptation around circular holes for finite element analysis

Through our research on the integration of finite element analysis in the design and manufacturing process with CAD, we have proposed the concept of mesh pre-optimization. This concept consists in converting shape and analysis information in a size map (a mesh sizing function) with respect to various adaptation criteria (refining the mesh around geometric form features, minimizing the geometric discretization error, boundary conditions, etc.). This size map then represents a constraint that has to be respected by automatic mesh generation procedures. This paper introduces a new approach to automatic mesh adaptation around circular holes. This tool aims at optimizing, before any FEA, the mesh of a CAD model around circular holes. This approach, referred to as “a priori” mesh adaptation, should not be regarded as an alternative to adaptive a posteriori mesh refinement but as an efficient way to obtain reasonably accurate FEA results before a posteriori adaptation, which is particularly interesting when evaluating design scenarios. The approach is based on performing many offline FEA analyses on a reference case and deriving, from results and error distributions obtained, a relationship between mesh size and FEA error. This relationship can then be extended to target user specified FEA accuracy objectives in a priori mesh adaptation for any distribution of circular holes. The approach being purely heuristic, fulfilling FEA accuracy objectives, in all cases, cannot be theoretically guaranteed. However, results obtained using varying hole diameters and distributions in 2D show that this heuristic approach is reliable and useful. Preliminary results also show that extension of the method can be foreseen towards a priori mesh adaptation in 3D and mesh adaptation around other types of 2D features

Modeling the microstructure of a heterogeneous particle-based material with high-volume fraction

Efficiently predicting the mechanical properties of particle-based heterogeneous materials in terms of both time and cost remains a significant research challenge. This paper introduces two distinct approaches to modify an existing method for the automatic generation of statistical volume elements (SVEs) based on multibody dynamics. These modifications aim at enhancing the accuracy of modeling SVEs with high particle volume fractions, particularly for complex particle shapes. By refining the SVE generation process, the two proposed approaches address challenges in particle positioning and meshing, ultimately contributing to more reliable predictions of materials macroscopic behavior. The first approach involves slightly adjusting the geometric parameters of particles to increase the number of particles that can be inserted and retained within the SVE. The second approach involves generating a larger domain with a target volume fraction, meshing the entire model of this larger domain, and subsequently cutting its mesh to achieve the SVE desired dimensions and to minimize boundary effects. Both approaches are applied to SVEs filled with spherical and cylindrical particles to achieve target volume fractions up to 30%. Results obtained with these two approaches are then compared to those obtained using the existing method. The findings indicate that the geometry correction approach effectively increases the volume fraction of SVEs containing spherical particles, while the mesh cutting approach successfully raises, to the target level, the volume fraction of SVEs containing even more complex elongated particles like cylindrical particles

Towards adaptive topology optimization

This paper presents a new fully-automated adaptation strategy for structural topology optimization (TO) methods. In this work, TO is based on the SIMP method on unstructured tetrahedral meshes. The SIMP density gradient is used to locate solid-void interface and h-adaptation is applied for a better definition of this interface and, at the same time, de-refinement is performed to coarsen the mesh in fully solid and void regions. Since the mesh is no longer uniform after such an adaptation, classical filtering techniques have to be revisited to ensure mesh-independency and checkerboard-free designs. Using this adaptive scheme improves the objective function minimization and leads to a higher resolution in the description of the optimal shape boundary (solid-void interface) at a lower computational cost. This paper combines a 3D implementation of the SIMP method for unstructured tetrahedral meshes with an original mesh adaptation strategy. The approach is validated on several examples to illustrate its effectiveness

Automatic reconstruction of beam structures from 3D topology optimization results

This paper presents a fully-automated reconstruction of beam-like CAD solid structures from 3D topology optimization (TO) results. Raw TO results are first processed to generate a triangulation that represents boundaries of the optimal shape derived. This triangulation is then smoothed and a curve skeletonization procedure is carried out to recover meaningful characteristics of this smoothed triangulation. The resulting skeleton, made with curvilinear geometry, is transformed into straight lines through a normalization process. These straight lines are used to generate a 3D beam structure. Thus, following these steps, a 3D beam structure is automatically derived from TO results. This 3D beam structure is meshed with beam finite elements and since TO non-design material is represented by 3D solid geometry, which is meshed using tetrahedron, the FEA beam structure needs to be rigidly connected with these tetrahedrons. Rigid connections between beam elements and 3D solid elements are ensured using specific FEA beam elements referred to as mini-beams. This results in a mixed-dimensional FEA model with beam and solid finite elements. Results obtained with this mixed-dimensional FEA model allow validating the beam structure obtained from TO results. Performance of the approach is demonstrated on several TO examples

Hygrothermal aging effects on mechanical and fatigue behaviors of a short-natural-fiber-reinforced composite

A new natural fiber composite made of high density polyethylene (HDPE) and 40% wt of short birch fibers (SBF) was developed to replace polyamide (better known under its industrial name “Nylon”) in spur gear manufacturing. The effect of hygrothermal aging on quasi-static and fatigue bending behaviors of this new composite has been studied in this work. Once hygrothermal aging is completed, flexural quasi-static tests have been performed on aged specimens and results compared with those obtained from unaged specimens. It has been observed that hygrothermal aging has no significant effect on flexural mechanical properties of this composite. After characterization, bending fatigue tests have been conducted on aged specimens and results have been compared with those of unaged specimens. These fatigue tests show that hygrothermal aging decreases the high cycles fatigue strength (HCFS) of this composite. The cause of this fatigue durability decrease has been investigated using Fourier transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA) and a scanning electron microscope (SEM). These tests show that the chemical composition and thermal behavior of this composite are not affected by hygrothermal aging. On the contrary, these tests show that damage mechanisms of this composite (HDPE/40% wt of SBF) are directly affected by this type of aging