Local scale fracture characterization of an advanced structured material manufactured by fused deposition modeling in 3D printing.

Additive manufacturing (AM) is a promising way to produce complex structures by adding layers. It arises great interest both in industrial and academic sectors to develop new advanced structured material. To benefit from its advantages, it is important to accurately characterize the obtained structures in order to ensure their integrity during operation. It becomes then important to characterize these structures at the local scale (micron and/or the nanometer scale). In the specific case of polymeric materials obtained by Fused Deposition Modeling (FDM), the comprehension of the mechanical behavior between adjacent layers during deformation can help improving mechanical properties. However, few studies in the literature have focused on implementing approaches to characterize local strains at the surface of these materials. In this study, an original approach based on the use of speckle pattern with particle average size of 20 microns in diameter was coupled to digital image correlation (DIC). It has been applied to the case of a SENT structure with a notch made by FDM. The successive images recorded by a digital microscope allow a qualitative analysis of the evolutions of the local strains. The kinematic fields are obtained by DIC. The strain evolutions at the tip of the notch are highlighted. The deformation mechanisms at the local scale are confronted with macroscopic behavior of the structure

Evaluation of the stress singularities of plane V-notches in bonded dissimilar materials

According to the linear theory of elasticity, there exists a combination of different orders of stress singularity at a V-notch tip of bonded dissimilar materials. The singularity reflects a strong stress concentration near the sharp V-notches. In this paper, a new way is proposed in order to determine the orders of singularity for two-dimensional V-notch problems. Firstly, on the basis of an asymptotic stress field in terms of radial coordinates at the V-notch tip, the governing equations of the elastic theory are transformed into an eigenvalue problem of ordinary differential equations (ODEs) with respect to the circumferential coordinate h around the notch tip. Then the interpolating matrix method established by the first author is further developed to solve the general eigenvalue problem. Hence, the singularity orders of the V-notch problem are determined through solving the corresponding ODEs by means of the interpolating matrix method. Meanwhile, the associated eigenvectors of the displacement and stress fields near the V-notches are also obtained. These functions are essential in calculating the amplitude of the stress field described as generalized stress intensity factors of the V-notches. The present method is also available to deal with the plane V-notch problems in bonded orthotropic multi-material. Finally, numerical examples are presented to illustrate the accuracy and the effectiveness of the method

A new boundary element approach of modeling singular stress fields of plane V-notch problems

In this paper, a new boundary element (BE) approach is proposed to determine the singular stress field in plane V-notch structures. The method is based on an asymptotic expansion of the stresses in a small region around a notch tip and application of the conventional BE in the remaining region of the structure. The evaluation of stress singularities at a notch tip is transformed into an eigenvalue problem of ordinary differential equations that is solved by the interpolating matrix method in order to obtain singularity orders (degrees) and associated eigen-functions of the V-notch. The combination of the eigen-analysis for the small region and the conventional BE analysis for the remaining part of the structure results in both the singular stress field near the notch tip and the notch stress intensity factors (SIFs). Examples are given for V-notch plates made of isotropic materials. Comparisons and parametric studies on stresses and notch SIFs are carried out for various V-notch plates. The studies show that the new approach is accurate and effective in simulating singular stress fields in V-notch/crack structures

Fracture mechanics and crack growth / Naman Recho.

Includes bibliographical references and index.Book fair 2013.xxiii, 479 p. :This book presents recent advances related to the following two topics: - how mechanical fields close to material or geometrical singularities such as cracks can be determined; - how failure criteria can be established according to the singularity degrees related to these discontinuitie

Fissuration en fatigue des structures mécano-soudées soumises à un environnement mécanique complexe

Dans ce travail, une démarche d'analyse en fatigue des structures mécano-soudées industrielles soumises à des environnements mécaniques complexes est proposée. Basée sur une approche multi-échelle et sur le principe de superposition, elle utilise la méthode des éléments finis pour déterminer une carte du dommage de la structure avant de se focaliser sur l'amorçage de fissures. La propagation est traitée en couplant l'approche locale du dommage - le multi amorçage -, avec la prise en compte de la souplesse de la stucture fissurée au moyen d'éléments ressorts et grâce au developpement de Boites à Fissures, utilisées pour le calcul des facteurs d'intensité de contrainte, l'analyse de la bifurcation et de l'ouverture des fissures pour les chargements variables. Tous ces développements ont permis de créer une démarche et un outil permettant de traiter, sans remaillage, de l'amorçage d'une fissure jusqu'à la ruine, et qui ont été mis en oeuvre sur une structure industrielleCLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Analyse fiabiliste de la fatigue des joints soudés soumis à l'effet de surcharge

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

COMPORTEMENT ET DUREE DE VIE D'UNE JONCTION TUBULAIRE SOUDEE EN 316L A 600\C

CLERMONT FD-BCIU Sci.et Tech. (630142101) / SudocSudocFranceF

Fracture Improvement by Reinforcing the Structure of Acrylonitrile Butadiene Styrene Parts Manufactured by Fused Deposition Modeling

International audienceFused deposition modeling deposits a filament layer by layer and according to a trajectory. Based on stress criterion for filament deposition, this work suggests reproducing the principal directions of the stress in the sample through the control of the filament direction. A number of compact-tension (C-T) specimens have been printed with and without respecting this criterion. The fracture toughness test of these specimens was realized to compare the results. The results show that the suggested criterion leads to an improvement of 30% in the fracture toughness. Digital images correlation has been extensively used to study the local strain field in the specimens. Strain mapping reveals an important change in fracture behavior. The modification of filament direction leads to “ductile-like behavior” in crack extension, which is characterized by a large deformation zone associated with a slow crack growth rate during crack propagation

Low cycle fatigue of welded joints : coupled initiation propagation model

International audienceThis paper deals with the low-cycle fatigue (LCF) design of welded structures, the aim being the critical analysis of the rule used in the RCC-MR [Design and construction rules for mechanical components of FBR nuclear islands, AFCEN, 1993], for the design and construction of fast breeder reactors. The study takes into account the evolution of the material behavior laws and damage accumulation during the fatigue loading. The adopted model consists of analyzing separately the behavior and the damage evolutions. It allows us to determine the damage ratio corresponding to initiation and propagation of a significant crack in order to determine the life duration. This model suggests the existence of a threshold level of loading, above which micro-cracks initiate. The initiation fatigue life can then be neglected below the threshold level. This work shows also that the RCC-MR rules are valid below this threshold load level