In order to address the objectives mentioned above, the expected scientific program is the following:
Â• Improved kill-element technique: This first axis will consist in improving the actual kill element technique by using mesh adaption techniques in order to control the mesh refinement perpendicular to the failure plane. Such technique will allow limiting the volume loss during kill-element and will induce smoother fracture surfaces . Finally, additional mesh smoothing techniques could be applied in order to improve surfaces smoothness.
Â• Damage to fracture transition and crack initiation: Many studies were conducted in the past to predict ductile fracture in Forge [1-3]. Ductile damage models of failure criteria define a damage variable that grows and give raise to failure initiation once a threshold is reached. This damage analysis is based on continuous mechanics and the transition to discontinuous fracture will be addressed here. In particular, the insertion of a discontinuity, representing the crack surfaces, will be handled in a full 3D parallel environment based on continuous damage fields [5, 6].
Â• 3D Crack propagation: Once initiated, 3D crack propagation will raise two main challenges that should be addressed: (i) prediction of crack path based on damage fields and (ii) development of advanced remeshing techniques to propagate cracks in the 3D mesh [6-8]. The idea would be to define fracture surfaces by Level-Set functions and to enhance a recently developed body-fitted mesh adaptation technique [9,10] to handle 3D crack propagation in a robust way.
The PhD student will benefit from lectures in materials science, non-linear solid mechanics, damage and fracture. These competences will provide opportunities to develop future activities in various R&D sectors in energy, transport and metallurgical industries.
'Transvalor is a software engineering company developing products dedicated to material forming processes applications. The main product FORGE® is a finite element software that enables to model material behavior under large plastic strain and complex loading conditions representative of forming processes. FORGE® is a leading software in this field used in more than 350 companies worlwide from various sectors of the mechanical industry including automotive, aerospace and energy industry.
In most forming processes, it is essential to predict and avoid the initiation of defects during material forming. Such predictions require appropriate material behavior law and ductile damage models, already available in FORGE® [1-3]. However, in some cases, the modeling of failure is essential and an accurate and robust numerical technique is necessary to predict correct failure surfaces (blanking and fine blanking processes, machining …). Although the context of this project is centered on numerical modeling of industrial manufacturing processes, the underlying physical phenomena and numerical developments are also relevant in other fields (e.g. biomechanics, geoscience, physics, among many others).
Nowadays, the modeling of fracture in the finite element (FE) software Forge® is based on the so-called “kill-element” technique. This technique consists in deleting elements from the mesh once a user-defined damage variable reaches a threshold. The kill-element technique is both easy to use and robust, but it also has major limitations. Its main limitation relies on its inherent mesh dependency. In addition, this approach gives raise to volume loss and the prediction of an accurate fracture surface is impossible (See Fig. 1). It is therefore necessary to improve the way fracture is modeled in a 3D environment and within the context of metal forming applications. To reach this goal, TRANSVALOR is hiring a Cifre PhD student and wishes to collaborate with CEMEF for its scientific supervision.
CEMEF (Center for Material Forming Processes) MinesParisTech has a strong expertise in the numerical modeling of material forming processes (in particular in FORGE®) and a long experience in the study and the modeling of ductile damage [1-3] and fracture with advanced use of automatic remeshing techniques [4, 7-10].
The aim of this PhD project is the modeling of 3D ductile fracture in the FE software Forge®. This requires the development of new numerical techniques to model surface discontinuities and automatic crack propagation in a robust environment. '
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