3D dAta DriVEn iNvestigation of faTigUe cRack growth with ovErload effects – ADVENTURE
ADVENTURE: 3D dAta DriVEn iNvestigation of faTigUe cRack growth with ovErload effects
The aim of ADVENTURE is to study the influence of overloads on 3D fatigue cracks in order to build predictive models to manage even short cracks with a complexity and history effect similar to those encountered in real structures.
Taking into account the influence of overloads on 3D cracks: a safety issue
Reliable models are essential in all areas where cracking is a safety issue. Although structural materials are subjected to variable amplitude fatigue loading, the effect of overloads remains difficult to predict. After an overload, the relationship between the crack growth rate before overload and Stress Intensity Factor (SIF) fails. Although the phenomenon is known, the underlying mechanisms remain controversial and often studied on the surface. Understanding the 3D effects resulting from the variation in plastic zone size along the crack front requires further experimental techniques.<br /><br />A coupling of fatigue tests under synchrotron tomography with digital volume correlation (DVC) will allow to measure the closure along the crack front and its evolution after overload. To obtain high resolution of the DVC, a fine-grained Al-Si alloy with a natural speckle will be fabricated. Tests will also be carried out in 2D on specimens allowing different structure/constraint effects to be obtained in order to extend the experimental database. Indeed, the 2D and 3D data (displacement fields, cracks), never seen at this scale, will feed a new Generalized, compared to those in the literature, and Incremental, such as plasticity, Model (GIM), via a Data-Driven approach that breaks away from the Paris law. Since the crack growth rate is related to plasticity, the plasticity at the crack tip will be measured by topological descriptors of the plastic zone forming a Plastic Flow Indicator (PFI). The crack will also be described by an extended SIF (SIF++) including T and B stresses related to structural/constraint effects. The GIM model consists in using an interpolation/regression technique within the experimentally fed database to obtain, in a linear elastic numerical simulation, the propagation velocity estimate from the evaluation of the SIF++ along the crack front and the evolution of the PFI.
The proposed methodology can be summarized as follows: (1) A structural material, a fine-grained Al-Si casting alloy with a speckle of silicon particles, will be developed to promote the propagation of a crack that is relatively easy to model; (2) Overload fatigue tests will be carried out under synchrotron tomography to monitor 3D crack growth and distinguish fine Si particles. Tests will also be carried out with 2D observation on specimens allowing to vary the structure/constraints effects; (3) 2D/3D field measurements from the tests will allow to understand the mechanisms at play during overload by monitoring the evolution of the crack and growth rates but also to extract the SIF++ and to interpret the mechanisms observed in the light of this parameter; (4) These data will feed the database of the GIM model with the SIF++ and the PFI deduced from the displacement fields by a non-parametric approach; (5) The validation will consist in reproducing the experimental observations by a 3D X-FEM numerical simulation using the GIM.
The first results obtained in the project are as follows.
(1) Achievement of a fine-grained Al-Si alloy:
CTIF has succeeded in rapidly elaborating a fine-grained (~100 µm) Aluminium-Silicon alloy with a eutectic Silicon distribution forming a natural speckle essential for image correlation. The first tests confirm the feasibility of the correlation on the tomographic images obtained (adequate Si speckle) and the relative flatness of the cracks thanks to the sufficiently fine grains. Three campaigns of specimen production have been delivered.
(2) Fatigue crack growth test with 3 overloads performed in-situ under synchrotron tomography:
A test campaign was performed in December 2021 at SLS. The specimens were machined in the fine-grained Aluminium Silicon alloy developed by CTIF. We successfully completed a cracking test with 3 overloads. After each overload, a crack arrest is observed and regular tomographic acquisitions allowed to detect the resumption of the propagation. Tomographic acquisitions were performed at the minimum and maximum cycle loads during propagation before the overload, and then at different intermediate loads at the discharge of the cycles before and after the overload. The objective is to study the evolution of the closure with overloading to better understand the slowing down induced by the overload on the cracking. The results are currently being analyzed.
(3) Cracking test on SENT specimens:
A chain of experimental tools has been developed that makes the performance of fatigue tests on SENT specimens completely automatic. The decision making for the realization of the overloads is facilitated by a follow-up by image correlation in real time.
The numerous data (3D under tomography and 2D on SENT specimens) obtained during crack growth clearly show the retardation after overload. An important work of processing and analysis is planned for the next few months: image correlation, extraction of stress intensity factors, topological description of the plastic zone... Once completed, we will have a database from which to develop the MIG model using a data-driven approach.
*In-situ 3D study of fatigue crack growth with overload effects in AlSi alloy. L. Sanciet--Munier, N. Limodin, J-Y Buffière, J-F Witz, M. Coret, G. Bahaj Filali, Y. Gaillard, M. Fleuriot, A. Weck. 5th International Conference on Tomography of Materials & Structures (ICTMS 2022), 27 Jun – 1 Jul 2022, Grenoble.
*Étude 3D in-situ de la propagation de fissures de fatigue avec effets de surcharge dans un alliage AlSi. L. Sanciet--Munier, N. Limodin, J-Y Buffière, J-F Witz, M. Coret, G. Bahaj Filali, Y. Gaillard, M. Fleuriot, A. Weck, A. Bonnin, G. Lovric, J. Lachambre. Congrès Français de Mécanique 2022, 29 Aoû – 2 Sep 2022, Nantes.
*Metalnews CTIF Avril 2022 www.ctif.com/en-cours-adventure-etude-3d-data-driven-de-la-propagation-des-fissures-de-fatigue-avec-effets-de-surcharge/
The aim of ADVENTURE is to study the influence of overloads in order to build predictive models to handle even short 3D fatigue cracks with a complexity and history effect similar to those encountered in real structures.
Reliable models are essential in any industry where cracking is a safety issue. The relationship between crack growth rate before overload and Stress Intensity Factor (SIF) fails. Even if the phenomenon is known, the mechanisms remain controversial and, often, studied on the surface. An understanding of the 3D effects resulting from the variation in size of the plastic zone along the crack front requires further experimental techniques.
Coupling fatigue tests under synchrotron tomography with digital volume correlation (DVC) will make it possible to measure the deformations and their evolution after overload. To obtain a high resolution of the DVC, a fine-grained Al-Si alloy with a natural speckle will be fabricated. 2D tests will allow to enlarge the experimental database. The 2D and 3D data (displacement fields, cracks), which are unique at this scale, will feed a new Generalized Incremental (as well as plasticity) crack propagation Model (GIM) that breaks away from the Paris law. The crack propagation rate being linked to the plasticity at the crack tip, the latter will be measured by a Data-Driven approach and characterized by topological descriptors of the plastic zone forming a Plastic Flow Indicator (PFI). The crack will also be described by an extended SIF (SIF++) that includes T- and B- stresses related to structure/constraint effects. The GIM model consists in searching the experimental database to obtain, during an elastic numerical simulation, the crack growth rate estimate from the evaluation of the SIF++ along the crack front and the evolution of the PFI.
The proposed methodology can be summarized as follows: (1) A structural material: a fine-grained Al-Si casting alloy with silicon particles; (2) Overload fatigue tests performed under synchrotron tomography to distinguish the fine Si particles and follow the 3D crack growth. Complementary 2D tests allowing to vary the effects of structure/constraint; (3) 2D/3D field measurements allowing to understand the mechanisms acting during an overload by monitoring the crack and the propagation velocities but also the extraction of SIF++; (4) The data will feed the database of the GIM model with the SIF++ and the PFI deduced from the displacement fields by a Data-Driven approach; (5) The validation will consist in reproducing, by a 3D X-FEM numerical simulation using the GIM, the experimental observations.
To achieve these goals, the 4 partners will share their expertise in aluminum alloy metallurgy (CTIF), in fatigue tests coupled with field measurements (LaMcube) and performed in situ under X-ray tomography (MATEIS) and in Data-Driven identification techniques (GeM).
This collaborative project meets the objectives of the "Metallic and Inorganic Materials and Associated processes" axis. It will enable an understanding of 3D cracking mechanisms by coupling in situ tests with measurements of an unseen resolution in 3D. The richness of the experimental data will allow to propose and validate a new 3D propagation prediction model that can be implemented in any software. More predictive tools will give more reliable structures, for example in transport and energy.
Madame Nathalie Limodin (Laboratoire de Mécanique, Multiphysique et Multiéchelle)
The author of this summary is the project coordinator, who is responsible for the content of this summary. The ANR declines any responsibility as for its contents.
MATEIS Matériaux : Ingénierie et Science
GeM INSTITUT DE RECHERCHE EN GÉNIE CIVIL ET MÉCANIQUE
LaMcube Laboratoire de Mécanique, Multiphysique et Multiéchelle
CTIF CENTRE TECHNIQUE INDUSTRIES FONDERIE
Help of the ANR 540,616 euros
Beginning and duration of the scientific project: - 48 Months