At IRDL, André Calazans Menescal de Souza explored metal dissipation under cyclic loading using the FFT method.
Key Takeaway: At IRDL, André Calazans Menescal de Souza explored metal dissipation under cyclic loading using the FFT method.
André Calazans Menescal de Souza, researcher at IRDL (Institut National Polytechnique de Bretagne).
Thesis defended in 2026 at the doctoral school École doctorale Sciences pour l'ingénieur et le numérique.
Referenced in the ABES/STAR network, this thesis meets the rigor standards of French higher education.
Context and Problem Statement
The analysis of thermal dissipation under cyclic loading, commonly referred to as self-heating measurements, is an essential experimental method for estimating the high-cycle fatigue properties of materials. Evaluating this dissipation is particularly relevant in the field of materials mechanics, where understanding the underlying mechanisms can significantly influence the reliability and durability of materials used in various industrial applications. Current research focuses on establishing models that link self-heating measurements to fatigue properties, an approach that could optimize the application of this experimental technique.
Polycrystalline aggregates, as composite materials, display heterogeneous behavior under cyclic loading. Uniaxial cyclic loading, specifically with a load ratio of R = -1, highlights the heterogeneous emergence of microplasticity phenomena within these aggregates. This type of plasticity manifests as localized deformations occurring within specific slip bands, making a detailed analytical approach essential to grasp these complex mechanisms.
Methodology
This study implements a method based on the fast Fourier transform (FFT) to analyze the evolution of dissipation under low-amplitude cyclic loading applied to a representative volume of polycrystalline aggregates. Applying the FFT in this context aims to reproduce, both qualitatively and quantitatively, self-heating curves as a function of loading amplitude.
The methodological approach includes simulations that assess the average cyclic dissipation per cycle. The technique captures the effects of microplasticity, which manifests as localized activation of certain slip bands. In parallel, a dialogue is established between this detailed approach and coarser methods, such as Poisson point processes (P.P.P.), making it possible to explore the dynamics of the emergence of these mechanisms in a progressive, localized manner.
The simulation results are compared against experimental data available in the literature, in order to assess their validity and relevance. This comparison helps refine the established models and enrich the understanding of dissipation phenomena under cyclic loading.
Key Findings
The simulations carried out show significant agreement with reported experimental results, thereby validating the use of the FFT method for analyzing thermal dissipation in polycrystalline aggregates. The results indicate that average cyclic dissipation varies with loading amplitude, making it possible to plot self-heating curves representative of test conditions.
A fatigue indicator parameter (FIP), based on cumulative slip, has been proposed. This parameter suggests a link between slip band activation, self-heating measurements, and the scatter observed in high-cycle fatigue test results. The analysis of the results reveals that the fatigue scatter observed is directly associated with the activation of slip mechanisms, underscoring the importance of these phenomena in materials mechanics.
Discussion and Outlook
The results of this research make a significant contribution to understanding thermal dissipation mechanisms in polycrystalline aggregates subjected to cyclic loading. Establishing a model linking self-heating measurements to fatigue properties opens up prospects for optimizing material testing methods, enabling better prediction of their behavior under real loading conditions.
The practical implications of these results could transform testing standards and industrial practices in materials mechanics. Particular attention could be paid to developing standards based on the proposed fatigue indicator parameter (FIP), thereby providing an effective tool for assessing material fatigue in various contexts.
Future research could further explore the interactions between microplasticity mechanisms and thermal dissipation, as well as the impact of different types of loading on the overall behavior of materials. An in-depth exploration of the relationship between fatigue parameters and self-heating measurements could also enrich knowledge in this field, facilitating the development of more reliable and durable materials.
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Sources and Access
André Calazans Menescal de Souza. Apports des simulations par la méthode FFT sur des agrégats polycristallins à l'étude de la dissipation des métaux sous sollicitations cycliques de faible amplitude. Matériaux et structures en mécanique [physics.class-ph]. École Nationale Supérieure de Techniques Avancées, 2026. Français. ⟨NNT : 2026ESTA0001⟩. ⟨tel-05605680⟩