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{ "count": 3, "next": null, "previous": null, "results": [ { "id": 71250, "title": "MechE Colloquium: When Materials Bend the Rules: Buckling Response of Slender Structures Born of Constitutive Nonlinearities", "slug": "meche-colloquium-when-materials-bend-the-rules-buc", "event_url": "https://memento.epfl.ch/event/meche-colloquium-when-materials-bend-the-rules-buc", "visual_url": "https://memento.epfl.ch/image/32609/200x112.jpg", "visual_large_url": "https://memento.epfl.ch/image/32609/720x405.jpg", "visual_maxsize_url": "https://memento.epfl.ch/image/32609/max-size.jpg", "lang": "en", "start_date": "2026-04-14", "end_date": "2026-04-14", "start_time": "12:00:00", "end_time": "13:00:00", "description": "<strong>Abstract: </strong>Buckling of slender structures, such as perforated columns and cylindrical shells, underpins a wide range of systems and processes, from the structural failure of rocket fuselages and grain silos to engineered devices such as shock absorbers and crumple zones. Historically, research has primarily focused on predicting the onset of buckling—that is, the loss of the original configuration under excessive loading—rather than on understanding how structures evolve in the post-buckling regime. Recently, however, the study of buckling has experienced a renaissance, with post-buckling mechanical responses increasingly exploited to achieve new functionalities, for example enhancing fracture resistance in stretchable electronics and flexible displays.<br>\r\n<br>\r\nWhile most existing studies consider elastically deforming systems whose behaviour arises primarily from geometric nonlinearities, this talk presents examples in which geometric effects are coupled with nonlinear constitutive responses, giving rise to new post-buckling mechanisms. First, we investigate the buckling of hard, perforated (“holey”) structures that exhibit auxetic behaviour but, unlike their purely elastic counterparts, undergo post-buckling softening. The resulting negative stiffness is captured using a pseudo-plastic constitutive model that describes nonlinearities emerging from the structural microarchitecture.<br>\r\n<br>\r\nWe then apply a similar framework to examine the buckling of beverage cans largely filled with liquid under axial compression. Whereas empty cylindrical shells typically develop periodic buckling patterns that break both axial and circumferential symmetry, liquid-filled cylinders buckle axisymmetrically. The resulting ring-shaped buckles are localized and emerge sequentially, progressively covering the can surface. We show that this behaviour arises from nonlinear, spatially anisotropic hoop stresses that soften and subsequently re-stiffen during compression.<br>\r\n<br>\r\n<strong>Biography: </strong>Draga Pihler-Puzovic is a Reader in the Department of Physics and Astronomy at the University of Manchester and a core member of the Manchester Centre for Nonlinear Dynamics. Her research focuses on fluid–structure interactions, low-Reynolds-number flows, and the deformation of slender solid structures. She employs a combination of experimental, numerical, and analytical approaches to investigate fundamental problems in fluid and solid mechanics, and has made significant contributions to the understanding of instabilities arising in fluid–structure interactions, including viscous fingering beneath elastic sheets, sedimentation dynamics and deformation of mechanical metamaterials.", "image_description": "", "creation_date": "2026-02-26T14:40:18", "last_modification_date": "2026-02-26T14:52:52", "link_label": "", "link_url": "", "canceled": "False", "cancel_reason": "", "place_and_room": "MED 0 1418", "url_place_and_room": "https://plan.epfl.ch/?room==MED%200%201418", "url_online_room": "https://epfl.zoom.us/j/61360740951", "spoken_languages": [ "https://memento.epfl.ch/api/v1/spoken_languages/2/?format=api" ], "speaker": "<a href=\"https://personalpages.manchester.ac.uk/staff/draga.pihler-puzovic/\">Prof. Draga Pihler-Puzović</a>, <a href=\"https://www.physics.manchester.ac.uk/\">Department of Physics and Astronomy</a>, <a href=\"https://www.manchester.ac.uk/\">University of Manchester</a>", "organizer": "<a href=\"mailto:[email protected]\">Institute of Mechanical Engineering (IGM)</a>", "contact": "<a href=\"https://people.epfl.ch/pedro.reis?lang=en\">Prof. Pedro M. Reis</a>", "is_internal": "False", "theme": "", "vulgarization": { "id": 1, "fr_label": "Tout public", "en_label": "General public" }, "registration": { "id": 3, "fr_label": "Entrée libre", "en_label": "Free" }, "keywords": "MechE Colloquium: When Materials Bend the Rules: Buckling Response of Slender Structures Born of Constitutive Nonlinearities", "file": null, "icalendar_url": "https://memento.epfl.ch/event/export/119899/", "category": { "id": 1, "code": "CONF", "fr_label": "Conférences - Séminaires", "en_label": "Conferences - Seminars", "activated": true }, "academic_calendar_category": null, "domains": [], "mementos": [ "https://memento.epfl.ch/api/v1/mementos/1/?format=api", "https://memento.epfl.ch/api/v1/mementos/6/?format=api", "https://memento.epfl.ch/api/v1/mementos/8/?format=api", "https://memento.epfl.ch/api/v1/mementos/232/?format=api", "https://memento.epfl.ch/api/v1/mementos/270/?format=api" ] }, { "id": 71345, "title": "MechE Colloquium : Instability and breakdown phenomena in vortical flows", "slug": "meche-colloquium-instability-and-breakdown-pheno-2", "event_url": "https://memento.epfl.ch/event/meche-colloquium-instability-and-breakdown-pheno-2", "visual_url": "https://memento.epfl.ch/image/32805/200x112.jpg", "visual_large_url": "https://memento.epfl.ch/image/32805/720x405.jpg", "visual_maxsize_url": "https://memento.epfl.ch/image/32805/max-size.jpg", "lang": "en", "start_date": "2026-04-28", "end_date": "2026-04-28", "start_time": "12:00:00", "end_time": "13:00:00", "description": "<strong>Summary</strong><br>\r\nVortical structures generated by fixed or rotating lifting surfaces play a central role in many aerodynamic and hydrodynamic flows. Their stability and eventual breakdown influence wake dynamics, mixing processes, and overall flow performance. This seminar presents two recent studies exploring vortex stability and vortex breakdown.<br>\r\nPart I – Short-wave instability of a helical vortex<br>\r\nThe first part of the seminar discusses the short-wave instability of a helical vortex generated by a rotating blade. Combining experimental dye visualisations, numerical simulations, and theoretical analysis, the study identifies displacement perturbations whose wavelengths are small relative to the helix radius and pitch but may remain large compared with the vortex core size. Stability analysis based on experimentally measured vortex profiles reveals broad bands of unstable wavenumbers for several vortex bending modes. These results differ from predictions of existing theories for short-wave vortex instability. Similar instability modes are also observed in arrays of straight vortices, indicating that the phenomenon is not related to vortex curvature. A theoretical examination of the dispersion relation of Kelvin modes for the measured vortex profiles uncovers a previously unidentified family of modes associated with the specific vorticity distribution. Their non-resonant interaction through the strain field provides a plausible explanation for the experimentally observed instability features.<br>\r\nPart II – Two-phase wing-tip vortex breakdown<br>\r\nThe second part presents the discovery of a new flow feature observed in the wake of a rectangular wing in water: the breakdown of the wing-tip vortex triggered by the injection of air into the vortex core downstream of the wing. Experiments show that, for certain combinations of Reynolds number and angle of attack, a stationary air bubble becomes trapped within the vortex core at a finite distance behind the wing and can persist for several minutes even after the air injection is stopped. Under different conditions, the bubble may drift upstream or downstream, or it may disintegrate immediately. Measurements of bubble properties and vortex characteristics reveal that the breakdown behaviour depends primarily on the vortex circulation and on the axial flow component within the core. The formation of a stable breakdown bubble occurs only when a velocity excess relative to the free stream is present.<br>\r\nThe two studies highlight new mechanisms governing the stability and transformation of vortical flows, offering insight into the dynamics of vortex instabilities and vortex-core modifications in fluid systems.<br>\r\n<br>\r\n<br>\r\n<strong>Biography</strong><br>\r\nThomas Leweke graduated from RWTH Aachen University in Germany in 1990 with a “Diplom” (Master) in Physics. He completed his PhD in 1994 at the Université de Provence in Marseille, on the experimental study and modelling of bluff-body wakes. After a post-doctoral stay at Cornell University on vortex instabilities, he joined the IRPHE institute in Marseille in 1996 as a CNRS Researcher and became a Senior Researcher in 2007. His research focusses on the experimental study of fundamental aspects of fluid mechanics, especially in vortex dynamics and fluid-structure interactions, with relevance to applications. He was the co-organiser of a conference series on Bluff-Boddy Wakes and Vortex-Induced Vibrations (BBVIV), and an associate editor for the Journal of Fluids and Structures and the Journal of Visualization", "image_description": "", "creation_date": "2026-03-10T14:46:55", "last_modification_date": "2026-03-26T08:56:55", "link_label": "", "link_url": "", "canceled": "False", "cancel_reason": "", "place_and_room": "MED 0 1418", "url_place_and_room": "https://plan.epfl.ch/?room==MED%200%201418", "url_online_room": "https://epfl.zoom.us/j/61360740951", "spoken_languages": [ "https://memento.epfl.ch/api/v1/spoken_languages/2/?format=api" ], "speaker": "Prof. Thomas Leweke, IRPHE, CNRS, Marseille, France", "organizer": "MechE Colloquium", "contact": "Prof. Eunok Yim", "is_internal": "False", "theme": "", "vulgarization": { "id": 1, "fr_label": "Tout public", "en_label": "General public" }, "registration": { "id": 3, "fr_label": "Entrée libre", "en_label": "Free" }, "keywords": "MechE Colloquium : phenomena in vortical flows", "file": null, "icalendar_url": "https://memento.epfl.ch/event/export/120036/", "category": { "id": 1, "code": "CONF", "fr_label": "Conférences - Séminaires", "en_label": "Conferences - Seminars", "activated": true }, "academic_calendar_category": null, "domains": [], "mementos": [ "https://memento.epfl.ch/api/v1/mementos/1/?format=api", "https://memento.epfl.ch/api/v1/mementos/6/?format=api", "https://memento.epfl.ch/api/v1/mementos/8/?format=api", "https://memento.epfl.ch/api/v1/mementos/232/?format=api", "https://memento.epfl.ch/api/v1/mementos/270/?format=api" ] }, { "id": 71360, "title": "MechE Colloquium: Toward a unified variational model of material failure", "slug": "meche-colloquium-toward-a-unified-variational-mode", "event_url": "https://memento.epfl.ch/event/meche-colloquium-toward-a-unified-variational-mode", "visual_url": "https://memento.epfl.ch/image/32710/200x112.jpg", "visual_large_url": "https://memento.epfl.ch/image/32710/720x405.jpg", "visual_maxsize_url": "https://memento.epfl.ch/image/32710/max-size.jpg", "lang": "en", "start_date": "2026-05-19", "end_date": "2026-05-19", "start_time": "12:00:00", "end_time": "13:00:00", "description": "<strong>Abstract: </strong>The need to understand and predict material and structural failure has led to the development of several theoretical frameworks, including plasticity, limit analysis, damage mechanics, and cohesive fracture models. <br>\r\n<br>\r\nI first review how these rate-independent theories can be formulated as energy minimisation problems and discuss their main properties and limitations. I then introduce a regularised fracture model, akin to the phase-field regularisation used for softening plasticity, that we recently proposed in [1]. Unlike standard gradient damage or phase-field fracture models, in this approach damage affects the material strength rather than its stiffness.<br>\r\n<br>\r\nThrough analytical and numerical examples, I show how this model, within a consistent variational framework, provides a path toward reconciling several key concepts developed over the centuries, including Griffith and cohesive crack models, damage mechanics, plasticity, strength criteria, and limit analysis.<br>\r\n<br>\r\n[1] B. Bourdin, J.-J. Marigo, C. Maurini, C. Zolesi, <em>A variational approach to fracture incorporating any convex strength criterion</em>, arXiv:2506.22558. <a href=\"https://www.arxiv.org/pdf/2506.22558?utm_source=chatgpt.com\">arXiv PDF</a><br>\r\n<br>\r\n<strong>Biography: </strong>Corrado Maurini is Professor of Solid Mechanics at the d'Alembert Institute, Sorbonne Université, Paris. He received his Ph.D. in Mechanics in 2005 through a joint programme between the University of Rome La Sapienza and Paris 6. His research focuses on the theoretical and computational mechanics of nonlinear solids, with interests spanning fracture and damage, phase-field models, structural stability, rods, plates and shells, and active materials.", "image_description": "", "creation_date": "2026-03-12T14:17:01", "last_modification_date": "2026-03-12T15:43:58", "link_label": "", "link_url": "", "canceled": "False", "cancel_reason": "", "place_and_room": "MED 0 1418", "url_place_and_room": "https://plan.epfl.ch/?room==MED%200%201418", "url_online_room": "https://epfl.zoom.us/j/61360740951", "spoken_languages": [ "https://memento.epfl.ch/api/v1/spoken_languages/2/?format=api" ], "speaker": "<a href=\"http://www.lmm.jussieu.fr/~corrado/\">Prof. Corrado Maurini</a>, <a href=\"https://www.dalembert.upmc.fr/ijlrda/\">∂'Alembert Institute</a>, <a href=\"https://www.sorbonne-universite.fr/\">Sorbonne University Paris</a>", "organizer": "<a href=\"mailto:[email protected]\">Institute of Mechanical Engineering (IGM)</a>", "contact": "<a href=\"https://people.epfl.ch/pedro.reis?lang=en\">Prof. Pedro M. Reis</a>", "is_internal": "False", "theme": "", "vulgarization": { "id": 1, "fr_label": "Tout public", "en_label": "General public" }, "registration": { "id": 3, "fr_label": "Entrée libre", "en_label": "Free" }, "keywords": "MechE Colloquium: Toward a unified variational model of material failure", "file": null, "icalendar_url": "https://memento.epfl.ch/event/export/120055/", "category": { "id": 1, "code": "CONF", "fr_label": "Conférences - Séminaires", "en_label": "Conferences - Seminars", "activated": true }, "academic_calendar_category": null, "domains": [], "mementos": [ "https://memento.epfl.ch/api/v1/mementos/1/?format=api", "https://memento.epfl.ch/api/v1/mementos/6/?format=api", "https://memento.epfl.ch/api/v1/mementos/8/?format=api", "https://memento.epfl.ch/api/v1/mementos/232/?format=api", "https://memento.epfl.ch/api/v1/mementos/270/?format=api" ] } ] }
