Virtual MEchanics GAthering -MEGA- Seminar: Talk 1 - A Kirchhoff-like theory for the mechanics of magnetic rods; Talk 2- Magneto-active elastic shells with tunable buckling strength
Event details
| Date | 26.11.2020 |
| Hour | 16:15 › 17:30 |
| Speaker | Tomohiko Sano & Dong Yan (fleXLab, EPFL) |
| Location |
Zoom: epfl.zoom.us/s/98393329833 Room Passcode: 349948
Online
|
| Category | Conferences - Seminars |
Talk 1: A Kirchhoff-like theory for the mechanics of magnetic rods, by Tomohiko Sano (fleXLab, EPFL)
Magneto-rheological elastomers (MREs) are functional materials that can undergo deformations when subject to external magnetic fields. MREs consist of hard magnetic particles dispersed into a nonmagnetic elastomeric (soft) matrix. There have been recent advances in the theoretical description of MREs using the framework of (3D) continuum mechanics. Reduced-order structural theories have also been developed for magnetic linear beams and elastica, based on the planar (2D) deformation of the centerline. In this talk, we derive an effective theory for rods made of MRE undergoing 3D geometrically nonlinear deformations. Our theory is based on the procedure of dimensional reduction of the 3D magneto-elastic energy functional of the MRE into a 1D (centerline and Kirchhoff-like) description, which encompasses the previous 2D theories under appropriate limits. We demonstrate the accuracy of our theory by performing precision-model experiments to explore a set of specific problems involving the buckling behavior of MRE rods. These experiments are also used to test the range of validity of our theory.
Bio Tomohiko Sano is a post-doc at the Flexible Structures Laboratory at EPFL. He completed his bachelor’s and Ph.D. courses at the Graduate School of Science, Kyoto University, Japan. After he got a Ph.D. in 2016, he worked as a post-doctoral researcher at Ritsumeikan University, near Kyoto, Japan, from 2016 to 2019. His research interests are mechanical functionalities in structures and geometry.
Talk 2: Magneto-active elastic shells with tunable buckling strength, Dong Yan (fleXLab, EPFL)
It has long been recognized that the buckling of shell structures is highly sensitive to material or geometric imperfections, leading to observed critical loads that are significantly lower than classic predictions. In this class of problems, the knockdown factor is defined as the ratio between the experimentally measured critical load and the classic theoretical prediction. This knockdown is typically regarded as an intrinsic property of the structure since the type and distribution of defects are encoded into the shell during fabrication. Here, we demonstrate the ability to actively tune the knockdown factor of pressurized spherical shells. We fabricate our spherical shells with a magneto-rheological elastomer (MRE) using a coating technique. The shells are first magnetized and then loaded by pressure under a uniform magnetic field. We find that, by adjusting the strength and polarity of the field, the knockdown factor of the magnetically active shells can be increased or decreased up to a maximum change of 30%. As such, we can externally tune their intrinsic buckling strength, on-demand. An axisymmetric shell model is used to rationalize the experimental results on how the magnetic field interacts with the buckling of imperfect shells.
Bio Dong Yan got his Ph.D. in Mechanical Engineering at Beijing Institute of Technology, China, in 2017. Then he joined the Flexible Structures Laboratory (the fleXLab) at EPFL as a post-doc, working with Prof. Pedro Reis on shell buckling and magneto-elastic structures.
Magneto-rheological elastomers (MREs) are functional materials that can undergo deformations when subject to external magnetic fields. MREs consist of hard magnetic particles dispersed into a nonmagnetic elastomeric (soft) matrix. There have been recent advances in the theoretical description of MREs using the framework of (3D) continuum mechanics. Reduced-order structural theories have also been developed for magnetic linear beams and elastica, based on the planar (2D) deformation of the centerline. In this talk, we derive an effective theory for rods made of MRE undergoing 3D geometrically nonlinear deformations. Our theory is based on the procedure of dimensional reduction of the 3D magneto-elastic energy functional of the MRE into a 1D (centerline and Kirchhoff-like) description, which encompasses the previous 2D theories under appropriate limits. We demonstrate the accuracy of our theory by performing precision-model experiments to explore a set of specific problems involving the buckling behavior of MRE rods. These experiments are also used to test the range of validity of our theory.
Bio Tomohiko Sano is a post-doc at the Flexible Structures Laboratory at EPFL. He completed his bachelor’s and Ph.D. courses at the Graduate School of Science, Kyoto University, Japan. After he got a Ph.D. in 2016, he worked as a post-doctoral researcher at Ritsumeikan University, near Kyoto, Japan, from 2016 to 2019. His research interests are mechanical functionalities in structures and geometry.
Talk 2: Magneto-active elastic shells with tunable buckling strength, Dong Yan (fleXLab, EPFL)
It has long been recognized that the buckling of shell structures is highly sensitive to material or geometric imperfections, leading to observed critical loads that are significantly lower than classic predictions. In this class of problems, the knockdown factor is defined as the ratio between the experimentally measured critical load and the classic theoretical prediction. This knockdown is typically regarded as an intrinsic property of the structure since the type and distribution of defects are encoded into the shell during fabrication. Here, we demonstrate the ability to actively tune the knockdown factor of pressurized spherical shells. We fabricate our spherical shells with a magneto-rheological elastomer (MRE) using a coating technique. The shells are first magnetized and then loaded by pressure under a uniform magnetic field. We find that, by adjusting the strength and polarity of the field, the knockdown factor of the magnetically active shells can be increased or decreased up to a maximum change of 30%. As such, we can externally tune their intrinsic buckling strength, on-demand. An axisymmetric shell model is used to rationalize the experimental results on how the magnetic field interacts with the buckling of imperfect shells.
Bio Dong Yan got his Ph.D. in Mechanical Engineering at Beijing Institute of Technology, China, in 2017. Then he joined the Flexible Structures Laboratory (the fleXLab) at EPFL as a post-doc, working with Prof. Pedro Reis on shell buckling and magneto-elastic structures.
Practical information
- General public
- Free
Organizer
- MEGA.Seminar Organizing Committee