http://talks.cam.ac.uk/show/rss/10139

The large geometrical freedom allowed by developments in additive manufacturing (AM) allows for realization of extreme, complex structures and has spurred a surge in the use and manufacturing of architected lattice structures and meta materials. Apart from purely structural applications, inverse design and multiscale optimization has applications in thermal, optical, hydraulic and many others.

Topology optimization (TO) is a highly efficient inverse design tool for optimizing complex problems modelled by partial differential equations and builds on voxel-based design parameterizations, deterministic optimization approaches based on adjoint methods for computing gradients. TO has been implemented as interactive apps (see TopOpt and TopOpt3D apps on AppStore) and has been applied to full-scale airplane wing design with discretizations by billions of finite elements on super computers.

Different paths may be considered for saving CPU costs. Although popular, and showing promise in many areas, AI or CNN -based approaches have so far not been proven efficient in solving TO problems directly. Main issues are high cost of training and data generation (high break-even costs) and low generality (change of boundary conditions requires retraining).

A promising path is multiscale optimization that makes use of the knowledge of the homogenized properties of extreme microstructures to perform the optimization on coarse meshes and sub-sequently realizing the multiscale structure by so-called dehomogenization. Dehomogenization is based on computer graphics techniques and the combined procedure thus has potential to be solved interactively on apps, as for the single scale apps mentioned above, albeit with much higher resolutions.

The talk will give a brief introduction to TO and a discussion of the relevance of various optimization techniques, followed by a deeper dive into multiscale and dehomogenization techniques that take stiffness, strength as well as local and global buckling stability of multiscale lattice structures into account. Time permitting, recent results on design of meta materials with extreme non-linear responses as well as non-perfect realizations will also be included.

• Speaker: Prof. Ole Sigmund, Technical University of Denmark
• Friday 14 June 2024, 14:00-15:00
• Venue: Department of Engineering - tbc.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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Living systems adopt a diversity of curved and highly dynamic shapes. These diverse morphologies appear on many length-scales, from cells to tissues and organismal scales. The common driving force for these dynamic shape changes are contractile stresses generated by myosin motors in the cell cytoskeleton, that converts chemical energy into mechanical work. A good understanding of how contractile stresses in the cytoskeleton arise into different 3D shapes and what are the shape selection rules that determine their final configurations is still lacking. To obtain insight into the relevant physical mechanisms, we recreate the actomyosin cytoskeleton in-vitro, with precisely controlled composition and initial geometry. A set of actomyosin gel discs, intrinsically identical but of variable initial geometry, dynamically selforganize into a family of 3D shapes, such as domes and wrinkled shapes, without the need for specific pre-programming or additional regulation. Shape deformation is driven by the spontaneous emergence of stress gradients driven by myosin and is encoded in the initial disc radius to thickness aspect ratio, which may indicate shaping scalability. Our results suggest that, while the dynamical pathways may depend on the detailed interactions between the different microscopic components within the gel, the final selected shapes obey the general theory of elastic deformations of thin sheets. Altogether, our results emphasize the importance for the emergence of active stress gradients for buckling driven shape deformations and provide novel insights on the mechanically induced spontaneous shape transitions in contractile active matter, revealing potential shared mechanisms with living systems across scales.

• Speaker: Prof. Anne Bernheim, Ben-Gurion University of the Negev
• Friday 03 May 2024, 14:00-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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• Speaker: Prof. Anne Bernheim, Ben-Gurion University of the Negev
• Friday 03 May 2024, 14:00-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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In the last two decades, a new class of ceramics has emerged that has challenged their typical description as materials that are hard, difficult to machine, and susceptible to damage and thermal shock. This class of 160+ members – known as the MAX phases – share common unique chemical formula Mn+1AXn, (where n = 1, 2 or 3, M is and early transition metal, A is an mostly group 13-16 elements, and X is either C or N) and naonolayered crystal structure in which strongly bonded MX layers are interleaved by weakly bonded A layers. The main reason for growing interest in MAX phases lies in their unusual mechanical properties in general, and high damage tolerance in particular. In general, MAX phases are elastically stiff, good thermal and electrical conductors, resistant to chemical attack, and have relatively low thermal expansion coefficients, but also relatively soft and most readily machinable, thermal shock resistant and damage tolerant. Moreover, some of them – notably Ti2AlC and Ti3SiC2 – are fatigue, creep, and oxidation resistant. Therefore, MAX phases are considered to be a good candidate materials, especially for high temperature structural applications in extreme environments. This seminar lecture provides an overview of the current understanding of mechanical behavior of MAX phases, with the special focused on their deformation by kinking that can be traced back to their naolaminated crystal structure. Deformation and failure mechanisms below and above brittle to plastic transition temperature in MAX phases are reviewed, as well as effect of microstructure (i.e. grain size and secondary phases) on the observed mechanical behavior of polycrystalline MAX phases. Furthermore, anisotropic deformation and failure mechanisms in MAX single crystals, micropillars and cantilevers is discussed in more details. Possibilities for further improvements in mechanical properties of MAX phases by tailoring their composition and microstructure are also briefly discussed in this presentation.

• Speaker: Professor Miladin Radovic, Texas A&M University
• Friday 17 May 2024, 14:00-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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• Speaker: Prof. Christopher Pierre, Stevens Institute of Technology
• Friday 24 May 2024, 14:00-15:00
• Venue: Department of Engineering - LT6.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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• Speaker: Prof. Christopher Pierre, Stevens Institute of Technology
• Friday 24 May 2024, 14:00-15:00
• Venue: Department of Engineering - tbc.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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• Speaker: Prof. Ole Sigmund, Technical University of Denmark
• Friday 14 June 2024, 14:00-15:00
• Venue: Department of Engineering - tbc.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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A rapidly expanding research area involves the development of routes to shape programmable three-dimensional (3D) structures with feature sizes in the mesoscopic range (that is, between tens of nanometres and hundreds of micrometres). A goal is to establish methods to control the properties of materials systems and the function of devices, through not only static architectures, but also morphable structures and shape-shifting processes. Soft matter equipped with responsive components can switch between designed shapes, but cannot support the types of dynamic morphing capabilities needed to reproduce continuous shape-shifting processes of interest for many applications. Challenges lie in the establishment of 3D assembly/fabrication techniques compatible with wide classes of materials and 3D geometries, and schemes to program target shapes after fabrication. In this talk, I will introduce a mechanics-guided assembly approach that exploits controlled buckling for constructing complex 3D micro/nanostructures from patterned two-dimensional (2D) micro/nanoscale precursors that can be easily formed using established semiconductor technologies. This approach applies to a very broad set of materials (e.g., semiconductors, polymers, metals, and ceramics) and even their heterogeneous integration, over a wide range of length scales (e.g., from 100 nm to 10 cm). To allow realization of 3D mesostructures that are capable of qualitative shape reconfiguration, we devise a loading-path controlled strategy that relies on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via nonlinear buckling. I will also introduce a recent work on shape programmable soft surface, constructed from a matrix of filamentary metal traces, driven by programmable, distributed electromagnetic forces that follow from the passage of electrical currents in the presence of a static magnetic field. Under the guidance of a mechanics model-based strategy to solve the inverse problem, the surface can morph into a wide range of 3D target shapes and shape-shifting processes. The compatibility of our approaches with the state-of-the-art fabrication/processing techniques, along with the versatile capabilities, allow transformation of diverse existing 2D microsystems into complex configurations, providing unusual design options in the development of novel functional devices.

Short Bio

Yonggang Huang is the Achenbach Professor of Mechanical Engineering, Civil and Environmental Engineering, and Materials Science and Engineering at Northwestern University. He is interested in mechanics of stretchable and flexible electronics, and mechanically guided deterministic 3D assembly. He has published 2 books and more than 700 journal papers and book chapters, including 15 in Science and 7 in Nature. He is a member of the US National Academy of Engineering, US National Academy of Sciences, a fellow of American Academy of Arts and Sciences, and a foreign member of the Royal Society (London). He has received numerous medals for his research contributions including most recently the IUTAM 2024 Rodney Hill Prize. He has also received awards for undergraduate teaching and advising at all universities he has taught. For his contribution to engineering science and his leadership in the society, the Society of Engineering Sciences renamed its Engineering Science Medal to Yonggang Huang Engineering Science Medal in 2024.

• Speaker: Prof. Yonggang Huang, McCORMICK school of Engineering, Northwestern University.
• Thursday 21 March 2024, 14:00-15:00
• Venue: Department of Engineering - LR5.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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A rapidly expanding research area involves the development of routes to shape programmable three-dimensional (3D) structures with feature sizes in the mesoscopic range (that is, between tens of nanometres and hundreds of micrometres). A goal is to establish methods to control the properties of materials systems and the function of devices, through not only static architectures, but also morphable structures and shape-shifting processes. Soft matter equipped with responsive components can switch between designed shapes, but cannot support the types of dynamic morphing capabilities needed to reproduce continuous shape-shifting processes of interest for many applications. Challenges lie in the establishment of 3D assembly/fabrication techniques compatible with wide classes of materials and 3D geometries, and schemes to program target shapes after fabrication. In this talk, I will introduce a mechanics-guided assembly approach that exploits controlled buckling for constructing complex 3D micro/nanostructures from patterned two-dimensional (2D) micro/nanoscale precursors that can be easily formed using established semiconductor technologies. This approach applies to a very broad set of materials (e.g., semiconductors, polymers, metals, and ceramics) and even their heterogeneous integration, over a wide range of length scales (e.g., from 100 nm to 10 cm). To allow realization of 3D mesostructures that are capable of qualitative shape reconfiguration, we devise a loading-path controlled strategy that relies on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via nonlinear buckling. I will also introduce a recent work on shape programmable soft surface, constructed from a matrix of filamentary metal traces, driven by programmable, distributed electromagnetic forces that follow from the passage of electrical currents in the presence of a static magnetic field. Under the guidance of a mechanics model-based strategy to solve the inverse problem, the surface can morph into a wide range of 3D target shapes and shape-shifting processes. The compatibility of our approaches with the state-of-the-art fabrication/processing techniques, along with the versatile capabilities, allow transformation of diverse existing 2D microsystems into complex configurations, providing unusual design options in the development of novel functional devices.

Short Bio

Yonggang Huang is the Achenbach Professor of Mechanical Engineering, Civil and Environmental Engineering, and Materials Science and Engineering at Northwestern University. He is interested in mechanics of stretchable and flexible electronics, and mechanically guided deterministic 3D assembly. He has published 2 books and more than 700 journal papers and book chapters, including 15 in Science and 7 in Nature. He is a member of the US National Academy of Engineering, US National Academy of Sciences, a fellow of American Academy of Arts and Sciences, and a foreign member of the Royal Society (London). He has received numerous medals for his research contributions including most recently the IUTAM 2024 Rodney Hill Prize. He has also received awards for undergraduate teaching and advising at all universities he has taught. For his contribution to engineering science and his leadership in the society, the Society of Engineering Sciences renamed its Engineering Science Medal to Yonggang Huang Engineering Science Medal in 2024.

• Speaker: Prof. Yonggang Huang, McCORMICK school of Engineering, Northwestern University.
• Thursday 21 March 2024, 14:00-15:00
• Venue: Department of Engineering - LT2.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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A rapidly expanding research area involves the development of routes to shape programmable three-dimensional (3D) structures with feature sizes in the mesoscopic range (that is, between tens of nanometres and hundreds of micrometres). A goal is to establish methods to control the properties of materials systems and the function of devices, through not only static architectures, but also morphable structures and shape-shifting processes. Soft matter equipped with responsive components can switch between designed shapes, but cannot support the types of dynamic morphing capabilities needed to reproduce continuous shape-shifting processes of interest for many applications. Challenges lie in the establishment of 3D assembly/fabrication techniques compatible with wide classes of materials and 3D geometries, and schemes to program target shapes after fabrication. In this talk, I will introduce a mechanics-guided assembly approach that exploits controlled buckling for constructing complex 3D micro/nanostructures from patterned two-dimensional (2D) micro/nanoscale precursors that can be easily formed using established semiconductor technologies. This approach applies to a very broad set of materials (e.g., semiconductors, polymers, metals, and ceramics) and even their heterogeneous integration, over a wide range of length scales (e.g., from 100 nm to 10 cm). To allow realization of 3D mesostructures that are capable of qualitative shape reconfiguration, we devise a loading-path controlled strategy that relies on elastomer platforms deformed in different time sequences to elastically alter the 3D geometries of supported mesostructures via nonlinear buckling. I will also introduce a recent work on shape programmable soft surface, constructed from a matrix of filamentary metal traces, driven by programmable, distributed electromagnetic forces that follow from the passage of electrical currents in the presence of a static magnetic field. Under the guidance of a mechanics model-based strategy to solve the inverse problem, the surface can morph into a wide range of 3D target shapes and shape-shifting processes. The compatibility of our approaches with the state-of-the-art fabrication/processing techniques, along with the versatile capabilities, allow transformation of diverse existing 2D microsystems into complex configurations, providing unusual design options in the development of novel functional devices.

• Speaker: Prof. Yonggang Huang, McCORMICK school of Engineering, Northwestern University.
• Thursday 21 March 2024, 14:00-15:00
• Venue: Department of Engineering - LT2.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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• Speaker: Prof. Yonggang Huang, McCORMICK school of Engineering, Northwestern University.
• Thursday 21 March 2024, 14:00-15:00
• Venue: Department of Engineering - LT2.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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Metals and alloys have never been more important for the benefit of mankind. But physical metallurgy is a long-established field – what should now be emphasised? In this seminar, the speaker will argue that the underlying physical principles are often established well enough to allow design to become the important paradigm. Alloy design approaches are emphasised particularly for nickel and titanium alloys. Applications in the aerospace, defence and biomedical sectors are given. Moreover, the advent of additive manufacturing allows new types of structures to be proposed with useful properties.

• Speaker: Roger Reed, University of Oxford
• Friday 08 March 2024, 14:00-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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X-ray computed tomography (XCT) is a reliable tool for measuring internal flaws and microstructural features in engineering materials. As an extension to XCT , Digital Volume Correlation (DVC) methodology enables tracking 3D deformation field based on local grayscale contrast. Nevertheless, its applicability and spatial resolution have been limited by the need for tracer particles or inherent microstructural features that are distributed in the material volume. To address these limitations, we developed a Flux Enhanced Tomography for Correlation (FETC) technique that leverages inherent inhomogeneities in engineering materials (polymers to metals) to measure all nine components of the deformation gradient without relying on artificial X-ray tracers. Via this unprecedented full-filed measurement technique, the mechanical behaviour of various engineering polymers was examined, and new observations was made on the well-established rubber elasticity. It was found that many polymers undergo significant local volume changes but the overall volume remains constant during mechanical loading. The presence of a mobile phase within the material volume has been proved which gives rise to negative local bulk moduli. By extending its application on other materials, FETC is expected to bring more electrifying discoveries of new material physics.

• Speaker: Dr Zifan Wang, CUED
• Friday 16 February 2024, 14:00-14:30
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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• Speaker: Professor Laura De Lorenzis, ETH Zurich
• Friday 15 March 2024, 14:00-15:00
• Venue: Department of Engineering - LT6.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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In the past two decades, huge advancements have been made in X-ray and neutron based techniques. This enables new discoveries in materials science and engineering across the meso-, micro-, and nano- scales.

In this short seminar, I would like to present an overview of state-of-the-art radiation techniques that are available and prevailing in experimental solid mechanics. This will include various diffraction and imaging technologies using X-ray and neutron sources, both at the gigantic synchrotron facilities and compact university labs.

The outcome of joining this seminar will be to have a general understanding of what is currently achievable in experimental micromechanics using X-ray and neutron methods.

• Speaker: Dr Zifan Wang, CUED
• Friday 16 February 2024, 14:00-14:30
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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• Speaker: Dr Zifan Wang, CUED
• Friday 16 February 2024, 14:00-14:30
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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Parametrized partial differential equations are used to model problems in engineering. Design of engineering systems is governed by physical parameters such as material properties, boundary conditions and geometric parameters such as shape of the components. In order to rapidly explore the variation in quantity of interest with respect to the physical or geometrical parameters, model order reduction is used as a computationally faster alternative with an “affordable” compromise in accuracy.

Deep learning based model order reduction methods have gained traction in recent years. These methods can be non-intrusive in nature and may not require access to source code used to solve the high-fidelity model. In the case of offline-online two stage procedure, deep learning methods are quicker in the online phase. However, during the offline phase, they suffer from severe computational costs associated with generation of training data and training of artificial neural network. On exascale systems, such approaches require more careful numerical implementation due to heterogeneous mixed CPU /GPU devices.

In this talk, we will focus on problems involving geometric parameters. Further, we will introduce data-parallel distributed training of the artificial neural network in order to address the issue of high offline cost. We will also introduce PyTorch-RBniCSx-FEniCSx based open source package, DLR BniCSx, for deep learning based model order reduction.

• Speaker: Dr Nirav Vashant Shah, CUED
• Friday 16 February 2024, 14:30-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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I begin with a pedagogical introduction to how grain boundaries and other interfaces in crystalline materials move. My approach focuses on bicrystallography and the special types of line defects that only exist at interfaces, i.e., disconnections. Disconnections have both step character and dislocation character. Their step nature implies that their motion leads to interface motion and their dislocation nature means that they interact with and are sources of stress. The main focus of this presentation is how to apply this modern understanding of how interfaces move to the evolution of microstructure and morphology. I will show several examples from atomic-scale simulations and microstructure evolution simulations based on front tracking and phase field. I will show some surprising results that demonstrate that the application of cyclic stress and/or temperature drive grain boundary migration in particular directions and accelerate grain growth

• Speaker: Professor David Srolovitz, The University of Hong Kong
• Friday 09 February 2024, 14:00-15:00
• Venue: Department of Engineering - LT2.
• Series: Engineering - Mechanics Colloquia Research Seminars; organiser: div-c.

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• Speaker: Roger Reed, University of Oxford
• Friday 08 March 2024, 14:00-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: div-c.

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• Speaker: Dr Ashley Roach
• Friday 02 February 2024, 14:30-15:00
• Venue: Oatley 1 Meeting Room, Department of Engineering.
• Series: Engineering - Mechanics and Materials Seminar Series; organiser: Elizabeth Howard.

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