Francisco López Jiménez

Seminar: Geometry and Mechanics in the Design of Aerospace Structures - Sept. 20

Jeff Zehnder — Tue, 17 Sep 2024 15:54:33 +0000

Seminar: Geometry and Mechanics in the Design of Aerospace Structures - Sept. 20 Jeff Zehnder Tue, 09/17/2024 - 09:54

Francisco López Jiménez
Assistant Professor, Smead Aerospace
Friday, Sept. 20 | 10:40 a.m. | AERO 111

Abstract: Lightweight materials and structures are essential in the aerospace industry, from enabling the large space structures required to advance science missions to reducing fuel consumption. Their mechanical response is often a result of the interplay between material properties and their geometry across different scales. As an example, we will present our work on high strain composites for deployable structures. First, how thickness controls the mode of failure of composites under bending. Second, how the geometry of composite flexures determines the balance between stiffness when deployed and compliance for better stowage. Finally, how curvature in composite booms can enable the ultra-lightweight booms necessary for the next generation of solar sails. We will also discuss other examples of our work, from ablative composites in hypersonics to animal architecture.

Bio: Francisco López Jiménez is an Assistant Professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder. He received his B.S. in Mechanical Engineering from the University of Seville, and a M.S. in Aerospace Engineering and a Ph.D. in Aeronautics from the California Institute of Technology. Before joining CU Boulder, he held postdoctoral research appointments at the Laboratoire de Mécanique des Solides (École Polytechnique, France) and the Massachusetts Institute of Technology. His research focuses on the design, fabrication, and analysis of lightweight materials and slender structures, with an emphasis in composite materials and deployable structures.

Lightweight materials and structures are essential in the aerospace industry, from enabling the large space structures required to advance science missions to reducing fuel consumption...

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CU Boulder researchers explore the engineering of bee honeycombs

Anonymous — Tue, 19 Jul 2022 15:16:39 +0000

CU Boulder researchers explore the engineering of bee honeycombs Anonymous (not verified) Tue, 07/19/2022 - 09:16

Jeff Zehnder

Francisco López Jiménez is taking on an unusual research subject for an assistant professor in aerospace -- honeycombs.

A faculty member in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder, López Jiménez is buzzing with a new $497,000 National Science Foundation grant to investigate the crystallography of honey bee comb construction.

The three-year project, an interdisciplinary effort with Prof. Orit Peleg in the Department of Computer Science, will explore how bees build honeycombs. The long-term goal is to leverage that understanding to create bio-inspired system designs in the fields of swarm robotics, collective construction, and lightweight cellular structures.

What are you studying with this research grant?

The bee honeycomb is a masterpiece of animal architecture, constructed distributively by thousands of bees. This structure is used to store honey and to house the larvae, and it is essential for the survival of the colony. It is constructed in a near-optimization of building material and space, but the principles governing how bees build them are still poorly understood.

With this project, we are studying how bees modify their construction process in cases where they cannot build a regular hexagonal lattice due to different constraints, such as boundaries, curvature, or mismatch in angle or size between regions of the comb. These situations happen naturally, such as honeycomb built inside of tree cavities, but it is hard to isolate each parameter to understand their effect.

We are using 3D printing to build foundation panels for the comb, in which we carefully introduce controlled constraints.

We track how the bees progress in building the comb and measure how they alter the cells by changing their size or their topology (that is, building cells with other than six neighbors) to resolve the “challenges” we have imposed. We hope to identify the rules they follow and then use them as inspiration to design new lightweight cellular structures.

This almost seems like biology research. How do bee honeycombs connect to engineering?

It is definitely rooted in biology. However, the bee honeycomb is a very interesting solution for a complex engineering problem.

First, producing the wax is a very expensive process for the bees. They consume roughly 8 lb of honey to secrete 1 lb of wax, so it is very advantageous for the hive to minimize wax use.

Second, they need to combine cells with different sizes for different functions (honey storage, workers eggs, drone eggs, etc.) and adapt the comb to different surfaces, such as cavities in trees, which results in a very complex geometry problem.

It has been shown that the regular pattern is very close to being the mathematical optimum, but we still do not understand how they adapt the process in cases when they cannot just build a regular hexagonal lattice.

We anticipate that the solution still follows rules honed by evolution to minimize the waste of wax and space. Our hope is that understanding those rules will help us come up with new bio-inspired designs for cellular solids in complex geometries, which is a long-standing challenge in structural mechanics.

You’ve already written one paper related to this work. What have you learned so far?

We have explored a few cases of possible constraints. For example, we have use panels in which we imprint a shallow regular hexagonal pattern, that the bees can use as a start for the comb.

These regions are oriented at different angles, with regions with no imprinted pattern between them. As the bees build the comb and they connect these regions, they need to resolve the misalignment.

We have found very consistent patterns and a clear dependence on the angle of misalignment. We were also very excited to find that the patterns found in the bee comb are similar to patterns found in very different systems, such as a graphene.

Your background is in aerospace and computational research, what drew you to work with bees?

My colleague in the project, Prof. Orit Peleg, is a leader in the field of collective behavior. In other words, she studies how social insects cooperate, from bees forming swarms to the communication between fireflies.

She gave me a piece of honeycomb that I could bring to some of my classes as an example of a lightweight structure. I had never seen a piece of bee honeycomb up close before and I found it fascinating. We started discussing the fabrication process and we came up with the idea of using 3D printed panels to control the experiments.

What is it like working with insects? Have you been stung yet?

I am not going to lie: I don’t really deal with the bees. I have only visited the apiary a couple of times. We have a great PhD student, Golnar Gharooni Fard, and several undergraduate students, directly working with the bees. They are the ones risking being stung.

Who else is involved in this research? Are there opportunities for interested students to participate?

The project is a true interdisciplinary collaboration with the Peleg Lab, where everybody involved brings new techniques and ideas. It is very exciting to learn from experts in areas very different from your own. Besides the PhD student currently working on the project, we are hoping to recruit other students interested in participating, particularly during summer, which is when the bees build the comb.

Want to know more? Contact Francisco López Jiménez.

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Seminar: High Strain Composites for Deployable Structures - Sept. 22

Anonymous — Tue, 21 Sep 2021 20:50:05 +0000

Seminar: High Strain Composites for Deployable Structures - Sept. 22 Anonymous (not verified) Tue, 09/21/2021 - 14:50

Francisco López Jiménez
Assistant Professor, Smead Aerospace
Wednesday, Sept. 22 | 12:00 P.M. | Zoom Webinar

Abstract: Deployable space structures are compacted and stowed during launch, and unfurled to their full dimensions once in space, enabling the large systems necessary to advance space science and technology. They often rely on the bending deformation of thin elements, and benefit from materials that can achieve large curvatures before failure.

In recent years, the industry has started relying on high strain composites: thin fiber composite laminates, whose failure curvature is underpredicted by traditional failure analysis of composites. This is due to several effects that can be neglected in thick laminates, but are relevant for these thin laminates. However, the lack of predictive tools makes the development of new designs expensive and time consuming.

We will present results from recent experiments characterizing the failure properties of high strain composites, and discuss the specific micromechanics taking place. We will share preliminary efforts to develop predictive tools, and their application in new deployable systems.

Bio: Francisco López Jiménez is an Assistant Professor in the Ann and H.J. Smead Department of Aerospace Engineering Sciences at the University of Colorado Boulder. He received his Ph.D. in Aeronautics from the California Institute of Technology in 2011. Prior to joining the faculty in 2017, he held postdoctoral research appointments at the Laboratoire de Mécanique des Solides (École Polytechnique, France) and the Massachussets Institute of Technology. His research focuses on the mechanics of lightweight and slender structures.

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