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ES 240 Project: Analysis of a Fin Design for use in a Micromechanical Fish

I am preforming my research at the Microrobotics Laboratory. Here I am will be designing systems for a micromechanical fish. One of the researchers in the lab has been prototpying a design for the fin mechanism. For this project, I plan to analyze and optimize her design using ABAQUS. The need for this is clear: due to the size and inertia restrictions of working on the millimeter scale, it is important to not overdesign the systems. We will be working near the limits of the materials.

The fin I will be analyzing makes use of a shape-memory alloy (SMA) in constant tension with an elastic material. When heat is applied to the SMA (via an electrical current), it returns to the memorized shape. The elastic material is used to pull the SMA out of the memorized shape after the heat is removed. The design calls for several holes where the SMA and elastic material are attached. I will look at the stress concentrations in these areas, both in the pre-stressed state, and when heat is applied to the SMA. I will then make a recommendation as to the limits of the design (i.e. hole size, location from the edge of the material, greatest pre-stress, etc.).

The fin is to be constructed from composite materials making use of a carbon-fiber preimpregenated with an uncured epoxy. By varying the alignment of the carbon-fiber layers, we can control the structural properties of the fin. My project will aim to include an analysis of various alignments of these anisotropic layers.

The abstract and citation for an article which describes the use of composite materials in the Micromechanical Flying Insect at UC Berkeley can be found here.

I have a hard copy of this article if anyone would like it.

One book I will be using as a references is Microstructural Design of Fiber Composites by Tsu-Wei Chou.


Xuanhe Zhao's picture

It's an interesting topic to model the fin of a micromechanical fish. The fin is made of shape-memory alloy and layered carbon-fiber composites. The system is driven by electricity, which is first converted into thermal energy, and then mechanical energy. I expect two major difficulties in your work:

1) The materials properties: The constitutive behavior of shape-memory alloy doesn’t follow the linear-elastic or plastic rules. It means you may need to implement shape-memory alloy’s properties in ABAQUS through user material subroutine, e.g. UMAT.

2)  The interaction between shape-memory alloy and layered carbon-fiber composites: You mentioned they are connected via holes on them. As the thermal expansion coefficients of the two materials are different, mismatch stress is expected as temperature varies. The size, number, and distribution of the holes are supposed to have significant effects on the residual stress field.

Madhav Mani's picture

Hey Mike,So there is this guy who is now a post doc at harvard and he has done a lot of work on fins, active control of fins (since fish do actually have control over them) and how the fish deforms it's fins to optimise either speed or lift etc.He did some really good work when he was at NYU and one of his papers is in preprint but you can get a preprint of it at his website:
There is also a group at ESPCI (paris) which actually built a micron scale swimmer but I am not sure how far they have got with analyses.
Hope this helps...

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