Choosing Materials for the Structure of our AUV - Part 2
Updated: May 7, 2021
Continuing the study of material selection for our AUV, we will talk about some more materials that we use and that we think about using in the team, and their main characteristics, advantages and disadvantages.
Fiberglass, whose most appropriate name would be Fiberglass Reinforced Polymer, is a material resulting from the superposition of very thin ductile and flexible glass filaments. Polymerization is done by applying some type of resin (in general, polyester), which is responsible for the union of these fibers.
At BrHue, this material was used to make the drawers that hold the electronics inside the main hull. It was chosen because it has a number of advantageous characteristics, such as: lightness, high mechanical resistance and low thermal conductivity, which is very useful because the temperature of certain electronic components usually rises during operation.
Widely used in the nautical industry (in the manufacture of hulls from small to medium-sized vessels and kayaks, for example), fiberglass has become a powerful option for manufacturing the structure of our next AUV. It is worth remembering that factors such as lightness must be considered a lot in the manufacture of a new robot for competition, so that we are not penalized for exceeding the weight limit, and also the high mechanical resistance of this polymer would guarantee us a greater durability of the autonomous vehicle. Furthermore, as it is a recyclable material, we would have a chance to combine technology with sustainable development.
It is a highly corrosion resistant metal alloy. This is due to the fact that it has chromium in its composition, which makes this material, when in contact with oxygen (responsible for oxidation), create an impermeable protective film, preventing it from being corroded.
In addition to this advantage, through the analysis of its mechanical properties and a structural simulation made in Ansys, we saw that stainless steel would be the ideal material for making the rods that support the electronics drawers inside the main cylinder. Among the different materials analyzed, it was the one that presented the least degree of deformation, when the weight of the electronics was equally distributed in the clips responsible for fixing these drawers.
In the image, we see that the material provides us with a high safety factor, which indicates less possibility of plastic deformation with the weight of the distributed electronics.
A disadvantage of stainless steel, however, is the fact that it is not a very light component. Consequently, it is not something that we consider a lot when we think about making our next structure. However, due to its ease of purchase and good cost benefit ratio, there are high chances that certain components of our next AUV will be made of this material.
It is a material resulting from a long chain of united atoms, which form resistant crystalline chains. A single fiber of this polymer is about 0.005 to 0.01 mm in diameter. However, by joining thousands of wires like this one results in an extremely strong material, managing to overcome the resistance of materials such as steel.
The fact of having a great lightness is what makes the industry, more and more, choose carbon fiber as raw material for the manufacture of its components. It is one of the main composite materials used in the aeronautical industry (because it can efficiently withstand high mechanical efforts and stresses), as well as in the manufacture of Formula 1 vehicle components, which have been able to achieve higher speeds thanks to the innovation of this fiber.
In view of this, carbon fiber, currently, also proves to be a great option for making our next structure.
Acrylonitrile Butadiene Styrene, better known as ABS plastic, is a material that has become increasingly famous thanks to the growing adhesion of 3D prints in large projects and is already present in much of our daily lives. It consists of copolymerization - a mixture of two or more monomers - of acrylonitrile, butadiene and styrene.
ABS plastic is extremely practical because it is easily molded, which allows it to take the shape we want without needing much effort in addition to good modeling on CAD platforms. The extremely low production cost is just one of its many benefits, another important feature is resistance to impacts, traction and thermal variations. This material is also very light, enabling future projects, just as it was with our current robot, BrHue.
High Density Polyethylene (HDPE):
Obtained through the polymerization of ethylene, this is one of the most delicate and important materials of our project, since it is responsible for the tightness of part of the robot, since the covers of the battery attachment are made of HDPE. The slightly higher investment - although not so expensive - is justified by its high resistance to impacts, a service life of more than 50 years, ensuring that the wear of the parts is not a problem in the near future. In addition, this material is slightly flexible, making it difficult to deform.
Despite being more dense than ordinary polyethylene, high density polyethylene is relatively light and, added to the fact that it is one of the materials that most guarantees tightness for the reasons mentioned above, it becomes an option with great cost benefit and will certainly make part of our next projects both for the covers of future attachments and for the structure of the future robot.
Ultra High Molecular Weight Polyethylene, is one of the materials we have in mind to be carried out in future projects. This is due to its high impact resistance, wear and low friction coefficient. It has a density close to that of High Density Polyethylene, which, for our parameters, is a light material with high potential. Like HDPE, it meets the requirements for good tightness, so we thought about using UHMW for future covers, in addition to the robot's structure, especially if we choose a frame geometry, which tends to make it heavier.
It is important to note that the study and analysis of materials is also subject to errors and uncertainties. The choice of materials is always made thinking about how to minimize the problems that we may face while the AUV is performing its tasks, in a way that the project becomes economically viable. Some of these materials, as they have not yet been tested by our members, do not give us a 100% guarantee that they are the best option we have at the moment. Thus, it is clear that the culture of research and the search for material selection in the team is a continuous task and one that is innovating as the technological industry is also undergoing innovations.
Written by Ramon Christian and Vinicius Feij