Research Goal/Thesis

The purpose of this research project is to investigate the effectiveness and viability of composite chassis components through the design and implementation of structural “sandwich” panels. These will be pursued for an increased strength-to-weight ratio as well as higher stiffness as compared to a conventional tubular frame.

Design Process

Sandwich Panel

To start, the design of the structural “sandwich” panel is achieved by utilizing two outer carbon fiber layers and inserting a core structure between them, typically with aluminum honeycomb, foam, or Nomex.

Each carbon fiber layer is created by using multiple carbon fiber lamina at different orientations to create a laminate, bonded together with epoxy resin. The orientation stacking of the carbon fiber lamina is to maximize material properties in multiple directions, in order to retain high stiffness and low deformation properties in a multitude of loading situations.

Additionally, the core material of the panel is utilized to effectively transfer loads across the entire of area of the carbon fiber, as well as resist shear loads and bending stresses across the carbon fiber. The material of the core structure is determined based upon the application.

Honeycomb Properties and Dimensions

• Look into the differences in each material (stiffness, use case, sourceability, cost, focus on nomex and aluminum)

• Understand and label how each property of honeycomb affects the properties of the core material (length, width, thickness, cell size, cell shape, density, etc.)

• Decision matrix between aluminum honeycomb and nomex honeycomb

Carbon Fiber Properties and Dimensions

• Look into the different types of carbon fiber available (uni-directional, twill weave, figure out their stiffness, use case, sourceability, cost, ease of manufacturing when creating a laminate)

• Understand pre-preg vs non pre-preg

• Look into the bonding process for each type of carbon fiber (necessary epoxy/resin properties), as well as how orientation affects a composite structure

Open

Mounting Solutions

In terms of mounting components to the panels or even mounting the panels themselves to a tubular area of the car, there are various solutions to accommodate each specific application.

Open

A commonly used solution is using thru-bolts, which can end up leading to shear and moment in the core material or compression and bearing stress if an axial load is placed on it. This means that selecting a core material and evaluating the loads of each mounting joint go hand in hand together, as they can both directly affect the effectiveness of the joint and panel as a whole.

Potted inserts are another viable mounting solution, which utilizes an insert that is placed in a cutout section of the core material and adhered to the panel by a potting adhesive, which constrains the insert in all six degrees of freedom.

Additionally, thru-bolts could be used in a different configuration, where a custom mounting bracket is created that bolts onto the panel, and any moving part/anything experiencing load is mounted to the bracket, and not directly onto the panel.

Mounting Solution Specifics

• need to examine each one of these mounting capabilities

  • Strengths, weaknesses, ease of manufacturing, cost, usable applicationsetc.

  • Decision matrix

Manufacturing Process

tbd → advait helping with this

Testing Methodology

In order to test the viability and capabilities of the structural composite panels, both empirical testing and FEA simulation shall be utilized.

To start, materials testing, which includes tensile, 3-point bend, shear, and compression testing, shall be employed to understand the material properties of the composite paneling, as well as ensure the panels are viable at least in the early stage to continue research, in pursuit of a fully composite panel chassis. Each material test will result in critical numerical data, such as yield and ultimate strength, elastic modulus, as well as fracture toughness and flexural modulus. Each one of these data points can then be used to characterize the composite material as a whole. Additionally, this data can be used in hand calculations or brought into a Finite Element Analysis program such as ANSYS, to then predict and understand how the material, based on its properties, will react in situations relevant to the ASC and FSGP competitions.

In terms of FEA testing, ANSYS, utilizing its ACP program, can accurately represent the composite structure in junction with the data collected from the empirical testing, which allows us to simulate the entire chassis structure as one piece, helping us account for the complex geometry of the chassis and load cases of the ASC regulations, which would be hard to replicate in an empirical testing setup.

Empirical Testing

• need to go into specifics on how each empirical test will be conducted to get accurate results

  • Also explain how each material property will be extracted/calculated given the test results

ANSYS Composite Simulation

• need to explain a little bit more about how ANSYS/FEA testing works as it pertains to a composite structure

  • I (noah) can fill in this section but we need to essentially explain the features of pre-ACP and post-ACP on ANSYS, how they reflect the IRL sandwich panels in a simulation setting, and how we plan on using it to prove to ASC that our panels actually pass regs

KETIV Technologies Video: Intro to Composite Analysis Using Ansys Mechanical [Devansh]

Vocabulary

Ply - a bunch of fibers put together with some kind of adhesive.

Laminate - stack of plies.

How to model? (9:40)

Shell Method

• Use a shell element (planar element)

• Define material for each layer, and define stiffness for each layer. Ansys will then supposedly “automatically” recognize this and will make it so that you can simulate it.

There are two other methods - solid shell and layered solid - but I don’t really understand what the guy in the video is saying.

What data do you need? (11:23)

Orthotropic material properties, Ply thickness and orientation, stacking sequence, the orthotropic strengths, and failure theory/theories.

Mentions that Tsai-Wu failure criteria is apparently a pretty popular one for composites (may want to look into this more):

Example from video:

I don’t really understand this, so I found a quick explanation online by SolidWorks that’s more understandable: https://help.solidworks.com/2021/English/SolidWorks/cworks/r_tsaiwu_failure_criterion.htm

After identifying composite material, you can pretty much do whatever you want with it.

Delamination Analysis:

Two things you can do with ansys:

CZM (Cohesive Zone Modeling) - Calculates energy needed to pry/shear apart a composite panel structure (I think this would be useful for sandwich panels). Guy in video does not go too much in-depth on this but I found a pretty good pdf over it online (will take notes later on it).

VCCT (Virtual Crack Closure Technique) - Another method to see how composite panels can delaminate.

Found two things over this:

Science Direct article

NASA Research

Basic Overview of how to Simulate a Panel: (17:40)

1. Insert a “Layered Section”

2. Specify what Geometry layered section applies to

3. Define a coordinate system (pretty much tell ansys what a “zero degree” orientation looks like)

4. Define layers - select worksheet option, and define each layer

Demonstration: (19:50)

1. If you go to engineering data on the ANSYS workbench → composites material, there are a lot of predefined ones to use.

2. Click coordinate sys → insert new coordinate sys → from there, can go to properties of coord plane and set geometry relative to plane.

AFTER SETTING COORDINATE PLANE:

3. Right click geometry → Insert layered section → select surface for lay sec geom → select coordinate system to use

4. Go to worksheet, from there can add different layers, different thickness, different angle.

5. From there can treat it as a normal ANSYS simulation (inserting various tests and defining certain wanted solutions)

   1. Can also define which specific layer you want.

Note: Remember the tsai-wu stuff from above? apparently you can code ANSYS to do it:

Geometry Preparation of FSAE Composite & Monocoque Chassis in ANSYS SpaceClaim - Part 1

Basically just a demonstration of how to generate a good mesh.

Some notable tools:

• Stich - select this tool under repair to make your mesh better

• Split edges - merges all edges that ansys thinks are seperate

• Imprint - if you have suspension mounts you can do this so coincident edges are “imprinted” (red areas)

• Can also create “origins” at tire locations (unhide tire) if applicable in order to simulate torsion

Materials & Meshing Setup for FSAE Composite & Monocoque Chassis Using ANSYS Mechanical - Part 2

In ANSYS mechanical do the following…

1. Upload your model

2. Go to engineering data and remove the default materal, then go to engineering data sources → composite materials

   1. Should you want to use a material other than those already in ansys, go to DoD Composite Materials Handbook (has mat properties)

3. Adds epoxy carbon woven, honeycomb, and resin epoxy (last two are relevant to what we want)

4. Close engr data tab and go to model tab

   1. If there is a question mark then smt needs to be fixed before you proceed

5. In materials tab u see ur materials

6. Mesh it

Note that curves and suspension attachment areas are weirdly meshed (see part 1 image)

Supposedly if you change element size to 10mm, Capture Curvature to “No”, and select faces of high curvature then “insert → face meshing” your mesh would be a lot better.

7. From there you can go to “Named Selections” select various panel(s) and name them things like “Top Mold” “Bottom Mold” etc.

   1. Helps with defining materials.

Research Results and Findings

Resources

HexCell documentation/manuals

FSAE/ASC composite research

UMinn Solar Car Chassis Explanation

Effects of core cell size and panel width on stiffness