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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)
Honeycomb is a core material used as a structural stiffening medium between plies of Carbon Fiber. A honeycomb structure is the ideal material for energy absorption because ----- . Because of this, the use of honeycomb materials creates a great strength-to-weight ratio, when comparing the capabilities of sandwich panels to that of conventional tubing.
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With these sources, we understand the differences in shear and compression strength between the two materials.
Carbon Fiber Properties and Dimensions
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Look into the different types of carbon fiber available (uni-directional, twill weave, figure out their stiffness, use case, source ability, cost, ease of manufacturing when creating a laminate)
Unidirectional (UD) Carbon Fiber:
It UD carbon fiber can be used in both prepreg and non-prepreg forms
Non-women, and features all fibers running in a single, parallel direction.
Light , meaning that a dry or wet layup manufacturing process can be utilized to manufacture parts with UD.
UD carbon fiber is a non-woven carbon fiber sheet, which features all fibers running in a single, parallel direction. This makes UD carbon fiber light weight compared to woven counterparts.
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Able to stack/overlap fabrics at varying angle orientations to achieve strength in multiple directions w/o sacrificing stiffness
Ideal for applications where front-to-back strength is most important.
Not suitable for draping, can reveal gaps, wrinkles or creases when draped over complex surfaces
Improved with resin infusion
Sourceability/Cost:
Compared to woven, due to Great choice for maximizing compressive/tensile with low weight, but must have many layers of UD to create a quasi-isotropic laminate
Sourceability/Cost:
Compared to woven, due to lower fiber content, and less intensive weaving process, save on production costs
Straightforward production, involving less complexity
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Can be laid down in multiple directions = , allowing us to achieve balanced properties
Orientated with greater percentage along single axis = Different , creating different stiffness and strength along different axes
Spreading resin going against the grain will cause nonwoven fibers to break free from binder
Vacuum A vacuum bag manufacturing process = produces the greatest strength-to-weight ratio
Vacuum
bag manufacturing process utilizes a sealed bag in
With vacuum infusion, you can get the ideal resin-to-fabric ratio
Compared to woven fabric, it is more difficult due to the slower resin infusion process
The process is can be detailed due to the preciseness when generating directional strength
Tends to fall apart during layup process due to lack of interlaced fibers
Twill Weave Carbon Fiber:
Characterized TW carbon fiber is characterized by a diagonal pattern, fibers are woven in a staggered manner, which causes a more
Used much more in an aesthetic with suitable strength properties
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Used in many cosmetic and decorative applications while having moderate formability and moderate stability
Can be utilized in combination with UD carbon fiber to create a high strength laminate with improved machinability
Sourceability/Cost:
Higher production costs, due to intricate diagonal pattern = result which results, in more advanced weaving techniques and additional processing steps
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Must be handled more carefully than a plain weave fabric to avoid adding distortions to the weave
More complex, a traditional vacuum bagging process and autoclaving prepreg will produce what appears to be a flattened or crushed surface
Added layer of deep epoxy surface allows the carbon fiber to develop full depth, and preserve a 3D appearance.
Understand pre-preg vs non pre-preg
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Pre-preg vs Non Pre-Preg
Pre-Preg Carbon Fiber
Created by impregnating carbon fiber fabrics with a controlled amount of resin (epoxy or phenolic) in a factory setting
Cut into sheets/rolls and stored in a cooled area to prevent complete curing
Requires an oven or autoclave to fully cure and form the final composite part
Advantages:
Higher fiber-to-resin ratio
Better mechanical properties + lighter weight
Better control over resin content + distribution
Consistent quality + performance, as opposed to wet layup
Less waste due to excess resin removed during the impregnation process
Cleaner + safer = resin exposure minimized
Disadvantages:
Higher cost = materials are more expensive than dry fabric + resin
Complex processing - Specialized equipment + skills to handle and cure
Automotive Use Cases:
Body panels, Chassis,
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Applying resin to dry carbon fiber by hand or machine in a mold
Placing resin-coated fabrics into a mold, and manually removing air bubbles with a roller or brush
Resin can be epoxy, polyester, or vinyl ester
Cured at room temperature or with heat
Advantages:
Lower cost = process use cheaper materials + equipment
More flexibility = process can accommodate complex shapes + large parts
Disadvantages:
Lower fiber-to-resin ratio = lower mechanical properties + heavier
Less control over resin content + distribution
Variable quality + performance
More waste = Excess resin discarded or cured in the mold
Messier + riskier = resin exposure is higher
Automotive Use Cases:
Bumpers, Hoods, Fenders
Look into the bonding process for each type of carbon fiber (necessary epoxy/resin properties), as well as how orientation affects a composite structure
Bonding Processes + Orientation
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Bonding Processes + Orientation
Unidirectional (UD) Carbon Fiber
Bonding Process (Epoxy/resin properties)
Fibers are bound by trace amount of polyester binder (composed of less than 3% of overall construction)
Spread of fibers against the grain causes nonwoven fibers to break free from the binder
More of a risk with UD because carbon fiber is not woven together
Align with high stiffness, strength, and specific orientation
High shear + tensile strength = support direction of fibers
Needs to have excellent bonding properties for layer stacking, in order to achieve the desired stiffness
Precise Resin to fiber ratio = ease of application
Orientation
Binder is used on one side of material to provide clean, opposite face of the carbon
No twisting or crimping of fibers
Some brands have a slight weave in-and-out of binder (not true UD fabric)
Slight weave reduces single direction max strength
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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.
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Thru Bolts
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.
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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
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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:
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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:A thru bolt solution is effective when the bolted joint is transferring loads to the panel that are in-plane, as opposed to out of plane. Additionally, a custom flange can be utilized with thru bolts, in order to mount any part to the paneling which could be effective for suspension mounting.
Potted Inserts
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.
There can be 3 types of potted inserts, one being through-the-thickness inserts, which have inserts bonded through the the entire thickness of the sandwich panel with potting material around the insert. Next, fully potted inserts include an insert that sits in the core material of the laminate, that does not go through both sides of the thickness, where potting material sets it inside the sandwich panel, reaching the bottom layer of the laminate. Lastly, partially potted inserts are smaller inserts that only go through about half of the laminate, with potting material around the insert.
In addition, there are various potting methods that have their own benefits and drawbacks
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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
KETIV Technologies Video: Intro to Composite Analysis Using Ansys Mechanical
FEA Testing
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To utilize FEA to simulate composite structures, shell elements are utilized
Use a shell element (planar element). This creates a model based on the length and width dimensions, while using tabular data for thickness, making the simulation run more efficiently.
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.
To run the FEA simulation, we need orthotropic material properties, ply thickness and orientation, stacking sequence, the orthotropic strengths, and failure theory/theories.
We will utilize the Tsai Wu failure criterion in order to determine the factor of safety and tensile/compressive failure strengths
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Delamination Analysis:
A common failure method of composites is the delamination of the laminate, in which the plies of the material start to separate, which disallows the composite to transfer load and stresses throughout the entire structure, leading to stress concentrations and failure of the structure.
There are a few ways you could approach analyzing this in 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.
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Define layers - select worksheet option, and define each layer
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If you go to engineering data on the ANSYS workbench → composites material, there are a lot of predefined ones to use.
Click coordinate sys → insert new coordinate sys → from there, can go to properties of coord plane and set geometry relative to plane.
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From there can treat it as a normal ANSYS simulation (inserting various tests and defining certain wanted solutions)
Can also define which specific layer you want.
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Note: Remember the tsaiTsai-wu stuff from above? apparently you can code ANSYS to do it:code below
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Geometry Preparation of FSAE Composite & Monocoque Chassis in ANSYS SpaceClaim - Part 1
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