Carbon Fiber Properties and Dimensions

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 can be used in both prepreg and non-prepreg forms

Non-women, and features all fibers running in a single, parallel direction.

Light weight compared to woven counterparts.

Stiffness:

• Provides a concentrated density of fibers to provide max longitudinal tensile potential, extremely stiff

• Resin ratio is usually low (prepreg) = high stiffness and strength to weight

• Dry form (non-prepreg) = requires binding fibers that run perpendicular to the direction of the carbon fiber

Use Case:

• 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 lower fiber content, and less intensive weaving process, save on production costs

• Straightforward production, involving less complexity

Ease of Manufacturing:

• Can be laid down in multiple directions = to achieve balanced properties

• Orientated with greater percentage along single axis = Different stiffness and strength along different axes

• Spreading resin going against the grain will cause nonwoven fibers to break free from binder

• Vacuum bag process = greatest strength-to-weight ratio

• Vacuum infusion = 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 by diagonal pattern, fibers are woven in a staggered manner

Used much more in an aesthetic with suitable strength properties

Stiffness:

• Good pliability and can form to complex contours

• Better at painting its fabric stability than satin weave but not as good as plain weave

Use Case:

• Used in many cosmetic and decorative applications while having moderate formability and moderate stability

Sourceability/Cost:

• Higher production costs, due to intricate diagonal pattern = result in more advanced weaving techniques and additional processing steps

Ease of Manufacturing:

• 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

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

  • 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,

Non Pre-Preg Carbon Fiber (Wet)

• 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

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

  • Epoxy/Resin Properties

    • 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

Twill Weave Carbon Fiber

• Bonding Process (Epoxy/resin properties)

  • Expoxies should offer high tensile + flexural strength

    • Require durability + strong adhesion properties due to woven layers with varying orientations

    • High modulus of elasticity = Enhance resistance to deformation + improve load-bearing capcity

• Orientation

  • 2x2 Twill Weave

    • Diagonals are synchronized

    • Braid is over-over-under-under

      • Provides an elastic pattern = used for complex chapes because weave is looser

  • 4x4 Twill Weave

    • Fancier pattern, looks like arrow heads/tractor traces

    • Not as popular, but will bend around curves better than 2x2 twill weave