Composite Fabricating Basics

By resolute definition, a fabricated COMPOSITE material is a manufactured collection of two or more ingredients or products intentionally combined to form a new homogeneous material that is defined by its performance that should uniquely greater than the sum of its individual parts. This method is also defined as SYNERGISTIC COMPOSITION.

COMPOSITE MATERIAL COMPOSITION

Reinforcing Fabric

Impregnating Resin

MaxBondMed-2Gal

Follow the epoxy mixing video using our fabrics and impregnating resins to produce structurally strong composite laminate.

With respect to the raw materials selection (fabric and resin), the fabricating process, and the intended composite properties, these three aspects must be carefully considered in the engineering phase of the composite.

Step 1: Fabric Selection

TYPES OF FABRIC WEAVE STYLE AND SURFACE FINISHING
FOR RESIN TYPE COMPATIBILITY

Fabrics are generally considered ”balanced” if the breaking strength is within 15% warp to fill and are best in bias applications on lightweight structures. “Unbalanced” fabrics are excellent when a greater load is required in one direction and a lesser load in the perpendicular direction.

  • Tow: The bundle of individual carbon filaments used to weave carbon fabric. 50k tow means there are 48-50,000 carbon filaments in the tow. Smaller tow, i.e., 12k, 6k, 3k, and 1k, are obtained by dividing the 50k tow into smaller bundles.
  • Thread Count: The number of threads (tow in carbon and yarn in Aramid) per inch. The first number will be the warp count, and the second will be the fill count. Fill The threads that run the width of the roll or bolt and are perpendicular to the warp threads.
  • Warp: The threads that run the length of the roll or bolt and are perpendicular to the fill threads.
  • Finish: The chemical treatment of fiberglass makes it compatible with resin systems, therefore improving the bond between the fiber and the resin. Finishing fiberglass typically decreases the fiber strength by as much as 50%. Both Silane and Volan finishes are epoxy compatible. Historically, Volan has been considered a softer finish for a more pliable fabric, but recent advances have yielded some excellent soft Silane finishes.
  • Thickness: Measured in fractions of an inch. The thicker the fabric, the more resin is required to fill the weave to obtain a smooth finished part.

Weaves:

  • Plain weave means the warp and fill threads cross alternately. This is the most common weave.
  • 4 Harness (4 HS Satin or crowfoot) weave means the fill thread floats over three warp threads, then under one warp thread. This weave is more pliable than the plain weave, therefore conforms to complex curves more easily.
  • 8 Harness (8 HS Satin) weave means the fill thread floats over seven warp threads, then under one warp thread. This weave is the most pliable of the standard fiberglass weaves.
  • 2 x 2 Twill weave means the fill thread floats over two warp threads, then fewer than two warp threads. This weave is found most commonly in carbon fabrics and is more pliable than plain weave.

Most fabrics are stronger in the warp than the fill because higher tension is placed on the warp fiber, keeping it straighter during the weaving process. Rare exceptions occur when a larger, therefore stronger thread is used in the fill direction than the warp direction.

PLAIN WEAVE is a very simple weave pattern and the most common style. The warp and fill yarns are interlaced over and under each other in alternating fashion. The plain weave provides good stability, porosity, and the least yarn slippage for a given yarn count.

8 HARNESS SATIN WEAVE  is similar to the four-harness satin except that one filling yarn floats over seven warp yarns and under one.

This very pliable weave is used for forming over curved surfaces.

4 HARNESS SATIN WEAVE  is more pliable than plain weave and is easier to conform to curved surfaces, which is typical in reinforced plastics. This weave pattern has three-by-one interfacing, where a filling yarn floats over three warp yarns and under one.

2×2 TWILL WEAVE is more pliable than the plain weave and has better drivability while maintaining more fabric stability than a four or eight-height satin weave. The weave pattern is characterized by a diagonal rib created by one warp yarn floating over at least two filling yarns.

COMMERCIAL FIBERGLASS-FABRIC WEAVER

Finishing Cross Reference
And
Resin Type Compatibility

RESIN COMPATIBILITY

BurlingtonIndustries

Clark Schwebel

J.P Stevens

Uniglass Industries

Epoxy, Polyester

VOLAN A

VOLAN A

VOLAN A

VOLAN A

Epoxy, Polyester

I-550

CS-550

S-550

UM-550

Phenolic, Melamine

I-588

A1100

A1100

A1100

Epoxy, Polyimide

I-589

Z6040

S-920

UM-675

Epoxy

I-399

CS-272A

S-935

UM-702

Epoxy

CS-307

UM-718

Epoxy

CS-344

UM-724

Silicone

112

112

n-pH (neutral pH)

Satin Weave Style For Contoured Parts Fabricating

These styles of fabrics are some of the easiest to use, and they are ideal for laying up cowls, fuselages, ducts, and other contoured surfaces with minimal distortions.

The fabric is more pliable and can comply with complex contours and spherical shapes. Because of their tight weave style, satin weaves are typically used as the surface ply for heavier and coarser weaves.

This technique helps reduce fabric print and requires less gel coat to create a smoother surface.

Satin weave type conformity unto curved shapes

Plain Weaves, Bi-axial, Unidirectional Styles For Directional High Strength Parts

Use this weave-style cloth when high-strength parts are desired.
It is ideal for reinforcement, mold making, aircraft and auto parts tooling, marine, and other composite lightweight applications.

Plain weave style for high strength

Step 2: Choose the best epoxy resin system

FRP – FIBER REINFORCED PLASTIC.
The epoxy resin used in fabricating a laminate will dictate how the FRP will perform when load or pressure is implied on the part.
To choose the proper resin system, consider the following factors that are crucial to a laminate’s performance.

SIZE AND CONFIGURATION OF THE PART
NUMBER OF PLIES AND CONTOURED, FLAT OR PROFILED

CONSOLIDATING FORCE
FREESTANDING DRY OR HAND LAY-UP, VACUUM BAG, OR PLATEN PRESS CURING

CURING CAPABILITIES
HEAT CURED OR ROOM TEMPERATURE CURED

LOAD PARAMETERS
SHEARING FORCE, TORSIONAL AND DIRECTIONAL LOAD, BEAM STRENGTH

ENVIRONMENTAL EXPOSURE
The principal role of the resin is to bind the fabric into a homogeneous rigid substrate.
OPERATING TEMPERATURE, AMBIENT CONDITIONS, HUMIDITY, CHEMICAL EXPOSURE, CYCLIC FORCE LOADING

MATERIAL AND PRODUCTION COST
BUYING IN BULK WILL ALWAYS PROVIDE THE BEST OVERALL COSTS, AS WELL AS DOING IT RIGHT THE FIRST TIME
These factors will dictate the part’s design and composition and must be carefully considered during the design and engineering phase of the fabrication.

OUR GENERAL EPOXY RESIN SYSTEM SELECTION FORMULATED FOR SPECIFIC APPLICATIONS

  • MAX BOND THIXOTROPIC A/B MARINE GRADE HIGH-STRENGTH ADHESIVE
  • MAX BOND LOW VISCOSITY A/B MARINE GRADE STRUCTURAL EPOXY RESIN
  • MAX HTE A/B HIGH-TEMPERATURE EPOXY RESIN SYSTEM
  • MAX PCR A/B WOOD ROT REPAIR AND PROTECTIVE COATING RESIN
  • MAX GRE A/B GASOLINE RESISTANT EPOXY RESIN
  • MAX GPE COLORED EPOXY RESIN
    • AVAILABLE IN WHITE, BLACK, RED YELLOW & BLUE
  • MAX CLR-HP
    HIGH-PERFORMANCE VERSION WITH HIGHER HEAT RESISTANCE, TOUGHNESS AND SURFACE HARDNESS
  • MAX GPE A/B CLEAR LOW-COST GENERAL-PURPOSE EPOXY RESIN
  • MAX CLR CLEAR LIQUID RESIN SYSTEM**
    LOW VISCOSITY VERSION EXTENDED POT LIFE AND IMPROVED FLEXIBILITY
  • MAX CLR FAST 30% FASTER SETTING VERSION
  • MAX CLR TC
    IMPROVED DEGASSING AND SURFACE QUALITY
    MAX CLR TC FOR TOP COAT USE ONLY
  • ** AN ALIPHATIC-BASED TOP COAT IS REQUIRED FOR OUTDOOR AND DIRECT SUNLIGHT APPLICATION
    MAX SEAL
    NON-YELLOWING ALIPHATIC POLYURETHANE TOP COAT

MAX GPE FOR GENERAL CONSTRUCTION LOW-COST APPLICATIONS

SAFE TO USE ON POLYSTYRENE FOAM

MAX CLR HP CRYSTAL CLEAR HIGH-PERFORMANCE APPLICATION

MaxSealCERAMICTILE1

NOTE HOW THE WATER BEADS WHEN THE WATER IS APPLIED OVER THE COATED AREA

MaxSealB

MAX BOND LOW VISCOSITY FOR MARINE APPLICATIONS

MAX GPE FOR GENERAL CONSTRUCTION
LOW-COST APPLICATIONS

SAFE TO USE ON POLYSTYRENE FOAM

MAX CLR HP CRYSTAL CLEAR HIGH-PERFORMANCE APPLICATION

MAX HTE FOR HIGH-TEMPERATURE RESISTANCE APPLICATIONS

Specimens were cured for 3 Hours at 25˚C plus 2 Hours At 155˚C

Step 3: Proper Lay-Up Technique

Pre-lay-upnotes

  • Layout the fabric and precut to size and set aside
  • Avoid distorting the weave pattern as much as possible
  • For fiberglass molding, ensure the mold is clean and adequate mold release is used
  • View our video presentation “MAX EPOXY RESIN MIXING TECHNIQUE
  • Mix the resin only when all needed materials and implements needed are ready and within reach

Mix the proper amount of resin needed and accurately proportion the resin and curing agent. Adding more curing agents than the recommended mix ratio will not promote a faster cure. Over saturation or starving the fiberglass or any composite fabric will yield poor mechanical performance. When mechanical load or pressure is applied to the composite laminate, the physical strength of the fabric and not the resin should bear the stress. If the laminate is over-saturated with the resin, it will most likely fracture or shatter instead of rebounding and resist damage.

Don’t know how much resin to use to go with the fiberglass?
A good rule of thumb is to maintain a minimum of 30 to 35% resin content by weight; this is the optimum ratio used in high-performance prepreg (or pre-impregnated fabrics) typically used in aerospace and high-performance structural applications. For general hand lay-ups, calculate using 60% fabric weight to 40% resin weight as a safe factor. This will ensure that the fabricated laminate will be below 40% resin content, depending on the waste factor accrued during fabrication.

Place the entire precut fiberglass to be used on a digital scale to determine the fabric-to-resin weight ratio. Measuring by weight will ensure accurate composite fabrication and repeatability rather than using OSY data.

Typical fabric weights, regardless of the weave pattern

1 yard of 8 OSY fabric at 38 inches wide weighs 224 grams

1 yard of 10 OSY fabric at 38 inches wide weighs 280 grams

Ounces per square yard or OSY is also known as aerial weight, which is the most common unit of measurement for composite fabrics.

To determine how much resin is needed to impregnate the fiberglass adequately, use the following equation:

(Total Weight of Fabric divided by 60%)X( 40%)= weight of mixed resin needed
OR
fw= fabric weight
rc= target resin content
rn=resin needed

MASTER EQUATION
(fw/60%)x(40%)=rn
FOR EXAMPLE
1 SQUARE YARD OF 8-OSY FIBERGLASS FABRIC WEIGHS 224 GRAMS
(224 grams of dry fiberglass / 60%) X 40% = 149.33 grams of resin needed
So for every square yard of 8-ounce fabric,
It will need 149.33 grams of mixed resin.
Computing for resin and curing agent requirements based on
149.33 grams of resin needed
THE MIX RATIO OF THE RESIN SYSTEM IS 2:1 OR
50 PHR (per hundred resin)
2 = 66.67% (2/3)
+
1 = 33.33%(1/3)
=
(2+1)=3 or (66.67%+33.33%)=100% or (2/3+1/3)= 3/3
149.33x 66.67%= 99.56 grams of Part A RESIN
149.33x 33.33%= 49.77 grams of Part B Curing Agent
99.56+ 49.77 = 149.33 A/B MIXTURE

GENERAL FIBERGLASSING AND FRP FABRICATION
A 4 X 8 FEET 3/8 INCH THICK FIBERGLASS PANEL WAS FABRICATED WITH 18 PLIES OF 24-OUNCE FIBERGLASS ROVING IMPREGNATED WITH MAX GPE RESIN SYSTEM. THE PANEL WAS VACUUM-CURED FOR 24 HOURS AT ROOM TEMPERATURE AND THEN POST-CURED FOR 2 HOURS AT 200°F AND THEN TESTED USING THE ASTM D695 TEST PROCEDURE.

32 PERCENT AVERAGE RESIN CONTENT

DETERMINATION OF FIBER-TO-RESIN RATIO

NOTE THE MODE OF FAILURE OF THE COMPRESSION SPECIMENS ILLUSTRATING A CROSS-AXIS FROM THE TOP AND BOTTOM OF THE SPECIMEN.

UNDER MAGNIFIED EXAMINATION, EVIDENCE OF RESIN MATRIX RESIDUE WAS PRESENT ON EACH PLY OF THE FIBERGLASS; THIS MODE OF FAILURE DENOTES A COHESIVE FAILURE OR A DIRECT SPLITTING OF THE RESIN ITSELF.

15,116 PSI MAXIMUM COMPRESSIVE STRENGTH (0.417 load area)

Common Factors Of 100% Solids (Zero volatiles and unfilled epoxy resin)
1 gallon of resin = 4239 grams (1.12 g/cc)
1 gallon = 128 fluid ounces
1 gallon of resin = 231 cubic inches
1 fluid ounce of resin = 33.17 grams

Apply the mixed resin onto the surface, lay the fabric, and allow the resin to saturate through the fabric.
NOT THE OTHER WAY AROUND
This is one of the most common processing errors that yields sub-standard laminates. By laying the fiberglass onto a resin film, fewer air bubbles are entrapped during the wetting-out stage. Air is pushed up and outwards instead of forcing the resin through the fabric, which will entrap air bubbles. This technique will displace air pockets unhindered and uniformly dispersed throughout the fiberglass with minimal mechanical agitation or spreading.

Note the slide show presentation.

Typical Fiberglass Reinforcing Technique Unto A Wood Substrate

For Vacuum Bagging Process

VACUUM BAGGING

MAX BOND LOW VISCOSITY A/B
LAMINATE CONFIGURATION FLAT PANEL
USED FOR STRUCTURAL APPLICATIONS
ROOM TEMPERATURE CURED
HEXCEL 7781 9-OUNCE 8-HARNESS SATIN WEAVE TOP AND BOTTOM PLIE
PLUS
15 LAYERS CORE 24-OUNCE FIBERGLASS PLAIN WEAVE ROVING
LAMINATE CONFIGURATION CONTOURED SPEAKER ENCLOSURE

MAX CLR-HP A/B used
FOR CARBON FIBER CRYSTAL CLEAR HIGH-PERFORMANCE SINGLE-PLY 12-OUNCE 2X2 TWILL WEAVE CARBON FIBER

Given enough time and the proper selection of the fabric surface treatment (fabric-to-resin compatibility), a dry fabric will seek a state equilibrium, distribute the applied resin, and naturally release air bubbles entrapped within the laminate. It is then very important that the proper viscosity, working time, and surface treatment of the fabric are considered depending on the application of the composite structure. There are also fabricating techniques that can be employed to yield high-performance laminates. Depending on the part size processes such as high-pressure pressing, vacuum bagging, and vacuum-assisted resin transfer molding are superior methods over hand dry lay-up. Air voids or porosity within the laminate is typically where failure propagates when the load is applied (fracturing, compression failure, tearing, torque, tensile strength, creep).

VACUUM RESIN FUSION PROCESS WITH MAX 1618 A/B

Step 4: Proper Curing

Allow the lay-up to cure for at least 24 to 36 hours before handling.

Optimum cured properties can take up to 7 days, depending on the ambient cure condition.

The ideal temperature cure condition of most room-temperature epoxy resin is 22 to 27 degrees Celsius at 20% relative humidity.

Higher ambient curing temperatures will promote faster polymerization and the development of cured mechanical properties.

Improving mechanical performance via post-heat cure
A short heat post-cure will further improve the mechanical performance of most epoxy resins. Allow the applied resin system to cure at room temperature for 18 to 24 hours and expose it to heat if possible. Cure it in an oven or other radiant heat source (220°F to 250°F) for 45 minutes to an hour. You can also expose it to direct sunlight but place a dark-colored cover, such as a tarp or cardboard, to protect it from ultraviolet exposure.

Generally, room-temperature cured epoxy resin has a maximum operating temperature of 160°F or lower.

A short heat post-cure will ensure that the mixed epoxy system is fully cured,
especially for room-temperature cured systems that can take up to 7 days to achieve 100% cure.

Some darkening or yellowing of the epoxy resin may occur if overexposed to high temperatures (>250 F).

AMINE BLUSH
The affinity of an amine compound (curing agent) to moisture and carbon dioxide creates a carbonate compound and forms what is called an amine blush. Amine blush is a wax-like layer that forms as most epoxies cure if the epoxy system is cured in extreme humidity (>70%).

It will be seen as a white and waxy layer that must be removed by physical sanding of the surface followed by an acetone wipe.

Although we have formulated the MAX CLR, MAX BOND, and MAX GPE product line to be resistant to amine-blush, it is recommended not to mix any resin systems in high humidity conditions, greater than 60%.

Always ensure the substrate or material the epoxy resin system is being applied to is as dry as possible to ensure the best-cured performance.

OTHER TYPES OF EPOXY RESIN CURE MECHANISM

LATENT CURING SYSTEMS
Latent epoxy resins are systems that are mixed together at room temperature and will begin polymerization, but they will not achieve full cure unless they are exposed to a heat cure cycle. These high-performance systems demonstrate exceptional performance under extreme conditions, such as high mechanical performance under heat and cryogenics temperatures, chemical resistance, or any environment where epoxy room temperature systems perform marginally or poorly.

Polymerization will begin after mixing the resin and curing agent and only achieve a partial cure. Some resins may appear cured or dry to the touch, this state is called ‘B-Stage Cure’, but upon application of force will either be gummy or brittle almost glass-like and will dissolve in most solvents. The semi-cured resin must be exposed to an elevated temperature for it to continue polymerization and achieve full cure.

UV CURING SYSTEMS
Like “addition cure” or catalytic polymerization, ultraviolet curing is another method that has gained popular use in applying polymer adhesives and coatings. It offers a unique curing mechanism that converts a liquid polymer into a solid plastic upon exposure to UV radiation. The two common commercially significant methods are “FREE RADICAL INITIATION” and CATIONIC REACTION. In both reactions, polymerization occurs via the decomposition of a Photoiniator blended within the resin system; upon exposure to the adequate wavelength of Ultraviolet energy, the photoinitiator degrades and causes a ring opening or cleavage of the photoinitiator molecule and induces rapid polymerization or cross-linking.

The polymerization reaction can be either free radical or cationic and occurs almost instantaneous creation of a polymer network.

HEAT ACTIVATED CURING SYSTEMS
This type of epoxy system will not polymerize unless it is exposed to the activation temperature of the curing agent, which can be as low as 200F and as high as 400F. In most instances, our MAX EPOXY SYSTEMS epoxy system can be stored at room temperature and remain liquid for up to six months and longer.

USE AN INFRARED HEAT LAMP FOR LARGER PARTS IF A PROCESS OVEN IS NOT AVAILABLE

POSSIBLE HEAT CURING TECHNIQUES
If an oven is unavailable to provide the needed thermal post-cure, exposing the assembled part to direct solar heat (sun exposure) for a period will provide enough heat cure for the part to be handled.

Other heat curing, such as infrared heat lamps, can be used if a heat chamber or oven is unavailable.