Learning Centre

Learning Centre2018-09-24T14:56:12+00:00

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What Are Composites?

In a general sense, a composite material is comprised of two or more sub-materials with different properties. In industry however, composite materials are typically referred to those which are comprised of a reinforcement material suspended in a plastic matrix. The reinforcement and matrix material are selected for the application and final properties for the composite part.

History

    • Ancient times
      Homes in the ancient Egyptian civilization were constructed using composite bricks. The composite bricks used a clay or mud matrix which was reinforced by dried straw. The addition of the straw improved the compressive strength of the brick and prevented bricks from crumbling and mitigated crack growth.
    • Early 1900’s
      With innovations in the synthetic polymer industry, plastics such as vinyl, and polyester were developed. These polymers are still extensively used in the manufacturing of consumer goods. For higher strength applications, additional reinforcement material was added. The first appearance of modern composite materials came in 1930’s with the production of fine glass fiber filaments used as insulation and the advent polyester resin systems.
    • Mid 1900’s
      During the war era, lighter, more durable materials were sought after. Naval vessel hulls were constructed using glass fiber reinforced plastics and had the advantage over metal and wooden constructs of being more resistant to corrosion and fouling due to sea water. After the war, these materials became extensively used marine, aerospace, automotive applications.
    • Late 1900’s
      Further development in reinforcement material saw the origin of carbon and aramid materials which offered higher strength and improved wear properties. These materials became extensively used in sporting equipment, and the aerospace and automotive industries.
    • Modern Day
      Currently, composites are used extensively in consumer products and building materials in addition to the traditional industries as a lightweight, cost efficient alternative to metals. Currently, parts as large as passenger aircrafts fuselages are being constructed as a single unit from composite materials. In the automotive industry, as fuel consumption becomes increasingly important, composite materials are being used in structural components such as the chassis and body to help reduce the mass of a vehicle. Composite materials are also being extensively tested on a nano and micro-scale to improve electrical conductive properties for electronics.

Anatomy of a Composite Part

Composite materials have 3 main constituents which can be tailored to meet the needs of a particular application. By changing the thickness, density, orientation, material, and type of each of these constituents, the overall properties of the composite part can be altered to meet a customized need.

Sandwich Panel Image

Reinforcement

The reinforcement material serves as the primary load bearing component as it is significantly stiffer and stronger than other constituents in the composite structure. The most common reinforcement materials are glass, carbon and aramid fibers.

Glass Fiber
Molten glass can be spun and formed into a fine (order of 10 micron) filament. Depending on the chemical combination of the silicates being melted, a different type of glass fiber can be produced. The two most common types are S-Glass and E-Glass. S-Glass (also known as Structural Glass) has a larger percent composition of Silicone Oxide and Aluminum Oxide giving it superior stiffness and tensile strength over E-Glass. E-Glass (also known as Electrical Glass) has improved electrical insulating properties over S-Glass due to a larger composition Calcium Oxide. A variety of other derivatives exist, each catered to a particular need and application.

Fiber Glass image

Carbon Fiber
Carbon Fiber is produced from high temperature heating (1500 °C) and stretching of a high carbon polymer (such as Polyacrylonitrile (PAN)) in an inert atmosphere. On a molecular scale, this process burns off impurities on the main chain such as Hydrogen and Nitrogen atoms, leaving behind a linear carbon chain which are very high strength and stiffness. This process can be repeated in many stages at higher temperatures to produce higher purity carbon filaments. Carbon Fiber is classified into groups based on its tensile stiffness ranging from a low modulus to an ultra-high modulus fiber. There is a usual trade-off between the stiffness of the fiber filament and how brittle it becomes. These individual filaments are then placed parallels to one another and bundled. The number of individual filaments in a buddle is designated in thousands where a 3K (3000 filaments/bundle) is the most commonly produced.

Carbon Fiber image

Aramid Fiber
These types of fibers are produced by spinning an amine group polymer in the presence of acid which has a specific arrangement of Carbon, Oxygen and Hydrogen. This chemical reaction and spinning process produces a fine filament of aramid fiber which is wound on spools. Aramid products are usually used in applications where high strength, stiffness and good abrasion properties are required. Similar to carbon fiber, individual filaments are typically bundled in a parallel arrangement and designated based on the number on the number of filaments per bundle.

Aramid Kevlar image

The table below presents typical stiffness properties of uncured glass, carbon and aramid fibers.

PropertyTypical S-Glass
(Dry Fiber)
Intermediate Modulus Carbon Fiber
(Dry Fiber)
Typical Aramid Fiber
(Dry Fiber)
Tensile Modulus (GPa)87231179


Source:

Reinforcement Material Forms

Based on the type of manufacturing method and the desired characteristics of the composite part, reinforcement material can be processed into different forms. Generally speaking, processed reinforcement materials can be classified into two main sub-categories:

Continuous Fibers: This form of reinforcement has fibers which are full length and arranged in a particular orientation with respect to neighboring fibers. Continuous fibers have an extremely large fiber length: diameter ratio and typically exhibit excellent strength and stiffness properties.

Discontinuous Fibers: These fibers are processed to a random orientation and often have smaller length fiber length to diameter ratios. These fibers are either cut into small strands during manufacturing or processed into sheets with fibers randomly dispersed and overlapping.

Continuous and Discontinuous Fibers image

Continues fibers are commonly used when strength and stiffness are required. In the design process, designers use the orientation of the fibers to strengthen parts in the direction in which they are being loaded. When strength and stiffness are not a concern, discontinuous fibers products are often used and usually offer benefits in manufacturing speed.

Continuous Fiber Products:

Tow /Ribbon: This form has spooled bundles of individual filaments. The number of filaments per bundle is usually the main defining feature which differentiates tows from one another. This form is typically used in filament winding processes to produce cylindrical structures. Tows are also used for localized reinforcement or repairs.
In some manufacturing methods (spray-up lamination) tows are cut into small fiber lengths and sprayed with a mixture of resin.

Tow Ribbon image

Woven Fabrics: These fabrics are processed by taking individual tows and woven bi-directionally, thus producing strands that’s are perpendicular to one another (0° strands and 90° strands). The two most common styles of woven fabric are:

Plain Weave: In this arrangement, each 0° strand alternately passes over and under each 90° stand. This arrangement is repeated over the entire woven fabric width and length. This produces a symmetrical pattern and uniform material properties in the 0° and 90° directions. This weave is easier to produce than most other weaves but results in a large amount of fabric ‘crimp’ (geometric reduction in length of woven fabric compared to full strand due to fiber curvature in the over and under arrangement). Since fibers produce the most strength when they are aligned with the load, this arrangement reduces the mechanical properties of the material when compared to other weaves. Plain weaves have good stability and offer easier handling, but are more difficult to drape around complex curvature.

Twill Weave: In this arrangement, each 0° stand alternatively passes over and under two 90° stands in a repeating pattern along the width and length of the fabric. This type of weave produces less fabric ‘crimp’ and twill weaves generally have improved mechanical properties over plain weaves. The arrangement has reduced stability and are more difficult to handle. They are easier to drape around curves but careful handling must be used to ensure gaps and porosity is not introduced in manufacturing process.

Twill and Plain Weave image

Non-woven Fabrics: These fabrics are processed by taking individual tows and creating an arrangement using nylon stiches or through the use of a mild adhesive. These fabrics are usually arranged in a uni-directional (0°) or bi-directional (0° and 90°) arrangement.

Discontinuous Fiber Products:

Fiber Mat: This processed form typically contains chopped filaments of reinforcement material which is suspended in a binding agent. The amount of chopped filament, length of filaments and the type of binder will determine the properties and manufacturing methods suitable for a particular mat. This materials are easy to work with and reduce the amount of time required to produce a laminate. Mats can also be produced from continuous fibers where the fibers are randomly dispersed.

A veil is a special type of fiber mat which contains fine fibers and is usually used on the surface of a laminate to reduce the fiber imprint and improve the surface finish.

Matrix Material

The matrix material suspends and binds the reinforcement material and hardens to determine the shape of the final part. Compared to the reinforcement material, the matrix material is relatively weak and lacks stiffness. In a loading scenario, the matrix material holds the fibers in place and transfers load between fibers and layers. Matrix material in composite part manufacturing is typically polymer based and hardens from a liquid state in the presence of a hardening agent, air, or heat.

Polymer matrix materials can be broken into two main categories, thermoset and thermoplastic.

Thermoset polymers are most popular in current composite parts. These polymers begin in a liquid state and cure to form a 3 dimensional molecular network. This process is termed as cross-linking and it produces a dimensionally stable solid which has the advantage of being resistant to heat and chemicals. In addition, the 3 dimensional network of molecular bonds gives these forms of polymers good mechanical strength properties. Most polyesters, vinyl esters, and epoxies resins used in industry are thermoset polymers.

Thermoplastic polymers are typically heated to above 500 °C and formed into the part shape. These polymers offer an advantage in being faster to produce as the curing process consists of only cooling. These polymers are not temperature resistant and will melt to a viscous liquid if exposed to high temperature. Some polyester resins are thermoplastic polymers.

Currently, the main matrix materials being used in industry are polyesters, vinyl esters, and epoxies resins. The resin system is selected based on the application and the final part properties required. Fillers and additives can often be added to most resin systems obtain characteristics such as flame resistance.

Polyester Resins
Polyester resins are the most widely used resin system. These resins are roughly half ester polymers blended into styrene monomers. In the molecular structure, the styrene enables the cross-linking by bonding between neighboring polyester chains at specific reactive sites along the chain. Typical polyester resins require a catalyst agent to begin the cross linking process with the styrene. This process is termed polymerization. Polyester resins offer a good price point and a quick cure time compared to other resin systems. This resin system work well in the presence of water and can be tailor to be chemical resistant. Polyester resins offer reasonable adhesive and mechanical properties compared to other resin systems.

Vinyl Ester Resins
Vinyl Ester Resin systems carry the same backbone structure of Polyester resin systems but have most of the reactive sites on the ends of the base polymer chain. In addition, Vinyl Ester resins have fewer ester groups which make it more resistant to water. Vinyl ester resins offer improved crack inhibiting abilities over polyester resins due to the location of cross-linking. With cross-linking only happening at the ends of parallel chains, Vinyl Ester resin systems are able to absorb more energy before cracks begin to form from an impact. In addition, Vinyl Ester resins offer improved adhesion and mechanical stiffness and strength over a Polyester resin.

Epoxy Resins
Epoxy resins are similar to Vinyl Esters resins systems in the manner that reactive sites exist at the ends of the base polymer chain. The main difference between these resin systems is the absence of ester groups in the base chain. Instead, epoxide groups are found at the reactive sites. Epoxy resins are also different in the manner that they require a hardener agent which is an amine group which is mixed with the resin to allow for it to cure. The ratio of the hardener to the resin is important as any excess of either component will remain uncured. Epoxy systems offer superior adhesion and mechanical stiffness and strength. In addition, with the absence of ester groups, the epoxy system performs extremely well in marine applications and are resistant to many industrial chemicals.

Resin TypeTypical Tensile Modulus (GPa)Typical Utilmate Tensile Strength (MPa)
Polyester Resins3.4555
Polyester Resins3.5980
Polyester Resins10.585

Data from: http://home.engineering.iastate.edu – pdf to article for unreinforced resins

Gel Coats
Gel coats are often used in conjunction with Polyester and Vinyl Ester resin systems and are a thermoset plastic. They serve as a protective and aesthetic topcoat which protects the matrix and the reinforcement material from UV light and chemical degradation. They can also be tinted and dyed to replicate any color and offer a significant advantage over paint in both labor and cost for finishing a composite part. In addition, in the event of damage to the top coat, gel coats can be resurfaced and restored far quicker and at a smaller cost than painted surfaces.

Gel coat is sprayed or brushed on in a thick (10-20mm) layer directly onto the prepared mold surface prior to lamination. The desired thickness is typically built up to in 2 or 3 layers with sufficient time between coats. The rest of the lamination process remains unchanged and the overall part finish upon release is greatly improved.

Core Material

Core material is often adhered in between ‘skins’ of reinforced plastic. Cores are typically used to add thickness to parts at little penalty of weight or cost. Adding core greatly improves the flexural (bending) stiffness and strength of a part.

When a material is being loaded in bending, the top surface of the material is being compressed while the bottom surface is being stretched. The further apart the top and bottom surfaces of a part in bending are spaced from each other, the greater the stiffness and strength of the part. In this form of loading, the core material sees what is known as a shear load as the top and bottom of the material is being pulled in opposite directions.

Core materials range widely based on the application, lamination method, and environmental conditions.

PVC Foam
PVC (polyvinyl chloride) cores are a chemical/moisture resistant, closed cell foam which offers good shear strength and adhesive properties. These cores are a rigid thermoset but can be thermoformed easily with the use of heat and pressure. They are manufactured in a variety of thicknesses and densities and are compatible with most resin systems and lamination methods.

PVC Core image

SAN Foam
SAN Foam (Styrene acrylonitrile) cores are a closed cell, light weight foam core which offers excellent chemical resistance. They are often used in very demanding manufacturing where high heat or high pressure is required. SAN has the unique property of being a thermoplastic and can easily be molded using heat.

Honeycomb Cores
Honeycomb cores can be manufactured from a variety of material but are typically produced from aluminum or a Kevlar based paper known as Nomex. The cells are arranged in a honeycomb pattern which offers a good compromise between strength and weight. These cores can easily be bent and molded to complex shapes. With hand laminations and resin infusion lamination methods, this type of core is susceptible to being saturated with resin.

Honeycomb Core image

Wood Cores
Wood cores offer very good compressive strength and shear properties at the expense of weight. End grain Balsa wood is typically used. This type of core is frequently used in local loading scenarios where high compressive stresses are expected. In addition, this core is often used at discontinues such as bolt holes and other local stress concentrators. Balsa cores treated with sealers can be used in environments with moisture and can be used with most resin systems and manufacturing methods.

Fabric Cores
Fabric cores and mats are typically far thinner than other core materials. They are usually referred as ‘bulking’ materials are opposed to a core and add marginal thickness to the laminate. They are mostly polyester woven sheets which are closed cell so they will not absorb resin during the lamination process. These cores are flexible and conform to bends and curves in a part. Fabric cores are typically very low density and not used where high core shear strength is required.

Fabric Core image

How they are made?

Composite parts manufacturing methods have been adapted to meet the needs of the part and material. Almost all manufacturing methods require the need for a mold to designate the shape of the composite part.

Molds (or tools) are designed around the final part which is to be produced, the manufacturing method selected and the required accuracy of the finished part. In the composites industry, there are two main designations for tooling. Namely, hard and soft tools.

Hard tools are made from ceramics, metals and high density woods. They require a larger initial investment in both material and machining costs. These types of tools are typically used repeatedly and the material is selected based on the robustness required for the mold. In addition, the material is selected based on the manufacturing method (ie. For a temperature cure part, the correct tooling material must be used for simultaneous thermal expansion). These types of tools are also able to hold dimensional tolerances better.

Soft tools are made from foams, composites or other machine-able medium which will wear and degrade as more parts are manufactured. These tools are lower cost and not as well suited for holding strict dimensional tolerances.

Tools preparation is essential to the final finish of the part. New tools are prepared for use by first polishing the surface to a desired roughness index. The roughness of the tooling surface has a direct impact on the surface roughness which will be imprinted on the part. Next the surface is sealed with an interfacial coating with fills very small scale pits and scratches. A release agent is then applied to the tool surface which allows the part to be removed after a full cure. The interfacial layer provides a good surface for the release agent to adhere to. Traditionally, release agents were a consumable material and would need to be applied after each part is removed from a tool. Recently, semi-permanent release agents are being used which can last up to 20 parts and can be left on the mold surface when a new coat is required.

There are constantly new methods for composite part manufacturing as the diversity or parts and applications grow. In general, most manufacturing methods can be classified into 5 general categories:

Open Mold/Hand Lamination
This is the most basic form of lamination. Plies of reinforcement material and core are stacked in a prescribed sequence and wet out with the resin system layer by layer over top of a prepared mold. The completed laminate is then allowed to cure based on the requirements for the resin system. This curing processes can be aided by the use of heat.

Hand Layup image

This method is typically used for custom one-off parts and small production runs. Hand lamination requires no complex machinery, tools, or consumables. This process produces some variation in part quality and strength due to inconsistency in resin distribution and entrapment of air voids between layers. Hand laminations are also difficult to efficiently scale up in production quantity as they are a labor intensive process. Efficiency for this process can be improved by using a spray on resin system and by having reinforcement material pre-cut prior to the lamination.

Spray-Up Lamination
This form of lamination utilizes a pneumatic spray gun which chops strands of reinforcement material and a mixture of resin directly onto the mold surface. This method usually begins with an application of a gel coat on the mold surface. A mixture of resin, catalyst and chopped reinforcement material is then sprayed overtop of the mold and compacted using a roller. Core and subsequent layers can be applied to add addition stiffness. Typically the laminate is then allowed to cure at room temperature or in an oven based on the requirements of the resin. The part is then removed and the mold can be prepared for the next manufacturing cycle.

This method reduces the time required to complete a lamination. In addition it is suitable for larger parts as this method allows for a large coverage area. Spray-up lamination methods utilize discontinuous fibers which greatly reduces the strength of a part. In addition, due to inconstancies in spraying, tolerances can be difficult to maintain. There are also health and environmental concerns over this form of manufacturing as large amounts of styrene content is released into the atmosphere.

Wet Bagging
Similar to a hand lamination, this process requires reinforcement plies to be wet out with a resin system layer by layer over top of a prepared mold. Prior to the resin curing, a consumable release ply, resin absorption material, and vacuum bagging film is placed over top of the final ply of reinforcement material. The vacuum bagging film is then sealed to the ends of the mold using an air tight mastic tape. A vacuum is then used to draw out air from between the mold surface and the vacuum bagging film thus applying pressure and removing voids of air entrapped between plies of reinforcement material. Vacuum port positioning and the use of ‘breather’ material in strategic locations is important to ensure equal vacuum pressure is applied across the entire part.

This process greatly improves inter-laminar bonds resulting in greater structural integrity. For this method of lamination, a resin system with the appropriate cure time must be selected to ensure the plies can be thoroughly wet out and bagged prior to cure. Resin systems can be designed to offer different cure times.

Wet Bagging image

Resin Infusion
In a resin infusion lamination, dry plies of reinforcement material and core are placed in the correct sequence overtop of a prepared mold surface. The mold is also strategically fitted with a resin supply line and a vacuum draw line. The laminate is then covered with a porous releasing ply, and a flow medium which allows for the flow of resin during the infusion process. An air tight vacuum bag is then fitted which seals around the part and the supply and draw lines. Air is then evacuated out from the draw line while catalyzed resin is injected from the opposite end of the part. Resin supply and vacuum pressure are monitored carefully during this process to ensure the entire part is uniformly wet out with resin and has equivalent vacuum pressure throughout the part. Once the correct amount of resin is injected, the supply line is sealed off and the laminate is allowed to cure under a regulated vacuum pressure and temperature conditions.

This method allows for larger, more complex parts to be manufactured compared to hand lamination and wet bagging methods. In addition, part quality and consistency is improved as resin uniformity and the curing cycle are more closely regulated between parts. This method is suited for both small and large production runs and is increasingly being automated. This method has many variants such as Resin Transfer Molding (RTM), Vacuum Assisted Resin Transfer Molding (VARTM), and Resin Injection Molding (RIM) which all have similar processes but differ in how and when the resin is injected and distributed. Increasingly, a matching male and female mold technique is being employed in fully automated settings to allow labor and consumables such as vacuum bagging film to be reduced.

Resin Infusion image

Autoclave Cure
Autoclave cure techniques are most commonly used with pre-impregnated (prepreg) reinforcement material when very high quality parts are required. This form of material has an un-catalyzed resin film which is applied to one or both side of the reinforcement material by the manufacturer. This material is always stored in a climate controlled environment as the resin is catalyzed by heat. These materials have a prescribed shelf life.

During the lamination process, the prepreg and core material is place over top of a prepared mold surface in the prescribed sequence and orientation. A slight amount of tack is present on the surface of the prepreg allowing it to hold is place on the mold surface without voids and gaps being created. Fine contours and tight corners are laminated using the help of a heat gun to ensure the prepreg covers the entirety of the mold surface. Since the prepreg material has the perfect amount of resin for the amount of reinforcement material, any gaps or voids will remain unfilled in the finished part, thus making the initial uncured lamination process the limiting factor in the parts final quality. A film adhesive is often used between prepreg material and the core to ensure a quality bond is formed. In an autoclave cure, the laminate and mold are fitted with a vacuum bag which draws out air during the curing process. The mold and the entire part is placed inside of the autoclave which has control over the pressure and temperature of the environment. The autoclave has the advantage of producing conditions above 1 atmosphere (14.7 psi) during the curing process, allowing for more force to be applied on the part surface thus reducing voids and improving the inter-laminar bonds. This increased force is only typically required for extremely high grade parts and is almost exclusively used in aerospace and performance automotive settings.

Autoclave image

In an autoclave cure cycle, the temperature is ramped up to an intermediate temperature causing the impregnated resin viscosity to drop, enabling it to flow and wet out the fibers of the reinforcement material. The temperature is then raised to the final cure temperature where the resin begins to catalyze and form chemical bonds. This process is carefully monitored using thermocouples to ensure that all areas of the part see the correct temperature conditions for a complete cure.

Autoclave processes require expensive prepreg material which has a limited shelf-life. In addition, there is a large capital cost associated with procuring equipment for an autoclave production run. Typically, parts will also spend upwards of 8 hours to go through a full autoclave cure cycle thus lowering the productively and usage of the autoclave and mold.

Oven Cure
Similar to Autoclave cures, oven cures can be used to manufacture parts from pre-impregnated reinforcement material. An oven cure is typically used when the additional force of a high pressure atmosphere is not required. This dramatically reduces the initial capital cost for the production of prepreg parts. Oven cures are also often used with standard resin systems in certain applications where specific properties of the final cured part are required.

Post Cure Finishing
Composite parts are often trimmed and finished to the desired specification after final cure. Like metals and other materials, composites can be cut, trimmed, sanded and machined.

In low volume production runs, hand trimming, sanding and finishing is commonly used. These methods do not scale up well and are extremely labor intensive. They also cause health concerns due to exposure to fine particulate matter.

Composite parts are frequently brought down to exact dimensions through the use of precision automated part trimming tools which are able to remove material from ends and produce clean holes. The finished part is free of stray fibers or built up resin. Composite parts can also brought down to final dimensions using sheet metal manufacturing methods such as a water jet which leaves behind clean, smooth edges.

When very precise fits and tolerances are required, composite parts can be machined using traditional machining methods. Typically, compression style tool bits are used to maintain the structure and distribution of reinforcement material in the polymer matrix. For drilling holes, an orbital style bit is used to prevent delamination and improve the dimensional accuracy throughout the hole depth.

Applications

The applications of composite parts are endless. Given the design freedom and variation which is attainable with different combinations of materials, almost any application and material requirement can addressed with composites.

Material & Process Selection

The selection of the material and manufacturing process is directly related the desired properties and use of the finished part. When considering the applications of a composite part, here are some elements to consider during material and process selection:

Stiffness & Strength

The stiffness and strength of a part will be a function of the part composition and the direction of load. Most composite materials are what is known as anisotropic – meaning they have differing mechanical properties in different directions. For example, a composite part with reinforcement fibers parallel to the direction of the applied load will be orders of magnitude stiffer and stronger than a part where the reinforcement fibers are perpendicular to the applied load. For structural applications, that allows designer to reinforce parts in directions where higher stresses are anticipated. In addition, composite parts allow for certain areas which are not loaded to have fewer plies and areas of higher stresses (bolt holes, joints, and bends) to have addition reinforcement material. This helps drastically bring down the weight of a part without large machining costs. When designing a composite part for stiffness and strength here are some factors to consider:

– Reinforcement: Material, orientation, thickness, plies, content (% vol.)

– Matrix material: Type, content (% vol.), coverage/distribution

– Core Material: Type, thickness, adhesion

Simple analysis techniques can be used to give a rough, upper limit on the stiffness of a composite part. Using the rule of mixtures, an upper limit on the elastic tensile stiffness and density of cured fiber and resin can be established based on the reinforcement material: matrix volume ratio. This model assumes that loads are applied parallel to the fiber direction and that reinforcement material is uniformly distributed in the matrix material. This is known as the same strain, different stress model for a composite:

Equation

Where E is the elastic modulus and ρ is the density

These properties can then be used in a simple beam calculation to determine the upper limit on the bending stiffness for a composite beam with a core. This model assumes that the cured reinforcement and matrix skins are far stiffer than the core material and that there is no slip between the core and laminate skins. It also assumes that shear properties of the core material do not dictate the behaviour of the loaded structure.

The moment of inertia for the composite beam shown below can be given as:

Beam Bending Equation

This model can then be used with the properties of the composite skins established from the rule of mixtures and used with standard engineering beam tables to determine an approximate stiffness of a panel. This makes assumptions (such as no transverse expansion/ contraction from Poison Effect) which are not necessary true, but offers a simple method of approximating and comparing stiffness’s and final part weights to metal counterparts. More accurate methods of analysis are available but require more in-depth calculations.

Chemical and UV Resistance

Composite materials provide good resistance to many industrial chemicals and offers exceptional protection from UV light damage.

When selecting a composite matrix material, it is important to ensure there is compatibly and that corrosion or chemical attack won’t damage the part. Several online resources are available to see which composite material will meet the needs of your application. The chemical resistance will change based on trade name for resin and the concentration and temperature of the reactive compounds. A few resources and comparisons to standard engineering materials are presented below:

http://spectrumlabs.com/dialysis/Compatibility.html

http://www.hubbellpowersystems.com/drain-systems/polycast/technical-info/pdf/Vinyl-Ester-Resin.pdf

UV light from the sun is known to damage and degrade surface coatings like paint. In addition, in some materials like polypropylene, UV light can cause mechanical properties such as stiffness and strength to be severely reduced.

Pigmented UV resistant gel coats can maintain their color for far longer than paint surfaces in areas of direct sunlight. Specialty resin systems such as polyester resins based on neopentyl-glycol are also available to extend the life of a pigmented surface.

UV stabilizers are often used in extreme applications where long term exposure is expected and the pigment of the composite part is very critical.

Process Selection

The manufacturing processes selected will have a significant effect on the final structural, and geometric properties of the part. In addition, the repeatability and variation amongst parts will be larger in some manufacturing techniques compared to others.

Effects on Structure, Performance and Geometry

The strength, stiffness and weight of a composite part is directly related to the control available to manufacturer in maintaining correct ratios between fibers and resin, vacuum pressure and temperature. In hand laminations, resin is often added onto dry fibers using a roller and is controlled by the laminator. Too much resin and the part will be heavier than anticipated. Too little resin and the parts structural integrity can be compromised.

A study from the Department of Mechanical Engineering at Washington State University conducted by Dave Kim et al. looked at the variation present in the physical and structural properties of glass reinforced composites in the manufacture of recreational yacht hulls. The study looked at comparing a hand lamination (HL) vs. a low pressure vacuum infusion (VL) (20” Hg) vs. a high pressure vacuum infusion process (VH) (28” Hg) for a typical glass fiber laminate used on recreational yachts.

Properties Table

Effect on physical properties of a sample laminate as a function of manufacturing methods (from Dave Kim et al.)

Form the data available, it is evident that hand lamination techniques resulted in parts with a larger proportion of resin content when compared to a vacuum infusion process. In addition, the void space in hand laminates is 3.5 time larger than in a high pressure vacuum infused laminate. This void space is a result of interstitial air which is entrapped in the laminate due the plies not being compressed together. Voids can also be caused by air bubbles being created as resin is brushed on.

Entrapped air and excess resin also resulted in poor thickness control in this experiment. There is only a 3% variation in thickness between a 20” Hg sample vs a 28” Hg sample, whereas the is a 40% difference in thickness between a hand lamination sample and a 20” Hg sample. This data clearly suggests that the application of even a small vacuum can greatly improve the thickness consistency between parts.

Thickness Study

Effect on sample thickness as a function of manufacturing method (adapted from Dave Kim et al.)

Air entrapment and voids were seen to causes a drastic reduction in both the tensile stiffness and tensile strength of the samples.

Strength Data

Effect on strength, stiffness and strain to failure as a function of manufacturing methods and vacuum pressure (adapted from Dave Kim et al.)

In this study, there was a 60% increase in strength when comparing a high pressure infusion composite to a hand laminate.

When samples were examined upon testing, millimeter scale air voids where seen in the laminate structure of the hand laminated samples.

Voids

Air entrapment in a hand laminated sample (from Dave Kim et al.)

From this study it is clear that the lamination method and anticipated properties are directly related and vacuum infusions techniques offer superior part quality over a hand laminated part.

Benefits

Material Comparison

Composite materials offer a distinct advantage over metals in stiffness, strength, and weight.

Part Stiffness

When designing a part for stiffness and mass, it should be noted that all metals have an upper bound on the stiffness of a part for a given mass (regardless of metal material selection). Stiffness is a base material property which is unaffected by alloying elements and material processing. The nominal stiffness per unit density (Stiffness/Density) remains a constant for all industry used metals, therefore there is a threshold on how light parts can be made regardless of metal choice.

PropertyAluminumSteelTitaniumInfused Unidirectional CF
(65 wt%. Fiber)
Tensile Stiffness (GPa)6820011698
Density (kg/m3)2700797045001525
Nominal Stiffness Per Unit Density0.0250.0250.0250.064

Sources:

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  • VectorPly Material Directory C-LA 1812 Infused

Part Strength

Part strength is typically a tradeoff between strength, cost, and manufacturability. Most exotic alloys for aluminum and steel can cost twice as much as a standard alloy and drive up manufacturing cost and time.

Property3003 H16 AluminumAISI 1005 Cold Drawn SteelGrade 5 TitaniumInfused Unidirectional CF
(65 wt%. Fiber)
Ultimate Tensile Strength (MPa)179330620988
Density (kg/m3)2700797045001525
Nominal Strength Per Unit Density0.0660.0410.1370.65
  • http://www.matweb.com/search/DataSheet.aspx?MatGUID=88e1df51ed674c6b9fac45ed79108f2d
  • http://www.matweb.com/search/datasheet.aspx?MatGUID=9d1e943f7daf49ef92e1d8261a8c6fc6
  • http://www.matweb.com/search/DataSheet.aspx?MatGUID=a0655d261898456b958e5f825ae85390
  • VectorPly Material Directory C-LA 1812 Infused

Design freedom

Traditional sheet metal parts are processed on press brakes and stamping machines resulting in limited design freedom. Designs are limited to being prismatic and not aesthetically pleasing. In addition, localized yielding on bend edges in sheet metal parts can be starting points for cracks and could lead to unexpected part failure. Designers are also limited to using a single thickness throughout a part because of manufacturing reasons. This often leads to heavier, parts. To bring down weight and remove material in regions of low stresses, additional manufacturing costs are endured and the amount of wasted material is increased.

Composite parts offer designers more freedom as molds can easily be produced to allow curved surfaces with no significant increase in cost. In addition, designers have control over the number of plies in particular regions allowing for pad-up in regions of concentrated stress and a reduced number of plies in areas of low stresses. This produces no significant increase in the costs required to manufacture the part and reduces the material consumption.

Markets Served

Aerospace

The aerospace market continues to be one of the largest contributors to demand in the composites industry due to a need for lightweight components. On newer aircrafts, over 50% of the parts are manufactured with composites materials. These parts range from entire fuselage sections, wings, interior components, and even components near and inside the aircraft engine.

Transportation

The automotive market is a quickly growing market as manufactures develop new methods to make lighter, more fuel efficient vehicles. In addition, composite parts are allowing vehicles to be safer in the event of a collision. Currently some manufactures are using composites to build bumpers, body paneling, interior components, and structural members. The automotive industry is a leader in incorporating automation in composite manufacturing.

Marine

The marine industry has used composites since the 1930’s with the advent of glass fiber reinforced plastics. Composites off a lightweight option for producing complex curved geometry found in boat hulls. Composites are also heavily used in recreational marine equipment like canoes and kayaks.

Sporting Equipment

Due to inherent advantages in mass and stiffness, composites are used in many high performance applications like bike frames, tennis racquets, fishing rods, and golf clubs. These materials also offer increased damping abilities which decreases the vibrations felt by users.

Medical Devices

Increasing manufactures of prosthetic implants and other assistive devices are turning to composites to meet the complex need of their parts.

Industrial Applications

Composites are widely used in the mining industry to build tanks that store corrosive and toxic materials. They are also used to build chutes and feeders in agricultural applications and offer good wear properties with increased design flexibility.

Renewable Energy

Composites continue to be the primary structural components in large scale wind turbine, making up most of the turbine rotor and tower.

Construction Materials

Light weight paneling, deck board, doors, bath tubs, pools and roofing materials can all made from composite materials. These materials offer the advantage maintain their color in the presence of constant UV light and are resistance to corrosion when constantly exposed to water.

Glossary

A mathematical depiction of the stiffness properties of a laminate structure. Used in Classical Laminate Theory

A additional substance typically added to ester based resin systems which will increase the rate of reaction between the resin and catalyst. This term is also commonly referred to as an activator or promoter.

A see-through thermoplastic commonly used in industry and consumer products

A substance added to a resin system to enhance certain physical or chemical attributes. Examples are: Flame-retardant additives, UV blockers.

A solid film used in a composite part which bonds to neighboring materials when activated by heat.

Entrapment of air in the inter- or intralaminate structure. Usually undesired and degrades mechanical properties and visual appeal.

Industry name for a tack-free solution added to polyester resins to create a sandable surface

A surface defect during manufacturing in gel coats caused by contamination. The roughness resembles a scale-like skin.

A chemical functional group. A derivative of ammonia (NH3) that is typically found in most epoxy hardeners.

Varying mechanical properties along different directions of a part or material. Typical laminate structures display some form of anisotropicity.

Fire-retardant additive commonly used in conjunction with ester based resin systems

An organic reinforcement material that is used in high strength, high stiffness applications. This material is very resistant to wear. It is often referred to by its trade name Kevlar.

The mass of reinforcement material per unit area. Typical units of measurement are grams/sq. meter (GSM) and ounces/sq. yard.

In composites, the aspect ratio is used to indicate the ratio of the length of a filament to the diameter.

A pressure vessel for creating high temperature and high pressure environment. Autoclaves are typically used with prepreg material.

Manufacturing process which used computer programmed robots to layer pre-cut reinforcement material

Short for a vacuum bag.

A laminate structure where subsequent plies are 90 degrees + the original ply angle to one another. This usually results in similar properties in orthogonal directions.

A high compressive strength wood product commonly used as a core material.

A fabric weave pattern with 0° fibers go over and under 90° fibers in pairs

The bearing load which can be sustained before failure. Usually determined by comparing the failure stress to the bearing force over the projected bearing area

A loading scenario where an applied force or moment puts opposite faces of a material in inverse stress states to one another (i.e.. Top face – compression, bottom face -tension)

Assembly of fibers that are oriented at 0° and 90°. This style of reinforcement material has superior strength and stiffness properties along these axes.

An intermediate adhesive that holds together fibers in a laminate construct. Typically used in fiber mats and veils

A consumable-cotton like- cloth used to allow excess resin to escape during cure. Also used to prevent the vacuum bag from sealing on part areas with orthogonal faces

Manufacturing defect where equivalent vacuum pressure is not applied in areas with insufficient draft angle and a void is created

Material/Part failure mode dominated lateral deflection under compressive load instead of part breakage.

Common term used to describe a mold which has already been used in the production of parts.

A resin and reinforcement material mixture commonly used in compression molding techniques

Low density filler material used for thickening resins, and adding hardness to cured products

Percent carbon in a carbon fiber filament/fabirc. Usually described in %

A reinforcement material made from a high carbon polymer such as Polyacrylonitrile (PAN) which exhibits high strength and stiffness.

Typical carbon fiber laminate

Carbon Nano-structure with extremely large aspect ratios. One of the strongest and stiffest materials made. Typically only used in a research capacity and as a small weight % filler in specialized electronics manufacturing.

Term used for a compound mixed with ester based resins to initiate the curing process

Discontinuous fibers adhered using a binding agent. Typically these mats are used to increase part thickness

Manufacturing and processing equipment which cuts reinforcement material and sprays with an activated resin

Extension of Plate Theory in solid mechanics. Analysis method used to determine in-plate properties of a laminate structure

A process where composite parts are produced using contact of two or more mating surfaces

Element. Typically used in composites industry to accelerate gel and cure time in ester based resin systems.

Strain per unit temperature change. Usually an important design factor when selecting tooling material for oven and autoclave cures

Material comprised of two or more sub-materials with vastly different properties

Manufacturing process where material is placed in an open mold cavity and is compressed to a final shape using a matching male mold. Typically used in an automated setting and with the use of heat to aid in the curing of the composite part. This process uses materials such as sheet molding compound (SMC) and bulk molding compound (BMC).

The compressive stress per unit compressive strain. Can be thought of as the stiffness of a material in compression. Typical units of Pascals or PSI

The maximum compacting load per unit area for a material. Units of Pascals or PSI

A lighweight mid-plane material used to add thickness to a laminate. Typically structural, and can significantly improve bending strength and stiffness of a laminate

Failure scenario where the core of a laminate fails compressivel

Process/Technique of removing the core material and adding additional reinforcement material to replenish thickness in a localized area. Typically used at stress concentrations such as bolt holes where bending stiffness and strength must be maintained.

Failure scenario where the core of a laminate fails due to shear loads.

Material degradation. Typically occurs over the course of a long period of time.

Internal crack formation in matrix material

The geometric reduction in length of a fiber after it has been woven. In woven fabrics, crimp can reduce mechanical properties such as stiffness and strength

Molecular process of forming 3 dimensional chemical bonds. Crosslinking occurs during the cure of thermoset polymers such as polyester resins and epoxies.

The time required for a resin system to set and hold its shape. Typically, two cure times are given for a resin system. A cure time for handling a part and a time before peak mechanical properties are reached.

The process of compacting a laminate to a specific thickness during the lay-up process. Also removes air bubbles which could be trapped in the laminate. Typically done with using a roller

General term characterizing the change in a parts shape due to the application of a load.

Mode of failure where plies begin to separate in a laminate structure.

Process of removing a part from a mold

The angle between a mold cavity side wall and the parting line for the mold. Typical composite parts require a slightly larger draft angle than metal to ensure easy demolding.

The ability for a fabric to ‘drape’ or conform to a curved surface. This property is effected by the weave type of a fabric.

Type of fiberglass which is very popular in manufacturing. Originally designed for electrical insulating purposed (E Glass = Electrical Glass), it is now commonly used in glass fiber reinforced structures

The max stress before a material or part deforms permanently

The ability for a material to return to its original shape after being loaded and unloaded.

A type of chemical reaction which takes in heat from the surroundings. Typical curing process for ‘cold curing’ type epoxy resins

A class of polymers which react and harden in the presence of co-reactants such as amines. In composites, epoxy is generalized to be a high strength, high end application, types matrix material.

A mathematically consolidated stress state which is a combination of multidimensional stresses. Also known as the Von-Mises stress

A type of chemical reaction which rejects heat to the surroundings. Typical curing process for most polyester, vinyl ester, and epoxy resins.

Mode of failure of a composite sandwich structure when in a bending scenario. Typically characterized by the compression side skin failing.

A lightweight additive to a resin system to produce a sanding putting which is used for final part finishing.

Generalized term for cyclical loading over a period of time. This type of loading can cause a part or material to fail below calculated loads.

The number of loading cycles until part failure. Usually an estimated number based on material testing.

Mold Type where the part sits inside the cavity of a mold. The parts finished surface is usually in contact with the mold surface

The ratio of dry fibers to resin. Typically given as a weight % (wt. %) or a volume % (v. %)

The angular placement of fibers in a laminate structure (typically given in degrees from a common reference). The fiber orientation has a large influence on the stiffness of parts in different directions

Mode of failure where in tension, the reinforcement material pulls out of the matrix material. Typically occurs with very weak resin systems or small aspect ratio reinforcement materials.

General term for a composite part with reinforcement fiber and a plastic matrix material

Reinforcement material which is composed of spun-glass filaments. Very commonly used in the fabrication of composite parts.

A single strand of reinforcement material. Typical thickness of a filament is 10 microns

Manufacturing technique used for producing hollow cylindrical composite parts. Involves a rotating mandrel and a filament being wound along the length of mandrel.

Additive to a resin which is used to thicken and/or stretch the volume of a resin without adding substantial mass

Analysis technique which segments a complex part geometry into discrete sections and applies basic stress/strain relationships on the simplified discrete sections. The behavior of each discrete section cumulatively is then used to determine the global behavior of the complex part geometry

A mesh screen type fabric used in an infusion process to allow resin to flow between the laminate and vacuum bag

The temperature at which a thermoplastic begins to flow.

Type of failure due the growth of a crack or defect resulting in the complete segmentation of a part or material

The ability for a material to resist crack growth and fracture.

A type of material degradation which is due to a large gap in the relative ‘pull’ on electrons between two dis-similar materials in-contact. Certain composite materials form galvanic series with materials such as steel and aluminum and this should be considered in the design process.

The amount of time before a resin system starts increasing greatly in viscosity.

A protective and aesthetic topcoat which protects the matrix and the reinforcement material from UV light and chemical degradation. Gelcoats can also be tinted and dyed to replicate any color and offer a significant advantage over paint in both labor and cost for finishing a composite part. Gel coats are typically applied straight to the mold surface prior of lamination.

Additive to a gel coat to alter the color of the final cured part

Typical glass fiber laminate. The glass fibers are stiffer and stronger than the plastic and reinforce the structure

Term used for a new mold which has yet to be used to produce a part. Green molds need to be sealed thoroughly with an interfacial sealer before a release agent can be applied.

A material comprised of small diameter fiberglass filaments that are combined to form a small a bundle and later used in the spray up process.

This is the most basic form of lamination. Plies of reinforcement material and core are stacked in a prescribed sequence and wet out with the resin system layer by layer over top of a prepared mold. The completed laminate is then allowed to cure based on the requirements for the resin system. This curing processes can be aided by the use of heat.

Hard tools/molds are made from ceramics, metals and high density woods. They require a larger initial investment in both material and machining costs. These types of tools are typically used repeatedly and the material is selected based on the robustness required for the mold.

A substance added to an un-saturated plastic to promote it to cure. Typically this word is used for the co-reactant used to cure epoxy.

The measure of a materials resistance to surface indentation. There are a wide variety of standardized tests to measure the hardness. The most common test used for composites and plastics is the Rockwell hardness measure.

Typically used to describe a core type with hexagonal shaped open cells. These core types offers a good balance between mass and strength

A fabric composed of two different reinforcement fibers. Typical combinations include Fiberglass/Aramid, Carbon/Aramid.

Composite manufacturing process where dry fibers are placed in a closed mold cavity and pressure is used to either pull or push resin into the cavity. This is a preferred method for high quality, lightweight composite parts which are free of voids.

A substance added to a resin system to slow down the processes of curing. It can also be used to extend the shelf life of a resin system.

A plastic part manufacturing method which pushes a liquefied thermoplastic into a closed mold cavity and allows it to cool to a final part shape

Characteristic of having the same material properties regardless of direction. Most metals are isotropic

Registered trademark of DuPont. Commonly used in conversation to describe an aramid type fabric

Generalized term for two or more layers which are bonded together. In composites, it usually means a sequence of reinforcement material in a plastic matrix.

The angular placement of fibers in a laminate structure (typically given in degrees). The laminate direction has a large influence on the stiffness or parts in different directions

The orientation, reinforcement type, and sequence of a laminate

Joining method where materials are placed side by side with a certain amount of overlap.

The process of placing and orienting reinforcement material in a mold

A mold where the desired composite part fits on top and around the mold. Typically the finished side of the laminate is not in contact with the mold surface. This is also known as a plug.

Name for a cylindrical mold used in the filament winding process

Gum like tape used to seal vacuum bags. Also known as sealant tape, gum tape, vacuum bagging tape

A blanket like prepared reinforcement material which has either chopped strands or randomly distributed fiber lengths bound together using a binding agent.

Material which suspends and binds the reinforcement material and hardens to determine the shape of the final part. Compared to the reinforcement material, the matrix material is relatively weak and lacks stiffness. In a loading scenario, the matrix material holds the fibers in place and transfers load between fibers and layers.

Catalyst which initiates the crosslinking of unsaturated polyester resins used in fiber reinforced plastic

Additive to a resin system to add volume and create a sandable putty

A term to describe a materials resistance to be stretched without permanently deforming. Can be thought of as the stiffness. Typically has units for pressure (Pascal’s or PSI).

A shape or cavity which is used in composite manufacturing to give parts their shape

A compound which is used on a mold surface to allow a part to be separated from the mold after it has cured.

A layer which is used on green molds to ensure small scratches and imperfections are sealed

Composite material which uses reinforcement material on a Nano-meter scale. Typically used for research surfaces and electronics

Localized reduction in cross sectional area under the application of a tensile load

Process where a part is manufactured where substantial material does not need to be removed in post processing

Material manufactured by DuPont. It is a variant of an aramid and offers good fire protection and can also be used as a main constituent for an honeycomb core

In service examination techniques which uses tools like ultrasound to detect cracks and other forms of damage in a part. Commonly used in the aerospace industry

Surface deformation/bucking of a thin laminate sheet structure thus producing waviness on the surface

Poor surface finish on a composite part consisting of wrinkles and pin holes resembling an orange peel

Having 3 mutually orthogonal planes of mechanical property symmetry

Similar to mold release, parting wax is usually one time only

Term for a template or parent mold.

A very fine woven fabric which is used in the manufacturing of pressure assisted composites. It does not stick to a composite part and is typically placed above the top layer of a laminate.

The strength of a part/bond in peel. Peel is a type of loading where the two material joined together are being pulled apart orthogonal to the bond line.

A consumable cloth with evenly spaced holes to control the flow of resin in a vacuum assisted composite part

Small defects on the surface of a part typically caused from poor mold preparation or a fault during the manufacturing process. Usually they take away from the aesthetic appeal of a composite part

Arrangement in a reinforcement fabric where each 0° strand alternately passes over and under each 90° stand. This arrangement is repeated over the entire woven fabric width and length. This produces a symmetrical pattern and uniform material properties in the 0° and 90° directions.

A intermediate tooling piece which is used to create the final mold

A single layer in a laminate structure

PAN is used as the main precursor in carbon fiber manufacturing

Polyester resins are the most widely used resin system. These resins are roughly half ester polymers blended into styrene monomers. . This resin system work well in the presence of water and can be tailor to be chemical resistant. Polyester resins offer reasonable adhesive and mechanical properties compared to other resin systems.

A larger molecule constructed of building blocks called monomers in a repeating patter

The chemical reaction involved in producing a polymer

A spray on compound which can be used as a mold release

Thermoset plastic type. Typically foamed to produce a high mass, high strength core material

The amount of voids in a laminate structure. Typically expressed as % void as a function of volume

The amount of time a resin can be catalyzed before it becomes too thick to be used in the manufacturing process

Pre-cut and pre shaped reinforcement material

A fabric type which has inbedded adhesive which is activated and cured by heat.

The amount of force per unit area

Manufacturing defect where the pattern of the final layer in a laminate is exposed on the surface and produces a rough surface

Automated manufacturing process were reinforcement material is pulled through a die or head while being saturated with catalyzed resin. Used commonly in the production of composite tubes.

Direct translation : “Seemingly Isotropic”. This form of laminate has very similar properties regardless of direction. This term is often used incorrectly when interchanged with a Balanced Laminate/Layup.

General term used for the raw material used in a compression molding technique

A thin film which is used in a manufacturing process which does not stick to the cured part. This film can be used between the laminate and mold surface to help with release.

Areas of a part which have excess built up resin content.

Areas of a part where sufficient resin was not available. Usually characterized by dry spots

Resin transfer molding is an infusion process where catalyzed resin is injected and the laminate is compressed used a matching mold or has pressure applied. This process insures consistent part thickness and minimal voids

An analysis method which says the properties of a composite are a volume or mass fraction of the constituents of the composite

Structural glass. A form of fiberglass with improved mechanical strength and stiffness. It has a larger percent composition of Silicone Oxide and Aluminum Oxide compared to other fiberglass forms

A laminate which is composed of two reinforced fiber skins which ‘sandwich’ a core material

A low cost fiber reinforcement material which typically caries an adhesive layer

Mode of loading where forces are applied in opposite directions which attempt to laterally shift layers relative to one another

The resistance to subsequent layers being laterally stretched without permanently deforming. Can be thought of as the stiffness in shear. Typically has units of pressure (Pascal’s or PSI).

The shear stress required to rip apart subsequent layers relative to one another

A manufactured sheet which is a resin and reinforcement material mixture commonly used in compression molding techniques

The relative change in length of the part after taken out of a mold. Typical composites shrink well under 1% of a given dimension

A layer of sequenced reinforcement material which has been saturated with resin. Typically used in a sandwich structure

Mold or tool made from low density foam or composite which is not intended to be used repeatedly. These types of molds do not hold tolerances as well as hard tools.

A consumable perforated tube which is used to control and disperse resin in an infusion laminate

This form of lamination utilizes a pneumatic spray gun (chopper gun) which sprays chopped strands of reinforcement material and a mixture of resin directly onto the mold surface.

Additive to a resin system which maintains a particular property

Engineering term used to describe the dimenisionless change in length. Calculated by dividing the change in length by the original length.

The applied force over the loaded area for a part or material

A geometric feature which concentrates stresses in a particular locality. A stiffness gradient can also be a stress concentrator. Typical examples include holes and sharp radii.

Thermoplastic which is commonly foamed to produce a chemically resistant core material

A thin sheet of reinforcement material and binder used as the top layer which is specially designed to mask the surface from fiber patterns from layer below it

The stickiness or ability to temporarily hold placement

Powdered mineral added to resin systems to economically increase volume and make a sanding putty

The process of controlling the temperature in an autoclave or oven environment to control the cure and laminate of pre-preg parts

A term to describe a materials resistance to be stretched in tension without permanently deforming. Can be thought of as the stiffness. Typically has units of pressure (Pascals or PSI).

The tensile stress required to cause a part to fail in tension

A tension test (standardized by ASTM) which is used to determine the tensile properties for a material

Type of plastic that become a liquid and moldable as the temperature is increased

Type of plastic that will not become a liquid and moldable as the temperature is increased

Material added to resin which increases viscosity. Often used when resin needs to be used on vertical surfaces.

A term used to describe a substance which has different viscosities at different shear rates. Most adhesives, and resin systems display some degree of thixotropic behavior.

Also known as a mold. A shape or cavity which is used in composite manufacturing to give parts their shape

The ability to absorb energy and deform without fracturing. Typically aramid composites have high toughness values

Spooled bundles of individual filaments. The number of filaments per bundle is usually the main defining feature which differentiates tows from one another

Type of fabric weave. In this arrangement, each 0° stand alternatively passes over and under two 90° stands in a repeating pattern along the width and length of the fabric

Term used in mold design. It is a feature or indentation which will prevent the part removal in a one piece mold

A stress state where all stresses are along one axis

An arrangement of fibers where all fibers are arranged parallel to one another.

A flexible, air-tight plastic bag which is used in composites manufacturing. Air is evacuated out between the part and the vacuum bag, this applying atmospheric pressure on the part

A device which uses compressed air or a stream of air, to draw out air in a vacuum bag set up. This device typically has a diverging-converging-diverging cross section. The low pressure in the smallest cross section is used to draw air out of the vacuum bag.

A fluids resistance to deformation when a shear stress is applied. Fluids that are thick are termed as viscous

a weave is used to describe the arrangement of fibers in a woven reinforced fabric

Manufacturing process that requires reinforcement plies to be wet out with a resin system layer by layer over top of a prepared mold. Prior to the resin curing, a consumable release ply, resin absorption material, and vacuum bagging film is placed over top of the final ply of reinforcement material. The vacuum bagging film is then sealed to the ends of the mold using an air tight mastic tape. A vacuum is then used to draw out air from between the mold surface and the vacuum bagging film thus applying pressure and removing voids of air entrapped between plies of reinforcement material.

A layup technique where layers or reinforcement are manually wet-out with resin

The degree and/or rate at which each individual filament is “wet” or encapsulated by the resin in a composite sheet.