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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.

Further Learning About Composites