Two-component compression


Two-component injection



3D printing 

3D printing is a form of additive manufacturing. It creates a three-dimensional object by depositing successive layers of material in a computer controlled-process.

3D textile preform

A layered preform that incorporates yarns binding it through the thickness.



Advanced Composite Materials

Acrylic resin 

Acrylic resins are typically derived from acryclic acid or methacrylic acid. They exist both in thermoplastic and thermoset versions and feature excellent transparency and durability. 

Additive manufacturing 

Additive manufacturing processes are processes in which objects are created by adding material. If the addition is performed layer by layer it is often referred to as 3D printing.


Automated Dry Material Placement (ADMP®), a DANOBAT proprietary technology.


Automated fibre placement is a process that automatically places multiple individual prepreg tows onto a mandrel at high speed, using a numerically controlled, articulating robotic placement head to dispense, clamp, cut and restart as many as 32 tows simultaneously.


Aramid fibre reinforced polymer is a composite containing aramid fibres as reinforcement.


Amorphous materials are materials that lack the long-range order of crystals. They are the opposite of crystalline materials.

Angle-ply laminate

Angle-ply laminates are laminates that have plies of the same thickness and material and that have orientations +θ and –θ. Angle-ply laminate are often symmetric and/or balanced, but not always.

Anti-symmetric laminate

Anti-symmetric laminates are laminates where symmetrically located plies have mutually reversed orientations. The simplest example would be [θ,-θ].

AR-glass fibre

AR-glass fibre is a fibre type specifically developed for excellent resistance to alkali environments ("Alkali Resistant"). This makes it ideally suited for use in concrete.

Aramid fibre 

Aramid fibres are a class of heat-resistant, stiff and strong synthetic polymer fibres. They are often used in aerospace and military applications for ballistic-rated body armour fabric and ballistic composites.


One of the largest voluntary standards development organisations in the world, originally known as the American Society for Testing and Materials (ASTM).


Alumina or aluminium trihydrate is a widely used additive for polymers. It acts as a flame retardant and smoke suppressor. It is a white powder derived from bauxite ore.


Similar to automated fibre placement (AFP), Automated Tape Laying (ATL) is an even speedier automated process in which prepreg tape, rather than single tows, is laid down continuously to form parts.

Autoclave moulding process

In the autoclave moulding process, prepregs are laid up, vacuum bagged and consolidated under vacuum, and then cured in an autoclave (which is a pressurised oven).


Industrial automation is the control of industrial machinery and whole industrial processes through the use of tailored equipment and software. Such automation ensures a continuous, smooth and efficient running of machines and processes while reducing the need for human intervention.


Balanced laminate

A laminate is balanced when it has pairs of plies with the same material and thickness and the angles of the plies are +θ and –θ. Note that in this definition, it is considered that 0°=-0° and 90°=-90°. Balanced laminates will have no shear-extension coupling according to the classical laminate theory.


Wood of balsa tree (Ochroma pyramidale) wth exceptional strength-to-weight ratio, used as core for sandwich composites in wend energy, aviation, marine and other applications

Bamboo fibre

A cellulosic fibre extracted from the bast of a bamboo plant. 

Basalt fibre 

Basalt fibre is a material made from basalt rocks, which are formed when lava cools down. It offers better mechanical properties than E-glass fibres, and similar to S-glass fibres. It is significantly cheaper than carbon fibre.


Basalt Fiber Reinforced Polymer


Bladder inflation moulding is a process to create hollow structures by the inflation of an internal bladder. The process can be applied to prepreg-based or resin-infusion processes.

Bio-based material

Material fully or partially derived from biomass.

Bio-based product 

A product wholly or partially derived from biomass.


A material is considered 'biodegradable' if it can be decomposed by microorganisms such as bacteria, fungus, algae, earthworms, etc. As a result, water (H20), carbon dioxide (CO2) and/or methane (CH4), and by-products (residue, new biomass) form, which are non-toxic for the environment.


Material of biological origin, excluding material embedded in geological formations and/or fossilised. Terrestrial vegetation, algae, animals, microorganisms and biowastes make up or produce biomass. They are directly or indirectly derived from photosynthesis and are renewable.


Bioplastics are materials that are either bio-based, biodegradable, or both.


Natural polymers derived from renewable plant or animal resources. They may be directly synthesised by plants or animals as in the case of polysaccharides (starch, cellulose, chitosan, etc.), proteins (collagen, gelatine, casein, etc.) and lignins, or synthesised from biological resources such as vegetable oils (rapeseed, soy, sunflower, etc.). Other biopolymers, like PHA, are produced by microorganisms (bacteria) through the fermentation of sugars and starch.


Biowastes are the organic wastes derived from plant or animal natural resources. Household biowastes include kitchen waste (vegetable peelings and other food scraps) and green waste from the garden (hedge clippings, lawn trimmings, dead leaves, etc.).


Bulk moulding compounds are ready-to-mould fibre-reinforced thermoset polymer materials primarily used in compression moulding and injection moulding. The chopped fibres inside BMCs tend to be randomly oriented in 3D.


Bismaleimide, a polymer type used in composite applications that require high temperature resistance and toughness.


Braiding is the process of interlacing three or more threads in such a way that they cross one another in diagonal formation. Flat, tubular or solid constructions may be formed in this way.



Computer-aided design/manufacturing.

Carbon fibre tow 

The multi-filament continuous strand used to make carbon fibre textile preforms. As a standalone product, it can be used to make wound parts, in pultrusion, or chopped as a local reinforcement. 

Carbon fibre 

A high-performance reinforcement fibre with a high strength-to-weight and stiffness-to-weight ratio. It tends to be used in high-performance applications, where the mechanical performance benefits outweight the higher cost compared to glass fibres.


Composite concept vehicle, which is a vehicle used to demonstrated the state-of-the-art technology.


Carbon Fibre


Computational fluid dynamics (CFD) is a field of mechanics that studies the flow of liquids through simulations. It is often used to predict the flow of resins in composite preforms.


Carbon Fibre Reinforced Plastics/Polymer


Continuous fibre-reinforced thermoplastic composite, which is a continuous fibre-reinforced composite with a thermoplastic matrix. CFRTP could also refer to a carbon fibre-reinforced thermoplastic composite.


Carbon Fiber-Reinforced Wood


Continuous Fibre Thermoplastic

Circular economy

An economic model whose goal is to produce goods and services in a sustainable way, by limiting consumption and wasted resources (raw materials, water, energy) as well as waste generation. The idea is to make a break from linear models (extract, manufacture, consume, discard) and to adopt a 'circular' one where a product’s entire life cycle is integrated, starting with eco-design, through consumption, then to waste management, while limiting wastage at every step.

Classical laminate theory

A basic theory to predict the strains and stress in the plies of a laminate based on the external loading conditions. It is often used in initial designs of composite laminates.

Closed moulding process 

In closed moulding, materials (fibres and resin) cure inside a two-sided mould or within a vacuum bag (shut off from air). Closed moulding processes include compression moulding, injection moulding, vacuum infiltration and resin transfer moulding.


Coefficient of linear thermal expansion, which is measure for the expansion of a material upon heating. Often abbreviated as CTE.


Computerised numerical control, which is used to automate the control of machines and tools.


Carbon nanofibres are cylindrical nanostructures composed of graphene layers. They are much larger than carbon nanotubes.


Carbon nanotubes are composed of rolled up graphene sheets, with diameters in the order of nanometres. They can be single-walled or multiwalled. Their mechanical properties are exceptional with a stiffness of up to 1000 GPa and strengths well above that of carbon fibres. However, their properties are often not fully transferred to composite-level properties.

Combined-loaded compression test

In combined-loaded compression, the compression loads are transferred by a combination of shear and end-loading. This leads to lower stress concentrations near the grips than a shear-loaded tests, and therefore often to better results.

Composite materials

Composite materials, also widely known to 'composites,' are materials composed of at least two components with significantly different physical or chemical properties that, when combined, form a new material with superior performance and with properties different from the individual components. Fibre reinforced polymer (FRP) composites are the dominant type of composite material.

Compound / compounding

Semi-products derived from plastics, in the form of pellets that are ready for final forming. They may contain fillers (such as talc), reinforcements (such as glass fibre), plastifiers and additives pre-mixed with a polymer. These pellets are melted, extruded or moulded, to manufacture objects. By definition, a compound is thermoplastic and the polymers most frequently used are PP, PE or PA. Compounding, therefore, is producing such compounds.

Compression after impact

Compression after impact (CAI) is a measure for the residual properties after an impact event. A rectangular specimen is first impacted with an energy level that is insufficient to cause penetration. This damaged specimen is then subjected to compression loading. CAI is an important property for aerospace applications.

Compression moulding 

A high volume process where a preform is assembled in mould. The mould is closed and pressure is applied. The material flows to fill the mould cavity and the preform is further compacted. For thermoset preforms, the part cures quickly inside the hot mould, and is then demoulded. For thermoplastic preforms, the preforms are heated and moulded in a cold mould, which enables rapid cooldown and solidification.

Compression strength 

Compression strength is defined as the capacity of a material or structure to withstand loads tending to reduce its size i.e. tending to compress it. In composites, compressive failure is often triggered by microbuckling followed by kinking.

Computed tomography

During X-ray computed tomography, many radiographs are taken at different angles. This collection of radiographs is then reconstructed into a 3D image or tomogram. This enables looking inside the material, potentially even during loading.

Core material

Engineering theory shows that the flexural stiffness of any panel is proportional to the cube of its thickness. The purpose of a core in a composite laminate is therefore to increase the laminate’s stiffness by effectively ‘thickening’ it with a low-density material. This can provide a dramatic increase in flexural stiffness for very little additional weight. Composites containing a core material are often called sandwich composites.


Crimp is a measure for the out-of-plane orientation in a textile preform.

Cross-ply laminate

Cross-ply laminates are laminates consisting of only 0 and 90° plies. Cross-ply laminates are always balanced (see term "Balanced laminate").


Crystallisation is a process in which atoms or molecules form highly organised structures known as crystals. Controlling crystallisation is important for semi-crystalline thermoplastics, as it plays an important role in their mechanical properties.


Coefficient of Thermal Expansion: A measure of how much a material expands on heating.


The hardening of a polymer material by crosslinking of polymer chains, brought about by heat, chemical additives, etc. The curing process has a stong influence on the final properties of thermoset composite parts. Curing is not needed for thermoplastic polymers, as they do not form crosslinks.


Chemical vapour deposition is a vacuum deposition process used to make a wide variety of solid materials. In the field of composites it is commonly used to manufacture carbon nanotubes.



Direct long fibre thermoplastics are fibrous strands that are fed directly into molten polymer without first going through a compounding step, which is commonly the case for regular LFT.


In the double diaphragm forming process the material to be shaped is placed in between two diaphragms and then deep-drawn into a mould under hydostratic pressure.


A damage mechanism in which the ply become detached from each other. 


Dimethyl aniline (a curing agent for polyester and vinyl ester resins) or dynamic mechanical analysis (a technique to measure the change of modulus as a function of temperature)


Dough moulding compound is a thermoset compound reinforced with short fibres that have no significant preferred orientation. It can, for example, be used in compression moulding. Typical compounds would likely contain glass fibres in a polyester matrix.


Dynamic mechanical thermal analysis (DMTA) is often also called dynamic mechanical  analysis (DMA). A sinusoidal stress is applied and the resulting strain is measured, allowing to determine the storage modulus, loss modulus and phase lag. The temperature or frequency are often varied during the test, which enables the determination of the glass transition temperature.


Differential scanning calorimetry is a thermal analysis technique that measures the difference in heat required to heat up a specimen and a reference. DSC is commonly used to determine the melting enthalpy, crystallisation enthalpy and glass transition temperature, and to study the curing behaviour of thermosets. 


E-glass fibre

E-glass fibre offers lower stiffness, strength and chemical resistance than S-glass fibres, but they are also significantly cheaper. "E" means "electric", as these fibres were originally developed for electrical insulation applications


Endless long fibre thermoplastics is a type of long fibre thermoplastic (LFT) reinforced by continuous fibres. The continuous nature of the fibres improves the performance compared to traditional LFT.


Takes into account environmental aspects throughout the life cycle (from extraction of raw materials up to elimination as waste), starting with the design phase of a product (good or service), in order to improve the environmental performance and ensure that the service rendered is equivalent or superior.

Elementary fibre

One cell-fibre of flax, consisting of cellulose, hemi-celluloses and pectins. Several elementary fibres form a technical fibre.

End-loaded compression test

In an end-loaded compression test, the compression load is built up through the specimen ends.

Epoxy resin 

Epoxy resins are thermosetting resins widely used with carbon fibre to manufacture high performance composite structures with superior mechanical properties.


Expanded polystyrene, a rigid and tough closed-cell foam, often used in helmets and food containers.


Expanded polyurethane is a closed-cell foam, often used for insulation purposes.


A thermomechanical manufacturing process by which a compressed material is forced through an opening in the shape of the part to be obtained. A long product or a flat one can therefore be formed, like tubes, profiles, sheets or boards. Production outputs are high.



An individual or company that manufactures polymer based parts via one or more moulding processes. The term fabricator is often used interchangeably with the term moulder although fabrication could imply processes other than moulding alone e.g. assembly, painting.

Failure criterion

A failure criterion is a criterion or a set of equations that predicts failure of a material based on the various stress or strain components acting on the material. A common example for composites is the Tsai-Wu criterion.

Fatigue resistance 

Fatigue resistance is the ability of a material to resist weakening caused by repeatedly applied (cyclical) loads.


Fibre Bragg grating sensors are composed of optical glass fibres which contain a periodic variation of the refractive index. This pattern creates a wave-length specific dielectric mirror, enabling it to measure strains. The sensors can be integrated into composite structures to perform structural health monitoring.


Finite element analysis is a method for numerically solving differential equations. It is often used to solve problems in structural analysis, fluid and heat problems.


Fused filament fabrication is an additive manufacturing process where continuous thermoplastic filaments are fed through an extruder and deposited layer by layer. The filaments can also be reinforced with continuous or short fibres, which helps to increase the mechanical performance and reduce warpage. It is sometimes also referred to as fused deposition modelling, but this name is trademarked by Stratasys.

Fibre-hybrid composite

A fibre-hybrid composite is a composite that contains two different fibre types.

Fibre-metal laminate

A fibre-metal laminate is a combination of metal plies with composite plies. The most common example is GLARE, which combines aluminium plies with glass fibre-reinforced prepregs.

Filament winding process

Filament winding process is a technique where tows are wound on a mandrel in the desired orientations. In most cases the tows are impregnated in-line during the process, but the process can also use pre-impregnated tows. The process is often used to manufacture pipes and tanks.


Fillers are sometimes added to a composite formulation to reduce cost or improve performance. They differ from fibres in their smaller aspect ratio. Typical composite fillers are calcium carbonate and talc. 

First ply failure

First ply failure is a term linked to the classical laminate theory: the moment of the first failure of a ply in the laminate. The first ply failure is usually linked to the development of significant cracking in an off-axis ply due to transverse and/or shear stresses, but can also be longitudinal tensile or compressive failure.

Flax fibre

A cellulosic fibre extracted from the flax plant. Composites reinforcements are made of so-called "technical fibres", with diameter 50 - 100 µm, consisting of elementary fibres. 

Foam core 

Foam cores are one of the possible core materials for composite sandwich structures. They can be based on PVC, PET, PS or other polymers. 


Fibre-reinforced concrete is concrete which has been reinforced either by the addition of random chopped fibre strands or by some type of continuous strand either as-is or in the form of a textile.


Fibre reinforced polymer is a polymer matrix reinforced by fibres. Often called a polymer composite.


Fire (or flame), smoke and toxicity standards are safety standards relating to materials used in the passsenger transportation industry.


Fibre volume fraction, or fibre volume ratio, is the percentage of fibre volume in the entire volume of a fibre-reinforced composite. A higher fibre volume fraction usually means higher mechanical properties.


GF (Glass fibre)

Glass fibre is the most widely used reinforcement fibre in polymer composite materials. Depending on the type, it has a stiffness between 70 and 90 GPa. Its strength is lower than that for most carbon fibres, but it is also significantly cheaper.


Glass Fibre Reinforced Plastics


Glare is a fibre-metal laminate composed of thin aluminium sheets and prepreg-based glass fibre layers. The glass fibre layers can be either UD or cross-plies.

Glass fibre reinforced gypsum 

A composite where the matrix is inorganic gypsum and the reinforcement is glass fibre.

Glass transition

see Tg

Glass veil 

A glass fibre-based nonwoven fabric made via a dispersion of chopped glass fibre strands in water and processed on a paper making machine creating a thin, flat, compact fibre structure. Typically used to improve surface appearance.


Glass mat thermoplastics consist of randomly oriented glass mats that are pre-impregnated with a thermoplastic matrix.


The unit commonly used for modulus values of composites, and sometimes for strength.


Allotrope of carbon: a monolayer of carbon atoms bonded in a repeating hexagonal pattern


A gridshell is initially a flat structure which is then raised into a double-curved shape. The forces transform what were initially square grids into similar parallelograms causing the diagonal lines through the nodes to change and to create a self-supporting structure.


Glass Reinforced Plastics


Hand lay-up (also known as contact moulding)

An open moulding process where fibre reinforcements are placed by hand in a mould and resin is applied with a brush or roller.


Heat distortion temperature or heat deflection temperature, which is the temperature at which a material becomes too soften to bear significant loads. The value is often determined using the following two standards: ASTM D 648 or ISO 75.

Heat conductivity (λ)

Expressed in W/mK or W/m°C, it represents the capacity of a material to conduct heat. The lower the value for heat conductivity, the better heat insulation it will provide.


High modulus, often used to refer to a type of carbon fibre with a modulus above 330 GPa.


High-modulus polyethylene, which is a type of polyethylene that is highly drawn to achieve a high modulus and tensile strength. The polymers themselves are typically based on ultra-high molecular weight polyethylene (UHMWPE).

Honeycomb core

A core material that consists of hexagonal cells.


High Performance


High strength, an abbreviation typically used for carbon fibres with a modulus of 230-330 GPa. This is in contrast with high modulus carbon fibres, which have moduli above 330 GPa, but tend to have lower strength.

Hygrothermal stress

A stress that is caused by hygroscopic swelling or thermal expansion.


IM (Injection Moulding)

Injection moulding is one of the most common plastic part manufacturing processes. It can be used for producing parts from both thermoplastic and thermoset polymers. The process usually begins by taking the polymers in the form of pellets or granules and heating them to the molten state. The melt is then injected/forced into a chamber formed by a split-die mould. 

IM (Intermediate Modulus)

Intermediate modulus, typically used to refer to carbon fibres with a modulus of 290-330 GPa.


In mould coating is an alternative to painting: injection of a liquid thermoset on surface of a thermoplastic part while it is in mould.

Impact strength 

Defined as the ability of a material to absorb shock and impact energy. It can refer to the amount of energy required for penetration, but also to the amount of damage created at a given energy level or the residual properties after impact.

Impregnation (resin impregnation) 

Resin impregnation of the reinforcement is very important as the mechanical properties of the composite will depend on the degree of contact between the resin and all the individual fibres in the strands or tows of reinforcement being used.

In-situ polymerisation

In-situ polymerisation start off with a mixture of monomers or oligomers, which are impregnating a fibrous preform. Upon curing, the thermoplastic polymer chains are formed. It therefore combines the processing benefits of thermoset composites with the recycling, reshaping and toughness benefits of thermoplastic composites.

Interlaminar fracture toughness

The interlaminar fracture toughness is a measure for the resistance against the separation of the plies in a laminate. 

Interlaminar shear strength test

Interlaminar shear strength tests is a test to measure the delamination resistance of a composite under shear forces parallel to the layers of the laminate. The test typically consists of bending tests at short span lengths, although other test methods have also been developed.

Iosipescu test

The Iosipescu test is a popular method for determining the shear properties of polymers and composites. The specimen is rectangular with a double notch.


Kevlar fibre

Trade name (DuPont) of a para-aramid fibre, high-modulus, high-strength, heat resistant, used in ballistic protection, in tires, sails, ropes and other applications.


Constructing fabric by interlooping of yarn loops, through the use of needles and a 'loop within a loop.' Two classes of the process are weft- and warp-knitting. The latter is also used as a stitching process in non-crimp fabrics.


Laid scrim 

Textile structure in which the weft and warp yarns are linked together by an adhesive.


Composite material consisting of multiple bonded plies (laminae), reinforced with unidirectional fibres or fabrics.

Last ply failure

Last ply failure is a term linked to the classical laminate theory: the moment of the failure of the last still load-carrying ply; final loss of load-carrying ability of the laminate.. The last ply failure is usually linked to longitudinal tensile or compressive failure of a ply, and is only relevant once first ply failure has occurred.


Life cycle analysis, or life cycle assessment, is used as a tool to assess the environmental impacts of a product, process or activity throughout its life cycle.


Liquid-crystal polymers are polymers exhibiting liquid crystallinity, which is a phase in between liquid and solid phase. Liquid crystal polymers can exhibit anisotropy even in the liquid phase. The most common example for composite applications is aramid fibre.


Lower Explosive Limit which is the level of concentration in percentage by volume in air above which explosion can occur upon ignition in a confined area


Long fibre injection. Endless fibre is chopped in a cutter and a blower then separates the filaments. Immediately after the cutter the fibres are wetted with a matrix.


Long fibre thermoplastic is a type of prepreg contain long fibres in a thermoplastic matrix.

Life cycle inventory

Life cycle inventory is a method to account for all possible life cycle impacts of a certain system or material. It requires a very detailed tracking of all flows in and out of the system, including raw materials, energy, water and air emissions.


Liquid Resin Infusion


Low styrene emission is an indication used for resins that have a low emission of styrene. This is mainly relevant for unsaturated polyester and vinyl ester resins and can, for example, achieved by additives.


Linear Variable Differential Transducer


Low-weight reinforced thermoplastic composites (automotive industry).



The macroscale for composites is the scale of parts, components, and subcomponents. At this scale, the composite material is assumed to be homogeneous.


The material that bonds the fibres together. In fibre-reinforced polymer composites this matrix is a thermoplastic or thermoset polymer. In other types of composites the matrix can be a metal or a ceramic.


Methyl ethyl ketone is a a common and powerful solvent.


Methyl ethyl ketone peroxide is an organic peroxide commonly used in vulcanising rubbers.


The mesoscale for composites is the scale of the laminate plies or fabrics. The layup of the laminate or the internal structure of the fabric is visible at this scale. The fibrous yarns and plies, as well as matrix pockets are assumed to be homogeneous materials.

Microbond test

A micromechanical test to characterise the fibre-matrix interface. A small resin droplet is added to the fibre and then cured (for thermosets). During the test, the droplet is pulled off the fibre. The measured load and displacement can be used to extract the mode II interfacial strength (and in some cases fracture toughness).


The microscale for composites is the scale of the fibres and matrix. The plies or fabrics are not visible at this scale.


Multiple insert resin transfer moulding is a resin transfer moulding process where the skin of the mould is held in place by vacuum, allowing it to be easily replaced.


Metal matrix composites are composites where the matrix is a metal, often copper, aluminium or steel. In contrast with the matrix in polymer composites, the reinforcement does not always have a structural purpose, and can also be used to change physical properties such as friction or wear.

Mould, a 

The moulds used for forming composites are key to the process. They are also known as tools and can be made from virtually any material ranging from composite to aluminium or steel.

Mould, to 

To mould is to shape and form an object by the use of a mould. A key benefit of composites over metals is the fact that most composite processes enable more complex shapes to be moulded.


An individual or company that manufactures polymer based parts via one or more moulding processes. The term moulder is often used interchangeably with the term fabricator.

Moulding process 

A process that produces shaped parts through the use of a mould. The composites industry distinguishes between open mould processes and closed mould processes, which is an important difference in terms of mould costs and the escape of volatile (and often harmful) compounds.


The unit commonly used for stress and strength values of composites.

Multiaxial fabric 

Multiaxial reinforcements are fabrics made up of multiple plies (layers) of parallel fibres, each laying in a different orientation or axis - hence the term ‘multiaxial’. These layers are typically stitch-bonded (usually with a polyester thread) to form a fabric. Multiaxial fabrics are sometimes called non-crimp fabrics. Multiaxial fabrics include unidirectional (UD), biaxial, triaxial and quadraxial products.



A nanometer-scale hollow tube-like structure; single-wall carbon nanotube is a rolled-up sheet of graphene.

Natural technical fibres

Natural fibres have a complex hierarchical structure. After extraction from the plant, technical fibres are typically obtained. These technical fibres are composed of many elementary fibres, but such elementary fibres are not used in practice.


Non-crimp fabric is another word for a multiaxial fabric. The word emphasis the lack of crimp in the fabric, which is a measure for the out-of-plane orientation of the yarns.








Non-destructive testing is a method to evaluate properties without causing damage to the material. The terms NDC (non-destructive control), NDE (non-destructive evaluation), NDI (non-destructive inspection) and NDT (non-destructive testing) are often used interchangeable depending on the field, although some nuance differences do exist. NDT and NDE would both be used to determine the location of a defect, whereas NDE would also quantify its size and shape. Common NDT techniques for composites include acoustic emission and ultrasound C-scan.


Natural fibre composites are composites reinforced by natural fibres. Common examples include flax, hemp and bamboo composites.

Nonwoven fabric 

A textile structure produced by bonding or interlocking of fibres, or both, accomplished by mechanical, chemical, thermal or solvent means and combinations thereof. Nonwoven fabrics tend to have a 2D random fibre orientation, although it is also possible to introduce fibre orientation.



Original Equipment Manufacturer: Producer or manufacturer of a complete end product (such as a car engine, cooling unit, or a circuit board) or a sub-assembly (such as a carburettor, compressor, or a chip) used in an end product.

Off-axis cracks

Off-axis cracks are cracks in off-axis plies, which can occur due to tension, compression or shear loads. They can cause a significant degradation of the performance of the laminate.

Open moulding process 

In open moulding, materials (resins and fibre reinforcements) are exposed to air as they cure or harden. Open moulding processes include hand lay-up, spray-up, casting, filament winding and pultrusion. In these process, volatile (and often harmful) compounds can escape more easily than in closed mould processes.



Polyamide is an engineering polymer with intermediate stiffness, strength and Tg. It is widely used in short fibre reinforced injection moulding and in applications where moisture absorption is less critical.


Polyamide-imide is an amorphous high-performance polymer that is available in both thermoplastic and thermoset versions. It is mainly used in applications that require excellent mechanical, thermal and chemical properties.


Polyacrylonitrile is a common precursor material for the production of cabron fibres. PAN fibres are produced using wet-spinning. They are oxidised and later carbonised to form high strength carbon fibres. To achieve higher moduli an additional graphitisation step can be added.


Polybutylene terephthalate is a semi-crystalline thermoplastic polymer that is closely related to polyethylene terephthalate (PET). It also exists in fibre form.


Polycarbonate is a thermoplastic polymer that contains a carbonate group (R−O−C(=O)−O−R'). They are strong and tough materials, and some grades are optically transparent.


Polyether ether ketone is a high performance polymer with intermediate stiffness, high strength, high Tg and good creep resistance. Used for demanding applications such as with high constant loads and at elevated temperatures.


Polyether imide is an amorphous thermoplastic polymer. Similar to PEEK, it has excellent mechanical properties and temperature resistance, but is cheaper and has a lower impact resistance.


Polyetherketoneketone is a semi-crystalline thermoplastic polymer used in high-performance applications that require its good mechanical, chemical and thermal properties.


Polyethersulfone is an amorphous thermoplastic polymer with good temperature resistance, but high moisture absorption.


Polyethylene terephthalate is a common thermoplastic polymer that exists both in amorphous and semi-crystalline versions. It is well known for its use in bottles, but can also be used as fibre or matrix in composites.


Phenolic resins are thermoset polymers that are known for their high temperature and chemical resistance. It is most often used in parts that are subjected to strict fire smoke and toxicity regulations. It is used as the basis for Bakelite.


Polyimide is a high-performance polymer that is availabe in both thermoplastic and thermoset versions. They have very high temperature resistance.


Polylactic acid: Bio-based and bio-degradable polymer. Relatively low mechanical performance and thermal stability restrict the use cases for this material. It is commonly used for 3D printing.

Poisson's ratio

Negative of the ratio of lateral contraction strain to the applied longitudinal elongation strain. The Poisson's ratio is most often positive, but exceptions exist: "auxetic" materials have negative Poisson's ratio.

Polyester resin 

Polyester resins are one of the most commonly used matrices in the polymer composites industry. They are often combined with glass fibres.

Polymer composites

Fibre reinforced polymer (FRP) materials consisting of resins, fibre reinforcements and additives. They usually bring high mechanical properties and light weight to final applications.


A large molecule formed by combining smaller molecules or monomers in a regular pattern. Polymers are one of the most common matrices for composites. There are thermoplastic and thermoset polymers.


Polyoxymethylene is a semicrystalline thermoplastic polymer. It is known for its low friction and excellent dimensional stability.


Personal protective equipment is often required when working with composites, and especially with thermoset resins and release agents. This could include rubber gloves and safety goggles.


Parts per million is a way to express the concentration of a solution.


Polyphenylene oxide (or poly-p-phenylene oxide) is a thermoplastic polymer used mainly in applications where its high temperature resistance is required.


Polyphenylene sulfide is a high-performance thermoplastic polymer, typically used in applications that require high temperature and chemical resistance.


A pre-shaped three-dimensional agglomeration of fibres designed to fit neatly into a mould. Mainly used in the RTM process to save time in preparing the mould.


Reinforcement material that has been impregnated with the resin system in a previous process and is ready to be cured. Prepregs are commonly cured using an autoclave. They provide the highest material performance and are commonly used in aerospace production.


Polyphenylene sulphone is a high-performance thermoplastic polymer, typically used in applications that require high temperature resistance and toughness.


Pullwinding combines pultrusion and filament winding, by adding helical or off-axis fibres through winding right before the profile enters the die for impregnation.

Pultrusion process

A continuous moulding process in which reinforcing fibres or fabric are impregnated with resin by passing through a resin bath and then pulled through a heated die to form a part that is basically a profile. The profile leaving the machine is cut to required lengths by an automated saw. Typical products are structural sections, cable trays, bars and tubes.


Polyvinyl chloride is one of the most common thermoplastic polymers worldwide. The basic polymer is rigid, but it is often softened through the addition of plasticisers.


Quasi-isotropic laminate

A laminate is called quasi-isotropic when it behaves like an isotropic material in the laminate plane. Quasi-isotropic laminates are obtained when the angles of the plies consist of increments of π/n with n being an integer larger than 2. 


Random mat

Non-woven material, consisting of randomly arranged straight or curved fibres with primarily planar orientation


The key element added to a matrix to provide the required properties of the resulting composite. Reinforcements are usually in the form of fibres which can be short, continuous or as some woven or nonwoven textile form.

Resin infusion 

A process by which vacuum draws resin into a dry fibre laminate in a one-sided rigid mould, the other side being made by a plastic film with a seal between the two. Other names for this process include vacuum infusion, vacuum assisted resin infiltration (VARI) or vacuum assisted resin transfer moulding (VARTM).


Sometimes used interchangeably with the word polymer. Thermoset and thermoplastic resins are used as matrices in FRP composites.


Resin film infusion uses thermoset resin films to impregnate fibrous plies.


Reaction injection moulding is a process similar to injection moulding, but it uses thermosets rather than thermoplastics. The reactive components are mixed right before injection under high pressure. Discontinuous fibres can be included to increase stiffness and strength.


Reinforced thermoplastic laminates are fibre-reinforced composite laminates containing a thermoplastic matrix.


Resin transfer moulding is a closed mould process in which dry fabric is laid into a two (or more) part mould. Resin is injected under pressure from one side and vacuum from the other side. When the fabric layup is fully impregnated the moulds are heated to cure the resin.


S-glass fibre

S-glass fibre offers higher stiffness, strength and chemical resistance than E-glass fibres, but it is also more expensive. "S" stands for "(high) strength"


Structural reaction injection moulding is a variant of the reaction injection moulding process, which uses preforms and random mats to increase the part stiffness. The thermoset resin is mixed right before it is injected under high pressure into the preforms. The process is completed within a few minutes, which enables high-volume production.

Scanning electron microscopy

A scanning electron microscope scans the surface of a material by a focused beam of electrons. These electrons interact with the beam, which produces a variety of signals that can be used to visualise and analyse composition of the specimen. Its high field-of-depth makes it ideally suited for fractography analyses.


Seemann Composites Resin Infusion Moulding Process is a vacuum-assisted resin transfer moulding process that uses vacuum to draw in the liquid thermoset resin. It has many overlaps with the traditional vacuum-assisted resin transfer moulding process with the distinguishing feature often being the fact that SCRIMP uses a distribution medium to facilitate flow.


Scrims are woven or nonwoven fabrics in which the yarns are regularly and widely spaced. They can, for example, be used to hold together a dry UD preform or to yield an aesthetic finish.


Semi-crystalline materials are materials that contain crystalline and amorphous regions. Fully crystalline materials are extremely difficult to manufacture in practice, so most materials are either amorphous or semi-crystalline.

Shear-loaded compression test

In a shear-loaded compression, the specimen is mounted in wedge grips, and the compression loads are transferred through shear. It is sometimes also referred to as IITRI test, which stands for Illinois Institute of Technology Research Institute. It is an improved version of the Celanese test. 


Sandwich injection is a type of injection moulding process that allows the creation of at least three layers in the material.

Single fibre fragmentation test

A micromechanical test to characterise the fibre strength distribution and fibre-matrix interface. The specimen consists of a single fibre embedded in resin, which is then gradually loaded up. The load causes the fibre to break into many fragments until saturation is reached.


Sheet moulding compound : A semi-finished product used in compression moulding processes. SMC is composite sheet material made by sandwiching chopped fibres between two layers of thick resin paste. To form the sheet, the resin paste transfers from a metering device onto a moving film carrier.


Seamless modelling pastes are thixotropic pastes that can be used to replace more expensive mould materials. They can be extruded over an inexpensive core and will then cure to the final shape.

Spray-up process

An open moulding process where resin is fed through a tube and mixed with catalyst in a hand-held spray gun. The fibre (fed from a bobbin) is chopped into the resin stream as it is sprayed onto the mould. This is then left to cure at ambient temperature. This process results in limited mechanical performance, but requires only limited tooling investments.


Self-reinforced composites are thermoplastic composites where the reinforcement fibre is of the same polymer type as the matrix. This is very useful for a recycling perspective. The most common type is self-reinforced polypropylene. They are also called single-polymer composites or all-polymer composites.


Structure repair manual is a set of instructions for making minor repairs to aircraft structures, which is approved by the relevant regulatory aviation bodies.

Symmetric laminate

A laminate is symmetric when it is symmetric in both geometry and material properties about its mid-surface. Symmetric laminates have no bending-twist coupling according to the classical laminate theory.



Transmission electron microscopy is a microscopy technique where a beam of electrons is transmitted through a specimen to form an image. This techniques requires very thin specimens, but is able to achieve sub-nanometer resolutions.

Tensile strength 

Tensile strength is the resistance against fracture under tensile load. It is typically listed in units of MPa (and sometimes in GPa).


Glass transition temperature, which is the temperature at which the glass transition happens. During the glass transition, the amorphous phase changes from a hard and relatively brittle material into a viscous, rubbery state.


Thermoforming is a manufacturing process where thermoplastic sheets are heated and then formed over a mould to the desired shape. It enables low cycle times with minimal labour time.


Thick moulding compound is a type of sheet moulding compound with significant thickness (up to 50 mm). It contains chopped fibres in a resin.


Thermoplastic polymers turn into liquid when heated and become solid again when cooled. They can be repeatedly melted and moulded which is important for recyclability purposes. Examples include polyvinyl chloride (PVC), polypropylene (PP), polycarbonate (PC), polyethylene (PE), polyether ether ketone (PEEK), and acrylonitrile butadiene styrene (ABS).

Translaminar fracture toughness

The translaminar fracture toughness is a measure for the resistance against fracture through the fibres. It is typically measured in a compact tension test.


Textile-reinforced concrete is a type of reinforced concrete which is reinforced by a textile preform rather than steel bars. This is sometimes also referred to as fabric-reinforced cementitious matrix.


Thermoset resins are resins that create crosslinks between the polymer chains upon curing. This polymerisation reaction is irreversible, which causes them to degrade before they melt. The crosslinks improve their temperature and creep resistance, but hamper their recyclability compared to thermoplastic resins. The most common examples for composite applications are unsaturated polyester, vinyl ester and epoxy.



Unidirectional, which indicates that all the fibres are oriented in the same direction.


Unsaturated polyester is a common resin type used in lower performance composite applications and mainly in combination with glass fibres. It contains styrene, which is a carcinogenic compound, and should therefore be treated with extra care.


Vacuum bagging 

Vacuum bagging is a technique employed to create mechanical pressure on a laminate during its cure cycle.

Vacuum infusion 

A process that uses vacuum pressure to drive resin into a laminate. Materials are laid dry into the mould and the vacuum is applied before resin is introduced. Once a complete vacuum is achieved, resin is literally sucked into the laminate via carefully placed tubing.


Vacuum-assisted resin tranfer moulding places a fibrous reinforcement inside a vacuum bag, and then draws in the resin by applying vacuum. Because of the low pressure, the volume fractions that can be achieved are lower than in RTM, but it enables very large parts to be manufactured in one piece (such as boat hulls or wind turbine blades).


Vinyl ester is a resin type that combines the processing benefits of polyester resins, but yields properties closer to those of epoxies. Similar to unsaturated polyester, it contains styrene, but in lower concentrations.

Vinyl ester resins

Vinyl ester resins offer corrosion resistance and durability and are widely used in chemicals processing equipment, boat hulls and other demanding applications The handling characteristics, properties, and even price, of vinyl ester resins generally fall between those of polyester and epoxy resin.


Viscosity is a measure for the resistance of a fluid against deformation. It is an important parameter in the impregnation of fibrous preforms.


Volatile organic compounds are organic chemicals with a high vapour pressure at room temperature. This enables them escape from resins and pose short- and/or longterm health hazards to the people handling the resins.



A knitting process where a simultaneous yarn feeding and loop forming action occurs at every needle in the needle bar during the same knitting cycle.


Lengthwise strands or yarns in a woven fabric. 


The pattern of interlacing of warp and weft in a woven fabric.


A knitting process, where yarn feeding and loop formation occur at each needle in succession across the needle bed during the same knitting cycle.


Strands or yarns that are woven in the cross direction of a woven fabric. 

Weibull strength distribution

Fibres do no have a unique strength value but rather follow a strength distribution. It is commonly assumed that the strength of a reinforcement fibre follow a Weibull distribution, which is a distribution based on the weakest link theory. 


Wetting is the ability of a liquid to maintain contact with a solid surface. A good wetting is required to achieve good impregnation of the fibres with resin. 

Woven fabric

A fabric made by the interlacing of warp and weft threads.

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