Glossary:Index

Term	DefinitionThis property is a special property in this wiki.
AIM event	Application and Impact Mobilization Events (AIM).
CMC	Ceramic Matrix Composites (CMC).
DSC	Differential Scanning Calorimetry (DSC).
LCM	Liquid Composite Moulding (LCM), a family of infusion processes refers to processes that saturate a dry reinforcement that is on/in the mould by means of a pressure differential (injection pressure, vacuum, combination of both).
LRTM	Light Resin Transfer Moulding (LRTM) uses a semi rigid tool half (A side) that is similar to those used in VIP and a semi flexible tool half (B side) (typically made of thin fibreglass).
MMC	Metal Matrix Composites (MMC).
MRCC	Manufacturer's Recommended Cure Cycle (MRCC).
MSTE factory ontology	A systems level description of manufacturing problems relating to the physical factory and part producibility. The MSTE factory ontology consists of four classes: Material and process (M), Shape (S), Tooling and consumables (T) & Equipment (E); and the concept: The factory (F) consisting of the MSTE within the MSTEP approach.
MSTEP	Material and process (M), Shape (S), Tooling and consumables (T) & Equipment (E) - all have an interlinked effect on the Process step (P). (See MSTE factory ontology)
PMC	Polymer Matrix Composites (PMC).
RTM	Resin transfer moulding (RTM) involves loading a preform into a two (or more) piece, matched tool, closing it, and injecting resin under pressure (~15-100 psi, or ~1-7 bar). Well suited to small to medium sized parts, limited to large sizes due to injection pressure loads and tool cost.
SAMPE	The Society for the Advancement of Material and Process Engineering (SAMPE).
SME	Small and medium-sized enterprises (SME).
VARI	Vacuum assisted resin infusion (VARI) - also known as vacuum assisted resin transfer moulding (VARTM), vacuum infusion process (VIP) or often just resin infusion. VARI is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.
VARTM	Vacuum assisted resin transfer moulding (VARTM) - also known as vacuum assisted resin infusion (VARI), vacuum infusion process (VIP) or often just resin infusion. VARTM is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.
adhesive bonding	A joining process where a polymeric material (the adhesive) joins two separate structural pieces called adherends. Adhesive bonding is used instead of, or in parallel with mechanical means of joining such as riveting or bolting.
advanced manufacturing	The development and adoption of emerging innovation/technology that establishes new ways to manufacture existing products and enhance existing processes, manufacture new products from new advanced technologies, and develop cost-efficient ways of working (e.g. new business models, integrating all parts of the value chain).
amorphous	Literally "without structure", randomly coiled molecular polymer chains.
aramid fibre	Generic name for fibres composed of aromatic polyamide. Best known fibre is Kevlar, introduced by DuPont (USA) in early 1970s. Also, Technora (Japan), and Twaron (Europe). Originally developed to replace steel belts in radial tires, increased durability and increased strength.
areal weight	Areal weight (or fibre areal weight, AW ) refers to the mass/weight of fibre per unit area. (Typically in g/m2 gsm ) or ounces/yard2 (often just called ounces). Areal weight depends on tow size and fibre architecture (weaving, density, etc.).
balanced laminate	A laminate whose in-plane shear coupling stiffness is zero. This occurs if all plies in a laminate that are not oriented parallel or perpendicular to the primary laminate axis (i.e. non 0 or 90 degree plies) occur only in ±θ pairs that have the same thickness and elastic properties.
building block approach	An approach where risk is incrementally assessed in the scale-up of part size and complexity. Material and process (M&P) variabilities are evaluated at lower scales; While at higher scales, load paths and structural designs are verified. This approach involves three complementary engineering design activities: Material qualification Structural certification, and Production approval.
carbon fibre	Carbon fibres are composed of large aromatic sheets similar to those in graphite. These graphitic layers form the basic structural units in the shape of ribbons. The structure of carbon fibre ribbon is believed to be a columnar arrangement of disoriented graphite crystallites parallel to the ribbon length. The idealized tetragonal crystallites are stacked above one another, with slight disorientation between the crystals in the direction of fibre axis, trapping sharp needle like voids, where the boundaries between the stacks represent the disordered regions.
composite	Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.
computational thinking	A problem solving process where computational skills (e.g. thinking logically, algorithmically, and recursively), can be used to express solutions in a manner than can be actioned effectively by human intervention or machine. (Same as simulation based thinking)
constituent materials	The individual materials that combine to form the composite material. The constituent materials are separate and distinct on a macroscopic level.
crystalline	Periodic 3-D, repeating array of molecules.
cure window	The allowable range of temperature, pressure, and vacuum values at specific times in the cure cycle. These limits are usually defined as process requirements.
deconvoluted	Separating a complex process involving several interacting phenomenon into several simple processes involving straightforward (easy to understand) phenomena.
degree of cure	Degree of cure (DOC) is an indication of how far the chemical curing reaction (crosslinking process) has advanced in a thermoset resin. DOC is defined with a number between 0 and 1 (or 0% and 100%) where 100% is a fully cured resin. It does not have to fully reach 100% for the resin to become solid or the part to be used. In some aerospace applications, resins are only cured to about 90%. Higher the degree of cure, higher the mechanical properties.
delamination	The failure mode characterized by a partial or full separation of adjacent laminae. Delamination is unique to laminated structures, and can be induced by impact load, fatigue load, and quasistatic load. (Also known as interlaminar separation)
design for manufacturing	Design for manufacturing (DFM) is the general engineering practice of designing parts with manufacturing in mind; typically with regard to the cost of manufacturing and the ease in which the part can be made. Typically, a part that has good DFM characteristics will have good producibility and a robust process. (Same as "Design for manufacture" or "Design for manufacturability")
development design cycle	The key design phases in new product development (NPD), particularly for complex engineering systems. This includes conceptual design, preliminary design (trade study), detail design, and production.
drapeability	Drapeability refers to how well a material conforms to a complex shape (non developable surface). Trade off: typically the more drapeable a fabric, the less dense the weave (lower Vf), and less stable during processing.
dry-spot	Areas or patches of fibre that are not fully wet out with resin. All LCM process are susceptible to flow induced dry spots. Dry spots are typically caused by one or all of the following: An inadequate flow strategy inlet/outlet port placement) that allows the resin to reach the outlet before it has fully saturated the mould Racetracking, which allows resin to reach the outlet before resin has fully saturated the mould Inadequate working time, which causes the resin to gel before the mould is fully saturated A change in laminate thickness, which causes the resin to trap dry fibre under the surface
effective heat transfer coefficient	The heat transfer coefficient applied to surface boundaries that include lumped bagside and/or toolside effects. These effects include bagging and consumables, tool size effects, tool substructure and heat transfer due to convection (e.g. airflow) and radiation (e.g. wall, rack effects).
factory cell	An individual station within a factory where a given set of tasks are accomplished (also known as a "work cell"). Some cells may directly add value to the product (e.g. deposition), while others may serve support roles that are critical to maintaining part quality (e.g. receiving, storage, inspection & shipping).
fibre architecture	Fibre architecture refers to how the fibre is assembled. Most common architectures: Unidirectional Chopped strand mat (CSM) and chopped fibre (chopper gun) Continuous filament mat (CFM) Woven fabric Non crimp fabric (NCF) Braided Prepreg
fibre bed compaction	In an unconstrained state, fibre has loft (springiness), when it goes into a mould it must be compacted to obtain the desired Vf. As the compaction increases, the permeability decreases.
fibre washout	Fibre washout refers to the displacement of fibre by resin due to excessive shear stress. This can occur locally (i.e. in a small, contained region) or throughout the whole preform (i.e. sliding the preform and/or wrinkling it).
filament	A single unit of fibre reinforcement that cannot be separated further without breaking it. It often has a circular cross section that is formed by the dies used to create it or its precursor material. Many filaments are manufactured in parallel to produce a strand or tow. The number of filaments in a strand or tow is often references by how many thousands of filaments comprise the tow. e.g. an 18k tow is made up of ~18000 filaments.
flow and consolidation management	A central processing theme in the manufacturing cycle. This theme concerned with managing changes in the physical response of parts/tools when the resin is predominantly in a liquid phase (e.g. pre-gelation, pre-solidification) and the prevention of manufacturing defects.
flow front	Flow front refers to the leading edge of the resin as it is flowing into and through the fibre preform.
glass transition temperature	The glass transition temperature (Tg) is the temperature region where the polymer transitions from a hard, glassy material to a soft, rubbery material. It is one of the most important properties of any amorphous polymer.
graphene	Graphene is a one atom thick two dimensional honeycomb layer of bonded carbon atoms. When many graphene layers are stacked regularly in three dimensions and held together with weak forces, graphite is created.
heat of reaction	Polymerization of thermoset resins is an exothermic reaction and heat is generated during the curing process. A thermosetting resin has the potential to release a certain amount of energy while curing. This is called the total heat of reaction, HR, with a unit of J/g (SI units). The heat of reaction during polymerization is measured using a Differential Scanning Calorimeter (DSC) equipment measuring much energy/heat comes out of the reaction for a small resin sample.
knowledge	In the context of knowledge in practice, knowledge refers to the systematic use of science based knowledge in composites manufacturing practice. There is a distinction between experience based knowledge and science based knowledge: Experience based knowledge (‘know-how’) is an understanding of potential outcomes and their relationships that is founded on pragmatism and experience accumulated over time in individual programs, companies and in the industry more broadly. Science based knowledge (‘know-why’) is an understanding of potential outcomes and their relationships, based on the important processing physics, that is mature enough to be codified using the appropriate governing laws and constitutive equations.
knowledge in practice	A framework for formalizing effective and low risk science based composites manufacturing practice and the process of knowledge translation.
macroscopic flow	Resin flow in between fibre tows.
manufacturing outcomes	Outcomes represent the range of response/sensitivity to factory system attributes. Those that fail to satisfy manufacturing requirements are known as defects. Examples of manufacturing outcomes include process parameter outcomes, material structure outcomes, and material performance outcomes.
material deposition	The act of combining reinforcement fibre, resin to shape on a mould (tool). There are three main methods to combine resin and fibre to deposit onto a tool (i.e. material deposition): Wet Processes: Mixing liquid resin and dry fibre directly in the mould, e.g. Wet Compression Moulding process for parts in BMW 7 series Liquid Composite Moulding (LCM) processes: Infusing dry fabric with resin using a pressure gradient, e.g. High Pressure Resin Transfer Moulding process (HP RTM) for parts in BMW i3 Prepreg Processes: Laying up using prepreg where resin and fibre are already combined, e.g. Automated Tape Laying (ATL) process for some of the parts in Boeing 787.
material deposition management	A central processing theme in the manufacturing cycle. It includes the steps primarily involved in moving material into the correct position on the tool or with combining fibre, resin and other constituents in-situ on tools.
material equivalency	The commonality of material level properties at all scales of the ‘building block’ (coupon level to production scale structures) in terms of chemical–physical–mechanical states such as degree of cure/degree of crystallization, fibre volume fraction, residual stresses, etc.
material qualification	An engineering design activity that relates to the determination of material level properties that will be used in the structural design and certification.
matrix	The continuous material phase that binds the reinforcement together, maintains shape, transfers load, protects the reinforcement from environment and damage, and provides the composite support in compression. Desirable characteristics: Moisture/chemical resistance Low density Processability
microscopic flow	Resin flow in between fibres.
modelling	The use of multiphysics models to predict the outcome of real-world scenarios. May be analytical (closed form, "hand calculations") or computational (implementation on computers is required due to the large number of calculations involved. e.g. finite element method, finite difference method) Most often in composite materials engineering, modelling refers to either: Process modelling (predicting manufacturing outcomes, or the inverse problem of predicting manufacturing parameters to achieve a desired outcome), or Performance modelling (predicting the stiffness/strength/suitability of a structure, or the inverse problem of the material properties and dimensional requirements to achieve a desired stiffness/strength/suitability of a structure) (same as "Simulation")
objective function	A rubric used to provide a measure of performance that describes the producibility of a part. They may be quantitative or qualitative. There are three objective functions in manufacturing: Cost Rate Quality Objective functions are typically minimized or maximized to achieve a certain optimal condition; but in the context of manufacturing, maintaining the value of an objective function or achieving a nominal (target) value is a common goal (e.g. maintaining quality while increasing rate is a common workflow to achieve business growth; producing a new part for a target cost is important to maintaining a business case)
permeability	Permeability refers to the resistance to fluid flow through a porous material. Resin flow through fibre Gas flow through prepreg
practice	Any manufacturing and/or decision making activity that occurs during any stage of the development design cycle (e.g. conceptual design to production). In the context of Knowledge in Practice, practice refers to the systematic use of science based knowledge to reduce composites manufacturing risk, cost, and development time.
preform	‘Preform’ is the term for the fibre reinforcement. This is the stage between the raw material form after it is processed into an architecture (fabric, mat, etc.) and becoming a composite.
preforming	‘Preforming’ refers to the task of preparing the fibre. Cutting it out Assembling a number of pieces (stitching, bonding, etc.) Forming on a (heated) tool
prepreg	Pre-impregnated (prepreg) material refers to fibre that is already combined with resin. It is the most common material form used in aerospace. During prepreg production, (e.g. fibres are run through a resin bath), prepreg is heated and partially cured to B Stage (< 5 % degree of cure). Thermoset prepregs (e.g. epoxy prepreg) have to be kept in a freezer at around -20 °C. At room temperature, the epoxy starts to cure.
processing themes	Key components of all composite manufacturing processes. Collectively, the four themes represent the time-temperature-pressure-vacuum history, which is traditionally used to define a manufacturing cycle. The four processing themes are: Thermal management Material deposition management Flow and consolidation management Residual stress and dimensional control management (Same as "Theme")
producibility	The capability of the manufacturing process to produce parts of acceptable quality (e.g. meet engineering, manufacturing, regulatory requirements), repeatably and robustly.
production approval	An engineering design activity that ensures that the material qualification and structural certification steps are properly linked once the structure enters production.
racetracking	Racetracking is when resin takes the path of least resistance through a tool. This typically occurs at the outer edges of the reinforcement (between the fibre and tool). Depending on the severity, this can lead to dry spots (resin starved regions). Racetracking is not consistent and difficult to predict accurately (a ‘range’ of racetracking effects is predicted).
residual stress and dimensional control management	A central processing theme in the manufacturing cycle. This theme relates to management of internal stresses that occur as the material undergoes differential thermal and physical phase change volume changes and viscoelastic property development.
resin	For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.
risk	With regards to manufacturing, risk is the combination of the probability and consequences of undesirable manufacturing outcomes. Manufacturing risk can lead to technical issues, program/schedule delays, and cost overruns.
robust process	A process whose outcomes are relatively insensitive to variability of manufacturing parameters.
semi-crystalline	A portion of the molecular polymer chains tend to ‘fold up’ into densely packed regions called crystals.
simulation	The use of multiphysics models to predict the outcome of real-world scenarios. May be analytical (closed form, "hand calculations") or computational (implementation on computers is required due to the large number of calculations involved. e.g. finite element method, finite difference method) Most often in composite materials engineering, simulation refers to either: Process simulation (predicting manufacturing outcomes, or the inverse problem of predicting manufacturing parameters to achieve a desired outcome), or Performance simulation (predicting the stiffness/strength/suitability of a structure, or the inverse problem of the material properties and dimensional requirements to achieve a desired stiffness/strength/suitability of a structure) (same as "Modelling")
simulation based thinking	A problem solving process where computational skills (e.g. thinking logically, algorithmically, and recursively), can be used to express solutions in a manner than can be actioned effectively by human intervention or machine. (Same as computational thinking)
sizing	Sizing or fibre sizing refers to a coating that is applied to fibre during manufacturing. Highly proprietary (formulation and process). Sizing serves two functions: Protects and aids fibre during processing Aids in the bonding of fibre and matrix
structural certification	An engineering design activity that relates to the acceptance of the as manufactured structure being able to sustain the necessary loads and other service conditions determined by engineering, manufacturing, and regulatory requirements.
theme	A key component of all composite manufacturing processes. Collectively, the four themes represent the time-temperature-pressure-vacuum history, which is traditionally used to define a manufacturing cycle. The four processing themes are: Thermal management Material deposition management Flow and consolidation management Residual stress and dimensional control management (Same as "Processing themes")
thermal diffusivity	A quantitative measure of how a material will respond to transient thermal conditions. It is defined as the ratio of thermal conductivity to the volumetric heat capacity of the material (density times the specific heat capacity). Materials with large thermal diffusivity have a high thermal conductivity relative to their capacity to store energy (heat capacity) and will rapidly distribute the thermal energy throughout its volume and rapidly change temperature to reach the new equilibrium temperature. Materials with small thermal diffusivity have a low thermal conductivity relative to their capacity to store energy (heat capacity) and will have a sluggish temperature response to a change in thermal conditions (large temperature lag). This is because it takes more energy per unit volume to change the temperature, and the low thermal conductivity means it takes longer to distribute the thermal energy throughout its volume.
thermal management	A central processing theme in the manufacturing cycle. This theme is concerned with managing the thermal response of materials during storage and handling or parts/tools when they are subsequently heated.
thermal profiling	Experimental thermal profiling is a typical practice where part/tool temperatures and temperature rates are empirically measured using temperature measurement devices (typically thermocouples). This activity is performed to ensure that representative locations in the part of interest satisfy the cure window with respect to minimum/maximum heat up and cool down rates and length (duration) of temperature holds.
thermoplastic	A class of polymer, some common examples include polypropylene and polyethylene. They soften and melt upon heating (i.e. potentially recyclable), high viscosity when melted, therefore difficult to saturate fibres. Usually needs a lot of pressure and heat to process.
thermoset	Thermosets are a class of polymer that undergo polymerization and crosslinking during curing with the aid of a hardening agent and heating or promoter. Initially they behave like a viscous fluid. During curing, they change from viscous fluid to rubbery gel (viscoelastic material) and finally glassy solid. If heated after curing, initially they become soft and rubbery at high temperatures. If further heated, they do not melt but decompose (burn) Comes in two parts: part A (resin) and B (hardener). When mixed, curing reaction starts and is not reversible. Examples include epoxy or polyester.
tow	A tow is a bundle or yarn of individual fibres. The tow size is inherent to the fibre manufacturing process (i.e. a tow is manufactured in one process, rather than each fibre individually then bundled together after). Typically, smaller tows are better because they result in a more homogeneous material. The larger the tow: The faster it is to deposit material The easier is it for resin to flow between tows Harder for resin to saturate Typical tow sizes: 1k (thousand) 3k 6k 12k 24k 50k
uncertainty	A general term for the variability that affects the accuracy of a metric, statement or thought. Modelling & simulation In modelling & simulation a distinction is made between uncertainty and error: Uncertainty Aleatory uncertainty: associated with inherent variability. Process requirements, such as material and process specifications are typically used to manage aleatory uncertainty. Epistemic uncertainty: unknowns due to a lack of knowledge, or imperfect knowledge. Typically managed by improving the understanding of manufacturing outcomes and their interactions (e.g. process-structure-property relationships) Error Acknowledged errors: Explicit assumptions and/or simplifications (e.g. modelling practices) Unacknowledged errors: Mistakes and/or blunders (e.g. using the wrong material model) Innovation management As defined in terms of commercialization opportunities/risks: Technological uncertainty: Relates to the feasibility of an innovation idea and/or the economic viability of scaling (e.g. from primary research to production). Market uncertainty: Exists if the innovation idea cannot sufficiently meet market needs, where the market opportunity is not obvious/cannot be guaranteed, or where competitors are working on alternative solutions.
uncertainty quantification	An emerging discipline that relates to the characterization of modelling and simulation uncertainties. There are four key aspects of uncertainty quantification (UQ) that can be used to manage uncertainty to establish an ‘evidence of credibility’ in a computational model: Identification and classification ranking propagation (probabilistics or uncertainty analysis), and management.
vacuum infusion process	Vacuum Infusion Process (VIP) involves placing a preform on a one sided tool, sealing a vacuum bag on top of it, and drawing resin through the preform with vacuum. Vacuum Infusion Process (VIP) - also known as vacuum assisted resin infusion (VARI), vacuum assisted resin transfer moulding (VARTM) or often just resin infusion. VIP is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.
validation	With regards to modelling & simulation, validation demonstrates the accuracy of a computational model — in the context of its intended use — to check that it represents the physics of the problem and the ‘reality of interest’ (needs are satisfied).
verification	With regards to modelling & simulation, verification confirms the implementation of a computational model to ensure that it represents the mathematical model and equations used to describe it (requirements are met).
viscosity	In composites processing, viscosity is an indicator of how easily the resin matrix will mix with the reinforcement and how well it will stay in place during processing. The lower the viscosity, the more easily resin flows. Resin viscosity ranges considerably across chemistries and formulations. By scientific definition, viscosity is a measure of a material’s resistance to deformation. For liquids, it is in response to imposed shear stresses.
volume fraction	Volume fraction of either matrix or fibres with respect to total composite volume (matrix + fibre).
weight fraction	Weight fraction of either matrix or fibres with respect to total composite weight (matrix + fibre).
workflows	A set of steps/procedures that are intended to provide guidance in manufacturing and/or decision making activities. There are two types of workflows: Standard workflows are intended to formalize practices where the manufacturing science base exists. The focus is to provide guidance using manufacturing simulation as an enabling tool (e.g. design activities/decisions relating to thermal management). Complex workflows are intended to reduce the level of effort in practices where the existing manufacturing science base is not sufficiently mature to support production scale problems. The focus is to provide guidance using simulation based thinking and/or checklists (e.g. design activities/decisions relating to porosity management).

Ceramic Matrix Composites (CMC).

Differential Scanning Calorimetry (DSC).

Liquid Composite Moulding (LCM), a family of infusion processes refers to processes that saturate a dry reinforcement that is on/in the mould by means of a pressure differential (injection pressure, vacuum, combination of both).

Light Resin Transfer Moulding (LRTM) uses a semi rigid tool half (A side) that is similar to those used in VIP and a semi flexible tool half (B side) (typically made of thin fibreglass).

Metal Matrix Composites (MMC).

Manufacturer's Recommended Cure Cycle (MRCC).

The capability of the manufacturing process to produce parts of acceptable quality (e.g. meet engineering, manufacturing, regulatory requirements), repeatably and robustly.

A systems level description of manufacturing problems relating to the physical factory and part producibility. The MSTE factory ontology consists of four classes: Material and process (M), Shape (S), Tooling and consumables (T) & Equipment (E); and the concept: The factory (F) consisting of the MSTE within the MSTEP approach.

Material and process (M), Shape (S), Tooling and consumables (T) & Equipment (E) - all have an interlinked effect on the Process step (P). (See MSTE factory ontology)

Polymer Matrix Composites (PMC).

Resin transfer moulding (RTM) involves loading a preform into a two (or more) piece, matched tool, closing it, and injecting resin under pressure (~15-100 psi, or ~1-7 bar).

Well suited to small to medium sized parts, limited to large sizes due to injection pressure loads and tool cost.

‘Preform’ is the term for the fibre reinforcement. This is the stage between the raw material form after it is processed into an architecture (fabric, mat, etc.) and becoming a composite.

For polymer matrix composites (PMCs), resin refers to the matrix; the continuous material phase that binds the reinforcement together, maintains shape, and transfers load. Resins are divided into two main groups: thermosets and thermoplastics.

The Society for the Advancement of Material and Process Engineering (SAMPE).

Small and medium-sized enterprises (SME).

Vacuum assisted resin infusion (VARI) - also known as vacuum assisted resin transfer moulding (VARTM), vacuum infusion process (VIP) or often just resin infusion. VARI is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.

Vacuum assisted resin transfer moulding (VARTM) - also known as vacuum assisted resin infusion (VARI), vacuum infusion process (VIP) or often just resin infusion. VARTM is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.

Vacuum Infusion Process (VIP) involves placing a preform on a one sided tool, sealing a vacuum bag on top of it, and drawing resin through the preform with vacuum.

Vacuum Infusion Process (VIP) - also known as vacuum assisted resin infusion (VARI), vacuum assisted resin transfer moulding (VARTM) or often just resin infusion. VIP is a liquid composite moulding (LCM) closed mould process with a single side tool and vacuum bag where the resin is drawn through the preform using vacuum.

Engineered materials (designed to have specific properties) made from two or more constituent materials with different physical or chemical properties. The constituents remain separate and distinct on a macroscopic level within the finished structure.

Areal weight (or fibre areal weight, AW ) refers to the mass/weight of fibre per unit area. (Typically in g/m² gsm ) or ounces/yard² (often just called ounces). Areal weight depends on tow size and fibre architecture (weaving, density, etc.).

A tow is a bundle or yarn of individual fibres. The tow size is inherent to the fibre manufacturing process (i.e. a tow is manufactured in one process, rather than each fibre individually then bundled together after).

Typically, smaller tows are better because they result in a more homogeneous material.

The larger the tow:

• The faster it is to deposit material
• The easier is it for resin to flow between tows
• Harder for resin to saturate

Typical tow sizes:

• 1k (thousand)
• 3k
• 6k
• 12k
• 24k
• 50k

Fibre architecture refers to how the fibre is assembled.

Most common architectures:

• Unidirectional
• Chopped strand mat (CSM) and chopped fibre (chopper gun)
• Continuous filament mat (CFM)
• Woven fabric
• Non crimp fabric (NCF)
• Braided
• Prepreg

With regards to manufacturing, risk is the combination of the probability and consequences of undesirable manufacturing outcomes. Manufacturing risk can lead to technical issues, program/schedule delays, and cost overruns.

Carbon fibres are composed of large aromatic sheets similar to those in graphite. These graphitic layers form the basic structural units in the shape of ribbons. The structure of carbon fibre ribbon is believed to be a columnar arrangement of disoriented graphite crystallites parallel to the ribbon length. The idealized tetragonal crystallites are stacked above one another, with slight disorientation between the crystals in the direction of fibre axis, trapping sharp needle like voids, where the boundaries between the stacks represent the disordered regions.

The individual materials that combine to form the composite material. The constituent materials are separate and distinct on a macroscopic level.

A problem solving process where computational skills (e.g. thinking logically, algorithmically, and recursively), can be used to express solutions in a manner than can be actioned effectively by human intervention or machine. (Same as computational thinking)

Thermosets are a class of polymer that undergo polymerization and crosslinking during curing with the aid of a hardening agent and heating or promoter. Initially they behave like a viscous fluid. During curing, they change from viscous fluid to rubbery gel (viscoelastic material) and finally glassy solid.

If heated after curing, initially they become soft and rubbery at high temperatures. If further heated, they do not melt but decompose (burn)

Comes in two parts: part A (resin) and B (hardener). When mixed, curing reaction starts and is not reversible.

Examples include epoxy or polyester.

Degree of cure (DOC) is an indication of how far the chemical curing reaction (crosslinking process) has advanced in a thermoset resin.

DOC is defined with a number between 0 and 1 (or 0% and 100%) where 100% is a fully cured resin. It does not have to fully reach 100% for the resin to become solid or the part to be used. In some aerospace applications, resins are only cured to about 90%. Higher the degree of cure, higher the mechanical properties.

Any manufacturing and/or decision making activity that occurs during any stage of the development design cycle (e.g. conceptual design to production).

In the context of Knowledge in Practice, practice refers to the systematic use of science based knowledge to reduce composites manufacturing risk, cost, and development time.

A process whose outcomes are relatively insensitive to variability of manufacturing parameters.

A single unit of fibre reinforcement that cannot be separated further without breaking it. It often has a circular cross section that is formed by the dies used to create it or its precursor material. Many filaments are manufactured in parallel to produce a strand or tow. The number of filaments in a strand or tow is often references by how many thousands of filaments comprise the tow. e.g. an 18k tow is made up of ~18000 filaments.

Permeability refers to the resistance to fluid flow through a porous material.

• Resin flow through fibre
• Gas flow through prepreg

A key component of all composite manufacturing processes. Collectively, the four themes represent the time-temperature-pressure-vacuum history, which is traditionally used to define a manufacturing cycle.

The four processing themes are:

• Thermal management
• Material deposition management
• Flow and consolidation management
• Residual stress and dimensional control management

(Same as "Processing themes")

The glass transition temperature (T_g) is the temperature region where the polymer transitions from a hard, glassy material to a soft, rubbery material. It is one of the most important properties of any amorphous polymer.

Literally "without structure", randomly coiled molecular polymer chains.

Graphene is a one atom thick two dimensional honeycomb layer of bonded carbon atoms. When many graphene layers are stacked regularly in three dimensions and held together with weak forces, graphite is created.

Polymerization of thermoset resins is an exothermic reaction and heat is generated during the curing process. A thermosetting resin has the potential to release a certain amount of energy while curing. This is called the total heat of reaction, H_R, with a unit of J/g (SI units).

The heat of reaction during polymerization is measured using a Differential Scanning Calorimeter (DSC) equipment measuring much energy/heat comes out of the reaction for a small resin sample.

A framework for formalizing effective and low risk science based composites manufacturing practice and the process of knowledge translation.

In the context of knowledge in practice, knowledge refers to the systematic use of science based knowledge in composites manufacturing practice.

There is a distinction between experience based knowledge and science based knowledge:

• Experience based knowledge (‘know-how’) is an understanding of potential outcomes and their relationships that is founded on pragmatism and experience accumulated over time in individual programs, companies and in the industry more broadly.
• Science based knowledge (‘know-why’) is an understanding of potential outcomes and their relationships, based on the important processing physics, that is mature enough to be codified using the appropriate governing laws and constitutive equations.

Outcomes represent the range of response/sensitivity to factory system attributes. Those that fail to satisfy manufacturing requirements are known as defects. Examples of manufacturing outcomes include process parameter outcomes, material structure outcomes, and material performance outcomes.

The act of combining reinforcement fibre, resin to shape on a mould (tool).

There are three main methods to combine resin and fibre to deposit onto a tool (i.e. material deposition):

• Wet Processes: Mixing liquid resin and dry fibre directly in the mould, e.g. Wet Compression Moulding process for parts in BMW 7 series
• Liquid Composite Moulding (LCM) processes: Infusing dry fabric with resin using a pressure gradient, e.g. High Pressure Resin Transfer Moulding process (HP RTM) for parts in BMW i3
• Prepreg Processes: Laying up using prepreg where resin and fibre are already combined, e.g. Automated Tape Laying (ATL) process for some of the parts in Boeing 787.

Pre-impregnated (prepreg) material refers to fibre that is already combined with resin. It is the most common material form used in aerospace.

During prepreg production, (e.g. fibres are run through a resin bath), prepreg is heated and partially cured to B Stage (< 5 % degree of cure). Thermoset prepregs (e.g. epoxy prepreg) have to be kept in a freezer at around -20 °C. At room temperature, the epoxy starts to cure.

Volume fraction of either matrix or fibres with respect to total composite volume (matrix + fibre).

The use of multiphysics models to predict the outcome of real-world scenarios. May be analytical (closed form, "hand calculations") or computational (implementation on computers is required due to the large number of calculations involved. e.g. finite element method, finite difference method)

Most often in composite materials engineering, modelling refers to either:

• Process modelling (predicting manufacturing outcomes, or the inverse problem of predicting manufacturing parameters to achieve a desired outcome), or
• Performance modelling (predicting the stiffness/strength/suitability of a structure, or the inverse problem of the material properties and dimensional requirements to achieve a desired stiffness/strength/suitability of a structure)

(same as "Simulation")

A rubric used to provide a measure of performance that describes the producibility of a part. They may be quantitative or qualitative.

There are three objective functions in manufacturing:

• Cost
• Rate
• Quality

Objective functions are typically minimized or maximized to achieve a certain optimal condition; but in the context of manufacturing, maintaining the value of an objective function or achieving a nominal (target) value is a common goal (e.g. maintaining quality while increasing rate is a common workflow to achieve business growth; producing a new part for a target cost is important to maintaining a business case)

The key design phases in new product development (NPD), particularly for complex engineering systems. This includes conceptual design, preliminary design (trade study), detail design, and production.

Key components of all composite manufacturing processes. Collectively, the four themes represent the time-temperature-pressure-vacuum history, which is traditionally used to define a manufacturing cycle.

The four processing themes are:

• Thermal management
• Material deposition management
• Flow and consolidation management
• Residual stress and dimensional control management

(Same as "Theme")

An engineering design activity that relates to the determination of material level properties that will be used in the structural design and certification.

An engineering design activity that relates to the acceptance of the as manufactured structure being able to sustain the necessary loads and other service conditions determined by engineering, manufacturing, and regulatory requirements.

Racetracking is when resin takes the path of least resistance through a tool. This typically occurs at the outer edges of the reinforcement (between the fibre and tool). Depending on the severity, this can lead to dry spots (resin starved regions). Racetracking is not consistent and difficult to predict accurately (a ‘range’ of racetracking effects is predicted).

The continuous material phase that binds the reinforcement together, maintains shape, transfers load, protects the reinforcement from environment and damage, and provides the composite support in compression.

Desirable characteristics:

• Moisture/chemical resistance
• Low density
• Processability

A problem solving process where computational skills (e.g. thinking logically, algorithmically, and recursively), can be used to express solutions in a manner than can be actioned effectively by human intervention or machine. (Same as simulation based thinking)

Sizing or fibre sizing refers to a coating that is applied to fibre during manufacturing. Highly proprietary (formulation and process).

Sizing serves two functions:

• Protects and aids fibre during processing
• Aids in the bonding of fibre and matrix

A quantitative measure of how a material will respond to transient thermal conditions. It is defined as the ratio of thermal conductivity to the volumetric heat capacity of the material (density times the specific heat capacity).

Materials with large thermal diffusivity have a high thermal conductivity relative to their capacity to store energy (heat capacity) and will rapidly distribute the thermal energy throughout its volume and rapidly change temperature to reach the new equilibrium temperature.

Materials with small thermal diffusivity have a low thermal conductivity relative to their capacity to store energy (heat capacity) and will have a sluggish temperature response to a change in thermal conditions (large temperature lag). This is because it takes more energy per unit volume to change the temperature, and the low thermal conductivity means it takes longer to distribute the thermal energy throughout its volume.

Experimental thermal profiling is a typical practice where part/tool temperatures and temperature rates are empirically measured using temperature measurement devices (typically thermocouples). This activity is performed to ensure that representative locations in the part of interest satisfy the cure window with respect to minimum/maximum heat up and cool down rates and length (duration) of temperature holds.

The allowable range of temperature, pressure, and vacuum values at specific times in the cure cycle. These limits are usually defined as process requirements.

In composites processing, viscosity is an indicator of how easily the resin matrix will mix with the reinforcement and how well it will stay in place during processing. The lower the viscosity, the more easily resin flows. Resin viscosity ranges considerably across chemistries and formulations.

By scientific definition, viscosity is a measure of a material’s resistance to deformation. For liquids, it is in response to imposed shear stresses.

The use of multiphysics models to predict the outcome of real-world scenarios. May be analytical (closed form, "hand calculations") or computational (implementation on computers is required due to the large number of calculations involved. e.g. finite element method, finite difference method)

Most often in composite materials engineering, simulation refers to either:

• Process simulation (predicting manufacturing outcomes, or the inverse problem of predicting manufacturing parameters to achieve a desired outcome), or
• Performance simulation (predicting the stiffness/strength/suitability of a structure, or the inverse problem of the material properties and dimensional requirements to achieve a desired stiffness/strength/suitability of a structure)

(same as "Modelling")

A general term for the variability that affects the accuracy of a metric, statement or thought.

Modelling & simulation In modelling & simulation a distinction is made between uncertainty and error:

• Uncertainty
  • Aleatory uncertainty: associated with inherent variability. Process requirements, such as material and process specifications are typically used to manage aleatory uncertainty.
  • Epistemic uncertainty: unknowns due to a lack of knowledge, or imperfect knowledge. Typically managed by improving the understanding of manufacturing outcomes and their interactions (e.g. process-structure-property relationships)
• Error
  • Acknowledged errors: Explicit assumptions and/or simplifications (e.g. modelling practices)
  • Unacknowledged errors: Mistakes and/or blunders (e.g. using the wrong material model)

Innovation management As defined in terms of commercialization opportunities/risks:

• Technological uncertainty: Relates to the feasibility of an innovation idea and/or the economic viability of scaling (e.g. from primary research to production).
• Market uncertainty: Exists if the innovation idea cannot sufficiently meet market needs, where the market opportunity is not obvious/cannot be guaranteed, or where competitors are working on alternative solutions.

An emerging discipline that relates to the characterization of modelling and simulation uncertainties. There are four key aspects of uncertainty quantification (UQ) that can be used to manage uncertainty to establish an ‘evidence of credibility’ in a computational model:

• Identification and classification
• ranking
• propagation (probabilistics or uncertainty analysis), and
• management.

With regards to modelling & simulation, validation demonstrates the accuracy of a computational model — in the context of its intended use — to check that it represents the physics of the problem and the ‘reality of interest’ (needs are satisfied).

With regards to modelling & simulation, verification confirms the implementation of a computational model to ensure that it represents the mathematical model and equations used to describe it (requirements are met).

A set of steps/procedures that are intended to provide guidance in manufacturing and/or decision making activities.

There are two types of workflows:

• Standard workflows are intended to formalize practices where the manufacturing science base exists. The focus is to provide guidance using manufacturing simulation as an enabling tool (e.g. design activities/decisions relating to thermal management).
• Complex workflows are intended to reduce the level of effort in practices where the existing manufacturing science base is not sufficiently mature to support production scale problems. The focus is to provide guidance using simulation based thinking and/or checklists (e.g. design activities/decisions relating to porosity management).

A central processing theme in the manufacturing cycle. This theme is concerned with managing the thermal response of materials during storage and handling or parts/tools when they are subsequently heated.