Angle-ply laminate - Possessing equal plies with positive and negative angles. This bi-directional laminate is orthotropic. [+- 45] is a common example. 

Autoclave - A pressure vessel that can maintain temperature and pressure of a desired air or gas for the curing of organic-matrix composite materials. 

Automated fibre placement (AFP) - Processes that use computer-guided robotics to lay one or several layers of narrow carbon fibre tows on a mold. Used for tube production. 

Automated tape laying (ATL) - Processes that use computer-guided robotics to lay one or several layers of wide carbon fibre tapes on a mold. Used for cable production. 


Balanced laminate - A composite laminate in which all laminate at angles other than 0 and 90 degrees occur only in + pairs and are symmetrical around the centre line. 

Bending moment - Stress couple that changes curvature of a plate. 

Boundary conditions - Load and environmental conditions that exist at the boundaries of an object. Conditions must be specified to perform stress analysis. 

Brittle fracture - Fracture that occurs by rapid crack propagation and without macroscopic deformation.

Buckling - Unstable lateral displacement of a structural part caused by excessive compression or shear.


CCRP - Carbon cloth reinforced plastic.

CFRP - Carbon fibre reinforced plastic.

CFRTP - Carbon fibre reinforced thermoplastic.

Co-cured - Cured and simultaneously bonded to another prepared surface. 

Compliance - Measurement of softness as opposed to stiffness of a material. 

Coupling (Interaction) - Linking a side effect to a principal effect. Example - longitudinal tensile strength is affected by the presence of transverse stress. Coupling of composites are unique and provide the opportunity to perform extraordinary functions. 

Creep - The time-dependant permanent deformation that occurs under stress; for most materials it is only important at elevated temperatures. 

Cross-ply laminate - Special laminate that contains only 0 and 90 degree plies. 

Cure - To change the properties of a thermosetting resin irreversibly by chemical reaction. 

Curvature - Geometric measure of the bending and twisting of a plate. 


Debond - Area of separation between or within plies in a laminate, or between a bonded joint caused by contamination.

Debulking - Compacting of a thick laminate under moderate heat and pressure and/or vacuum to remove most of the air, to ensure seating on the tool and to prevent wrinkles. 

Deformation - Changes in size and shape of a body resulting from externally applied forces. 

Deflection - Displacement of a structure.

Degradation - Loss of property due to ageing, corrosion and repeat or sustained stress.

Delamination - Debonding process primarily resulting from unfavourable interlaminar stresses. 

Ductility - A measure of a materials ability to undergo appreciable plastic deformation before fracture; may be expressed as percent elongation (%EL) or percent are reduction (%AR). 

Ductile fracture - A mode of fracture that is attended by extensive gross plastic deformation.


Elastic deformation - Deformation that is nonpermanent, that is, totally recovered upon release of an applied stress.

Elastic recovery - Nonpermanent deformation this is recovered or regained upon the release of a mechanical stress. 

Equilibrium - The state of a system where the phase characteristics remain constant over indefinite time periods. At equilibrium the free energy is a minimum.

Erosion-corrosion - A form of corrosion that arises from the combined action of chemical attack and mechanical wear.

Excited state - An energy state, not normally occupied, to which an object may be promoted to move by the absorption of some type of energy (heat, wind, etc).

Exotherm - The liberation or evolution of heat during the curing process. 

Extrusion - A forming technique whereby a material is forced, by compression, through a die of the desired cross-section.


Fatigue - Failure, at relatively low stress levels, of structures that are subjected to fluctuating and cyclic load stresses.

Fatigue life - The total number of stress cycles that will cause a fatigue failure at some specified stress amplitude.

Fatigue limit - For fatigue, the maximum stress amplitude level below which a material can endure an essentially infinite number of stress cycles and not fail.

Fatigue strength - The maximum stress level that a material can sustain, without failing, for some specified number of cycles. 

Fibre - Single filament, rolled or formed in one direction, and used as the principal constituent of woven and nonwoven composite materials. 

Fibre content - Percent volume of fibre in a composite material. 

Fibre direction - The orientation or alignment of the longitudinal axis of the fibre with respect to stated reference axis. 

Fibre reinforcement - Strengthening or reinforcement of a relatively weak material by embedding a strong fibre phase within the weak matrix.

Filament - Continuous fibre with exceptionally high specific stiffness and strength. 

Filament winding - Automated process of placing filament onto a mandrel in prescribed patterns. The resin impregnation can be before or during the winding, known as prepreg or wet winding, respectively. 

Fracture toughness - Critical value of stress intensity factor for which crack extension occurs. 

Free energy - A thermodynamic quantity that is a function of both of the internal energy and entropy (or randomness) of a system. At equilibrium, the free energy is at a minimum.

Frequency - Number of cycles per second, expressed in Hertz. 



Hardness - The measure of a material's resistance to deformation by surface indentation or by abrasion.

Hooke's Law - A linear relationship between stress and strain.


Impregnate - To saturate voids and interstices of carbon fibre with resin. 

Interlaminar - Existing or occurring between two or more adjacent laminae. 

Interlaminar shear - A shearing force tending to produce a relative displacement between two laminae along the plane of their interference. 

Isotropic - Having identical values of a property when measured in different directions.



Kinetics - Study of reaction rates and the factors that affect them.


Lamina - Ply or layer of unidirectional composite. 

Laminate - Plate consisting of layers of uni or multidirectional plies of one or more composite materials.

Laminar composite - A series of two-dimensional sheets, each having a preferred high-strength direction, fastened one on top of the other at different orientations; strength in the plane of the laminate is highly isotropic. 

Layup - Ply stacking sequence or ply orientations of a laminate. 

Longitudinal direction - The length-wise dimension, for a fibre the direction of the long axis.

Longitudinal modulus - Elastic constant along the fibre direction in a unidirectional composite; eg - longitudinal Young's or shear modulus. 


Mandrel - Male mould used for filament winding.

Mechanical load - Mechanically applied load as distinguished from cure, or environment, induced load. 

Modulus - Elastic constants such as Young's modulus, shear modulus, or stiffness modulus. 

Modulus of Elasticity (E) - The ratio of stress to strain when deformation is totally elastic; also a measure of the stiffness of a material.

Mold - Cavity on which a composite part is placed, and from which it takes shape after curing.

Multidirectional - Having multiple ply orientations in a laminate. 


Neutral plane - Plane which experiences no stretching. 


Ohmic curing - The processes of generating heat to cure the resins by applying an electrical current to the cables. 


Peel ply - Fabric material applied to a laminate to protect the clean, ready-to-use bonding surface and peeled off prior to curing. 

Plastic deformation - Deformation that is permanent or nonrecoverable after release of the applied load. It is accompanied by permanent atomic displacements.

Poisson's Ratio (v) - The ratio of transverse strain to the corresponding axial strain resulting from the applied axial load below the elastic limit of the material. 

Post-cure - Additional exposure to temperature after initial cure. The post cure temperature may be higher than the cure temperature. 

Preform - Layup made on a mandrel or mockup that is subsequently transferred to the curing tool or mold.

Prepreg - Continuous fibre reinforcement preimpregnated with a polymer resin which is then partially cured. 

Principal direction - Specific coordinate axes orientation when stress and strain components reach maximum and minimum for the normal components, and zero for shear.

Property - A material trait expressed in terms of the measured response to a specific imposed stimulus.

Proportional limit - The point on a stress-strain curve at which the straight line proportionality between stress and strain ceases. 



Recovery - The relief of some of the internal strain energy of a previously exerted load.

Residual stress - A stress that persists in a material that is free of external forces or temperature gradients. 

Resilience - The capacity of material to absorb energy when it is elastically deformed.

Resin - Organic material with high molecular weight, insoluble in water, with no definite melting point and no tendency to crystalize.

Resin content - Precent resin in a composite material.  

Resistivity - The reciprocal of electrical conductivity, and a measure of a material's resistance to the passage of electric current.

Resolved shear stress - An applied tensile or compressive stress resolved into a shear component along a specific plane and direction within that plane.

Roving - Loose assemblage of filaments. 

Rupture - Failure that is accompanied by significant plastic deformation: often associated with creep failure. 


Safe stress - A stress used for design purposes. 

Safety factor - The ratio of the ultimate strength to the design or allowable stress. 

Sandwich panel - A type of structural composite consisting of two stiff and strong outer faces that are separated by a lightweight core material.

Secondary bonding - Joining by adhesive bonding parts which have already been cured. 

Shear - A force applied so as to cause or tend to cause two adjacent parts of the same body to slide relative to each other, in a direction parallel to their place of contact.

Shear coupling - Induced shear strain from normal stress. 

Shear strain - The tangent of the shear angle that results from an applied shear load.

Shear stress - Component that results in distortion, not extension or contraction. The instantaneous applied shear load divided by the original cross-sectional area across which it is applied. 

Shrinkage - Contraction of molded part during and after cure. Parts can meet dimensional tolerance if the dimensional changes due to temperature of that part and the mold are properly considered. 

Specific modulus (specific stiffness) - The ratio of elastic modulus to specific gravity for a material. 

Specific strength - The ratio of tensile strength to specific gravity for a material.

Stacking sequence - Ply ordering in a laminate. 

Stiffness - Ratio between the applied stress and the resulting strain. Young's modulus is the stiffness of a material subjected to uniaxial stress; shear modulus to shear stress. Stiffness depends on a materials orientation. 

Strain - The change in gauge length of a specimen (in the direction of an applied stress) divided by its original strain length. 

Strength - Maximum stress that a material can sustain. Strength is highly dependent on the direction as well as the applied stress; eg - axial tensile, transverse compressive. 

Stress - The instantaneous load applied to a specimen divided by its cross-sectional area before any deformation. Normal stress induces length or volume change, shear stress induces shape change. 

Stress concentration - Increased ratio of a local stress over the average stress. 

Stress-strain relation - Linear relation is usually assumed for calculating stress from strain, or from strain to stress. Can include in-plane stress-strain and flexural stress-strain relations. 

Structural composite - A composite the properties of which depend on the geometrical design of the structural elements. Laminar composites and sandwich panels are two sub classes. 


Tensile strength - The maximum engineering stress, in tension, that be sustained without fracture. Often termed ultimate strength.

Thermal conductivity - A parameter characterizing the ability of a material to conduct heat.

Thermal expansion coefficient - The fractional change in length divided by fluctuating thermal stresses.

Thermal fatigue - A type of fatigue failure wherein the cyclic stresses are introduced by fluctuating thermal stresses.

Thermal stress - A residual stress introduced within a body resulting from a change in temperature. 

Thermoplastic (polymer) - A polymeric material that softens when heated and hardens upon cooling. While in the softened state, articles may be formed by moulding or extrusion.

Thermosetting (polymer) - A polymeric material that, once having cured (or hardened) by a chemical reaction, will not soften or melt when subsequently heated. 

Toughness - A measure of the amount of energy absorbed by a material as it fractures.

Tow - A loose, untwisted bundle of filaments. 

Transverse direction - A direction that crosses (uses perpendicular) the longitudinal or lengthwise direction.

True strain - The natural logarithm of the ratio of instantaneous gauge length to original gauge length of a specimen being deformed by a uniaxial force. 

True stress - The instantaneous applied load divided by the instantaneous cross-sectional area of a specimen. 


Ultrasonic testing - A nondestructive test applied to materials for the purpose of locating internal flaws or structural discontinuities by the use of high-frequency reflection or ultrasonic beam.

Unidirectional fibres - Having parallel fibres in a composite. 


Vacuum bag - Flexible nylon, mylar or elastomeric film that provides the outer cover of composite material cure assemblage, which can be sealed and evacuated to provide compaction pressure. The entire assemblage with the bag can be placed in an oven or autoclave for curing at desired temperature and additional pressure. 

Volume fraction - Fraction of a constituent material based on its volume.

Void - The space occupied by air or gas trapped in a composite material.


Wall thickness ratio - Ratio of outer radius to inner radius of a cylinder or tube. 

Weave - The particular manner in which a fabric is formed by interlacing yarns.

Wet layup - A method of making a reinforced product by applying the resin system as a liquid when the carbon fibre is put in place. 

Wet-out - The condition of an impregnated roving or yarn in which substantially all voids between the sized strands and filaments are filled with resin.

Winding angle - The angular measure between fibre direction and a reference axis (longitudinal axis or axis of rotation of a tube).  

Wrinkle - A surface imperfection in laminated carbon fibre that has the appearance of a crease or fold in one or more outer sheets of the paper, fabric, or other base, which has been pressed in.


X-axis - The axis in the plane of the laminate that is perpendicular to the y-axis.


Y-axis - The axis in the plane of the laminate that is perpendicular to the x-axis.

Yield strength - The stress required to produce a very slight yet specified amount of plastic strain.

Young's modulus - See Modulus of Elasticity. 


Z-axis - The reference axis normal to the plane of the laminate.