Composite Inspection and Defect Prevention 240

active mode

A thermographic testing mode in which the composite is subjected to mechanical stress.

amplitude

A measurement of the size of a wave. In ultrasonic testing, changes in signal amplitude may inidicate defects inside a composite.

aramid

A strong heat resistant fiber used primarily in aerospace and military applications.

benzene

An organic chemical compound that is often used as a solvent.

bridging

A defect that occurs when part of the vacuum bag remains above the composite surface instead of pressing against it during the vacuum process. Bridging prevents the composite from being properly compressed.

carbon

A non-metallic chemical element which, when added to iron, forms steel. Increasing carbon increases hardness in metal.

caul

A pad used to prevent bridging in vacuum bags by applying pressure to a specific area.

composite

A material made by combining a binding resin with small filaments of solid material. Composites have the strength of metal, the light weight of plastic, and the rigidity of ceramics.

compression stress

The internal load that a part is subjected to when a force squeezes or pushes down on it.

contamination

The presence of foreign materials such as dirt or debris in a substance.

crack

A visible fracture or point of separation in the surface of the composite.

debulking

Compressing a composite part to the desired thickness and shape. Debulking through vacuum bagging eliminates air, voids, and excess resin in a composite.

deformation

The change in an object's size or shape as a result of stress.

delamination

The separation of the layers in a laminate. Laminate is a sheet of material that has been created by stacking thin layers, or plies, and bonding them together. Delamination can occur locally, in a small area of the laminate, or it can affect the entire laminate.

diameter

The distance from one edge of a circle to the opposite edge that passes through the center.

drape test

A measure of the amount of flexibility in a prepreg. During drape testing, the prepreg is simply placed over a cylindrical object while the tester observes the stiffness of the prepreg. A prepreg must have a certain amount of drape in order to mold properly.

electromagnetic wave

An oscillating wave from a magnetic field that is produced by the motion of electric charges such as electric current.

environmental properties

The characteristics of a material that determine how it reacts to other objects, forces, and materials in close proximity. Environmental factors that affect a material include noise, air quality, machine vibration, moisture, and temperature, among other factors.

excess moisture

Any level of moisture that is higher than what is normal for the resin or reinforcement.

fatigue

Progressive structural damage to an object that is subjected to cumulative stress from repeated loads.

fiber damage

Structural damage to fiberglass including broken filaments, knots, or splicings in the roving or fabric yarns.

fiberglass

Reinforcement material made from extremely fine strands of glass. Fiberglass is the most commonly used composite reinforcement.

flame resistance

The ability of a material to resist catching fire.

flame spread

The broadening or spreading of a flame.

flame time

The amount of time a flame will burn before going out.

flammability

The characteristics of a material that determine its ability or tendency to ignite or burn when exposed to an open flame.

flammability test

A test that measures a material's ability or tendency to ignite or burn when exposed to an open flame.

flexural stress

The internal load that a part is subjected to when a force causes an object to bend perpendicular to the object's long axis.

force scale

A measure of the intensity of applied force required to remove a prepreg from a smooth surface.

halogen

A non-metallic element that is highly reactive. The risk of burning inherent in organic resins can be reduced by adding halogens.

infrared wave

Invisible rays emitted during the welding process. Infrared rays can damage vision.

laminate

A sheet of material created by stacking thin layers, or plies, and bonding them together.

load

The overall force applied to a material or structure. In a composite, the matrix transfers the load to the reinforcement fibers.

mandrel

The core around which resin-impregnated fibers are wound to create a part. Mandrels are used in filament winding.

mechanical properties

The characteristics of a material that determine how it reacts when it is subjected to a force that attempts to stretch, dent, scratch, or break it.

microcrack

A tiny crack in the matrix or in the laminate of a composite. Microcracks weaken the mechanical properties of the composite and can cause fiber breakage and delamination.

misaligned fibers

Fibers that deviate from the predetermined orientation of the reinforcement filaments or fabric.

necking

The reduction in diameter that occurs as a sample material is subjected to tensile stresses.

non-destructive testing

NDT. Testing methods that identify defects without damaging the composite. There are a variety of non-destructive testing methods, from simply looking at the composite to sending a signal through the composite.

organic resin

A resin made from natural materials such as plant secretions.

passive mode

A thermographic testing mode in which the surface of the composite is excited with a form of visible light.

porosity

The presence of tiny openings or spaces within a material.

prepreg

A ready-to-mold sheet of fiber reinforcement that has been preimpregnated with resin.

process control

The range of variation within a process after special causes have been eliminated.

pulse-echo testing

A non-destructive testing method in which the transmitter and receiver are together in the same unit. The signal sent through the composite bounces back to the receiver.

quality

Conformance to a set of standards or specifications. A product has quality if it meets or exceeds standards, but is defective if it does not meet standards.

quality management

A process improvement method that focuses on increasing customer satisfaction at a reasonable cost to the manufacturer.

radiography

A type of imaging technology used to view the insides of objects and detect changes in the density of material.

receiver

A device that receives signals. Receivers are used in ultrasonic testing of composites.

reinforcement

The part of the composite that provides strength, stiffness, and the ability to carry a load. In manufacturing, fibers are the most commonly used reinforcement.

residual stress

Stress that remains in the composite after the force that originally caused the stress has been removed. Typically, residual stress shows up as deformation or warping in the composite.

resin

A substance made from either synthetic or natural polymers and used for composite matrices. In essence, a resin is a polymer that has not been processed into its final form.

shear strength

The ability of a material to resist internal sliding.

shear stress

The internal force that causes a material to slide against itself or its internal components.

smoke density

The concentration of smoke emitted by a fire.

tack

A measure of the stickiness of a prepreg. The prepreg must have a certain amount of tack in order to mold properly.

tack test

A test that measures the stickiness of a prepreg. The prepreg must have a certain amount of tack in order to mold properly.

tap test

A non-destructive testing method. A tap test involves tapping on the composite with a small hammer, or another object such as a large coin, and listening for changes in sound as different places on the composite are impacted.

tensile stress

The internal load that a part is subjected to when pulled apart by an applied force. A material's ability to resist tensile stress is tested by pulling a sample part from each end.

thermal imaging

A non-destructive testing method that uses infrared waves to detect increases and decreases in the heat emitted or conducted by an object.

thermal profile

The range of temperatures involved in a heating process.

thermal properties

The characteristics of a material that determine how it reacts when it is subjected to excessive heat, or heat fluctuations over time.

thermography

A non-destructive testing method that uses infrared waves to detect increases and decreases in the heat emitted or conducted by an object.

through-transmission testing

A non-destructive testing method in which the composite is placed between a transmitter and receiver and an ultrasonic signal is passed through the composite.

torsion stress

A specific type of shear stress. Torsion stress is caused when a force is applied in a rotational motion on one end to twist the material.

total quality management

TQM. An administrative approach centered around consistent customer satisfaction and continuous improvement of product quality. Under TQM, quality becomes the focus of the design, creation, marketing, and maintenance of each product.

toxicity

The degree to which something is poisonous.

transmitter

A device that sends signals. Transmitters are used in ultrasonic testing of composites.

ultrasonic test

A non-destructive testing method in which a high frequency sound wave is sent through a part and changes in signal amplitude are observed. Typically the signal changes as the density of the part changes.

vacuum bag

Part of a vacuum bagging system that forms an airtight seal over an entire assembly.

viscosity

A measure of a fluid's thickness, stickiness, or resistance to flow.

viscosity test

A test that measures a fluid's thickness, stickiness, or resistance to flow. When molding parts from composites, the resin must have the proper viscosity.

visual test

A visual inspection for surface defects on the composite. Visual testing is one of the most commonly used non-destructive testing methods for composites.

void space

Empty space or pores in a composite.

warping

The physical twist or turn within a part caused by internal stress.

X-ray

An electromagnetic wave used in radiographic testing of composites. X-rays are used to view the insides of solid objects.