Composites Terms

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Halogenated resin

A resin combined with chlorine or bromine to increase fire retardancy.

Hand layup

A fabrication method in which reinforcement layers, preimpregnated or coated afterwards, are placed and arranged in a mold manually. (In contrast to sprayup or automated methods, such as fiber placement.)


see hazardous air pollutants.

Hard tool

A tool made of metal or any "hard" material that is generally impervious to process-related damage (e.g., exothermic distortion) during normal molding operations (in contrast to soft tool). See tool.


A substance that may be added to a resin to promote and/or control the curing process by participating in and being consumed by the cure reaction. (Also see accelerator, curing agent and catalyst.)

Hazardous air pollutants (HAPS)

Potentially airborne compounds determined to be hazardous to human health by the U.S. Environmental Protection Agency (EPA).


The term used colloquially to indicate any temperature above ambient (room) temperature to which a part or material is or will be subjected.

Heat-deflection temperature (HDT)

The temperature at which a standard plastic test bar deflects a specified distance under a stated load.


Describes ply laid onto a rotating mandrel at an angle, often at a 45° angle.

Helix angle

The angle at which continuous filaments are wound in relation to the longitudinal mandrel axis in the filament-winding process.

High-performance composites

Composites offering properties better than conventional structural metals, typically on a strength-to-weight or stiffness-to-weight basis. Such composites use continuous, oriented fibers in polymer, metal or ceramic matrices to achieve their superior properties.


A lightweight cellular structure (typically hexagonal nested cells) used as core in composite sandwich structures. May be made from either metallic (e.g., aluminum) or nonmetallic (e.g., resin-impregnated paper or woven fabric) sheet materials. Rectangular sheets are adhesively bonded together in stacks, by means of parallel stripes of adhesive placed at regular intervals along one axis. Stacks are sliced across the transverse axis, and each sliced stack is expanded to form a honeycomb grid.


Describes ply layed onto a rotating mandrel at a 90° angle to the long axis of the mandrel.

Hoop stress

Circumferential stress in a cylindrically shaped part as a result of internal or external pressure.

Hot-bond repair

Repair made on a hot-patch bonding machine to cure and monitor curing. Typically includes heat and vacuum source.

Hybrid composite

Composite containing at least two distinct types of matrix or reinforcement. The matrix or reinforcement types can be distinguished by their physical properties, mechanical properties, material form and/or chemical composition.


A material's readiness to absorb or retain moisture.