GLOSSARY OF TERMS
H

Hand: the softness of a piece of fabric, as determined by the touch (individual judgment).

Hand lay-up: the process of placing (and working) successive plies of reinforcing material or resin-impregnated reinforcement in position on a mold by hand. Method of molding room temperature curing thermosetting polymers, mainly epoxies and polyesters, in association with glass, mineral, or fiber reinforcements. Catalyzed resin mixtures are sprayed, brushed, or spatulated on a mold. A precut reinforcing layer is laid on the wet resin. After the resin soaks into the reinforcement, subsequent layers are built up to the required thickness and are cured, removed from the mold and trimmed. Some variations of hand lay-up techniques are bag molding, drape molding, vacuum molding and spray-up molding. Typical parts are custom auto bodies and boat hulls.

Hardener: a substance or mixture added to a plastic composition to promote or control the curing action by taking part in it.

Hardness: the resistance to surface indentation usually measured by the depth of penetration (or arbitrary units related to the depth of penetration) of a blunt point under a given load using a particular instrument according to a prescribed procedure.

Heat distortion point: temperature at which the strength of a material begins to degrade. Now called deflection temperature.

Heat resistance: the property or ability of plastics and elastomers to resist the deteriorating effect of elevated temperatures.

Heat sink: a contrivance for the absorption or transfer of heat away from a critical element or part. Bulk graphite is often used as a heat sink.

Helical winding: in filament wound items, a winding in which a filament band advances along a helical path, not necessarily at a constant angle except in the case of a cylinder.

Het-Acid Resin: polyester resin with exceptional fire qualities.

High-pressure laminates: laminates molded and cured at pressures not lower than 6.9 MP (1.0 ksi), and more commonly in the range of 8.3 to 13.9 Mpa (1.2 to 2.0 ksi).

Homogeneous: descriptive term for a material of uniform composition throughout.

Honeycomb: manufactured product of resin-impregnated sheet material (paper, glass, fabric, and so on) or metal foil, formed into hexagonal-shaped cells. Used as a core material in sandwich construction.

Hoop stress: the circumferential stress in a material of cylindrical form subjected to internal or external pressure.

Hybrid: a composite laminate consisting of laminae of two or more composite material systems. A combination of two or more different fibers, such as carbon and glass or carbon and aramid, into a structure.

Hydraulic press: a press in which the molding force is created by the pressure exerted by a fluid.

Hysteresis: the energy absorbed in a complete cycle of loading and unloading. This energy in converted from mechanical to friction energy (heat).

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