Definitions /Dictionary/Glossary - nptel

Lay: In glass fiber, the spacing of the roving bands on the roving package expressed in the
number of bands per inch; in filament winding, the orientation of the ribbon with some reference,
usually the axis of rotation.
Lay-down: The degree of uniformity in thickness that a bed of chopped glass fibers exhibits
across the width of the chopped pattern.
Layer: The horizontal plane of doffs on a pallet. A pallet usually has four layers of twelve doffs
each. also see Cell
Lay-up: Act of building up successive layers of polymer and reinforcement. Layers of catalyzed
resin and fiberglass or other reinforcements are applied to a mold in order to make a part. Also
refers to the reinforcing material placed in position in the mold, the process of placing
reinforcing material in position in the mold, or the resin-impregnated reinforcement.
L/D Ratio: A term used to define an extrusion screw, which denotes the ratio of the screw length
to the screw diameter.
Lengthwise Direction: Refers to the cutting of specimens and application of loads. For rods and
tubes, lengthwise is the direction of the long axis. For other shapes of materials that are stronger
in one direction than in the other, lengthwise is the direction that is stronger. For materials that
are equally strong in both directions, lengthwise is an arbitrarily designated direction that may be
with the grain, direction of flow in manufacture, longer direction, etc.
Liquid-Crystal Polymer: A newer thermoplastic polymer that is melt process capable and
develops high orientation in molding, resulting in tensile strength and high-temperature
capability.
Load-Deflection Curve: A curve in which the increasing tension or compressions of flexural
load are plotted on the ordinate axis and the deflections caused by those loads are plotted on an
abscissa axis.
Loom: A mechanical device that interlaces fibers at right angles with varying degrees of weave
construction (weight, thickness and design). More modern looms are air jet but rapier and more
traditional shuttle equipment is still in use.
Loom Beam: A large, flanged cylinder onto which all warp yarns are wound and from which
yarns enter the loom.
Loop: Small open place in the strands due to excessive length of one or more strands.
Loss on Ignition: Weight loss, usually expressed as a percent of the total, after burning off an
organic sizing from glass fibers, or an organic resin from a glass fiber laminate.
Low-Pressure Laminates: Laminated, molded, and cured using pressures from 400 psi down to
and including the pressure obtained by mere contact of the plies.