Definitions /Dictionary/Glossary - nptel

and removed by the vacuum. The part is cured with temperature, pressure and time. It is also
called bag molding.
Vacuum Molding: Low cost entry method into RTM which uses a rigid cavity mold half and a
semi-rigid upper mold half, both made of FRP. Capable of producing 3-4 times as many
moldings as that produced through open mold, with acceptable repeatability (but not equal to that
of RTM.)
Veil: Ultra thin mat similar to a surface mat.
Vinyl-Coated Glass Yarn: Continuous glass filament yarn coated with pigment and plasticized
vinyl chloride resin.
Vinyl Esters: Thermosetting resins containing esters of acrylic and/or methacrylic acids, many
of which have been made from epoxy resin. Cure is accomplished as with unsaturated polyesters
by CO-polymerization with other vinyl monomers, such as styrene.
Viscosity: Measure of a liquid’s resistance to flow.
Void Content: The percentage of voids in a laminate.
VM: See Vacuum Molding.
Warp: Yarn running lengthwise in a woven fabric. A group of yarns in long lengths and
approximately parallel, put on beams or warp reels for further textile processing including
weaving, knitting, twisting, dyeing, etc.
Warp Size: Chemicals applied to the warp yarn to improve strand integrity, strength and
smoothness in order to withstand rigors of weaving.
Weave: Particular manner in which a fabric is formed by interlacing yarns; usually assigned a
style number.
Weft: The system of yarns running crosswise in a fabric. It is also known as fill.
Wet Flexural Strength (WFS): It is the flexural strength after water immersion, usually after
boiling the test specimen for two hours in water.
Wet Lay-Up: Reinforced plastic with liquid resin applied after the reinforcement is laid up. It is
opposite of "dry lay-up", "prepreg".
Wet-Out Rate: Time required for a plastic to fill the interstices of a reinforcement material and
wet the surface of the reinforcement fibers; usually determined by optical or light transmission
means.