Definitions /Dictionary/Glossary - nptel

Twist multiplier: The ratio of turns per inch to the square root of the cotton count.
Typical Basis: A typical property value is a sample mean. Note that the typical value is defined
as the simple arithmetic mean which has a statistical connotation of 50% reliability with a 50%
confidence.
Ultimate Tensile Strength: The ultimate or final stress sustained by a specimen in a
tension test; the stress at moment of rupture.
Unbond: An area within a bonded interface between two adherends in which the intended
bonding action failed to take place. Also used to denote specific areas deliberately prevented
from bonding in order to simulate a defective bond, such as in the generation of quality standards
specimens (See Disbond, Debond).
Undercut: Having a protuberance or indentation that impedes the withdrawal from a two-piece,
rigid mold; any such protuberance or indentation, depending on the design of the mold (that is,
tilting a model in design of a mold for that model may eliminate an apparent "undercut").
Unidirectional: Refers to fibers that are oriented in the same direction, such as unidirectional
fabric, tape, or laminate, often called UD.
Unidirectional Fiber-Reinforced Composite: Any fiber-reinforced composite with all fibers
aligned in a single direction.
Unit Cell: The term applied to the path of a yarn in a braided fabric representing a unit cell of a
repeating geometric pattern. It is the smallest element representative of the braided structure.
Upper Confidence Limit: See Confidence Interval.
UV Stabilizer: A chemical compound which improves resistance to degradation from ultraviolet
radiation.
Vacuum-Assisted Resin Transfer Molding (VARTM): An infusion process
where a vacuum draws resin into a one-sided mold. A cover, either rigid or flexible, is placed
over the top to form a vacuum-tight seal.
Vacuum Bag Molding: A process in which the lay-up is cured under pressure generated by
drawing a vacuum in the space between the lay-up and a flexible sheet placed over it and sealed
at the edges.
Vacuum Infusion Processing: A process where the reinforcement is laid-up in the mold dry,
then vacuum bagged and the resin is pulled into the mold at lower then atmospheric pressure.
Vapor Barrier: A material through which water vapor will not pass readily or at all.