Impact strength

A material's ability to withstand shock loading as measured during a test in which a specimen is fractured.

Impregnate

To saturate the voids and interstices of a reinforcement with resin.

Impregnated fabric

See prepreg.

Inclusion

Physical and mechanical discontinuity occurring within a material or part.

In situ

In the original position; in filament winding, designates a mandrel that remains in place after winding, as opposed to a mandrel that is removed after winding. In pipe repair, a type of repair that does not require pipe excavation; rather a composite sleeve is inserted into the existing pipe through a manhole.

Inhibitor

A chemical additive that slows or delays a cure cycle.

Injection molding

A method of forming a plastic to the desired shape by forcibly injecting the polymer into a mold.

Integral heating

System in which heating elements are built into a tool, forming part of the tool and usually eliminating the need for an oven or autoclave as a heat source.

Interface

The plane formed when two material surfaces make contact: in glass fibers, for instance, the area at which the glass and sizing meet; in a laminate, the area at which the reinforcement and laminating resin meet.

Interlaminar

Existing or occurring between two or more adjacent laminae in a laminate.

Interlaminar shear

Shearing force that produces displacement between two laminae along the plane of their interface.

Intralaminar

Existing or occurring within a single lamina in a laminate.

Intumescent

Capable of swelling or enlarging. In reference to fire-retardants, describes a layer or coating of material designed to swells or thicken in order to form a more effective barrier to heat and/or flame when exposed to either.

Isotropic

Fiber directionality with uniform properties in all directions, independent of the direction of applied load.

Isotropic laminate

A laminate in which the strength properties are equal in all directions, such as contact-molded laminates or metals.