Materials 101
Fibrous reinforcement pre-impregnated with a controlled amount of polymeric matrix, partially cured to B-stage, and kept refrigerated.
What is Prepreg?
A single constituent layer used in, or occurring within, a composite stack.
What is a Ply (or Lamina)?
The structural arrangement consisting of two thin, stiff face sheets bonded to and separated by a thick, lightweight inner layer.
What is Sandwich construction?
Any empty pocket of enclosed gas or air trapped inside a cured composite part.
What is a Void?
This handheld tool is used to warm prepreg so it becomes tackier and easier to conform to a shape.
What is a heat gun?
The chemical reaction that transforms low-molecular-weight resin/hardener into a cross-linked, infusible solid.
What is curing?
In woven fabric, these are the yarns that run lengthwise, parallel to the roll direction.
What is Warp (or Warp yarns)?
The continuous matrix material that surrounds and binds reinforcement fibers; for polymers, it's also called resin content.
What is Matrix?
A defect where plies or the vacuum bag span across a tight radius or corner without pressing fully into the tool.
What is Bridging?
This non-structural, absorbent layer soaks up excess resin during cure and gets discarded afterward.
What is bleeder cloth?
A sacrificial top layer pulled off after curing to leave a clean, textured surface ready for secondary bonding.
What is a Peel Ply?
A laminate whose stacking sequence on one side of the geometric mid-plane perfectly mirrors the other side.
What is Symmetric?
A thick paste forced into honeycomb cells to locally strengthen the core around inserts or along the edges of a panel.
What is Potting compound?
Localized separation of plies within a cured laminate, or separation between the facing skins and the core.
What is Delamination?
This sacrificial top ply is peeled off after cure to leave a clean surface ready for bonding.
What is peel ply?
Applying a temporary vacuum bag to compact the lay-up and squeeze out trapped air before the final cure cycle.
What is Debulking?
Having three mutually perpendicular planes of elastic symmetry which define the principal material axes.
What is Orthotropic?
The specific cellular structure described by its anisotropic directions: L (ribbon), W (transverse), and T (thickness).
What is Honeycomb core?
Extra bagging material purposefully left at corners and deep recesses to prevent the bag from bridging and tearing.
What are Pleats (or ears)?
Thin, non-absorbent FEP or Teflon material used to prevent liquefied resin from sticking to downstream bagging elements like the breather.
What is Release film?
This polyester or fiberglass fabric is placed under the bag to provide a continuous path for air extraction but must never touch the resin directly.
What is Breather cloth?
A balanced, symmetric laminate whose in-plane elastic properties are approximately identical in all directions, such as a [0/45/90]s stack.
What is Quasi-isotropic?
Curing two or more uncured composite details together in a single step, bonding them via their own matrix.
What is Co-curing?
The cumulative clock time a perishable prepreg material has spent out of the freezer, which directly reduces its remaining working life.
What is Out-time?
Thin blue adhesive tape used under the vacuum bag to hold down thermocouples or caul plates, and applied to tools to protect the bare metal from mold release.
What is Flashbreaker tape?