Definition
A two-part synthetic resin adhesive that cures into a hard, strong, chemical-resistant solid when a resin is mixed with a hardener in the correct ratio. Epoxy is widely used in aircraft structures as a bonding agent, a matrix for composite materials such as fiberglass and carbon fiber, and as a base for protective coatings and fillers.
Plain English
A strong glue or plastic-like material made by mixing two liquids together. Once mixed, it slowly hardens into a tough solid that holds parts together or forms the body of composite panels.
Context Anchor
Seen in airframe maintenance when working with bonded repairs, composite parts, sealants, and protective coatings.
Derivation
From the Greek 'epi-' meaning 'on' or 'upon,' combined with 'oxy-' from oxygen. The name refers to the chemistry of an oxygen atom bridging two carbon atoms, which is the reactive group that gives epoxy its bonding strength once cured.
Why Pilots Care
Used to restore or maintain the load-carrying ability of composite airframe parts; a poor bond can lead to structural failure.
Intuition Check
Epoxy does not mean any strong glue. In aircraft work, it means a resin system that must be mixed and cured correctly to reach its intended strength.
Example Sentence 1
The technician mixed the epoxy resin and hardener before laying the fiberglass patch over the damaged panel.
Example Sentence 2
Epoxy was applied to the spar repair to ensure the joint could carry flight loads.