monocoque

Monocoque, from the French term meaning "single shell," is a structural design in which the external skin carries most or all of the stresses of the structure, reducing or eliminating the need for a separate internal frame. The concept contrasts with frame-based constructions, where a rigid skeleton bears the primary loads, and with semi-monocoque designs that use internal stiffeners such as frames or stringers to share loads with the skin.

In practice, monocoque structures can be categorized as full monocoque, where the skin alone sustains the loads, and semi-monocoque, where the skin works in concert with internal supports. Full monocoque designs are less common in metal structures due to buckling and manufacturing challenges, while semi-monocoque configurations are widespread in both aerospace and automotive engineering. Modern use often favors a form of semi-monocoque construction, especially in steel or aluminum airplanes and in unibody automobiles and many carbon-fiber or composite structures.

Materials used for monocoque construction include metals such as aluminum and steel, as well as composites like carbon fiber reinforced polymers and fiberglass. In aviation, many fuselages and wings employ semi-monocoque designs with frames and stringers integrated into a stressed skin. In automobiles, the term is closely related to unibody vehicles, where the body shell provides structural integrity for the entire vehicle. In bicycles and consumer products, monocoque frames may be molded in one piece, typically from carbon fiber or advanced polymers, to enhance stiffness and reduce components.

Advantages of monocoque construction include improved stiffness-to-weight ratio and potential packaging freedom, while drawbacks can include repair difficulty and higher manufacturing costs compared with traditional frame-based approaches.