Fiber-reinforced composites

A composite is a material made of two others that stay distinct but act together, each doing what the other cannot. In fiberglass the reinforcement is glass drawn into fibers thinner than a hair, which are extraordinarily strong when pulled along their length but, being glass, snap if bent sharply on their own. The matrix is a plastic resin — a thermoset like polyester or epoxy — which is tough and moldable but weak by itself. Embed the fibers in the cured resin and the resin holds each fiber straight, grips it along its length, passes load from one fiber to its neighbours, and blunts any crack before it can run through the whole part. The combination is far better than the sum: strong, stiff for its weight, and shapeable into anything a mould can hold.

Here was a structural material that was strong, light, electrically insulating, transparent to radio waves, and completely immune to the rust and rot that plague steel and wood — and it could be laid up by hand into complex curved shapes with no forging, casting, or machining, no press and no furnace. That combination did not previously exist. It gave designers a way to make large, strong, weatherproof shells cheaply, which is why fiberglass so quickly became the material of boat hulls, car bodies, tanks, and building panels.

The glass fiber came first, and partly by accident. Researchers at Owens-Illinois were chasing fine glass fibers when, in 1932, Dale Kleist tried to seal a joint between glass blocks with a spray gun built to throw molten metal; instead of a coating, the jet of compressed air tore the molten glass into a shower of fine filaments. Games Slayter developed the accident into a process for making glass wool in quantity, and Owens-Illinois registered the trademark "Fiberglas" in 1936; Owens-Corning was formed in 1938 to exploit it. The glass began as insulation and filtration, but paired with the new thermosetting resins of the late 1930s and 1940s it became glass-reinforced plastic, a structural material — famously used during the Second World War for aircraft radomes, where a strong shell transparent to radar was needed. The reason the thin fiber is so strong had already been explained by Griffith in 1920: strength is governed by surface flaws, and a fine fiber cannot contain a large one.

Fiberglass made moldable, corrosion-proof structures ordinary: pleasure-boat hulls, car and truck body panels, storage tanks, pipes, wind-turbine blades, printed circuit boards, and building cladding. More than any single product, it established the composite as a design principle — brittle fibers carrying load inside a tough matrix — and that principle carried straight on to the carbon-fiber composites now used in aircraft, spacecraft, and racing cars. It is the same bargain every time: take a material strong only as a thin thread, and lend it shape and toughness by casting it in plastic.