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Dr. Dmitri Kopeliovich

Kevlar is the trade name (registered by DuPont Co.) of aramid (poly-para-phenylene terephthalamide) fibers.

Kevlar fibers were originally developed as a replacement of steel in automotive tires.

Distinctive features of Kevlar are high impact resistance and low density.

Kevlar fibers possess the following properties:

High tensile strength (five times stronger per weight unite than steel);
High modulus of elasticity;
Very low elongation up to breaking point;
Low weight;
High chemical inertness;
Very low coefficient of thermal expansion;
High Fracture Toughness (impact resistance);
High cut resistance;
Textile processibility;
Flame resistance.

The disadvantages of Kevlar are: ability to absorb moisture, difficulties in cutting, low compressive strength.

There are several modifications of Kevlar, developed for various applications:

Kevlar 29 – high strength (520000 psi/3600 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used for manufacturing bullet-proof vests, composite armor reinforcement, helmets, ropes, cables, asbestos replacing parts.

Kevlar 49 – high modulus (19000 ksi/131 GPa), high strength (550000 psi/3800 MPa), low density (90 lb/ft³/1440 kg/m³) fibers used in aerospace, automotive and marine applications.

Kevlar 149 – ultra high modulus (27000 ksi/186 GPa), high strength (490000 psi/3400 MPa), low density (92 lb/ft³/1470 kg/m³) highly crystalline fibers used as reinforcing dispersed phase for composite aircraft components.

Kevlar filaments are produced by extrusion of the precursor through a spinnert. Extrusion imparts anisotropy (increased strength in the lengthwise direction) to the filaments.

Kevlar may protect carbon fibers and improve their properties: hybrid fabric (Kevlar + Carbon fibers) combines very high tensile strength with high impact and abrasion resistance.

The most popular matrix materials for manufacturing Kevlar (aramid) Fiber Reinforced Polymers are Thermosets such as Epoxies (EP), Vinylester and Phenolics (PF).

Kevlar Fiber Reinforced Polymers are manufactured by open mold processes, closed mold processes and Pultrusion method.