Shock wave theory and function of protection vests regarding BABT (Behind Armour Blunt Trauma)

Some different models for BABT (Behind Armour Blunt Trauma) are presented. One model describes how fragments and also projectiles from revolvers and pistols are stopped by protective vests consisting of many woven layers of fibres. Another model describes how projectiles from high velocity weapons, namely rifles and the like are stopped or at least retarded by metal plates, whereby the metal deformation is of elastic-plastic nature. If the projectile velocity thereby is reduced to about the muzzle velocity of projectiles from revolvers and pistols, then the projectiles and eventual fragments from the metal plate can be stopped by woven layers of fibres (and clothes) behind the plate. A third model describes how rifle projectiles are stopped or retarded by ceramic plates, whereby there is initial penetration via crushing and backward ejection of fragments from the front surface of the plate. This is eventually followed by perforation and forward ejection of fragments from the rear surface of the plate. If the latter occurs, then the fragments and the projectile can be stopped by woven layers of fibres. The stopping ability of such layers depends on whatever is behind. Accordingly the result is different if the vest is hanging free in air or worn by a person or an animal. If the woven layers of fibres manage to stop the projectile and the fragments, then the displacement of the vest will generate elastic-plastic waves in biological or simulated biological material behind the vest. The character of such waves is described for an exact one-dimensional model. Such character is also representative for the three-dimensional waves generated by a moving vest. If the vest displacement is small then the waves may be restricted to be elastic, but with displacements corresponding to the "44 millimetre criterion" they are always elastic-plastic, and then the energy contents of the plastic part is quite dominant. Elastic waves (with small energy contents) propagate through the entire body (but with amplitudes that decrease strongly with increasing distance). Plastic waves (with big energy contents) are stopped in the vicinity of where they are produced.