Toughened Glasses are of high tensile strength. Its impact resistance is 5-6 times more than annealed glass.If this glass gets broken, it shatters into several small pieces, which do not cut or harm and thus offers optimum safety.
Stress is added to the glass intentionally to import strength because glass breaks as a result of tensil stresses that originates across an infinitesmial surface scratch compressing the surface increases the amount of tensil stress that can be endured before breakage occurs.A method colled themral tempering induces surface compression by heating the glass almost to the softening point and thn cooling it rapidly with an air blast or by plumping it into a liquid buth. . The surface hardens quckly the subsequent contraction of the slow cooling interior the glass pulls surface into compression. Surface compression approaching 24100 N/SQcm can be obtained in the glasses by this method. Toughened is usually done to client specification