A measure in the stiffness of a compound. It provides a measure of how complicated it can be to increase a material, with a price supplied with the ratio of tensile toughness to tensile pressure. ?????? ? ?? ????? ??????? ?? ????? ?? ???? ?? ?? ? ???? ????? ? ???? ? ???? ????? ????? ???? ?? ??????? ??? ???? ????? ???? ? ????? ??? ?? ???. In 1993,

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