ity ▁▁▁ ▁Fl uid ▁and ▁solid ▁character ▁are ▁relevant ▁at ▁long ▁times : We ▁consider ▁the ▁application ▁of ▁a ▁constant ▁stress ▁( a ▁so - called ▁cre ep ▁experiment ): ▁ ▁if ▁the ▁material , ▁after ▁some ▁de formation , ▁eventually ▁res ists ▁further ▁de formation , ▁it ▁is ▁considered ▁a ▁solid ▁ ▁if , ▁by ▁contrast , ▁the ▁material ▁flows ▁in def initely , ▁it ▁is ▁considered ▁a ▁fluid ▁ ▁By ▁contrast , ▁el astic ▁and ▁vis c ous ▁( or ▁intermediate , ▁vis co el astic ) ▁behaviour ▁is ▁relevant ▁at ▁short ▁times ▁( trans ient ▁behaviour ): We ▁again ▁consider ▁the ▁application ▁of ▁a ▁constant ▁stress : ▁ ▁if ▁the ▁material ▁de formation ▁stra in ▁increases ▁linear ly ▁with ▁increasing ▁applied ▁stress , ▁then ▁the ▁material ▁is ▁linear ▁el astic ▁within ▁the ▁range ▁it ▁shows ▁recover able ▁stra ins . ▁El astic ity ▁is ▁essentially ▁a ▁time ▁independent ▁processes , ▁as ▁the ▁stra ins ▁appear ▁the ▁moment ▁the ▁stress ▁is ▁applied , ▁without ▁any ▁time ▁delay . ▁ ▁if ▁the ▁material ▁de formation ▁stra in ▁rate ▁increases ▁linear ly ▁with ▁increasing ▁applied ▁stress , ▁then ▁the ▁material ▁is ▁vis c ous ▁in ▁the ▁Newton ian ▁sense . ▁These ▁materials ▁are ▁character ized ▁due ▁to ▁the ▁time ▁delay ▁between ▁the ▁applied ▁constant ▁stress ▁and ▁the ▁maximum ▁stra in . ▁ ▁if ▁the ▁materials ▁behav es ▁as ▁a ▁combination ▁of ▁vis c ous ▁and ▁el astic ▁components , ▁then ▁the ▁material ▁is ▁vis co el astic . ▁The oret ically ▁such ▁materials