英语翻译
Outwardly directed normal stresses are called tension or tensile stresses and are considered positive.Shear stresses on a positive face of an element are positive if they act in the positive direction of a reference axis;such is the case in Fig.2-1a.The first subscript of a shear-stress component is the coordinate normal to the element face.The shear-stress component os parallel to the axis of the second subscript.Since the element shown is in static equilibrium,the negative faces will have shear stresses acting in the opposite direction;these are also considered positive.