英语翻译
Outwardlydirectednormalstressesarecalledtensionortensilestressesandareconsideredpositive.Shearstressesonapositivefaceofanelementarepositiveiftheyactinthepositivedirectionofareferenceaxis;suchisthecaseinFig.2-1a.Thefirstsubscriptofashear-stresscomponentisthecoordinatenormaltotheelementface.Theshear-stresscomponentosparalleltotheaxisofthesecondsubscript.Sincetheelementshownisinstaticequilibrium,thenegativefaceswillhaveshearstressesactingintheoppositedirection;thesearealsoconsideredpositive.