有一平板內一點的應力態為σx=20 MPa,σy=-10 MPa,σxy=20 MPa之平面應力,求其最大主應力為多少MPa?
σmax = (σx+σy)/2 + √{[(σx-σy)/2]^2 + τxy^2}= 1/2*[20+(-10)] + √{[(20+10)/2]^2 + 20^2}= 15+25= 40 (MPa)