Photoelastic study of the stresses near a cleavage crack

Photoelastic analysis has been used to determine the stress distribution near the tip of a cleavage crack. The crack bisects a slender rectangular bar along its length, and forces are applied at one end of it tending to open it out. The region of high stresses is localized in a region of the order of the half-width of the bar in size. Very near the crack tip, the stresses decrease in proportion to the inverse square root of the distance from the crack tip. The maximum gradient of the principal tensile stress lies at an angle of 70 to 80 deg from the plane of the crack. Contour maps of the principal stresses, the 45-deg shear stress and the maximum tensile stress are presented.