In thin sheets, tube walls, and small diameter rods, slant shear fracture may occur because through-the-thickness stresses re minimized that is, even though there may be a plane-strain condition, there may be minimal triaxial(hydrostatic tensile stresses Macroscopic examination can usually determine the direction of crack growth and hence the origin of failure. With brittle flat fractures, determination depends largely on the fracture surface showing a radial fanlike pattern of the type shown in Fig 3. Cracks propagate parallel to shear lips if they are present. Where fracture surfaces show both flat and slant surfaces, this can be the terminal end of a fast-moving brittle fracture where the crack speed has slowed significantly Crack extension can relax the stress so that final fracture occurs by slant shear fracture. Conversely, if a fracture has begun at a free surface, the fracture-origin area is usually characterized by a total absence of slant fracture or shear lip Fig 3 Surface of a fatigue fracture in a 4330V steel part. Chevron marks point to origin of fatigue in lower left corner. Arrows identify shear rupture along the periphery. Low-power examinations of fracture surfaces often reveal regions having a texture different from the region of final fracture. Fatigue, stress-corrosion, and hydrogen embrittlement fractures may also show these differences because the inal failure is due to overload after the cross section is reduced by one of the aforementioned crack-initiation modes Figure 4(a)shows the fracture surface of a steel tube and is an excellent example of the type of information that can be obtained by macroscopic examination. The V-shaped chevron marks and fanlike marks clearly indicate that the fracture origin is at the point marked by the arrow. This region, unlike the rest of the fracture, has no shear lip. The flat fracture surface suggests that the stress causing the failure was tension parallel to the length of the tube. The origin of the fracture as seen at higher magnification in Fig 4(b) shows several small fracture origins having a texture different from that of the remainder of the fracture surfaceIn thin sheets, tube walls, and small diameter rods, slant shear fracture may occur because through-the-thickness stresses are minimized; that is, even though there may be a plane-strain condition, there may be minimal triaxial (hydrostatic) tensile stresses. Macroscopic examination can usually determine the direction of crack growth and hence the origin of failure. With brittle, flat fractures, determination depends largely on the fracture surface showing a radial fanlike pattern of the type shown in Fig. 3. Cracks propagate parallel to shear lips if they are present. Where fracture surfaces show both flat and slant surfaces, this can be the terminal end of a fast-moving brittle fracture where the crack speed has slowed significantly. Crack extension can relax the stress so that final fracture occurs by slant shear fracture. Conversely, if a fracture has begun at a free surface, the fracture-origin area is usually characterized by a total absence of slant fracture or shear lip. Fig. 3 Surface of a fatigue fracture in a 4330V steel part. Chevron marks point to origin of fatigue in lower left corner. Arrows identify shear rupture along the periphery. Low-power examinations of fracture surfaces often reveal regions having a texture different from the region of final fracture. Fatigue, stress-corrosion, and hydrogen embrittlement fractures may also show these differences because the final failure is due to overload after the cross section is reduced by one of the aforementioned crack-initiation modes. Figure 4(a) shows the fracture surface of a steel tube and is an excellent example of the type of information that can be obtained by macroscopic examination. The V-shaped chevron marks and fanlike marks clearly indicate that the fracture origin is at the point marked by the arrow. This region, unlike the rest of the fracture, has no shear lip. The flat fracture surface suggests that the stress causing the failure was tension parallel to the length of the tube. The origin of the fracture as seen at higher magnification in Fig. 4(b) shows several small fracture origins having a texture different from that of the remainder of the fracture surface