Materials and Structure

The fracture surface associated with ductile fracture is shown in the photograph for a low carbon steel tested at high temperature. The top photograph shows the fracture surface at the center region of the fracture surface and the lower macroscopic pictures show the "cup" section of the ductile cup-cone fracture surface. In this case, voids formed at the center of the sample when neck formation starts at the ultimate tensile stress of the material join together to form a central failure surface with a mean orientation normal to the tensile axis. As this feature grows, the shear stress on the material closer to the sample surface increases and the final failure surface in the polycrystalline sample is at approximately 45⁰ to the tensile axis, the direction of maximum shear stress.

The microscopic picture shows the textured surface left by the joining together of voids and the local microscopic plastic deformation of the sample.

From: Schaffer et al, "The Science and Design of Engineering Materials," McGraw Hill (1999)