Grain Flow
About:
While installing this low carbon steel fastener to its specified clamp load, a crack formed internally and propagated to the periphery of the head. While the specimen shown here was only cracked, other samples experienced fracture where the top 1/2 or 2/3 of the head completely separated. Improper head forging caused the wire to buckle as indicated by the grain flow seen here. Grains in the origin of the crack were plate like (plates perpendicular to the axis of loading) resulting in poor axial strength between grains. Fasteners that fracture like this are usually limited to low carbon steels or non-heat treated steels and are a result of an issue called adiabatic shear banding.
