Fracture

A material which fails before the onset of plastic deformation
(glass, ceramics) is said to exhibit Brittle Fracture. One that shows
plastic deformation before fracture exhibits Ductile Fracture.

In a uniaxial tensile test at constant strain-rate, a brittle fracture surface
is approximately planar and normal to the tensile axis.

Under the same conditions, a ductile material shows a rough "cup & cone"
fracture surface of the type shown opposite. In the central region, this is
approximately normal to the tensile axis, but in the outer regions the failure
occurs at about 45 degrees to the tensile axis, forming a cup on one
surface and a cone on the other. In the picture, the final shear failure at
45 degrees to the vertical tensile axis has a region on both parts of the
fractured sample. This is a common feature that depends on the details
of the stress distribution in the neck region.