Crack characterization

In the following, general terms are explained which relate to cracks in castings. These denominations are mainly based on the crack-related terms mentioned in the Stahl-Eisen Testing Guidelines SEP 1100 (Part 1).

A crack is a material discontinuation which does not extend over the entire cross section of a casting or specimen (see Crack).

Crack origin:
The crack origin is the area where the discontinuation in the casting starts.


A microcrack is a crack of grain-size dimensions. If the grain size is not known, the term microcrack is commonly used for cracks which can only be detected under the light microscope from a magnification of at least 10-fold (in the metallographic specimen).

Incipient crack:
An incipient crack is a crack which is already present in the casting before it is subjected to stresses. The term stresses as used here means mechanical, thermal and chemical (corrosive) influences on the casting.

Crack front (crack tip):
The crack front is the boundary between the discontinued and continued casting material.

Crack flanks:
The casting material surfaces resulting from a discontinuation are known as crack flanks.

Crack length:
The crack length is the largest dimension of the discontinued casting section in the considered plane. This can refer to the dimension at the surface or in the metallographic specimen.

Crack depth:
The crack depth is the largest dimension of the crack in perpendicular direction to the considered (casting) surface.

Crack opening:
The distance between the crack flanks at the casting surface is called crack opening.

Capillary crack:
A capillary crack is a crack with a small crack opening which means that it is hardly detectable macroscopically or without aids.

Internal crack:
An internal crack is a material discontinuation without any link to the casting surface.

Main crack:

In the case of multiple cracks or a branched crack path, the main crack is the one with the greatest crack length.

Secondary crack:
A secondary crack is a crack starting at the main crack or branched off from it.

Crack path:
The crack path is the path of the discontinuation in the casting material.