Page:Report on the Shrivenham train crash of 15 January 1936 - MoT Shrivenham1936.pdf/17

 —continued.

I give below the results of my examination of the above broken drawbar hook

Description of fracture.

The hook broke in the position shown in the attached sketch in a plane at an angle of approximately 60 degrees to the axis of the drawbar. the fractured surface. having the appearance of a typical shock fracture. The cross-sectional area at the point of fracture was 5.9 square inches.

The whole of the face of the fracture was bright and had a coarsely crystalline appearance with the exception of a portion measuring 4 in. by 8 in. which extended inwards from the surface at the top of the hook. This area was covered with an oxide film and appeared to be a flaw which had been in existence for a considerable time and was produced probably during manufacture of the hook.

Chemical Analysis.

Analysis of the material adjacent to the fracture gave the following results:—

These results prove the material to be wrought iron. The proportion of phosphorus present in rather high, but not higher than is found frequently in iron having good physical properties.

Physical Tests.

Test pieces cut from the hook as close as possible to the fracture and in a direction parallel to the axis of the drawbar were tested with the following results:

A machined test piece measuring l½ in. by ¾ in. by 7 in. cut from the hook in a direction parallel to the axis of the drawbar broke when bent cold through an angle of 80° over a round bar 2½ in. in diameter.

The results of the tensile test are satisfactory for wrought iron of good quality. The Izod figure, however, is very low, being less than a third of that given by good quality iron. The result of the bend test is poor.

Macrostructure.

A sulphur print prepared from a transverse section adjoining the fracture showed the characteristic uneven distribution of sulphides normally encountered in wrought iron. In no part was there any indication of unduly high sulphur segregation.