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Appearance of Fatigue Failure
The structural engineer has abandoned cast iron as a constructional material largely because of its lack of ductility in the tensile test and demands nowadays that all metals used for load carrying parts should possess appreciable ductility. Ductility is of course an essential requirement for fabrication but with the use of ductile metals has grown up the idea that a structural part will exhibit appreciable deformation and so give warning before it fails. This is true enough if failure is due to an overload once accidentally applied but large numbers of failures in service occur every year which give no such warning, are not preceded by any visible deformation even in materials with 20 per cent. or more percentage elongation, and are not caused by loads in excess of those for which the part has been designed. The fracture appears as a crack, that is a clean break, and its surface is generally of smooth, velvety appearance. An example of two such cracks in one welded beam is shown in Fig. I. All such failures are caused by a very large number of load applications, often all of them in the range of permissible stresses. The phenomenon is known as “Failure from Fatigue.”
Under the Chairmanship of the President the discussion was opened by Mr. L. R. Creasy (Hon. Secretary), Mr. F. R. Bullen (Past President) and Mr. T. N. W. Akroyd (Member of Council). This discussion took place against the background of the note that appeared in The Structural Engineer, January, 1968, p. 3.
An informal discussion on ‘ What is the responsibility of the structural engineer? ’ replaces the open discussion on the Joint Institution/Concrete Society’s Report on Reinforced Concrete Detailing which appears in the sessional programme for 11 January. It is expected that the Reinforced Concrete Detailing Report will now be published within the next few weeks and the open discussion upon its recommendations will be held when members have had an opportunity of digesting them.