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A television case study in the form of a failure investigation into an industrial accident.
Metadata describing this Open University video programme
Module code and title: T351, Materials under stress
Item code: T351; 01
First transmission date: 21-02-1976
Published: 1976
Rights Statement:
Restrictions on use:
Duration: 00:24:00
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Producer: David Nelson
Contributors: Geoffrey Hollister; Nick Reid
Publisher: BBC Open University
Keyword(s): Failure investigation; Industrial accident; Metallurgical examination; Optical microscope; Photo-elastic models; Stress analysis; Structural analysis
Footage description: Nick Reid introduces the programme. Ken Reynolds explains the circumstances of an industrial accident which is the case study for this programme; the failure of four bolts securing a cat walk over a bath of molten zinc thus throwing two men into the gas burners. Reynolds goes on to look at the failed bolts and cat walk gantry frame. He draws several preliminary conclusions as to the cause of failure. Reynolds briefly explains how a scanning electron microscope works and then examines two of the failed bolts under low magnification. Reynolds next demonstrates a special feature of the scanning electron microscope, the ability to display the spectrum of elements found just beneath the surface of the material examined. He displays the spectra of the elements found in the corroded bolt and concludes from this that the cause of failure of this particular bolt was stress corrosion due to the presence of chlorine. Reynolds confirms this scanning electron microscope diagnosis by examining a polished section of the bolt under the light microscope. Geoff Holister examines a bolt which has been treated by brittle lacquer technique. He points out the crack patterns which appear and confirms from this that the bolt failed in torsion by overtightening. Holister goes on to demonstrate a polariscope by inserting a plastic model of a bolt for examination. He explains how the areas of strees are shown up on this model. Ken Reynolds sums up the reasons for failure of these bolts. Holister next loads a model of the cat walk gantry beam into the polariscope to illustrate where the areas of stress are. He then removes the two bolts from the ends of the beam and again notes the areas of stress. Reynolds looks at optical and electron micrographs of the sheared bolts. He points out the characteristic grain flow and cup and cone surface of a bolt which has failed through mechanical overload. Reynolds lists a set of criteria which, if observed, would have prevented this particular industrial accident. Holister discusses steps which could be taken to minimise the risk of materials failure in general. He points out the value of continuous monitoring using strain gauges and demonstrates a strain gauge on a model structure. Ken Reynolds briefly demonstrates a very simple technique for detecting cracks in materials using a dye and an absorbent powder. Nick Reid sums up the programme.
Master spool number: 6HT/71952
Production number: 00525_5252
Videofinder number: 1370
Available to public: no