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The programme examines the use of theory of creep failure to predict premature failure in jet turbine blades.
Metadata describing this Open University video programme
Module code and title: T351, Materials under stress
Item code: T351; 14
First transmission date: 25-09-1976
Published: 1976
Rights Statement:
Restrictions on use:
Duration: 00:24:00
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Producer: David Nelson
Contributor: Roger R Jones
Publisher: BBC Open University
Keyword(s): CERL; Graphic animations; Grid pattern of temperatures and stresses; Models
Footage description: Ron Jones introduces the programme. He reviews the manufacturing process of the Rolls Royce Conway turbine blade, pointing to an actual blade to illustrate his points. Jones explains why the Conway blade was chosen to illustrate the theoretical approach to failure prediction in this programme. Jones lists the data which are needed to make a prediction of turbine blade life (stress distribution, temperature distribution and creep forces). He goes on to look, at two very simple models of a turbine blade as starting points for predicting blade life. Jones points out the forces acting on these models. Jones examines a scale model of the turbine blade. An animation shows the temperature distribution over a cross section of the blade. Another animation of a blade cross section is used to demonstrate the finite difference technique for calculating a temperature profile. For modelling purposes, Jones visualises a turbine blade as being made up of a series of parallel bars. He explains, with the aid of a blade cross section model, why a complex model of some 200 bars is needed to calculate thermal stress in a blade. He goes on to explain how stress is calculated from this data. Animations show a stress distribution calculated from data gathered by the above methods. Jones explains, briefly, why a combination of temperature distribution, stress distribution, and materials properties is needed to extend the model further. Jones at the Central Electricity Research Laboratories, lists the variables which are measured when doing a creep test. Demonstration of a creep test apparatus being prepared for an experiment. Commentary by Jones. Jones shows a graph to demonstrate how creep fore data from creep tests are displayed graphically. He goes on to explain how these data are put into computer readable form. Jones points out a problem with the elastic stress data input to the computer. He explains that the are time dependent and therefore vary with time. A diagram illustrates the point. Jones explains how this problem is overcome. An animated diagram of a blade cross section shows a typical computer run in which the computer predicts creep values for squares over the blade section surface. A failure criterion for creep rupture is checked for by the computer during each iterative run. Jones compares the computer prediction with actual failures in Conway engine blades. He points out how the predictive theories from computer modelling helped to overcome premature failures in the engine. Jones goes on to preview, briefly, the next programme and then sums up.
Master spool number: 6HT/72064
Production number: 00525_5265
Videofinder number: 1425
Available to public: no