CREEP

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CREEP CASE STUDIES
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THE CREEP OF LEAD WATER PIPES
Lead pipes on a 75-year-old building in southern
New England. The creep-induced curvature of these
pipes is typical of Victorian lead water piping.
The two examples of sagging lead pipes analysed
in this case study. All dimensions are in mm.
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A map for antimonial lead with a grain size of
50 µm, showing the conditions of operation of the
pipes. Both deform by diffusional flow.
Antimonial lead with a grain size of 1 mm. If the
pipes had this grain size they would deform much
more slowly than they do.
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CREEP OF A SUPERALLOY TURBINE BLADE
The approximate distribution of axial stress and
temperature along a turbine blade operating in
the first sage of a typical turbine of the 1960s.
When a turbine is running at a steady speed,
centrifugal forces subject each rotor blade to an
axial tension.  If the blade has a constant cross
section, the tensile stress rises linearly from
zero at its tip to a maximum at its root.  As an
example, a rotor of radius r of 0.3 m rotating at
an angular velocity   of 1000 radians/s (11,000
r.p.m.) induces an axial stress  of order 10-3 µ.
Summary of average steady running conditions on
blade
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Improvements in blade microstructure
Equiaxed Crystal Structure
Directionally Solidified Structure
Single Crystal
From Cervenka, Rolls Royce, 2000
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A map for pure nickel with a grain size of 100
µm, showing the conditions of operation of the
blade
A map for MARM200, with the same grain size as
that for the nickel of Fig. 19.10 (100 µm). The
shaded box shows the conditions of operation of
the blade.
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A map for MARM200 with a large grain size (10
mm) approximating the creep behaviour of
directionally solidified or single crystal
blades. The shaded box shows the conditions of
operation of the blade.
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Superalloys as a class constitute the currently
reigning aristocrats of the metallurgical world.
They are the alloys which have made jet flight
possible, and they show what can be achieved by
drawing together and exploiting all the resources
of modern physical and process metallurgy in the
pursuit of a very challenging objective. from
R.W. Cahn The coming of materials science, 2001.
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THE CREEP OF TUNGSTEN LAMP FILAMENTS
Typical light bulb specifications

Summary of conditions under which filaments
operate
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