creep case studies. the creep of lead water pipes the two examples of sagging lead pipes analysed in...
TRANSCRIPT
CREEP
CASE STUDIES
THE CREEP OF LEAD WATER PIPES
The two examples of sagging lead pipes analysed in this case study. All dimensions are in mm.
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.
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.
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.
Range of temperature Range of Stressσs/µ
Maximum acceptablestrain rate
0.45–0.58 TM 0→2.3 x 10-3 ~10-8 /s
Summary of average steady running conditions on blade
Improvements in blade microstructure
EquiaxedCrystal Structure
DirectionallySolidified Structure
Single Crystal
From Cervenka, Rolls Royce, 2000
A map for pure nickel with a grain size of 100 µm, showing the conditions of
operation of the blade
A map for MAR–M200, 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.
A map for MAR–M200 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.
“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.
Typical light bulb specifications
110 volt single-coiled lamps 25 Watt 40 Watt
Burning temperature (°C)Design life (s)
Turns/metre (m-1)Spacing of turns, S (mm)Wire diameter, d (mm)Coil diameter, 2R (mm)
Total length of wire (mm)Total length of coil (mm)Total mass of coil (mg)Number of intermediate
supports
2250–23503.6 x 106
2.6 x 104
0.0380.0300.15660419.03
2400–25003.6 x 106
2.4 x 104
0.0430.0360.14430417.23
Power of lamp Range of σs/μ Range of T/TM Maximum
25 Watt40 Watt
0→1.0 x 10-4
0→6.2 x 10-5
0.68→0.710.72→0.75
3.0 x 10-9
3.6 x 10-9
Summary of conditions under which filaments operate
Typical dimensions of a 40 Watt, 110 Volt,
tungsten filament lamp. The filament is a simple
coil of doped tungsten
THE CREEP OF TUNGSTEN LAMP FILAMENTS
