Page 501 - Fluid-Structure Interactions Slender Structure and Axial Flow (Volume 1)

Appendix D

Experimental Methods for

Elastomer Pipes

The purpose of this appendix is to present some of the techniques, developed over the
past 30 years in the author’s laboratories, for manufacturing elastomer pipes, shells or
cylinders, as well as for determining some of their key physical properties. It is recalled
that experimentation with elastomer flexible structures translates into low-pressure test-
rigs, and hence easier experiments than with stiffer bodies, e.g. made of metal. In the
case of pipes, the home-made ones are far superior to those commercially available, as
explained for example in Section 3.5.6.

D.l MATERIALS, EQUIPMENT AND PROCEDURES

In most cases, the material used for making the flexible bodies is a room-temperature
vulcanizing (RTV) silicone rubber (e.g. ‘Silastic E RTV’ made by Dow Corning). It is
supplied in a two-component kit, and the two fluids, one of which is the catalyst, are
mixed in the prescribed ratio (typically 1O:l) just before manufacture. The mixture is
poured into a mould, cured, and then extracted, as described in what follows. Another
essential item is a liquid agent supplied by the manufacturer for coating surfaces to which
the silicone rubber should adhere; e.g. the edges of the metal strip sometimes embedded
in pipes (Figure D.l), which are thus constrained to oscillate in 2-D. A ‘releasing agent’
is also available, for coating surfaces on which the silicone rubber should not adhere at
all, e.g. the inner surface of the mould and the middle length of the metal strip. In what
follows, we shall continue using the moulding of a pipe as an example; a few words on
other structures are given in Section D.2.
Five basic pieces of equipment are required: (i) the mould; (ii) a large injector syringe;
(iii) a vacuum pump; (iv) a supply of compressed air; (v) a temperature-controlled oven
(optional).
A schematic of a mould for a pipe with an embedded metal strip is shown in
Figure D.2(a). It is basically composed of (a) a split outer mould and (b) a split cylindrical
core (or, when no metal strip exists, a whole cylinder). The outer mould is made of two
solid-block halves; after the interfaces are ground flat, semicircular grooves are carefully
milled in each with a ball end-mill, so as to produce a fine finish. Similar care should be
taken to make sure that the split core when sandwiching the metal strip is cylindrical and
of the required diameter. The mould can be made of Plexiglas to allow viewing while
casting or, for better dimensional tolerances and robustness, of brass. The alignment of

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