A STRAIN INDICATOR
Year: 1884

page_text: 1, EDMUND CHARLES STROMEYER, of 22 Southampton Buildings, Chancery Lane,
London, Civil Engineer, do hereby declare the nature of my Invention for
"A STRAIN INDICATOR," and in what manner the same is to be performed to be
particularly described and ascertained in and by the following statement:―
The object of my Invention is the production of an instrument capable of
indicating strains, (i.e. minute deformations of solids), produced by variations of
stresses, temperatures, or any other causes.
The instrument is therefore capable of indicating the elongations and contractions
produced by such causes in test pieces, bridges, machinery, ships, and other
structures, and also of indicating the causes which produce deformations.
Consequently it can also be used for weighing objects, and for measuring
temperatures, and other forces.
My Invention is characterised by accuracy and by simplicity in action and
application.
In order that my Invention, and the methods by which it can be advantageously
carried into effect, may be thoroughly understood, I will proceed to describe its
construction and methods of application.
I provide two plates of any hard material, such as steel, iron, brass, glass or hard
stone. These plates must be smooth, but need not be polished, nor perfectly flat,
and either one or both may be grooved longitudinally.
These plates are pressed together by springs, or by their own or added weights.
Before using the instrument, a loose index spindle is inserted between the
plates, and the weights or springs are then adjusted so that the two plates do not
touch each other. The insertion of an extra loose spindle, or other equivalent
guiding arrangement, should, if possible, be avoided, because of the friction.
The loose index spindle is not carried in any bearings, but is held in its position,
only by the pressure and the friction of the plates.
The pressure on the plates should be sufficient to prevent any motion of the
index spindle, except its revolution around its own axis, or the rolling to bo
produced by the relative notion of the two plates.
The following application of the instrument to structures subjected to stresses
will also exemplify the most convenient methods of attachment under any
circumstances where my Invention is applicable. The details depend on the
requirements of each individual case, and in arranging thein, care should always be
taken that all external influences are either entirely eliminated, or accurately taken
into account.

page_text: 1. When the strains are to be measured between two points sufficiently close
together to be spanned by the instrument, the one end of each plate is firmly
attached to one of the two points, and the index spindle is then inserted between
the plates. The least elongation or contraction, between these two points, causes
the index spindle to revolve, and the amount of the deformation can therefore be
ascertained.
This mode of application will be found convenient for ordinary test pieces.
2. When the points between which the strains are to be measured, are incon-
veniently far apart, one of the plates can be fixed firmly to one of the points, while
the other plate is attached to the other point by a bar, or by a light wire tightly
stretched by a long spring or a weight. A weight should only be used on
stationary structures, and on account of the friction of the necessary pulleys, it
should only be used when the two points are nearly in a vertical line.
The above method of attachment will be found convenient when experimenting
on bridges, machinery, ships, or similar structures.
3. When the points, between which the strains are to he measured, are difficult
of access, as for instance when they are inside a tube, in spaces of extreme heat,
cold or pressure; or when they are under water, both plates can be attached to
their respective points by long bars or wires, as in the case just considered.
In all these cases, an elongation or contraction between the two points of
attachment, will cause the index spindle to revolve pari passu with the relative
motion of the plates, and the amount of either elongation or contraction can then
be read off.
When it desired to obtain a diagram of the variations of the strains, any suitable
apparatus and gearing for recording the position of an index, can be attached to
the instrument.
The instrument can be used for many useful and for scientific purposes.
Thus when measuring temperatures, the instrument can be attached, by any of
the preceding methods, to two materials having different coefficients of expansion.
If it is desired to ascertain local temperatures, the connecting wires or bars, the
two plates and any necessary springs, should all be of the same material, and of
equal dimensions. When it is desired to obtain the average temperature
surrounding the instrument, it is preferable to make one half of them of one, and.
the other half of the other material. Preferably, the two plates and the index
spindle should always be of the same material.
By attaching it to a ring or frame, or to an elastic tube or bar, it can be used
for weighing light or very heavy objects, or for measuring pulls or thrusts, and, if
necessary, diagrams of these forces can be obtained.
And now, having particularly described and ascertained the nature of my said
Invention, and in what manner the saine is advantageously carried into effect,
I declare that what I claim is :-
The use of two plates pressed together by any convenient device, and having
between them a loose spindle carrying an index, said plates being attached
respectively (and directly or indirectly) to the two points in the structure
between which any deformation is to be indicated, substantially as herein
described.