Bookbinding and the Conservation of Books
A Dictionary of Descriptive Terminology

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Elmendorf test

A standard test for determining the internal TEARING RESISTANCE of paper, named after its inventor, Armin Elmendorf. The Elmendorf test determines the average force in grams required to tear a single sheet of paper after the tear has been started. In conducting the test, one or more sheets are torn through a fixed distance by means of a pendulum. The effort expended in tearing is measured by the loss of potential energy of the pendulum. The scale of the device is calibrated to indicate the average force exerted. If multiple sheets are used, which is necessary if the reading for one sheet would fall below the scale, resistance of one sheet is determined by the formula: 
    grams of force X 16
    -------------------    = grams required to tear one sheet,
    number of sheets
where 16 is the conversion factor, unless an augmenting weight is added to the pendulum, in which case the conversion factor becomes 32.

The Elmendorf tester consists essentially of a stationary clamp, a movable clamp carried on a pendulum formed by a sector of a circle free to swing on a ball bearing, a knife mounted on a stationary post for starting the tear, means for leveling the instrument, means for holding the pendulum in a raised position and for releasing it instantaneously, and means for registering the maximum arc through which the pendulum swings when released. (72 )




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