The New Student's Reference Work/Testing-Machine

Test'ing=Machine, a machine for testing materials. Testing-machines are arranged so as to apply measured forces to a sample of the material and to observe the corresponding deformation or breaking of the sample. The common tests are stretching, crushing, bending and tension. It is usual to apply the force either by a system of levers or by means of a hydraulic press. The forces are usually measured by a scale-beam. When large samples are to be tested, as long, heavy beams, the machine must be very large. The largest and finest testing-machine ever constructed is that at the Watertown arsenal, belonging to the United States government. It can exert a force of 450 tons, and yet it is extremely sensitive. At the time of its trial a rod of iron five inches in diameter was broken with a measured force of 722,000 pounds and immediately afterward a horse-hair was broken with a measured force of one pound. For loads of 200 pounds it is sensitive to less than one two-millionth of the whole. Testing-machines have so many special forms and appliances that special treatises must be consulted for details. See Unwin's Materials of Construction.