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Testing Machines (Used for the accurate testing)

machines used for the accurate testing of iron, steel and other materials used in constructive work. The problem which these machines are intended to solve is the adjustment with certainty of a safe margin of strength with a minimum of weight, which can be determined only by experimental tests on full sized sections of the materials used in the construction.

One method is to use machines designed to test small sample pieces under such conditions that the breaking strength of the test-piece is measured by the machine, and from the figures thus obtained is calculated the strength per square inch of the full-sized constructive material.

A common feature of such machines is the common steelyard balance, supported by knife edges. There are several machines of this class, some of them built up to 100,000 pounds capacity and over.

The hydraulic testing machine, invented by A. H. Emery, was originally used at the United States arsenal at Watertown, Mass. The greatest peculiarity of the Emery testing machine is the method by which the stress produced on the piece tested is conveyed to the scale and accurately weighed by mechanism that is entirely without friction, and hence responds to the same increment of load gardless of the amount of strain on the specimen. This result is accomplished by receiving the load against a flat closed cylinder called the hydraulic weighing head. One of the government experiments with this machine was the breaking by tension of a forged iron link ing by tension of a forged iron link 5 inches in diameter between the eyes, at a strain of 722,800 pounds, and immediately after a horse-hair of an inch 7 1000 in diameter was slowly strained, and, after stretching 30 per cent., snapped under the recorded strain of 16 ounces.