TESTING MACHINES, machines used for the accurate testing of iron, steel and other materials used in con structive work. The problem which these machines are intended to solve is the adjustment with certainty of a safe mar gin 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 ma chine, 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 ma chines 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 ac curately weighed by mechanism that is entirely without friction, and hence re sponds to the same increment of load re 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 experi ments with this machine was the break ing by tension of a forged iron link 5 inches in diameter between the eyes, at a strain of 722,800 pounnds, and imme 7 diately after a horse-hair — of an inch 1000 in diameter was slowly strained, and, after stretching 30 per cent., snapped under the recorded strain of 16 ounces.