Aircraft and Automobile Materials of Construction Volume 2 (Paperback)

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1921 Excerpt: ...Machines have been devised for testing specimen beams in bending impact; the beams are usually supported at the ends, and a heavy weight is caused to drop repeatedly upon the centre of the beam, the deflections being measured after each blow or recorded graphically. In the Olsen machine, shown in Fig. 93, the height of fall of the weight is increased See also Table LXXXIV on p. 263 and Table CVIII on p. 320. TABLE CIV. Shearing Strength Along And Across The Grain Of American Timbers. (U.S. Forestry Service Circular 213 and Trautwine.) Watertown Arsenal results upon small soason specimens, f Lanza's re3ults estimated from tests upon beams failing by shearing along neutral plane. 20--(5303) after each blow, and the deflections are continuously recorded right up to fracture. The total work done upon the beam is a measure of its bending impact resistance or strength. The value of the work done is generally computed from the deflection record, knowing the weight and height of fall. It is often arranged to measure the height of rebound after each fall, together with the deflection. The energy absorbed by the beam is given by the following relation: Energy absorbed=Weight Initial Height--Final Height. The heights are in each case measured from the same datum level--that is, from the original plane of the top surface of the beam. A typical bending impact test record taken at the first, fifth, tenth, and final or thirteenth blows, is represented in Fig. 94 for progressively increasing heights of fall of the hammer. Vertical distances such as H, measured above the datum line (taken as the initial line of the top of the beam), represent drops and rebounds of the hammer, and distances below the line such as D, deflections or springings of the beams. The alternating cha...