The tension test. 



The tension test piece is ent from one end of the broken beam. It is 16 inches long, 2J inches 

 wide, and li incites thick. Its tliickness at the center is reduced by cutting out with a band saw 

 circular segments, leaving a breaking section of some 2i inches by three-eighths inch. This 

 specimen is then placed between the plane wedge-shaped steel grips and pulled, the same as a 

 bar of iron in the Universal Machine (shown on Plate IV). This simple method has been found 

 very satisfactory in jjractice and is fully illustrated on Plate V. For this test care is taken to cut 

 the specimen as nearly parallel to the grain of the wood as iiossible, so that its failure will occur 

 in a condition of pure tension. 



The endwise compression test. 



Most of these test.s are made on sticks 4 inches square by 8 inches long, the ends having been 

 cut perfectly true and at right angles to the sides. They are tested in the Universal Machine, 

 the compression contiuning until the stick has been visibly crushed and has passed its maximum 

 load. Tlie crushing usually iiiauifests itself over a phxne section, by crushing down or bending 

 over all the fibers at this section, which may be either a right or an obli(iu(! section. The section 

 of failure, however, is seldem«it the very end. The slightest source of weakness may determine 

 its position, as a very small knot for example, for knots are a source of weakness, iu compression 

 as well as in tension. 



Some tests are made on columns 40 inches long by 4 inches square on the large beam machine, 

 but these usually fail the same as the short blocks, and not by bending sidewise. 



Compression across the grain. 



Specimens 4 inches square and C inches long are tested in compression across the grain. An 

 arbitrary limit of distortion, namely 3 per cent of the height, has been chosen as a reasonable 

 maximum allowable distortion in practice. 'I'liis limit is indicated iu the test by the ringing (d'an 

 electric bell and the load then on the specimen is called the compressive strength across the grain. 

 The test is then continued until the distortion has re-aclied l.T ]ier cent of its height, and l)o<h 

 results are given in the records. 



The shearing tests. 



Since timber fails by shearing or splitting ofteiier than any other way, this test becomes a 

 very important one. The specimen is taken 2 inches square and 8 inches long, and rectangular 

 holes mortised 1 in(!h from each end and at right angles to each other, as shown on Plate V. 

 The si)ecimen is then pulled, in the Universal Machine, by means of suitable stirrups and keys, 

 as shown in the plate. The ends are kept from spreading or splitting by putting on small 

 c]anii)s, with just enough initial stress in them to hold them in place. After one end shears ont 

 two auxiliary hoops or stiri-ups are used to conne<!t the key which sheared out to a i)iii ])ut 

 through the liole at the center of the specimen, as shown. The other end is then sheared, and two 

 results are obtained on planes at right angles to each other. In this way the shearing strength 

 is determined on two planes at right angles to each other. 



Test of full-sized columns. 



No set of experimental tests of timber would be complete without numerous tests on full- 

 sized columns. This requires a machine of not less than l,(M)(),(t(M) pimnds capacity, capable of 

 crushing to failure (columns from 12 to 14 inches square and at least 30 feet long. Such a machine 

 has been built expressly Hn- this work and is shown on Plate VI. It is cajiable of exerting a com- 

 pressive foi'ce of 1,000,000 pounds on a length of .'30 feet or less. The sides or tension mend)(>rs of 

 this machine are made of four long-leaf yellow pine sticks {Finm jialii.strus), from (ieorgia, eacli 8 

 by 12 inches and 45 feet long. The power is applied by the same hydraulic pump, which operates 



