THE WOOD AND ITS MECHANICAL PROPERTIES. 45 



the specimen and to do away with any friction at the end bearings. 

 The load was applied at the center by a screw testing machine. The 

 moving head of the machine descended at a uniform speed of 0.09 inch 

 per minute. The amount of bending was noted for each 100 pounds 

 increase in load up to the point where the stick began to give away, 

 after which the loads were read for each 0.1 inch increase in deflection. 

 The load bending curve was platted at the time of test, and the load 

 and deflection were recorded at first visible failure and at maximum 

 load. 



The following points were determined : Specific gravity as tested and 

 oven dry, weight per cubic foot as tested and oven dry, fiber stress 

 at elastic limit, modulus of rupture, modulus of elasticity, horizontal 

 shear at maximum load, work or resilience to elastic limit, work to 

 maximum load, and total work. 



Of these, the most important, in the consideration of a timber like 

 hickory, are the strength at maximum load, as shown by the modulus 

 of rupture, and work to maximum load. 



Strength at maximum load is a measure of the ability of the timber 

 to hold a load applied without shock. 



Work to maximum load is a measure of the ability of the timber 

 to withstand a shock or blow or any very suddenly applied load. 

 It is a measure of toughness. 



Other tests were also made in compression parallel to the grain, 

 compression perpendicular to the grain, shear, abrasion, shrinkage, 

 impact, and torsion. 



HICKORY WOOD AS COMPARED WITH OTHERS. 



None of the pines or other conifers compare with hickory in strength 

 and toughness. 



Of the broad-leaf trees, some varieties of eucalyptus have about 

 the strength of good hickory, but the grain is locky and the wood 

 hard to work; furthermore, they have not the toughness of hickory, 

 especially in the small sizes, where the locky grain might cause 

 failure. 



Hard maple wagon axles are more nearly comparable to hickory 

 than those of any other wood. Hard maple has about the strength 

 of hickory, though it is somewhat inferior in toughness. For this 

 use hard maple would be a good substitute for hickory, except for 

 the fact that it is likely to have twisted or spiral grain. White oak 

 is too useful for other purposes to be considered as a substitute for 

 hickory at the present time. Moreover, it is somewhat inferior to 

 hickory in strength and toughness. Red oak, carefully selected, 

 may be used as a substitute for the poorer grades of hickory. Ash 

 also may be substituted for hickory in some of its uses. While 



