ft FOREST PRODUCTS LABORATORY. 



Industrial investigations. Methods and practices in the lumber and 

 other wood-using industries, grades, specifications, and mill scale studies. 



Pathology (in cooperation with the Bureau of Plant Industry). Decay 

 of timber, molds, stains in manufactured wood products, and antiseptic 

 properties of wood preservatives. 



TIMBER MECHANICS. 



N. 



Knowledge of the mechanical properties of woods and wood products is 

 essential for their intelligent and economic use, whether in the factory, on 

 the farm, in the home, on the railroad, in the mine, or in the air. Thus 

 development of the airplane and progress in many other lines depend 

 in a large measure on accurate information as to the strength, toughness, 

 elasticity, and other mechanical properties which determine the suitability 

 of different woods for various purposes. To supply this information, over 

 500,000 mechanical tests have been made, as nearly as possible under 

 standardized conditions, so that the tests made for a single purpose will 

 have the broadest application and will serve for many uses. 



STRENGTH OF VARIOUS SPECIES. 



Data from tests of small clear specimens are now available in 150 species 

 of woods grown in the United States, as well as data, in some cases 

 meager, in some cases fairly complete, on about 60 species, principally 

 from South America and the Philippines. These data are of particular 

 value in comparing the properties of the different species, in finding 

 substitutes for the scarcer and higher-priced woods, in selecting species 

 for particular uses, and in establishing correct working stresses. The 

 results of these tests on small clear specimens also furnish definite 

 information on the variability of wood and show the necessity of grading 

 timber for all uses where strength is of prime importance. 



A large number of tests have also been made on full-size'd timbers, 

 such as bridge stringers, factory-building timbers, and car sills. These 

 tests have demonstrated the influence of defects, such as knots, shakes, 

 and checks, on strength ; and, altogether with the results of tests on small 

 clear specimens, furnish the basis for the establishment of grading rules 

 and correct working stresses for structural timbers. 



Tests have been made on plywood to determine the strength of different 

 combinations of species, the effect of increasing the number of plies, and 

 the effect of varying the ratio of core thickness to total panel thickness. 

 Some data are also available on factors affecting warping, on strength 

 of fastenings for plywood, on the efficiency of joints in plywood, and on 

 the strength in tension. Information on such points as these places the 

 Laboratory in a position to assist users and manufacturers of plywood 

 and veneer products in solving problems encountered in developing new 

 uses for these products in the various industries. 



