445 
RELATION OF TESTS. 
The relation betwéen the strength under various kinds of tests, such 
as shear, bending, etc., and compression parallel to the grain, have not 
been determined yet by an analysis of the data. It is doubtful if any 
one test can be used to predict the strength of the material under other 
forms of tests when conditions vary with respect to previous heat treat- 
ment, moisture, drying or preservative treatment. For instance, brittle- 
ness induced by overheating is evident in impact tests, but this will not 
necessarily be evident from the compression test parallel to the grain. 
An investigation of the effect of speed of test is a part of the general 
study of behavior of wood under three conditions of loading: 
(a) Dead or constant load. 
(b) Ordinary static test with increasing load. 
(c) Impact test. 
(a) Dead load tests exhibit the plasticity of wood. Nearly all defor- 
mations increase with duration of load, but the deformed beams subse- 
quently tested show no loss of ultimate strength. Deflection brought about 
by humid atmosphere is not recovered by subsequent drying. The ques- 
tion is often asked: “What per cent of the load, as determined by the 
ordinary static test, will break a beam if left on indefinitely?’ This has 
no answer. 
(c) Under impact loading, wood will submit to greater elastic defor- 
mation than under the ordinary static tests. Impact bending tests show 
elastic deformation largely in excess of those experienced under static 
load. The impact test is made under increasing height of drop.’ The order 
of resistance of air dry woods at the ultimate failure strength, so far 
obtained is as follows: 
Hickory, Longleaf Pine, Douglas Fir, Loblolly Pine, Chestnut, Spruce, 
Yellow Poplar, Western Yellow Pine, Western Hemlock, Sugar Pine, and 
Coast Redwood. 
(d) Abrasion Test. The abrasion test is under study." Wood is 
worn by sand-paper in the Dorrey Machine. 
5 Circular 38, Revised, Forest Service. ‘Instructions to Engineers in Timber 
Tests,” by W. K. Hatt. 
6 See American S. for '[T. M., Vol. 7, 1907. ‘P. U. Impact Testing Mach.,” by 
W. K. Hatt. 
