MECHANICAL PROPERTIES OF WOODS GROWN IN UNITED STATES. 15 
WORK TO ELASTIC LIMIT. 
Work to elastic limit in static bending is a measure of the work 
which a beam is able to resist or the shock which it can absorb 
without being stressed beyond the elastic limit as determined under 
slowly applied loads. 
WORK TO MAXIMUM LOAD. 
Work to maximum load in static bending represents the ability of 
the timber to absorb shock with a slight permanent or semi-permanent 
deformation and with some injury to the timber. Wood, especially 
in small sizes, can be bent somewhat beyond its elastic limit with only 
slight injury if the load is removed at once. Work to maximum load 
is a measure of the combined strength and toughness of a material 
under bending stresses. Superiority in this quality is the character- 
istic which makes hickory better than ash, and oak better than 
longleaf pine, for such uses as handles and vehicle parts. Many 
species yield butt cuts that exceed upper cuts in combined strength 
and toughness, hickory showing this characteristic most markedly. 
The superiority of butt cuts of hickory to upper cuts for ax handles 
is well known to experienced woodsmen. 
IMPACT BENDING. 
The impact bending test is made upon a beam 2 by 2 by 30 inches 
over a 28-inch span. A 50-pound hammer is dropped upon the stick 
at the center of the span, first from a height of 1 inch, next 2 inches, 
etc., up to 10 inches, then increasing 2 inches at a time until complete 
failure occurs. The deflections of the specimen are recorded on a 
revolving drum by a pointer attached to the hammer. This pointer 
also records the position the specimen assumes after the shock. 
Thus data are obtained for determining the various properties of the 
wood when subjected to shock. 
FIBER STRESS AT ELASTIC LIMIT. 
Fiber stress at elastic limit is the greatest stress to which a timber 
may be subjected under impact loading and recover immediately. 
Fiber stress at elastic limit in impact is approximately double the 
fiber stress at elastic limit in static bending. This is an expression 
of the fact that a small beam, if suddenly strained, bends approxi- 
mately twice as far to the elastic limit as when loaded slowly. (See 
also fiber stress at elastic limit, p. 13.) 
WORK TO ELASTIC LIMIT. 
Work in bending to the elastic limit in impact is a measure of the 
ability of a timber to absorb shock and recover therefrom imme- 
diately and without injury. The values apply only to resistance 
