ON IMPACT TESTS. 25 
A small style attached to the tup describes a curve on the drum as 
shown below :— 
The velocity of the tup before and after impact is v,=V tan a and 
Vv .=V tan B 
where V is the velocity of the drum. 
Connection is made to a chronograph, controlled from the testing 
laboratory, which indicates revolutions of the drum and 3 seconds, thus 
fixing V. 
We can therefore either calibrate the apparatus for any given hammer 
and height of fall, by dropping the tup without the insertion of the test- 
piece and calculating the per cent. loss of energy, or we can determine 
the actual loss for every test. The former method would be used for 
ordinary commercial testing, as the latter involves the use of a chronograph 
for every test. 
The former was used for R11 R19 R31 and 5960 steels, and the more 
accurate method for 3198 5184 2300 1324 and the gun steels. 
When the chronograph is not employed, the method of calculation 
is as follows :— 
Veloc. at A is v,=V tan a and at B is v»=V tan B 
2— Ih 2—9oh, .. J h end 2 2) v1" U9”) __ V,? 
VO S=4gN, Ve =SgGNg o. My — = 59 X (01 =aUs ag adeh Oc ). 
v7 
V_*_tan?p , bap __ tan? B 
But pF tanta hy—hy=h, (1 fan? a)" 
: tan? . 
The energy of rupture is therefore » [ Wh( 1 +Wh } 
~~ tan2a 
where h’ is the height between the zero line and point A and nis a 
constant less than unity determined by calibration of the machine as 
above. 
The height f, calculated in this manner is always less than the 
actual height h, and the difference h—h, due to frictional losses is greater 
as the weight of the hammer decreases. Let the weight of the hammer 
_ be 12 kilos. If sp = the speed of the drum in feet per sec. = 11°6 ee 
_ the velocity of the hammer at the moment of impact is :— 
11.6 n.7.d 
sp. tan B="49x%60 . tan B=n.k, tan B. 
