1908-9.] 
443 
End Friction in Crushing Tests. 
The strength, as calculated for the actual area at the middle of the bar, 
shows a decrease for the shorter specimens ; though the nominal strength, 
calculated for the original area, shows the usual increase. 
Original Ratio 
Length/Diameter 
or Length/Side. 
r> , • Original Area 
Ratl ° Final Area ' 
Crushing Stress, Tons per Square Inch. 
Calculated on 
Original Area. 
Calculated on 
Final Area. 
Round Bars, originally 1 Inch 
Diameter. 
1-44 
1-24 
40*5 
32*7 
U01 
U39 
38*9 
28*0 
0-51 
1-47 
44*2 
30*1 
Square Bars, originally 1 Inch Square. 
1*56 
1*13 
37*8 
33*5 
1-01 
U33 
42*0 
31*6 
0-51 
1*48 
45*3 
30*6 
9. Practical Determination of Compressive Strength from 
Crushing Tests. 
It would appear from the foregoing discussion that, in order to obtain 
the true compressive strength of a material by means of a crushing test it 
is necessary to reduce the friction at the ends of the specimen to zero. 
This result could be obtained only if the surfaces in contact were deformed 
at the same rate in contiguous parts throughout their whole area. The 
application of lubricants to the surfaces, for the purpose of reducing the 
end friction and of obtaining a closer approximation to the true crushing 
strength, is not to be recommended. For with specimens of high crushing 
strength the lubricant is soon squeezed out, and if the lubricant is possessed 
of a sufficiently high viscosity to allow a soft material to be crushed, it 
exerts a weakening influence upon the specimen. Graphite, boric acid, and 
similar solids possessed of lubricating properties are possible exceptions to 
this statement, but the writer has not yet investigated the effects of these. 
Summary. 
The effect of the friction of the crushing plates upon the yield point of 
short compression specimens has been investigated. 
With plates harder than the material under test, the end friction causes 
an increase in the apparent yield point. This increase is calculated as 
18 per cent, for wrought iron and mild steel, 20 per cent, for cast iron, and 
