i l - 3
«is -§§§¿■3
0m® S §|2a£S
O%
ss
1 : : 1 : l eo
•s to : S -*
g «
s CO
? : : rH : ? : 2 .
1 fl
D O O O O O 0 s |
0*^3 O OJ OO 000^004
¿f^5 iO>K A to »O *0 c-3 IQ ■** US »O OOO WO C5 O *0 O ^ ? *?“ *■? U? S1 ?
... -*-••• -* *- n. m Q 92 S? !£3
o«ocb oi
to s co
HC) <M C3 t^c>
ia Co Cl ‘-'5 r-*<2>
»OiO «>« <M <M rH 1-1 i-i a a
aft *Q *Q M O M C>C1 O > 5 ? > O <2» o ^ ? S ’ S 1 ""^
•*«?<*»» CO - r ¿£2 i « r-< S fa C4CO « ©•» r-i •*■• 3 ^ ° * a ‘3 C^OiOs^M «(MO O}«
1 5 N N « ».-S ITS r t O
«1-1'M‘O C* C* «
< ¿ ¿ 0 0 0 0 0 ¿ 0
0 0> OC)0 'T|
OCI O^ Oto COOC5
•3 -3 I I
*2 ' 30 <
‘ ¿ I *
••o 2 *
Is go^
,.S .1 id !*
S8?l si 8" .giS
« «S a
B S g p d g l d S. . S o £ o £ „ g.S_ .. s n ?
1 1 . K
¿4
I .3 1 3 ■*>• ~
s s 1 s
a l i i i s l i s p a S f e f e i i
vb q C oj o c c-?, a » nco c Cuj o Co ap oj o g .:
S i l l s I i l l i l i l g § 1 * e l s I l s I f £ s h
TableII.—Non-Ferrous Materials. Figures in ordinarytype - High-Speed Tensile Test Eeaulte. Figures in Itolio- Slow-SpeedTensileTest Eesults. * Fractureslightlydamaged.
TableIII.—Analyses of Ferrous Materials.
M Tj< CO « ^
o o o o o
o o o o o
m O 1.0 ^ IO
o o ■-< o o o o o o o
P4
1.0 O CO Tt* CO CO O H CO C O O O O h
¿ 6 6 6 6 6
m
lO l-O O Ol CO W fN C i h -0 -0 -0 9 -0 9
6 6 6 6 6 6
A -* CO »0 —< 00 0 I - 1.0 I’- C O O ’ t 0 0 0 0 0 0
«3
"rff ■—(
W5 0 w ^ 0 0
6 6 6 6 6h
d
l O t C C i O C O 1.0
»7« CO -* 17 CO 19
6 6 6 6 6 «
"5 oei
CarbonSteels : E.B. B.C. E.D. E.E. E.r. Cast Iron
Î3 K
O 0-043
*3in rH9 6
V
i/5 co ^Oi <>J 6 6
to CO 9 co 0 6 6
3 0
0
S r-4 O 9 0 6 6 V <0-01 <0-01
I 0 0 6 6 V V
*-* O O O 6 6 V
rc3 CO 00 0 6 6
CO 01.0 '■f 6 6
j5 P4
rH lO O O 6 6
V
AC/2 1— i>
* 6
Nà t" »O -f 9 Ol rj<6 6
t"r—
Th
CJu. CD CO tJ<9 uo t-~
6 6 6 0 M .0
CÏ 0 cq Th^
5 M • •
O 1
Copper 70: 30Brass 00: 40Brass AlnminiuraA1 2.L.32 . Duralumin
point in the other specimens. The fact that the vibration after the complete release of the load in the case of cast iron had not the datum line for its axis was accounted for in the design of the apparatus. Al
though a true diagram was not obtained, a mean line through the vibration could readily be drawn, and the vibration was extremely useful in showing the exact yield-point, as whilst the load was being applied uniformly no vibration could take place, since it was equivalent to steadily loading a spring system. At the yield-point a change of rate of loading took place, equivalent to a force in the opposite direction, which made the system vibrate. (The bottom of the recording appara
tus showed a movement of 0-0025 in., relative to the top, under a static load of 2-44: tons.) (See further discussion, p. 78.)
In measuring the yield-stress, the point on the diagram at which the vibration first showed was taken as the yield-point.
The maximum stress was measured by means of a mean line drawn through the vibration.
The natural frequency of vibration of the spring was 35-7 per second.
This was obtained by vibrating the beam by means of an electromagnet excited by a variable frequency generator.
The calculation of the time to fracture a specimen assumed no change in this frequency, owing to the presence of the specimen. A mathe
matical analysis showed that this assumption was justified.
The force due to the acceleration of the recording apparatus was estimated, and shown to give an error of less than 1 per cent, on the recorded load on the specimen.
The time taken to reach the yield-point was very small, and a high degree of accuracy could not be obtained in the measurement of this quantity. An average figure was 0-001 second.
Results.
The results are given in Tables I and II. The figures in italic type were obtained from tensile tests taking approximately 2 minutes in a Hounsfield Tensometer. The shanks of specimens broken in the high
speed tests were used to obtain test-pieces for this purpose. One only of each type was tested in this way. To check these results, speci
mens of the steels marked E.B. and E.F. were turned from bars in the
" as received ” condition, and broken in the Hounsfield Tensometer, and 0'564-in. diameter standard screwed end test-pieces made of these materials were pulled in the Avery testing machine. It was found that, whereas the results from the Hounsfield and Avery test-specimens in the
“ as received ” condition agreed quite closely, using the material from the shanks of broken specimens, the tensile strengths were higher than
those obtained for the “ as received ” material, suggesting some work- hardening. For this reason it must be assumed that unless the slow-test specimens were annealed, the recorded yield and maximum stresses for these materials in the Tensometer test are probably high.
Ferrous Alloys.
In general, the type of diagram obtained was similar in shape to the ordinary slow-test diagram (Fig. 3), except that the yield-stress in the lower-carbon steels was the maximum stress reached. The yield-stress was increased very considerably as compared with the slow test, but the maximum stress showed a much smaller increase. The type of fracture was the same as that obtained in the slow test (see Fig. 5, Plate Y). The percentage elongation and the percentage reduction in area were gener
ally slightly decreased. The yield in mild steel (E.B.) was sudden, as shown by the sudden and irregular vibration which was introduced at that point. The suddenness of the yield decreased as the carbon content increased.
A photomicrograph was taken of a mild steel (E.B.) specimen in a direction parallel to the line of application of the load ; this showed the typical distortion of the crystals in the direction of loading, and was indistinguishable in appearance from a similar section from a slow-test specimen.
Non-Ferrous Alloys.
In general, the type of diagram obtained was similar in shape to the slow-test diagram. Again, the yield-point was increased considerably, but the maximum stress showed comparatively less change. The appearance of the fracture was very similar to that obtained in the slow test (see Fig. 6, Plate VI).
The percentage elongations showed varying changes. Copper and the brasses showed a very slight decrease in percentage reduction of area, but the aluminium alloys showed a slight increase, as compared with the slow test.
An interesting result was obtained by breaking Duralumin very shortly after quenching; this showed that at that time the material was in a very soft condition, as age-hardening had not had time to start.
Su m m a r y.
The results varied considerably with different materials, but, in general, when materials were broken in tension at high speeds (the average time to reach the yield-point being 0-001 second, and an average
fracture taking 0-005 second), as compared with the properties obtained in the ordinary commercial tensile test,
(a) The yield-point was increased very considerably, over 100 per cent, increase being recorded for some materials.
(b) The maximum stress was increased by a much smaller amount.
(c) The percentage elongation and the percentage reduction of area showed comparatively small changes.
(d) The types of fracture were almost identical with those obtained for the slow test.
Ac k n o w le d g m e n ts.
The author’s thanks are due to Professor C. E. Inglis, who suggested the need for this investigation, and who gave the facilities to undertake it, to Dr. P. Postlethwaite for his assistance with the electrical technique, to Mr. E. Colbeck, and to the many members of the staff of the Engineering Laboratories at Cambridge for their help, and especially to Mr. A. Hall, who assisted with the experiments.
Re f e b e n c e s.
1 B. Hopkinson, Proc. Soy. Soc., 1905, 74, 498.
2 Proc. Amer. Soc. Test. Mat., 1922, 22, (II), 1-137.
3 F. Korber and H. A. von Storp, Milt. E. W. Inst. Eisenforschunq, 1925,7, 81; 1926, 8, 127.
1 H. Quinney, Engineer, 1936, 161, 669.
6 Brit. Pat. No. 448,130.
Ad d i t i o n a l No t e.
Table V (page 72) gives the values of the energy absorbed by the specimens during fracture. These were calculated from the areas under the load-elongation diagrams. In all cases the values are probably high, owing to the elongation recorded on the diagram being greater than that measured on the test-length of the specimens. This is due to the type of specimen that was used. The recorded elongation was that of the whole specimen including the shanks, together with any give under the heads of the specimen or in the apparatus.
72 Discussion on Ginns’ Paper
T a b l e V .—Energy Absorption During Fracture o f Specimens.
D iam eter, In ch .
E nergy to Fracture, F t.-lb.
Fe r r o u s Ma t e r ALS.
Carbon Sleds.
E.B. As received . . . . 0-252 92
Annealed from 850° C. 0-252 86
Annealed from 900° C. 0-236 10 1
Quenchcd from 900° C. 0-252 58
, E.C. As received . . . . 0-252 90
E.D. „ . . . . 0-252 95
E.E. „ . . . . 0-226 55
E.F... . . . . 0-226 52
Cast Iron.
As recei ved. . . 0-292 4
No n- Fe r r o u s Ma tF.RIALS.
Copper.
As received. . . . 0-292 56
Annealed from 550° C. . . . 0-292 123
70 : 30 Brass.
As received. . . . 0-252 78
Annealed from 550° C. . . . 0-252 118
60 : 40 Brass.
As recei ved. . . 0-292 147
Annealed from 550° G. . . . 0-292 163
Aluminium Alloy : 2.¿.32.
As recei ved. . . 0-292 35
Duralumin.
As recei ved. . . 0-252 55
Annealed from 350° C. . . . 0-252 26
Quenched from 500° C. 0-252 32
Age-hardened at 150° C. 0-252 50