Mechanical testing equipment for material characterization
A mechanical testing apparatus for a specimen is presented. The mechanical testing apparatus comprises a drop table system and a Hopkinson bar. The drop table system has a drop carriage. The Hopkinson bar is positioned parallel to a motion of the drop carriage and connected to the drop table system by the specimen.
1. A mechanical testing apparatus for a specimen, the mechanical testing apparatus comprising:
a drop table system having a drop carriage; and
a Hopkinson bar positioned parallel to a motion of the drop carriage and connected to the drop table system by the specimen;
wherein the drop table system comprises:
an impact plate having a threaded hole configured to hold a first end of the specimen, wherein the drop carriage is configured to move towards the impact plate;
an impactor connected to the drop carriage, the impactor configured to strike a pulse shaper associated with the impact plate;
an accelerometer connected to the impact plate;
a plurality of guide rods extending through the impact plate;
a plurality of springs surrounding each of the plurality of guide rods;
a bottom plate connected to the plurality of guide rods; and
a bumper connected to the bottom plate, wherein the bumper is configured to absorb momentum and stop the impact plate.
2. The mechanical testing apparatus of claim 1 , wherein the mechanical testing apparatus is configured to obtain a tensile stress-strain response of the specimen at intermediate strain rates in the order of 10 2 s −1 .
3. The mechanical testing apparatus of claim 2 , wherein the mechanical testing apparatus is further configured to obtain a tensile stress-strain response at higher or lower strain rates by varying an impact speed of the drop carriage of the drop table system.
4. The mechanical testing apparatus of claim 1 , wherein the specimen has a threaded engagement with each of the drop table system and the Hopkinson bar.
5. The mechanical testing apparatus of claim 1 , wherein a strain of the specimen is calculated as
ɛ
(
t
)
=
∫
0
t
ɛ
.
dt
=
∫
0
t
∫
0
t
a
(
t
)
dt
-
C
0
ɛ
0
(
t
)
L
s
dt
wherein a(t) is an acceleration history recorded by the accelerometer; C 0 is a speed of an elastic stress wave in a material of the Hopkinson bar; wherein
C
0
=
E
0
ρ
0
;
wherein ρ 0 is a density of the material of the Hopkinson bar; and L s is a gauge length of the specimen.
6. The mechanical testing apparatus of claim 1 , wherein the Hopkinson bar comprises a metal bar and a number of strain gauges connected to a surface of the metal bar.
7. The mechanical testing apparatus of claim 6 , wherein specimen stress is calculated as
σ
(
t
)
=
A
0
A
S
E
0
ɛ
0
(
t
)
,
wherein A 0 is a cross-sectional area of the Hopkinson bar, wherein A s is a cross-sectional area of the specimen, E 0 is a Young's modulus of the Hopkinson bar, and ε 0 is a bar strain recorded with the number of strain gauges.
8. The mechanical testing apparatus of claim 6 , wherein the metal bar is suspended by a spring attached to a first end of the metal bar.
9. A mechanical testing apparatus for a specimen, the mechanical testing apparatus comprising:
a drop table system having a drop carriage; and
a Hopkinson bar positioned parallel to a motion of the drop carriage and connected to the drop table system by the specimen;
wherein the drop table system comprises:
an impact plate configured to hold the specimen;
a plurality of guide rods extending through the impact plate;
a plurality of springs surrounding each of the plurality of guide rods;
a bottom plate connected to the plurality of guide rods; and
a bumper connected to the bottom plate, wherein the bumper is configured to absorb momentum and stop the impact plate.
10. The mechanical testing apparatus of claim 9 , comprising an accelerometer connected to the impact plate.
11. The mechanical testing apparatus of claim 9 , wherein the specimen is threadably engaged with each of the drop table system and the Hopkinson bar.
12. The mechanical testing apparatus of claim 9 , wherein the mechanical testing apparatus is configured to obtain a tensile stress-strain response of the specimen at intermediate strain rates in the order of 10 2 s −1 .
13. The mechanical testing apparatus of claim 12 , wherein the mechanical testing apparatus is further configured to obtain a tensile stress-strain response at higher or lower strain rates by varying an impact speed of the drop carriage.