Page 118 - Template Tesis UTM v2.0

Table 3.4 Specimen size for SHPB test

Sample Layup Thickness (mm) Diameter (mm)

1 G2/B3/G2 2.1 4.2

2 G2/J3/G2 4.2 8.4

3 G2/F3/G2 3.0 6.0

4 [G/B]3G 2.3 4.6

5 [G/J]3G 4.2 8.4

6 [G/F]3G 2.8 5.6
7 G7 3.0 6.0

8 B7 1.2 2.4

9 J7 5.0 10.0

10 F7 3.1 6.2

Typically, there are three types of waves that occur when dealing with SHPB

compression - incident wave, transmitted wave and reflected wave. Initially, the

generated pressure from nitrogen tank was transferred to the striker bar and the applied
pressure would accelerate the striker bar and collide with the incident bars. As a result

of the collision, the compression wave was generated and travelled down along the
incident bar and is known as incident wave ( ). Meanwhile, at the specimen interface,

the wave was partially transmitted into the specimen and referred to as the transmitted
wave ( ), the remaining wave was reflected and known as reflected wave ( ) due to

the impedance mismatch between the incident bar and the specimen. A relatively

uniform stress condition would be reached after a series of passages waves passed
through the specimen. Figure 3.12 presents the propagation behaviour of the elastic

stress waves via Lagrangian x-t diagram as suggested from a previous literature [113].

Prior to test, the piezoelectric strain gages were mounted between the incident bar and
the transmitter bar to capture the incident, reflected and transmitted pulse during the

collision. Due to the resistance change in the piezoelectric strain gages, the signals
measured from piezoelectric strain gages were converted into voltage signals by using

the Wheatstone bridge circuits. Then, the voltages were transferred and amplified
using a transducer amplifier. The amplified signals were then captured by a digital

oscilloscope with 12.5 MHz before being transferred to a computer for data processing.

88