**2.3 Dynamic test**

High strain rate tests were performed using a split-Hopkinson pressure bar apparatus available in the Aerospace Structures Laboratory at Instituto Tecnológico de Aeronáutica (ITA) composed by three cylindrical bars: striker, incident, and transmitted bar. All three bars are made of high strength steel AMS 5629 with Young's modulus of 198 GPa, density of 7700 kg/m3 , yield stress of 1.4 GPa, and diameter of 19.05 mm. Striker length is 350 mm, and incident/transmission bars have 1000 mm, with length/diameter ratio of 50.0, that ensures the validity of unidimensional wave propagation assumption. The strain measurement system has four strain gauges HBM, model LY11–3/350 with 3 mm grid enabling measurements up to 100 kHz, which are disposed diametrically opposed in order to compensate bending and are located at 50 cm of the contact edge between specimen/incident bar and specimen/transmitted bar, respectively, and a data acquisition and conditioning system HBM Genesis 7 t, with a 16 bit resolution analog/ digital card, four strain gauge channels, and sampling rate of 1 MHz. The present configuration has a momentum trap after the transmission bar to preserve the strain gauges [29, 39]. Additionally, a Photron high-speed imaging system (HSIS) composed of a high-speed camera model FASTCAM SA-Z and FASTCAM analysis software was set up with the SHPB apparatus to capture videos and images during the experiments. **Figure 4** shows the schematic SHPB testing setup used for the dynamic tests.

Data acquisition and conditioning system signals were post-processed using an in-house Python program, which computes the stress, strain, and strain rate on the specimen using the classical SHPB analysis based on the one-dimensional wave propagation theory, which implies elastic deformation in the bars during the tests, unidirectional elastic pulses propagate along the bars, uniform deformation process in the specimen, and no dispersion of waves throughout the bars and the specimen [11, 24, 26, 28, 29].

Tests were done at two different pressure values in the air chamber, 1.2 and 1.6 bar, which correspond to two different strain rates for each material (558.5 and 891.1 s<sup>−</sup><sup>1</sup> for glass fiber, and 400.5 and 832.2 s<sup>−</sup><sup>1</sup> for carbon fiber).

Stress-strain database were used to build up the stress–strain curves for specimens tested in dynamic regime and to calculate mechanical properties (peak stress, strain at peak stress, and Young's modulus). Experimental Young's modulus is determined as the slope of the linear regression (LR) applied to the stress-strain curve in the range of strain data between 0.7 and 1%.

**33**

*High Strain Rate Characterization of Thermoplastic Fiber-Reinforced Composites…*

Digital image correlation (DIC) technique was used to measure strain during dynamic tests using the HSIS images obtained. 2D deformation vector fields and strain maps were built for specimens at each high strain rates tested, obtaining strain measures in an overall area and along an inspection line (L0) at each deformation state (**Figure 5**). Strain data from the center portion of the inspection line (L0) was synchronized with stress data from SHPB apparatus, and stress-strain curves were built using strain measured by DIC in order to compare the DIC-based results with the results obtained

*Inspect line L0 (middle white line) and overall area (purple square) used for DIC measurements.*

Quasi-static tests are performed to failure, under the three deformation rates

obtained for each strain rate applied, while **Table 1** summarizes the post-processed results. The results obtained show that material's peak stress remains constant under quasi-static regime with an average value of 532.603 MPa; this is based on the low value of the standard deviation (std. dev.) and the coefficient of variation (CV). The same

). **Figure 6** shows stress-strain curves

from SHPB strain gauge measurements and quasi-static regime results.

**3. Experimental results and discussion**

**3.1 PPS carbon fiber-reinforced composite**

previously specified (0.001, 0.01, and 0.1 s<sup>−</sup><sup>1</sup>

*3.1.1 Quasi-static tests*

*DOI: http://dx.doi.org/10.5772/intechopen.82215*

*Schematic SHPB apparatus and HSIS set up.*

**2.4 Digital image correlation**

**Figure 4.**

**Figure 5.**

*High Strain Rate Characterization of Thermoplastic Fiber-Reinforced Composites… DOI: http://dx.doi.org/10.5772/intechopen.82215*

**Figure 4.** *Schematic SHPB apparatus and HSIS set up.*

*Aerospace Engineering*

**2.3 Dynamic test**

*Quasi-static compression test setup.*

**Figure 3.**

dynamic tests.

[11, 24, 26, 28, 29].

891.1 s<sup>−</sup><sup>1</sup>

High strain rate tests were performed using a split-Hopkinson pressure bar apparatus available in the Aerospace Structures Laboratory at Instituto Tecnológico de Aeronáutica (ITA) composed by three cylindrical bars: striker, incident, and transmitted bar. All three bars are made of high strength steel AMS 5629 with

diameter of 19.05 mm. Striker length is 350 mm, and incident/transmission bars have 1000 mm, with length/diameter ratio of 50.0, that ensures the validity of unidimensional wave propagation assumption. The strain measurement system has four strain gauges HBM, model LY11–3/350 with 3 mm grid enabling measurements up to 100 kHz, which are disposed diametrically opposed in order to compensate bending and are located at 50 cm of the contact edge between specimen/incident bar and specimen/transmitted bar, respectively, and a data acquisition and conditioning system HBM Genesis 7 t, with a 16 bit resolution analog/ digital card, four strain gauge channels, and sampling rate of 1 MHz. The present configuration has a momentum trap after the transmission bar to preserve the strain gauges [29, 39]. Additionally, a Photron high-speed imaging system (HSIS) composed of a high-speed camera model FASTCAM SA-Z and FASTCAM analysis software was set up with the SHPB apparatus to capture videos and images during the experiments. **Figure 4** shows the schematic SHPB testing setup used for the

Data acquisition and conditioning system signals were post-processed using an in-house Python program, which computes the stress, strain, and strain rate on the specimen using the classical SHPB analysis based on the one-dimensional wave propagation theory, which implies elastic deformation in the bars during the tests, unidirectional elastic pulses propagate along the bars, uniform deformation process in the specimen, and no dispersion of waves throughout the bars and the specimen

Tests were done at two different pressure values in the air chamber, 1.2 and 1.6 bar, which correspond to two different strain rates for each material (558.5 and

Stress-strain database were used to build up the stress–strain curves for specimens tested in dynamic regime and to calculate mechanical properties (peak stress, strain at peak stress, and Young's modulus). Experimental Young's modulus is determined as the slope of the linear regression (LR) applied to the stress-strain

for carbon fiber).

for glass fiber, and 400.5 and 832.2 s<sup>−</sup><sup>1</sup>

curve in the range of strain data between 0.7 and 1%.

, yield stress of 1.4 GPa, and

Young's modulus of 198 GPa, density of 7700 kg/m3

**32**

**Figure 5.** *Inspect line L0 (middle white line) and overall area (purple square) used for DIC measurements.*
