**Figure 20.**

*Images sequence taken by HSIS for PPSGFC tested at 558.5 s<sup>−</sup><sup>1</sup> .* *High Strain Rate Characterization of Thermoplastic Fiber-Reinforced Composites… DOI: http://dx.doi.org/10.5772/intechopen.82215*

and dynamic regimes are compared (358.295 and 496.758 MPa), which is expected given that the determination of the peak stress is made with the same data. However, the increase in the strain at peak stress is just 21% based on the average values for each regime (1.676% quasi-static and 2.034% dynamic). The aforementioned affects the behavior of the Young's modulus, which presents an increase of 23% according to the average values for quasi-static and dynamic regimes (21.999 and 27.168 GPa). The behavior previously described is graphically evidenced in **Figure 23** where the properties' tendency with respect to the strain rate is shown.

**Figure 21.** *Images sequence taken by HSIS for PPSGFC tested at 891.1 s<sup>−</sup><sup>1</sup> .*

#### **Figure 22.**

*SEM images for PPSGFC tested at 891.1 s<sup>−</sup><sup>1</sup> . (a) "Melted" surface at 100× with 500× zoom of the marked zone, (b) "un-melted" surface at 100× with 500× zoom of the marked zone.*

*Aerospace Engineering*

mode I (opening) [44].

*3.2.3 Mechanical property comparison for PPSGFC*

that of the semi-static regime (2% increase).

The analysis of the fracture surface for the material tested at 891.1 s<sup>−</sup><sup>1</sup>

the development of two types of surface as in the PPSCFC on the highest strain rate. A surface appears "melted" (**Figure 22a**), while the other appears "unmelted" (**Figure 22b**). The "melted" surface exhibits signs of abrasive wearing possibly due to the movement between sheets observed on the HSIS images [50, 51], while the "unmelted" surface presents cusps (red circle) which appears to be the weft as in

The data obtained by the SHPB system (**Table 7**) evidence an increase of 27% on the peak stress when the average values for the quasi-static and dynamic regimes are compared (358.295 and 491.554 MPa). Similarly, the deformation on the ultimate stress is increased by 36% when the average values for the quasi-static and dynamic regimes are compared (1.676 and 2.647%). It was not evidenced a significant change in the Young's modulus for the material tested in the dynamic regime with respect to

According to the data obtained when strain is measured by DIC (**Table 8**), the tendency of strength increase is kept at 38% when the averages of the quasi-static

*Stress-strain curve obtained for PPSGFC with strain measured by DIC and SHPB strain gages under (a)* 

*.*

indicates

**44**

**Figure 20.**

**Figure 19.**

 *and (b) 891.1 s<sup>−</sup><sup>1</sup>*

*.*

*Images sequence taken by HSIS for PPSGFC tested at 558.5 s<sup>−</sup><sup>1</sup>*

*558.5 s<sup>−</sup><sup>1</sup>*


#### **Table 7.**

*Average mechanical properties for PPSGFC with strain measured by SHPB system.*


#### **Table 8.**

*Average mechanical properties for PPSGFC with strain measured by DIC.*

#### **Figure 23.**

*PPSCFC properties as function of the strain rate: (a) strength-strain rate plot, (b) ultimate strain-strain rate plot and (c) Young's modulus-strain rate plot.*

Results indicate that the material is strain rate dependent presenting an increase in the properties when strain rate applied increases, which is evidenced more accurately with DIC strain measurement and comparing it with the quasi-static results. The mechanical behavior observed on this material coincides with data reported for other similar materials in open literature (thermoplastic matrixes reinforced with glass fibers) [4, 16–18, 38, 52, 53].

**47**

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

The fractographic observation performed in both regimes indicates that the failure mechanism is not strain rate dependent since there is no significant variation in the failure aspects observed in specimens tested at high strain rates in comparison to those tested quasi-statically. The failure mechanism for the material is mixed (delamination and shear) in all the strain rates with a notorious dominance of the shear mode, which in the high deformation rates becomes balanced with the delamination. This behavior is expected due to the tendency of the glass fiber to fail at 45° when submitted to compression, and the laminate dilation turns the material more susceptible to delamination at high strain rates, according to Greenhalgh [40].

The mechanical behavior of the materials is linear elastic at all tested strain rates. Mechanical properties remain constant with respect to the strain rate applied for each regime. Results obtained for PPSCFC indicate compressive strength of 532.603 MPa, failure strain of 1.284%, and Young's modulus of 43.859 GPa for quasi-static regime and 534.93 MPa for compressive strength, 1.345% for failure strain, and 53.014 GPa for Young's modulus at high strain rates. PPSGFC results give compressive strength of 358.295 MPa, failure strain of 1.676%, and Young's modulus of 21.999 GPa for quasi-static regime and for the dynamic regime 496.758 MPa for compressive strength, 2.034% for strain failure, and 27.168 GPa for Young's

Comparing the obtained values for the mechanical properties calculated under the quasi-static and dynamic regimes, it is found that the PPSCFC exhibits a strain rate insensitive mechanical behavior with respect to the strain rates applied, while the PPSGFC is strain rate dependent, which means enhancement on mechanical properties when the strain rate increased. Compressive strength increases by 38%,

According to the strain spectrum obtained from the strain measurement by DIC, the strain measurement by the SHPB system shows the highest strain value in the specimen; however, due to the strain behavior at dynamic tests, it is better to perform strain localized measurement, in order to compare mechanical properties

The behavior for the PPSCFC reported herein is not in accordance with data and similar material reports elsewhere. This can be attributed to the fact that the resin used for this material (PPS) is semicrystalline and presents a reaction with the carbon fibers at the crystallization moment during the cooling, generating transcrystallinity on the fiber-resin interphase which affects the mechanical properties. Further studies

The behavior obtained for the PPSGFC is what is expected according to data and similar material reports published in the literature; the strain rate dependency of

must be performed to establish if this is why the material behavior is affected.

the mechanical properties is attributed to the viscoelasticity of the resin. The failure mode observed for the materials, in general terms, is mixed. Delamination and shear mode are identified, and it is observed that the failure aspects are not significantly affected by strain rates, which in tum leads to conclude that the failure mechanism is not strain rate dependent. The failure mechanisms are governed by the material configuration and the fiber-resin interphase more than the strain rate applied, which explain that typical fractographic characteristics for

composite materials submitted to uniaxial compression were developed.

Bigger efforts must be made to understand the generation and dissipation of heat during the material strain process for high strain rates to understand better their effect on the fractographic aspects of the material ("melted" surfaces).

failure strain increases by 21%, and Young's modulus increases by 23%.

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

**4. Conclusions**

modulus.

calculated in both regimes.

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

The fractographic observation performed in both regimes indicates that the failure mechanism is not strain rate dependent since there is no significant variation in the failure aspects observed in specimens tested at high strain rates in comparison to those tested quasi-statically. The failure mechanism for the material is mixed (delamination and shear) in all the strain rates with a notorious dominance of the shear mode, which in the high deformation rates becomes balanced with the delamination. This behavior is expected due to the tendency of the glass fiber to fail at 45° when submitted to compression, and the laminate dilation turns the material more susceptible to delamination at high strain rates, according to Greenhalgh [40].
