*3.1.2 Dynamic tests*

The dynamic tests are performed up to failure under two average strain rates of 400.5 and 832.3 s<sup>−</sup><sup>1</sup> ; all these tests achieved equilibrium forces on specimen's surfaces, which is evidenced in **Figure 8** where forces applied on each contact surface of the specimen are showed for a test under each strain rate.

Stress-strain curves and data obtained for each strain rate applied at dynamic regime (**Figure 9** and **Table 2**) evidenced that the mechanical behavior of the material is not significantly affected by the strain rate effects presenting an average strength of 530.237 MPa, failure strain of 2.141%, and elasticity modulus of 34.273 GPa when strain is measured by SHPB strain gauges.

The same behavior remains when strain is measured by DIC; however the strain measured on the center portion of the specimen by DIC is lower than SHPB strain of about 38.856 and 36.605% for 400.5 and 832.3 s<sup>−</sup><sup>1</sup> , respectively, which leads to

**35**

832.3 s<sup>−</sup><sup>1</sup>

**Figure 8.**

*(a) 400.5 s<sup>−</sup><sup>1</sup>*

 *and (b) 832.3 s<sup>−</sup><sup>1</sup>*

*.*

**Figure 7.**

*500×), (b) 0.01 s<sup>−</sup><sup>1</sup>*

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

an increase in the Young's modulus of about 90.65% for 400.5 s<sup>−</sup><sup>1</sup>

*Quasi-static failure modes observation by SEM for PPSCFC under (a) 0.001 s<sup>−</sup><sup>1</sup>*

 *(at 25× with amplified zone at 500×) and (c) 0.1 s<sup>−</sup><sup>1</sup>*

. This difference can be seen in **Figure 10**, where stress–strain curves with

*.*

strain measured by SHPB system and by DIC are shown at each tested strain rate. The strain map for the overall area at the moment of the failure obtained by DIC strain analysis indicates that strain value measured by strain gauges was reached

*Force equilibrium on the edge of the incident bar (red line) and transmitted bar (blue line) for PPSCFC under* 

and 71.606% for

 *(at 25× with amplified zone at* 

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

*Experimental results for PPSCFC at quasi-static regime.*

**Table 1.**

**Figure 6.** *Stress-strain curve obtained for PPSCFC at quasi-static regime.*

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


**Table 1.**

*Aerospace Engineering*

*3.1.1.1 Fractographic observation*

*3.1.2 Dynamic tests*

400.5 and 832.3 s<sup>−</sup><sup>1</sup>

load [40]. The specimens tested under 0.01 s<sup>−</sup><sup>1</sup>

the weft fibers and microbuckling (discontinued red line).

of the specimen are showed for a test under each strain rate.

34.273 GPa when strain is measured by SHPB strain gauges.

of about 38.856 and 36.605% for 400.5 and 832.3 s<sup>−</sup><sup>1</sup>

*Stress-strain curve obtained for PPSCFC at quasi-static regime.*

trend is observed for the Young's modulus obtaining an average value of 43.859 GPa. On the other hand, the strain at peak stress shows an average of 1.284% with a variation coefficient of 22.45%, which indicates that it varies considerably; however, it does not show a sensitivity on the strain rate or a correlation with a variation in the failure modes observed by fractographic observation, which indicates that dispersion in the measurements can be attributed to intrinsic errors in the measurement method. Having this in mind, it can be concluded that the mechanical behavior of the material is not strain rate sensitive within the strain rate range tested in the quasi-static regime.

Scanning electron microscopy (SEM) images for the specimens tested in the quasi-static regime can be observed in **Figure 7**. The material tested at 0.001 s<sup>−</sup><sup>1</sup> (**Figure 7a**) presents a mixed failure mode (shear, yellow arrows; delamination, red arrows) due to the configuration of the fiber. Woven fiber laminates commonly present delamination through the warp fibers and shear through the weft fibers. Additionally, local kinkbands (**Figure 7a**, discontinued white lines) are evidenced in the warp fiber bundles, which is common in compression load failure due to the microbuckling that is developed in the fibers aligned in the direction of the

present similar behavior, which is observed a mixed failure mode (delamination and shear) and the development of local kinkbands. The material tested at 0.01 s<sup>−</sup><sup>1</sup> develops intralaminar failure (discontinued yellow lines) related to the failure of

The dynamic tests are performed up to failure under two average strain rates of

faces, which is evidenced in **Figure 8** where forces applied on each contact surface

Stress-strain curves and data obtained for each strain rate applied at dynamic regime (**Figure 9** and **Table 2**) evidenced that the mechanical behavior of the material is not significantly affected by the strain rate effects presenting an average strength of 530.237 MPa, failure strain of 2.141%, and elasticity modulus of

The same behavior remains when strain is measured by DIC; however the strain measured on the center portion of the specimen by DIC is lower than SHPB strain

; all these tests achieved equilibrium forces on specimen's sur-

(**Figure 7b**) and 0.1 s<sup>−</sup><sup>1</sup>

, respectively, which leads to

(**Figure 7c**)

**34**

**Figure 6.**

*Experimental results for PPSCFC at quasi-static regime.*

#### **Figure 7.**

*Quasi-static failure modes observation by SEM for PPSCFC under (a) 0.001 s<sup>−</sup><sup>1</sup> (at 25× with amplified zone at 500×), (b) 0.01 s<sup>−</sup><sup>1</sup> (at 25× with amplified zone at 500×) and (c) 0.1 s<sup>−</sup><sup>1</sup> .*

#### **Figure 8.**

*Force equilibrium on the edge of the incident bar (red line) and transmitted bar (blue line) for PPSCFC under (a) 400.5 s<sup>−</sup><sup>1</sup> and (b) 832.3 s<sup>−</sup><sup>1</sup> .*

an increase in the Young's modulus of about 90.65% for 400.5 s<sup>−</sup><sup>1</sup> and 71.606% for 832.3 s<sup>−</sup><sup>1</sup> . This difference can be seen in **Figure 10**, where stress–strain curves with strain measured by SHPB system and by DIC are shown at each tested strain rate.

The strain map for the overall area at the moment of the failure obtained by DIC strain analysis indicates that strain value measured by strain gauges was reached

**Figure 9.**

*Stress-strain curves obtained under dynamic regime for PPSCFC. (a) 400.5 s<sup>−</sup><sup>1</sup> and (b) 832.3 s<sup>−</sup><sup>1</sup> .*


**Table 2.**

*Comparison of mechanical properties under high strain rates for PPSCFC.*

in localized points of the specimen, generally on the edges (2.25% in the DIC spectrum and 2.088% according to SHPB measure for 400.5 s<sup>−</sup><sup>1</sup> ; and 2437% on the DIC spectrum and 2.346% according to SHPB measure for 832.3 s<sup>−</sup><sup>1</sup> ). This indicates that dynamic test behaves according to the theory and generates deformation highly localized or not homogeneous along the specimen due to the test high speed [24–26, 28, 41, 42]; also, the value measured by strain gauges is a real value of strain within the specimen; however, this value is the highest reached in all the specimen; in consequence, it is wise to measure strain by the DIC technique to obtain an accurate value on the center of the specimen where it can be assured that the behavior of the material is not influenced by the effect of the edges, where higher tendency to failure can be present as a consequence of the specimen machining [43].
