*3.2.2 Dynamic tests*

The dynamic tests are performed up to failure under two average strain rates of 558.5 and 891.1 s<sup>−</sup><sup>1</sup> ; all these tests achieved equilibrium forces on specimen's surfaces which is evidenced in **Figure 17** where forces applied on each contact surface of the specimen are showed for a test under each strain rate.

According to the results (**Figure 18** and **Table 6**), material's mechanical behavior is constant for the dynamic regime presenting 491.554 MPa as peak stress, 2.647% as failure strain, and 22.498 GPa as Young's modulus when strain is measured by SHPB strain gauges.

**41**

**Table 5.**

**Figure 15.**

**Figure 14.**

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

*PPSCFC properties as function of the strain rate: (a) strength-strain rate plot, (b) ultimate strain-strain rate* 

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

*plot and (c) Young's modulus-strain rate plot.*

*Stress-strain curve obtained for PPSGFC under compression at (a) 0.001 s<sup>−</sup><sup>1</sup>*

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

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

 *and (c) 0.1 s<sup>−</sup><sup>1</sup>*

*.*

For this material it is also performed the strain measurement processing the high-speed videos under DIC, as it was done for the PPSCFC. **Figure 19** shows

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

#### **Figure 14.**

*Aerospace Engineering*

**3.2 PPS glass fiber-reinforced composite**

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

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

*3.2.1.1 Fractographic observation*

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

for each strain rate applied, while **Table 5** summarizes the post-processed results.

average value obtained for the peak stress for the quasi-static regime is 358.295 MPa with a coefficient of variation (CV) of 5.235%, which means that it is constant. Strain at peak stress and modulus presents the same behavior with values as of 1.676%–(CV) 8.875% and 21.999 GPa–(CV) 2.623%, respectively. Due to this it is

Fractographic observation by SEM for the PPSGFC specimens tested under quasistatic regime evidences a mixed failure mode (delamination and shear) for the laminate submitted to compression according to what is reported by Greenhalgh for fabrics [40]. **Figure 16** shows the failure modes for the three strain rates identifying delamination with red arrows and the shear with yellow arrows. The material tested at 0.001 s<sup>−</sup><sup>1</sup> developed an early stage kinkband (**Figure 16b**), which indicates basic failure mode for composites under compression [38, 40, 44]. **Figure 16e** indicates the formation of a

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

According to the results (**Figure 18** and **Table 6**), material's mechanical behavior is constant for the dynamic regime presenting 491.554 MPa as peak stress, 2.647% as failure strain, and 22.498 GPa as Young's modulus when strain is measured by

which is evidenced in **Figure 17** where forces applied on each contact surface of the

For this material it is also performed the strain measurement processing the high-speed videos under DIC, as it was done for the PPSCFC. **Figure 19** shows

; all these tests achieved equilibrium forces on specimen's surfaces

said that mechanical behavior remains constant in quasi-static regime.

fiber bridging characteristic of mode I delamination (opening) [44].

specimen are showed for a test under each strain rate.

). **Figure 15** shows stress-strain curves obtained

tests was discarded due to reload during the test. The

*3.2.1 Quasi-static tests*

**Table 4.**

Sample S1 for 0.001 s<sup>−</sup><sup>1</sup>

*3.2.2 Dynamic tests*

558.5 and 891.1 s<sup>−</sup><sup>1</sup>

SHPB strain gauges.

**40**

*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.*


**Table 5.**

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

#### **Figure 16.**

*SEM images for PPSGFC tested under quasi-static strain rates. (a) 0.001 s<sup>−</sup><sup>1</sup> at 25×, (b) marked zone in (a) at 100×, (c) 0.01 s<sup>−</sup><sup>1</sup> at 25×, (d) 0.1 s<sup>−</sup><sup>1</sup> at 25× and (e) marked zone in (d) at 250×.*

#### **Figure 17.**

*Force equilibrium on the edge of the incident bar (red line) and transmitted bar (blue line) for PPSGFC under (a) 558.5 s<sup>−</sup><sup>1</sup> and (b) 891.1 s<sup>−</sup><sup>1</sup> .*

the variation of the stress-strain curves built up with the strain data measured by SHPB and DIC. Results obtained for this material are similar to PPSCFC; the strain measured by DIC is lower in 25.495 and 19.627% for 558.5 and 891.1 s<sup>−</sup><sup>1</sup> , respectively, with respect to the deformation measured with the SHPB strain gauges. As it was expected, the peak stress remains equal what leads to modulus increase (38.054% for 558.5 s<sup>−</sup><sup>1</sup> and 6.553% for 891.1 s<sup>−</sup><sup>1</sup> ) with respect to the data obtained by the SHPB.

The behavior observed in the strain map obtained by DIC is the same to the one analyzed for PPSCFC; the highest strain is very close to the value measured by the SHPB system (2.437% DIC–2.573% SHPB at 558.5 s<sup>−</sup><sup>1</sup> ; 2.843% DIC–2.68% SHPB at 891.1 s<sup>−</sup><sup>1</sup> ), which reaffirms what was previously said; the SHPB system obtains the highest strain value in the entire specimen. Resulting strain in the specimen is not

**43**

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

*Stress-strain curves obtained under dynamic regime for PPSGFC: (a) 558.5 s<sup>−</sup><sup>1</sup>*

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

homogeneous along it and is more critical on the edges, and the measurement of the

The same that for PPSCFC, failure process monitoring is performed for PPSGFC through the high-speed image system; additional SEM post-failure observation was

on the specimen/transmitted bar contact edge and it propagates as delamination (**Figure 20b** and **c**, white arrow). A second crack front is developed on the inferior part of the specimen/incident bar contact edge in shear (**Figure 20c**, blue circle), which propagates and meets other crack front forming a "v" shape and continuing the propagation as delamination (**Figure 20d**), resulting in a mixed failure mode

mens tested in other strain rates. The beginning of the failure starts on the inferior region of the specimen/transmitted bar contact edge, and it propagates in shear (**Figure 21b**, blue circle); on its way it is bifurcated; and on one side, it continues in shear toward the superior opposite edge; and on the other side, it propagates as delamination forming a "v" shape in the material (**Figure 21c**, white arrows). Additionally, another crack front is developed on the superior part of the specimen/transmitted bar contact edge in form of delamination, which is propagated separating the part and allowing relative movement with respect to the other parts (**Figure 21d**). For this strain rate, the material is divided in

several parts which were submitted to SEM observation on the fracture surface.

(**Figure 20**) indicate that the failure starts

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

*.*

is similar to that observed in speci-

strain DIC allows obtaining data without the influence of the machining.

*3.2.2.1 Fractographic observation*

(delamination and shear).

Images for material tested at 558.5 s<sup>−</sup><sup>1</sup>

Failure behavior for the material tested at 891.1 s<sup>−</sup><sup>1</sup>

realized.

**Table 6.**

**Figure 18.**

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

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

**Figure 18.**

*Aerospace Engineering*

**42**

558.5 s<sup>−</sup><sup>1</sup>

**Figure 17.**

*(a) 558.5 s<sup>−</sup><sup>1</sup>*

**Figure 16.**

*100×, (c) 0.01 s<sup>−</sup><sup>1</sup>*

891.1 s<sup>−</sup><sup>1</sup>

and 6.553% for 891.1 s<sup>−</sup><sup>1</sup>

*.*

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

SHPB system (2.437% DIC–2.573% SHPB at 558.5 s<sup>−</sup><sup>1</sup>

*SEM images for PPSGFC tested under quasi-static strain rates. (a) 0.001 s<sup>−</sup><sup>1</sup>*

 *at 25×, (d) 0.1 s<sup>−</sup><sup>1</sup>*

the variation of the stress-strain curves built up with the strain data measured by SHPB and DIC. Results obtained for this material are similar to PPSCFC; the strain

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

 *at 25× and (e) marked zone in (d) at 250×.*

with respect to the deformation measured with the SHPB strain gauges. As it was expected, the peak stress remains equal what leads to modulus increase (38.054% for

The behavior observed in the strain map obtained by DIC is the same to the one analyzed for PPSCFC; the highest strain is very close to the value measured by the

highest strain value in the entire specimen. Resulting strain in the specimen is not

), which reaffirms what was previously said; the SHPB system obtains the

) with respect to the data obtained by the SHPB.

, respectively,

; 2.843% DIC–2.68% SHPB at

 *at 25×, (b) marked zone in (a) at* 

measured by DIC is lower in 25.495 and 19.627% for 558.5 and 891.1 s<sup>−</sup><sup>1</sup>

*Stress-strain curves obtained under dynamic regime for PPSGFC: (a) 558.5 s<sup>−</sup><sup>1</sup> and (b) 891.1 s<sup>−</sup><sup>1</sup> .*


#### **Table 6.**

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

homogeneous along it and is more critical on the edges, and the measurement of the strain DIC allows obtaining data without the influence of the machining.

#### *3.2.2.1 Fractographic observation*

The same that for PPSCFC, failure process monitoring is performed for PPSGFC through the high-speed image system; additional SEM post-failure observation was realized.

Images for material tested at 558.5 s<sup>−</sup><sup>1</sup> (**Figure 20**) indicate that the failure starts on the specimen/transmitted bar contact edge and it propagates as delamination (**Figure 20b** and **c**, white arrow). A second crack front is developed on the inferior part of the specimen/incident bar contact edge in shear (**Figure 20c**, blue circle), which propagates and meets other crack front forming a "v" shape and continuing the propagation as delamination (**Figure 20d**), resulting in a mixed failure mode (delamination and shear).

Failure behavior for the material tested at 891.1 s<sup>−</sup><sup>1</sup> is similar to that observed in specimens tested in other strain rates. The beginning of the failure starts on the inferior region of the specimen/transmitted bar contact edge, and it propagates in shear (**Figure 21b**, blue circle); on its way it is bifurcated; and on one side, it continues in shear toward the superior opposite edge; and on the other side, it propagates as delamination forming a "v" shape in the material (**Figure 21c**, white arrows). Additionally, another crack front is developed on the superior part of the specimen/transmitted bar contact edge in form of delamination, which is propagated separating the part and allowing relative movement with respect to the other parts (**Figure 21d**). For this strain rate, the material is divided in several parts which were submitted to SEM observation on the fracture surface.

#### *Aerospace Engineering*

The analysis of the fracture surface for the material tested at 891.1 s<sup>−</sup><sup>1</sup> indicates 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 mode I (opening) [44].
