*3.1.2.1 Fractographic observation*

The fractographic observation for dynamic regime is performed by monitoring the failure through the high-speed image system and SEM post-failure observation. **Figure 11** shows the sequence of the material's failure submitted to 400.5 s<sup>−</sup><sup>1</sup> where the red arrow indicates the direction of the compressive wave. It can be observed the specimen at the beginning of the failure without any failure indication in **Figure 11a**; in the next image (**Figure 11b**) is shown the beginning of the failure on transmitted bar/specimen edge (blue circle), which is attributed to material's edges weakening by machining effect. The beginning of the failure is given in the form of delamination, and then it is propagated diagonally or in shear mode (**Figure 11c**). Besides, other two crack fronts are initiated on incident bar/specimen edge (blue circle **Figure 11c**), which join in a "v" shape, and then it is propagated in delamination mode. The specimen finishes its failure process with a partial separation of the surfaces (**Figure 11d**).

**37**

**Figure 11.**

**Figure 10.**

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

*.*

*Images sequence taken by HSIS for PPSCFC tested at 400.5 s<sup>−</sup><sup>1</sup>*

*400.5 s<sup>−</sup><sup>1</sup>*

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

until the specimen is entirely divided in several pieces (**Figure 12e**).

different recovered parts of the material tested under 832.2 s<sup>−</sup><sup>1</sup>

The material's failure process observed by HSIS for strain rate of 832.3 s<sup>−</sup><sup>1</sup>

in **Figure 12**. The beginning of the failure is observed in two regions of the transmitted bar/specimen edge (blue circle) taking as reference the direction of wave propagation (red arrow) (**Figure 12b**). The upper region is submitted to bending, which is why the material looks bended upward, while the lower region develops two delamination fronts. The delaminations are propagated, while the bending on the upper region is intensified generating delamination and separation of the plies (**Figure 12c**) indicating failure of the resin, until the failure of the fibers under shear is initiated (**Figure 12d** yellow line). The propagation of the different crack fronts is prolonged

SEM fractographic observation was performed on the fracture surface of the

a surface that appears to be "melted," while **Figure 13b–d** presents other surface that is "unmelted." This behavior indicates that heat generation during the test may have affected the crystallinity degree of the thermoplastic matrix. The "melted" surface (**Figure 13a**) is characterized for being smooth and without any distinctive features; observation at high zooms show the presence of fibrils in the interior of a crack, which look like resin threads that try to keep the crack faces together and oppose the propagation. On the "unmelted" surface (**Figure 13b**), two zones can be observed, Z1 which seems to be a zone directly over the fabric (it is not possible to identify if it is warp or weft) and Z2 which seems to be an interstitial site or a high resin content site. The zone Z1 (**Figure 13c**) shows cusps and scallops (red arrows),

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

*.*

is shown

. **Figure 13a** shows

*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*

The material's failure process observed by HSIS for strain rate of 832.3 s<sup>−</sup><sup>1</sup> is shown in **Figure 12**. The beginning of the failure is observed in two regions of the transmitted bar/specimen edge (blue circle) taking as reference the direction of wave propagation (red arrow) (**Figure 12b**). The upper region is submitted to bending, which is why the material looks bended upward, while the lower region develops two delamination fronts. The delaminations are propagated, while the bending on the upper region is intensified generating delamination and separation of the plies (**Figure 12c**) indicating failure of the resin, until the failure of the fibers under shear is initiated (**Figure 12d** yellow line). The propagation of the different crack fronts is prolonged until the specimen is entirely divided in several pieces (**Figure 12e**).

SEM fractographic observation was performed on the fracture surface of the different recovered parts of the material tested under 832.2 s<sup>−</sup><sup>1</sup> . **Figure 13a** shows a surface that appears to be "melted," while **Figure 13b–d** presents other surface that is "unmelted." This behavior indicates that heat generation during the test may have affected the crystallinity degree of the thermoplastic matrix. The "melted" surface (**Figure 13a**) is characterized for being smooth and without any distinctive features; observation at high zooms show the presence of fibrils in the interior of a crack, which look like resin threads that try to keep the crack faces together and oppose the propagation. On the "unmelted" surface (**Figure 13b**), two zones can be observed, Z1 which seems to be a zone directly over the fabric (it is not possible to identify if it is warp or weft) and Z2 which seems to be an interstitial site or a high resin content site. The zone Z1 (**Figure 13c**) shows cusps and scallops (red arrows),

#### **Figure 10.**

*Aerospace Engineering*

**Figure 9.**

**Table 2.**

in localized points of the specimen, generally on the edges (2.25% in the DIC

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

The fractographic observation for dynamic regime is performed by monitoring the failure through the high-speed image system and SEM post-failure observation.

; and 2437% on the

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

*.*

). This indicates

where

spectrum and 2.088% according to SHPB measure for 400.5 s<sup>−</sup><sup>1</sup>

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

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

DIC spectrum and 2.346% according to SHPB measure for 832.3 s<sup>−</sup><sup>1</sup>

failure can be present as a consequence of the specimen machining [43].

**Figure 11** shows the sequence of the material's failure submitted to 400.5 s<sup>−</sup><sup>1</sup>

the red arrow indicates the direction of the compressive wave. It can be observed the specimen at the beginning of the failure without any failure indication in **Figure 11a**; in the next image (**Figure 11b**) is shown the beginning of the failure on transmitted bar/specimen edge (blue circle), which is attributed to material's edges weakening by machining effect. The beginning of the failure is given in the form of delamination, and then it is propagated diagonally or in shear mode (**Figure 11c**). Besides, other two crack fronts are initiated on incident bar/specimen edge (blue circle **Figure 11c**), which join in a "v" shape, and then it is propagated in delamination mode. The specimen finishes its failure process with a partial separation of the

*3.1.2.1 Fractographic observation*

**36**

surfaces (**Figure 11d**).

*Stress-strain curve obtained for PPSCFC with strain measured by DIC and SHPB strain gages under (a) 400.5 s<sup>−</sup><sup>1</sup> and (b) 832.3 s<sup>−</sup><sup>1</sup> .*

*.*

**Figure 11.** *Images sequence taken by HSIS for PPSCFC tested at 400.5 s<sup>−</sup><sup>1</sup>*

while the zone Z2 (**Figure 13d**) presents riverlines (yellow arrows) and feather marks (red circles). This fractographic aspects are typical of a composite submitted to compression [40, 44–46].
