PSI - Issue 35

Kadir Bilisik et al. / Procedia Structural Integrity 35 (2022) 210–218 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 3.(a) Mode-II fracture toughness test in universal testing machine, actual view (digital image); (b) three-point flexure for interlaminar fracture toughness applied on the specimen illustrating the compliance marks, schematic, Bilisik et al. (2020). 3. Results and Discussion 3.1. In-plane shear test results The in-plane shear strength, strain and modulus of all composite samples are exhibited in Figure 4 (a-c). As depicted in Figure 4, the maximum shear strength, strain and modulus of composite samples ranged 17.23-21.05 MPa, 6.14-11.51% and 0.66-0.91 GPa, respectively. The shear strength value of aramid stitched composites (TB TS) was 14.83% inferior compared to the TBU. Contrarily, the nanostitched aramid composite (TB-TS-N) was 12% greater than the TBU. Stitched and nanostitched aramid composites demonstrated the lower shear strength because of possible weak adhesion between para-aramid filament assemblage and phenolic matrix. This was also referred to the processing defect during stitching and probably needle penetration to the thickness of preform during fiber insertion in which this action caused stress concentration in the structure under shear loading.

Fig.4. Graphical representations of shear properties of composite samples. (a) Shear strength (MPa); (b) shear strain (%) and (c) shear modulus (GPa).