PSI - Issue 21

Kadir Bilisik et al. / Procedia Structural Integrity 21 (2019) 146–153 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

149

4

Table 1. Specifications of multiwall carbon nanotubes (www.nanothinx.com (2019). Nanomaterial

Tensile strength (GPa)

Tensile modulus (TPa)

Surface area (m 2 /g)

Molecular weight (g/mol)

Density (g/cm 3 )

Particle dimensions (nm x micron x nm)

Purity (%)

Melting temperature (°C)

MWCNTs, (Nanothinx,GR)

15- 35 x 10≥ x 1 - 2≥

12.01

>100

≥97

1.74

200

1.0

3550

Fourth type was nanostitched preforms. The CS-CS-N was carbon nanostitched, nanoprepreg four layer preforms. The CS-TS-N was Twaron CT nanostitched, nanoprepreg four layers satin preform. Stitched yarns in all preforms were placed at their through-the-thickness (Fig. 1) and their properties are provided in Table 2. Nanostitched composites were created by utilizing the nanostitched preforms. More detail explanation on the composite fabrication was provided in the reference Bilisik et al. (2019 b). Table 2. Specifications of untwisted stitching yarns. Fiber type Fiber diameter (µm) Fiber density (g/cm 3 ) Tensile strength (GPa) Tensile modulus (GPa) Elongation at break (%) Yarn linear density (dtex)

Twaron CT (Para-aramid fiber, Teijin, JP) Polyacrylonitrile (PAN) Carbon (Carbon fiber, Aksaca, TR)

12

1.45

3.2

115

2.9

3360

6

1.78

4.2

240

1.8

6 K

2.2. Mode‒II interlaminar fracture t oughness (G IIC ) test Mode-II properties of all developed carbon/epoxy composites were determined via end notch flexure (ENF) method. ASTM Standard D7905‒14 (2014) was followed. Fig. 2 shows the mode‒II testing by using the 3-point flexture fixture. The test was conducted to obtain G IIC for both non-precrack (NPC) and precrack (PC) cases.

Fig. 2. ENF sample during mode-II testing (left) and failed samples (right) (digital image).

3. Results and discussion 3.1. Mode‒II fracture toughness results

Fig. 3(a‒b ) illustrated the load (P)‒displacement(δ) curves of composites for NPC and PC cases. The carbon and para-aramid nanostitched and stitched composites showed greater values considering to the nano and base composites . The load‒displace ment curves of all composites become almost linear vertical slope.