Issue 78

N. Nayak et alii, Fracture and Structural Integrity, 78 (2026) 378-392; DOI: 10.3221/IGF-ESIS.78.22

(b) Tensile Dog-Bone Specimen (ASTM D790)

(a) Tensile Dog-Bone Specimen (ASTM D638)

(c) Notched Izod Impact Specimen (ASTM D4812)

(d) Tensile Dog-Bone Specimen (ASTM D638)

Figure 3: Standard specimens prepared for tensile, flexural, impact and dielectric characterization

Mechanical characterization Tensile testing was carried out according to ASTM D638 using a ZWICK/ROELL Z020 universal testing machine equipped with a 20 kN load cell. The specimens were securely gripped, an initial preload of 0.1 MPa was applied and testing was conducted at a constant crosshead speed of 1 mm/min. Flexural properties were determined by three-point bending according to ASTM D790 using the same universal testing machine. The support span was maintained at 16 times the specimen thickness, an initial preload of 0.1 MPa was applied and the test was conducted at 1 mm/min until failure. Impact strength was evaluated according to ASTM D4812 using a ZWICK/ROELL HIT 50P impact testing machine. The theoretical pendulum velocity was 3.458 m/s. Three specimens were tested for each composite composition in tensile and flexural tests, and five specimens were tested for impact strength; the mean values were used for subsequent analysis. Fractured specimens were preserved for SEM analysis to correlate fracture morphology with mechanical performance [10, 11, 17]. The workflow followed for mechanical testing, SEM fractography and correlation of fracture mechanisms with measured properties is presented in Fig. 4. Compression-moulded composite laminates Laminates prepared for mechanical, dielectric and microstructural characterization ↓ Specimen preparation Specimens machined according to ASTM D638, ASTM D790, ASTM D4812 and ASTM D150 ↓ Mechanical and dielectric testing Tensile, flexural, impact and dielectric responses measured under standard test conditions ↓ SEM fractography Fractured tensile specimens examined for fibre pull-out, interfacial bonding, voids and matrix cracking ↓ Performance correlation Fracture mechanisms correlated with mechanical, dielectric and RSM optimization results Figure 4: Characterization workflow adopted for mechanical testing, dielectric testing, SEM fractography and performance correlation. Dielectric characterization and SEM analysis Dielectric characterization was conducted according to ASTM D150 at 10 Hz, 100 Hz, 1000 Hz and 10000 Hz to evaluate the electrical insulating behaviour of the composites over a low-frequency range [4, 18, 19]. Circular specimens of 10 mm diameter were cut from the compression-moulded plates, and the end faces were silver coated to ensure electrical contact. The specimens were placed between test electrodes in a chamber maintained at 10 -4 torr pressure. Dielectric constant was

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