Fig. 1

Dumbbell-shaped specimens according to ISO standard 527–3 type 5. L1: length of testing part, 33 mm ± 2 mm; L2: length between clasps, 80 mm ± 5 mm; L3: total length, ≥ 115 mm. W1: width of testing part, 6 mm ± 0.4 mm; W2: total width, 25 mm ± 1 mm. T: thickness, 1 mm ± . R1: large radius, 25 mm ± 2 mm; R2: small radius, 14 mm ± 1 mm. The green rectangular part in the middle of specimen represents testing part