PSI - Issue 28

Koji Uenishi et al. / Procedia Structural Integrity 28 (2020) 2072–2077 Uenishi et al. / Structural Integrity Procedia 00 (2020) 000 – 000

2074

3

a

b

c

45 mm

Fig. 1. (a) A rectangular polycarbonate specimen with multiple cracks set in the experimental apparatus, uniaxial tensile testing machine; (b) a typical specimen with multiple small-scale parallel cracks prepared in a staggered manner; and (c) a specimen specially arranged for the observation of the propagation of the primary fracture that is found in the dynamic fracture process of the specimen (b). The small-scale cracks exist only along one single straight line [unit: mm].

1.3  10 − 4 /s 1.3  10 − /s 1.3  10 − 2 /s

Nominal stress [MPa]

Nominal strain

Fig. 2. Typical global stress-strain relation under application of different values of external uniaxial strain rate for the specimen shown in Fig. 1b. The global tensile strength increases with the strain rate. Upon a complete split of the specimen by the primary fracture, the stress drops, that is, no additional loading is possible and the nominal stress becomes zero. Usually, this stress drop is regar ded as the “end” of the fracture development in a specimen, but as indicated in Fig.3, dynamic phenomena continue occurring even after this abrupt stress drop.