PSI - Issue 68

Koji Uenishi et al. / Procedia Structural Integrity 68 (2025) 554–558 Uenishi et al. / Structural Integrity Procedia 00 (2025) 000–000

556

3

a

b

0 µ s

5 µ s

10 µ s

Fracture at supershear speed

10 mm

Fig. 1. (a) Dynamic fracture development along a straight perforation line with relatively densely distributed small-scale cracks in a polycarbonate specimen shown in (b) [unit: mm]. The specimen is under quasi-static tension at a constant strain rate of 1.67 ´ 10 - 1 /s, and the dynamic fracture behavior is visualized using a high-speed video camera at a frame rate of 400,000 frames per second (fps). As can be seen from the isochromatic fringe patterns (contours of the maximum in-plane shear stress), the propagation speed of fracture fluctuates between low (wavefronts indicated in blue) and supershear (above the shear wave speed of the specimen with Mach (shock) wavefronts in red) levels. this fluctuation at supershear levels can generate multiple Mach wavefronts with different Mach angles (indicated in red). The fracture behavior seems more complex than the previous case and the fracture propagates not only from right to left but also from left to right starting at the right edges of preexisting small-scale cracks, and therefore, the physical background behind the multiple Mach wavefronts generated by the dynamic fracture is still unclear. Together with the preexisting small-scale crack, if merged, subsonic fracture from right to left and that from left to right may seem to have an apparent speed exceeding the shear wave speed of the specimen. Further investigation including more thorough experimental observations is needed. 3. Conclusions We have shown two typical examples of fracture propagation along a single straight perforation line with small scale cracks in a two-dimensional polycarbonate specimen under quasi-static tension. If the preexisting small-scale cracks are densely distributed, the dynamic fracture does propagate unidirectionally in an “unzipping” way along the