PSI - Issue 28

7

Liu H et al./ Structural Integrity Procedia 00 (2020) 000–000

Haibao Liu et al. / Procedia Structural Integrity 28 (2020) 106–115

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Table 1. Comparison of some key results obtained from the experimental studies for the impact of the composites struck at two different velocity levels using the round-nosed steel (RNS) impactor.

Maximum load (kN)

Duration time (ms)

Maximum displacement (mm)

Area of damage (mm 2 )

Impact velocities

2.40 m.s -1 4.16 m.s -1

4.7 8.3

6.0 9.8

6.7 6.2

1180 2530

4.2. Effects of impactor geometry A comparison of the loading responses of the composites struck with the round-nosed steel (RNS) and the flat faced steel (FFS) impactors is shown in Fig. 7. At the same impact energy level of 15 J, the average duration time of the impact event for the composites struck with the flat-faced steel impacted is about 1 ms shorter than that for the composites struck with the round-nosed steel impactor. Further, the average maximum load for the flat-faced steel impactor (i.e. 7.1 kN) is about 50% higher than that of the round-nosed steel impactor (i.e. 4.7 kN). In terms of the maximum out-of-plane displacement of the composite specimen, values of 6.0 mm and 4.7 mm are observed for the round-nosed steel impactor and the flat-faced steel impactor, respectively. This indicates that, compared to the round nosed steel impactor, a higher effective stiffness of the composite specimen is observed when it is struck with the flat faced steel impactor.

(a) (b) Fig. 7. Loading responses obtained from the impact experiments performed using the round-nosed steel (RNS) and the flat-faced steel (FFS) impactors: (a) load versus time curves and (b) load versus displacement curves. (Results from the three replicate tests for each test condition using an impact energy of 15 J are shown.) Fig. 8 shows the delamination maps obtained from the composites impacted by the round-nosed steel and flat-faced steel impactors at 15 J. The comparison shows that average areas of the damage footprints caused by the round-nosed steel impacted and flat-faced steel impacted specimens are very similar in value, but that the shape of the contours shows a large difference. The round-nosed steel impacted composites show a localised damage area under the impactor. On the other hand, the flat-faced steel impacted composites exhibit two separated damage areas, between which an area of much less damage is observed.