PSI - Issue 13

Stefan Reich et al. / Procedia Structural Integrity 13 (2018) 28–33 Author name / Structural Integrity Procedia 00 (2018) 000 – 000

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Figure 7: Typical fracture pattern at drop heights of 11.75 cm, and 16.75 cm

Figure 7: Crack length depending on the drop heights of 11.75 cm, and 16.75 cm

Despite measuring the crack length, the exact crack surface is unknown, as the crack is not smooth and perpendicular to the surface (Figure 8). In addition, many small glass fragments – powder – are visible, especially at the impact point and at larger drop heights. For further calculation the measured crack length is multiplied by 1.15 to consider these effects. Nevertheless, a more detailed consideration of the actual crack surface is necessary for further investigation.

Figure 8: The typical crack is not smooth, therefore its calculation length is factored by 1.15

Table 2 shows the average crack length at drop heights and the calculated surface energy coefficients  s that seems to be constant at average values, but 10 to 20 times larger than determined with static testing techniques (Table 1).

Table 2: Average results with the 1000 g steel ball at 8 mm glass, glass laid in rubber gaskets Drop height h [cm] Potential EnergyU 0 m*h*g [Nm] Average measured crack length l [cm]

Average crack length per drop height l/h [cm/cm]

 s U 0 / (2*x*l*1,15) [Nm/m²]

6.75

0.662 1.153 1.643

67.3

10.0 10.8

53.5 49.4 53.8

11.75 16.75

126.9 165.9

9.9