PSI - Issue 42

K. Koch et al. / Procedia Structural Integrity 42 (2022) 506–512 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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The vibrations after force release were recorded and evaluated, see Fig. 3b. Frequencies in the range of 14 to 15 kHz were observed for both materials. With an increasing impact energy, an increase in the vibration amplitude of the steel specimens could be observed. The cast iron material showed almost constant vibration amplitudes, independent of the impact energy. This can be attributed to the damping ability of the nodular cast iron. The maximum dissipated energy considering all tests was approximately 0.5 mJ at 0 = 7.0 J. It corresponds to the kinetic energy of the specimen, which is calculated using the maximum velocity of the vibrations. In both cases, the energy loss resulting from the specimen vibrations is not significant. The remaining displacements of the support and the tup at the time of force release were examined for both materials as a function of the impact energy. The results are shown in Fig. 4. In general, a similar behavior could be observed for both materials. With an increasing impact energy, the amounts of displacement of the support and the tup at the moment of force release increase. The elastic displacement of the support is more significant in tests on 42CrMo4, see Fig. 4a. This can be explained by the high stiffness of the steel specimens and the higher force. Also, plastic deformation of the nodular cast iron generally occurs at lower forces due to the low yield strength. This is shown in Fig. 3a, regarding the slope of the force-displacement-curve. Therefore, the energy which is absorbed by the steel specimens themselves is generally lower compared to nodular cast iron. Additionally, the nodular cast iron showed small amounts of damage even at low impact energies. This led to a higher energy dissipation by the specimen and thus to larger displacements of the tup. This effect is more significant on notched specimens due to the lower stiffness or higher compliance, see Fig, 4b. In addition, it cannot be neglected that support displacement and plastic deformation of the specimen are superimposed during the test. In this case a brief relaxation of the support can occur, see Fig. 2b.

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10 20 30 40 50 60 70 Support displacement [µm] 42CrMo4 a 0 / W = 0.2 a)

b)

EN-GJS-400-18 a 0 / W = 0.2

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EN-GJS-400-18 a 0 / W = 0

300

200

42CrMo4 a 0 / W = 0.2

EN-GJS-400-18 a 0 / W = 0.2

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Tup displacement [µm]

0 1 2 3 4 5 6 7 8 9 10 0

0 1 2 3 4 5 6 7 8 9 10 0

Impact energy [J]

Impact energy [J]

Fig. 4. Effect of the impact pulse a) on the support and b) on the tup displacement. Based on the results of the displacement measurements and energy calculations, dynamic fracture toughness tests were carried out on specimens with fatigue cracks 0 / = 0.5. The displacement measurement in the tests was corrected considering the compliance of the support, which was estimated earlier. The values for cd were calculated according on ISO 26843 and compared with corrected values. In the case of 42CrMo4, no stable crack growth was observed until the onset of unstable crack growth, since the material is relatively brittle. In this case, was calculated for the maximum force in the test.