PSI - Issue 19

Rainer Wagener et al. / Procedia Structural Integrity 19 (2019) 380–387 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Figure 2: Specimen geometry for strain- and stress controlled fatigue tests to investigate influences on the cyclic material behavior related to additive manufacturing

Figure 3: Coordinate-system to identify orientation of built to load direction

2.1 Test facilities

Due to the different test requirements of strain- and stress-controlled fatigue test two different types of test rigs were used. In order to perform stress controlled fatigue tests with constant amplitudes, a piezo driven test-rig was used, Fig. 4. The specimen is fixed in clamping devices, which are directly mounted on the piezo stack actuator on one side and on the load cell on the other side. In this way, the dynamic properties and the high resolution of the piezo stack actuator can directly be employed to fatigue the specimens. The test-frequency was limited to 100Hz within this test series in order to prevent an influence of the test-frequency on the resulting fatigue strength and life, even test frequency up to 1000Hz are possible.

Figure 4: Piezo based test-rig for cyclic tests

Figure 5: E-Cylinder test-rig for strain-controlled fatigue tests

The strain-controlled fatigue test were carried out using an E-Cylinder test rig. This type of fatigue testing machines has been specially designed to perform strain-controlled fatigue tests with high precision at low test frequencies. In order to prevent buckling under compression, an anti-buckling device was used.

2.2 Load-time functions

Besides the cyclic tests with constant amplitudes, so-called Wöhler-tests, also strain-controlled Incremental Step Tests were performed. Landgraf et al. have introduced the test procedure of the Incremental Step Test in 1968. This test enables the derivation of a cyclic stress-strain behavior by loading blocks with incrementally decreasing and