PSI - Issue 53

Rainer Wagener et al. / Procedia Structural Integrity 53 (2024) 161–171 Author name / Structural Integrity Procedia 00 (2019) 000–000

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To calibrate the material behavior additional heat treatments are used after the manufacturing processes. In order to distinguish whether the stress-strain or the strain-life correlation are affected by the heat treatment, further cyclic tests with heat-treated polished specimens are carried out. The results are depicted in Fig. 4.

Fig. 4: Cyclic stress-strain chart and strain-life chart showing the Fatigue Life Curves of different the build-to-force orientation and the influence heat treated of aluminum AA2319 specimens manufactured by WAAM.

As expected, the heat treatment leads to a stress reduction and thus to a more homogeneous material behavior at the expense of a lower cyclic stress-strain curve. Therefore, it can be observed that the heat treatment leads to a reduced cyclic yield strength compared to the not heat-treated material state. In case of the Fatigue Life Curve this leads to a shift of the first knee-point towards higher number of cycles and smaller amplitudes. Accordingly, the Low Cycle Fatigue regime, i.e. the number of cycles to failure in which the stress leads to plastic strain, increases. The second knee-point of the Fatigue Life Curve is not affected because it is not depending on the cycle yield strength. 5. Roughness To transfer the fatigue properties derived by the usage of specimens to components a definition of the cross-section is needed. Keeping the rough and more or less regular surface topology in mind it is hard to define a cross-section. Somebody emphasizes to use the fracture surface to measure the cross-section, because this should be the relevant cross-section for fatigue. Other ones suggest measuring several positions and use the minimum value. Both methods have right to exist to derive material properties, but to transfer these properties into a fatigue approach is challenging. Because neither the cross-section of the fracture surface nor the minimum cross-section dimensions are known in the design phase. The remedy can be to use the nominal dimension of the drawing, well-knowing that the real dimensions can differ. In doing so everybody along the production chain talks about the same dimensions and finally, the dimensions and the cyclic material properties are directly linked to the component.