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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6. Cross-section To enable the usage of RSE within a fatigue approach of arbitrary components the loading acting on the component (force) has to be transferred into stresses. For this reason, the cross-section of the specimen is required. In case of polished specimens or specimens with smooth surfaces this is not worth mentioning. It is different with very rough surfaces as mentioned above. For example, the influence of minimum and maximum as-built cross-sections as well as polished surfaces for the selected specimen dimensions is shown in Fig. 8 schematically. It can be assumed that the actual stress-strain behavior lies between the curve for the minimum and maximum cross-section. Furthermore, it should be noted that the minimum thickness is not necessarily measured at the same location as the minimum width, respectively the maximum thickness at the same location as the maximum width, especially, if a certain length of nominal constant cross-section is present. For specimens, a post-mortem determination of the cross-section could be performed. However, this is only true, if the fracture surface does not deform beforehand due to plastic strains.

Fig. 8: Influence of the cross-section on the stress-strain-correlation, schematically

It should be kept in mind, that the aim of the Representative Structural Elements is to enable a fatigue approach in order to leverage the lightweight potential of additive manufacturing, which means to get reliable properties for the design. During the design process, on the contrary, the actual geometry, including the shape of individual weld beads, is not known, as this only becomes apparent after web planning or finally after the manufacturing process. Even if one is willing to consider the real dimensions, this is hardly possible, at least for component sections with as-built surfaces. One solution may be to use the nominal cross-section, i.e. the drawing cross-section. This has the advantage that the dimensions are known throughout the production chain and serve as a target size. Deviations of the nominal cross section from the actual cross-section are reflected in the value of a property in this way, that a larger scatter of the test results might occur. This deviation must be considered whether directly in a value of a specific property or, in general, as an influencing factor.