Issue34

A. Riemer et alii, Frattura ed Integrità Strutturale, 34 (2015) 437-446; DOI: 10.3221/IGF-ESIS.34.49 441 the threshold values for conventionally processed material. The fatigue crack growth curves and further details for the static and fatigue data as well as for the influence of Hot Isostatic Pressing (HIP) on porosity and residual stresses are presented in [7]. Stainless steel 316L For the material 316L the level of anisotropy in the as-built condition is higher than for titanium alloy. The threshold values vary from 3.0 MPa·m 1/2 for CD BD to 4.3 MPa·m 1/2 for CD BD , Fig. 5a and b. Moreover, the threshold values are not affected by the heat treatment at 650°C which aims at the stress relieving, Fig. 5b. Following heat treatment at 650°C, the residual stresses were found to be reduced by half, cf. [8]. Consequently, the internal stresses do not seem to affect the crack growth performance of stainless steel. The threshold values of 316L could only been improved by application of Hot Isostatic Pressing. Moreover, the anisotropy in threshold values was eliminated completely by the use of HIP process, Fig. 5b. Furthermore, the values were increased due to the HIP treatment compared to the threshold values for the as-built condition. Figure 5 : Crack growth curves for the as-built condition and the orientations CD BD and CD BD a) and the threshold values following heat treatments b) . In further studies it was shown that in case of 316L the process-specific microstructure shows the highest influence on the evaluation of fracture-mechanical data. More details concerning the effect of microstructure on the crack growth data may be deduced from [8]. N UMERICAL CRACK GROWTH ANALYSIS n this study, the effect of treatment (and consequently of the residual stresses) was analysed. For that reason titanium alloy Ti-6-4 in the conditions as-built and 800° was examined. The required fatigue crack growth data was obtained from [7] and characterised by the FORMAN/METTU-equation. Afterwards, this mathematical description was implemented into numerical crack growth simulation program ADAPCRACK3D [9]. The object for the lifetime study is the hip joint implant. This part has to be personalised and consequently suitable for production employing the SLM process. The boundary conditions used for the crack growth simulation are presented in Fig. 6 schematically. These boundary conditions correspond to the load case “Normal Walking” and are in accordance with the mechanical models developed by Pauwels [10]. Therefore, the initial crack in the region where the highest I