PSI - Issue 68

Mirko Teschke et al. / Procedia Structural Integrity 68 (2025) 936–941 M. Teschke and F. Walther / Structural Integrity Procedia 00 (2025) 000–000

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in additive manufacturing. Instead, they must be integrated into the design and calculation of components and structures. The increased stress concentration at the defect itself can lead to premature failure. To determine this increased stress concentration, the approach according to Murakami et al. [1] describes the defect-specific stress intensity factor (SIF) as a function of the stress range ∆ , the defect size a ! and a geometry factor , which takes into account the position of the defect (Eq. (1)). ∆ = ∙∆ ∙* ∙√ = ∆ ∙ ∙2 ∙ (1) √Area= a ! : Defect size = Square root of the projected fracture-inducing critical defect Y : Geometric factor Y = 0.65 for surface defect Y = 0.50 for volume defect For the fatigue behavior of materials dominated by crack propagation, the Shiozawa approach [2] can be used for a modified representation and interpretation of fatigue results. In this context, the Paris-Erdogan law is integrated to describe the crack propagation behavior from the initial crack or defect size a ! to the critical crack length a # and is transformed as follows in Eq. (2): ∆K ! =8 %∙(( $ )$) 9 "! ∙ 8 + # , $ 9 ) "! = A - ∙ 8 + # , $ 9 . % ; C,m = const. (2) Titanium aluminides are an intermetallic alloy of titanium and aluminum whose mechanical properties are between those of metals and ceramics. Due to their high specific strength and creep resistance at high application temperatures up to 850 °C, they are currently used as turbine blades in the low-pressure turbines of modern airplanes [3]. As conventional manufacturing processes are very challenging, AM, in particular, electron beam powder bed fusion (PBF EB/M) and laser-based directed energy deposition (DED-LB), are ideal manufacturing processes [4]. However, due to the low ductility and fracture toughness of TiAl, a deep understanding of the occurring effects of manufacturing defects on fatigue behavior is very important for a safe application [5]. 2. Material and methods In this paper, the third-generation TiAl alloy TNM-B1 manufactured by PBF-EB/M and DED-LB was investigated. Besides the as-built (AB) condition, the additional hot isostatic pressed (HIP) condition was examined. The specimen geometry, shown in Fig. 1, was manufactured by turning and polishing. The specimens were tested in constant amplitude fatigue tests, which were performed on an Instron 8801 servohydraulic fatigue testing system. Each material condition was tested at room temperature (RT) and the application temperature of 800 °C. The test frequency of the stress-controlled fatigue tests was 20 Hz. The test setup is shown in Fig. 2.

Fig.1: Specimen geometry for fatigue tests.