Fatigue strength assessment of additively manufactured metallic structures considering bulk and surface layer characteristics

Schneller, Wolfgang; Leitner, Martin; Pomberger, Sebastian; Grün, Florian; Leuders, Stefan; Pfeifer, Tanja; Jantschner, Oliver

doi:10.1016/j.addma.2021.101930

Cited by 14 publications

(12 citation statements)

References 43 publications

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“…Notably, a highly accurate 10-node quadratic-type element and fine mesh were employed, as shown in Figure 4b. Based on the SWT method, which is widely used for titanium and aluminum alloys [35], and the Baumel and Seeger rule, the parameters were calibrated for CPTi and Ti64. In future, they must be validated through experiments on clasps with different shapes.…”

Section: Discussionmentioning

confidence: 99%

Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing

et al. 2023

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In this study, the fatigue properties of additively manufactured titanium clasps were compared with those of commercially pure titanium (CPTi) and Ti-6Al-4V (Ti64), manufactured using laser powder-bed fusion. Methods: Fourteen specimens of each material were tested under the cyclic condition at 1 Hz with applied maximum strokes ranging from 0.2 to 0.5 mm, using a small stroke fatigue testing machine. A numerical approach using finite element analysis (FEA) was also developed to predict the fatigue life of the clasps. Results: The results showed that although no significant differences were observed between the two materials when a stroke larger than 0.35 mm was applied, CPTi had a better fatigue life under a stroke smaller than 0.33 mm. The distributions of the maximum principal stress in the FEA and the fractured position in the experiment were in good agreement. Conclusions: Using a design of the clasp of the present study, the advantage of the CPTi clasp in its fatigue life under a stroke smaller than 0.33 mm was revealed experimentally. Furthermore, the numerical approach using FEA employing calibrated parameters for the Smith-Watson-Topper method are presented. Under the limitations of the aforementioned clasp design, the establishment of a numerical method enabled us to predict the fatigue life and ensure the quality of the design phase before manufacturing.

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Section: Discussionmentioning

confidence: 99%

Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing

et al. 2023

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“…For future work on hybrid manufactured PBF-LB/M stainless steels and industrial applications, the authors recommend the application of local fatigue assessment methods either based on short fatigue crack growth models 52 or effective stress-based concepts in combination with models to account for production-related defects, for example, Schneller et al 53,54…”

Section: Discussionmentioning

confidence: 99%

Fatigue strength of PBF‐LB/M and wrought 316L stainless steel: effect of post‐treatment and cyclic mean stress

Braun

Mayer²,

Kryukov

et al. 2021

Fatigue Fract Eng Mat Struct

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Additive manufacturing (AM) enables the cost-effective production of complex components, many of which are traditionally manufactured using costly subtractive processes. During laser-based powder bed fusion of metals (PBF-LB/M), internal pores and rough surfaces are typically inevitable, reducing fatigue and corrosion resistance compared to traditional processes.Additionally, large defects often occur near to or at surfaces. Thus, this study investigates the effect of hybrid additive and subtractive manufacturing on the fatigue strength of AISI 316L. To this goal, different post-treatment routes are compared with wrought material. Additionally, computed tomography is used to determine the necessary machining depth of the surface layer. In this study, heat treatment and machining are both found to significantly increase fatigue strength (17% and 87%). Finally, the mean stress sensitivity M of as-built PBF-LB/M and wrought material is found to be highly affected by the assessed number of cycles to failure and residual stresses in PBF-LB/M material.

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“…Internal defects in the metallic bulk material may be evaluated by a combined Murakami approach, as demonstrated for laser powder bed fusion material [28]. This approach can also be expanded to surface defects and the interaction of stress raining surface features and internal defects [29]. Based on a knowledge about the defects of AM metal, fracture mechanics may be applied as well [30].…”

Section: Fatigue Of Weld Metal and Metallic Am Componentsmentioning

confidence: 99%

The effects of building position on surface and fatigue of DED-arc steel components

et al. 2022

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Recently, additive manufacturing (AM) of structural metallic components is analyzed regarding its potential use by industry and research. Next to the development of manufacturing processes, the mechanical properties are under investigation today. One of the quality measures of metallic components is the surface topography. DED-arc processes (direct energy deposition) result in relatively coarse surfaces, characterized by a distinct waviness with wave amplitudes in the mm-range. This is enhanced when applying horizontal building position in comparison to vertical position. Next to increased waviness, the load-bearing net cross sections are reduced as well. The surface topography determines the fatigue life properties of metallic components. While stress raising surface effects are generally well understood and fatigue (Structures 31: 576–589, 2021) of welded metals is established well, the fatigue behaviour of additively manufactured components is less investigated yet. In order to define surface quality levels for DED-arc components, the effects of surface topography on mechanical performance need to be understood. This article presents the manufacturing of high strength steel test coupons by the DED-arc process. The process parameters were varied with regard to the building position and different levels of surface quality were generated. The surfaces of different specimens were characterized and fatigue tests were conducted. The results were used to derive the surface influence on both, the effective load-bearing wall thickness and notch effects induced by the layer-by-layer building approach. A correlation between building position, surface waviness and fatigue strength was proven. In general, higher waviness resulted in reduced effective wall thickness and lowered fatigue strength. A difference in fatigue strength at 2 million load cycles of 20 to 30% was proven when printing in different building positions. The surface effect can be captured in the design concept when applying the effective notch stress approach with an averaging length of of ρ* = 0.4 mm. The fatigue strength is describable by a design S–N curve FAT160 and a k-value of 4.

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Fatigue strength assessment of additively manufactured metallic structures considering bulk and surface layer characteristics

Cited by 14 publications

References 43 publications

Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing

Comparison of the fatigue life of pure titanium and titanium alloy clasps manufactured by laser powder bed fusion and its prediction before manufacturing

Fatigue strength of PBF‐LB/M and wrought 316L stainless steel: effect of post‐treatment and cyclic mean stress

The effects of building position on surface and fatigue of DED-arc steel components

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