Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties

Wycisk, Eric; Solbach, Andreas; Siddique, Shafaqat; Herzog, Dirk; Walther, Frank; Emmelmann, Claus

doi:10.1016/j.phpro.2014.08.120

Cited by 411 publications

(221 citation statements)

References 11 publications

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“…Fatigue specimens with rough as-built surfaces generally have fatigue failure starting from the rough surface [11,23,47,48], see Figure 19, and results from the present study show that there is a distinct trend that a rougher surface contribute to a reduced fatigue limit as illustrated by Figure 20. For machined AM surfaces, however, fatigue cracks can either start from internal features or from the surface, at internal features that is located at the after machining [11,21], see Figure 21.…”

Section: Effect Of Surface Roughnesssupporting

confidence: 51%

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Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications

Kahlin¹

2017

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Additive Manufacturing (AM) for metals includes is a group of production methodst hat use a layer-by-layer approach to directly manufacture final parts. In recent years, the production rate and material quality of additive manufactured materials have improved rapidly which has gained increased interest from the industry to use AM not only for prototyping, but for serial production. AM offers a greater design freedom, compared to conventional production methods, which allows for parts with new innovative design. This is very attractive to the aerospace industry, in which parts could be designed to have reduced weight and improved performance contributing to reduced fuel consumption, increased payload and extended flight range. There are, however, challenges yet to solve before the potential of AM could be fully utilized in aerospace applications. One of the major challenges is how to deal with the poor fatigue behaviour of AM material with rough as-built surface. The aim of this thesis is to increase the knowledge of how AM can be used for high performance industrial parts by investigating the fatigue behaviour of the titanium alloy Ti6Al4V produced with different AM processes. Foremost, the intention is to improve the understanding of how rough as-built AM surfaces in combination with AM built geometrical notches affects the fatigue properties.This was done by performing constant amplitude fatigue testing to compare different combinations of AM material produced by Electron Beam Melting(EBM) and Laser Sintering (LS) with machined or rough as-built surfaces with or without geometrical notches and Hot Isostatic Pressing (HIP) treatment. Furthermore, the material response can be different between constant amplitude and variable amplitude fatigue loading due to effects of overloads and local plastic deformations. The results from constant amplitude testing were used to predict the fatigue life for variable amplitude loading by cumulative damage approach and these predictions were then verified by experimental variable amplitude testing. The constant amplitude fatigue strength of material with rough as-built surfaces was found to be 65-75 % lower, compared to conventional wrought bar, in which HIP treatments had neglectable influence on the fatigue strength. Furthermore, the fatigue life predictions with cumulative damage calculations showed good agreement with the experimental results which indicates that a cumulative damage approach can be used, at least for a tensile dominated load sequences, to predict the fatigue behaviour of additive manufactured Ti6Al4V

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Section: Effect Of Surface Roughnesssupporting

confidence: 51%

“…The fatigue behaviour of un-notched (type 1) Ti6Al4V specimens with rough asbuilt AM surface has been investigated in previous studies, [13,21,22,[45][46][47][48]. Few aerospace parts have, however, simple flat geometries without any radii or corners that would introduce local stress concentrations.…”

Section: Fatigue Notch Factormentioning

confidence: 99%

Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications

Kahlin¹

2017

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“…In completely tensile cyclic loading, crack initiation shifts from the surface to subsurface locations [8]. Linear-elastic fracture mechanics (LEFM) calculated fatigue lifetime reliably when long cracks existed but overestimated the lifetime in case of short cracks [9]. In this study, PH did not increase fatigue strength until a peak hardening treatment is applied after processing [2].…”

Section: Introductionmentioning

confidence: 73%

Qualification of selective laser-melted Al alloys against fatigue damage by means of measurement and modeling techniques

et al. 2018

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Abstract. Aluminum alloys processed through selective laser melting possess unique features of microstructure, defect morphology and mechanical properties. Constitution of fine cellular dendrites results from the high-cooling rate of the melt pool during the consolidation process. Investigation of the microstructure by scanning electron microscopy identifies supersaturation of Si particles as a secondary strengthening mechanism. On the contrary, platform heating that induces coarser microstructure leads to migration of Si particles from the Al matrix to the eutectic phase. As a result, tensile strength is reduced by 3%, while fracture strain is increased by 17%. Fine-grained structures exhibit a lower amount of plastic damage accumulation as well as delayed crack initiation as determined by the applied measurement techniques. Finite element models of the investigated configurations are obtained using scans of computed tomography under consideration of process-induced defects. Comparison of modeling and experimental results concluded that dominant fatigue damage mechanisms are related to the loading regime from low-cycle (LCF) to very-high-cycle fatigue (VHCF). Thus, process-inherent features of microstructure and porosity have different quantitative effects concerning the applied load. In VHCF, a material configuration with platform heating possesses an improved fatigue strength by 33% at 1E9 cycles, concerning the material configuration without platform heating.

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“…Fatigue and crack propagation properties of additive manufactured materials are not very well known yet [1], because a lack of process understanding and a lack of in situ process monitoring and control, especially in metal AM systems, currently results in unknown porosity levels and distributions [2]. Multiple sources report a reduced fatigue lifetime.…”

Section: Additive Manufacturingmentioning

confidence: 99%

Proof of Concept of Crack Localization Using Negative Pressure Waves in Closed Tubes for Later Application in Effective SHM System for Additive Manufactured Components

2016

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Additive manufactured components have a different metallurgic structure and are more prone to fatigue cracks than conventionally produced metals. In earlier papers, an effective Structural Health Monitoring solution was presented to detect fatigue cracks in additive manufactured components. Small subsurface capillaries are embedded in the structure and pressurized (vacuum or overpressure). A crack that initiated at the component's surface will propagate towards the capillary and finally breach it. One capillary suffices to inspect a large area of the component, which makes it interesting to locate the crack on the basis of the pressure measurements. Negative pressure waves (NPW) arise from the abrupt encounter of high pressure fluid with low pressure fluid and can serve as a basis to locate the crack. A test set-up with a controllable leak valve was built to investigate the feasibility of using NPW to localize a leak in closed tubes with small lengths. Reflections are expected to occur at the ends of the tube, possibly limiting the localization accuracy. In this paper, the results of the tests on the test set-up are reported. It will be shown that the crack could be localized with high accuracy (millimeter accuracy) which proves the concept of crack localization on basis of NPW in a closed tube of small length.

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Effects of Defects in Laser Additive Manufactured Ti-6Al-4V on Fatigue Properties

Cited by 411 publications

References 11 publications

Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications

Fatigue Performance of Additive Manufactured Ti6Al4V in Aerospace Applications

Qualification of selective laser-melted Al alloys against fatigue damage by means of measurement and modeling techniques

Proof of Concept of Crack Localization Using Negative Pressure Waves in Closed Tubes for Later Application in Effective SHM System for Additive Manufactured Components

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