Interrupted fatigue testing with periodic tomography to monitor porosity defects in wire + arc additive manufactured Ti-6Al-4V

Biswal, Romali; Zhang, Xiang; Shamir, Muhammad; Mamun, Abdullah Al; Awd, Mustafa; Walther, Frank; Syed, Abdul Khadar

doi:10.1016/j.addma.2019.04.026

Cited by 25 publications

(19 citation statements)

References 33 publications

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Section: Draft Articlementioning

confidence: 99%

“…In the case of WAAM, a low density of defects can be achieved using the Cold Metal Transfer (CMT) technology [28,29]. Typical WAAM defects are round smooth pores, with sizes ranging from a few micrometers to more than half a millimeter [23,30]. Fatigue samples extracted from optmized WAAM blocks show rare isolated pores with an important discrepancy in size and distance to free surface.…”

Section: Draft Articlementioning

confidence: 99%

“…From this observation a novel approach is proposed in [16], where the total plastic zone in the vicinity of a defect is considered from Finite Element Analysis (FEA). Although gas pores found in WAAM parts have much larger dimensions (>100µm) and have smooth near-spherical shapes [23][24][25], to which notch fatigue and crack initiation approaches are best suited [26,27].In the case of WAAM, a low density of defects can be achieved using the Cold Metal Transfer (CMT) technology [28,29]. Typical WAAM defects are round smooth pores, with sizes ranging from a few micrometers to more than half a millimeter [23,30].…”

mentioning

confidence: 99%

“…Although gas pores found in WAAM parts have much larger dimensions (>100µm) and have smooth near-spherical shapes [23][24][25], to which notch fatigue and crack initiation approaches are best suited [26,27].In the case of WAAM, a low density of defects can be achieved using the Cold Metal Transfer (CMT) technology [28,29]. Typical WAAM defects are round smooth pores, with sizes ranging from a few micrometers to more than half a millimeter [23,30]. Fatigue samples extracted from optmized WAAM blocks show rare isolated pores with an important discrepancy in size and distance to free surface.…”

mentioning

confidence: 99%

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A probabilistic approach for high cycle fatigue of Wire and Arc Additive Manufactured parts taking into account process-induced pores

Bercelli

Moyne

D’Hondt

et al. 2021

Additive Manufacturing

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Wire and Arc Additive Manufacturing (WAAM) is a direct-energy deposition technique (unlike SLM or EBM) that builds up a part in a layer-by-layer fashion, each layer being constituted of interlaced weld beads. It is the best suited Additive Manufacturing (AM) technique for large structures thanks to its high deposition rate (5kg/h). The resulting material shows a rough surface, strong residual stress induced by its complex thermal history, a heterogeneous microstructure marked by the different weld passes as well as defects formed by gas pockets. Despite their rarity, pores are found to have a first-order influence on the fatigue life of machined specimens. The discrepancy in their size (> 100µm) and position is responsible for a considerable scatter that makes classical fatigue tests ineffective. The aim of this study is to propose a novel approach to take into account the effect of rare WAAM-induced defects in high cycle fatigue. To achieve this, numerical porous structures are generated from the knowledge of the real pore population determined by tomography. Their fatigue performances are predicted via a two-scale probabilistic model identified on experimental self-heating results, on which pores have no influence. In that sense, the probabilistic model describes the behaviour of a virtually healthy material. Then, by computing a database of representative pore cases, the whole bundle of Wöhler curves for each numerical porous structure is determined. Finally, the numerical fatigue scatter is in close agreement with experimental data, and it is shown that the ranking in pore criticality according to the model matches the fractography observations. Keywords: Wire and Arc Additive Manufacturing (WAAM) ; High cycle fatigue ; Pores ; Self-heating ; Poisson point process Draft articleIRDL fatigue life of the position of an isolated pore over its size. From this observation a novel approach is proposed in [16], where the total plastic zone in the vicinity of a defect is considered from Finite Element Analysis (FEA). Although gas pores found in WAAM parts have much larger dimensions (>100µm) and have smooth near-spherical shapes [23][24][25], to which notch fatigue and crack initiation approaches are best suited [26,27].In the case of WAAM, a low density of defects can be achieved using the Cold Metal Transfer (CMT) technology [28,29]. Typical WAAM defects are round smooth pores, with sizes ranging from a few micrometers to more than half a millimeter [23,30]. Fatigue samples extracted from optmized WAAM blocks show rare isolated pores with an important discrepancy in size and distance to free surface. As a result, a considerable scatter in fatigue data is observed [31] (for example compared to casting materials), posing quite a challenge to the assessment of fatigue properties by conventional methods (ASTM E466-15 standard [32], the staircase method [33]). These samples do not constitute a Representative Volume Element (RVE) of the material's fatigue behaviour: each sample can be seen as a unique structure. This is t...

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Section: Draft Articlementioning

confidence: 99%

Section: Draft Articlementioning

confidence: 99%

mentioning

confidence: 99%

mentioning

confidence: 99%

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A probabilistic approach for high cycle fatigue of Wire and Arc Additive Manufactured parts taking into account process-induced pores

Bercelli

Moyne

D’Hondt

et al. 2021

Additive Manufacturing

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“…The latter is widely accepted as a marginal phase of fatigue lifetime in the presence of internal defects, especially at critical locations. Instead of the threshold representation, other attempts utilized microcomputed tomography (µ-CT) to build three-dimensional finite element models that mimic the morphology of the internal pores, as has been progressively represented in the following research [15,16].…”

Section: Introductionmentioning

confidence: 99%

Towards Deterministic Computation of Internal Stresses in Additively Manufactured Materials under Fatigue Loading: Part I

et al. 2020

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The ongoing studies of the influence of internal defects on fatigue strength of additively manufactured metals adopted an internal crack or notch-like model at which the threshold stress intensity factor is the driving mechanism of fatigue failure. The current article highlights a shortcoming of this approach and offers an alternative based on X-ray microcomputed tomography and cyclic plasticity with a hybrid formulation of Chaboche and Armstrong–Frederick material laws. The presented tessellation and geometrical transformation scheme enabled a significantly more realistic morphological representation of internal defects that yielded a cyclic strain within 2% of the experimental values. This means that cyclic plasticity models have an accurate prediction of mechanical properties without repeating a full set of experiments for additively manufactured arbitrary microstructures. The coupling with a material law that is oriented towards the treatment of cyclic hardening and softening enabled more accurate computation of internal stresses under cyclic loading than ever before owing to the maturity of tessellation and numerical tools since then. The resulting stress–strain distributions were used as input to the Fatemi–Socie damage model, based on which a successful calculation of fatigue lifetime became possible. Furthermore, acting stresses on the internal pores were shown to be more than 450% concerning the applied remote stress amplitude. The results are a pretext to a scale bridging numerical solution that accounts for the short crack formation stage based on microstructural damage.

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X‐ray Tomography and Tomoscopy on Metals: A Review

et al. 2023

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X‐ray tomography is a versatile tool in materials research and engineering since it allows for a non‐destructive and three‐dimensional mapping of the constituents of a heterogeneous material as long as they differ in their interactions with X‐rays. Recent developments of the technique have brought down the time needed for the acquisition of a single tomogram by many orders of magnitude compared to what was needed 25 years ago. Nowadays, up to 1000 full tomograms can be recorded in a second, which enables real‐time studies of changes in samples caused by reactions or by applied processing operations. The term tomoscopy has been coined for such sequences of 3D images. We review the application of X‐ray tomography and tomoscopy on metals and describe each step required and the associated challenges. A selection of representative investigations is presented with a focus on time‐resolved phenomena in metals and alloys ranging from mechanical deformation, solidification to metals processing processes such as welding and additive manufacturing. Finally likely future developments are discussed.

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Interrupted fatigue testing with periodic tomography to monitor porosity defects in wire + arc additive manufactured Ti-6Al-4V

Cited by 25 publications

References 33 publications

A probabilistic approach for high cycle fatigue of Wire and Arc Additive Manufactured parts taking into account process-induced pores

A probabilistic approach for high cycle fatigue of Wire and Arc Additive Manufactured parts taking into account process-induced pores

Towards Deterministic Computation of Internal Stresses in Additively Manufactured Materials under Fatigue Loading: Part I

X‐ray Tomography and Tomoscopy on Metals: A Review

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