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See detailStrength Properties of 316L and 17-4 PH Stainless Steel Produced with Additive Manufacturing
Kedziora, Slawomir UL; Decker, Thierry UL; Museyibov, Elvin UL et al

in Materials (2022), 15(18), 6278

The number of additive manufacturing methods and materials is growing rapidly, leaving gaps in the knowledge of specific material properties. A relatively recent addition is the metal-filled filament to ... [more ▼]

The number of additive manufacturing methods and materials is growing rapidly, leaving gaps in the knowledge of specific material properties. A relatively recent addition is the metal-filled filament to be printed similarly to the fused filament fabrication (FFF) technology used for plastic materials, but with additional debinding and sintering steps. While tensile, bending, and shear properties of metals manufactured this way have been studied thoroughly, their fatigue properties remain unexplored. Thus, the paper aims to determine the tensile, fatigue, and impact strengths of Markforged 17-4 PH and BASF Ultrafuse 316L stainless steel to answer whether the metal FFF can be used for structural parts safely with the current state of technology. They are compared to two 316L variants manufactured via selective laser melting (SLM) and literature results. For extrusion-based additive manufacturing methods, a significant decrease in tensile and fatigue strength is observed compared to specimens manufactured via SLM. Defects created during the extrusion and by the pathing scheme, causing a rough surface and internal voids to act as local stress risers, handle the strength decrease. The findings cast doubt on whether the metal FFF technique can be safely used for structural components; therefore, further developments are needed to reduce internal material defects. [less ▲]

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See detailPractical Implementation of Functionally Graded Lattice Structures in a Bicycle Crank Arm
Decker, Thierry UL; Kedziora, Slawomir UL; Wolf, Claude UL

in 850th International Conference on Science, Technology, Engineering and Management (2020, November 25)

Functionally graded lattice structures (FGLS) were studied thoroughly for the past years, mostly focusing on specific synthetic tests in the context of additive manufacturing while rarely being actually ... [more ▼]

Functionally graded lattice structures (FGLS) were studied thoroughly for the past years, mostly focusing on specific synthetic tests in the context of additive manufacturing while rarely being actually applied outside of this specific domain. This paper examines a way to practically implement them in a commonly used appliance and study their potential for its improvement. A bicycle crank arm was chosen for this purpose, and a solid aluminium reference model (Shimano FC-R450-453) is used as a performance baseline. The novel design is composed of a hollow body containing a beam-based, non-stochastic, functionally graded lattice structure and is planned to be manufactured on a Markforged Metal X system using 17-4 PH stainless steel. It aims to increase the total stiffness under EN ISO 4210-8 norm loading conditions compared to the reference model while limiting mass and stress values to acceptable degrees. Two crank arm variants, containing a face-centred cubic (FCC) and re-entrant auxetic lattice respectively, are optimised by locally altering their beam radii in eight separate regions. The displacement at the load application point is minimised using Altair OptiStruct and HyperStudy. The reference crank, weighing 213g, exhibits a deflection magnitude of 7.1mm in the most demanding load case while the newly designed and optimised versions only showed displacements of 2.52mm (FCC lattice, 340g) and 2.58mm (re-entrant lattice, 339g) respectively. In addition, the stress distribution was significantly enhanced compared to the reference model, as the latter would not pass the fatigue tests required by the norm. This demonstrates that FGLS, in combination with high-strength materials and additive manufacturing, can increase the performance of many parts, although in this case, with a trade-off in terms of its mass. In future projects, it might be considerably reduced by utilising alternative lattice types lattices or other materials while preserving the benefits of FGLS. [less ▲]

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