1,721,036 research outputs found
Smooth and notch fatigue behavior of selectively laser melted Inconel 718 with as-built surfaces
No full textThe selective laser melting (SLM) technology applied to Inconel 718 produces near-net shape parts of unlimited geometrical complexity directly from a CAD model and a metal powder bed processing system. With respect to conventional manufacturing, SLM potentially fabricates parts that can be lighter in weight, cheaper and have complex geometries that are difficult or impossible to produce otherwise. However, the surface quality of SLM parts with as-built surfaces negatively affects their fatigue performance and post fabrication surface finishing may be cost-wisely unacceptable in most applications and often impossible because of surface inaccessibility.Two aspects significantly affecting the fatigue performance of SLM Inconel 718 parts have been investigated and are reported here: (i) the directional knock-down factor of the as-built surface state with respect to the surface machined condition, and (ii) the role of a geometrical notch in the as-built surface state as commonly found in complex SLM parts.Eight batches of un-notched and notched miniature specimens of heat treated SLM Inconel 718 with as-built surfaces were tested in cyclic plane bending. The unnotched fatigue strength was found to be sensitive to direction of the applied stress with respect to build direction. The as-built notch fatigue strength of heat treated SLM Inconel 718 is also highly directional in nature. Four SLM-technology-dependent factors are introduced and determined. The un-notched and notched fatigue behavior of SLM Inconel 718 with as-built surfaces obtained here compares satisfactorily with recently published data for the same material and SLM technology but different specimen geometry and test method. Therefore, the proposed experimental methodology based on the use of miniature specimens in cyclic bending may a viable tool for the efficient evaluation of the fatigue response of SLM metals
Fatigue Behavior of L-PBF Metals: Cost-Effective Characterization via Specimen Miniaturization
No full textHigh-performance metal parts are presently produced by the powder bed fusion (PBF) technology. When considered for structural applications, a key ingredient that would promote technology acceptance in industry is know-how on fatigue properties of PBF metals. The typical approach of published fatigue characterizations uses specimens of standard geometry with machined gage sections. However, surface machining of PBF parts should be minimal to be competitive with conventional fabrication technologies while the influence of rough as-built surfaces on fatigue performance should be experimentally quantified to overcome unacceptable trial-and-error approach to part design and qualification. To support this critical task, an original testing approach based on drastic specimen miniaturization to reduce cost and increase flexibility (i.e., the specimen is 22 mm long and 5 × 5 mm2 in minimum cross section) and plane cyclic bending to highlight the role of surface state. The method has been first published in 2017 and since then it has successfully applied to the fatigue characterization of L-PBF metals under a variety of surface conditions, surface orientations and surface finish. Factors such as as-built versus machined surfaces, surface orientation with respect to reference build direction, geometrical notches have been investigated for different L-PBF metals. The paper presents this cost-effective test method and reviews its recent applications to the fatigue characterization of Ti6Al4V, AlSi10Mg and In718 under different L-PBF processing and surface finishing conditions
INFLUENCE OF ROUGH AS-BUILT SURFACES ON SMOOTH AND NOTCHED FATIGUE BEHAVIOR OF L-PBF AlSi10Mg
No full textNear-net shape metal parts of great geometrical complexity are fabricated by the Laser Powder Bed Fusion (L-PBF) technology directly from a CAD model. Therefore, parts can be lightweight, less expensive in terms of material use and with shapes that may be impossible to produce by conventional technology. The fatigue behavior of L-PBF part in as-built condition is negatively affected by poor surface quality. Surface finishing after fabrication may be either unacceptably costly or impossible because the surface is inaccessible. Fatigue performance can be further reduced by the notch effect due to local geometrical variations. Among the Al-alloys, AlSi10Mg is readily processed with L-PBF and it is of interest for different industrial sectors. In this contribution two aspects, that is: i) the directional smooth fatigue behavior of as-built AlSi10Mg, and ii) the notch fatigue behavior with as-built surfaces are investigated. Eight sets of un-notched and notched miniature specimens of AlSi10Mg were produced as a single batch by L-PBF and tested in the as-build state under cyclic plane bending loading. The smooth fatigue behavior was determined as very sensitive to applied stress direction with respect to the build direction. The directional nature of the fatigue behavior was confirmed by notch fatigue data. Therefore, four notch fatigue factors that depend on the PBF technology were introduced and determined. The fatigue behavior of L-PBF AlSi10Mg obtained here was compared satisfactorily against recent data obtained with standard specimen geometries and test methods. The present methodology using mini specimens under cyclic bending efficiently determines the fatigue response of L-PBF metals
An Efficient Test Method for the Quantification of Technology-Dependent Factors Affecting the Fatigue Behavior of Metallic Additive Manufacturing Components
No full textPowder bed fusion (PBF) is the most widely used additive manufacturing (AM) technology for producing high-performance metal parts. The fatigue characterization of PBF metals is a fundamental step toward technology acceptance for structural applications. Most published fatigue characterizations have adopted standard specimens with machined gage sections, although, to be competitive with conventional technologies, machining of PBF parts should be minimized. Therefore, the impact of the as-built surface quality on the fatigue performance of PBF parts is a major concern for part design and qualification. We describe a novel testing approach that adopts miniature specimens and plane cyclic bending for the fatigue characterization of as-built PBF metals and assess this approach for the case of a Ti6Al4V alloy against data obtained with standard specimen geometries and test methods. The role of factors such as stress versus build directionality, geometrical notches, and PBF technology on the high-cycle fatigue of Ti6Al4V is then quantified. The proposed method is cost-effective and has flexible applicability. Therefore, it is useful for basic fatigue research of PBF metals and for supporting the qualification of fatigue-critical PBF parts
Influence of surface orientation and segmentation on the notch fatigue behavior of as-built DMLS Ti6Al4V
No full textDesign and qualification of load-bearing metal parts produced by the additive manufacturing technology is a critical issue. Such metal parts are complex in geometry with notches that are critical locations under fatigue loading. Notch surfaces are typically in the as-built state because post-fabrication surface finishing is not a viable approach in most applications. Here fatigue experiments using notched specimens produced according to different orientations with respect to build direction are presented and used to discuss the notch fatigue behavior of DMLS Ti6Al4V. Notch fatigue factors depend on the process itself and on fabrication details such as up-skin versus down-skin surface orientation, stair-stepping of the notch surface due to the layer-by-layer segmentation and intrinsic as-built surface roughness
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