Additive Manufacturing Fatigue and Fracture IV: Toward Confident Use in Critical Applications: Joint Session with Fatigue in Materials Symposium - Microstructure-based Fatigue Studies on Additive-Manufactured Materials
Sponsored by: TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Nik Hrabe, National Institute of Standards and Technology; Steve Daniewicz, University of Alabama; Nima Shamsaei, Auburn University; John Lewandowski, Case Western Reserve University; Mohsen Seifi, ASTM International/Case Western Reserve University
Wednesday 2:00 PM
February 26, 2020
Room: 10
Location: San Diego Convention Ctr
Session Chair: Garrett Pataky, Clemson University; Nik Hrabe, National Institute of Standards and Technology
2:00 PM Invited
Fracture and Fatigue Issues for (Metal) Additive Manufacturing: John Lewandowski1; 1Case Western Reserve University
The talk will cover recent works that are exploring the location- and orientation-dependence of mechanical properties in various builds and structures of various materials. Work at CWRU, and in collaboration with others, is examining the microstructure (e.g. morphology and defect density) and mechanical behavior (e.g. tension, fracture toughness, fatigue crack growth, high cycle fatigue) of both specimens and parts made with different materials. In addition to printing and testing bulk samples, miniature samples have been excised from both bulk samples as well as prototype parts for both as-deposited and post-processed builds. Existing and evolving ASTM/ISO standards for additively manufactured materials were used to illustrate the range of microstructural features and mechanical properties that are being reported for a few commonly studied alloy systems and AM techniques. The opportunities and challenges facing the more widespread use of additive manufactured components in structural applications will be discussed.
2:30 PM Invited
Fatigue Crack Growth Mechanisms and Design-qualification Considerations in Ti-6Al-4V Alloys Fabricated by Three Powder-based Additive Manufacturing Technologies: Yuwei Zhai1; Haize Galarraga1; Robert Warren1; Diana Lados1; 1Worcester Polytechnic Institute
There are many additive manufacturing (AM) processes that have been used for the fabrication and repair of Ti-6Al-4V components, each process providing different mechanical properties due to its unique thermal history. This presentation systematically discusses and compares the processing-microstructure-property relationships in Ti-6Al-4V alloys produced by three powder-based AM technologies: Laser Engineered Net Shaping (LENS), Electron Beam Powder Bed Fusion (EBM), and Laser Powder Bed Fusion (LPB). First, the relationships between thermal histories and resulting microstructures will be presented and discussed. Further, the fatigue crack growth behavior for different orientations (with respect to the deposition direction), stress ratios, and heat treating conditions will be addressed, and damage mechanisms at the microstructural scale at different crack growth stages will be identified. The results will then be broadly reviewed from the perspective of design for fatigue resistance and life predictions in high-integrity applications. Opportunities and directions towards material/part qualification will also be discussed.
3:00 PM Invited
Microstructure-oriented Studies of Fatigue Damage in Additive Manufacturing Using Combined Enhanced Measurement Techniques: Frank Walther1; 1TU Dortmund University
The evolution of the microstructure in additive manufacturing (AM) processes is the detrimental effect on the fatigue strength in technical applications. Modern microscopy and intermittent testing with applied enhanced measurement techniques enable higher precision tracking of the influence of microstructure on fatigue damage stages. Intermittent fatigue testing of selective laser melted (SLM) Al alloys revealed the interaction between porosity and microstructure under loading in very-high cycle fatigue (VHCF) conditions. The grain boundary strengthening of the microstructure increased VHCF strength by 33%. Modification of AlSi10Mg composition with Sc leads to precipitation with enhanced elastic strength of SLM Al alloys by about 100 MPa. Nanodispersion of oxides into steels increased high-temperature strength significantly especially in steels modified interstitially by C and N. The previous examples of microstructure control as well as other examples are presented to reveal the potential to enhance the reliability of application of AM components based on microstructural improvements.
3:30 PM Break
3:50 PM Invited
Relating Additive Manufacturing Processing Conditions to Surface Roughness, Porosity and Microstructure Influencing Fatigue Life: Joy Gockel1; Luke Sheridan2; Eric Tatman1; Dino Celli2; Wesley Eidt1; 1Wright State University; 2Air Force Research Laboratory
Additive manufacturing (AM) is unique because the material is being built at the same time as the component. Process condition variations in specific geometric sections of the component result in material variations. The relationships of processing conditions to surface roughness, porosity, microstructure and fatigue performance are investigated for alloy 718 fabricated using laser powder bed fusion AM. Both standard fatigue test bars and custom geometries with structurally relevant as-built features are utilized. Material characterization using traditional, experimental methods requires numerous specialized tests under various conditions, but the cost of manufacturing and preparing the AM test specimens (time, material, post-processing, etc.), often makes high volume testing infeasible. A novel method is applied to analyze a single axial fatigue test to provide information for crack initiation and growth behavior. Understanding the component-specific crack growth data provides insight for identifying microstructure causing structural performance variation in AM components.
4:20 PM Invited
An Investigation into Property-performance Relationships in Additive Manufacturing: Nima Shamsaei1; 1Auburn University
Before additively manufactured (AM) parts can be trusted in load-bearing applications, their fatigue performance should be well-characterized. However, due to variations in geometries, and therefore, thermal histories experienced, the mechanical properties of witness coupons may not be representative of the critical location of AM parts. Differences in thermal history can influence the microstructure and porosity level in the material, thus affecting the specimen property-to-part performance relationships. This presentation provides an overview on the challenges in generating fatigue data and design allowables for AM materials. Results show that the process parameters can be adjusted by understanding the effect of geometry on the thermal history to fabricate specimens with the same microstructure and defect level as the material at the critical location of the part in service. It will be argued that property-performance relationships, i.e. specimen property-to-part performance, can be further established by fully understanding the process-structure relationships for AM materials/parts.
4:50 PM Invited
“Lessons Learned” for Structural Alloys and Implications for Metal AM Fatigue and Damage Tolerance Considerations: Michael Gorelik1; 1Federal Aviation Administration (FAA)
Metal AM is still a relatively new technology, with very limited full-scale production and field experience in Aviation. The expanding use of AM, heading towards the safety-critical applications, prompts F&DT considerations, both to ensure product safety and to meet certification requirements. Most of the current “lessons learned” for AM are based on either academic R&D, or industry development work (the latter typically being proprietary). While such work is very important and helps with identification of AM-specific properties and attributes, and the means of addressing them in the context of Q&C, it cannot replace decades of production and field experience for more conventional forms of structural alloys, e.g. castings, wrought products, powder metallurgy etc. Thus, examining some of the relevant lessons learned for such legacy alloy systems can help with shaping the appropriate F&DT framework for metal AM materials. These considerations, illustrated by specific examples, will be discussed in this presentation.