Session Tu1: Tuesday, June 13, 10:30-12:30
Tuesday Jun 13 2023
10:30 - 10:50
PREDICTING MICROSTRUCTURE-SENSITIVE FRACTURE BEHAVIOR IN AM IN625 USING A DAMAGE-ENABLED ELASTO-VISCOPLASTIC FFT FRAMEWORK
Ashley SpearGrand Ballroom E
In this work, we use a large-strain elasto-viscoplastic fast Fourier transform (LS-EVPFFT) code enhanced with a continuum damage mechanics model to predict failure response of a subcontinuum mesoscale tensile specimen in the context of the National Institute of Standards and Technology (NIST) 2022 Additive Manufacturing Benchmark (AM-Bench) Challenge. In the Challenge, participants were provided with data from X-ray computed tomography and electron backscattered diffraction (EBSD) for an AM IN625 sample and asked to predict stress and strain response and locations of necking and fracture. To account for uncertainty in the subsurface microstructure, we instantiated 10 semi-synthetic microstructures using a Potts model in a modified version of the open-source software SPPARKS. While all 10 models maintain identical surface grain structure, surface roughness, and internal porosity, their subsurface grain structures vary due to randomness in the microstructure-generation procedure. Results from the blind predictions using the LS-EVPFFT framework are compared to the experimental results. Lessons learned are discussed.
10:50 - 11:10
EFFECTS OF PROCESS CONDITIONS AND MICROSTRUCTURE ON THE FATIGUE AND FRACTURE OF AM IN718 UNDER
Alexander CaputoGrand Ballroom E
Additive manufacturing (AM) dramatically increases the design freedom for difficult to machine alloys like IN718. For turbine applications for aerospace and energy, additional freedom in component design allows for lightweighting and better cooling efficiency. This study seeks to elucidate and model the effects of porous and crystallographic microstructural elements on the fatigue life and fracture behavior of AM IN718 through X-ray computed tomography (XCT), scanning electron microscopy (SEM), and electron backscatter diffraction (EBSD) of specimens tested under high temperature high cycle fatigue.
11:10 - 11:30
MICROSTRUCTURE-PROPERTY PREDICTIONS AND MULTISTAGE FATIGUE LIFE PREDICTION OF HOLE RESTORATION COUPONS USING AFSD
Jim LuaGrand Ballroom E
Military aircrafts operate frequently in a highly corrosive environment. Corrosion in aluminum aircraft structures with holes and adhesive-bonded lap joints promotes multi-site cracking, which can lead to failure of major aircraft components. To expedite and facilitate the corrosion repair process, an emerging solid-state process, additive friction stir deposition (i.e. AFSD) is applied for the hole restoration followed by the fatigue performance evaluation. Because of the friction stir induced material flow of the deposited and substrate materials, the resulting microstructure and its associated properties are position-dependent. The weak metallurgical bond at the bottom of the repaired hole coupon can promote a crack initiation under cyclic loading and the total life consists of crack initiation, short crack growth, and long crack propagation. This paper describes the use of a multiphysics modeling approach to characterize the process-driven properties evolution and to evaluate the effects of a kissing bond on the total life of hole restoration coupons.
11:30 - 11:50
SHORT CRACK GROWTH BEHAVIOR OF IN718 UNDER HIGH TEMPERATURE CONDITIONS IN CONSIDERATION OF PLASTICITY INDUCED CRACK CLOSURE
Timo BruneGrand Ballroom E
The behavior of short fatigue cracks under high temperature conditions is of significant importance for lifetime predictions and defect assessment of components in aircraft and gas turbine applications. The cyclic R(esistance) curve provides a possibility to describe phenomenologically the crack growth behavior below the long crack threshold. Within this paper experimentally determined cyclic R-curves of the nickel based alloy IN718 for varying load ratios (Rσ = -1, 0 and 0.5) at 650 °C are compared to each other. Furthermore, an approach supporting a mechanism-based understanding of the cyclic R-curves, taking plasticity induced crack closure (PICC) into account, is developed. Finite element analysis is used to estimate the amount of PICC in the short crack regime. For a systematic investigation of the impact of different ductility properties on short crack behavior, results from an additively and two conventionally (cast and wrought) manufactured material variants of IN718 are part of the investigations.
11:50 - 12:10
MICROSTRUCTURALLY INFORMED HIGH-VELOCITY IMPACT EXPERIMENTATION ON ADDITIVELY-MANUFACTURED METALLIC MATERIALS
Juan Carlos Nieto-FuentesGrand Ballroom E
This work presents a flexible experimental setup to study dynamic fragmentation of additively-manufactured metallic materials using two different configurations: (i) rapid axial penetration of thin-walled tubes, and (ii) rapid radial expansion of rings. In the first approach, the experiment consists of a light-gas gun that fires a conical nosed cylindrical projectile that impacts axially on a thin-walled cylindrical tube fabricated by 3D printing. The diameter of the cylindrical part of the projectile is approximately twice greater than the inner diameter of the cylindrical target, which is expanded as the projectile moves forward, eventually breaking into fragments. In the second approach, using a similar technique, a ring is inserted over a high-ductility tube, which expands after penetration by the conical projectile, pushing the metallic ring radially outwards, ultimately breaking into multiple fragments. The experiments have been performed for impact velocities ranging from 180 m/s to 390 m/s. A salient feature of this work is that we have characterized by X-ray tomography the porous microstructure of selected specimens before and after testing. Moreover, two high-speed cameras have been used to film the experiments and thus to obtain time-resolved information on the mechanics of formation and propagation of fractures.
12:10 - 12:30
CRACK GROWTH-BASED FATIGUE-LIFE PREDICTION OF ADDITIVELY MANUFACTURED MATERIALS
Mohammadbagher MahtabiGrand Ballroom E
In this study, a plasticity-induced crack closure model, FASTRAN, was used to predict the fatigue life of Inconel 718, 17-4 precipitation hardening (PH) stainless steel (SS), and Ti-6Al-4V alloys fabricated via additive manufacturing (AM) systems. Results indicated that in the presence of large defects (e.g., lack-of-fusion defects), the total fatigue life of AM specimens is dominated by crack growth. Results indicated that variations in the fatigue lives of specimens in machined and as-build surface conditions can be predicted based on the characteristics of AM process-induced defects and surface profile. Effect of build orientation on fatigue life was also captured based on the size of defects projected on a plane perpendicular to the loading direction. In addition, maximum valley depth of the surface profile can be used as an appropriate parameter for the fatigue-life prediction of AM specimens in their as‐built surface condition.
Session Tu2: Tuesday, June 13, 14:00-16:00
Tuesday Jun 13 2023
14:00 - 14:20
INFLUENCE OF THE CONTOUR PARAMETER IN MICROSTRUCTURE DUALITY AND FRACTURE INITIATION IN NON-COMBUSTIBLE MAGNESIUM ALLOYS FABRICATED BY LASER POWDER BED FUSION
Bryan ProanoGrand Ballroom E
Non-combustible Mg alloy components fabricated by laser powder bed fusion in as-built conditions have an average ultimate tensile strength (UTS) of 320 MPa, a significantly larger value than its casting counterparts, which present an average UTS of 200 MPa. In addition, it was determined that stable crack extension always starts at the outer surface due to the coarsened microstructure regions present in the area. Therefore, this paper will use fracture mechanics to predict the UTS value by determining the size of the coarsened microstructure region and considering it as a surface crack with the √area parameter. Then, by using a fixed fracture toughness value, the UTS will be predicted. Furthermore, a processing parameter known as contour, which is used for remelting the outer surface of the specimen, can also smoothen the microstructure and potentially increase the UTS value. Results showed that the √area of the surface crack responsible for fracture was 730 μm for the no-contour specimen and 630 μm for a contour specimen. Subsequently, using Murakami’s theory, the predicted UTS is 320 MPa and 345 MPa respectively. Finally, tensile testing was performed to confirm the prediction, showing similar results with an average deviation of 2.9%.
14:20 - 14:40
EVALUATION OF STRENGTH CHARACTERISTICS FOR NON-COMBUSTIBLE MAGNESIUM ALLOY PRODUCTS FABRICATED BY LASER POWDER BED FUSION UNDER AS-BUILT CONDITION
Taeseul ParkGrand Ballroom E
It is difficult to evaluate fracture toughness according to ASTM standards for non-combustible magnesium alloy fabricated by Laser Powder Bed Fusion (LPBF) in as-built conditions. The reason is its microstructure duality between inner and outer surfaces. The microstructure duality can be eliminated by heat treatment. However, heat treatment reduces the strength of the material by around 11%. Therefore, heat treatment was not performed. In addition, the greatest advantage of LPBF is maximized when it can be used immediately without post-processing. Therefore in this study, the as-built condition was targeted. In the case of non-combustible Mg products, the mechanical properties of the inner and outer microstructures have a non-negligible difference. The difference is expected to affect the fracture behavior, so it is important to consider the difference in microstructure in strength evaluation. Therefore, this paper explains why ASTM standards are difficult to apply to non-combustible magnesium products fabricated by LPBF in as-built conditions with their microstructure differences. Furthermore, the alternative methods for measuring the fracture toughness of metals fabricated by the LPBF in as-built conditions with these characteristics are introduced and discussed.
14:40 - 15:00
REDUCING LOW CYCLE FATIGUE LIFE SCATTER OF ADDITIVE MANUFACTURED ALSI10MG USING LASER SHOCK PEENING
Garrett PatakyGrand Ballroom E
Additive manufactured (AM) alloys are still prone to critical manufacturing flaws, such as gaseous bubble entrapment. These defects can lead to early crack initiation reducing fatigue life and increasing scatter, especially when near surface. This research investigated the effect of femtosecond laser shock peening (FLSP) on the fatigue life of AM AlSi10Mg. Due to the low penetration of the FLSP, fatigue life remained consistent between treated and untreated specimens. Of equal importance though, the scatter was found to be reduced in the FLSP treated samples. From the high resolution DIC results, the average strain per grain in the untreated specimens showed a higher increase of strain from initial loading to final fracture as compared to the FLSP samples. Implementing the use of FLSP onto AM materials could lead to more consistent fatigue life despite the presence of porosity, leading to a path of easier certification and improved confidence in their behavior.
15:00 - 15:20
COMPUTATIONAL MODELING FOR IDENTIFYING VOIDS IN ADDITIVELY MANUFACTURED AL-SI10-MG
Nha Uyen HuynhGrand Ballroom E
Additive manufacturing (AM) is a quicker and more cost-effective technique to produce complex parts that can perform similar to or better than conventionally manufactured parts. However, due to the dissimilar microstructure compared to conventional parts, there is a lack of understanding in the physical and mechanical response of AM alloys under different loading conditions and strain rates, and thus the suitability of using AM parts is uncertain. Notably, the presence of voids in AM metal alloys is more prevalent. By developing a computational model that can represent plasticity and track fracture initiation at the void sites in AM alloys such as Al-Si10-Mg, the failure response can be predicted. Therefore, the objective of this research is to use in-situ micro-computed tensile testing to identify individual voids or networks of voids that are likely to cause fracture initiation in an AM Al-Si10-Mg alloy.
15:20 - 15:40
FINITE ELEMENT MODELLING IN PREDICTING THE EFFECT OF DEFECTS ON STRESS CONCENTRATION AND FATIGUE LIFE OF L-PBF ALSI10MG ALLOY
Raj DasGrand Ballroom E
The elastic-plastic finite element analysis is performed to obtain the stress field around pores and evaluate their resultant effects on fatigue life for L-PBF (Laser Powder Bed Fusion) produced AlSi10Mg alloy. The stress field is calculated for both single and multiple pore models, where stress concentration is evaluated as a function of the pore location and its size. A multi-scale finite element (FE) model is proposed based on the inherent porosity data from Computed Tomography (CT) to predict the overall fatigue life with high (90%) accuracy. The predicted fatigue life (cycles) are calculated using the rainflow counting algorithm in fe-Safe software using the stress-strain data obtained from the proposed FE model developed using the Abaqus software. Using the proposed model, it is possible to generate S-N curves for any loading condition for a given porosity characteristic (porosity density and average pore size).
Session W1: Wednesday, June 14, 10:30-12:30
Wednesday Jun 14 2023
10:30 - 10:50
IMPACT OF MICRO AND MESOSTRUCTURE ON THE FAILURE RESISTANCE OF LASER POWDER BED FUSION-PROCESSED MATERIALS
Bernd GludovatzGrand Ballroom E
Engineering materials processed using additive manufacturing (AM) techniques such as laser powder bed fusion (LPBF) often exhibit unique microstructures and defects that must be controlled to obtain peak performance in mechanical properties and as such a level of damage-tolerance that cannot be achieved in cast alloys. However, our understanding of how processing conditions control micro- and mesostructure and, in turn, mechanical performance, particularly regarding failure resistance, is weak. Furthermore, heat treatments that have been designed to achieve peak performance in cast alloys are often not optimized for alloys that have been processed using AM techniques. Here, we report our work on the effect of processing parameters such as layer thickness, hatch spacing, and scan strategy on crack resistance curve (R-curve) behavior in different orientations of LPBF-processed AlSi10Mg and correlate mechanical performance with meso- and microstructural features such as melt pool arrangement, cell morphology, grain size, grain orientation, and texture. Compared to that we show how heat-treatments impact fracture resistance as well as their anisotropy in two orthogonal orientations in an LPBF-processed 18Ni-300 maraging steel.
10:50 - 11:10
PREDICTING SURFACE ROUGHNESS IN METALLIC ADDITIVELY MANUFACTURED PARTS USING MACHINE LEARNING
Nagaraja IyyerGrand Ballroom E
A melt pool geometry-based approach is developed to predict surface roughness in metal additively manufactured parts for a range of processing parameters. It is shown that surface roughness on a particular facet can be estimated by stacking melt pools along the facet, extracting their outer contour and applying the necessary transformations. To be able to predict surface quality of various processing parameters in a reasonable time frame, a machine learning framework is developed. This framework is trained over melt pool data generated by high-fidelity FE simulations.
11:10 - 11:30
ANALYSIS OF FATIGUE CRACK GROWTH WITH OVERLOAD EFFECTS THROUGH T-STRESS
Ghita Bahaj FilaliGrand Ballroom E
Fatigue crack is a major concern to all industries for safety reasons. Fatigue life predictions for structural components such as railways or turbine disks are based on fracture mechanics analysis. Such components are inevitably submitted to underloads or overloads. The aim of this paper is to provide a DIC-BASED experimental analysis of overload 2D fatigue cracks using higher order terms in the Williams’ series expansion.
The prediction of the fatigue life of these components is often based on crack propagation calculations. However, overloads and underloads perturb steady state fatigue crack growth conditions and affect the growth rates by retarding or accelerating growth. The application of overloads generates complex effects on the crack behavior which induce delays that are difficult to predict. The mechanisms that have been proposed to explain retardation after tensile overload include, e.g. residual stress, crack closure and plasticity ahead of the crack tip.
In this work, based on DIC we use full-field measurements to obtain LEFM crack tip features (Stress Intensity Factor and T-stress). Therefore, with these crack tip features, we propose to analyze the T-stress effect on the crack growth propagation.
11:30 - 11:50
FATIGUE LIFE OF LASER POWDER BED FUSION (L-PBF) ALSI10MG ALLOY: EFFECTS OF SURFACE ROUGHNESS AND POROSITY
Raj DasGrand Ballroom E
The fatigue life of components manufactured by the laser powder bed fusion (L-PBF) process is dominated by the presence of defects, such as surface roughness and internal porosity. The present study focuses on the relative effect of surface roughness and porosity in determining the fatigue properties of AlSi10Mg alloy produced by L-PBF built in the Z direction for as-built (ASB), machined (M) and machined & polished (M&P) conditions. As-built L-PBF samples possess higher surface roughness (1.5-2 µm) compared to the machined (0.8-1.0 µm) or polished ones (0.3-0.75 µm). For ASB samples, surface roughness was found to be the dominant factor affecting fatigue life. However, for M or M&P samples with relatively low surface roughness, the subsurface porosity becomes the dominant factor affecting fatigue failure rather than variations in the surface roughness. The pore size and location effects are analysed using linear elastic fracture mechanics theory, and the critical stress intensity factors (SIF) for L-PBF AlSi10Mg alloy samples are estimated.
Session W2: Wednesday, June 14, 14:00-16:00
Wednesday Jun 14 2023
14:00 - 14:20
HIGH CYCLE FATIGUE OF AM PRODUCED HOT WORK TOOL STEEL
Dimitrios NikasGrand Ballroom E
Additive manufacturing as a mean to produce near net shape components of metal alloys has evolved in many commercial applications during the last decade. Still, development of additive processes and alloy grades requires new research knowledge. In the present study focus is on advanced high strength martensitic steels and fatigue properties. They are used in demanding tooling and high performance applications where high strength and toughness, both static and dynamic, are required. Fatigue strength and failure defect distributions of one AISI H13 AM grade and one corresponding ingot cast and forged grade have been characterized and modelled.
14:20 - 14:40
ON THE MECHANISTIC ORIGINS OF THE INCREASED HYDROGEN ENVIRONMENT-ASSISTED CRACKING SUSCEPTIBILITY OF AM 17-4PH STEEL
Zachary HarrisGrand Ballroom E
Literature results indicate that the hydrogen environment-assisted cracking susceptibility of additively manufactured (AM) 17-4PH steel fabricated using laser powder bed fusion is increased relative to comparable wrought 17-4PH. This study seeks to understand the mechanistic origins of this increased susceptibility through a detailed examination of near-crack deformation, alloy microstructure, and hydrogen-metal interactions. Based on these data, it is determined that sub-micrometer porosity present in the AM material provides a primary contribution to the degradation in HEAC resistance. The mechanistic basis for the influence of porosity is considered in the context of an existing model for HEAC. The implications of these findings on the broader AM community are then discussed.
14:40 - 15:00
ENVIRONMENTAL CRACKING OF ADDITIVELY MANUFACTURED 316L STAINLESS STEEL
Michael RoachGrand Ballroom E
The widespread use of 316L stainless steel for applications requiring increased corrosion resistance has motivated interest in leveraging additive manufacturing (AM) for in-service production of replacement components. However, while a large number of studies have examined the effect of AM processing parameters on yield strength and fracture toughness, detailed assessments of the environment-assisted cracking (EAC) susceptibility of AM alloys are limited. The objective of this study is to compare the corrosion fatigue and stress corrosion cracking behavior of AM and wrought 316L with similar yield strengths in aqueous chloride environments at temperatures ranging from 293 to 358 K. As built material will be compared with cold drawn bar, and hot isostatic pressed (HIP) material will be compared with plate in the annealed state to minimize the effect of different yield strength between material form. Differences in microstructure and build-introduced stresses are correlated with EAC performance, thereby providing mechanistic insights into the factors governing EAC behavior of AM 316L. In particular, the influence of build direction, residual stresses, texture, and compositional heterogeneities are all assessed.
15:00 - 15:20
DEFECT STATISTICS AND FRACTURE INITIATION MECHANISMS IN AS-BUILT AND HEAT-TREATED ADDITIVE MANUFACTURED 17-4 STEEL
Ravi KiranGrand Ballroom E
Defects in additively manufactured metals are detrimental to the manufactured components. Due to the rapid melting and solidification during printing, a non-homogeneous microstructure is typical in the metal specimens additively manufactured using laser powder bed fusion. The present study aims to understand the fracture initiation mechanism in as-built and heat-treated additively manufactured 17-4 stainless steel. To this end, 17-4 stainless steel unnotched and notched specimens additively manufactured using direct metal laser sintering were used. Solution annealing and subsequent aging were performed as the post-heat treatment of the stainless steel test specimens. Postmortem fractography using scanning electron microscopy (SEM) of the fracture surface and micro-computed tomography (micro-CT) of the test specimens before and after fracture revealed that the large coalesced microvoids with sizes greater than 120 µm significantly influence the ductile fracture initiation in the additively manufactured steel specimens.
Session Th1: Thursday, June 15, 10:30-12:30
Thursday Jun 15 2023
10:30 - 11:00
RESISTANCE TO FRACTURE AND FATIGUE IN ADDITIVELY MANUFACTURED ALLOYS [Keynote]
Punit KumarGrand Ballroom E
Ti-6Al-4V fabricated by the laser powder bed-fusion (LPBF) process consists of metastable α' microstructure and columnar prior β grain (PBGs) mesostructures. These micro-and mesostructures adversely affect fracture toughness (KIc) in as-built conditions. After an optimized post-processing heat-treatment, the KIc of LPBF Ti-6Al-4V improves by ⁓104%; however, the anisotropy in KIc persists due to preferential crack growth along the columnar PBGs. In another LPBF fabricated β Ti-alloy, Ti41Nb, the crack tortuosity from the mesostructures formed by compositional segregation improves the KIc by ⁓80%. These results demonstrate extrinsic toughening in AM alloys. While such toughening from mesostructures enhances AM alloys' reliability, the processing-induced defects present in them, i.e., porosity, significantly reduce their high cycle fatigue (HCF) resistance. Therefore, in the second part of the present study, the HCF life of 316L and 17-4 PH steels produced by the binder jet printing process was investigated. The hot isostatic pressing (HIP) was employed on these steels to improve their HCF life. The HCF life of HIPed 17-4 PH steel is comparable to their conventionally manufactured counterparts; however, in 316L, HIP fails to improve fatigue life. Based on these findings, the microstructural origin for fracture and fatigue resistance in AM alloys are discussed.
11:00 - 11:20
VERY HIGH-CYCLE FATIGUE BEHAVIOR OF ADDITIVELY MANUFACTURED TI-6AL-4V USING ULTRASONIC FATIGUE MACHINE AND SELF-HEATING TESTING.
Grégoire BrotGrand Ballroom E
Accelerated characterization of high-cycle fatigue properties is necessary in order to enable the optimization of parameters of additive manufacturing processes such as LPBF (Laser Powder Bed Fusion). Therefore, two accelerated characterization methods are applied and compared on Ti-6Al-4V samples produced using the LPBF process. The first method uses an ultrasonic fatigue machine and the second one determines the fatigue limit using self-heating testing. To study the interactions between the material and the accelerated testing methods, fatigue tests are carried out on different grades of Ti-6Al-4V-LPBF differing by their microstructure or their porosity. Three grades have the same microstructure but different porosity levels and three grades have different microstructures with the same porosity. Both properties showed a strong impact on VHCF strength and affected the mechanisms at fatigue crack initiation.
11:20 - 11:40
ANALYSIS OF POROSITY EFFECTS ON SPALL FAILURE OF ADDITIVELY MANUFACTURED 316L SS
Taylor SloopGrand Ballroom E
Additive manufacturing (AM) allows for tuning of mechanical properties for unique functionalities, and stainless steel is a prime candidate for use in many applications due to its high strength, ductility, and corrosion resistance. AM fabricated 316L stainless steel samples with intentionally random pore placement are compared to samples with known pore placement to study the interaction of the shock wave with individual and grouped pores. Velocity profiles were obtained using photon doppler velocimetry (PDV) probes placed strategically along the location of the known pores to understand the limits of local influence for the known pores. Post-mortem characterization of soft-recovered samples using electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) was performed to investigate the strain accommodation around pores. It was observed that shock wave fronts are highly dispersed and slow as they propagate through the pore due to strain accommodation around individual pores. As a result, there is shifting of the spall plane away from the impact face. This slow wave front propagation also results in slow rise time and lack of velocity plateau in the collected velocity profiles when areas with pores were probed.
11:40 - 12:00
FAILURE CHARACTERIZATION IN 17-4PH STAINLESS STEEL ACROSS MULTIPLE MANUFACTURING METHODS
Brian FuchsGrand Ballroom E
Accurate models of additively manufactured (AM) materials require extensive mechanical testing for proper calibration and verification/validation. The process-structure-property relationships in 17-4PH stainless steel from multiple manufacturing modes were examined via mechanical testing across several strain rates and post-mortem characterizations of the fracture surfaces and microstructure. Under all manufacturing modes and testing conditions, optical and scanning electron microscopy showed ductile failure characteristics. Higher porosity concentration (determined by density measurement) resulted in lower ultimate strength in cast samples; the pores often acted as crack initiation points. Strain-rate dependence and failure modes were also affected by process-dependent anisotropy in the microstructure, which was quantified through electron backscatter diffraction (EBSD) imaging. This data will be used to inform models of failure in the 17-4PH for multiple manufacturing forms.
Session Th2: Thursday, June 15, 14:00-16:00
Thursday Jun 15 2023
14:00 - 14:20
MODELING OF MIXED-MODE CRACK GROWTH BEHAVIOR IN LB-PBF TI-6AL-4V USING A CRITICAL PLANE FRAMEWORK
Ali FatemiGrand Ballroom E
Many service loading conditions are multiaxial, and small cracks have been shown in many situations to grow in mode II or mixed-mode due to the orientation of defects and microstructural effects, particularly in additively manufactured metals. This paper uses fracture mechanics with a critical plane framework to predict crack growth rates using only mode I constants from the literature.
14:20 - 14:40
SIGNIFICANCE OF INTRA-BUILD DESIGN VARIABLES ON THE FRACTURE TOUGHNESS PROPERTIES OF ELECTRON BEAM MELTED TI6AL4V
Melody MojibGrand Ballroom E
Structurally reliable materials are essential for adopting additive manufacturing (AM) metals in safety-critical applications. Limited data on the damage-tolerance properties of metal AM materials exists, hindering the acceptance of AM metals in fracture-critical applications. A design of experiments (DOE) is used in this study to investigate the role of build space and part design parameters on the fracture toughness properties of Electron Beam Melted (EBM) Ti6Al4V. ASTM E399 tests were performed on over 100 compact tension (CT) samples in the as-built and machined conditions to obtain fracture toughness properties and evaluate the influence of part size and location within 80% of the build space. Results were comparable to wrought annealed titanium, with less than 10% variation in overall fracture toughness. Specimen location within the build envelope contributed to the observed variation, with an increase in properties with build height and specimens located in the center of the build envelope. The location-dependent properties result from changes in microstructure and porosity throughout the build space. While the experimental EBM Ti6Al4V fracture toughness properties are promising for future applications, it is crucial to consider the variation in properties due to build space location and design parameters when designing for consistency.
14:40 - 15:00
FACTORS GOVERNING THE FATIGUE PERFORMANCE OF AM TI-6AL-4V COMPONENTS
Derek WarnerGrand Ballroom E
Before an additively manufactured component can be safely used in a load bearing application, its mechanical performance must be qualified. Traditional qualification approaches, involving the fabrication and testing of many identical components, negate one of the greatest benefits of additive manufacturing, i.e. the ability to quickly and cheaply fabricate one-off components. Thus, qualification methods that rely less on mechanical testing and more on predictive modeling are of value. This is most true for high cycle fatigue performance, where mechanical testing requires significant resources and produces stochastic results.
High cycle fatigue failure is difficult to predict because it can depend nonlinearly on many parameters, e.g. part geometry, residual stresses, surface characteristics, material defect characteristics, grain and dislocation structures, mechanical and environmental loading characteristics and their history. This has motivated a succession of fatigue models with ever increasing mechanistic fidelity, with some now diving down to the atomic scale. This raises the question of: what level of mechanistic detail is required to sufficiently predict the performance of AM Ti-6Al-4V components? In this talk, I will give my perspective on this question, building from a decade of AM Ti-6Al-4V fatigue modeling and experimentation across scales.
15:00 - 15:20
FATIGUE LIFE PREDECTION OF THE AA2024-T351 ALUMINUM ALLOY
Naila HfaiedhGrand Ballroom E
The purpose of this styudy is to investigate the cyclic behaviour of the AA2024-T351 aluminum alloy widely used in the aircraft industry. This alloy shows a relatively low ductility at room temperature and is generally heat treated in various conditions to suit particular applications. Monotonic and cyclic tests have been conducted in order to characterize the fatigue behaviour and determine the fatigue life of aluminum alloy. Cyclic tests in the Low Cycle Fatigue (LCF) regime were performed under fully reversed total strain amplitudes ranging between 0.6% and 1.2%. The elastoplastic behaviour was analysed through the stress-strain hysteresis loops leading to evaluate kinematic and isotropic hardenings. The AA2024-T351 was also shown to be prone to cyclic strain hardening. Besides, symmetric High Cycle Fatigue (HCF) tests were also performed and the Stress-Number of cycles (S-N) curve until 107 cycles was plotted. A fatigue limit of about 150 MPa was found. Based on all LCF and HCF tests, the fatigue life could be represented in a strain approach by the Manson-Coffin-Basquin law. Moreover, observations of the fracture surfaces were carried out using a Scanning Electron Microscope (SEM) in order to detect the crack initiation and follow the propagation for the two fatigue regimes.
15:20 - 15:40
MECHANICAL RESISTANCE ASSESMENT OF 316L STAINLESS STEEL ADDITIVELY-REPAIRED STRUCTURES
Fabien SzmytkaGrand Ballroom E
To quickly characterize the static and cyclic mechanical strength of a structure repaired by additive manufacturing, a specific specimen is developed and then repaired using two processes (laser direct energy deposition and cold spray) with adjustable parameters. The fundamental role of the microstructure in the vicinity of the repaired area in the initiation and propagation of cracks under cyclic loading is highlighted and discussed
15:40 - 16:00
FRACTURE TOUGHNESS OF A DUPLEX STAINLESS STEEL BUILT BY DIRECTED ENERGY DEPOSITION : EFFECT OF THE DEPOSITION DIRECTION
David RoucouGrand Ballroom E
Additive manufacturing of duplex stainless steels (DSS) has recently seen some research interest. In particular, the use of directed energy deposition (DED) is still new and the fabricated materials remain to be fully characterized. In addition, materials produced by additive manufacturing can present anisotropic fracture properties. This study aims to characterize the fracture toughness of a DSS manufactured by DED, taking into account the orientation with regard to the printing strategy.
Session F1: Friday, June 16, 10:30-12:30
Friday Jun 16 2023
10:30 - 10:50
ACCELERATED DESIGN AND INTEGRITY ASSESSMENT OF ADDITIVELY MANUFACTURED METALLIC STENTS USING MACHINE-LEARNING MODELS
Aida NonnGrand Ballroom E
In this work, we investigate the potential of laser powder bed fusion (L-PBF) to meet the stringent requirements imposed on metallic stents for the treatment of aortic dissection. Here, we use microstructure-based modeling to describe the mechanical properties of L-PBF 316L stainless steel. The derived structure-property relationships then serve as a database for training machine learning (ML) models, such as convolutional networks (CNN) and graphical neural networks (GNN). Based on the established modeling framework, we are able to predict the deformation and fracture behavior of 316L stents and identify the improved stent design in an efficient manner.
10:50 - 11:10
EFFECTS OF DEFECT, LOADING MODE AND MICROSTRUCTURE ON LPBF 316L FATIGUE BEHAVIOR
Franck MorelGrand Ballroom E
The present study aims to investigate the high cycle fatigue (HCF) performance of steel 316L fabricated by the laser powder bed fusion (LPBF) process. Bending and torsional fatigue test specimens built horizontally (0°), inclined (45°), and vertically (90°) have been prepared and tested in the as-built and polished states. The presence of multiple lack-of-fusion defects at the surface or subsurface is detrimental to the endurance under cyclic loading. A more pronounced defect sensitivity in bending compared to torsion is found. Microstructural features are seen to compete with inherent defects to affect fatigue performance in the condition that the effective defect sizes are close to the critical fatigue crack size.
11:10 - 11:30
CORRECTING FOR RESIDUAL STRESS EFFECTS ON FATIGUE CRACK GROWTH RATES OF ADDITIVELY MANUFACTURED TYPE 304L STAINLESS STEEL
Michael HillGrand Ballroom E
Additively manufactured (AM) metal builds contain residual stress that can influence measured fatigue crack growth rates (FCGRs), which may then bias the interpretation of the performance of AM materials. In the present work, the on-line crack compliance (OLCC) method was used to determine the residual stress intensity factor, Kres, while simultaneously collecting fatigue crack growth rate data in edge crack compact (C(T)) specimens of both AM and wrought materials. Measured near-threshold FCGR data in AM 304L C(T) specimens appear elevated in comparison with data from wrought specimens over a range of applied ∆K. By quantitatively accounting for residual stress, the results for materials processed by the different methods are brought into good agreement, demonstrating the importance of accounting for residual stress when interpreting fatigue crack growth data in AM materials.