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.
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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.
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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.
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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.
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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.
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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
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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.
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