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1. Ductile Fracture Modeling of Flaw-Containing Additively Manufactured SS316L: Application to Complex Structures

   https://doi.org/10.1007/s11340-024-01141-2  

   Furton, E T; Beese, A M (February 2025, Experimental Mechanics)

   Background To ensure reliability of additively manufactured components in structural applications, an understanding of the combined behavior of pores and stress state on failure behavior is required. Objective This research aims to identify the capabilities and limitations of stress- and strain-based fracture models in describing failure in complex additively manufactured structures. Methods SS316L brackets with a three-dimensional truss-based geometry, in which stress state and pore size varied among struts, were fabricated with laser powder bed fusion. Fracture models considering both stress state and pore size, formulated in terms of stress (pore-size dependent Mohr–Coulomb, or P-MC) and strain (pore-size dependent Modified Mohr–Coulomb, or P-MMC), were calibrated and used to predict the fracture behavior of the brackets. Results The P-MMC fracture model correctly predicted the experimentally observed fracture locations for 11 out of 12 samples, while the P-MC fracture model correctly predicted 10 out of 12 samples. Below a critical pore size, stress state effects dominated the fracture behavior, and above this, pore size was the critical factor, where capturing both factors was crucial at intermediate pore sizes. Conclusions The P-MC fracture model was appropriate for predicting the maximum load-bearing capacity for all samples in this study, while the P-MMC fracture model was shown to be only applicable for samples containing small pores. The importance of incorporating both stress state and the presence of pores in a fracture model is necessary to ensure confidence in the load carrying capacity of additively manufactured structures. 

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2. Crack Growth of Defects in Ti-6Al-4V Under Uniaxial Tension: Measurements and Modeling

   https://doi.org/10.1007/s11340-023-01008-y  

   Furton, Erik T.; Beese, Allison M. (February 2024, Experimental Mechanics)

   This study investigates the effects of pores on the mechanical properties of metals produced by additive manufacturing, which can limit strength and ductility. This research aims to both measure and model the rate of crack growth emanating from these pores in additively manufactured Ti-6Al-4 V fabricated with laser powder bed fusion. Uniaxial tensile samples containing intentionally embedded penny-shaped pores were mechanically tested to failure, and loading was interrupted by a series of unload steps to measure the stiffness degradation with load. The factors contributing to reduction in stiffness, namely (1) elastic and plastic changes to geometry, (2) the effect of plastic deformation on modulus, and (3) crack growth, were deconvoluted through finite element modeling, and the crack size was estimated at each unloading step. The stiffness-based method was able to detect stable crack growth in samples with large pores (1.6% to 11% of the cross-sectional area). Crack growth as a function of strain was fit to a model where the crack driving force was based on equivalent strain and a model where the crack driving force was based on energy release rate. Significant crack growth occurred only after the onset of necking in samples containing small pores, while samples containing large pores experienced continuous crack growth with strain. 

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3. Defect Evolution in Tensile Loading of 316L Processed by Laser Powder Bed Fusion

   https://doi.org/10.1007/s11340-021-00815-5  

   Miers, J. C.; Moore, D. G.; Saldana, C. (January 2022, Experimental Mechanics)

   Background Porosity and other defects resultant by additive manufacturing processes are well-known to affect mechanical properties. However, there remains limited understanding regarding how the internal defect structure influences the evolution of the local strain field, as experimental investigations have not presented direct measurements of the evolving internal strain field in the presence of defects. Objective Interrupted in-situ tensile tests in a lab-based X-ray computed tomography machine were used to investigate the evolution of the strain field around internal defects. The evolution of the internal strain field facilitated examination of the role of specific defects in the macroscopic deformation of additively manufactured tensile coupons. Methods Samples were produced in 316L stainless steel by laser powder bed fusion. An in situ loading device was utilized to subject the samples to tensile failure within a tomographic scanning environment. Digital volume correlation was utilized to directly determine local strain levels within the additively manufactured components in the vicinity of porosity defects. Results Effects of porosity on strain localization and eventual failure of the samples were evaluated. Characteristics of the porosity distribution, including presence of porosity at the surface or near-surface of components, as well as the proximity of pores to each other were found to influence the evolution of failure. Early onset of failure was found to be associated with the availability of neighboring porosity that allowed for rapid progression of the fracture path. Conclusions The direct measurements of strain field evolution in the present study established understanding regarding how internal defect structure characteristics influence the evolution of the local strain field for additively manufactured components. This high fidelity characterization and the associated phenomenological observations have bearing for supporting validation of numerical modeling frameworks for describing failure in these materials. 

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4. Contrasting the Role of Pores on the Stress State Dependent Fracture Behavior of Additively Manufactured Low and High Ductility Metals

   https://doi.org/10.3390/ma14133657  

   Wilson-Heid, Alexander E.; Furton, Erik T.; Beese, Allison M. (July 2021, Materials)

   This study investigates the disparate impact of internal pores on the fracture behavior of two metal alloys fabricated via laser powder bed fusion (L-PBF) additive manufacturing (AM)—316L stainless steel and Ti-6Al-4V. Data from mechanical tests over a range of stress states for dense samples and those with intentionally introduced penny-shaped pores of various diameters were used to contrast the combined impact of pore size and stress state on the fracture behavior of these two materials. The fracture data were used to calibrate and compare multiple fracture models (Mohr-Coulomb, Hosford-Coulomb, and maximum stress criteria), with results compared in equivalent stress (versus stress triaxiality and Lode angle) space, as well as in their conversions to equivalent strain space. For L-PBF 316L, the strain-based fracture models captured the stress state dependent failure behavior up to the largest pore size studied (2400 µm diameter, 16% cross-sectional area of gauge region), while for L-PBF Ti-6Al-4V, the stress-based fracture models better captured the change in failure behavior with pore size up to the largest pore size studied. This difference can be attributed to the relatively high ductility of 316L stainless steel, for which all samples underwent significant plastic deformation prior to failure, contrasted with the relatively low ductility of Ti-6Al-4V, for which, with increasing pore size, the displacement to failure was dominated by elastic deformation. 

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5. Identifying fracture location in additively manufactured samples based on defect characteristics: Demonstration using AlSi10Mg

   https://doi.org/10.1016/j.addma.2025.104935  

   Huang, Nancy; Furton, Erik T; Mundada, Yasham A; Beese, Allison M (July 2025, Additive Manufacturing)

   A new metric was developed to quantify the impact of surface-connected defects and internal pores of different morphologies, namely irregular lack of fusion (LoF) pores and spherical keyhole pores, on the mechanical properties and fracture location of AlSi10Mg tensile samples fabricated using laser powder bed fusion additive manufacturing. As defect volume alone has been shown to be insufficient to predict fracture location, the proposed defect impact metric (DIM) incorporates contributions from additional defect features, including proximity to the surface, interaction with neighboring defects, morphology, and reduction in load-bearing cross-sectional area to better assess a defect’s propensity for corresponding to fracture location. The fracture location of keyhole samples was captured by large surface-connected defects with numerous neighboring defects and resulted in increased losses in load-bearing area. In contrast, LoF samples fractured at regions with either large surface-connected defects or large internal pores with many defects in close proximity, high curvatures, and large projected areas. The proposed DIM outperformed existing defect-based frameworks in identifying fracture locations in both LoF and keyhole samples by incorporating surface roughness, defect projected area, and interactions between defects based on distance, volume, and configuration. Additionally, the maximum DIM value within the fracture range was more strongly correlated to strength and ductility than porosity or defect size for LoF samples, demonstrating the potential of the DIM to non-destructively assess the effects of defects on mechanical behavior. The broader applicability of the DIM framework was demonstrated in its ability to capture fracture in both PBF-LB AlSi10Mg and Alloy 718. 

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