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1. SIMULATION OF DUCTILE FRACTURE PROPAGATION IN STRUCTURAL STEEL SUBJECTED TO ULTRA-LOW CYCLE FATIGUE

   Pericoli, V.S.; Lao, X; Terashima, M; Ziccarelli, A; Deierlein, G; Kanvinde, A.M. (January 2018, Eleventh U.S. National Conference on Earthquake Engineering)

   While considerable progress has been made in simulating the overall seismic response of steel structures using nonlinear response history (dynamic) analysis, techniques to simulate fracture propagation under large scale inelastic cyclic loading are not as well developed. This is despite the fact that fracture is often a critical limit state that can precipitate structural failure and collapse. To address this, a new ductile damage-based cohesive zone model is presented. The proposed model is an extension of the established continuum-based local or micromechanical ductile fracture models for evaluating ultra-low cycle fatigue in structural steels. This model is implemented in the finite element program WARP3D, and evaluated against tests of notched bars that fail by ductile crack propagation. The preliminary results indicate that the model is an effective tool for predicting ductile fracture initiation and propagation in structural steels subjected to monotonic and cyclic large scale inelastic loading. Implications of this for characterizing the post-fracture response of structural steel components are discussed, along with limitations of the research. 

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2. Simulation of Ductile Fracture Propagation in Structural Steel Subjected to Ultra-Low Cycle Fatigue

   Pericoli, VS; Lao, X; Terashima, M; Ziccarelli, A; Deierlein, G; Kanvinde, AM (January 2018, Eleventh U.S. National Conference on Earthquake Engineering)

   While considerable progress has been made in simulating the overall seismic response of steel structures using nonlinear response history (dynamic) analysis, techniques to simulate fracture propagation under large scale inelastic cyclic loading are not as well developed. This is despite the fact that fracture is often a critical limit state that can precipitate structural failure and collapse. To address this, a new ductile damage-based cohesive zone model is presented. The proposed model is an extension of the established continuum-based local or micromechanical ductile fracture models for evaluating ultra-low cycle fatigue in structural steels. This model is implemented in the finite element program WARP3D, and evaluated against tests of notched bars that fail by ductile crack propagation. The preliminary results indicate that the model is an effective tool for predicting ductile fracture initiation and propagation in structural steels subjected to monotonic and cyclic large scale inelastic loading. Implications of this for characterizing the post-fracture response of structural steel components are discussed, along with limitations of the research. 

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3. SIMULATION OF DUCTILE FRACTURE PROPAGATION IN STRUCTURAL STEEL SUBJECTED TO ULTRA-LOW CYCLE FATIGUE

   Pericoli, V.S. and (July 2018, Proceedings of the U.S. National Conference on Earthquake Engineering)

   While considerable progress has been made in simulating the overall seismic response of steel structures using nonlinear response history (dynamic) analysis, techniques to simulate fracture propagation under large scale inelastic cyclic loading are not as well developed. This is despite the fact that fracture is often a critical limit state that can precipitate structural failure and collapse. To address this, a new ductile damage-based cohesive zone model is presented. The proposed model is an extension of the established continuum-based local or micromechanical ductile fracture models for evaluating ultra-low cycle fatigue in structural steels. This model is implemented in the finite element program WARP3D, and evaluated against tests of notched bars that fail by ductile crack propagation. The preliminary results indicate that the model is an effective tool for predicting ductile fracture initiation and propagation in structural steels subjected to monotonic and cyclic large scale inelastic loading. Implications of this for characterizing the post-fracture response of structural steel components are discussed, along with limitations of the research. 

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4. Numerical Modelling of a Three-Story Building Using a Hybrid of Mass Timber Walls with Buckling-Restrained Braces

   https://doi.org/10.1007/978-3-031-03811-2_45  

   Araújo_R, Gustavo A; Simpson, Barbara; Ho, Tu X; Orozco_O, Gustavo F; Barbosa, Andre R; Sinha, Arijit (January 2022, Springer International Publishing)

   Mass timber buildings are gaining popularity in North America as a sustainable and aesthetic alternative to traditional construction systems. However, several knowledge gaps still exist in terms of their expected seismic performance and plausible hybridizations with other materials, e.g. steel energy dissipators. This research explores the potential use of mass plywood wall panels (MPP) in spine systems using steel buckling-restrained braces (BRBs) as energy dissipators. The proposed BRB-MPP spine assembly makes up the lateral load-resisting system of a three-story mass-timber building segment that will be tested under cyclic quasi-static loading at Oregon State University. The specimen geometry and material properties result in BRBs that are shorter and of smaller core area than in most common steel structural applications. Small BRBs are prone to exhibit a hardened compressive response and fracture due to ultra-low-cycle fatigue when subjected to repeated cycles of large strain amplitude. These issues, along with the limited availability of test data, make small BRBs difficult to model. To support the experimental testing program, a material model with combined kinematic and isotropic hardening is calibrated against the available experimental data for three BRB specimens to estimate the behavior of BRBs of short length (≤3,500 mm [138 in]) and small core area (≤2,600 mm2 [4 in2]), similar to the ones designed for the test specimen. The calibrated model is used to predict the behavior of the BRB-MPP spine experiment. 

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5. Ductile Fracture in Plane Stress

   https://doi.org/10.1115/1.4052106  

   Torki, Mohammad; Benzerga, Ahmed Amine (January 2022, Journal of Applied Mechanics)

   null (Ed.)

   Abstract A micromechanics-based ductile fracture initiation theory is developed and applied for high-throughput assessment of ductile failure in plane stress. A key concept is that of inhomogeneous yielding such that microscopic failure occurs in bands with the driving force being a combination of band-resolved normal and shear tractions. The new criterion is similar to the phenomenological Mohr–Coulomb model, but the sensitivity of fracture initiation to the third stress invariant constitutes an emergent outcome of the formulation. Salient features of a fracture locus in plane stress are parametrically analyzed. In particular, it is shown that a finite shear ductility cannot be rationalized based on an isotropic theory that proceeds from first principles. Thus, the isotropic formulation is supplemented with an anisotropic model accounting for void rotation and shape change to complete the prediction of a fracture locus and compare with experiments. A wide body of experimental data from the literature is explored, and a simple procedure for calibrating the theory is outlined. Comparisons with experiments are discussed in some detail. 

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