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1. Utilizing Stress-based Failure Criteria for Prediction of Curing Induced Damage in 3D Woven Composites

   Tsukrov, I.; Drach, B.; Drach, A.; Gross, T. (August 2017, Proceedings of 21st International Conference on Composite Materials)

   There are several possible mechanisms of failure of glassy polymers that can be activated by different states of stress in the material. They are reflected in the various failure criteria used to predict initiation of damage in the polymer based on the components of stress tensor. We investigated the applicability of several popular failure criteria (the von Mises, the Drucker-Prager, the parabolic stress, and the dilatational strain energy density) to predict processing-induced damage due to cooling after curing observed in 3D woven composites with high level of through-thickness reinforcement. We developed high-fidelity mesoscale finite element models of orthogonally reinforced carbon/epoxy composites and predicted their response to the uniform temperature drop from the curing to room temperature. Comparison of the simulation results with the X-ray computed microtomography indicates that matrix failure caused by the difference in thermal expansion coefficients of carbon fiber and epoxy resin is well predicted by the dilatational strain energy criterion. Initiation and propagation of this failure was numerically investigated using sequential deactivation of elements exceeding the allowable equivalent stress. 

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2. A double-yield-surface plasticity theory for transversely isotropic rocks

   https://doi.org/10.1007/s11440-022-01605-6  

   Zhao, Yang; Borja, Ronaldo I. (June 2022, Acta Geotechnica)

   We present a double-yield-surface plasticity theory for transversely isotropic rocks that distinguishes between plastic deformation through the solid matrix and localized plasticity along the weak bedding planes. A recently developed anisotropic modified Cam-Clay model is adopted to model the plastic response of the solid matrix, while the Mohr-Coulomb friction law is used to represent the sliding mechanism along the weak bedding planes. For its numerical implementation, we derive an implicit return mapping algorithm for both the semi-plastic and fully plastic loading processes, as well as the corresponding algorithmic tangent operator for finite element problems. We validate the model with triaxial compression test data for three different transversely isotropic rocks and reproduce the undulatory variation of rock strength with bedding plane orientation. We also implement the proposed model in a finite element setting and investigate the deformation of rock surrounding a borehole subjected to fluid injection. We compare the results of simulations using the proposed double-yield-surface model with those generated using each single yield criterion to highlight the features of the proposed theory. 

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3. The Anisotropic Yield Surface of Cellular Materials

   Conway, K.M.; Romanick, Z.; Cook, L.; Morales, L.; Despeaux, J.; Ridlehuber, M.; Fingar, C.; Doctor, D.; Pataky, G. (November 2021, JOM)

   The use of mechanical metamaterials in engineering applications is often limited because of uncertainty regarding their deformation behavior. This uncertainty necessitates large safety factors and assumptions about their behavior to be included in mechanical designs including metamaterials, which detracts from their greatest benefit, viz. their ultralight weight. In this study, a yield envelope was created for both a bending-dominated and a stretching-dominated cellular material topology to improve the understanding of the response of cellular materials under various load types and orientations. Experimental studies revealed that the shear strength of a cellular material is significantly lower than that predicted by Mohr’s criterion, necessitating a modification of the Mohr’s yield criterion for cellular materials. All topologies experienced tension–compression anisotropy and topology orientation anisotropy during loading, with the stretching-dominated topology experiencing the largest anisotropies. 

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4. Prediction of Damage Initiation and Simulation of Damage Propagation in 3D Woven Composites during Processing

   Kuksenko, D.; Drach, B; Tsukrov, I. (October 2017, Proceedings of the American Society for Composites Technical Conference)

   Some configurations of 3D woven composites are known to be susceptible to processing induced damage in the form of microcracks that develop in the polymer matrix during curing. The microcracking is believed to originate from high residual stresses that develop due to a significant mismatch in the coefficients of thermal expansion between the constituent materials. In this paper, we investigate the applicability of several commonly used stress-based failure criteria for glassy polymers – the von Mises, the Bauwens (Drucker-Prager), the parabolic stress, and the dilatational strain energy density. We study the microcracking phenomenon on the example of the one-to-one orthogonal configuration of the epoxy matrix/carbon fiber 3D woven composites. This configuration is characterized by the high level of the throughthickness reinforcement which appears to exacerbate the matrix damage. The investigation is based on a high-fidelity mesoscale finite element model of an orthogonally reinforced 3D woven composite. We simulate the material’s response to the uniform temperature drop from the curing to room temperature and compare the results of the simulation with the X-ray computed microtomography. We conclude that the curing induced matrix failure is well predicted by the parabolic stress criterion with a proper choice of the material constants. Initiation and propagation of this failure are simulated via sequential deactivation of the elements exceeding the allowable equivalent stress. 

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5. Effects of soil fabric on the triggering of static liquefaction – Implications on mine tailings

   Bokkisa, Vivek; Macedo, Jorge; Petalas, Alexandros; Arson, Chloe (November 2022, Tailings and Mine Waste Conference)

   Static liquefaction has been associated with the failure of several tailing storage facilities (e.g., the Brumadinho failure in 2019) and has been a persistent topic of discussion in the mining and tailings communities. Experimental studies have suggested that the onset of static liquefaction is dependent on the initial state (void ratio and confinement) and fabric anisotropy. In this context, traditional constitutive models developed under the critical state theory (CST) have been used to investigate the onset of static liquefaction for several complex loading paths. However, these models do not capture the effect of soil fabric anisotropy (inherent and induced) that are relevant in field conditions. In this study, the Anisotropic Critical State Theory (ACST) framework is used to assess the onset of static liquefaction in particulate materials, incorporating the effects of inherent and induced fabric. Our assessments derive an analytical criterion to assess static liquefaction that can be applied to screening assessments. The derived analytical criterion is a function of material properties, state, and fabric anisotropy, which couple the effects of fabric and loading direction. The use of the derived criteria in particulate materials is illustrated, and the implications of assessing the static liquefaction of mine tailings under generalized loading is also discussed. 

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