1,720,971 research outputs found
Stiffness, strength, energy dissipation and reusability in heterogeneous architected polycrystals
No full textWe design, fabricate and test heterogeneous architected polycrystals, composed of hard plastomers and soft elastomers, which thus show mechanical resilience and energy dissipation simultaneously. Grain boundaries (GBs) that separate randomly oriented single crystalline grains are carefully designed, enabling coherent connectivity and strength in the GB regions throughout the polycrystalline network. By combining experiments and numerical simulations on three-dimensional (3D)-printed prototypes, we show that the interplay between grain interiors (GIs) and GBs is responsible for the grain-size effects on elastic stiffness and inelastic strength; furthermore, we demonstrate, when damaged, the engineered GBs are crucial for reusability and energy dissipation capability in these architected materials by impeding the propagation of local failures. Direct visualization of inter- and intra-grain deformation and failure mechanisms at the macroscopic scale also reveals that crystallographic texture throughout the architected polycrystalline aggregates plays a fundamental role in the key mechanical features. Our results show that the engineered GBs and crystallographic textures not only modify the highly resilient yet dissipative global responses but also critically influence reusability in this new class of heterogeneous architected materials.
Extreme resilience and dissipation in heterogeneous elasto-plastomeric crystals
No full textWe present a microstructure-topology-based approach for designing macroscopic, heterogeneous soft materials that exhibit outstanding mechanical resilience and energy dissipation. We investigate a variety of geometric configurations of resilient yet dissipative heterogeneous elasto-plastomeric materials that possess long-range order whose microstructural features are inspired by crystalline metals and block copolymers. We combine experiments and numerical simulations on 3D-printed prototypes to study the extreme mechanics of these heterogeneous soft materials under cyclic deformation conditions up to an extreme strain of >200% with strain rates ranging from quasi-static (5.0 × 10−3 s−1) to high levels of >6.0 × 101 s−1. Moreover, we investigate the complexity of elastic and inelastic “unloading” mechanisms crucial for the understanding of shape recovery and energy dissipation in extreme loading situations. Furthermore, we propose a simple but physically intuitive approach for designing microstructures that exhibit a nearly isotropic behavior in both elasticity and inelasticity across different crystallographic orientations from small to large strains. Overall, our study sets a significant step toward the development of sustainable, heterogeneous soft material architectures at macroscopic scales that can withstand harsh mechanical environments.peer-reviewed2024-11-0
Examination of Plastic Flow and Structural Evolution of Additively Manufactured Stainless Steels
No full textDeformation of tantalum: non-schmid effect, rate and temperature-dependence, and evolution of dislocations
No full textFinite element implementation of a gradient-damage theory for fracture in elastomeric materials
No full textWe present a finite element implementation procedure for a phase-field framework for fracture in elastomeric materials based on the gradient-damage theory. Governing equations of macroscopic and microscopic force balances, and constitutive theories for large elastic deformation and damage are summarized, and the computational implementation is described in significant detail. To facilitate the computational implementation of the gradient-damage theory for elastomeric materials in a widely available finite element program, the source codes are provided as online Supplemental Materials to this paper. Furthermore, we provide a comparative study of the gradient-damage models with two distinct driving forces for damage: (1) entropy-driven and (2) internal energy-driven. We then show that the internal energy-driven damage model presents more realistic descriptions of the failure that accompanies extreme stretching and scission in elastomeric networks.
Data-Driven Statistical Reduced-Order Modeling and Quantification of Polycrystal Mechanics Leading to Porosity-Based Ductile Damage
Full text linkPredicting the process of porosity-based ductile damage in polycrystalline
metallic materials is an essential practical topic. Ductile damage and its
precursors are represented by extreme values in stress and material state
quantities, the spatial PDF of which are highly non-Gaussian with strong fat
tails. Traditional deterministic forecasts using physical models often fail to
capture the statistics of structural evolution during material deformation.
This study proposes a data-driven statistical reduced-order modeling framework
to provide a probabilistic forecast of the deformation process leading to
porosity-based ductile damage, with uncertainty quantification. The framework
starts with computing the time evolution of the leading moments of specific
state variables from full-field polycrystal simulations. Then a sparse model
identification algorithm based on causation entropy, including essential
physical constraints, is used to discover the governing equations of these
moments. An approximate solution of the time evolution of the PDF is obtained
from the predicted moments exploiting the maximum entropy principle. Numerical
experiments based on polycrystal realizations show that the model can
characterize the time evolution of the non-Gaussian PDF of the von Mises stress
and quantify the probability of extreme events. The learning process also
reveals that the mean stress interacts with higher-order moments and extreme
events in a strongly nonlinear and multiplicative fashion. In addition, the
calibrated moment equations provide a reasonably accurate forecast when applied
to the realizations outside the training data set, indicating the robustness of
the model and the skill for extrapolation. Finally, an information-based
measurement shows that the leading four moments are sufficient to characterize
the crucial non-Gaussian features throughout the entire deformation history
단결정 및 다결정 탄탈럼의 변형 메커니즘
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학과, 2022.8,[vi, 65 p. :]A physically-informed continuum crystal plasticity model is presented to elucidate the deformation mechanisms and microstructural evolution in body-centered-cubic (bcc) tantalum. We show that our structurally unified modeling framework informed by mesoscopic dislocation dynamics simulations is capable of capturing salient features of the large inelastic behavior of tantalum at quasi-static (0.001 s) to extreme strain rates (10 s) and at 77 K and higher (to 873 K) at both single- and polycrystal levels. Notably, we consider the contribution of the non-Schmid effect at 77 K to capture tension-compression asymmetry. Moreover, we also validated our model for the underlying microstructural evolutions in polycrystal tantalum. Toward this end, we compare the experimental data of texture and dislocation density evolution with our corresponding numerical results, and show that our modeling framework is capable of capturing the important features of polycrystal plasticity. The slip instability analysis in our crystal plasticity model shows that the numerical model reflects physical features of the slip instability widely observed in experiments and dislocation dynamics simulations. Notably, we show that instability is mainly attributed to non-convexity due to strong collinear interaction. Our results at both single- and polycrystal levels provide critical insights into the plastic deformation mechanism for the microscopic and macroscopic responses and their relations in this important class of refractory bcc materials undergoing severe plastic deformations.한국과학기술원 :항공우주공학과
Engineering the Mechanics of Heterogeneous Soft Crystals
Full text linkThis work demonstrates how the geometric and topological characteristics of substructures within heterogeneous materials can be employed to tailor the mechanical responses of soft crystals under large strains. The large deformation mechanical behaviors of elastomeric composites possessing long-range crystalline order are examined using both experiments on 3D-printed prototype materials and precisely matched numerical simulations. The deformation mechanisms at small and large strains are elucidated for six sets of morphologies: dispersed particles on each of the simple cubic, body-centered cubic or face-centered cubic lattices, and their bi-continuous counterparts. Comparison of results for the six types of morphologies reveals that the topological connectivity of dissimilar domains is of critical importance for tailoring the macroscopic mechanical properties and the mechanical anisotropy
아키텍티드 마이크로구조체의 대변형 형상회복 및 에너지 소산
No full text학위논문(석사) - 한국과학기술원 : 항공우주공학과, 2022.8,[viii, 57 p. :]In this paper, we investigated the mechanical behavior of architected microstructures on cubic crystal lattices under large deformation and cyclic loading condition. Interpenetrating morphologies were presented as a counter part of dispersed morphologies. We investigated the effect of co-continuity on the mechanical performance at large strain. Representative volume elements in the principal crystallographic directions were presented to evaluate the anisotropy of the architected microstructures at large strain. The mechanical behavior of each constituent material under large deformation has been characterized. Then, a non-linear constitutive model for each constituent material was suggested and applied to a boundary value problem for the architected microstructures under finite deformation. Representative architected microstructures were fabricated on a high-resolution 3D printer, and compression tests were conducted using a mechanical testing machine. In experimental data and numerical simulation results, we elucidated the effect of co-continuity on stiffness, energy dissipation, shape recovery, and anisotropy of architected microstructures at large strain. Further, we presented architected microstructures that exhibit no reduction in stress response during cyclic loading at extreme stains.한국과학기술원 :항공우주공학과
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