10 results
Filters
Settings
Now showing1 - 10 of 10
- Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Introducing long-range particle interactions into phase-field models of sintering using continuum mechanics principles(Elsevier, 2025-04-10); ; ; ; This work presents a novel meso-scale phase-field model of solid-state sintering that couples the continuum thermodynamics and continuum mechanics governing the sintering process. The microstructure evolution is described by a system of equations consisting of one Cahn–Hilliard equation and a set of Allen–Cahn equations to distinguish neighboring particles. These equations are coupled with the balance of momentum of linear elasticity. The latter is defined by applying the Wang sintering forces as distributed body loads to compute advection velocities for the phase-field equations. This introduces long-range interaction mechanisms between particles. Our numerical implementation uses monolithic coupling and implicit time integration. It is based on the hpsint code, an efficient matrix-free finite element solver for phase-field simulations of many-particle sintering processes with advanced grain tracking capabilities and block preconditioning. With a simple academic test setup that analyzes a chain of identical particles we investigate in detail the problems of the original sintering model proposed by Wang around two decades ago and then clearly demonstrate how our new coupled approach resolves them. We then study a series of two- and three-dimensional benchmark problems to demonstrate the advantages of our novel model that clearly exhibits invariance of shrinkage regarding the model size (number of particles in the packing) and renders microstructures whose metrics agree well with estimates based on analytical and experimental studies.Publicationtype: Journal Article9 22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , On the construction of an efficient finite-element solver for phase-field simulations of many-particle solid-state-sintering processesWe present an efficient solver for the simulation of many-particle solid-state-sintering processes. The microstructure evolution is described by a system of equations consisting of one Cahn–Hilliard equation and a set of Allen-Cahn equations to distinguish neighboring particles. The particle packing is discretized in space via multicomponent linear adaptive finite elements and implicitly in time with variable time-step sizes, resulting in a large nonlinear system of equations with strong coupling between all components to be solved. Since on average 10k degrees of freedom per particle are necessary to accurately capture the interface dynamics in 3D, we propose strategies to solve the resulting large and challenging systems. This includes the efficient evaluation of the Jacobian matrix as well as the implementation of Jacobian-free methods by applying state-of-the-art matrix-free algorithms for high and dynamic numbers of components, advances regarding preconditioning, and a fully distributed grain-tracking algorithm. We validate the obtained results, examine in detail the node-level performance and demonstrate the scalability up to 10k particles on modern supercomputers. Such numbers of particles are sufficient to simulate the sintering process in (statistically meaningful) representative volume elements. Our framework thus forms a valuable tool for the virtual design of solid-state-sintering processes for pure metals and their alloys.Publicationtype: Journal ArticleScopus© Citations 1 26 147 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , A comparison of ligament geometries in real and computer-generated nanoporous gold based on cross-section descriptors(2023-10-05); Nanoporous gold (np-Au) exhibits a bi-continuous network structure of nanoscale pores and solid ligaments, which form a random 3D network. Geometrical descriptors are developed that allow for characterization, statistical analysis and comparison of a large number of ligaments in real and computer generated np-Au structures. In addition to the voxel resolution and ligament length, the cross-sections of the ligaments are described by roundness, circularity, and compactness. The structures are analyzed in initial and coarsened conditions for various solid fractions. Although the structures do not change topologically, the results confirm significant changes in the geometry during coarsening. It is found that after coarsening the computer-generated structures compare much better to tomographic reconstructions of annealed np-Au structures, although there are still differences in the free ligament length. Therefore, in addition to the topological similarity, similarity of geometrical descriptors is found to be equally important for deriving predictive models based on computer-generated structures.Publicationtype: Journal Article23 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simulated annealing framework for generating representative volume elements of materials with complex ligamentous microstructuresAt the microscale, various materials from biological tissues to nanoporous metals are formed by networks of ligaments. Here we propose a highly efficient simulated annealing (SA) framework for generating synthetic representative volume elements (RVE) of such materials. It can produce RVE where the microstructural characteristics both on the network level (e.g., node valency and ligament length) and on the level of individual ligaments (e.g., curvature) can be predefined by the user via probability distributions. As an application example of our framework, we generate a large variety of RVEs, analyze their mechanical properties by the finite element method, and establish through this approach links between microstructural descriptors and macromechanical properties of materials with ligamentous microstructures.Publicationtype: Journal Article48 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Computational study of the geometric properties governing the linear mechanical behavior of fiber networks(Elsevier, 2021-11); ; ; ; Materials whose microstructure is formed by random fiber networks play an important role both in biology and engineering. So far, it still remains unclear which geometric properties of the fiber network determine the macroscopic mechanical properties of such materials. This paper presents a computational study based on a large number of representative volume elements of random fiber networks. Our study reveals that the linear mechanical properties of fiber networks (i.e., Young's modulus and Poisson's ratio) are largely determined by only four scalar key descriptors. These are the number of fibers per volume, the mean node valency, the mean fiber length, and the mean direction cosine between fibers adjacent to the same node. Number of fibers per volume and node valency were found to be responsible for around 80% of the variance of the mechanical properties, making them the two by far dominant microstructural descriptors. In the part of the configuration space covered by our study, we observed a linear or quadratic relationship between the above four scalar microstructural descriptors and the Young's modulus. For the number of fibers per unit volume we propose a theoretical explanation for this simple relation.Publicationtype: Journal ArticleScopus© Citations 8 85 51 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Monolayer SnC as anode material for Na ion batteries(Elsevier, 2021-09-01); 5 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Simulation-based investigation of core-shell agglomerates: Influence of spatial heterogeneity in particle sizes on breakage characteristics(2017-09); ; ; ; The stability and breakage behavior of agglomerates is of interest in many applications. It is well known that the internal microstructure is of great influence thereupon. However, the precise relationship of structural properties and mechanical behavior is not yet known for many scenarios. In this paper, we consider a flexible stochastic model to analyze the strength of spherical agglomerates consisting of spherical primary particles, arranged as core and shell. Structural properties can be varied in core and shell independently. Applying the bonded-particle model (BPM), we investigate the influence of the primary particle size distributions in core and shell on the breakage behavior under uniaxial compressive load. To get more meaningful results, we perform numerical studies of the same agglomerate with different directions of force and investigate the variation in breakage behavior.Publicationtype: Journal Article141 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: with files , Deformation mechanisms in nanoporous metals : effect of ligament shape and disorderThe current work presents a numerical modelling approach for investigating the effect of ligament shape and disorder on the macroscopic mechanical response of nanoporous gold (NPG). The approach starts from a ‘single ligament’ analysis with respect to three fundamental deformation modes, bending, torsion, and compression, that depend on the ligament shape. It can be shown that the predictive capability of the highly computationally efficient beam model is sufficient for a large variation in ligament shapes. Using a representative volume element (RVE) composed of such ligaments, different degrees of disorder are included. For both the single ligament and RVE models, the cylindrical beam serves as a common reference to compare the results when varying the ligament shape. From the comparison of the RVE elastic response with the single ligament results and the further analysis of statistical information from the elements in the RVE, it is found that bending is the major deformation mode for perfectly ordered RVEs, whereas torsion gains importance for increasing RVE disorder. The effect of compression of the ligaments can be neglected in general. It is concluded that the transition to torsion deformation due to disorder is the cause of the strongly reduced lateral expansion during compression deformation of NPG.Publicationtype: Journal ArticleScopus© Citations 39 348 416 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Towards bio-inspired engineering materials : modeling and simulation of the mechanical behavior of hierarchical bovine dental structure(Elsevier, 2013-07-19); ; ; ; Dental enamel is the outermost layer of a tooth crown consisting of a hierarchical and graded structure. Approx. 85 vol.% of enamel consist of the hydroxyapatite mineral, the rest being protein and water. This contribution is concerned with the modeling and computation of the mechanical behavior, in particular with the failure, of the enamel of a bovine tooth. For the underlying model description, we resort to a non-linear Neo-Hookean model for the mineral and to the Arruda-Boyce model for the protein, in combination with a cohesive zone approach. The model accounts for non-linear, large-deformation kinematics and softening at the first level hierarchy, and it is validated against experimental data. The numerical implementation is carried out with the help of the finite element method. Here, we resort to a three-dimensional cohesive zone model which maps cracking of the mineral fibers as well as debonding between the mineral fiber and the protein. A complex microstructure representing bovine enamel is studied in the numerical examples. The results capture major features of the physical experiments, such as non-linear stress-strain behavior, stiffness and failure strength.Publicationtype: Journal Article83 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Application of non-convex rate dependent gradient plasticity to the modeling and simulation of inelastic microstructure development and inhomogeneous material behaviorIn this study, a two-dimensional rate-dependent gradient crystal plasticity model for non-convex energetic hardening is formulated and applied to the simulation of inelastic microstructure formation. In particular, non-convex hardening is modeled via a Landau-Devonshire potential for self-hardening and two interaction-matrix-based forms for latent hardening. The algorithmic formulation and the numerical implementation treats the displacement and the glide-system slips as the primary field variables. The numerical simulations are carried out for the case of tensile loading with periodic displacement and slip boundary conditions. The results for the formation of inelastic microstructures and their evolution under mechanical loading are illustrated together with the macroscopic stress-strain responses.Publicationtype: Journal Article88