Computational thermal homogenization is applied to the microscale and mesoscale of concrete sequentially. Microscale homogenization is based on a 3D micro-CT scan of hardened cement paste (HCP). ...Mesoscale homogenization is carried out through the analysis of aggregates which are randomly distributed in a homogenized matrix. The thermal conductivity of this matrix is delivered by the homogenization of HCP, thereby establishing the link between micro-mesoscale of concrete. This link is critical to capture the dependence of the overall conductivity of concrete on the internal relative humidity. Therefore, special emphasis is given to the effect of relative humidity changes in micropores on the thermal conductivity of HCP and concrete. Each step of homogenization is compared with available experimental data.
•Analyze ASR induced damage at the microscale of concrete for the first time.•Upscale microscale damage to mesoscale through homogenization technology.•Hydro-thermo-chemo-mechanical coupling at the ...mesoscale.•Multiscale model is able to reflect damage at the microscale due to ASR.
Alkali–Silica Reaction (ASR) is a complex chemical process that affects concrete structures and so far various mechanisms to account for the reaction at the material level have already been proposed. The present work adopts a simple mechanism, in which the reaction takes place at the micropores of concrete, with the aim of establishing a multiscale framework to analyze the ASR induced failure in the concrete. For this purpose, 3D micro-CT scans of hardened cement paste (HCP) and aggregates with a random distribution embedded in a homogenized cement paste matrix represent, respectively, the microscale and mesoscale of concrete. The analysis of the deterioration induced by ASR with the extent of the chemical reaction is initialized at the microscale of HCP. The temperature and the relative humidity influence the chemical extent. The correlation between the effective damage due to ASR and the chemical extent is obtained through a computational homogenization approach, enabling to build the bridge between microscale damage and macroscale failure. A 3D hydro-thermo-chemo-mechanical model based on a staggered method is developed at the mesoscale of concrete, which is able to reflect the deterioration at the microscale due to ASR.
The abrasion processes of rubber or tires are extremely complex phenomena and basically different from those of other materials. Much research in tire industry has been done to predict the wear of a ...tire tread. However, such studies have not considered the history dependency of abrasion as well as directional effects. This paper is to propose an advanced abrasion model for rubber that will takes these two effects into account. As a result the new model can be applied to predict tire tread wear. Within this model, directional damage will be introduced to characterize the history of frictional sliding contact including the change of slip directions. It also covers local contact conditions such as contact pressure, slip velocity or flash temperature. The model will be analyzed theoretically and numerically. A FEM simulation for the Grosch-wheel with different loading conditions using the new abrasion model is performed and validated by experimental data.
•An advanced abrasion model for rubber abrasion as well as for tire wear is proposed.•The history dependency of abrasion and directional effects are considered.•The strong prediction capability of the model is investigated thoroughly.•The model can describe Schallamach’ observations and Grosch wheel measurements.•A thermo-mechanical FEM simulation for the Grosch wheel based on the ALE framework.
Standard homogenized formulations of problems posed on microheterogeneous domains provide a lower order of accuracy in regions where highly localized variations are observed in the solution fields. ...In order to account for this loss of accuracy for the finite deformation analysis of generally inelastic macrostructures, a scale adaptation strategy is developed where a transition from a homogenized description to an explicit microstructural resolution is pursued in designated zones of interest. Motivated by higher-order homogenization techniques, the adaptation zones are identified based on a post-processing step on the homogenized solution and correspond to regions with high strain-gradients. In order to avoid modeling errors emanating from the use of approximate explicit macroscale constitutive formulations, an exact homogenization procedure based on databased and direct multilevel finite element computations is employed. The overall methodology is investigated in a two-dimensional setting where special attention is paid to the underlying multiscale mesh resolution and additionally demonstrated with a three-dimensional problem. Numerical observations suggest the concept of a representative adaptation zone within which scale adaptation effects can be assessed.
This paper presents an isogeometric formulation for frictionless contact between deformable bodies, based on the recently proposed concept of the third medium. This concept relies on continuum ...formulations not only for the contacting bodies but also for a fictitious intermediate medium in which the bodies can move and interact. Key to the formulation is a suitable definition of the constitutive behavior of the third medium. In this work, based on a number of numerical tests, the role of the material parameters of the third medium is systematically assessed. We also assess the rate of spatial convergence for higher-order discretizations, stemming from the regularization of the non-smooth contact problem inherent to the third medium approach. Finally, problems with self contact are considered and turn out to be an attractive application of the method.
Industrial forming processes depend on several physical effects, including large deformation thermomechanical damage, localized near the contact zone of the forming tools. The main challenge in this ...process relies on the detailed knowledge of the desired thermoplastic effects at finite strains and the undesired initiation of macro-cracks. For the numerical solution of this problem, a regularized sharp crack surface in the framework of a phase-field approach is combined here with a modified, thermomechanical Gurson–Tvergaard–Needelman GTN-type plasticity model, such that we obtain a thermodynamically consistent framework. This allows to adapt this highly complex multi-field model using variationally consistent Mortar contact formulations in a straightforward manner. Eventually, the proposed approach is tested on complex three-dimensional geometries, emanating from industrial relevant forming processes.
Based upon a three-dimensional computer-tomography of hardened cement paste, a finite-element mesh at micrometer length scale is introduced. Effective material properties are obtained through ...numerical homogenization techniques using representative volume elements. Statistical tests, two- and three-dimensional computations and a comparison with experimental data are shown. For the hydration products of hardened cement paste a visco-plastic constitutive equation of P
erzyna
type including isotropic damage is introduced. The inelastic material parameters are identified solving an optimization problem through a combination of a stochastic genetic algorithm and the deterministic L
evenberg
-M
arquardt
method. The time-consuming evaluations of the corresponding objective function are distributed within a network environment automatically.
In this paper, a polygonal finite element method is presented for large deformation frictionless dynamic contact-impact problems with non-conformal meshes. The geometry and interfaces of the problem ...are modeled independent of the background mesh based on the level set method to produce polygonal elements at the intersection of the interface with the regular FE mesh. Various polygonal shape functions are employed to investigate the capability of polygonal-FEM technique in modeling frictionless contact-impact problems. The contact constraints are imposed between polygonal elements produced along the contact surface through the node-to-surface contact algorithm. Several contact-impact problems are modeled using various polygonal interpolation functions, including the Wachspress interpolation functions, the metric coordinate shape functions, the natural neighbor based functions, and the mean value coordinate functions to demonstrate the efficiency of proposed technique in modeling contact-impact problems.
The mechanical response of filled rubber depends on load history, strain rate and state, temperature and even direction of previous loading. Although there is a plurality of both physical and ...phenomenological models, only few are able to reproduce this rich spectrum of effects. Moreover, many of them suffer from physical or mathematical inconsistencies. We present a model, which is based on physical ideas and plausible assumptions about the material’s microstructure, while being designed for high efficiency and robustness in finite element applications. It is shown by fits to extensive experimental data that it reproduces almost the full phenomenology of filled rubbers, both at low and high strains, for different deformation states and rates, holding times, and at different temperatures. The main modeling paradigm is the stress-induced breakdown and reorganization of microscopic structures which defines the time-dependent behavior of the material and allows to reproduce logarithmic relaxation effects. Moreover, its nine fit parameters evolve in a physically reasonable way under variation of filler and cross-linker content. A static limiting case of the model is derived, reducing the number of parameters and computational effort wherever necessary. Finally, a FE-implementation using computer-generated subroutines is presented and tested against experimental data of a simplified bushing under torsional, radial, cardanic and axial loading.
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