Bauhaus University, Weimar

About: Bauhaus University, Weimar is a education organization based out in Weimar, Thüringen, Germany. It is known for research contribution in the topics: Finite element method & Isogeometric analysis. The organization has 1421 authors who have published 2998 publications receiving 104454 citations. The organization is also known as: Bauhaus-Universität Weimar & Hochschule für Architektur und Bauwesen.

Limitations of the CIBSE design summer year approach for delivering representative near-extreme summer weather conditions

Abstract: Representative, site-specific weather data is a key requirement for building performance simulation. In the UK, such data is available in two formats, Test Reference Years for analysing building services loads under ‘typical’ year conditions and Design Summer Years for estimating summer discomfort of naturally ventilated and free-running buildings. Currently, Design Summer Years are determined as a complete year based on the rank of the average dry bulb temperature from April to September. The simplicity of this approach does not take into account extreme temperature values in individual months or the incident solar radiation, both of which are however of great significance for the summer overheating performance of a building. This paper analyses the implications of this simplified approach for the resulting data. It is shown that there is no consistent relation between the Design Summer Years and the corresponding Test Reference Years and that, for some sites, building performance simulations using Desig...

Micromechanics-based investigation of the elastic properties of polymer-modified cementitious materials using nanoindentation and semi-analytical modeling

Abstract: Cementitious materials are modified by the addition of polymers in order to improve the durability and the adhesive strength. However, polymer-modified mortars and concretes exhibit lower elastic moduli in comparison to unmodified systems. The macroscopic properties are governed by microstructural changes in the binder matrix, which consists of both cementitious and polymer components. Herein, different polymer-modified cement pastes were characterized using nanoindentation to better understand the microscopic origin of the macroscopic elastic modulus. By means of the statistical nanoindentation technique, the existence of three micromechanical phases in plain and polymer-modified cement pastes with a water-to-cement mass ratio of 0.40 is evidenced, illustrating that the polymer modification does not induce the formation of additional reaction products. Instead, the polymers adsorb on the hydration products as well as on unhydrated clinker grains and decrease the indentation moduli of the micromechanical phases. The link between the microscopic and macroscopic mechanical properties is established by means of a continuum micromechanics approach. A multiscale model aimed at the prediction of the elastic moduli of polymer-modified cementitious materials is developed with input parameters that are partially obtained from the nanoindentation tests. The comparison of the modeling results with the experimentally determined elastic (macroscopic) moduli at the scales of cement paste, mortar, and concrete is satisfactorily good, underlining the predictive capability of the modeling approach. The improvement of prediction models is essential for the application of polymer-modified cementitious materials in construction and will encourage their integration into design guidelines.

Computation of limit load using edge-based smoothed finite element method and second-order cone programming

Abstract: This paper presents a novel numerical procedure for limit analysis of plane problems using edge-based smoothed finite element method (ES-FEM) in combination with second-order cone programming. In the ES-FEM, the discrete weak form is obtained based on the strain smoothing technique over smoothing domains associated with the edges of the elements. Using constant smoothing functions, the incompressibility condition only needs to be enforced at one point in each smoothing domain, and only one Gaussian point is required, ensuring that the size of the resulting optimization problem is kept to a minimum. The discretization problem is transformed into the form of a second-order cone programming problem which can be solved using highly efficient interior-point solvers. Finally, the efficacy of the procedure is demonstrated by applying it to various benchmark plane stress and strain problems.

A surface stacking fault energy approach to predicting defect nucleation in surface-dominated nanostructures

Abstract: We present a surface stacking fault (SSF) energy approach to predicting defect nucleation from the surfaces of surface-dominated nanostructure such as FCC metal nanowires. The approach leads to a criterion that predicts the initial yield mechanism via either slip or twinning depending on whether the unstable twinning energy or unstable slip energy is smaller as determined from the resulting SSF energy curve. The approach is validated through a comparison between the SSF energy calculation and low-temperature classical molecular dynamics simulations of copper nanowires with different axial and transverse surface orientations, and cross sectional geometries. We focus on the effects of the geometric cross section by studying the transition from slip to twinning previously predicted in moving from a square to rectangular cross section for 〈 100 〉 / { 100 } nanowires, and also for moving from a rhombic to truncated rhombic cross sectional geometry for 〈 110 〉 nanowires. We also provide the important demonstration that the criterion is able to predict the correct deformation mechanism when full dislocation slip is considered concurrently with partial dislocation slip and twinning. This is done in the context of rhombic 〈110〉 aluminum nanowires which do not show a tensile reorientation due to full dislocation slip. We show that the SSF energy criterion successfully predicts the initial mode of surface-nucleated plasticity at low temperature, while also discussing the effects of strain and temperature on the applicability of the criterion.