Comparison of XFEM and Voxelbased FEM for the Approximation of Discontinuous Stress and Strain at Material Interfaces

When analyzing bimaterial problems, often stress concentrations appear close to material interfaces and cause nonlinear effects like damage or plastic yielding. Therefore, a precise approximation of stresses at interfaces is desirable. However, jumps in material parameters lead to non-smooth solutions (i.e. kinks in the displacements and jumps in the stresses and strains), which reduce the accuracy of standard discretization methods including the finite element method (FEM). The popular extended finite element method (XFEM) belongs to the class of methods, where additional unknowns are introduced to approximate jumps of the unknowns on meshes which are not aligned to the interface or boundaries. The field of application is the stress analysis of microstructures of two-phase materials with high contrast between the phases including nonlinear effects. The focus of this paper is to considers the XFEM approximation quality of strains and displacements at material interfaces. XFEM and standard FEM solutions are compared for varying mesh sizes. Therefore an analytical solution for a spherical inclusion in a finite domain under specific loading conditions is considered. This analytical solution is then compared in detail to different finite element discretizations with standard FEM and XFEM

Multi-Scale Simulation of Viscoelastic Fiber-Reinforced Composites

This paper presents an effective algorithm to simulate the anisotropic viscoelastic behavior of a fiber-reinforced composite including the influence of the local geometric properties, like fiber-orientation and volume fraction. The considered composites consist of a viscoelastic matrix which is reinforced by elastic fibers. The viscoelastic composite behavior results anisotropic due to the local anisotropic fiber-orientations. The influence of the local time-dependent viscoelastic properties are captured within two elastic microscopic calculations for each fiberorientation in the composite part. These calculations can be performed within a preprocessing step, and thus no expensive, time-dependent viscoelastic multi-scale simulation has to be carried out to incorporate the local properties. The advantage of the presented approach is that the locally varying microscopic properties can be captured in a one-scale simulation within a commercial finite element tool like ABAQUS

Giant Thermoelectric Effect from Transmission Supernodes

We predict an enormous order-dependent quantum enhancement of thermoelectric effects in the vicinity of a higher-order `supernode' in the transmission spectrum of a nanoscale junction. Single-molecule junctions based on 3,3'-biphenyl and polyphenyl ether (PPE) are investigated in detail. The nonequilibrium thermodynamic efficiency and power output of a thermoelectric heat engine based on a 1,3-benzene junction are calculated using many-body theory, and compared to the predictions of the figure-of-merit ZT.Comment: 5 pages, 6 figure

Breakdown into nanoscale of graphene oxide: Confined hot spot atomic reduction and fragmentation

Nano-graphene oxide (nano-GO) is a new class of carbon based materials being proposed for biomedical applications due to its small size, intrinsic optical properties, large specific surface area, and easy to functionalize. To fully exploit nano-GO properties, a reproducible method for its production is of utmost importance. Herein we report, the study of the sequential fracture of GO sheets onto nano-GO with controllable lateral width, by a simple, and reproducible method based on a mechanism that we describe as a confined hot spot atomic fragmentation/reduction of GO promoted by ultrasonication. The chemical and structural changes on GO structure during the breakage were monitored by XPS, FTIR, Raman and HRTEM. We found that GO sheets starts breaking from the defects region and in a second phase through the disruption of carbon bonds while still maintaining crystalline carbon domains. The breaking of GO is accompanied by its own reduction, essentially by the elimination of carboxylic and carbonyl functional groups. Photoluminescence and photothermal studies using this nano-GO are also presented highlighting the potential of this nanomaterial as a unique imaging/therapy platform

Quantification of the effectiveness of a safety function in passenger vehicles on the basis of real-world accident data

In this paper we deal with dierent statistical modeling of real world accident data in order to quantify the eectiveness of a safety function or a safety conguration (meaning a specic combination of safety functions) in vehicles. It is shown that the eectiveness can be estimated along the so-called relative risk, even if the eectiveness does depend on a confounding variable which may be categorical or continuous. For doing so a concrete statistical modeling is not necessary, that is the resulting estimate is of nonparametric nature. In a second step the quite usual and from a statistical point of view classical logistic regression modeling is investigated. Main emphasis has been laid on the understanding of the model and the interpretation of the occurring parameters. It is shown that the eectiveness of the safety function also can be detected via such a logistic approach and that relevant confounding variables can and should be taken into account. The interpretation of the parameters related to the confounder and the quantication of the in uence of the confounder is shown to be rather problematic. All the theoretical results are illuminated by numerical data examples

Quantification of the effectiveness of a safety function in passenger vehicles on the basis of real-world accident data

In this paper we deal with dierent statistical modeling of real world accident data in order to quantify the eectiveness of a safety function or a safety conguration (meaning a specic combination of safety functions) in vehicles. It is shown that the eectiveness can be estimated along the so-called relative risk, even if the eectiveness does depend on a confounding variable which may be categorical or continuous. For doing so a concrete statistical modeling is not necessary, that is the resulting estimate is of nonparametric nature. In a second step the quite usual and from a statistical point of view classical logistic regression modeling is investigated. Main emphasis has been laid on the understanding of the model and the interpretation of the occurring parameters. It is shown that the eectiveness of the safety function also can be detected via such a logistic approach and that relevant confounding variables can and should be taken into account. The interpretation of the parameters related to the confounder and the quantication of the in uence of the confounder is shown to be rather problematic. All the theoretical results are illuminated by numerical data examples

Comparison of XFEM and Voxelbased FEM for the Approximation of Discontinuous Stress and Strain at Material Interfaces

When analyzing bimaterial problems, often stress concentrations appear close to material interfaces and cause nonlinear effects like damage or plastic yielding. Therefore, a precise approximation of stresses at interfaces is desirable. However, jumps in material parameters lead to non-smooth solutions (i.e. kinks in the displacements and jumps in the stresses and strains), which reduce the accuracy of standard discretization methods including the finite element method (FEM). The popular extended finite element method (XFEM) belongs to the class of methods, where additional unknowns are introduced to approximate jumps of the unknowns on meshes which are not aligned to the interface or boundaries. The field of application is the stress analysis of microstructures of two-phase materials with high contrast between the phases including nonlinear effects. The focus of this paper is to considers the XFEM approximation quality of strains and displacements at material interfaces. XFEM and standard FEM solutions are compared for varying mesh sizes. Therefore an analytical solution for a spherical inclusion in a finite domain under specific loading conditions is considered. This analytical solution is then compared in detail to different finite element discretizations with standard FEM and XFEM

Evaluation of the safety benefits of passive and/or on-board active safety applications with mass accident data-bases

One of the main objectives of the European TRACE project (Traffic Accident Causation in Europe, January 2006 - June 2008) was the development of methodology for the evaluation of the safety benefit of existing on-board safety applications in passenger cars with the use of mass accident data-bases only. The challenge was to evaluate passive safety applications as well as active applications and especially combinations of the two within a single investigation. In order to do so the well known concept of odds-ratio has been generalized for jointly evaluating injury mitigating effectiveness as well as accident avoiding effectiveness at once. This paper describes statistical sound methodology that is able to evaluate the safety benefit of either a single on-board safety function or the additional gain of specific safety feature(s) (i.e. a selection of various passive safety functions and active safety functions), given that some other safety applications already are on board. In particular, the method allows for evaluation of accident avoiding effectiveness as well as injury mitigating effectiveness. Hence, it can be applied for joint evaluations of passive and on-board active safety applications. The focus of the paper lies on the presentation of a ready-to-apply methodology, including detailed examples as well as a discussion on its advantages and its limitations

A three-dimensional realistic microstructure model of particle-reinforced metal matrix composites

A new and robust methodology is presented for the complete computer simulation of large three-dimensional (3D) microstructures of particle-reinforced metal matrix composites (PRMMCs), by integrating the boundary representation scheme, the random cutting algorithm and the random sequential adsorption algorithm. The methodology allows large realistic 3D microstructure models to be generated that can be used for multi-scale investigation of PRMMC structure and design. The effect of the simulation parameters on the simulated microstructure is investigated by applying a quantitative metallographic analysis of the distribution functions of aspect ratio, diameter and the area of reinforcements. Simulated large realistic homogenous 3D microstructures of PRMMC are in close agreement with the experimental microstructures