bluuebunny/crossref_metadata_2025_split huggingface dataset:
Intraoperative Enteral Nutrition Feeding in Free‐Flap Healing after Reconstruction Surgery for Head and Neck Cancers
Authors: Hwang Tzer‐Zen , Wang Yi‐Ming , Jeng Seng‐Feng , Lee Yi‐Chen , Chen Tzu‐Shan , Su Shin‐Ying , Huang Chien‐Chi , Lam Chen‐Fuh 
Published: March 2023

AbstractObjectiveTo investigate the beneficial outcomes of intraoperative enteral feeding in free‐flap regeneration after extended head and neck cancer resection and flap reconstruction surgery.Study DesignA pilot randomized, double‐blind, placebo‐controlled clinical trial.SettingSingle tertiary care center.MethodsPatients with advanced head and neck cancers requiring radical tumor resections and free‐flap reconstruction were randomly assigned to receive intraoperative enteral nutrition feeding (100 kcal/100 mL at 10‐20 mL/h) via a nasogastric tube during free‐flap reconstruction (n = 28) or continue fasting (n = 28). The primary outcome was impaired free‐flap regeneration that required surgical reintervention within 90 days after the operation. Participants were enrolled between April 2020 and January 2022; the 90‐day follow‐up ended in April 2022.ResultsThe incidence of total or partial flap failure was similar between the 2 groups (14.2% or n = 4 in each group), but the rate of wound dehiscence or edge necrosis was significantly reduced in the feeding group (n = 6 vs 0 for fasting vs feeding; absolute risk reduction, 25.0% [95% confidence interval, 6.9‐43.0]%; p = 0.022). Hospital stay length was shorter (p = 0.042) and hand grip strength was better preserved (p = 0.025) in the feeding group. Plasma concentrations of interleukin (IL)‐6 and IL‐8 after the operation increased significantly more in the fasting group. Perioperative adverse events did not differ between the 2 groups.ConclusionPerioperative enteral feeding is a simple, safe, and effective approach to improve perioperative systemic catabolism and proinflammatory reactions, thereby enhancing early wound regeneration after major operations.
Numerical Simulation of Thermo‐electro‐elastic Interactions in Electro‐active Polymers
Authors: Kanan Anas , Kaliske Michael 
Published: March 2023

AbstractThe actuation response of electro‐active polymers (EAP) relies mainly on the coupling between the electric field and the mechanical field. However, the response of polymers can generally be temperature sensitive. Therefore, taking into account the thermal field in addition to the mechanical and the electric fields within a numerical framework may prove necessary to analyze the response of EAP, where temperature changes in the material may influence its behaviour significantly. This contribution presents a coupled thermo‐electro‐mechanical model, where from a numerical point of view direct temperature dependency of the electric and the coupled electro‐mechanical response can be either considered or neglected. Entropic thermo‐electro‐elasticity is adopted. Moreover, a corresponding monolithic and mixed finite element is used to simulate the response of quasi‐incompressible heterogeneous structures under different temperature conditions.
Optimization of Glulam Beams with Spatially Dependent Polymorphic Uncertainty Modeling of Structural Inhomogeneity in Virtual Boards
Authors: Schietzold F. Niklas , Richter Bertram , Graf Wolfgang , Kaliske Michael 
Published: March 2023

AbstractSeveral uncertainties are induced by the natural growth of wood. The properties of timber components are affected by naturally varying material characteristics. In addition, structural inhomogeneity has to be accounted for solid wood components. Structural inhomogeneity is dependent on, e.g., natural fissures, inclusions, and especially branches that pervade wooden boards. Those pervasions result in timber boards containing multiple scattered knots.Polymorphic uncertainty models are required to account for diverse uncertainty characteristics. Natural variability and lack of knowledge are persistent for the uncertainty modeling of natural materials, such as wood. To incorporate those aleatoric and epistemic uncertainty characteristics, uncertainty analyses are performed based on combined fuzzy and stochastic models.In this contribution, fuzzy probability based random fields are proposed as polymorphic uncertainty approach, with respect to spatial dependencies of the uncertain variables. Methods for the simulation of timber boards are introduced, where knots are established referred to the specific position of the tree trunk axis and spread over the components.Glulam beams, containing multiple slats of wooden boards, are investigated for bending load cases as numerical example. The tensile zone is simulated with knots in the timber boards. The basic deterministic solution is performed with a local‐orthotropic material formulation, with respect to the grain directions of the wood matrix and knots. Therefore, the knots are discretized separately in the FE mesh. Distinct material properties and grain directions are assigned to the discrete knots and to the surrounding wood matrix, while the grain directions are dependent on the tree trunk axis.Both, stochastic and fuzzy models are used in field formulations for the spatially dependent polymorphic uncertainties. The knottiness of timber boards – specified by parameters of knot geometry, location and incidence – is dependent on the wood grade. In this contribution, methods for decision making of glulam beam designs are suggested. For this purpose, several design variables are examined. First, the knottiness or wood grade, where a higher grade results in reduced structural inhomogeneity, and second, the thickness of the slats in the glulam beam are considered. Both aspects influence the reliability and robustness of the component, but affect the costs. The maximum endurance of the glulam beam under bending is desired. Therefore, an optimization of the glulam beam design is performed, with respect to the multiple conflicting objectives.
Bifurcation of fiber reinforced inflated membranes with different natural configurations of the constituents
Authors: Topol Heiko , Demirkoparan Hasan , Stoffel Marcus , Markert Bernd , Merodio José 
Published: March 2023

AbstractThis article studies the inflation and bulging of fiber‐reinforced hyperelastic membranes. A neo‐Hookean model describes the mechanical behavior of the ground substance, and a relatively standard reinforcing model describes the mechanical behavior of fibers. The natural configuration of the constituents may differ, for example, because the fiber may be pre‐stretched in comparison to the natural configuration of the ground substance. Additionally, the fibers may be dispersed. Both the pre‐stretch and dispersion of the fibers have an effect on the formation of a bulge. The results explore how material stiffness ratios and fiber arrangements are involved in initiating bulging instabilities. The herein presented results may provide a contribution to understanding the formation of aneurysms.
Modeling the Response of NiTi Endodontic Files Subjected to Cyclic Non‐proportional Loading
Authors: Woodworth Lucas A. , Kaliske Michael 
Published: March 2023

AbstractNickel‐Titanium (NiTi) endodontic files have emerged as valuable tools for root canal treatment due to their high strength and flexibility. During treatment, the files are rotated in the bent configuration of the root canal, which leads to cyclic non‐proportional loading. With the goal of understanding the mechanical response of NiTi endodontic files and to allow for an enhanced design of these structures, a constitutive model for shape memory alloys is developed. This model incorporates several of the features present in SMAs relevant for the mechanical response of endodontic files including: transformation, reorientation, yield plasticity, functional fatigue, tension‐compression asymmetry and internal loops. The model is implemented in Ansys using a small strain formulation and extended to finite strains using the nonlinear geometry algorithm in Ansys. Validation of the model is performed by simulating a cyclic torsional experiment from the literature using a simplified file geometry. Finally, the model is applied to simulate a simplified file under torsional rotation in a bent configuration. The results illustrate that the endodontic file develops a torsional oscillation during the course of the cyclic loading, which is directly associated with an increase in residual stresses. Furthermore, the torsional oscillation leads to higher values of the martensite volume fraction and stress.
Application of Statistically Similar Representative Volume Elements of Metal Matrix Composites for the Efficient Simulation of Crack Propagation on the Microscale
Authors: Wingender Dennis , Balzani Daniel 
Published: March 2023

AbstractThe efficiency of various drilling and cutting processes is strongly determined by the wear resistance of the applied tools. For example in mechanized tunnel drilling, metal matrix composites, used as reinforcements on the chisels, are primarily exposed to surface spalling. This wear mechanism is governed by subcritical crack propagation through the material's microstructure, which consists of brittle carbide inclusions surrounded by a ductile matrix. The microstructure morphology strongly influences the crack propagation and thus, the resistance against wear. In order to improve the material's microstructure regarding wear, numerical simulations on the microscale are an important tool to gain knowledge about the influence of the morphology on the crack propagation. The investigated microstructure is given as voxel data obtained from a µCT scan. Because of the high complexity of the microstructure, simulations of crack propagation through it are computationally costly, in particular under cyclic loads. Hence, simplified artificial microstructures are constructed which resemble the morphological as well as mechanical properties of the full microstructure. Here, these less complex microstructures are constructed according to the method in [1,2] for the generation of so‐called Statistically Similar Representative Volume Elements (SSRVE). For the efficient simulation of crack propagation through heterogeneous microstructures based on voxel data, the framework in [10] is applied on the SSRVEs. In numerical simulations, the capability of the SSRVEs to represent the crack behavior of the full microstructure is investigated by comparing with the results are compared to simulations on a cutout of the full microstructure.
Configurational Forces in a Phase Field Model for Fatigue
Authors: Yan Sikang , Schlüter Alexander , Müller Ralf 
Published: March 2023

AbstractIn the last decades, the phase field method has drawn much attention for its application in fracture mechanics because it offers a simple unified framework for crack propagation. The core idea of phase field models for fracture is to introduce a continuous scalar field representing the discontinuous crack. Recently, a phase field model for fatigue has been proposed along this path. The fatigue failure differs from the other fracture scenarios since cracks only occur after a considerable number of load cycles. As fracturing happens, changes of the material microstructure are involved, which causes the evolution of the structural configuration. Thus, a new mathematical description not based on traditional spatial coordinates but the material manifold is desired, which will serve as an elegant analysis tool to understand the energetic forces for crack propagation. Configurational forces are a suitable choice for this purpose, as they describe the energetic driving forces associated with phenomena changing the material itself. In this work, we present a phase field model for fatigue. Furthermore, the phase field fatigue model is analyzed within the concept of configurational forces, which provides a straightforward way to understand the phase field simulations of fatigue fracture.
Structural stress prediction based on deformations using artificial neural networks trained with artificial noise
Authors: Gottardi Nicola , Freitag Steffen , Meschke Günther 
Published: March 2023

AbstractArtificial Neural Networks (ANN) have found application for multiple problems in structural mechanics and civil engineering. In the new approach developed here, ANNs are used for the determination of the maximum stress resultants in a structure on the basis of monitored displacements. Initially, a simple supported beam subjected up to two vertical forces is considered. The beam is solved analytically for different combinations of load positions and magnitudes defined by Monte‐Carlo sampling. The resulting beam deflections and maximum stress resultants are employed for the training of feedforward neural networks in order to generate metamodels able to predict the maximum bending moment knowing only a few beam input deflections. Subsequently, the concept is applied to a real beam experiment, where a reinforced concrete beam has been tested. It is shown, that the perfect correlation of the beam displacements used as inputs for the ANN training leads to extrapolations when the metamodel is applied to the measured displacements of the real experiment, which are not perfectly correlated. This is source of wrong predictions when the network is applied to these data. The introduction of artificial noise in the synthetic input data in a controlled way before training helps to overcome extrapolation and to increase repeatability and robustness of the metamodels. Various noise levels are applied to the synthetic data to monitor how the ANN performances change over increasing noise and the results along with the limitations of the approach are illustrated.
Modeling the thermomechanical processes and residual stresses in additive manufacturing of metallic components
Authors: Ali Baharin , Heider Yousef , Markert Bernd 
Published: March 2023

AbstractIn additive manufacturing of metallic components and fusion welding, undesirable deformations and residual stresses are common drawbacks, which directly influence the performance and functionality of the manufactured components. In this work, a thermomechanical continuum model is developed by using the phase‐field method to track the evolution of the melting/remelting‐solidification occurring due to the incident of localized heat input sources, e.g, by means of a laser heat source. The result of the thermal analysis is then employed for the mechanical analysis to predict the residual stresses. In the thermal and mechanical analysis, the thermomechanical properties are considered to evolve with the phase‐field variable. In addition, a scalar‐valued history variable is introduced to distinguish between consolidated and loose powder materials. This enables single‐track additive manufacturing simulations with a possible extension to multi‐layer and multi‐track simulations. To verify and validate the modeling approach, the coupled system of equations is implemented in the open‐source FEniCS project and a numerical example for additive manufacturing is solved and compared qualitatively and quantitatively with reference results from the literature.
A surrogate model for the prediction of permeabilities and flow through porous media
Authors: Niekamp Rainer , Niemann Johanna , Schröder Jörg 
Published: March 2023

AbstractIn this contribution we present an approach to generate a data driven surrogate model for the prediction of permeabilities and flow through two dimensional random micro‐heterogeneous materials. The laminar flow is well described by Darcy's law. In order to achieve an efficient computational tool for the generation of the database (up to 103 realizations), needed for the training of the neural networks, we apply a stochastic model based on the Brownian motion. The stationary state of the resulting stochastic model solves the Darcy equation and can be iteratively solved by a Monte Carlo approach applied to a particle simulation. Improved numerical efficiency can be yield by usage of the related transition matrix.
A Penalty Method for Coupling of Finite‐Element and Peridynamic Models
Authors: Pernatii Anna , Gabbert Ulrich , Naumenko Konstantin , Hesse Jan-Timo , Willberg Christian 
Published: March 2023

AbstractA classical continuum mechanics model no longer fulfills its basic assumptions, when the deformations are not smooth or discontinuous. Peridynamics (PD) as an integral formulation could better overcome these issues. Therefore, it is better suited to solve fracture problems such as crack initiation, its growth and formation of crack patterns. In PD the magnitudes of internal forces at a material point depend on the collective interaction of all material points within a subdomain called horizon. To take advances from the formulation, typically it is implemented in a mesh‐free form. In that case, it is easy to separate interactions between different material points. As consequence, a relatively high resolution is required to describe continuous deformation functions and, consequently computationally expensive. Therefore, the application of mesh‐free PD in undamaged regions requires an unnecessary high effort for receiving sufficient accurate results. In contrast, the finite element method (FEM) as a classical continuum mechanics‐based approach, is very efficient, if continuous stress distributions can be assumed. Consequently, a computational cost reduction can be achieved, if the PD is applied in the local damaged zone only and the remaining area is modeled and analyzed with the classical FEM. Realization of such an approach requires a sufficient accurate coupling of the PD and the FEM subdomains.A brief overview about different coupling approaches is given. Then the general approach of an Arlequin based method is presented. Here the coupling is achieved via an overlapping of PD and FEM areas. The coupling equations are developed and realized with help of the Penalty method. The Penalty method is considered as an alternative procedure to the Lagrange multiplier strategy without creating new unknowns, which essentially simplifies the coupled PD‐FEM approach. The validity and limits of the proposed technique are demonstrated through analysis, where the choice of the Penalty number is discussed as well as artificial wave oscillations, caused by the coupling area.
Variety of Planar Fourth‐Order Fiber Orientation Tensors and Implications on Effective Elastic Stiffnesses
Authors: Bauer Julian Karl , Seelig Thomas , Hrymak Andrew , Böhlke Thomas 
Published: March 2023

AbstractIn this contribution, selected results from [1–3] are presented in a compact and simplified way. In addition, the variety of fiber orientation tensors is used to determine a maximum deviation of the direction‐dependent Young's modulus, which can arise if only second‐order directional information is included in a specific meanfield homogenization. Focusing on the special case of planar fiber distributions, the variety of fiber orientation tensors identified in [1] is considered as a design space. This design space is completely explored for the orientation‐averaging homogenization following [4], fixed material parameters and fixed fiber volume content. The possible directional dependence of the resulting effective stiffnesses is graphically presented using polar plots of the direction‐dependent Young's modulus. These polar plots are arranged on two‐dimensional slices within the parameter space of planar fourth‐order fiber orientation tensors. This gives a complete representation of the influence of the orientation tensor on the anisotropic stiffness tensor. Consequences of closure approximations, i.e., restriction to second‐order directional information, are demonstrated and motivate measurement of fourth‐order fiber orientation tensors.
Mathematical modeling of electro‐elastic dislocations in piezoelectric materials
Authors: Agiasofitou Eleni , Lazar Markus 
Published: March 2023

AbstractIn this work, based on the theory of linear incompatible piezoelectricity with eigendistortion and eigenelectric field, the concept of electro‐elastic dislocations is presented. Both field variables, the displacement vector u and the electrostatic potential φ, possess a jump discontinuity at the dislocation surface. Electro‐elastic dislocations are described not only by the dislocation density tensor but also by a new introduced field, the so‐called electric dislocation density vector. In addition to electro‐elastic dislocations, inhomogeneities, body forces and body charges are also considered. Within this framework, material balance laws that correspond to the symmetries of translation, scaling and rotation are derived. All fundamental fields of configurational mechanics like the Eshelby stress tensor, the electro‐elastic Peach‐Koehler force, the Cherepanov force, the Eshelby force among others, which take place in the broken (translational, scaling and rotational) conservation laws anymore are given.
Two‐scale FE‐FFT‐based thermo‐mechanically coupled modeling of elasto‐viscoplastic polycrystalline materials at finite strains
Authors: Schmidt Annika , Gierden Christian , Waimann Johanna , Svendsen Bob , Reese Stefanie 
Published: March 2023

AbstractDue to the general pursuit of technological advancement, structural components need to meet increasingly higher standards. In order to optimize the performance behavior of the used materials, detailed knowledge of the overall as well as microscopic material behavior under certain mechanical and thermal loading conditions is required. Hence, we present a two‐scale finite element (FE) and fast Fourier transformation (FFT)‐based method incorporating finite strains and a thermo‐mechanically coupled constitutive model for elasto‐viscoplastic polycrystalline materials. Assuming that the length scale of the microscale is sufficiently smaller compared to the length scale of the macroscale, we consider the macroscopic and microscopic boundary value problem as two coupled subproblems. The macroscopic boundary value problem is solved utilizing the finite element method. In each macroscopic integration point, the microscopic boundary value problem is embedded as a periodic unit cell whose solution fields are computed utilizing fast Fourier transforms and a Newton‐Krylov solver. The scale transition is performed by defining the macroscopic quantities via the volume averages of their microscopic counterparts. In order to demonstrate the use of the proposed framework, we predict the macroscopic and microscopic fields of a polycrystalline material within a numerical example using an efficient and accurate FE‐FFT‐based two‐scale method.
A comparative study between phase‐field and micromorphic gradient‐extended damage models for brittle fracture
Authors: Harandi Ali , Tabib Majd , Alatassi Baker , Brepols Tim , Rezaei Shahed , Reese Stefanie 
Published: March 2023

AbstractTo circumvent a mesh dependency of damage models, non‐local approaches such as phase‐field and gradient‐extended damage models have shown a good capability and attracted a lot of attention for modeling fracture. These models can predict crack nucleation, kinking, and branching. The gradient‐extended formulation proposed by [1, 2], which includes a micromorphic degree of freedom for damage, is connected to a phase‐field damage model presented in [3]; by connecting fracture parameters in brittle fracture. The latter is followed by comparing the thermodynamic consistency of these models. Despite having similarities in the formulation, gradient‐extended models differ from the standard phase‐field ones by having a damage threshold. Besides that, the local iteration exists in the gradient‐extended damage models. By employing the cohesive phase‐field model or the Angiotensin type 1 (AT1), a damage threshold appears in the formulation; by having a linear term for damage in the crack density function, see [4,5,12]. A comparison between these models is made, by taking several numerical examples and comparing their responses in a quasi‐static case. Moreover, the feasibility of different responses is addressed when one uses a standard Newton‐Raphson solver or the arc‐length one for solving a boundary value problem.