bluuebunny/crossref_metadata_2025 huggingface dataset:
The talar morphology of a hypochondroplasic dwarf: A case study from the Italian Late Antique period
Authors: Sorrentino Rita , Carlson Kristian J. , Figus Carla , Pietrobelli Annalisa , Stephens Nicholas B. , DeMars Lily J. D. , Saers Jaap P. P. , Armando Jessica , Bettuzzi Matteo , Guarnieri Tiziana , Oxilia Gregorio , Vazzana Antonino , Parr William , Turley Kevin , Morigi Maria Pia , Stock Jay T. , Ryan Timothy M. , Benazzi Stefano , Marchi Damiano , Belcastro Maria Giovanna
Published: December 2021

This project aims to test whether geometric morphometric (GM) and trabecular analyses may be useful tools in identifying talar characteristics related to hypochondroplasia. We quantified the external and internal talar morphology of a hypochondroplasic dwarf (T17) from Modena (northern Italy) dated to the sixth century AD. External talar morphology of T17 was compared with a broad sample of modern human tali (n = 159) using GM methods. Additionally, a subsample of these tali (n = 41) was used to investigate whole talar trabecular changes in T17. Our results show that GM and trabecular analyses identify a combination of traits linked to the dwarfing disorder of hypochondroplasia. These traits include decreased scaled talar dimensions compared with normal‐sized individuals, presence of an accessory antero‐lateral talar facet, high bone volume fraction, and high anisotropy values throughout the entire talus. In our case study, hypochondroplasia does not appear to substantially modify external talar morphology probably due to the fast growth of the talus. We suggest that small talar dimensions are associated with hypochondroplasia. An antero‐lateral talar facet may result from the talus and calcaneus coalition (i.e., talocalcaneal abnormal bridging) possibly related to an everted foot posture that was limited by overgrowth of the fibula. We suggest that high talar trabecular density and strut orientation provide insights into pathological development of the trabecular plates in T17. Finally, our study suggests that high talar trabecular density and strut orientation, and small talar dimensions, may be added as possible concomitant talar hallmarks for hypochondroplasia.
The external debt‐inflation nexus in Egypt
Authors: Helmy Heba E.
Published: December 2021

Egypt has a long history with external financing dating back to the 19th century. Nevertheless, Egypt's external debt has been mounting remarkably in the past few years. This paper examines the impact of Egypt's external debt on its price level, a topic ignored by researchers. Nonetheless, as inflation is a hydra‐headed problem, this paper develops several models which incorporate fiscal and monetary policies besides other inflation‐inducing internal and external factors using monthly data extending from 2000M1 to 2020 M1. By employing ARDL cointegration analyses on monthly time series variables and using Egypt's wholesale price index to account for inflation, the paper concludes that external debt raises prices both in the short and long runs. Moreover, money supply and interest rate were also found to increase prices in the long run long despite decreasing them in the short run. Finally, upsurges in the international prices of primary products stimulate domestic prices both in the short and long terms, while depreciation in the local currency aggravates inflation in the short and long terms as well. As external debt raises inflation and affects many other inflation‐inducing factors indirectly, the paper concludes that reducing Egypt's external debt may help in curbing Egypt's inflation.
Numerical convergence of discrete extensions in a space‐time finite element, fictitious domain method for the Navier–Stokes equations
Authors: Anselmann Mathias , Bause Markus
Published: December 2021

A key ingredient of our fictitious domain, higher order space‐time cut finite element (CutFEM) approach for solving the incompressible Navier–Stokes equations on evolving domains (cf. [1]) is the extension of the physical solution from the time‐dependent flow domain Ωtf to the entire, time‐independent computational domain Ω. The extension is defined implicitly and, simultaneously, aims at stabilizing the discrete solution in the case of unavoidable irregular small cuts. Here, the convergence properties of the scheme are studied numerically for variations of the combined extension and stabilization.
Fully Implicit RUNGE‐KUTTA Schemes for Ideal Elastoplasticity
Authors: Schröder Bettina , Kuhl Detlef
Published: December 2021

The present paper derives a multifield formulation of ideal elastoplasticity to enable the consistent application of higher order accurate RUNGE‐KUTTA schemes. With the help of an axisymmetric model problem the appearing time discretization errors of distinct schemes are determined and compared.
High‐order SBFEM solution of the Reynolds equation
Authors: Pfeil Simon , Gravenkamp Hauke , Duvigneau Fabian , Woschke Elmar
Published: December 2021

A semi‐analytical solution of the Reynolds equation for hydrodynamic bearings in rotordynamic simulations is investigated, which is based on the Scaled Boundary Finite Element Method (SBFEM). The numerical efficiency of this approach is compared to the Finite Element Method (FEM), considering linear as well as higher‐order shape functions. It is observed that the SBFEM requires significantly less computational time than the FEM, especially with respect to high‐order formulations.
Simulation of granular materials with the discrete element method to investigate their suitability as crash‐absorber in ship collisions
Authors: Kraus Sonja , Woitzik Christian , Dosta Maksym , Düster Alexander
Published: December 2021

In recent years, the idea of increasing the crash‐worthiness of ships by filling their double hull structure with granules has been studied. To this end, different granular materials have been investigated in [1, 2] with the result, that expanded glass materials are best suited for this purpose. Based on this work, it is important to gain deeper insights into the breakage behavior of expanded glass particles performing numerical investigations. The corresponding simulation procedure as well as the computational results are presented in this contribution.
Efficient modeling of material dissolution in electrochemical machining
Authors: van der Velden Tim , Rommes Bob , Klink Andreas , Reese Stefanie , Waimann Johanna
Published: December 2021

The manufacturing process of electrochemical machining (ECM) allows for the precise machining of high‐strength materials. In order to save time and reduce experimental costs, one depends on efficient simulation tools. Numerous modeling approaches consider the anodic material dissolution in ECM based on a high resolution of the material (see e.g. [2], [3]). However, these models require computationally expensive remeshing after every time step. Therefore, we propose a novel approach that describes the dissolution process based on effective material parameters (see [5]). Faraday's law of electrolysis provides the evolution of the dissolution level which is described by an internal variable that relates the dissolved volume to a reference volume. The dissolution level in turn controls the effective material parameters. This procedure allows for the simulation of the entire process with a fixed finite element mesh. Moreover, the model considers the full coupling of the thermoelectric boundary value problem to accurately account for the electric current density distribution. The comparison of the model with analytical and experimental reference solutions yields realistic results and, hence, motivates the model's application to predict the surface roughness evolution in a pulsed electrochemical machining process.
Macroscopic modelling of stress driven anisotropic growth in bioengineered tissues
Authors: Lamm Lukas , Holthusen Hagen , Böhm Christian , Jockenhövel Stefan , Reese Stefanie
Published: December 2021

Within this contribution we present a new approach to macroscopically describe stress‐driven volumetric growth occurring in soft tissues. To overcome the limitations of an a‐priori prescribed structure of the growth tensor, the existence of a general growth potential is postulated. Such a potential aims to describe a homeostatic stress state that is ultimately reached as a result of the growth process. Similar to well established methods from the field of visco‐plasticity, we formulate the evolution of the growth related right Cauchy‐Green tensor as a time dependent associative evolution law with respect to the given growth potential. This approach is not restricted to describe either isotropic or anisotropic growth related changes in geometry, but can cover both, which gives the model a flexibility that many other established models are lacking. Besides the main aspects of the theoretical development, we also show numerical examples comparing the newly derived model with a standard formulation of isotropic growth.
Consideration of rubber bushings in a multi‐body simulation by detailed finite element models
Authors: Marter Paul , Daniel Christian , Duvigneau Fabian , Woschke Elmar , Juhre Daniel
Published: December 2021

Within a multi‐body simulation (MBS) a three‐dimensional FE model is employed to represent the nonlinear properties of rubber bushings. This is implemented via a sequential force‐displacement coupling between the two solvers. For a first material modelling approach of the elastomer, the modified Neo Hooke model is used in conjunction with the generalized Maxwell model. Later, however, a physically motivated material model will be used. First results for a single‐mass oscillator are presented and show the general functionality of the coupled approach. Since the use of FE models in MBS causes a significantly higher computational effort, it is necessary to realize the coupling between FEM and MBS as efficient as possible, which is also a future task.
Schur‐type preconditioning of a phase‐field fracture model in mixed form
Authors: Heister Timo , Mang Katrin , Wick Thomas
Published: December 2021

In the context of phase‐field modeling of fractures in incompressible materials, a mixed form of the elasticity equation can overcome possible volume locking effects. The drawback is that a coupled variational inequality system with three unknowns (displacements, pressure and phase‐field) has to be solved, which increases the overall workload. Efficient preconditioning at this point is an indispensable tool. In this work, a problem‐specific iterative solver is proposed leveraging the saddle‐point structure of the displacement and pressure variable. A Schur‐type preconditioner is developed to avoid ill‐conditioning of the phase‐field fracture problem. Finally, we show numerical results of a pressure‐driven benchmark which to confirm the robustness of the solver.
Constitutive artificial neural networks: a general anisotropic constitutive modeling framework utilizing machine learning
Authors: Hillgärtner Markus , Linka Kevin , Abdolazizi Kian P. , Aydin Roland C. , Itskov Mikhail , Cyron Christian J.
Published: December 2021

In this contribution, a novel machine learning architecture for data‐driven modeling of the mechanical constitutive behavior of materials, constitutive artificial neural networks (CANNs) [1], will be introduced. CANNs incorporate basic material modeling fundamentals from continuum mechanics while relying on artificial neural networks for material‐specific relations. Their architecture allows them to process stress‐strain curves and arbitrary additional information (e.g., about the microstructure or manufacturing parameters). With only a low‐to‐moderate amount of training data and training time, they can predict the constitutive behavior of complex nonlinear and anisotropic materials. The ability to utilize additional material‐specific information enables CANNs to predict the mechanical behavior of previously unseen materials if the CANN was sufficiently trained with many similar materials.
Symplectic Partitioned Runge‐Kutta Methods for High‐Order Approximation in Linear‐Quadratic Optimal Control of Hamiltonian Systems
Authors: Herrmann-Wicklmayr Markus , Flaßkamp Kathrin
Published: December 2021

Symplectic partitioned Runge‐Kutta (SPRK) methods are known to be a good choice in forward simulations of Hamiltonian systems due to their structure‐preserving properties. Recent works study the application of SPRK methods to nonlinear and linear‐quadratic optimal control problems howing various advantages of these methods compared to standard non‐symplectic integration schemes. Now, our focus is on extending the comparison to SPRK and RK methods of higher orders. For linear‐quadratic optimal control problems, we consider the discrete‐time Riccati feedback as well as the feedforward control implementation. For applications in which computational power or computation time is limited, low sampling rates are of particular interest. Hence we study this case for the n‐fold harmonic oscillator.
Reanalysis for local quantities of interest
Authors: Materna Daniel
Published: December 2021

In this contribution a method for the prediction of the change in a quantity of interest due to structural modifications is considered. The approach is based on a goal‐oriented method by using the primal and dual problems. The method can be used in order to reduce the overall computational cost in the numerical simulation. Furthermore, the proposed method is easily to implement in existing finite element programs, because no derivatives with respect to the design variables are necessary.
Application of variable excitation frequency for amplitude reduction
Authors: Simader Victoria , Holl Helmut J.
Published: December 2021

Dynamic systems are faced with large vibration amplitudes if they operate near the resonance frequency of the system or while passing through the resonance. With a suitable external excitation a reduction of the amplitude of the oscillation can be achieved. The analysis of a variable excitation frequency was first carried out on the force driven single degree of freedom harmonic oscillator. The influence of various excitation parameters can be seen after a mathematical transformation of the excitation signal. The elimination of the natural frequency of the system from the excitation signal is possible with specially selected parameters. It is demonstrated that suitable numerical values, correlations between the parameters and functions allow to reduce the oscillation of the amplitude of the system if the operation takes place near the resonance frequency and also during the resonance passage. The theoretical assertions are validated with an experimental setup and a parameter identification has been made. In addition a worst case scenario is analysed on the test rig. The developed requirements are extended to force driven harmonic oscillators with multi degree of freedom.
Approximate computational model for shear loaded stiffened composite panels
Authors: Schilling Jakob C. , Mittelstedt Christian
Published: December 2021

The stability behavior is critical for thin‐walled composite structures. This type of structures is for example employed in aircraft, spacecraft and marine vessels, where weight is an important factor in the design. For stiffened panels of, e.g. a fuselage structure, shear is a relevant load case. A new approximate computational model for the local buckling behavior of omega‐stringer‐stiffened panels under shear loading is presented that is based on energy methods. To assess the quality of the derived solution, the results of suitable parameter studies are discussed. In comparison to numerical methods, the new model reduces the computational effort necessary for the preliminary design of omega‐stringer‐stiffened composite panels. Thus, it contributes to increase the performance of structures and consequently reduces the weight of the mentioned applications.
On the Correspondence between Replicator Dynamics and Assignment Flows
Authors: Boll Bastian , Schwarz Jonathan , Schnörr Christoph
Published: December 2021

Assignment flows are smooth dynamical systems for data labeling on graphs. Although they exhibit structural similarities with the well‐studied class of replicator dynamics, it is nontrivial to apply existing tools to their analysis. We propose an embedding of the underlying assignment manifold into the interior of a single probability simplex. Under this embedding, a large class of assignment flows are pushed to much higher‐dimensional replicator dynamics. We demonstrate the applicability of this result by transferring a spectral decomposition of replicator dynamics to assignment flows.
Analysis of the remote laser cutting process induced damage in carbon fibre reinforced polymers
Authors: Schmidt Benjamin , Husert Markus , Rose Michael , Zimmermann Martina , Kästner Markus
Published: December 2021

In this contribution a modelling approach for the laser cutting process simulation of carbon fibre reinforced polymers is introduced. The cutting process is modelled in a 3D thermal simulation, the material is modelled layer‐wise orthotropically. For the evaporation of matrix and fibre phase transitions are utilised. The laser spot is modelled with its gaussian distribution as a heat input on the upper side.
Exploring the interplay between cellular development and mechanics in the developing human brain
Authors: Zarzor M. S. , Kaessmair S. , Steinmann P. , Blümcke I. , Budday S.
Published: December 2021

The human brain has a complex structure on both cellular and organ scales. This structure is closely related to the brain's abilities and functions. Disruption of one of the biological processes occurring during brain development on the cellular scale may affect the cortical folding pattern of the brain on the organ scale. However, the link between disruptions in cellular brain development and associated cortical malformation remains largely unknown. From a mechanical perspective, the forces generated during development lead to mechanical instability and, eventually, the mergence of cortical folds. To fully understand mechanism underlying malformations of cortical development, it is key to consider both the events that occur on the cellular scale and the mechanical forces generated on the organ scale. Here we present a computational model describing cellular division and migration on the cellular scale, as well as growth and cortical folding on the tissue or organ scale, in a continuous way by a coupled finite growth and advection‐diffusion model. We introduce the cell density as an independent field controlling the volumetric growth. Furthermore, we formulate a positive relation between cell density and cortical layer stiffness. This allows us to study the influence of the migration velocity, the cell diffusivity, the local stiffness, and the local connectivity of cells on the cortical folding process and mechanical properties during normal and abnormal brain development numerically. We show how an increase in the density of the neurons increases the layer's mechanical stiffness. Moreover, weWe validate our simulation results through the comparison with histological sections of the fetal human brain. The current model aims to be a first step towards providing a reliable platform to systematically evaluate the role of different cellular events on the cortical folding process and vice versa.
Numerical simulation of low cycle fatigue behavior, combining the phase‐field method and the Armstrong‐Frederick model
Authors: Wiegold Tillmann , Aygün Serhat , Klinge Sandra
Published: December 2021

The present work couples the phase field method of fracture to the Armstrong‐Frederick model of plasticity with the kinematic hardening. The chosen approach inherits the advantages of both techniques and is aimed at the study of low cycle fatigue effects in ductile materials. However, the numerical implementation of this promising concept brings with it several challenges, such as the definition of a unique framework for both setups, the derivation of coupled evolution equations, the distinction between tension and compression mode and the development of a computationally efficient algorithm. In the approach developed, the derivation of evolution equations uses the minimum principle of the dissipation potential. This step requires the expression of the dissipation potential of the classic Armstrong‐Frederick model in terms of the internal variable rates by using the Legendre transformation. The model is eventually implemented in the FE‐program and applied in order to investigate the life‐time of the cold‐formed carbon steel and the cold‐formed stainless steel.
Long‐term stability and debonding of cementless implants
Authors: Immel Katharina , Nguyen Vu-Hieu , Haiat Guillaume , Sauer Roger A.
Published: December 2021

This work presents a three‐dimensional FE frictional contact formulation with NURBS‐enriched contact elements for the debonding of partially osseointegrated, cementless implants. The contact model is based on a modified Coulomb's friction law [1] that can model the tangential debonding of partially osseointegrated implants. Here, a smooth transition function between the two friction coefficients is used to model the decrease of friction due to debonding of the implant. The model is applied to simulate the debonding of a hip implant to determine the influence of partial osseointegration on the stability of the implant.
Thermomechanical analysis of actuation mechanism of a microgripper fabricated with direct laser writing
Authors: Huang Wenjie , de Payrebrune Kristin M.
Published: December 2021

With direct laser writing micro structures can be manufactured by solidifying a photo resist when the laser beam triggers a photochemical reaction in the focal voxel. We have used direct laser writing to fabricate a thermally actuated microgripper, which can move its two cantilever like arms to grip micro‐objects. One cantilever consists thereby of two strips with different coefficients of thermal expansion such that both cantilevers bends towards each other for an increasing temperature like a welded bimetal.

This work investigates the impact of each cantilever's geometry on the gripping performance of the micro gripper theoretically. The tip deflection of the gripper is calculated by the analytical model of Timoshenko's theory of elasticity. After fabricaiton of the microgripper, its gripping performance is observed under the microscope while heated by a heating element.
On a hybrid approximation concept for self‐excited periodic oscillations of large‐scale dynamical systems
Authors: Kappauf Jonas , Hetzler Hartmut
Published: December 2021

When approximating periodic solutions in the context of large‐scale dynamical systems involving strong local nonlinearities, efficiency is of special interest. Hence, the literature suggests a combination of two approximation methods for increasing the ratio of computational cost to accuracy. Within this contribution, a combination of Finite Difference and Harmonic Balance method is proposed. Due to the usage of Harmonic Balance it is shown, that the resulting equations only depend on the degrees of freedom that are affected by nonlinear forces. As an application, a self‐excited limit cycle of a chain of oscillators is approximated and results are compared against numerical time integration to highlight qualitative accuracy.
Experimental investigations on rising bubbles in stagnant water in vertical capillaries
Authors: Grünendahl Sabrina , Danila Kevin , Brandner Dean Martin , Ehrhard Peter
Published: December 2021

We investigate how the walls of cylindrical capillaries affect the velocity of rising gas bubbles of various diameters. Of course, as the capillary diameter increases, the velocity of the rising bubble will approach the case of free rising. Such systematic experiments on the bubble rise in capillaries, in which the ratio of bubble diameter and capillary diameter is varied from one towards smaller values, can hardly be found in literature. Experiments within the system water/air have been conducted in stagnant water and will be discussed in this paper.
Macroscopic model for steel fiber reinforced high performance concrete based on unit cell calculations
Authors: Pise Mangesh , Brands Dominik , Schröder Jörg , Gebuhr Gregor , Anders Steffen
Published: December 2021

The influence of reinforced steel fiber on the failure behavior of high performance concrete (HPC) is mainly characterized by the complex fiber‐matrix interaction at microscale. A phenomenological material model is developed for more efficient simulation of the overall material behavior of fiber reinforced HPC. For the calibration of the material parameters and to verify the efficiency of the presented phenomenological material model the simulation results of a virtual experiment using an ellipsoidal RVE and a macroscopic boundary value problem (BVP) are compared.
Constitutive modelling of the deformation‐induced martensite transformation observed in metastable austenitic CrNi steels
Authors: Thammineni Hari Kisan , Zhu Tong , Smaga Marek , Beck Tilmann , Müller Ralf
Published: December 2021

Metastable austenitic CrNi steels undergo phase transformation when loaded or deformed plastically. In the current work a macroscopic and phenomenological constitutive model is presented to model the strain induced transformation of austenite to martensite. The approach is based on the previous works of Olsen and Cohen [1] & Stringfellow et al. [2]. The kinetics of the phase transformation is modelled based on the assumption that the intersections of the shear bands in the austenitic phase, act as potential martensite nucleation locations. Evolution of the shear band density and their intersections are modelled using the plastic strain in the austenitic phase. The probability of the intersection creating martensite is given by a Gaussian cumulative distribution, which in turn depends on the temperature and stress triaxiality. The resulting stress‐ strain behavior considers the volume fraction, plastic strains and the strain hardening parameters of the individual phases as internal variables. An explicit formulation of the material model is implemented as a user subroutine in a bi‐linear element formulation of FEM. Some of the required material parameters are estimated by fitting experimental stress‐strain and martensite volume evolution curves. For the purpose of illustrating the model's behavior, boundary value problems of components with structured surfaces are presented.
On the incorporation of curvature effects into the isogeometric analysis of fibre‐reinforced solids
Authors: Witt Carina , Kaiser Tobias , Menzel Andreas
Published: December 2021

In the context of engineering on the micro‐ and nanoscale, size‐dependency is an important characteristic of material behaviour. In order to avoid complex experiments and predict size effects in simulations instead, classic continuum approaches are extended by the introduction of a length scale, e.g. through the consideration of gradient contributions. For the particular case of fibre‐reinforced materials, such a gradient‐enhanced approach can be achieved by introducing the fibre curvature as an additional kinematic quantity. This implies that basis functions with a global continuity higher than C0 are required for a finite element‐based approach which accounts for these fibre curvature effects. The present contribution shows that the isogeometric finite element method can provide a framework for the simulation of the respective higher‐gradient continua.
Surrogate Modeling of a Nonlinear, Biphasic Model of Articular Cartilage with Artificial Neural Networks
Authors: Egli Franziska S. , Straube Richard C. , Mielke André , Ricken Tim
Published: December 2021

The increasing number of cartilage diseases negatively affects the quality of life for a large part of the population. Understanding the mechanical properties of cartilage is a key component in investigating and mitigating the effects of such diseases. To describe the behavior of articular cartilage, a biphasic fiber‐reinforced numerical model based on the Theory of Porous Media (TPM) has been developed. To possibly provide an alternative for the corresponding time‐consuming computational simulations, the suitability of Artificial Neural Networks (ANNs) as surrogate models is investigated. For this purpose, the simulation results of a compression‐relaxation test are compared with the predictions of the ANN.
A multi‐level data‐driven finite element method in polymorphic uncertainty quantification
Authors: Korzeniowski Tim Fabian , Weinberg Kerstin
Published: December 2021

This contribution explores the ability to conduct polymorphic uncertainty computations within the data‐driven finite element framework. The constitutive equation is replaced by data sets that determine the material behavior, and a fuzzy load is used for the polymorphic approach. To conduct many simulations with the discretized variables and to increase numerical efficiency, the numerical cost is reduced by a multi‐level method.
A strain gradient enhanced model for the phase‐field approach to fracture
Authors: Makvandi Resam , Abali Bilen Emek , Eisenträger Sascha , Juhre Daniel
Published: December 2021

Phase‐field modelling has been shown to be a powerful tool for simulating fracture processes and predicting the crack path under complex loading conditions. Note that the total energy of fracture in the classical phase‐field formulations includes the strain energy density from the linear elasticity theory resulting in singular stresses at the crack tip. Recently, we have demonstrated that integrating the strain gradient elasticity into the conventional phase‐field fracture formulations may improve the final results by alleviating the effects of a singular stress field around the crack tip [1]. The current contribution focuses on a more general formulation of strain gradient elasticity.
Integral effects of the Debye layer on a sedimenting particle with zeta‐potential variations
Authors: Marthaler Philipp G. , Class Andreas G.
Published: December 2021

Fluid‐solid interfaces give rise to electro‐hydrodynamic effects at microscale. In a macroscale model, those effects can be represented by jump conditions. This report focuses on the derivation of such jump conditions for integral parameters, like mass flux, forces and charge fluxes. In particular, the effect of spatial and temporal variations in the ζ‐potential on the solid's surface are discussed, using the generic problem of a sedimenting particle.
Remarks on a primal‐dual interior point algorithm for single crystal plasticity
Authors: Scheunemann Lisa , Nigro Paulo S. B. , Schröder Jörg
Published: December 2021

In the field of single crystal plasticity, different algorithms exist for the solution of the constitutive equations. They can be grouped into rate independent and rate dependent approaches, where both classes are governed by inherent shortcomings, as discussed in, e.g., [3]. This contribution outlines an algorithmic formulation for single crystal plasticity at small strains for the rate independent case relying on an infeasible primal‐dual interior point method, which has been presented in [5]. It is able to bypass several issues known in rate independent algorithms. Besides a brief overview of the continuum mechanical and algorithmic framework, aspects on different formulations related to the Karush‐Kuhn‐Tucker (KKT) conditions are discussed.
Energy related thermomechanical material model validation in complex tensile testing with self heating
Authors: Sparr Holger , Roszak Robert , Sagradov Ilja , Schob Daniela , Ziegenhorn Matthias
Published: December 2021

The objective of this work is the application of viscoplastic material models in a consistent thermomechanical framework to make use of infrared thermography as one source of a phenomenological model validation. The thermomechanical foundation led to the understanding, that each mechanical deformation can be analysed as a thermodynamical process. The usual balance equations applied in a mechanical process are completed by the first and second law of thermodynamics. In this setup, the classical stress‐strain characteristics is accompanied by the temperature evolution and the evolution of derived quantities such as the energy resp. energy‐rate transformation ratio (ETR). These three characteristics combined can improve the assessing procedure of the investigated deformation load path qualitatively as well as quantitatively. The initial boundary value problem of the coupled displacement and temperature fields is experimentally well supported by a high‐resolution infrared camera. A reduced thermal boundary value control simplifies the experimental measures to be realised. It is shown in the analysis, that the attained surface temperature accuracy is well‐suited for the identification of model parameters related to dissipative deformation phenomena. The common split into different fractions of free energy allows a detailed evaluation in terms of hardening related stored energy and other derived state entities. The potential of the instantaneous rate of energy storage is with respect to the comparability of different modelling approaches explained and is illustrated by experimental results. As a further consequence, a more complex tensile testing regime is proposed to validate the applied material model for metals.
Model‐free Data‐Driven simulation of inelastic materials using structured data sets, tangent space information and transition rules ‐ convergence test
Authors: Ciftci Kerem , Hackl Klaus
Published: December 2021

Data‐driven computational mechanics replaces phenomenological constitutive functions by performing numerical simulations based on data sets of representative samples in stress‐strain space. The distance of modeling values, e.g. stresses and strains in integration points of a finite element calculation, from the data set is minimized with respect to an appropriate metric, subject to equilibrium and compatibility constraints, see [1,2]. Although this method operates well for elasticity problems it challenges dealing with history‐dependent materials. One approach by [3], is the inclusion of local histories into the data set. However, it is still necessary to include models for the evolution of specific internal variables. In the presented approach, the data set is augmented with directions in the tangent space of points in stress‐strain space. Moreover, the data set is divided into subsets corresponding to different material behavior, e.g. elastic and inelastic. Based on the classification, transition rules map the modeling points to the various subsets. The convergence will be demonstrated by applying it to a model of elasto‐plasticity with isotropic hardening.
Analysis‐Suitable T‐Splines of arbitrary degree and dimension
Authors: Morgenstern Philipp , Görmer Robin
Published: December 2021

This paper defines analysis‐suitable T‐splines for arbitrary degree (including even and mixed degrees) and arbitrary dimension. We generalize the concept of anchor elements known from the two‐dimensional setting, extend two existing concepts of analysis‐suitability and justify their sufficiency for linear independence of the T‐spline basis.
Using Deep Learning to Enhance Compton Camera Based Prompt Gamma Image Reconstruction Data for Proton Radiotherapy
Authors: Barajas Carlos A. , Kroiz Gerson C. , Gobbert Matthias K. , Polf Jerimy C.
Published: December 2021

Proton beam radiotherapy is a cancer treatment method that uses proton beams to irradiate cancerous tissue while simultaneously sparing doses to healthy tissue. In order to optimize radiational doses to the tumor and ensure that healthy tissue is spared, many researchers have suggested verifying the treatment delivery through real‐time imaging. One promising method of real‐time imaging is through a Compton camera, which can image prompt gamma rays emitted along the beam's path through the patient. However, the images reconstructed with modern reconstruction algorithms are often noisy and unusable for verifying proton treatment delivery due to limitations with the camera. This paper demonstrates the ability of deep learning for removing false prompt gamma couplings and correcting the improperly ordered gamma interactions within the data for the case of Triples and Doubles‐to‐Triple events.
Structural topology optimization of 3D‐printable microlattices for lightweight materials
Authors: Krischok Andreas , Keip Marc-André
Published: December 2021

We present a micro‐macro approach for the structural optimization of graded microlattices that contain unit cells with a triply periodic structure. These individual unit cells are based on minimal surface problems such as the the Schwarz Primitive surface or the Gyroid and exhibit a porous structure that allows for a macroscopic grading of the material fraction of the cells. Both the macro‐scale and the micro‐scale are optimized by means of a Cahn‐Hilliard phase‐field model that is coupled with an elastic problem. The optimization on the macro‐scale is performed with the finite element method (FEM) while the micro‐scale optimization makes use of a spectral method that solves the periodic problem in a fast manner by means of fast Fourier transforms (FFT).
Neural Network Parameter Identification Based Constitutive Modeling of Superelastic Shape Memory Alloys
Authors: Kaup Andreas , Lenzen Niklas , Altay Okyay
Published: December 2021

Superelastic shape memory alloys (SMAs) are two‐phase polycrystal materials with hysteretic energy dissipation and deformation recovery capabilities. This feature opens numerous application possibilities, particularly using SMA wires in structural vibration control. However, vibrations, such as wind and earthquake induced, may occur in high rate regimes with alternating amplitudes. Experiments show that the thermodynamically coupled SMA behavior is highly sensitive to strain rate and amplitude. Accordingly, the prediction accuracy of the constitutive models depends notably on their thermodynamic parameters, such as latent heat, heat transfer coefficient and specific heat. The identification of these parameters requires extensive experiments. To circumvent this challenge, this study proposes for SMA wires a machine learning based parameter identification procedure using artificial neural networks (ANNs). In this approach, a recently improved uniaxial macroscopic constitutive SMA model is utilized as a forward physics based model to compute all possible responses in an expected parameter space. With the generated data, a multilayer ANN is trained as a data based inverse model. The Latin hypercube sampling and the backpropagation learning algorithms are applied. After training, the data based model is able to identify suitable thermodynamic parameters from SMA stress responses. With the identified parameters, the constitutive model replicates the strain rate and amplitude dependent SMA response effects. The experimental results are matched by the model with high accuracy.
Investigation of high temperature vulcanized and room temperature vulcanized silicone rubber based on flexible piezo‐electric energy harvesting applications with multi‐walled carbon nanotube reinforced composites
Authors: Manikkavel Amutheesan , Kumar Vineet , Kim Jaehoon , Lee Dong Joo , Park Sang Shin
Published: December 2021

Flexible energy harvester can be able to produce continuous voltage output under the mechanical deformations. High temperature vulcanized (HTV) and room temperature vulcanized (RTV) silicone rubbers are used for making the flexible piezo‐electric energy harvester. A total of 1 and 2 phr of multi‐walled carbon nanotube (MWCNT) are used as the electrode material mixed with the rubber solution for the preparation of flexible electrode. Cyclic loading machine is used for the application of 2 Hz of bi‐axial load and uniaxial compression load in the specimen. One centimeter depth of displacement is applied during the bi‐axial cyclic loading and 4 mm amplitude of displacement is applied during the compression loading. Tensile and compression tests are performed to determine the engineering properties of the material. Tensile load withstanding value of the silicone rubber is increasing as increasing the MWCNT filler in the rubber. Tensile value of the pure HTV silicone rubber is 10.020 N and for 2 phr MWCNT reinforced rubber is 22.106 N. Compressive withstanding load of pure HTV rubber is 189.565 N and for 2 phr MWCNT reinforced rubber is 287.066 N. HTV silicone rubber is the highly stiffness material on compares with RTV rubber based on the tensile and the compressive value. Transmission electron microscopy, optical micrographs, and scanning electron microscope show the morphology of MWCNT and surface image of specimen. A total of 2 mm substrate based 2 phr MWCNT reinforced HTV flexible energy harvester undergo decrease in voltage during the cyclic loading due to breakage of electrode. A total of 2 phr MWCNT electrode‐based sample can be able to produce more output voltage than 1 phr MWCNT electrode‐based sample during bi‐axial and compression loading. More voltage is produced in the compression specimen than bi‐axial one.
Covalent crosslinks turn natural Eucommia ulmoides gum/polybutene‐1 composites into multiple shape memory materials
Authors: Wang Yan , Pei Xianqiang , Xia Lin , Xin Zhenxiang
Published: December 2021

A series of shape memory natural Eucommia ulmoides gum (EUG)/polybutene‐1 (PB‐1) composites were developed based on polymer blending. It was revealed that covalent crosslinks turned typical “sea‐island” phase morphology in the EUG/PB‐1 blend into a chemical co‐continuous structure, which played a vital role in promoting mechanical performances and fulfilling multiple shape memory effect dominated by the two well‐separated crystalline and melting phase transitions. Although the increase in cross‐linking density was a disadvantage to mechanical performances and shape fixing, the composite with more covalent crosslinks displayed better shape recovery capacity. The EUG/PB‐1 composite crosslinked by 0.4 phr diycumyl peroxide (DCP) displayed the highest shape fixing capacity, while the best shape recovery ability was given by that crosslinked by 1.6 phr DCP. The findings would provide a new technique to develop intelligent materials applied in smart packaging and hot‐shrinkable products.
Accuracy of identifying diagnosis of moderate to severe chronic kidney disease in administrative claims data
Authors: Paik Julie M. , Patorno Elisabetta , Zhuo Min , Bessette Lily G. , York Cassandra , Gautam Nileesa , Kim Dae Hyun , Kim Seoyoung C.
Published: December 2021

Background

Prior validation studies of claims‐based definitions of chronic kidney disease (CKD) using ICD‐9 codes reported overall low sensitivity, high specificity, and variable but reasonable PPV. No studies to date have evaluated the accuracy of ICD‐10 codes to identify a US patient population with CKD.

Methods

We assessed the accuracy of claims‐based algorithms to identify adults with CKD Stages 3–5 compared with laboratory values in a subset (~40%) of a US commercial insurance claims database (Optum's de‐identified Clinformatics® Data Mart Database). We calculated the positive predictive value (PPV) of one or two ICD‐9 (2012–2014) or ICD‐10 (2016–2018) codes for CKD compared with a lab‐based estimated glomerular filtration rate (eGFR) occurring within prespecified windows (±90 days, ±180 days, ±365 days) of the ICD‐based CKD code(s).

Results

The study population ranged between 104 774 and 161 305 patients (ICD‐9 cohorts) and between 285 520 and 373 220 patients (ICD‐10 cohorts). The mean age was 74.4 years (ICD‐9) and 75.6 years (ICD‐10) and the median eGFR was 48 ml/min/1.73 m2. The algorithm of two CKD codes compared with a lab value ±90 days of the first code achieved the highest PPV (PPV 86.36% [ICD‐9] and 86.07% [ICD‐10]). Overall, ICD‐10 based codes had comparable PPVs to ICD‐9 based codes and all ICD‐10 based algorithms had PPVs >80%. The algorithm of one CKD code compared with laboratory value ±180 days maintained the PPV above 80% but still retained a large number of patients (PPV 80.32% [ICD‐9] and 81.56% [ICD‐10]).

Conclusion

An ICD‐10‐based definition of CKD identified with sufficient accuracy a patient population with CKD Stages 3–5. Our findings suggest that claims databases could be used for future real‐world research studies in patients with CKD Stages 3–5.
Biases associated with epidermal necrolysis reporting in pharmacovigilance: An exploratory analysis using World Health Organization VigiBase
Authors: Bettuzzi Thomas , Ingen‐Housz‐Oro Saskia , Maison Patrick , de Prost Nicolas , Wolkenstein Pierre , Lebrun‐Vignes Bénédicte , Sbidian Emilie
Published: December 2021

Background

Possible biases in pharmacovigilance reporting may impact epidermal necrolysis (EN) and drugs associations.

Objectives

To assess biases associated with EN‐reporting.

Methods

Using VigiBase, the World Health Organization‐pharmacovigilance database, among drugs associated with EN between 2016 and 2020, we used an unsupervised clustering including reports characteristics, that is, reporter quality, time from drug intake to EN onset, and only one suspected drug in the report.

Results

Among 152 drugs, three clusters were identified. Cluster 1 (n = 41) exhibited drugs frequently reported within a time from intake to onset longer than 4 days, in 57 ± 13% of reports. It corresponded to well‐reported drugs and was composed mainly of antivirals and antiepileptics. Cluster 2 (n = 42) exhibited drugs frequently reported within a time from drug intake to onset shorter than 4 days, in 31 ± 12% of reports. It corresponded to drugs with a high risk of protopathic bias and was composed of nonsteroidal anti‐inflammatory drugs (NSAIDs), analgesics, and antibiotics. Cluster 3 (n = 69) exhibited drugs frequently reported with an unavailable time from drug intake to reaction, in 66 ± 11% of reports, and reported by a high frequency of consumers (9 ± 9%). It corresponded to drugs reported with a high risk of classification bias, and was composed of anticancer therapies and cardiovascular drugs.

Conclusion

Protopathic and classification biases impact EN‐reporting and should be considered regarding associations with antibiotics, NSAIDs, analgesics, anticancer therapies, and cardiovascular drugs.
Does acute flaccid myelitis cause respiratory failure in children?
Authors: Lazzarini Laura M. , Werner Julie M. , Perez Iris A. , Seruya Mitchel , Ramos‐Platt Leigh , Tiongson Emmanuelle , Keens Thomas G.
Published: December 2021

Introduction

Acute flaccid myelitis (AFM) is a rare disease that affects spinal cord gray matter, results in acute flaccid weakness of one or more limbs and predominantly involves the cervical spinal cord, which places patients at higher risk for respiratory failure. Our study aims to describe respiratory failure in pediatric AFM patients with emphasis on the need for assisted ventilation and respiratory nerve involvement from an acute and long‐term perspective.

Materials and Methods

We reviewed the medical records of patients diagnosed with AFM seen in a multidisciplinary clinic for persistent limb weakness between 2016 and 2020.

Results

We studied 54 patients, 35% were female. The median age of patients at illness onset was 5 years (range 7 months−19 years). The median age of patients at the time of study was 8.5 years (range 2−20 years). Eleven patients (20%) required assisted ventilation for acute respiratory failure. Of those that experienced acute respiratory failure, 81% developed chronic respiratory failure. Fifty‐six percent of patients with chronic respiratory failure were able to wean off assisted ventilation by 1 year. All patients that experienced unilateral diaphragm impairment with AFM onset experienced acute and chronic respiratory failure.

Discussion

Many patients with AFM may experience respiratory compromise and develop chronic respiratory failure. However, most of these patients can be weaned off ventilatory support by 1 year from illness onset. Most children with unilateral diaphragm impairment can sustain adequate ventilation without the need for long‐term ventilatory support.