9 research outputs found
Macro-mechanical modelling and simulation of textile fabric and clothing with S-FEM
Tese de Doutoramento Programa Doutoral em Engenharia TêxtilEsta tese propõe um método de elementos finitos, designado por S-FEM (Smoothed Finite Element
Method), para modelação e análise mecânica de estruturas têxteis planas. Neste enquadramento
teórico, supõe-se que a estrutura têxtil não-tecida é um material isotrópico elástico, enquanto a
estrutura têxtil tecida é um material elástico com anisotropia ortotrópica, para os quais as leis
constitutivas utilizam propriedades mecânicas de baixa pressão (low stress) com base na Medição
Objetiva de Tecidos (FOM - Fabric Objective Measurement).
As formulações de elementos finitos de baixa ordem baseadas em deslocamento quando aplicadas a
elementos finitos de placas (plate/shell) quadriláteras de 4 nós, incluindo campos de tensão de
cisalhamento transversal, baseiam-se nas contribuições de Raymond Mindlin e por Eric Reissner, no
que agora se designa teoria de deformação por cisalhamento de primeira ordem (first-order shear
deformation, do inglês, ou FSDT de forma abreviada), ou simplesmente teoria de Mindlin-Reissner, e
nas abordagens MITC (Mixed Interpolation of Tensorial Components), são nesta tese combinadas com
a técnica de suavização do/da gradiente/tensão nos termos dos modelos S-FEM por forma a mitigar
problemas como são o caso da distorção de elementos finitos, da granularidade grosseira da malha,
bem como dos bem conhecidos fenómenos de bloqueio. As malhas de quadriláteros são utilizadas
nesta tese devido à sua capacidade de representar geometrias complexas de tecidos em resultado de
deformações mecânicas como são os casos da recuperação face à pressão planar, flexão,
deformação, vibração, drapejamento, etc.
Refira-se que foi desenvolvido e implementado em Matlab um software para os novos modelos de
elementos finitos, em grande medida devido à inexistência de modelos S-FEM em softwares de análise
de elementos finitos (finite element analysis ou FEA), lacuna esta que ocorre quer em softwares
comerciais, quer não comerciais, e até em códigos abertos. Exemplos numéricos para as aplicações
básicas de engenharia no que respeita à modelação mecânica de folhas de tecido fino e de folhas de
tecido de espessura média em estudos de casos típicos, como é o caso da recuperação face a pressão
planar, flexão, deformação e comportamento livre de vibrações, indicam que os elementos finitos
(plate/shell) desenvolvidos com a técnica de suavização de tensão e MITC acabam por aliviar os
efeitos de distorção dos elementos, a granularidade grosseira da malha e efeito de bloqueio na
modelação e análise mecânica de tecidos muito finos e até mesmo de tecidos de espessura média. Os modelos de elementos finitos de placas (plate/shell) desenvolvidos durante o trajeto desta tese,
bem como as suas propriedades mecânicas de baixa tensão em termos de FOM, são, portanto, bem
adaptados à modelação e análise numérica de deformação macro-mecânica de folhas de tecido muito
fino e de folhas de tecido de espessura média, incluindo ao mesmo tempo análise de deformação
mecânica simples e complexa.An S-FEM (Smoothed Finite Element Method) for mechanical analysis and modelling of the textile
fabrics is proposed. In this theoretical framework, one assumes that the non-woven fabric is an elastic
isotropic material, while the woven fabric is an elastic with orthotropic anisotropy for which the
constitutive laws formulated are using low-stress mechanical properties based on FOM (Fabric
Objective Measurement). The displacement-based low-order finite element formulations for four-node
quadrilateral plate/shell finite element, including assumed transverse shear strain fields, are based
on the contributions of Raymond Mindlin and by Eric Reissner as FSDT (first-order shear deformation
theory and so-called the Mindlin-Reissner theory) together with MITC (Mixed Interpolation of Tensorial
Components) approaches, which are combined with the gradient/strain smoothing technique in terms
of S-FEM models contributed by G. R. Liu et al. in order to mitigate problems as element distortion,
mesh coarseness as well as the well-known locking phenomena. Quadrilateral meshes are used due
to ability to represent complicated geometries of complex mechanical deformation of the fabric such
as plane stress recovery, bending, buckling, vibration, draping behavior, etc. The finite element
computer codes were developed in MATLAB for the new formulated plate/shell finite element models
due to the lack of FEM (Finite Element Method) packages for S-FEM models in both commercial and
non-commercial FEA (Finite Element Analysis) computer applications, and even from open-source
platforms. Numerical examples for the basic engineering applications of mechanical modelling of thin
to moderately thick fabric sheet in the typical case studies such as in-plane stress recovery, bending,
buckling and free-vibration behavior, indicate that the developed plate/shell finite elements with
assumed strain smoothing technique and MITC, do alleviate element distortion, mesh coarseness,
and locking effect even for mechanical analysis and modelling very thin to moderately thick fabric. The
developed plate/shell finite element models and low-stress mechanic properties in terms of FOM are,
therefore, well adapted for numerical analysis and modelling of macro-mechanical deformation of the
thin to moderately thick fabric sheet including both simple and complex mechanical deformation
analysis.EMECW L12 MOBILITY GRANT AWARD CONTRACT BTG_559
Grant agreement n 2009/1661-001 001EC
Textile materials
In this specialised publication, the reader will find research results and real engineering developments in the field of modern technical textiles.
Modern technical textile materials, ranging from ordinary reinforcing fabrics in the construction and production of modern composite materials to specialised textile materials in the composition of electronics, sensors and other intelligent devices, play an important role in many areas of human technical activity. The use of specialized textiles, for example, in medicine makes it possible to achieve important results in diagnostics, prosthetics, surgical practice and the practice of using specialized fabrics at the health recovery stage.
The use of reinforcing fabrics in construction can significantly improve the mechanical properties of concrete and various plaster mixtures, which increases the reliability and durability of various structures and buildings in general.
In mechanical engineering, the use of composite materials reinforced with special textiles can simultaneously reduce weight and improve the mechanical properties of machine parts. Fabric- reinforced composites occupy a significant place in the automotive industry, aerospace engineering, and shipbuilding. Here, the mechanical reliability and thermal resistance of the body material of the product, along with its low weight, are very relevant.
The presented edition will be useful and interesting for engineers and researchers whose activities are related to the design, production and application of various technical textile materials
A finite-element mechanical contact model based on Mindlin-Reissner shell theory for a three-dimensional human body and garment
7th International Conference on Scientific Computing and Applications, Dalian, Peoples R China, 13-16 June 2010Efficient numerical methods for describing a garment's mechanical behavior during wear have been identified as the key technology for garment simulation. This paper presents a finite-element mechanical contact model based on Mindlin-Reissner shell theory for a three-dimensional human body and garment. In this model, the human body and the garment are meshed as basic contact cells, these contact cells between the human body and the garment are defined as the contact pair to describe the contact relationship, and the mathematical formulation of the finite-element model is defined to describe the strain-stress performance of the three-dimensional human body and garment system. By using the solution given by the computer code and the programs specifically developed, the calculations of the mechanics in the basic cells of the human body and the garment have been able to be carried out. The simulation results show that the model of rationality, a good simulation results and simulation efficiency.Institute of Textiles and Clothin
Multiscale simulation methodology for the forming behavior of biaxial weft-knitted fabrics
Trotz der guten Drapierbarkeit ist das Formen von flachen Mehrlagen-Gestricken (MLG) zu 3D-Preforms für schalenartige Faser-Kunststoff-Verbund (FKV) Bauteile immer noch eine Herausforderung, da einige Defekte wie Falten, Gassenbildung oder Faserschäden nicht vollständig vermieden werden können. Daher ist vor der Massenproduktion eine Optimierung erforderlich. Die virtuelle Optimierung des Umformprozesses mit Hilfe von Finite-Element-Methode (FEM) Modellen ist ein attraktiver Ansatz, da die Rechenkosten immer geringer werden. Dazu wurde ein auf Kontinuumsmechanik basierendes Makromodell erfolgreich für MLG implementiert. Der makroskalige Modellierungsansatz bietet angemessene Rechenkosten und kann gängige Defekte wie Faltenbildung vorhersagen. Weitere Defekte wie Faserversatz, ondulierte Fasern, Knicken von Fasern, Faserschädigung und Gassenbildung können jedoch mit dem Makromodell nicht vorhergesagt werden. Da die Komplexität von Bauteilen aus FKV und die Qualitätsanforderungen an die 3D-Preforms zunehmen, sind FEM-Modelle mit höherem Darstellungsgrad erforderlich. Im am weitesten entwickelten mesoskaligen FEM-Modell für MLG verhindert die zu starke Vereinfachung des Strickfadensystems mit Federelementen jedoch die Fähigkeit dieses FEM-Modells, Faserverschiebungen und Gassenbildung bei großer Verformung zu beschreiben, wobei das Gleiten zwischen den Fäden berücksichtigt werden muss. Ziel ist daher die Entwicklung, Validierung und Anwendung eines mesoskaligen FEM-Modells für MLG, um die derzeitigen Einschränkungen zu überwinden. Es werden neue Modellierungsstrategien für biaxiale MLG auf der Mesoskala entwickelt. Die mechanischen Eigenschaften von MLG werden durch eine Reihe von textilphysikalischen Prüfungen charakterisiert und analysiert, die alle notwendigen Daten für den Aufbau sowie die Validierung der FEM-Modelle liefern. Es sollen zwei Ansätze zur Modellierung des Verstärkungsgarns implementiert und verglichen werden: durch Balken- und durch Schalenelemente. Die validierten Modelle können für die Umformsimulation verwendet werden.
Es folgt eine Benchmark-Studie über die Kapazität und Zuverlässigkeit der verfügbaren Makromodelle und der entwickelten Mesomodelle durch Umformsimulation. Als Grundlage für die Benchmark-Studie werden Umformversuche durchgeführt.
Das zweite Ziel der Arbeit ist die Modellierung von FKV auf verschiedenen Skalen. Die Modellierung von FKV auf der Makroebene wird mit den Daten der Faserorientierung durchgeführt, die aus der Umformsimulation gewonnen werden. Eine Mapping-Methode hilft dabei, die vorhergesagte Faserorientierung aus der Umformsimulation von dem MLG Mesomodell auf das FKV-Makromodell zu übertragen. Um den FKV zu charakterisieren und die Parameter für das FKV Modell vorzubereiten, werden Versuche mit FKV durchgeführt und ausgewertet. Basierend auf dem Mesomodell des MLG wird eine weiteres FKV-Modell vorgeschlagen, wobei Garn und Matrix getrennt modelliert werden.
Dieses mesoskalige FKV-Modell enthält auch eine Kontaktformulierung, mit der die
Delamination im FKV-Bauteil vorhergesagt werden kann. Prüfungen von Schale-Rippen Strukturen dienen als Grundlage für die Modellvalidierung. Das validierte Modell wird erfolgreich zur Vorhersage des mechanischen Verhaltens weiterer Schale-Rippen Strukturen mit unterschiedlicher Höhe und Anordnung der Rippen verwendet.:Kapitel 1 stellt die Einleitung und Problemstellung von dem Thema FKV vor. Kapitel 2 gibt eine Übersicht über Stand-der-Technik von den Hochleistungsfasern, Herstellung von textilen Verstärkungen und Halbzeugen, Fertigung von FKV sowie von Prüftechnik für Textilien und FKV. Zunächst wurden in Kapitel 3 eine Einführung in die Modellierung mit FEM allgemein und Stand-der-Technik der Modellierung von technische Textilien gegeben. In Kapitel 4 wurden die Zielsetzung und das Forschungsprogramm festgelegt. Die experimentellen Arbeiten werden in Kapitel 5 vorgestellt. Der erste Schritt ist die Auswahl des Materials und der Konfiguration für die MLG. Sowohl das Ausgangsmaterial als auch die produzierten MLG sollten systematisch getestet werden. Als Referenz wird auch ein Leinwandgewebe in die Prüfprogramme aufgenommen. Neben der Charakterisierung von textilen Flächengebilden sollen auch deren gleichwertige FKV geprüft werden. Das erste Ziel des Forschungsprogramms wird in Kapitel 6 erreicht, wobei verschiedene Ansätze zur Modellierung von MLG vorgestellt und validiert werden. Die entwickelten und validierten FEM-Modelle werden für die Benchmark-Studie der Umformsimulation in Kapitel 7 verwendet. Kapitel 8 befasst sich mit der Modellierung von FKV in verschiedenen Skalen. Zunächst wird das Mapping-Verfahren vorgestellt. Es wird
ein Mapping für ein schalenförmiges T-Napf-Bauteil durchgeführt. Die trukturanalyse für das T-Napf-Bauteil erfolgt für übliche Lastfälle. Zweitens wird ein mesoskaliges FEM Modell für MLG-verstärkte FKV vorgeschlagen. Dieses Modell wird auf der Grundlage der Prüfdaten aus Kapitel 5 validiert. Das validierte Modell wird dann zur Vorhersage des mechanischen Verhaltens eines Schale-Rippen-FKV-Bauteils unter Biegebelastung verwendet.
Kapitel 9 gibt eine Zusammenfassung von den Forschungsergebnissen und Vorschlägen für mögliche weitere Forschungen rund um dem Thema MLG als Verstärkung für FKV. Die Kombination von vorhandenen Makro-und Mesomodellen in einer einzigen Simulation kann die Berechnungskosten senken, ohne die Vorhersagenfähigkeiten des Modelles kompromittiert zu werden
The application of three-dimensional mass-spring structures in the real-time simulation of sheet materials for computer generated imagery
Despite the resources devoted to computer graphics technology over the last 40 years,
there is still a need to increase the realism with which flexible materials are simulated.
However, to date reported methods are restricted in their application by their use of
two-dimensional structures and implicit integration methods that lend themselves to
modelling cloth-like sheets but not stiffer, thicker materials in which bending moments
play a significant role.
This thesis presents a real-time, computationally efficient environment for simulations
of sheet materials. The approach described differs from other techniques principally
through its novel use of multilayer sheet structures. In addition to more accurately
modelling bending moment effects, it also allows the effects of increased temperature
within the environment to be simulated. Limitations of this approach include the
increased difficulties of calibrating a realistic and stable simulation compared to
implicit based methods.
A series of experiments are conducted to establish the effectiveness of the technique,
evaluating the suitability of different integration methods, sheet structures, and
simulation parameters, before conducting a Human Computer Interaction (HCI) based
evaluation to establish the effectiveness with which the technique can produce credible
simulations. These results are also compared against a system that utilises an
established method for sheet simulation and a hybrid solution that combines the use of
3D (i.e. multilayer) lattice structures with the recognised sheet simulation approach.
The results suggest that the use of a three-dimensional structure does provide a level of
enhanced realism when simulating stiff laminar materials although the best overall
results were achieved through the use of the hybrid model
Large space structures and systems in the space station era: A bibliography with indexes (supplement 05)
Bibliographies and abstracts are listed for 1363 reports, articles, and other documents introduced into the NASA scientific and technical information system between January 1, 1991 and July 31, 1992. Topics covered include technology development and mission design according to system, interactive analysis and design, structural and thermal analysis and design, structural concepts and control systems, electronics, advanced materials, assembly concepts, propulsion and solar power satellite systems
Generalized averaged Gaussian quadrature and applications
A simple numerical method for constructing the optimal generalized averaged Gaussian quadrature formulas will be presented. These formulas exist in many cases in which real positive GaussKronrod formulas do not exist, and can be used as an adequate alternative in order to estimate the error of a Gaussian rule. We also investigate the conditions under which the optimal averaged Gaussian quadrature formulas and their truncated variants are internal
MS FT-2-2 7 Orthogonal polynomials and quadrature: Theory, computation, and applications
Quadrature rules find many applications in science and engineering. Their analysis is a classical area of applied mathematics and continues to attract considerable attention. This seminar brings together speakers with expertise in a large variety of quadrature rules. It is the aim of the seminar to provide an overview of recent developments in the analysis of quadrature rules. The computation of error estimates and novel applications also are described