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Im Rahmen der vorliegenden Arbeit wurde erstmalig die Verarbeitungstechnik zur
Entwicklung und Herstellung von Microfibrillaren Composites (MFCs) im Bereich der
resorbierbaren Polymeren angewandt. Ziel war die Herstellung eines polymeren
MFC-Knochennagel-Implantats aus den zwei biodegradierbaren Werkstoffen
Polylaktid und Polyglykolid, um eine Verbesserung der mechanischen Eigenschaften
gegenüber den Ausgangswerkstoffen zu erzielen. Die biodegradierbaren MFCs
wurden schließlich bzgl. ihres mechanischen Leistungspotentials gegenüber der
alternativen Herstellungstechnik „Solid-State-Extrusion“ bewertet.
Die vier verschiedenen Polylaktide, Poly-L-laktid (PLLA), Polylaktid (PLA), Poly-DLlaktid
(PLDLA), Poly-LDL-laktid (PLDLLA) und der Werkstoff Polyglykolid (PGA)
bildeten vier Werkstoffpaarungen für die MFC-Versuchsreihen. Für die Solid-State-
Extrusion standen die vier Polylaktide aus der MFC-Serie sowie mehrere kompatible
Polylaktidmischungen zur Verfügung.
Innerhalb der Untersuchungen wurde zuerst das Verfahren der Solid-State-Extrusion
optimiert, da es hier auch Überschneidungen in den MFC-Verarbeitungsetappen gab.
Um den MFC-Prozess optimieren zu können, wurden theoretische Überlegungen
und schematische Modellansätze aufgestellt, die dann durch mikroskopische
Beobachtungen bestätigt und verifiziert wurden. Aus der entwickelten
Modellvorstellung konnten Lösungsansätze hergeleitet werden, welche die von
Fakirov et al. aufgestellten MFC-Bedingungen erweiterten und eine Herstellung von
resorbierbaren Microfibrillaren Composites ermöglichten.
Die 3-Punkt-Biegeuntersuchungen der MFC-Werkstoffpaarung zeigten für eine PGA/PLA 30:70-Mischung eine Erhöhung der mechanischen Steifigkeit um 30 % und
der Festigkeit um 20 % gegenüber dem reinen Polylaktid. Die initiale
Leistungssteigerung mittels der Solid-State-Extrusion fällt mit über 120 % Steigerung
deutlich stärker aus als die der MFCs, jedoch reduziert sich der Gewinn unter
Berücksichtigung eines Umformprozesses auf ca. 50 %. Weiterhin konnten die MFCs
mittels dem Spritzgießverfahren in komplexe Geometrien geformt werden.
Abschließend wurde für den MFC-Prozeß ein Verarbeitungsfenster hergeleitet.
This thesis aimed at developing and producing bioresorbable Microfibrillar
Composites (MFCs) for polymer bone nails. The main goal was to create a complete
resorbable Microfibrillar Composite made from the two common commercial
polymers polylactide (PLA) and polyglycolide (PGA). The mechanical strength and
stiffness of this new composite should be significantly higher in comparison to the
native materials. To evaluate their mechanical potential, the produced MFCs were
compared to the alternative technique of solid-state-extrusion.
Four different polymer blends in different component ratios were developed and
investigated for the MFC series. These blends werde made of four different
polylactides, two amorphous and two partially crystalline polylactides, together with
polyglycolide as the reinforcing material. For the solid-state-extrusion, four native
polylactides from the MFC series and several miscible polylactide blends were
produced.
Following the experimental studies, the process of solid-state-extrusion was
optimized first. Furthermore a theoretical model was developed for optimizing the
MFC process. This model was prooved by experimental data and microscopy
investigations. Due to the model it was possible to develop solutions for the MFCprocessing.
In addition the basic rules developed by Fakirov et al. were extended.
The mechanical properties were evaluated by 3 point bending tests. An increase of
30 % for the stiffness and 20 % for the bending strength in comparison to the native
polylactide was reached by a MFC-PGA/PLA 30:70. For the solid-state-extrusion, a
significant increase of 120 % was possible. But considering an additional forming
process, the mechanical properties dropped to 50 % of the initial values.
Furthermore, regarding the MFC-process, it was possible to get complex shapes like
the bone nails by injection molding. In conclusion a processing window was
established for the MFC-process.
Die effektive Nutzung der attraktiven Materialeigenschaften von Verbundwerkstoffen,
insbesondere die der langfaserverstärkten Polymere in Großserienbauteilen, macht
nicht nur die Entwicklung entsprechender Fertigungsverfahren sondern einhergehend
prognosefähige Berechnungsmethoden für Werkstoff und Bauweise notwendig.
Praxistaugliche Berechnungsmodelle beschränken sich in der Regel auf bewusst einfach
gehaltene analytische Modelle zur Grobdimensionierung oder auf Finite-Elemente-
Analysen. Letztere erlauben, lokale Konstruktionsaspekte darzustellen und
detaillierte Einsicht in das Strukturverhalten zu nehmen.
Am Beispiel von mit der Wickeltechnik hergestellter zylindrischer Vollkunststoff-
Druckbehälter wurden Auslegungsmethoden für unidirektional verstärkte FKV-Strukturen
erörtert, experimentell validiert und zusammen mit analytisch formulierten
Randbedingungen bzw. Modellen zu Geometrie, Werkstoff und Fertigung in ein vollparamtrisches,
dreidimensionales FE-Auslegungsmodul implementiert. Durch die
Auflösung der tragenden Tankstruktur in die einzelnen Wickellagen und der parametrischen
Variation von Lagenaufbau und Domgeometrie gestattet dieses eine effektive
Bauweisenoptimierung hinsichtlich Gewicht und Werkstoffausnutzung. Insbesondere
die neuartige, experimentell verifizierte Beschreibung der einzelnen Wickellagendicken
im Behälterdom erlaubt eine der Fertigung entsprechende, im jeweiligen
Wicklungslagenende wulstfreie Behältermodellgenerierung.
Gewebeverstärkte thermoplastische Halbzeuge können oberhalb ihrer Verformungstemperatur
wiederholt mittels Stempelumformprozess in aufeinander abgestimmten
Werkzeughälften umgeformt werden. Für eine effektivere Auslegung solcher Bauweisen
durch Verbesserung der Werkstoffmodellierung wird erstmalig die Prozesssimulation
mit der Strukturanalyse gekoppelt. Die hierfür entwickelte Schnittstelle vollzieht neben der Datenübersetzung die automatisierte Aufbereitung des Simulationsschalennetzes
zum voluminösen Strukturmodell nebst Modellbeschneidung und beinhaltet
erste Ansätze zur Abschätzung der Werkstoffkennwerte des infolge der Drapierung
nicht mehr orthogonal gewebeverstärkten FKV. Die Berücksichtigung von
Fadenorientierung, Dickenverteilung und auftretenden Falten durch Übertragung des
Simulationsnetzes erlaubt eine im Vergleich zum Stand der Technik realitätsnähere,
durch Bauteilprüfungen validierte Abbildung des mechanischen Strukturverhaltens.
The effective use of the attractive material properties of fiber reinforced plastics
(FRP), especially of long fiber reinforced polymers in mass production, requires an
advanced development of suitable manufacturing processes and prognostic design
and analysis methods for the material and structural behavior. This paper resulted
out of two research projects, accompanied by industrial, close to series development
tasks. The objective was to increase the efficiency of the material, structure and
manufacturing aspects of the prototype development through improved modeling
methods in analysis and simulation in close relationship with the design, material
development and testing facilities.
Mass production capability of thermoforming processing in combination with weight
saving potentials on the one hand and thermal and electrical insulation advantages of
thermoplastics in comparison to steel on the other hand was the motivation for the
development of a safety toe cap for safety shoes made of canvas reinforced thermoplastics.
An innovative analysis method for structures made of canvas reinforced
plastics which was initiated by this development program focus on a realistic
reproduction of the non-orthogonal fiber reinforcement of the woven fabric after the
thermoforming process. Canvas reinforced thermoplastics can be simplified as an
alignment of small unidirectional fiber reinforced sections in weft and warp direction.
The underlying design theories for unidirectional FRP were rehashed and advanced
in the framework of a full plastic high pressure vessel development program. To
improve the effectiveness of the pressure vessel design work, the mentioned design
theories and further specific manufacturing models were implemented in an innovative,
full-parametric design module validated by burst pressure vessel tests.
Of importance for the dimensioning and wide application of FRP-structures is the
ability to forecast the material behavior, particularly with regard to the frequent lack of measured material properties in practical design work. The conceptual formulation
was augmented for the quality assessment of the accomplished design work with a
systematic evaluation of the most well known estimations in regards to stiffness and
strength properties of unidirectional and canvas reinforced plastics. For non-orthogonal
canvas reinforced FRP, as in case of thermoformed components, no appropriate material model is available. A relative easy handling material model for orthogonal
canvas reinforced FRP known in literature was augmented to non-orthogonal.
This paper is not dealing with lightweight construction methods but in fact with the
objective to improve the praxis relevant design methods of unidirectional and bidirectional
fiber reinforced plastics; i.e. including estimations for material properties
and manufacturing influences.
The fundamentals of the presented analyses are the consideration of fiber orientation
and ply thickness close to reality by analytical models implemented in the FEA like
the description of the fiber deposition in a filament winding process.
A significant improvement of the design and analyses methods for unidirectional FRP
exemplarity in the case of high pressure vessels made of full plastic has been done
by the comprehension of relevant manufacturing parameters, especially through the
improved description of the ply thickness in the vessel domes. This was achieved by
combining two models, each separately known in literature, to level the bulges at the
end of each ply due to increasing fiber coverage and their mathematical description.
This leveling meets the practical corrections that also have to be done in a filament
winding program in the manufacturing process. Validating measurements on pressure
vessel prototypes were performed and showed excellent accordance.
Beyond it, the developed parametric FE analysis tool for cylindrical pressure vessels
produced with the filament winding technique enables a time efficient design optimization vessels in the analysis tool were set back to future work due to the unsufficient amount of vessel tests and for the benefit of a challenging design
analysis concept for canvas reinforced FRP.
For thermoformed canvas reinforced FRP the fiber orientation and play thickness can
be determined by process simulation. Interfaces to the structural analysis that particularly
include the theoretical estimation of material properties and the material
modeling are not available in the commercial market. Hence, even the structural
analysis of such constructions can not be assumed to be state of the art. Previous
analyses of thermoformed constructions depend on material isotropy or neglect the
canvas shearing during draping; i.e. the thermoformed woven fabric material is
modeled with orthogonal fiber orientation and constant ply thickness. The objective of
this paper is to combine forming simulation and structural analysis in a way, that
beside the pure data translation, the interface performs an automated transformation
of the shell based process simulation FE net to a volumetric structure model including
the model trimming and the estimation of the non-orthogonal material properties.
The consideration of fiber orientation, thickness distribution and eventually occurring
crinkles transferred with the FE net of the process simulation into the structural
analysis allows a much more reliable reproduction of the mechanical structure behavior
as in comparison to the traditional state of the art analysis which has been
validated by extensive prototype tests.
The static, non-linear analysis of the toe cap made of canvas reinforced thermoplastic
is accompanied by very successful prototype tests, which in turn pushed this
toe cap design ahead. This series are closely linked to material development, as well
as new manufacturing technology.
and analysis because of it's automated model generation. The analysis or
evaluation of variants of the load bearing FRP lay-up, the influence of different valve
geometry and dome contours necessitates now solely the modification of the input
parameters.
For a specific forecast of the achievable burst pressure of a pressure vessel design
additional work has to be done. A degradation model has to be implemented in the
analysis tool to evaluate the increasing local ply failures until the vessel burst. The
main objective for the unidirectional FRP essay of the paper was to improve the
model generation and to increase the time effectiveness of the design analysis,
which has been achieved. The originally planed implementation of a strength evaluation
of pressure
Die Luftfahrtindustrie und die meeresgestützte ölfördernde Industrie, die so genannte
Off-Shore Industrie, streben die Einführung bzw. Weiterverbreitung von faserverstärkten
Kunststoffen mit thermoplastischer Matrix an. Sowohl Leistungsverbesserung
aber auch Kosten- und Gewichtsreduktion sind die Treiber für diese Entwicklung.
Der sehr hohe Anspruch an die Qualität der Bauteile bedingt die Verfügbarkeit
geeigneter Herstellungsverfahren. Beispiele hierfür sind das Tapelege- und das Wickelverfahren.
Beide Prozesse sind allerdings bis heute nur in den Varianten für die
Verarbeitung duroplastischer Matrizes industriell umgesetzt und etabliert. Die Bauteilherstellung
geschieht bei Anwendung von Duroplasten für Hochtemperatur- oder
Primärstrukturanwendungen durch eine, dem formgebenden Prozess nachgeschaltete
Aushärtung im Ofen oder Autoklav. Thermoplaste bieten jedoch die Möglichkeit
zur Einsparung dieses Prozessschrittes durch die in-situ Konsolidierung, d.h. endkonturnahes,
formgebendes Ablegen und Verschweißen in einem Schritt. Die Komplexität
der Thermoplastprozesse ist jedoch durch die simultane Durchführung zweier
Aufgaben erhöht. Deshalb besteht ein großer Bedarf, die theoretischen Hintergründe,
das physikalische, thermodynamische und chemische Prozessverständnis stetig
grundlegend zu erarbeiten bzw. zu verbessern. Die rein experimentelle Prozessentwicklung
an Anlagen industriellen Maßstabs ist aus Kostengründen und dem Problem
der mangelhaften Auflösung einzelner Prozessphänomene dafür ungeeignet.
Daher wird seit vielen Jahren am Verständnis, der Abstraktion und der Simulation
dieser Prozesse gearbeitet. Die dabei entstandenen theoretischen Modellierungen
können allerdings nur selten einen Bezug zum realen Prozess nachweisen.Die vorliegende Arbeit schließt deshalb die Lücke zwischen Simulation und experimenteller
Prozessentwicklung. Auf Basis einer vielfach verwendeten mathematischen
Beschreibung der thermodynamischen Verhältnisse im Prozess, einer Energiebilanzgleichung,
die erstmals in diesem Zusammenhang um die Möglichkeit zur
Berechnung von Strahlungsrandbedingungen erweitert wird, beschreibt die Arbeit die
Entwicklung eines Prozesssimulationssystems. Das dazu neu entwickelte Finite-
Elemente-Methode Programm ProSimFRT, das auf der nicht-linearen Diskretisierung
der Energiebilanzgleichung basiert, bildet der Kern eines modularen Prozesssimulationspaketes, welches die ganzheitliche parametrische Berechnung der Temperatur
während des gesamten Prozesses und für alle Prozessteilnehmer erlaubt. Thermodynamische
Teilaspekte der Verfahren und somit auf rein theoretischem Weg unzugängliche
Prozessparameter, wie z.B. konvektive Randbedingungen oder durch eine
Wasserstoff-Sauerstoffflamme erzeugte Wärmeströme können mit ProSimFRT semiempirisch
ermittelt werden. Die hierfür angewandte Methodik der Simulationskalibrierung
bedarf jedoch einer experimentellen Verifikationsmöglichkeit. Daher wird eine
neu entwickelte Experimentalplattform vorgestellt. Ein spezieller Thermodynamikprüfstand
erlaubt die Ermittlung der Prozessparameter und eine flexible Möglichkeit
zum Nachweis der Funktionsfähigkeit der Simulation. Die Integration dieser Parameter
zu einem ganzheitlichen Prozessmodell am Beispiel des Thermoplasttapelegens
mit kohlenstofffaserverstärktem Polyetheretherketon und die ableitbaren Hinweise für
die Prozessentwicklung bilden abschließend die Grundlage für die zukünftige Integration
der Simulation in die Gesamtprozesskette.
The aerospace industry and the off-shore oil industry are facing the introduction and
evolution of fiber reinforced thermoplastics. Performance enhancements as well as
cost and weight savings are the drivers behind this development. The high level of
requirements concerning the quality of components leads to a need for applicable
manufacturing technologies. Filament winding and tape placement are examples for
such processes. Both have been successfully industrialized for thermoset materials.
Thermoset components for high temperature or primary structure applications are
typically manufactured in a multi-step approach. After a geometry determining step
consolidation and curing are introduced as further processing steps towards the final
component, often using ovens or autoclaves. Being weldable, thermoplastics give the
possibility to integrate this multi-step thermoset processes. Hence the complexity of
thermoplastic processing is increased, but the potential of saving manufacturing time
is obvious. This leads to the need of theoretic background know how about the
physical, thermodynamical and chemical phenomena behind the thermoplastic
manufacturing technologies. Due to that, since many years worldwide efforts are carried
out concerning the understanding, abstraction and simulation of this processes.
But, the developed models hardly have a direct relation to real processes.
The present work overcomes the gap between simulation and experimental process
development. Based on a widely used mathematical description of the thermodynamics
within the processes, an energy balance equation, which is enhanced with radiative
boundary conditions for the first time in this context, the present work describes
the development of a process simulation tool. The newly developed finite-element
program ProSimFRT, which is based on a non-linear discretization of the energy balance
equation, serves as kernel of a modular process simulation environment. This
package allows the parametric calculation of the temperature fields throughout the whole process and for all process participants. Thermodynamic aspects, hardly
available by analytical theory as convective boundary conditions or heat fluxes generated
by oxygen-hydrogen flames can be determined semi-empirically with
ProSimFRT. The method used for that needs a possibility for experimental investigations.
Hence, a thermodynamic test rig is introduced.This test rig allows the determination of process parameters and delivers a flexible
possibility for the validation and verification of the simulation. The integration of this
parameters into an overall process model for the thermoplastic tape placement process
using carbon fiber reinforced polyetheretherketone and derivable hints for the
process development conclude the present work. They are a baseline for the future
integration of the simulation into the manufacturing process.
Continuous fibre reinforced thermoplastics are a high competitive material class for
diversified applications because of their inherent properties like light-weight construction
potential, integral design, corrosion resistance and high energy absorption level.
Using these materials, one approach towards a large volume scaled part production
rate is covered by an automated process line, consisting of a pressing process for
semi-finised sheet material production, a thermoforming step and some additional
joining technologies. To allow short cycle times in the thermoforming step, the utilised
semi-finished sheet materials, which are often referred to as “organic sheets”, have
to be fully impregnated and consolidated.
Nowadays even this combination of outstanding physical and chemical material
properties combined with the economic processing technology are no guarantee for
the break-through of continuous fibre reinforced thermoplastics, mainly because of
the high material costs for the semi-finished sheet materials. These costs can be attributed
to a non adapted material selection or choice of process parameters, as well
as by unfavourable pressing process type itself.
Therefore the aim of the present investigations was to generate some alternatives
regarding the choice of raw materials, the set-up or the selection of the pressing
process line and to provide some theoretical tools for the determination of process
parameters and dimensions.
Concerning raw material aspects, the use of the blending technology is one promising
approach towards cost reduction for the matrix component. Novel characteristics
related to the fibre structure are CF-yarns with high filament numbers (e.g. 6K or 12K instead of 3K) or multiaxial fibre orientations. These two approaches were both conducted
for sheet materials with carbon fibre reinforcement and high temperature
thermoplastics.
Two new developed ternary blend matrices consisting of PEEK and PEI as the main
ingredients were tested in comparison with neat PEEK. PES and PSU were used as
the third blend component, which provides a cost reduction potential of approximately
30 % compared to the basis PEEK polymer. The results of the static pressing experiments
pointed out that the processing behaviour of the new blends is similar to
the neat PEEK matrix. A maximum process temperature of 410 °C should not be surpassed, otherwise thermal degradation will occur and will have a negative influence
on mechanical laminat properties. To accelerate the impregnation progress a
process pressure of 25 bar in combination with a sidewise opened tooling concept is
helpful. No differences were identified if film-stacking technique was substituted by
powder-prepreg-technology or vice versa. By increasing the yarn filament number
from 3K over 6K to 12K, which is equal to an increase in bundle diameter and therefore
transverse flow distance, the impregnation time has to be extended. If unspread
yarns are used, the risk of void entrapment rises tremendously, especially with 12K
and UD-structures. To reach full impregnation with a woven 6K-fabric, an increase of
process time of 20 to 30 % compared to a 3K textile structure is required. Furthermore,
it was shown that if only transverse flow is used for the impregnation of a UDstructure,
a maximum area weight of 300-400 g/m² should not be exceeded. Additionally,
the transport of air is strictly affected by the fibre orientation, because the
main amount of displaced air runs in longitudinal fibre direction. These facts play an
important role in the design of a multaxial laminat or an impregnation process for
such a structure and have to be taken into account.
Apart from these static pressing experiments the semi-continuous (stepwise compression
moulding) and continuous (double belt press processing) processing technology
were investigated and compared to each other. The first basic processing
trails on the stepwise compression moulding equipment were carried out with the material
system GF/PA66. Whereas the processing behaviour of this material combination
in a double belt press is known quite well, there is only little information about
semi-continuous processing. The performed trials pointed out that the resulting laminate
quality for both technologies only differs in the achievable local surface quality.
Mechanical laminate properties like three point bending stiffness and strength are
directly comparable. Due to the fact that there is only small experience with the stepwise
compression moulding process, potential improvements regarding surface Quality are feasible by adapting the step procedure and the temperature distribution within
the tooling concept. If laminates, produced by semi-continuous processing, are deployed
in a thermoforming process or in a non visible structural application, the surface
appearance only plays an inferior role.
The present results with high temperature thermoplastic matrices and CF do confirm
the positive assessment for the stepwise compression moulding technology, even though the mechanical laminate values have only reached 90 % of the data received
by static press processing. In comparison to the data from literature, 90 % is already
a high mechanical performance level. The results are quite promising for the use of
the semi-continuous technology, despite the process set-up and processing parameters
not being optimised. Furthermore there are tremendous advantages in processing
equipment costs.
Finally a process model was developed based on the experimental data pool. This
model can be characterised as a tool, which provides useful boundary conditions and
dimension values for the selection of a certain pressing process depending on the
desired material combination, laminate thickness and production output. The applicability
and accuracy of the model was proofed by a direct comparison between experimental
and calculated data.
First of all the temperature profile of the pressing process was generalised by a very
common structure. This profile reflects the main characteristics for the processing of
a thermoplastic composite material. Depending on the material combination, the
laminate thickness and the occurring heat transfers, several process- and processing-
portfolios were calculated. For a defined combination of the aforementioned parameters,
these portfolios directly provide the periods of time for heating and cooling
of the laminate structure. The last step is to convert these information into an equipment
dimension and to decide which machinery configuration fulfils these requirements.
We propose several algorithms for efficient Testing of logical Implication in the case of ground objects. Because the problem of Testing a set of propositional formulas for (un)satisfiability is \(NP\)-complete there's strong evidence that there exist examples for which every algorithm which solves the problem of testing for (un)satisfiability has a runtime that is exponential in the length of the input. So will have our algorithms. We will therefore point out classes of logic programs for which our algorithms have a lower runtime. At the end of this paper we will give an outline of an algorithm for theory refinement which is based on the algorithms described above.
UML and SDL are languages for the development of software systems that have different origins, and have evolved separately for many years. Recently, it can be observed that OMG and ITU, the standardisation bodies responsible for UML and SDL, respectively, are making efforts to harmonise these languages. So far, harmonisation takes place mainly on a conceptual level, by extending and aligning the set of language concepts. In this paper, we argue that harmonisation of languages can be approached both from a syntactic and semantic perspective. We show how a common syntactical basis can be derived from the analysis of the UML meta-model
and the SDL abstract grammar. For this purpose, conceptually sound and well-founded mappings from meta-models to abstract grammars and vice versa are defined and applied. On the semantic level, a comparison between corresponding language constructs is performed.
This report explains basic notions and concepts of Abstract State Machines (ASM) as well as notation for defining ASM models. The objective here is to provide an intuitive understanding of the formalism; for a rigorous definition of the mathematical foundations of ASM, the reader is referred to [2] and [3]. Further references on ASM-related material can be found on the ASM Web Pages [1].
Jahresbericht
(2003)
Congress Report 2003.12
(2003)
Congress Report 2003.11
(2003)