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In the last decade, injection molding of long-fiber reinforced thermoplastics
(LFT) has been established as a low-cost, high volume technique for manufacturing
parts with complex shape without any post-treatment [1–3]. Applications
are mainly found in the automotive industry with a volume annually
growing by 10% to 15% [4].
While first applications were based on polyamide (PA6 and PA6.6), the market
share of glass fiber reinforced polypropylene (PP) is growing due to cost savings
and ease of processing. With the use of polypropylene, different processing
techniques such as gas-assisted injection molding [5] or injection compression
molding [6] have emerged in addition to injection molding [7, 8].
In order to overcome or justify higher materials costs when compared to short
fiber reinforced thermoplastics, the manufacturing techniques for LFT pellets
with fiber length greater than 10mm have evolved starting from pultrusion by
improving impregnation and throughput [9] or by direct addition of fiber strands
in the mold [10–12].
The benefit of long glass fiber reinforcement either in PP or PA is mainly due
to the enhanced resistance to fiber pull-out resulting in an increase in impact
properties and strength [13–19], even at low temperature levels [20]. Creep
and fatigue resistance are also substantially improved [21, 22].
The performance of fiber reinforced thermoplastics manufactured by injection
molding strongly depends on the flow-induced microstructure which is
driven by materials composition, processing conditions and part geometry.
The anisotropic microstructure is characterized by fiber fraction and dispersion,
fiber length and fiber orientation.
Facing the complexity of this processing technique, simulation becomes a precious
tool already in the concept phase for parts manufactured by injection
molding. Process simulation supports decisions with respect to choice of concepts
and materials. The part design is determined in terms of mold filling
including location of gates, vents and weld lines. Tool design requires the
determination of melt feeding, logistics and mold heating. Subsequently, performance
including prediction of shrinkage and warpage as well as structural
analysis is evaluated [23].
While simulation based on two-dimensional representation of three-dimensional
part geometry has been extensively used during the last two decades, the
complexity of the parts as well as the trend towards solid modelling in CAD
and CAE demands the step towards three-dimensional process simulation. The scope of this work is the prediction of flow-induced microstructure during
injection molding of long glass fiber reinforced polypropylene using threedimensional
process simulation. Modelling of the injection molding process in
three dimensions is supported experimentally by rheological characterization
in both shear and extensional flow and by two- and three-dimensional evaluation
of microstructure.
In chapter 2 the fundamentals of rheometry and rheology are presented with
respect to long fiber reinforced thermoplastics. The influence of parameters
on microstructure is described and approaches for modelling the state of microstructure
and its dynamics are discussed.
Chapter 3 introduces a rheometric technique allowing for rheological characterization
of polymer melts at processing conditions as encountered during
manufacturing. Using this rheometer, both shear and extensional viscosity of
long glass fiber reinforced polypropylene are measured with respect to composition
of materials, processing conditions and geometry of the cavity.
Chapter 4 contains the evaluation of microstructure of long glass fiber reinforced
polypropylene in terms of two-dimensional fiber orientation and its dependence
on materials parameters and processing condition. For the evaluation
of three-dimensional microstructure, a technique based on x-ray tomography
is introduced.
In chapter 5, modelling of microstructural dynamics is addressed. One-way
coupling of interactions between fluid and fibers is described macroscopically.
The flow behavior of fibers in the vicinity of cavity walls is evaluated experimentally.
From these observations, a model for treatment of fiber-wall interaction
with respect to numerical simulation is proposed.
Chapter 6 presents the application of three-dimensional simulation of the injection
molding process. Mold filling simulation is performed using a commercial
code while prediction of 3D fiber orientation is based on a proprietary module.
The rheological and thermal properties derived in chapter 3 are tested by
simulation of the experiments and comparison of predicted pressure and temperature
profile versus recorded results. The performance of fiber orientation
prediction is verified using analytical solutions of test examples from literature.
The capability of three-dimensional simulation is demonstrated based on the
simulation of mold filling and prediction of fiber orientation for an automotive
part.
Solid particle erosion is usually undesirable, as it leads to development of cracks and
holes, material removal and other degradation mechanisms that as final
consequence reduce the durability of the structure imposed to erosion. The main aim
of this study was to characterise the erosion behaviour of polymers and polymer
composites, to understand the nature and the mechanisms of the material removal
and to suggest modifications and protective strategies for the effective reduction of
the material removal due to erosion.
In polymers, the effects of morphology, mechanical-, thermomechanical, and fracture
mechanical- properties were discussed. It was established that there is no general
rule for high resistance to erosive wear. Because of the different erosive wear
mechanisms that can take place, wear resistance can be achieved by more than one
type of materials. Difficulties with materials optimisation for wear reduction arise from
the fact that a material can show different behaviour depending on the impact angle
and the experimental conditions. Effects of polymer modification through mixing or
blending with elastomers and inclusion of nanoparticles were also discussed.
Toughness modification of epoxy resin with hygrothermally decomposed polyesterurethane
can be favourable for the erosion resistance. This type of modification
changes also the crosslinking characteristics of the modified EP and it was
established the crosslink density along with fracture energy are decisive parameters
for the erosion response. Melt blending of thermoplastic polymers with functionalised
rubbers on the other hand, can also have a positive influence whereas inclusion of
nanoparticles deteriorate the erosion resistance at low oblique impact angles (30°).
The effects of fibre length, orientation, fibre/matrix adhesion, stacking sequence,
number, position and existence of interleaves were studied in polymer composites.
Linear and inverse rules of mixture were applied in order to predict the erosion rate of
a composite system as a function of the erosion rate of its constituents and their
relative content. Best results were generally delivered with the inverse rule of mixture
approach.
A semi-empirical model, proposed to describe the property degradation and damage
growth characteristics and to predict residual properties after single impact, was
applied for the case of solid particle erosion. Theoretical predictions and experimental
results were in very good agreement.
Strahlerosionsverschleiß (Erosion) entsteht beim Auftreffen von festen Partikel
auf Oberflächen und zeichnet sich üblicherweise durch einen Materialabtrag aus, der
neben der Partikelgeschwindigkeit und dem Auftreffwinkel stark vom jeweiligen
Werkstoff abhängt. In den letzten Jahren ist die Anwendung von Polymeren und
Verbundwerkstoffen anstelle der traditionellen Materialien stark angestiegen.
Polymere und Polymer-Verbundwerkstoffe weisen eine relativ hohe Erosionsrate
(ER) auf, was die potenzielle Anwendung dieser Werkstoffe unter erosiven
Umgebungsbedingungen erheblich einschränkt.
Untersuchungen des Erosionsverhaltens anhand ausgewählter Polymere und
Polymer-Verbundwerkstoffe haben gezeigt, dass diese Systeme unterschiedlichen
Verschleißmechnismen folgen, die sehr komplex sind und nicht nur von einer
Werkstoffeigenschaft beeinflusst werden. Anhand der ER kann das
Erosionsverhalten grob in zwei Kategorien eingeteilt werden: sprödes und duktiles
Erosionsverhalten. Das spröde Erosionsverhalten zeigt eine maximale ER bei 90°,
während das Maximum bei dem duktilen Verhalten bei 30° liegt. Ob ein Material das
eine oder das andere Erosionsverhalten aufweist, ist nicht nur von seinen
Eigenschaften, sondern auch von den jeweiligen Prüfparametern abhängig.
Das Ziel dieser Forschungsarbeit war, das grundsätzliche Verhalten von
Polymeren und Verbundwerkstoffen unter dem Einfluss von Erosion zu
charakterisieren, die verschiedenen Verschleißmechanismen zu erkennen und die
maßgeblichen Materialeigenschaften und Kennwerte zu erfassen, um Anwendungen
dieser Werkstoffe unter Erosionsbedingungen zu ermöglichen bzw. zu verbessern.
An einer exemplarischen Auswahl von Polymeren, Elastomeren, modifizierten Polymeren und Faserverbundwerkstoffen wurden die wesentlichen Einflussfaktoren
für die Erosion experimentell bestimmt.
Thermoplastische Polymere und thermoplastische- und vernetzte- Elastomere
Die Versuche, den Erosionswiderstand ausgewählter Polymere (Polyethylene
und Polyurethane) mit verschiedenen Materialeigenschaften zu korrelieren, haben
gezeigt, dass es weder eine klare Abhängigkeit von einzelnen Kenngrößen noch von
Eigenschaftskombinationen gibt. Möglicherweise führt die Bestimmung der
Materialeigenschaften unter den gleichen experimentellen Bedingungen wie bei den Erosionsversuchen zu einer besseren Korrelation zwischen ER und
Materialkenngröße.
Modifiziertes Epoxidharz
Am Beispiel eines modifizierten Epoxidharzes (EP) mit verschiedener
Vernetzungsdichte wurde eine Korrelation zwischen Erosionswiderstand und
Bruchenergie bzw. Erosionswiderstand und Vernetzungsdichte gefunden. Die
Modifizierung erfolgte mit verschiedenen Anteilen von einem hygrothermisch
abgebauten Polyurethan (HD-PUR). Der Zusammenhang zwischen ER und
Vernetzungsparametern steht im Einklang mit der Theorie der Kautschukelastizität.
Modifizierungseffizienz in Duromeren, Thermoplasten und Elastomeren
Des weiteren wurde der Einfluss von Modifizierungen von Polymeren und
Elastomeren untersucht. Mit dem obenerwähnten System (d.h. EP/HD-PUR) läßt sich
auch der Einfluss der Zähigkeitsmodifizierung des Epoxidharzes (EP) auf das
Erosionsverhalten untersuchen. Es wurde gezeigt, dass für HD-PUR Anteile von
mehr als 20 Gew.% diese Modifizierung einen positiven Einfluss auf die
Erosionsbeständigkeit hat. Durch Variation der HD-PUR-Anteile können für dieses
EP Materialeigenschaften, die zwischen den Eigenschaften eines üblichen
Duroplasten und eines weniger elastischen Gummis liegen, erzeugt werden.
Deswegen stellt der modifizierte EP-Harz ein sehr gutes Modellmaterial dar, um den
Einfluss der experimentellen Bedingungen zu studieren, und zu untersuchen, ob
verschiedene Erodenten zu gleichen Erosionsmechanismen führen. Der Übergang
vom duroplastischen zum zähen Verhalten wurde anhand von vier Erodenten
untersucht. Aus den Versuchen ergab sich, dass ein solcher Übergang auftritt, wenn
sehr feine, kantige Partikel (Korund) als Erodenten dienen. Die Partikelgröße und -form ist von entscheidender Bedeutung für die jeweiligen Verschleißmechanismen.
Die Effizienz neuartiger thermoplastischer Elastomere mit einer cokontinuierlichen
Phasenstruktur, bestehend aus thermoplastischem Polyester und
Gummi (funktionalisierter NBR und EPDM Kautschuk), wurde in Bezug auf die
Erosionsbeständigkeit untersucht. Große Anteile von funktionalisiertem Gummi (mehr
als 20 Gew.%) sind vorteilhaft für den Erosionswiderstand. Weiterhin wurde
untersucht, ob sich die herausragende Erosionsbeständigkeit von Polyurethan (PUR)
durch Zugabe von Nanosilikaten eventuell noch steigern läßt. Das Ergebnis war,
dass die Nanopartikel sich vor allem bei einem kleinen Verschleißwinkel (30°) negativ
auswirken. Die schwache Adhäsion zwischen Matrix und Partikeln erleichtert den
Beginn und das Wachsen von Rissen. Dies führt zu einem schnelleren
Materialabtrag von der Materialoberfläche.
Faserverbundwerkstoffe
Ferner wurden Faserverbundwerkstoffe (FVW) mit thermoplastischer und
duromerer Matrix auf ihr Verhalten bei Erosivverschleiß untersucht. Es war von
großem Interesse, den Einfluss von Faserlänge und -orientierung zu untersuchen.
Kurzfaserverstärkte Systeme haben einen besseren Erosionswiderstand als die
unidirektionalen (UD) Systeme. Die Rolle der Faserorientierung kann man nur in
Verbindung mit anderen Parametern, wie Matrixzähigkeit, Faseranteil oder Faser-
Matrix Haftung, berücksichtigen. Am Beispiel von GF/PP Verbunden weisen die
parallel zur Verstreckungsrichtung gestrahlten Systeme den geringsten Widerstand
auf. Andererseits findet bei einem GF/EP System die maximale ER in senkrechter
Richtung statt. Eine Verbesserung der Grenzflächenscherfestigkeit beeinflusst die
Erosionsverschleißrate nachhaltig. Wenn die Haftung der Grenzfläche ausreichend
ist, spielt die Erosionsrichtung eine unbedeutende Rolle für die ER. Weiterhin wurde
gezeigt, dass die Präsenz von zähen Zwischenschichten zu einer deutlichen
Verbesserung des Erosionswiderstands von CF/EP- Verbunden führt.
Eine weitere Aufgabenstellung war es, die Rolle des Faservolumenanteils zu
bestimmen. „Lineare, inverse und modifizierte Mischungsregeln“ wurden
angewendet, und es wurde festgestellt, dass die inversen Mischungsregeln besser
die ER in Abhängigkeit des Faservolumenanteils beschreiben können.
Im Anwendungsbereich von Faserverbundwerkstoffen ist nicht nur die Kenntnis
der ER, sondern auch die Kenntnis der Resteigenschaften erforderlich. Ein
halbempirisches Modell für die Vorhersage des Schlagenergieschwellwertes (Uo) für den Beginn der Festigkeitsabnahme und der Restzugfestigkeit nach einer
Schlagbelastung wurde bei der Untersuchung des Erosionsverschleißes
angewendet. Experimentelle Ergebnisse und theoretische Vorhersagen stimmten
nicht nur für duromere CF/EP-Verbundwerkstoffe, sondern auch für
Verbundwerkstoffe mit einer thermoplastischen Matrix (GF/PP) sehr gut überein.
Zur nähtechnischen Konfektion von textilen Verstärkungsstrukturen für Faser-Kunststoff-Verbunde
(2002)
The further exploitation of Liquid-Composite-Moulding Technologies (LCM) for the
manufacture of Fiber-Reinforced-Plastics (FRP) relies on an eligible preforming
process. Preforming of fibrous reinforcements aspires the manufacture of dry
skeletons of the fiber assembly with the desired fiber orientation based on a predefined
fiber type. The LCM processing must be maintained by the preforming
technique. However, FRP part properties - given from fiber orientations - should not be
affected.
Sewing technologies, in all their varieties, can be applied as very flexible preforming
methods. Analogies between making-up dry reinforcement structures and the classical
field of sewing, e.g. garment manufacture, led to a substantial progress in technologies
available for preforimg as well as to increased economical benefits through the
application of sew-preforming.
A comprehensive understanding of the application of sewing technologies for FRP –
from the treatment of a semi-finished product to the infusion of a stitched preform – is
the basis for the design of an all new process chain.
The present work classifies this new preforming method within the existing
technologies. Furthermore, critical sewing machine elements are evaluated regarding
FRP compatibility. Stitching parameters and their impact on the reinforcement quality
as well as the FRP processing (LCM) are discussed.
Focusing on the economic efficiency of the sewing preforming technology, the critical
number of parts for selecting the right preform technology is discussed. The new
process chain enables the selection of the critical vertical range of preform
manufacture.
The large variety of preform design parameters, e. g. stitch density, needle thread
tension, seam type, sub-preform-structures etc., requires a “Preform-Engineering”,
covering an interface between preform manufacturing and FRP-part design. This
parallel engineering of part-, preform- and process-design leads to a global reflection
of the LCM technology. Thus, FRP part quality can be raised.
Endless fibre reinforced thermoplastic sheets (organic sheets) are significantly gaining
in importance due to their outstanding characteristics. In comparison to common
thermoplastic press moulding composites with random reinforcement like GMT and
LFRT they offer remarkably better specific mechanical properties (stiffness, strength).
And different from endless fibre reinforced thermosets, they also possess high
toughness and show good impact behaviour. Furthermore, they enable welding and
have an appreciable recycling potential.
The manufacturing steps, beginning from impregnation and consolidation of the
semi-finished sheets up to thermoforming and welding to obtain the final part, represent
a closed processing chain. This results in short cycle times and the potential for
mass production.
However, this material class is rarely used because of its cost and surface quality
problems. Therefore, only a few applications exist as demanding functional or structural
parts.
High costs emerge in consequence of either expensive raw materials (carbon fibres,
technical thermoplastics) or the sophisticated processing technique concerning the
impregnation and consolidation step (double belt press). The surface quality problem
is mainly caused by the print-through of reinforcing fibres, which therefore precludes
applications in visible regions, especially in the field of automotive exterior panels.
The aim of the thesis was to enhance the chances of application by improving the
surface quality of endless fibre reinforced thermoplastics. Thus the surface characteristics
and possibilities for reproducible quantitative measuring were identified. Surface
roughness, gloss rate, profile amplitude and wavelength as well as short (sw)
and long term (lw) waviness were chosen as appropriate values. By varying the type of fibre, matrix, fabric and coating the influence of material parameters on the surface
appearance could then be investigated.
It became obvious that the fibre print-through is a result of the significantly higher
volume shrinkage of the thermoplastic resin (higher coefficient of linear thermal expansion)
in comparison to that of the reinforcement during the cooling process, combined
with an uneven distribution of resin and fibres. Thus, amorphous matrices that
have no shrinkage due to crystallisation and a preferably small thermal induced density
growth lead to significantly better surface qualities (from lw = 60 to lw = 20). Qualitatively the texture is dominated by the reinforcing architecture. The kind of textile
weaving and fineness of the fibre bundles determine the wavelength of the profile
deflection.
It was found that the coating has the largest influence on the surface appearance. A
common varnish layer with a thickness of only 40 μm enhances the gloss of the substrate
which makes the surface waviness even more clearly visible. However, optimising
the varnish system with additional base coat or filling layers drastically reduced
the waviness but did not raze it completely (lw = 10). Only the application of a
thermoplastic varnish layer could diminish the waviness to the desired range below
10 (lw = 4).
Besides the experimental work a theoretical analysis of the consolidation and solidification
step was carried out. A finite element model has been created representing a
semi-finished sheet with four layers of a 2/2 twill textile reinforcement. Based on this
geometry various matrix characteristics as well as alterations of the global reinforcement
structure (more or less horizontal ply off-set) have been analysed.
The simulations supported the experimental results. They indicated the strong influence
of the matrix and showed that the off-set of the reinforcing layers plays an important
role concerning the resulting surface profile. Because the off-set of the plies
can not be controlled in the real material and therefore is at random, the profile
depths show a remarkable standard deviation (30 %). In the example considering a
2/2-twill reinforcement the optimum off-set could reduce the profile depth up to 40 %.
Furthermore, the influence of the process parameters (pressure and cooling rate)during the consolidation process was experimentally and theoretically investigated. In
addition to the non-isotropic characteristics of the textile, the time and temperature
dependent mechanical behaviour of the thermoplastic matrix had to be ascertained
and transferred into the model.
A rapid cooling rate was identified to reduce the surface profile of the substrate. The
profile depth of the simulated GF-PC could be decreased from 5 - 3 μm. However,
experimental tests concerning temperature changes and weathering showed that this
advantageous effect decreases with time due to the viscoelastic behaviour of the
polymer and resetting forces of the reinforcement.
The pressure can influence the texture phenomenon only by affecting the fibre volume
content of the sample. In case of static isobaric press processing a certain matrix
flow across the margins of the tool can not be totally averted. With a rising pressure the outflow becomes stronger and leads to a growing fibre volume content and
stronger surface waviness.
By carrying out several simulations with systematically varying material data a nomogram
could be created that represents a tool to predict the surface profile of comparable
composites (2/2 twill reinforcement, FVC around 50 %) just in dependence of
the matrix. It takes into account the specific matrix volume shrinkage and the pitch
from its solidification to usage temperature. Thus, the possibilities but also limitations
of a certain material combination concerning surface waviness can easily be estimated.
In order to reduce the heterogeneity of the fibre matrix distribution common textile
fabrics were substituted by unidirectional (UD) non-crimped structures and UD fabrics.
A newly established processing method was used to manufacture a noncrimped
and non-sewed endless fibre reinforced thermoplastic sheet by direct combination
of a multiaxial weft insertion machine and a continuous rotocure press. The
resulting product proved the potential for an improved surface quality. Despite the
use of relatively heavy rovings and not yet optimised fibre placement the surface profile
of this new kind of organic sheets is comparable with the one of those samples
having the fine 8-H-satin fabric reinforcement (lw = 20).
Finally it could be shown that the method of thermoplastic varnish layer lamination
which has successfully been used for semi-finished parts can also be integrated in a
thermoforming step to create three-dimensional components. The best results of this trial (lw = 10, sw = 14) do not reach the level of the flat sheets but almost meet the
requirements of the automotive “Class A” standard. With regard to economical and
weight saving aspects this material option can be considered a competitive alternative
to common car body panels.
In conclusion the investigations showed a notable feasibility to improve the surface
quality of endless fibre reinforced thermoplastic sheets. Therefore, this thesis represents
a contribution to amplify the application potential of this material class, particularly
in the fields of leisure and sports goods, and in the range of commercial vehicles.
Die Einmischung von Altgummipartikeln aus zerkleinerten Altreifen in Thermoplast-,
Elastomer- und Duromer-Matrizes im Sinne einer stofflichen Wiederverwertung führt
zu erheblichen Eigenschaftsverschlechterungen der altgummipartikelmodifizierten
Polymerblends. Vor diesem Hintergrund gewinnt die Modifizierung der Altgummipartikel
für eine Verbesserung der Verträglichkeit mit den Matrixmaterialien
zunehmend an Bedeutung.
Zur Modifizierung der Altgummipartikel wurden photochemische Pfropfungsreaktionen
mit Glycidylmethacrylat (GMA) und Methacrylsäure (MAA) nach einem
radikalischen Polymerisationsmechanismus durchgeführt.
Um Altgummipartikel erfolgreich chemisch modifizieren zu können, ist ein fundiertes
Wissen über die entscheidenden Parameter des Pfropfungsprozesses erforderlich.
So haben beispielsweise die Art und Konzentration der Pfropfungschemikalien wie
Monomer und Photoinitiator, die Art des Spülgases, die Temperatur sowie die
Bestrahlungszeit einen entscheidenden Einfluss auf das Pfropfungsergebnis. Der
Nachweis der Oberflächenmodifizierung erfolgte mit Hilfe chemischer Analytikmethoden
sowie mittels Kontaktwinkelmessungen.
Ein weiterer Schwerpunkt dieser Arbeit lag auf der Herstellung von altgummipartikelmodifizierten
Thermoplast-, Duromer- und Elastomer-Blends. Polyamid-6
(PA-6) und Polybutylenterephthalat (PBT) wurden als thermoplastische Matrixmaterialien
ausgewählt. Als Vertreter der Duromere wurde beispielhaft ein
Vinylester-Urethan-Hybridharz (VEUH) angewendet und als elastomeres
Matrixmaterial kam ein Polyurethan-Gießelastomer (PUR) zur Anwendung.
Bei höheren Gummipartikel-Konzentrationen zeigte sich, dass durch die Pfropfung
die Verträglichkeit zwischen Gummipartikeln und den o. g. Matrixmaterialien verbessert
wurde. Die Modifizierung von PA-6 und VEUH mit feinverteilten
Gummipartikeln bewirkte bei geringfügigen Einbußen an Festigkeit und Steifigkeit
deutliche Zähigkeitssteigerungen. Dieser Effekt war bei den GMA modifizierten
Gummipartikeln stärker ausgeprägt.
Bei der Anwendung von 10 Gew.% MAA gepfropften Gummipartikeln in PURElastomeren
konnten sehr gute mechanische Kennwerte erzielt werden. Damit
stellen altgummipartikelmodifizierte PUR-Blends eine interessante Recyclingoption für Altreifen und Altgummiabfälle dar.
The tape placement technique is of particular importance for the production of large
and weight optimized structural components especially in the aeronautic industry.
The components are produced independently of size and load directions by placing
single unidirectional fiber reinforced tapes automatically. Moreover, very large component
dimensions enable a reduction of joining processes.
In comparison to the thermoset tape placement, additional potentials can be set up
through the usage of thermoplastic semi-finished materials, as beside the high degree
of integration und the defined laminate construction less material specific problems
and a non-autoclave production can be realized. This thesis follows an allembracing
analyses and development of the thermoplastic tape placement process
to provide knowledge to overcome the deficits concerning semi-finished materials,
systems engineering and available models for the process description.
First, the process is described and differentiated. Within the scope of a strategic
process analyses, the potentials and strength of this process are worked out.
Through a succeeding operational process analyses, the process is pictured in detail
and further developments of the process and the control are made possible.
All aspects of the process in terms of quality of the semi-finished material, systems
engineering, process control, and quality assurance are considered for the process
development. Innovative concepts to solve the first layer problem and a new tape
placement head are worked out.
A new model is developed to support strategic decisions on basis of component specific
cycle times. A measure for the component shape complexity is derived and integrated
into a continuous approach. The model is based on the process physics and
can be applied to any component without a need for empiric data.
Finally, new process potentials are presented through a combination of thermoforming
and thermoplastic tape placement.
Styrene is most commonly used in Vinylester resins (VERs) and is the co-monomer
best described regarding VERs. However, there is little knowledge about the
influence of other co-monomers on properties of resins and castings. Because of
some unfavorable properties styrene provides in resins, e. g. the relatively low flash
point, public interest in the usage of styrene-free resins in chemically bonded anchors
has increased in the last couple of years.
To develop styrene-free VERs and to examine their qualifications when used in
chemically bonded anchors was one of the main purposes of this thesis. Properties
of several castings were examined and described and correlations between these
properties and those of co-monomers were investigated to find a pattern that would
allow facilitation for further examinations. One styrenated and seven styrene-free
resins were synthezised and compared to each other in several investigations.
Using these different co-monomers a great variety of fracture-mechanical and
mechanical properties of the castings can be achieved. Compared to the styrenecontaining
resin it is possible to get either higher, lower or equal strength, stiffness
and elongation. Castings containing HPMA and PEG200DMA proved to be of special
interest. VER/HPMA achieved highest results regarding modulus and strength.
Elongation was equal to that of the resin containing styrene. VER/PEG200DMA
showed the best results regarding elongation and had the lowest tensile modulus.
Tensile and flexural elongations were as high as those of the styrene reference
sytem.
Styrenefree systems showed a lower thermal resistance compared to the styrenated
resin and absorbed more water. There were significant differences in alkali
resistance as well. Only THFMA and PEG200DMA could deliver values similar to the
styrene system. The different amount of ester groups in the networks could not
explain these results but a correlation was found between residual strength and the
sum of hydroxy- and ester group concentrations.A method was deduced from these test results to allow assumptions on hydrophilicity
properties of castings by considering the molecular structure and the amount of comonomer
used.
Chemical bonding anchors containing the synthesised styrene-free resins were
produced. These showed high pull-out loads and little displacements under
permanent loading. Adhesive properties of the resins showed no direct correlation to
the bond strength of anchors. A tendency was found that resins with high stiffness
provide anchors with higher bond strength. Alkali resistance of the bonding material
was examined in slice tests. Even bonding materials containing resins that were
almost completely destroyed during a boiling test with NaOH showed good residual
strength here.
DSC-analysis of anchor grout samples collected from pulled out anchors showed low
glass transition temperature and locally inconsistent cure degrees. The possibility of
thermal postcure of anchor grouts after setting was examined to be able to better
compare the different systems when almost completely cured. Two methods were
considered: heating of the anchor rod using hot air and electromagnetic induction.
Based on a thermodynamical calculation model the heat loss proved to be high when
using hot air. Results of the induction method were promising, however. The degree
of cure and the glass transition temperature could be improved almost over the
complete embedment depth. A more homogenous network was achieved with a
reduced content of residuals and better chemical resistance.
We study high dimensional integration in the quantum model of computation. We develop quantum algorithms for integration of functions from Sobolev classes \(W^r_p [0,1]^d\) and analyze their convergence rates. We also prove lower bounds which show that the proposed algorithms are, in many cases, optimal within the setting of quantum computing. This extends recent results of Novak on integration of functions from Hölder classes.
Interactive graphics has been limited to simple direct illumination that commonly results in an artificial appearance. A more realistic appearance by simulating global illumination effects has been too costly to compute at interactive rates. In this paper we describe a new Monte Carlo-based global illumination algorithm. It achieves performance of up to 10 frames per second while arbitrary changes to the scene may be applied interactively. The performance is obtained through the effective use of a fast, distributed ray-tracing engine as well as a new interleaved sampling technique for parallel Monte Carlo simulation. A new filtering step in combination with correlated sampling avoids the disturbing noise artifacts common to Monte Carlo methods.
We present an algorithm for determining quadrature rules for computing the direct illumination of predominantly diffuse objects by high dynamic range images. The new method precisely reproduces fine shadow detail, is much more efficient as compared to Monte Carlo integration, and does not require any manual intervention.