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This thesis aims to establish a transient electro-thermomechanical model capable of characterizing the shape-morphing capabilities of shape memory alloy hybrid composites (SMAHCs). The particular SMAHC type examined in this study comprises a rigid substrate, a soft interlayer, and SMA wires sewed on top. The model was synthesized from the bottom up using well-established equations, methodologies, and solution procedures, taking into account appropriate simplifications and assumptions. The implementation was done with open-source solutions to ensure free availability. The model extends existing models to include aspects of external influences so that, for example, the efficiency and dynamics of the SMAHC can be predicted as a function of external mechanical loads and different ambient temperatures. Inputs to the model include geometric and material design factors and Joule’s heat and ambient conditions, while outputs include the SMAHC’s deflection, load-carrying capacities, bandwidth, and energy consumption. Individual components of the SMAHC were characterized to create simulation input parameters, and methodologies for characterization were devised. The thermomechanical and electro-thermomechanical model was validated by comparing experimental and simulated data. Regardless of the various assumptions and simplifications, the findings demonstrate that the transient deformation behavior during the electrically induced thermal activation of a SMAHC at room temperature and external loads of less than 19.2 N can be predicted with variations of less than 20 percent. With increasing mechanical stresses in the shape memory alloy attributable to external loads or rigid substrates and temperatures above the austenite start temperature or below -10°C, the model’s applicability may become unreasonable.
In order to exploit the full lightweight potential of fibre-reinforced plastics (FRP), a detailed knowledge of their progressive failure behaviour under load is required. In this context, acoustic emission analysis offers a method to characterize the underlying mechanisms in more detail. By detecting and analszing acoustic waves emitted during
crack initiation and growth, the location and type of damage can be described over the course of the test. A major challenge thereby is the differentiation between FRP specific damaging events, such as fibre and matrix fractures, on the basis of their acoustic emissions.
The present work deals with the influence of two parameters which can have a significant impact on the acoustic characteristics of damaging events. These include the depth in which the damaging event occurs (source depth) and the lateral distance the acoustic wave has to travel from the source to the sensor (source-to-sensor distance).
In order to gain an understanding of the effects of both parameters, the work highlights the properties of guided waves in fibre- reinforced plastics as crucial. By analysing artificial acoustic emission sources as well as acoustic emissions from real damaging
events, the work demonstrates that changes in source depth and source-to-sensor distance can be accompanied by strong changes in the modal and frequency content of the acoustic emissions. These changes can even lead to a fibre break being mistakenly classified as a matrix break and vice versa. Consequently, for more reliable results in
source identification, the influence of source depth and source-to-sensor distance must be considered. In this context, the use of modal acoustic emission analysis can be of great benefit in understanding the underlying phenomena and developing more robust evaluation methods.
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
The popularity of composite materials is constantly growing, which can be verified by
the rising number of composite parts in our everyday life. Examples of composite
parts can be found in the Airbus A 380 or the constantly increasing number of wind
turbines which contain composite rotor blades of over 50m length. Because of the
main features of composites, which are light weight combined with high strength and
the possibility of tailoring the strength and the stiffness of the composite according to
the requirements, their application is highly efficient and economic.
In order to manufacture a composite part by employing a Liquid Composite Molding
Process (LCM), it is first necessary to select an appropriate manufacturing process
such as the Resin Transfer Molding Process (RTM) and to design a mold which corresponds
to the requirements of the selected process. Then the stacking sequence of
the individual fibrous reinforcements is designed to withstand the loads on the final
part. To achieve an efficient composite manufacturing process, pre-shaped, handable,
dry reinforcing structures, so called preforms, need to be applied. Such preforms
can be assembled either by using conventional binder technologies or by the
recently developed “cut and sew approach”. A variety of available software simulation
tools support the design engineer in this task. These tools are, on the one hand, a
fast way of gaining information about the expected loads the mold has to endure during
the injection process. On the other hand, they provide the possibility to optimize
the injection process and its process parameters and to identify critical points of incomplete
saturation. With this information at hand, the design of the mold can be adjusted
in order to obtain optimal processing conditions for a slim and efficient production
cycle.
A prerequisite for employing these powerful simulation tools is to obtain thorough
knowledge of the required input parameters concerning the fibrous reinforcement to
be used. The most important input parameters are the compaction behavior and the
permeability of the fibrous stacking sequence. Because of the absence of modelbased
tools to provide this input information experimental determination methods
have to be employed.
This work introduces two semi-automated measurement cells which determine the inplane
permeability of fibrous reinforcements in an efficient manner, i.e. the dielectrical permeability work cell and the optical compaction and permeability work cell. The
latter of which can determine both the required compaction and the permeability information
in one single experiment. The design and manner of operating of the optical
compaction and permeability work cell is described and its functionality is validated
by a comparison of experimental results.