Дисертації з теми "Tensile creep behavior"

The role of bonding in the tensile creep behavior of paper was analyzed. This was accomplished by producing handsheets at a range of different bonding levels through manipulation of relative bonded area and specific bond strength. This was done by varying the level of wet pressing (to change relative bonded area) and using debonding and bonding agents (to change specific bond strength). Once manufactured, sheets underwent an extensive battery of physical testing and creep testing. Creep testing was conducted under constant humidity and cyclic humidity (accelerated creep) conditions. Microscopic analysis techniques were also employed to visually study bonded area loss from creep strain. Two mathematical models (one empirical and one rheological) were created to isolate, account for, and incorporate bonding into predicting tensile creep behavior in paper. Overall, the results from this thesis show that the role of bonding in tensile creep behavior (and accelerated creep behavior) is no different than its role in stress-strain behavior, which is a new finding. This means the bonding influence on tensile creep behavior is related to sheet efficiency and how effectively stress is distributed within the structure, bonded area loss is a strain-induced phenomenon and bonding is not the cause of accelerated creep behavior.

With the increasing requirements for higher strength materials with high electrical conductivity, a lot of interest has been paid to develop Cu-based composites in the last 25 years. These composites have superior tensile strength, combined with good electrical conductivity, to that exhibited by pure Cu and conventional Cu alloys. To date, much of the research carried out on this composite has focused on the mechanical and electrical properties of the as processed material. However, there is a basic lack of understanding of the way in which the properties may change or degrade during service. Without this knowledge, these composites cannot be fully and safely exploited. Thus the objective of this study was to investigate the thermo-mechanical behaviour of a Cu-Cr composite, and the nature and extent of any damage mechanisms occurring within the composite over a wide range of experimental conditions. Neutron diffraction was used to investigate the deformation behaviour of the individual phases in the composite and their interaction through elastic and plastic loading at room temperature. For the composite, a fairly good agreement was observed in the phase strains predicted by the Eshelby theory and measured by neutron diffraction. In-situ tensile tests in the SEM were also performed to study the damage mechanism of the composite. Tensile and creep tests were carried out in air and in vacuum over a wide range of temperatures. To provide data for comparison with the composite material, pure Cu specimens were tested whenever possible. Creep resistance increases significantly with the introduction of Cr fibres into Cu. The higher creep rate of the composite in air than in vacuum is due to the gradual decrease of the cross-sectional area of the matrix due to increasing thickness of the oxide layer. Damage characteristics and distributions were found to be similar during tensile and creep testing.

Additive manufacturing (AM), also known as 3D printing, is a concept and method of a manufacturing process that builds a three-dimensional object layer-by-layer. Opposite to the conventional subtractive manufacturing, it conquers various limitations on component design freedom and raises interest in various fields, including aerospace, automotive and medical applications. This thesis studies the mechanical behavior of thin-walled component manufactured by a common AM technique, laser powder bed fusion (LPBF). The studied material is Hastelloy X, which is a Ni-based superalloy, and it is in connection to a component repair application in gas turbines. The influence of microstructure on the deformation mechanisms at elevated temperatures is systematically investigated. This study aims for a fundamental and universal study that can apply to different material grades with FCC crystallographic structure. It is common to find elongated grain and subgrain structure caused by the directional laser energy input in the LPBF process, which is related to the different printing parameters and brands of equipment. This thesis will start with the study of scan rotation effect on stainless steel 316L in an EOS M290 equipment. The statistic texture analysis by using neutron diffraction reveals a clear transition when different level of scan rotation is applied. Scan rotation of 67° is a standard printing parameter with intention to lower anisotropy, yet, the elongated grain and cell structure is still found in the as-built microstructure. Therefore, the anisotropic mechanical behavior study is carried out on the sample printed with scan rotation of 67° in this thesis. Thin-walled effects in LPBF are investigated by studying a group of plate-like HX specimens, with different nominal thicknesses from 4mm down to 1mm, and a reference group of rod-like sample with a diameter of 18mm. A texture similar to Goss texture is found in rod-like sample, and it becomes <011>//BD fiber texture in the 4mm specimen, then it turns to be <001> fiber texture along the transverse direction (TD) in the 1mm specimen. Tensile tests with the strain rate of 10−3 s−1 have been applied to the plate-like specimens from room temperature up to 700 ℃. A degradation of strength is shown when the sample becomes thinner, which is assumed to be due to the overestimated load bearing cross-section since the as-built surface is rough. A cross-section calibration method is proposed by reducing the surface roughness, and a selection of proper roughness parameters is demonstrated with the consideration of the calculated Taylor’s factor and the residual stress. The large thermal gradient during the LPBF process induces high dislocation density and strengthens the material, hence, the LPBF HX exhibits better yield strength than conventionally manufactured, wrought HX, but the work hardening capacity and ductility are sacrificed at the same time. Two types of loading condition reveal the anisotropic mechanical behavior, where the vertical and horizontal tests refer to the loading direction being on the BD and TD respectively. The vertical tests exhibit lower strength but better ductility that is related to the larger lattice rotation observed from the samples with different deformation level. Meanwhile, the elongated grain structure and grain boundary embrittlement are responsible for the low horizontal ductility. A ductile to brittle transition is traced at 700 ℃, so a further study with two different slow strain rates, 10−5 s−1 and 10−6 s−1, are carried out at 700 ℃. Creep damage is shown in the slow strain rates testing. Deformation twinning is found only in the vertical tests where it forms mostly in the twin favorable <111> oriented grain along the LD. The large lattice rotation and the deformation twinning make the vertical ductility remain high level under the slow strain rates. The slow strain rate tensile testing lightens the understanding of creep behavior in LPBF Ni-based superalloys. In summary, this thesis uncovers the tensile behavior of LPBF HX with different variations, including geometry-dependence, temperature-dependence, crystallographic texture-dependence and strain rate-dependence. The generated knowledge will be beneficial to the future study of different mechanical behavior such as fatigue and creep, and it will also enable a more robust design for LPBF applications.
Additiv tillverkning, eller 3D-utskrifter, är tillverkningsmetoder där man skapar ett tredimensionellt objekt genom att tillföra material lager for lager. Till skillnad från konventionella avverkande tillverkningsmetoder elimineras många geometriska begränsningar vilket ger större designfrihet och metoderna har därför väckt stort intresse inom en rad olika områden, inklusive flyg-, fordons- och medicinska tillämpningar. I denna avhandling studeras mekaniska egenskaper hos tunnväggiga komponenter tillverkade med en vanligt förekommande laserbaserad pulverbädds-teknik, laser powder bed fusion (LPBF). Det studerade materialet är Hastelloy X, en Ni-baserad superlegering som är vanligt förekommande for både nytillverkning och reparation av komponenter för gasturbiner. Inverkan av mikrostruktur på deformationsmekanismerna vid förhöjda temperaturer undersöks systematiskt. Detta arbete syftar till att ge grundläggande och generisk kunskap som kan tillämpas på olika materialtyper med en kubiskt tätpackad (FCC) kristallstruktur. Det är vanligt att man hittar en utdragen kornstruktur orsakad av den riktade tillförseln av laserenergi i LPBF-processen, vilket kan relateras till olika processparametrar och kan variera mellan utrustningar frän olika leverantörer. Denna avhandling inleds med studien av effekten av scanningsstrategi vid tillverkning av rostfritt stål 316L i en EOS M290-utrustning. En statistisk texturanalys med hjälp av neutrondiffraktion påvisar en tydlig övergång mellan olika mikrostrukturer när olika scanningsstrategier tillämpas. En scanningsrotation på 67 mellan varje lager är en typisk standardinställning med avsikt att sanka anisotropin i materialet, dock finns den utdragna kornstrukturen oftast kvar. I denna avhandling studeras därför de anisotropa egenskaperna hos material tillverkade med 67 scanningsrotation. Effekten av tunnväggiga strukturer i LPBF undersöks genom att studera en uppsättning platta HX-prover, med olika nominella tjocklekar från 4 mm ner till 1 mm, samt en referensgrupp med cylindriska prov med en diameter på 18 mm. Kristallografisk textur som liknar den av Goss-typ återfinns i de cylindriska proverna vilket gradvis övergår från en fibertextur med <011> i byggriktningen for 4mm-proven till en fibertextur med <001> i tvärriktningen for 1mm-proven. Dragprovning med en töjningshastighet på 10−3 s−1 har utförts på de platta provstavarna från rumstemperatur upp till 700 ℃. En sänkning av styrkan uppvisas när proven blir tunnare, vilket kan antas bero på att det lastbarande tvärsnittet överskattas på grund av den grova ytan. En metod för tvärsnittskalibrering föreslås genom att kompensera for ytråheten, och valet av lämplig ytfinhetsparameter motiveras med hänsyn till den beräknade Taylor-faktorn och förekomsten av restspänningar. Den stora termiska gradienten som uppstår for LPBF-processen inducerar en hög dislokationstäthet vilket höjer materialets styrka och följaktligen uppvisar LPBF HX högre sträckgräns an konventionellt tillverkad, smidda HX, men förmågan till deformationshårdnande samt duktiliteten i materialet sänks samtidigt. Tester utförda i två olika belastningsriktningar, vertikalt respektive horisontellt mot byggriktningen, demonstrerar det anisotropiska mekaniska beteendet. De vertikala testerna uppvisar lägre hållfasthet men bättre duktilitet vilket kan relateras till en större benägenhet for kristallstukturen att rotera när deformationsgraden ökar. Samtidigt är den utdragna kronstukturen ansvarig for den lägre duktiliteten for de horisontella proverna. En övergång från ett duktilt till ett mer sprött beteende noterades vid 700 ℃, och därför initierades ytterligare en studie där tester med två lägre töjningshastigheter, 10−5 s−1 och 10−6 s−1, utfördes vid 700 ℃. Det kan noteras att krypskador återfinns i tester med en långsam deformationshastighet och deformationstvillingar uppstår endast i de vertikala provstavarna där det främst bildas tvillingar i korn orienterade med <111> riktningen längs belastningsriktningen. Den stora förmågan till rotation i kristallstrukturen och deformationstvillingarna bidrar till att den vertikala duktiliteten förblir hög även i testerna med en låg deformationshastighet. Testerna med en långsam draghastighet bidrar därför till en bättre förståelse av krypbeteendet i LPBF Nibaserade superlegeringar. Sammanfattningsvis så bidrar denna avhandling till bättre förståelse av de mekaniska egenskaperna hos LPBF HX i olika utföranden och förhållanden, inklusive geometriberoende, temperaturberoende, deformationshastighetsberoende samt inverkan av kristallografisk textur. Den genererade kunskapen kommer att vara till stor nytta vid fortsatta studier av olika mekaniska egenskaper som utmattning och kryp, samt bidrar till att möjliggöra en mer robust design for LPBF-tillämpningar.

Bestärkt durch das gesellschaftliche und wirtschaftliche Interesse an nachhaltigen und ressourcenschonenden Formen des Bauens gewinnen Holzkonstruktionen wieder unverkennbar an Bedeutung. Mit dieser Entwicklung bilden sich neue Konstruktionsprinzipien und Materialkombinationen im Bauwesen heraus, zu deren ingenieurtechnischer Beurteilung zum Teil keine ausreichenden Erkenntnisse vorliegen. Verbundkonstruktionen aus Holz und Glas sind eine innovative Bauweise, die zu einer höheren Materialeffizienz in Fassaden beiträgt, deren Wirkungsweise aber noch nicht ausreichend hinterfragt wurde. Werden Holz und Glas durch eine tragende Klebung verbunden, lässt sich das vielfach ungenutzte Tragpotenzial ausschöpfen, das eine in Scheibenebene belastete Verglasung aufweist. Die Qualität der Klebung entscheidet dabei über die Eigenschaften und das Leistungsvermögen des Bauteils. Die üblicherweise an dieser Schnittstelle eingesetzten Silikonklebstoffe weisen eine hohe Nachgiebigkeit und eine vergleichsweise geringe Festigkeit auf. Wenn die Verbundelemente als Aussteifung mitwirken sollen, bleibt ihr Einsatz deswegen auf Gebäude mit höchstens zwei Geschossen limitiert. Die vorliegende Arbeit trägt entscheidend zur Erweiterung der baulichen Möglichkeiten bei, indem sie der Anwendbarkeit von hochfesten Klebstoffen, die für den Einsatz im Bauwesen nur wenig erforscht sind, auf vielschichtige Weise nachgeht. Im Fokus stehen aussteifende Holz-Glas-Verbundelemente für die Fassade. Weder die Bauart noch das Bauprodukt Klebstoff sind derzeit in Deutschland in einer Norm erfasst. Das Klären der baurechtlichen Rahmenbedingungen ist daher unerlässlich und erfolgt mit engem Bezug zum konstruktiven Glasbau. Zusätzlich zur wissenschaftlichen Interpretation wird dadurch eine praxisnahe Bewertung der Versuchsergebnisse möglich, was ein Alleinstellungsmerkmal dieser Arbeit darstellt. Das Verformungsvermögen des Klebstoffs spielt eine zentrale Rolle bei der Materialauswahl und Gestaltung der Holz-Glas-Verbundelemente. Der Einfluss der Klebstoffsteifigkeit auf das Tragverhalten eines Einzelelements und auf dessen Interaktion mit den anderen Bestandteilen des Tragwerks wird an einem Modellgebäude untersucht. Auf Basis dieser Parameterstudie lassen sich drei Steifigkeitsbereiche definieren, auf die sich die Klebstoffauswahl für die weiteren Untersuchungen stützt. Der experimentelle Teil der Arbeit beginnt mit der ausführlichen Charakterisierung von sieben Klebstoffen. Davon werden zwei höherfeste Klebstoffe als geeignet identifiziert. Ein Silikonklebstoff wird als Referenzmaterial zur aktuellen Anwendungspraxis festgelegt. Das Hauptaugenmerk der folgenden Experimente richtet sich auf Aspekte der Alterungsbeständigkeit und des zeitabhängigen Materialverhaltens unter langandauernder mechanischer Beanspruchung. In labormaßstäblichen Alterungsprüfungen werden die Klebstoffproben unterschiedlichen Schadeinwirkungen ausgesetzt, die im Glas- und Fassadenbau relevant sind. Darüber hinaus erfolgen Kriechversuche an kleinen und großen Scherprüfkörpern. Letztere stellen einen besonderen Mehrwert dar, da sie eine realistische Klebfugengeometrie aufweisen und die Ergebnisse dadurch dem tatsächlichen Bauteilverhalten nahekommen. Für diese Zeitstandversuche wurde eine bislang einzigartige Versuchsanlage aus sechs Prüfrahmen mit Gasdruckfederbelastung entwickelt. Im Ergebnis zeigt sich, dass mit den gewählten höherfesten Klebstoffen die Festigkeit der nicht gealterten Klebschichten erwartungsgemäß gesteigert werden kann. Der Bruch des Fügepartners Holz wird zum maßgebenden Versagenskriterium. Die Verformungen des Verbundelements reduzieren sich gegenüber einer Silikonklebung deutlich. Allerdings offenbaren sich in einzelnen Alterungsszenarien und unter langandauernder Belastung auch Schwachstellen dieser Klebstoffe. Ihre Verwendung kann daher nur mit konstruktiven Kompensationsmaßnahmen oder durch Abschirmen der kritischen Einwirkungsgrößen empfohlen werden. Entsprechende Vorschläge werden bei der abschließenden Bewertung der Ergebnisse unterbreitet. Verfahren und Beurteilungsmethoden, die in dieser Arbeit angewendet und entwickelt werden, erleichtern die zukünftige Bewertung weiterer aussichtsreicher Klebstoffe für den Holz-Glas-Verbund
Wooden constructions are on the rise again – encouraged by a strong public and economic trend towards sustainable and resource efficient buildings. Spurred by this growing interest novel design principles and material assemblies in architecture and the building industry evolve. These developments require further research due to the absence of evaluation tools and insufficient knowledge about their design. Load-bearing timber-glass composite elements could contribute to a more efficient use of materials in façade constructions. In this case a linear adhesive bond connects the glass pane to the timber substructure. This enables an in-plane loading of the glass whose capacity is not used to its full potential in conventional façades as it is solely applied as an infill panel. The quality of the adhesive bond defines the characteristics and the performance of the whole structural component. Structural sealants such as silicones, which are typically used for the joint, provide a high flexibility and only a low load-bearing capacity. Considering such elements being part of a bracing system, the mentioned characteristics limit the application range to buildings with not more than two stories. This thesis widens the scope with an in-depth examination of high-modulus adhesives, which have not yet been evaluated for their use in building constructions. Timber-glass composite elements used as a bracing component in façades are the focus of this work. Neither the full structural component nor the adhesive have yet been included into German building standards. Hence it is essential to assess the general requirements of their application. The relevant aspects are clarified in the context of glass constructions. In addition to the scientific discussion of the results, this approach facilitates also a practical evaluation of the findings, which is a unique feature of this work. The deformability of the adhesive becomes a crucial criterion when selecting the individual materials and designing the timber-glass composite elements. A case study assesses the influence of the adhesive stiffness on the behavior of a single element and its interaction with other members of the structural system. Based on the results, three different stiffness classes are introduced to support the selection process of the adhesives to be examined in further investigations. The experimental part of this work is initiated by a comprehensive characterization of seven shortlisted adhesives. The results enable a further differentiation of suitable materials. Two adhesives qualified as suitable for the main experiments. A silicone adhesive complements the test series to serve as a reference material to the current practice. In the next phase attention is drawn to the ageing stability and on the time-dependent material behavior of the adhesives under long-term loading. Small-scale specimens made from adhesively joint timber and glass pieces are exposed to different ageing scenarios which relate to the impacts typically encountered in façades. Beyond that, creep tests are carried out on small and large shear specimen. The latter provide extra benefit as they comprise long linear adhesive joints resembling virtually the situation in a real-size element. A specific long-term test rig was developed for this purpose comprising a loading unit with gas pressurized springs. Based on the results it can be concluded that joints with adhesives of high and intermediate stiffness enable an increase of characteristic failure loads and a significant reduction of deformation. With the stiffer joint near-surface rupture of timber fibers becomes the prevailing failure mechanism. The timber strength limits further loading of the adhesive joint. However, ageing and creep testing reveal also shortcomings of the adhesives. Their application can only be recommended if redundant compensation measures are taken or the joint is protected against critical environmental impacts. Appropriate solutions are proposed with the final recommendations of this work. Methods and assessment tools that have been developed and tested for this work offer the possibility of a more straight-forward evaluation of further promising adhesives and their use in load-bearing timber-glass composites

A l’heure actuelle où la préservation de notre environnement est primordiale, les constructions en béton font intervenir de plus en plus des ciments comprenant des ajouts minéraux, tels que le laitier, les cendres volantes… En effet, la production des ciments composés permet de réduire le dégagement des gaz à effets de serre et de réutiliser des déchets industriels. Les bétons formulés à base de ciment au laitier de haut-fourneau (CEM III) sont également largement utilisés suite à leur bonne résistance aux réactions alcali-silices, à la diffusion des chlorures et aux attaques sulfatiques… Cependant, certains ouvrages construits avec ce type matériau ont présenté au jeune âge des problèmes de fissuration liés à la restriction de leurs déformations différées, telles que le retrait endogène, thermique et de dessiccation. Suite à cette observation, des essais préliminaires ont été réalisés au laboratoire du service BATir de l’Université Libre de Bruxelles. Ils ont mis en avant plusieurs caractéristiques du comportement de ces matériaux :

1. Lors du suivi du retrait restreint à l’aide de l’essai à l’anneau en condition de dessiccation, le béton formulé à base de ciment au laitier de haut-fourneau a fissuré bien avant le béton formulé à base de ciment Portland.

2. Le retrait total en condition libre du béton formulé à base de ciment au laitier de haut-fourneau est nettement supérieur à celui du béton formulé à base de ciment Portland. Cette différence de comportement est principalement due à l’accroissement rapide et plus élevé du retrait endogène des bétons formulés à base de ciment au laitier de haut-fourneau.

Au vu de ces résultats expérimentaux, il a semblé intéressant de déterminer quel était l’impact de la déformation endogène des bétons formulés à base de ciments au laitier de haut-fourneau (CEM III) sur leur sensibilité à la fissuration. Afin de répondre à cette question, les déformations différées (retrait endogène, fluage propre en compression et en traction) au jeune âge de trois compositions de béton avec différentes teneurs en laitier (0, 42 et 71%) ont été étudiées expérimentalement en conditions libre et restreinte. Cependant, le suivi du retrait endogène libre et restreint a nécessité le développement de plusieurs dispositifs expérimentaux limitant au maximum les artefacts de mesure, tels que la TSTM (Temperature Stress Testing Machine). De plus, l’interprétation de ces résultats expérimentaux a également nécessité une caractérisation du comportement de ces matériaux à l’échelle macro- et microscopique.

Finalement, cette étude a montré que malgré une déformation endogène plus élevée, les bétons formulés à base de ciment au laitier de haut-fourneau fissurent après le béton formulé à base de ciment Portland. Ce comportement est dû à :

-l’impact du laitier sur la réaction d’hydratation du matériau cimentaire ;

-la présence d’une expansion de la matrice cimentaire des bétons formulés à base de ciment au laitier de haut-fourneau au jeune âge qui retarde l’apparition des contraintes de traction au sein du matériau ;

-la plus grande capacité de ces matériaux cimentaires à relaxer les contraintes de traction/

Today, the use of concretes with mineral additions (fly ash, slag) for civil engineering structures is spreading worldwide. Indeed, the production of blended cements is more respectful of the environment than the production of Portland cement, because it allows reducing greenhouse gas emissions and using industrial wastes. Slag cement concretes are also largely used for their good resistance to alkali-silica reactions, sulphate attacks and chloride diffusion. However, some of constructions built with slag cement concretes have exhibited cracking at early age due to their restrained deformations, such as thermal, autogenous and drying shrinkage. Following these observations, a preliminary experimental study was realized in the laboratory of BATir Department at ULB. It revealed several characteristics of the behaviour of slag cement concretes:

1. The study of restrained deformations under drying conditions by means of ring tests showed that the slag cement concretes seem more prone to crack than the Portland cement concretes;

2. The total free shrinkage for slag cement concrete is clearly larger than for Portland cement concrete. This difference of behaviour is mainly due to the fast and large increase in the autogenous deformation of the slag cement concrete.

Following these experimental results, the effect of the autogenous deformation on the cracking sensibility of slag cement concretes seemed interesting to investigate. Their deformations (autogenous deformation, compressive and tensile basic creep) have been studied at early age for three concretes characterized by different slag contents (0, 42 and 71%) under free and restrained conditions. For monitoring free and restrained autogenous deformations, several test rigs aimed at limiting artefacts were designed, like the TSTM (Temperature Stress Testing Machine). Moreover, the behaviour of these concretes was also characterized by a study at a macro- and microstructure scale.

Finally, this study shows that the slag cement concretes under sealed and fully restrained conditions crack later than the Portland cement concrete, despite the fact that they are characterized by the largest autogenous deformation. This behaviour is due to:

- the slag effect on the hydration reaction of cementitious material;

- the cement matrix expansion of the slag cement concretes at early age which delays the occurrence of tensile stresses inside the material;

- the largest capacity of this concrete to relax tensile stresses.

Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

碩士
國立屏東科技大學
土木工程系所
100
The objective of the study is to investigate the effects of stressing and heating procedures during geogrid manufacture process on the tensile and creep behavior of polyester yarns. Three types of polyester yarns were used in the study. The nominal unit weight of the polyester yarns were 2000, 1500, and 2000 deniers for Type A, Type B, and Type C products, respectively. The test yarns were also treated under heating temperatures of 150C and 170C, and stressing at various loadings. After the heating and stressing process, the treated yarns were also evaluated their tensile strength and creep behavior according to ASTM D2256, ASTM D5262, and ASTM D6992 test methods. The polyester yarn shrinkage was observed under the heating process, higher heating process would induce higher shrinkage strain. A minimum of 5% UTS ~ 7.5% UTS prestressing load could be applied to eliminate the shrinkage strain. However, when the prestressing load increased up to 10% UTS, the stress strain tensile test curve changed from an S-Type curve to a near initial straight line failure curve. The initial creep strain of the convention long term creep tests for the treated products decreased as increasing pre-stressing loads and showed good repeatability. The creep strain rates were 0.0941~0.1017 %/log (t, H), 0.0895~0.1327 %/log (t, H), and 0.0499~0.0577 %/log (t, H) for Types A, B, and Type C polyester yarns, respectively. The creep strain rates also decreased as increasing the treated temperatures. The accelerated creep test (SIM) results indicated that the analyzed master creep curves using reference lag time (t-t’) of 3000 s would fit the best with that obtained from associated conventional creep tests. SEM test results indicated that no significant difference between the non-treated and treated samples before the creep test. However, a few dent spots and uneven waving surface areas on the scanning pictures of the treated samples after 1000 hours of conventional creep test were observed. The effects of the treated process and long term tensile load on the engineering behavior of polyester yarn need further investigation.

abstract: Materials have been the backbone of every major invention in the history of mankind, e.g. satellites and space shuttles would not exist without advancement in materials development. Integral to this, is the development of nanocrystalline (NC) materials that promise multitude of properties for advanced applications. However, they do not tend to preserve structural integrity under intense cyclic loading or long-term temperature exposures. Therefore, it is imperative to understand factors that alter the sub-features controlling both structural and functional properties under extreme conditions, particularly fatigue and creep. Thus, this dissertation systematically studies the tensile creep and fatigue behaviour of a chemically optimized and microstructurally stable bulk NC copper (Cu)-3at.% tantalum (Ta) alloy. Strategic engineering of nanometer sized clusters of Ta into the alloy’s microstructure were found to suppress the microstructure instability and render remarkable improvement in the high temperature tensile creep resistance up to 0.64 times the melting temperature of Cu. Primary creep in this alloy was found to be governed by the relaxation of the microstructure under the applied stress. Further, during the secondary creep, short circuit diffusion of grain boundary atoms resulted in the negligible steady-state creep rate in the alloy. Under fatigue loading, the alloy showed higher resistance for crack nucleation owing to the inherent microstructural stability, and the interaction of the dislocations with the Ta nanoclusters. The underlying mechanism was found to be related to the diffused damage accumulation, i.e., during cyclic loading many grains participate in the plasticity process (nucleation of discrete grain boundary dislocations) resulting in homogenous accumulation rather than localized one as typically observed in coarse-grained materials. Overall, the engineered Ta nanoclusters were responsible for governing the underlying anomalous high temperature creep and fatigue deformation mechanisms in the alloy. Finally, this study presents a design approach that involves alloying of pure metals in order to impart stability in NC materials and significantly enhance their structural properties, especially those at higher temperatures. Moreover, this design approach can be easily translated to other multicomponent systems for developing advanced high-performance structural materials.
Dissertation/Thesis
Doctoral Dissertation Materials Science and Engineering 2019

Directionally solidified Nickel-based superalloys are the workhorse for the Jet Engine turbine rotor blades and nozzle guide vanes (NGV) applications. Su 247LC DS is the material used for turbine rotor blades and NGVs of one of the gas turbine engines. This thesis aims to study elevated temperature deformation of this material as experienced by the alloy during its service exposure with particular attention to the effect of /’ eutectic content. Directionally solidified cast rods were subjected to varying extents of homogenization and solution treatment and two-step aging cycles (1080C and 870C) to arrive at different microstructures. A higher temperature final aging temperature (1000C instead of 870C) was selected to introduce a version of the microstructure (1250ST1000A (4% eutectic-48%’)) that would represent an overshoot of temperature during the service life of the jet engine components. Four different combinations of /’ eutectic and ’ precipitate microstructures (1260STA (2% eutectic-55%’), 1250STA (4% eutectic-55%’), 1254FSTA (6% eutectic-48%’) and 1250ST1000A (4% eutectic-48%’)) were selected in the present study. Mechanical testing, namely, monotonic tensile and tensile creep tests were conducted for all the four microstructures in a temperature range of 700-980C which is the typical operating range for the turbine blade and vane material. Fully reversed strain controlled low cycle fatigue (LCF) and stress controlled high cycle fatigue (HCF) tests were performed for three microstructures, namely, 1260STA (2% eutectic-55%’), 1250STA (4% eutectic-55%’) and 1254FSTA (6% eutectic-48%’) at a temperature of 700C over a range of strain amplitudes (0.7-1%) and stress amplitudes (400-600MPa) respectively. Creep tests were conducted over a temperature range of 700-980C while the stress level was varied between 250-900MPa. Monotonic tensile strengths (yield and ultimate tensile) were found to enhance with decreasing eutectic content and increasing ’ precipitate volume fraction with an exception to the 1250ST1000A (4% eutectic-48%’) microstructure. This microstructure achieved by following higher final aging temperature exhibited the lowest tensile strength over the entire test temperature range. Anomalous yield behavior was exhibited by all the microstructures in the temperature range of 700-850C. This was followed by a sharp reduction in strength level with a further increase in test temperature. Fracture of the samples was characterized by carbide particle cracking and slip initiation on octahedral slip planes. The dislocations were mostly restricted within  channels at 700C. Left over dislocation loops were occasionally observed within ’ precipitates. At, 850C, misfit dislocations were found to develop. The isothermal LCF life was found to reduce monotonically with increasing imposed strain amplitudes for all the three microstructures. Lower strain amplitude tests (strain amplitude level 0.8%) exhibited a marginal strengthening during the initial few cycles followed by a stabilized stress response. A gradually increasing stress response was observed for higher strain amplitude (0.8%) tests. The fatigue crack origin was associated with surface and near-surface casting porosity along with cracked carbide particles. Large carbide particle cracks were found to propagate into the matrix and activate slip on octahedral slip planes. The overload failure area decreased gradually as the imposed strain amplitude was reduced. The crack propagation region was characterized by faceted feature revealing fatigue crack propagation along well-defined slip planes. Samples tested with higher strain amplitudes exhibited wider hysteresis loop and hence higher plastic strains. Even though no significant difference was evidenced with respect to fatigue life and deformation characteristics as a function of eutectic content, the microstructure with highest eutectic content and lowest ’ precipitate volume fraction (1254FSTA (6% eutectic-48%’)) revealed highest plastic strain amplitudes over the entire strain amplitude range. The trend in fatigue life and fracture characteristics in high cycle fatigue was found to be similar to that observed in case of LCF behavior of the alloy. The tensile creep behavior of the alloy was found to be influenced by stress level and test temperature. The lower temperature and higher stress level tests (700C/900MPa and 760C/800MPa) exhibited dominance of primary creep, whereas the higher temperature lower stress level tests (980C/250MPa) revealed deformation by rafting. Initiation of rafting was observed at 850C (stress level 550MPa). Shearing of ’ precipitates were frequently observed at lower test temperatures (700C and 760C). The LMP plot showed a linear dependence on stress for all the four microstructures. Microstructures with similar ’ volume fraction but different eutectic content exhibited similar deformation behavior over the entire test range. Experimental evidence suggested a better homogenization and solution heat treatment process was beneficial in reducing the /’ eutectic content that resulted in a higher volume fraction of ’ precipitates in microstructures. The microstructures with highest precipitate content exhibited the highest tensile strength and creep resistance. The deformation microstructure did not reveal any direct role of /’ eutectic phase.

Ultra-high-performance fiber reinforced concrete (UHPFRC) has improved properties over conventional concrete, such as high tensile strength, greater compressive strength and enhanced post cracking characteristics. The steel fibers in UHPFRC are recognized as providing resistance to crack widening in tension zones because of the fibers bridge adjacent cracks, which consequently enhances the tensile performance. Although, UHPFRC is capable of resisting the induced tensile stresses, it has still limitations under sustained tensile loads. It is also not well understood whether these characteristics would resist the induced tensile stress over a longer period or if they would leave the serviceability of the structure at risk. Therefore, the research presented in this study is concerned with the time-dependent tensile behaviour of UHPFRC. The present study comprises of an experimental program based on the application of newly developed test rigs, preparation of the test specimens and investigations into the test results. The aims seek to provide an understanding of the instantaneous and time-dependent tensile behaviour of unreinforced and reinforced UHPFRC prisms. Instantaneous tensile tests were involved, applying axial tensile loads to UHPFRC prisms for both aged and unaged concrete. The time-dependent tensile behaviour of UHPFRC was investigated in terms of tensile creep and tension stiffening mechanisms under sustained tensile loads. The sustained tensile loads were considered as different percentages of cracking loads, such as 50% and 75% of the cracking loads of unreinforced UHPFRC specimens for the tensile creep test and 75%, 100%, 150%, and 200% of the cracking loads of reinforced UHPFRC specimens for the tension stiffening test. The cracking loads were determined from 28th day instantaneous tensile responses for both reinforced and unreinforced UHPFRC prisms. Two different test rigs were used to conduct the tensile creep and tension stiffening tests under sustained tensile loads. The rigs were modified to overcome the limitations identified through the critical literature review. The experimental results demonstrate that the tensile creep strain and tension stiffening mechanisms are greatly influenced by the shrinkage strain of UHPFRC. A significant portion of the measured total shrinkage was caused by autogenous shrinkage rather than drying shrinkage. The results demonstrate that higher sustained stress leads to higher tensile creep strain for the first 13 days, at a higher creep rate. Afterwards, the shrinkage strain dominates over the tensile creep strain. The extent of crack propagation and the deterioration of the bonds between the steel fibers and the cement matrix are also significantly affected by the sustained tensile loads.
Thesis (MPhil) -- University of Adelaide, School of Civil, Environmental and Mining Engineering, 2019

Student Number : 9800022T - PhD thesis - School of Mechanical, Industrial and Aeronautical Engineering - Faculty of Engineering and the Built Environment
For many applications, it may be useful to be able to estimate creep properties of a material from simpler testing procedures such as tensile tests than the conventional creep testing procedures. Most alloys used for creep service conditions are in a hardened condition and thus tertiary creep, controlled by micro structural degradation, is dominant. The object of the study was to investigate a reasonably simple method for estimating the creep behavior of a low alloy 1% Cr, 0.25 % Mo steel from tensile yield data. The study involved performing of series of investigations, including age hardening, tensile and creep tests. Microstructural degradation was monitored from specimens held in a furnace for different times and temperatures, which were then tested in tension at room temperatures. Tensile tests were carried out at different temperatures and strain rates and the data used to determine material parameters for use in kinetic equations describing deformation. For comparison, creep curves were obtained from both creep tests and tensile tests results. Tests on furnace aged specimens were used to quantify softening due to material degradation and formulate a structure evolution and kinetic expressions used to determine creep curves. The modified equation by Dorn was used to determine the material parameters and to predict flow characteristics. Two sets of mechanisms were observed. At low temperature and high stress (above 550MPa) dislocation by glide mechanism was investigated. At higher temperatures and low stress (below 550MPa), some form of power law creep was observed. Glide mechanism was investigated and material parameters σ ) , n and activation volume v, were calculated. The calculated value of σ ) was assumed for both plastic deformation and the softening kinetics. A reasonably good estimate of the creep behavior of the low alloy steel used in this investigation in which tertiary creep dominates can be calculated from tensile yield stress values. Furthermore, the creep rate and recovery have similar stress dependences, with the stress and temperature dependence similar to that predicted by recovery theory. The value of activation energy observed for creep for this alloy is in line with the processes which could be related to self diffusion. In order to justify the significance of this study, four existing empirical models are discussed, highlighting their merits and demerits with respect to the models used in this study. These are θ-Projection, Damage Mechanics, Estrin-Mecking and the Internal Stress Methods. Generally, in this class of alloys, recovery process occurs under an effective stress (i.e. an applied stress less the internal stress). Thus the possibility of using tensile data obtained in this study in the internals stress model was explored. The model could replicate the one used in this study if the change in internal stress value o σ is assumed to be negligible. This could be assumed to be true for tensile data at high stresses and low temperature especially during secondary creep rate when the internal stress approximates to the applied stress and at short test durations.

In the present thesis, the effects of combined additions of Ca and Sb on microstructure, tensile, creep and corrosion behaviour of AZ91 alloy fabricated by squeeze-casting have been investigated. For comparison, the same has also been studied on the squeeze-cast AZ91 alloy with and without individual additions of Ca and Sb. The composition of all the fabricated alloys are AZ91+0.59Sb (AZY911), AZ91+0.89Ca (AZX911), AZ91+0.91Ca+0.31Sb (AZXY9110), AZ91+0.89Ca+0.62Sb (AZXY9111) and AZ91+1.80Ca+0.33Sb (AZXY9120) (wt.%). A detailed microstructural characterization of all the fabricated alloys has been done. Tensile tests of all the specimens at ambient, 423 K and 473 K temperatures have been carried out. The impression creep tests are conducted in the stress range of 300 to 480 MPa and temperature range of 423 to 523 K for a dwell time of 7200 s. A detailed microstructural analysis of the creep tested specimens has been carried out to further interpret creep behaviour of the alloys. Compressive creep tests are carried out on all the modified alloys at a temperature 473 K and stress of 70 MPa. The corrosion tests have been performed in 0.5NaCl (wt.%) solution at neutral pH with specimen exposed area of 0.5 cm2 at ambient temperature. The results indicate that both individual and combined additions refine the grain size and β-Mg17Al12 phase, which is more pronounced with combined additions. Besides, α-Mg and β-Mg17Al12 phases, a new reticular Al2Ca and rod-shaped Mg3Sb2 phases are formed following individual additions of Ca and Sb in the AZ91 alloy. With combined additions, an additional Ca2Sb phase is formed suppressing Mg3Sb2 phase. Additions of both Ca and Sb increase yield strength (YS) at both ambient and elevated temperatures up to 473 K. However, both ductility and ultimate tensile strength (UTS) decrease first up to 423 K and then increase at 473 K. The increase in YS is attributed to the refinement of grain size, whereas, ductility and UTS are deteriorated by the presence of brittle Al2Ca, Mg3Sb2, and Ca2Sb phases. The best tensile properties are obtained in the AZXY9110 alloy owing to the presence of a lesser amount of brittle Al2Ca, and Ca2Sb phases resulted from the optimum content of 1.0Ca and 0.3Sb (wt.%). The fracture surface of the tensile specimen tested at ambient temperature reveals cleavage failure that changes to quasi-cleavage at 473 K. All the modified alloys exhibit superior creep resistance than the base AZ91 alloy. The combined additions of Ca and Sb are more effective in improving creep resistance than the individual additions. Individual Ca added AZX911 results superior creep resistance than the Sb added AZY911 is owing to the higher thermal stability of the Al2Ca phase in the former alloy compared to that of the Mg3Sb2 phase in the later one. The AZXY9120 alloy pertaining 2.0Ca and 0.3Sb (wt.%) exhibit the best creep resistance due to reduced amount of β-Mg17Al12 phase and presence of higher amount of dense network of thermally stable Al2Ca phase at grain boundaries. Post creep microstructural observation confirms the ability of the Al2Ca phase to withstand applied high stresses at elevated temperature without undergoing significant changes in its structure. The values of stress exponents and activation energies are in the range of 4.3 to 6.5 and 111.9±1.1 to 114.9±3.0 kJ/mol, which concludes dislocation climb controlled by pipe diffusion is the dominant creep mechanism for all the alloys in the temperature and stress level employed. The observed trend in creep rates with respect to the individual and combined additions of Ca and Sb in the AZ91 alloy was further confirmed by carrying out conventional compressive creep tests on all the alloys. It has been observed that the trend in creep rates, i.e., impression velocities in impression creep, and strain rates in compression creep obtained with respect to the individual and combined additions of Ca and Sb to the AZ91 alloy is the same. Corrosion resistance of all the modified alloys is better owing to the refined and reduced volume fraction of β-Mg17Al12 phase as well as grain refinement. Individual additions are better than mixed additions. The AZX911 alloy comprising individual Ca addition with a continuous network of Al2Ca phase reveals the lowest corrosion rate. Among the alloys comprising combined additions, the AZXY9120 alloy exhibits the best corrosion resistance due to higher and lower volume fraction of Al2Ca and Ca2Sb phases, respectively. To conclude, the individual and combined additions of Ca and Sb to the AZ91 alloy resulted in improved ambient and elevated temperature tensile properties as well as impression and compression creep behaviour without deteriorating corrosion resistance. Among the modified alloys, the AZXY9120 alloy exhibited the best properties considering its targeted powertrain application at elevated temperature. In addition, the tensile and creep properties of the squeeze-cast alloys in the present investigation were superior as compared to that of the alloys developed by gravity-cast.

In the present thesis, the influence of SiC nanoparticles additions on the creep, tensile, wear, and corrosion behaviour of the AZ91-2.0Ca-0.3Sb (wt.%) alloy fabricated by squeeze-casting has been investigated. For comparison, these properties are also investigated in the AZ91- 2.0Ca-0.3Sb alloy without nanoparticles addition. The nominal compositions of the fabricated alloy and nanocomposites are AZ91-2.0Ca-0.3Sb (AZXY9120), AZ91-2.0Ca-0.3Sb-0.5SiCnp (NC1), AZ91-2.0Ca-0.3Sb-1.0SiCnp (NC2), and AZ91-2.0Ca-0.3Sb-2.0SiCnp (NC3) (wt.%). A detailed microstructural characterization of the alloy and nanocomposites was carried out. An impression creep testing setup was employed for carrying out the creep tests in the stress and temperature range of 300-480 MPa and 448-523 K, respectively. The alloy and nanocomposites were tensile tested at ambient and elevated temperatures of 298, 423, and 473 K. The dry sliding wear tests were conducted employing a pin-on-disc setup at normal loads of 10, 20, 30 and 40 N at a sliding velocity of 1.2 m/s for a sliding distance of 1000 m. The corrosion responses of the alloy and nanocomposites in a 0.1 M NaCl solution at ambient temperature and pH 7.0 were evaluated by immersion, hydrogen evolution, and potentiodynamic polarization scan. The results indicate that the α-Mg, β-Mg17Al12, Al2Ca and Ca2Sb phases are present in both the alloy and nanocomposites. The additions of SiC nanoparticles refine the grain size, reduce the volume fraction of the β-Mg17Al12 phase, and increase the amount of Al2Ca phase, which is more pronounced with an increase in the nanoparticle content. All the nanocomposites exhibit superior creep resistance than the unreinforced alloy. The best creep resistance is obtained in the NC3 nanocomposite. The values of stress exponents and the activation energies are in the range of 4.5 to 6.2, and 101.9 ± 2.5 to 115.5 ± 3.2 kJ/mol suggesting the governing creep mechanism for the alloy and nanocomposites is dislocation climb controlled by pipe diffusion. The post creep microstructural observation confirms that the β-Mg17Al12 phase in the alloy is rigorously fragmented, and aligns in the direction of material flow, which deteriorates its creep resistance. In contrast, the presence of Al2Ca phase network and the SiC nanoparticles increase the dislocation pile-ups and dislocation tangling resulting in superior creep resistance of all the nanocomposites. All the nanocomposites illustrate greater yield strength (YS) and ultimate tensile strength (UTS) in contrast to the alloy at all the temperatures employed. The YS, UTS and elastic modulus of both the alloy and nanocomposites decline, whereas the work to fracture increases with a rise in temperature. Among the nanocomposites, the NC3 demonstrates the best tensile properties. All the nanocomposites display superior strain hardening response than the alloy, and the maximum strain hardening is perceived in the NC3 nanocomposite. The improved tensile properties of the nanocomposites are ascribed to the reduced grain size, the increase in dislocation density owing to CTE mismatch between the alloy and the SiC nanoparticles, the Orowan strengthening as well as the presence of a relatively higher amount of Al2Ca phase in the nanocomposites. The contributions to the improvement of strength of the nanocomposites in decreasing order of their influence are the Orowan strengthening, the strengthening due to CTE mismatch, and the Hall-Petch strengthening. The fracture surfaces of the tensile specimens tested at 298 K confirm the presence of transgranular cleavage fracture which remains unchanged at 473 K as well. The wear rate is lower for all the nanocomposites compared to the alloy. All the nanocomposites demonstrate the lower specific wear rates than the alloy. Among the nanocomposites, the NC3 exhibits the best tribological performance. The values of the coefficient of friction are lower for the nanocomposites than the alloy. The abrasion, adhesion, oxidation, and delamination are the dominant wear mechanisms. The 3D topography depicts that the addition of nanoparticles to the alloy results in the reduced surface roughness during the wear tests, confirming the superior wear behaviour of the nanocomposites compared to the alloy. All the nanocomposites demonstrate a superior corrosion resistance than the alloy, and the NC3 nanocomposite exhibits the highest corrosion resistance. The improved corrosion performance of the nanocomposites is attributed to the decrease in the potential difference between α-Mg and β-Mg17Al12 phases, reduced quantity of β-Mg17Al12 phase, and an increased amount of Al2Ca phase following the SiC nanoparticles additions. To conclude, all the nanocomposites display the superior creep, tensile, wear and corrosion response compared to the alloy. Among the nanocomposites, the NC3 nanocomposite illustrates the best creep, tensile, wear and corrosion performance. Therefore, the use of the nanocomposites would be more beneficial than the alloy.

In the present investigation, five new alloys AZ91+1.0Ca (AZX911), AZ91+0.5Bi (AZB910), AZ91+1.0Ca+0.5Bi (AZXB9110), AZ91+1.0Ca+1.0Bi (AZXB9111), AZ91+2.0Ca+0.5Bi (AZXB9120) (wt.%) have been fabricated by squeeze-cast. The first part of the thesis investigates the influence of combined additions of Ca and Bi on the microstructure, creep, tensile, and corrosion behaviour of the squeeze-cast AZ91 alloy. The same is also studied on the AZ91 alloy with and without single additions of Ca and Bi for comparison. Another three new alloys AZ91+0.5Bi+0.25Sr, AZ91+0.5Bi+0.5Sr, AZ91+1.0Bi+0.5Sr (wt.%) have also been fabricated by squeeze-cast. The second part of the thesis investigates the influence of combined additions of Bi and Sr on the microstructure and creep behaviour of the AZ91 alloy. The creep behaviour of all the alloys is evaluated using impression creep tests in the temperature and stress ranges of 423 to 523 K and 300 to 480 MPa, respectively. The tensile tests of the Ca and Bi added AZ91 alloys are performed at 298, 423, and 473 K with a strain rate of 8.33×10-5 s-1. The corrosion behaviour of the Ca and Bi added AZ91 alloys is studied by immersion, hydrogen evolution, and electrochemical corrosion tests at 0.5 wt.% NaCl solution (pH 7) at room temperature. Both the single and mixed contents of Ca and Bi in the AZ91 alloy refine the grain size of α-Mg and reduce the volume fraction of the β-Mg17Al12 phase considerably. The effect is more noticeable in combined additions than in individual additions. The reticular-shaped Al2Ca and needle-shaped Mg3Bi2 phases additionally form with the α-Mg and β-Mg17Al12 phases because of the sole Ca and Bi additions in the AZ91 alloy. The Al2Ca and Bi3Ca5 phases are formed when Ca and Bi are added together, suppressing the Mg3Bi2 phase formation. The modified AZ91-based alloys containing Ca and/or Bi exhibit improved creep behaviour than the AZ91 alloy at all the stress and temperature levels tested. The individual additions of the elements in the AZ91 alloy show a higher creep rate than the combined additions. The individual Ca addition is better than Bi addition for resisting creep deformation in the AZ91 alloy as the Al2Ca phase in the AZX911 alloy has superior thermal stability compared to that of the Mg3Bi2 phase in the AZB910 alloy. The AZXB9120 exhibits the best creep performance owing to the lower volume fraction of the β-Mg17Al12 phase and the existence of a larger quantity of thermally stable Al2Ca and Bi3Ca5 phases. The values of stress exponents and activation energies conclude that the dominant creep mechanism for all the alloys is dislocation climb aided by pipe diffusion. The microstructural investigation following creep indicates that the β-Mg17Al12 phase is broken into small pieces. In contrast, the thermally stable Al2Ca, Mg3Bi2, and Bi3Ca5 phases preserve their continuity, which results in piled-up dislocations and tangling of dislocations in the interior of the α-Mg grains that leads to the improved resistance to creep deformation of the modified AZ91 alloys. The values of yield strength (YS) are higher, and ductility is lower of all the modified alloys. The ultimate tensile strength (UTS) of the modified AZ91 alloys is lower except at 473 K. The UTS values decrease with an increase in test temperature for all the alloys. The improved YS of the modified alloys is owing to reduced grain size. The brittle Mg3Bi2, Al2Ca, and Bi3Ca5 phases in the modified alloys reduce their UTS and ductility. The transgranular cleavage fracture at 298 K changes to quasi-cleavage fracture at 473 K. Several dislocations piled up around the β-Mg17Al12 and Al2Ca phases are seen. All the modified alloys exhibit better corrosion resistance than the base AZ91 alloy. The AZX911 alloy unveils better corrosion resistance than the AZB910 alloy owing to the Al2Ca phase formation. The combined Ca and Bi added AZ91 alloys acquire better corrosion resistance than the individual Ca or Bi added AZ91 alloys. The AZXB9120 and AZXB9111 alloys exhibit the lowest and the highest corrosion rates among the combined additions. The combined Bi and Sr additions form the Al4Sr and Sr2Bi phases besides the α-Mg and β-Mg17Al12 phases and improve the creep resistance of the AZ91 alloy. The AZ91+1.0Bi+0.5Sr alloy reveals the best creep resistance among the alloys. The stress exponent and activation energy values of all the alloys confirm the pipe diffusion-controlled dislocation creep as the governing creep mechanism. The post creep microstructural study reveals several dislocations pile-ups around the Al4Sr and Sr2Bi phases resulting in improved creep resistance of the modified AZ91 alloys. To conclude, the additions of Ca and/or Bi improve the creep, tensile, and corrosion behaviour of the squeeze-cast AZ91 alloy. The effect is more significant with combined additions. The combined Bi and Sr additions also improve the creep behaviour of the AZ91 alloy. Therefore, the additions of Ca, Bi, and Sr to the AZ91 alloy are beneficial.

In the present investigation an attempt has been made to correlate microstructure with tensile, creep and corrosion behaviour of the AZ91 Mg alloy produced by three different casting techniques. All the as-cast alloys consist of primary Mg (α-Mg) and β-Mg17Al12 phases. The volume fraction of the β-Mg17Al12 phase is the highest in the ingot casting (IC), intermediate in the squeeze-casting (SC) and the lowest in the high pressure die-casting (HPDC). The tensile tests are performed at ambient, 150 and 200°C temperatures. The best tensile properties are exhibited by the SC alloy at all the temperatures employed in the present investigation owing to the presence of negligible porosity and relatively finer grain size. Fracture surfaces of the broken tensile specimens reveal quasi-cleavage fracture. The creep tests are performed in compression at a stress of 70 MPa and temperature of 150ºC. The best and worst creep resistance are exhibited by the SC and HPDC alloys with the IC alloy exhibiting the intermediate creep resistance. Poor creep resistance of the HPDC alloy is attributed to the presence of relatively higher amount of porosity that allows easy crack initiation and growth during creep tests. On the contrary, presence of negligible porosity and continuous network of eutectic phase contributes to the superior creep resistance of the SC alloy. Electrochemical corrosion tests of all the alloys are carried out at ambient temperature in 0.5 wt.% NaCl aqueous solution with neutral pH. The best and worst corrosion resistance are exhibited by the HPDC and IC alloys. The superior corrosion resistance of the HPDC alloy is attributed to the relatively finer grain size and higher percentage of Al dissolved in α-Mg phase. Thus, the SC alloy exhibits the best tensile and creep properties with intermediate corrosion resistance among the alloys employed in the present investigation.

Bestärkt durch das gesellschaftliche und wirtschaftliche Interesse an nachhaltigen und ressourcenschonenden Formen des Bauens gewinnen Holzkonstruktionen wieder unverkennbar an Bedeutung. Mit dieser Entwicklung bilden sich neue Konstruktionsprinzipien und Materialkombinationen im Bauwesen heraus, zu deren ingenieurtechnischer Beurteilung zum Teil keine ausreichenden Erkenntnisse vorliegen. Verbundkonstruktionen aus Holz und Glas sind eine innovative Bauweise, die zu einer höheren Materialeffizienz in Fassaden beiträgt, deren Wirkungsweise aber noch nicht ausreichend hinterfragt wurde. Werden Holz und Glas durch eine tragende Klebung verbunden, lässt sich das vielfach ungenutzte Tragpotenzial ausschöpfen, das eine in Scheibenebene belastete Verglasung aufweist. Die Qualität der Klebung entscheidet dabei über die Eigenschaften und das Leistungsvermögen des Bauteils. Die üblicherweise an dieser Schnittstelle eingesetzten Silikonklebstoffe weisen eine hohe Nachgiebigkeit und eine vergleichsweise geringe Festigkeit auf. Wenn die Verbundelemente als Aussteifung mitwirken sollen, bleibt ihr Einsatz deswegen auf Gebäude mit höchstens zwei Geschossen limitiert. Die vorliegende Arbeit trägt entscheidend zur Erweiterung der baulichen Möglichkeiten bei, indem sie der Anwendbarkeit von hochfesten Klebstoffen, die für den Einsatz im Bauwesen nur wenig erforscht sind, auf vielschichtige Weise nachgeht. Im Fokus stehen aussteifende Holz-Glas-Verbundelemente für die Fassade. Weder die Bauart noch das Bauprodukt Klebstoff sind derzeit in Deutschland in einer Norm erfasst. Das Klären der baurechtlichen Rahmenbedingungen ist daher unerlässlich und erfolgt mit engem Bezug zum konstruktiven Glasbau. Zusätzlich zur wissenschaftlichen Interpretation wird dadurch eine praxisnahe Bewertung der Versuchsergebnisse möglich, was ein Alleinstellungsmerkmal dieser Arbeit darstellt. Das Verformungsvermögen des Klebstoffs spielt eine zentrale Rolle bei der Materialauswahl und Gestaltung der Holz-Glas-Verbundelemente. Der Einfluss der Klebstoffsteifigkeit auf das Tragverhalten eines Einzelelements und auf dessen Interaktion mit den anderen Bestandteilen des Tragwerks wird an einem Modellgebäude untersucht. Auf Basis dieser Parameterstudie lassen sich drei Steifigkeitsbereiche definieren, auf die sich die Klebstoffauswahl für die weiteren Untersuchungen stützt. Der experimentelle Teil der Arbeit beginnt mit der ausführlichen Charakterisierung von sieben Klebstoffen. Davon werden zwei höherfeste Klebstoffe als geeignet identifiziert. Ein Silikonklebstoff wird als Referenzmaterial zur aktuellen Anwendungspraxis festgelegt. Das Hauptaugenmerk der folgenden Experimente richtet sich auf Aspekte der Alterungsbeständigkeit und des zeitabhängigen Materialverhaltens unter langandauernder mechanischer Beanspruchung. In labormaßstäblichen Alterungsprüfungen werden die Klebstoffproben unterschiedlichen Schadeinwirkungen ausgesetzt, die im Glas- und Fassadenbau relevant sind. Darüber hinaus erfolgen Kriechversuche an kleinen und großen Scherprüfkörpern. Letztere stellen einen besonderen Mehrwert dar, da sie eine realistische Klebfugengeometrie aufweisen und die Ergebnisse dadurch dem tatsächlichen Bauteilverhalten nahekommen. Für diese Zeitstandversuche wurde eine bislang einzigartige Versuchsanlage aus sechs Prüfrahmen mit Gasdruckfederbelastung entwickelt. Im Ergebnis zeigt sich, dass mit den gewählten höherfesten Klebstoffen die Festigkeit der nicht gealterten Klebschichten erwartungsgemäß gesteigert werden kann. Der Bruch des Fügepartners Holz wird zum maßgebenden Versagenskriterium. Die Verformungen des Verbundelements reduzieren sich gegenüber einer Silikonklebung deutlich. Allerdings offenbaren sich in einzelnen Alterungsszenarien und unter langandauernder Belastung auch Schwachstellen dieser Klebstoffe. Ihre Verwendung kann daher nur mit konstruktiven Kompensationsmaßnahmen oder durch Abschirmen der kritischen Einwirkungsgrößen empfohlen werden. Entsprechende Vorschläge werden bei der abschließenden Bewertung der Ergebnisse unterbreitet. Verfahren und Beurteilungsmethoden, die in dieser Arbeit angewendet und entwickelt werden, erleichtern die zukünftige Bewertung weiterer aussichtsreicher Klebstoffe für den Holz-Glas-Verbund.:1 Einleitung 13 1.1 Motivation 13 1.2 Zielsetzung 18 1.3 Abgrenzung 20 1.4 Vorgehensweise 21 2 Die Holz-Glas-Verbundbauweise 25 2.1 Tragprinzip und Wirkungsweise 25 2.2 Forschungsschwerpunkte und Anwendungen 27 2.2.1 Geklebte Verglasungssysteme für Fenster 27 2.2.2 Träger 28 2.2.3 Wandscheiben und Schubfelder 32 2.2.4 Verbundplatten 36 2.3 Tragendes Glas im Verbund 37 2.3.1 Relevanz für Holz-Glas-Verbundlösungen 37 2.3.2 Historische Vorbilder 37 2.3.3 Verbundglas und Verbund-Sicherheitsglas 38 2.3.4 Verbundträger 40 2.3.5 Wandscheiben aus Glas 43 2.4 Konstruktionsprinzipien von tragenden Wand und Fassadenelementen aus Holz und Glas 46 2.4.1 Aufbau 46 2.4.2 Verglasung 46 2.4.3 Ausbildung der Klebfuge 48 2.4.4 Marktreife Systeme mit Koppelleiste 49 2.4.5 Identifizieren geeigneter Tragsysteme 52 2.4.6 Skelett-, Tafel- und Massivholzbauweise 53 2.5 Zusammenfassung wesentlicher Erkenntnisse 55 3 Klebverbindungen im Glasbau 57 3.1 Fügen von Glas 57 3.1.1 Besondere Merkmale des Fügewerkstoffs 57 3.1.2 Wirkprinzip und Fügeverfahren 60 3.1.3 Vor- und Nachteile von Klebverbindungen 61 3.1.4 Glasoberfläche 65 3.2 Typische Anwendungsbeispiele im Glasbau 67 3.2.1 Klassifizierung 67 3.2.2 Einordung der Holz-Glas-Verbundbauweise 69 3.2.3 Structural Sealant Glazing 71 3.2.4 Ganzglaskonstruktionen 74 3.3 Planungsstrategien 76 3.3.1 Sicheres Bauteilversagen 76 3.3.2 Redundanz und Versagensszenarien 78 3.3.3 Besonderheiten bei geklebten Verglasungen 80 3.4 Baurechtliche Rahmenbedingungen 82 3.4.1 Normung und Verfahrensweise in Deutschland 82 3.4.2 Harmonisierung auf europäischer Ebene 84 3.4.3 ETAG 002 – Leitlinie für Structural Glazing 86 3.4.4 Der Weg zur geklebten Glaskonstruktion 88 4 Einfluss der Klebstoffsteifigkeit auf aussteifende Holz-Glas-Verbundtragwerke 91 4.1 Aussteifung von Holzbauten 91 4.2 Berechnungsverfahren 92 4.2.1 Begründung der Auswahl der Verfahren 92 4.2.2 Verteilung von Horizontallasten auf die Wandscheiben eines Aussteifungssystems 93 4.2.3 Wandscheibe als Schubfeld 95 4.2.4 Federmodelle 97 4.3 Randbedingungen für die Analyse 101 4.3.1 Modellgebäude 101 4.3.2 Konstruktive Gestaltung 103 4.3.3 Lastannahmen 104 4.4 Parameterstudie 107 4.4.1 Nachgiebigkeit der Kernwände 107 4.4.2 Nachgiebigkeit eines Verbundelements 108 4.4.3 Auswirkung der Elementanordnung 112 4.4.4 Lastumlagerung bei Ausfall von Elementen 114 4.4.5 Horizontallastanteil auf Fassade und Kern 116 4.5 Rückschlüsse auf die Tragsystemgestaltung und die Klebstoffauswahl 120 5 Materialauswahl und -charakterisierung 123 5.1 Untersuchungsprogramm 123 5.2 Materialeigenschaften der Fügeteile 124 5.2.1 Glas 124 5.2.2 Holz und Holzwerkstoffe 126 5.3 Klebstoffe 128 5.3.1 Auswahlkriterien für Holz-Glas-Klebungen 128 5.3.2 Vorauswahl der Klebstoffsysteme 130 5.4 Experimentelle Methoden zur Charakterisierung der Klebstoffe 134 5.4.1 Dynamisch-mechanische Analyse 134 5.4.2 Einaxialer Zugversuch 135 5.4.3 Scherversuch 138 5.5 Versuchsergebnisse 141 5.5.1 Glasübergangstemperatur 141 5.5.2 Spannungs-Dehnungs-Beziehung 145 5.5.3 Einpunktkennwerte 150 5.5.4 Scherfestigkeit und Bruchbildanalyse 151 5.6 Klebstoffauswahl für die Hauptuntersuchungen 155 6 Experimentelle Untersuchungen an Klebverbindungen im Labormaßstab 157 6.1 Methodik 157 6.1.1 Untersuchungsgegenstand 157 6.1.2 Beurteilungsgrundlagen 158 6.1.3 Untersuchungsprogramm 159 6.1.4 Auswertungsmethoden 162 6.2 Geometrie und Herstellung der Prüfkörper 164 6.2.1 Prüfkörper zum Bestimmen der Haftfestigkeit vor und nach künstlicher Alterung 164 6.2.2 Scherprüfkörper für Kriechversuche 165 6.2.3 Vorbereiten und Konditionieren der Proben 166 6.3 Verfahren zur mechanischen Prüfung und zur künstlichen Alterung 168 6.3.1 Zug- und Scherversuche 168 6.3.2 Lagerung unter UV-Bestrahlung 170 6.3.3 Lagerung in Reinigungsmittellösung 171 6.3.4 Holzfeuchtewechsel bei +20 °C 172 6.3.5 Lagerung in schwefeldioxidhaltiger Atmosphäre 173 6.3.6 Kriechversuche 174 6.4 Auswertung der Versuchsergebnisse 176 6.4.1 Anfangsfestigkeit im Scherversuch 176 6.4.2 Anfangsfestigkeit im Zugversuch 181 6.4.3 Sichtbare Veränderungen der Klebschicht 183 6.4.4 Restfestigkeit nach Alterung 185 6.4.5 Analyse der Versagensmuster 189 6.4.6 Kriechverhalten 192 6.4.7 Restfestigkeit nach Vorbelastung 198 7 Experimentelle Untersuchungen an bauteilähnlichen Prüfkörpern 201 7.1 Untersuchungsprogramm und Methodik 201 7.1.1 Ziel der Untersuchungen 201 7.1.2 Materialien 202 7.1.3 Großer Scherprüfkörper 203 7.1.4 Herstellung der Prüfkörper 205 7.1.5 Versuchsprogramm – Bauteilversuche 207 7.2 Entwicklung eines Kriechprüfstands 210 7.2.1 Prüfrahmen 210 7.2.2 Lasteinleitung 211 7.2.3 Belastungsvorgang 212 7.2.4 Messtechnik und Monitoring 213 7.2.5 Modifikation für Kurzzeitversuche 214 7.3 Große Scherversuche unter Kurz- und Langzeiteinwirkung 215 7.3.1 Tragfähigkeit bei kurzzeitiger Lasteinwirkung 215 7.3.2 Spannungsverteilung im Glas 219 7.3.3 Kriechversuche mit 1000 Stunden Laufzeit 221 7.3.4 Verlängerte Kriechversuche am Klebstoff mit mittlerer Steifigkeit 226 7.3.5 Tragfähigkeit nach Vorbelastung 230 8 Bewertung und Handlungsempfehlung 231 8.1 Alterungsverhalten 231 8.2 Korrelation der Ergebnisse aus Fügeteil- und 233 Bauteilversuchen 8.2.1 Versuche bei kurzzeitiger Lasteinwirkung 233 8.2.2 Versuche bei langandauernder Lasteinwirkung 235 8.3 Der Vorzugsklebstoff und seine Einsatzgrenzen 238 8.4 Konstruktion 241 9 Zusammenfassung und Ausblick 243 9.1 Zusammenfassung 243 9.2 Ausblick 249 10 Literatur 253 11 Abbildungsverzeichnis 263 12 Tabellenverzeichnis 267 13 Bezeichnungen 268 Anhang A Materialkennwerte zur Klebstoffauswahl 271 B Klebverbindungen im Labormaßstab 287 C Bauteilähnliche Prüfkörper 373
Wooden constructions are on the rise again – encouraged by a strong public and economic trend towards sustainable and resource efficient buildings. Spurred by this growing interest novel design principles and material assemblies in architecture and the building industry evolve. These developments require further research due to the absence of evaluation tools and insufficient knowledge about their design. Load-bearing timber-glass composite elements could contribute to a more efficient use of materials in façade constructions. In this case a linear adhesive bond connects the glass pane to the timber substructure. This enables an in-plane loading of the glass whose capacity is not used to its full potential in conventional façades as it is solely applied as an infill panel. The quality of the adhesive bond defines the characteristics and the performance of the whole structural component. Structural sealants such as silicones, which are typically used for the joint, provide a high flexibility and only a low load-bearing capacity. Considering such elements being part of a bracing system, the mentioned characteristics limit the application range to buildings with not more than two stories. This thesis widens the scope with an in-depth examination of high-modulus adhesives, which have not yet been evaluated for their use in building constructions. Timber-glass composite elements used as a bracing component in façades are the focus of this work. Neither the full structural component nor the adhesive have yet been included into German building standards. Hence it is essential to assess the general requirements of their application. The relevant aspects are clarified in the context of glass constructions. In addition to the scientific discussion of the results, this approach facilitates also a practical evaluation of the findings, which is a unique feature of this work. The deformability of the adhesive becomes a crucial criterion when selecting the individual materials and designing the timber-glass composite elements. A case study assesses the influence of the adhesive stiffness on the behavior of a single element and its interaction with other members of the structural system. Based on the results, three different stiffness classes are introduced to support the selection process of the adhesives to be examined in further investigations. The experimental part of this work is initiated by a comprehensive characterization of seven shortlisted adhesives. The results enable a further differentiation of suitable materials. Two adhesives qualified as suitable for the main experiments. A silicone adhesive complements the test series to serve as a reference material to the current practice. In the next phase attention is drawn to the ageing stability and on the time-dependent material behavior of the adhesives under long-term loading. Small-scale specimens made from adhesively joint timber and glass pieces are exposed to different ageing scenarios which relate to the impacts typically encountered in façades. Beyond that, creep tests are carried out on small and large shear specimen. The latter provide extra benefit as they comprise long linear adhesive joints resembling virtually the situation in a real-size element. A specific long-term test rig was developed for this purpose comprising a loading unit with gas pressurized springs. Based on the results it can be concluded that joints with adhesives of high and intermediate stiffness enable an increase of characteristic failure loads and a significant reduction of deformation. With the stiffer joint near-surface rupture of timber fibers becomes the prevailing failure mechanism. The timber strength limits further loading of the adhesive joint. However, ageing and creep testing reveal also shortcomings of the adhesives. Their application can only be recommended if redundant compensation measures are taken or the joint is protected against critical environmental impacts. Appropriate solutions are proposed with the final recommendations of this work. Methods and assessment tools that have been developed and tested for this work offer the possibility of a more straight-forward evaluation of further promising adhesives and their use in load-bearing timber-glass composites.:1 Einleitung 13 1.1 Motivation 13 1.2 Zielsetzung 18 1.3 Abgrenzung 20 1.4 Vorgehensweise 21 2 Die Holz-Glas-Verbundbauweise 25 2.1 Tragprinzip und Wirkungsweise 25 2.2 Forschungsschwerpunkte und Anwendungen 27 2.2.1 Geklebte Verglasungssysteme für Fenster 27 2.2.2 Träger 28 2.2.3 Wandscheiben und Schubfelder 32 2.2.4 Verbundplatten 36 2.3 Tragendes Glas im Verbund 37 2.3.1 Relevanz für Holz-Glas-Verbundlösungen 37 2.3.2 Historische Vorbilder 37 2.3.3 Verbundglas und Verbund-Sicherheitsglas 38 2.3.4 Verbundträger 40 2.3.5 Wandscheiben aus Glas 43 2.4 Konstruktionsprinzipien von tragenden Wand und Fassadenelementen aus Holz und Glas 46 2.4.1 Aufbau 46 2.4.2 Verglasung 46 2.4.3 Ausbildung der Klebfuge 48 2.4.4 Marktreife Systeme mit Koppelleiste 49 2.4.5 Identifizieren geeigneter Tragsysteme 52 2.4.6 Skelett-, Tafel- und Massivholzbauweise 53 2.5 Zusammenfassung wesentlicher Erkenntnisse 55 3 Klebverbindungen im Glasbau 57 3.1 Fügen von Glas 57 3.1.1 Besondere Merkmale des Fügewerkstoffs 57 3.1.2 Wirkprinzip und Fügeverfahren 60 3.1.3 Vor- und Nachteile von Klebverbindungen 61 3.1.4 Glasoberfläche 65 3.2 Typische Anwendungsbeispiele im Glasbau 67 3.2.1 Klassifizierung 67 3.2.2 Einordung der Holz-Glas-Verbundbauweise 69 3.2.3 Structural Sealant Glazing 71 3.2.4 Ganzglaskonstruktionen 74 3.3 Planungsstrategien 76 3.3.1 Sicheres Bauteilversagen 76 3.3.2 Redundanz und Versagensszenarien 78 3.3.3 Besonderheiten bei geklebten Verglasungen 80 3.4 Baurechtliche Rahmenbedingungen 82 3.4.1 Normung und Verfahrensweise in Deutschland 82 3.4.2 Harmonisierung auf europäischer Ebene 84 3.4.3 ETAG 002 – Leitlinie für Structural Glazing 86 3.4.4 Der Weg zur geklebten Glaskonstruktion 88 4 Einfluss der Klebstoffsteifigkeit auf aussteifende Holz-Glas-Verbundtragwerke 91 4.1 Aussteifung von Holzbauten 91 4.2 Berechnungsverfahren 92 4.2.1 Begründung der Auswahl der Verfahren 92 4.2.2 Verteilung von Horizontallasten auf die Wandscheiben eines Aussteifungssystems 93 4.2.3 Wandscheibe als Schubfeld 95 4.2.4 Federmodelle 97 4.3 Randbedingungen für die Analyse 101 4.3.1 Modellgebäude 101 4.3.2 Konstruktive Gestaltung 103 4.3.3 Lastannahmen 104 4.4 Parameterstudie 107 4.4.1 Nachgiebigkeit der Kernwände 107 4.4.2 Nachgiebigkeit eines Verbundelements 108 4.4.3 Auswirkung der Elementanordnung 112 4.4.4 Lastumlagerung bei Ausfall von Elementen 114 4.4.5 Horizontallastanteil auf Fassade und Kern 116 4.5 Rückschlüsse auf die Tragsystemgestaltung und die Klebstoffauswahl 120 5 Materialauswahl und -charakterisierung 123 5.1 Untersuchungsprogramm 123 5.2 Materialeigenschaften der Fügeteile 124 5.2.1 Glas 124 5.2.2 Holz und Holzwerkstoffe 126 5.3 Klebstoffe 128 5.3.1 Auswahlkriterien für Holz-Glas-Klebungen 128 5.3.2 Vorauswahl der Klebstoffsysteme 130 5.4 Experimentelle Methoden zur Charakterisierung der Klebstoffe 134 5.4.1 Dynamisch-mechanische Analyse 134 5.4.2 Einaxialer Zugversuch 135 5.4.3 Scherversuch 138 5.5 Versuchsergebnisse 141 5.5.1 Glasübergangstemperatur 141 5.5.2 Spannungs-Dehnungs-Beziehung 145 5.5.3 Einpunktkennwerte 150 5.5.4 Scherfestigkeit und Bruchbildanalyse 151 5.6 Klebstoffauswahl für die Hauptuntersuchungen 155 6 Experimentelle Untersuchungen an Klebverbindungen im Labormaßstab 157 6.1 Methodik 157 6.1.1 Untersuchungsgegenstand 157 6.1.2 Beurteilungsgrundlagen 158 6.1.3 Untersuchungsprogramm 159 6.1.4 Auswertungsmethoden 162 6.2 Geometrie und Herstellung der Prüfkörper 164 6.2.1 Prüfkörper zum Bestimmen der Haftfestigkeit vor und nach künstlicher Alterung 164 6.2.2 Scherprüfkörper für Kriechversuche 165 6.2.3 Vorbereiten und Konditionieren der Proben 166 6.3 Verfahren zur mechanischen Prüfung und zur künstlichen Alterung 168 6.3.1 Zug- und Scherversuche 168 6.3.2 Lagerung unter UV-Bestrahlung 170 6.3.3 Lagerung in Reinigungsmittellösung 171 6.3.4 Holzfeuchtewechsel bei +20 °C 172 6.3.5 Lagerung in schwefeldioxidhaltiger Atmosphäre 173 6.3.6 Kriechversuche 174 6.4 Auswertung der Versuchsergebnisse 176 6.4.1 Anfangsfestigkeit im Scherversuch 176 6.4.2 Anfangsfestigkeit im Zugversuch 181 6.4.3 Sichtbare Veränderungen der Klebschicht 183 6.4.4 Restfestigkeit nach Alterung 185 6.4.5 Analyse der Versagensmuster 189 6.4.6 Kriechverhalten 192 6.4.7 Restfestigkeit nach Vorbelastung 198 7 Experimentelle Untersuchungen an bauteilähnlichen Prüfkörpern 201 7.1 Untersuchungsprogramm und Methodik 201 7.1.1 Ziel der Untersuchungen 201 7.1.2 Materialien 202 7.1.3 Großer Scherprüfkörper 203 7.1.4 Herstellung der Prüfkörper 205 7.1.5 Versuchsprogramm – Bauteilversuche 207 7.2 Entwicklung eines Kriechprüfstands 210 7.2.1 Prüfrahmen 210 7.2.2 Lasteinleitung 211 7.2.3 Belastungsvorgang 212 7.2.4 Messtechnik und Monitoring 213 7.2.5 Modifikation für Kurzzeitversuche 214 7.3 Große Scherversuche unter Kurz- und Langzeiteinwirkung 215 7.3.1 Tragfähigkeit bei kurzzeitiger Lasteinwirkung 215 7.3.2 Spannungsverteilung im Glas 219 7.3.3 Kriechversuche mit 1000 Stunden Laufzeit 221 7.3.4 Verlängerte Kriechversuche am Klebstoff mit mittlerer Steifigkeit 226 7.3.5 Tragfähigkeit nach Vorbelastung 230 8 Bewertung und Handlungsempfehlung 231 8.1 Alterungsverhalten 231 8.2 Korrelation der Ergebnisse aus Fügeteil- und 233 Bauteilversuchen 8.2.1 Versuche bei kurzzeitiger Lasteinwirkung 233 8.2.2 Versuche bei langandauernder Lasteinwirkung 235 8.3 Der Vorzugsklebstoff und seine Einsatzgrenzen 238 8.4 Konstruktion 241 9 Zusammenfassung und Ausblick 243 9.1 Zusammenfassung 243 9.2 Ausblick 249 10 Literatur 253 11 Abbildungsverzeichnis 263 12 Tabellenverzeichnis 267 13 Bezeichnungen 268 Anhang A Materialkennwerte zur Klebstoffauswahl 271 B Klebverbindungen im Labormaßstab 287 C Bauteilähnliche Prüfkörper 373