In this experimental investigation, the tensile creep behavior of commercial-purity molybdenum sheet at temperatures between 1300°C and 1700°C is critically evaluated, based upon experimental creep testing and microstructural characterizations. The high-temperature properties of molybdenum are of interest because there are many applications in which molybdenum and molybdenum alloys are used at elevated temperatures. Understanding of the creep mechanisms and the constitutive relations between stress and strain at elevated temperatures is needed in order to determine if molybdenum is an appropriate choice for a given high-temperature design application and to accurately predict its creep life. The creep behavior of two commercially-available grades of molybdenum was determined using short-term creep tests (1/2 to 14 hours) at slow to moderate true-strain rates of 10⁻⁶ to 10⁻⁴ s⁻¹ and temperatures between 1300°C and 1700°C. High-temperature, uniaxial tensile testing was used to produce data defining the relationship between tensile creep strain-rate and steady-state flow stress at four temperatures: 1340°C, 1440°C, 1540°C, 1640°C. Microstructural changes that occurred during creep testing were evaluated and compared to changes resulting from elevated temperature exposure alone. Mechanisms for dynamic abnormal grain growth that occurred during creep testing and the causes of the microstructural changes that occurred as a function of temperature are discussed. / text

Bioinspirierte Polymere, die die Multidomänenstruktur des Muskelproteins Titin imitieren, wurden auf Grundlage von zuvor synthetisierten, zyklischen Präpolymeren, die Wasserstoffbrückenbindungen-tragende Monomere enthalten, hergestellt und hinsichtlich ihrer mechanischen Eigenschaften untersucht.  Zunächst wurde die Ringexpansionspolymerisation (REP) zur Erzeugung zyklischer Makromoleküle, die auf einer von Nishikubo et al. entwickelten, lebenden Gruppentransferpolymerisation von Thiiranmonomeren mit Acylgruppen-tragenden Initiatoren basiert, eingehend untersucht. Im Speziellen wurde ein System, bestehend aus dem zyklischen Initiator 2,4-Thiazolidindion (TZD) und Derivaten desselben, dem Katalysator Tetrabutylammoniumchlorid, verschiedenartig substituierten Thiiranmonomeren 2-(Phenoxymethyl)thiiran (PMT), 2-Methylthiiran (MT), 2-(tert-Butoxymethyl)thiiran (TBMT), 2-((o-Methylphenoxy)methyl)thiiran (MPMT) und dem Lösungsmittel N-Methylpyrrolidin-2-on verwendet. Bei der Insertion der Monomere MT, TBMT und MPMT in TZD, die unter guter Kontrolle des Polymerisationsgrads und der Dispersität stattfand, wurde eine Verschmelzung der Ringe zu größeren Ringstrukturen mit einem Verschmelzungsgrad von bis zu zwei, bei Verwendung von PMT sogar von bis zu vier beobachtet. Der Grad dieser Verschmelzung nahm im Fall von PMT mit zunehmender Monomerkonzentration, zunehmendem molaren Monomer-zu-Initiator-Verhältnis und zunehmender Reaktionstemperatur ab, während er bei den anderen Monomeren keine Konzentrations- und Temperaturabhängigkeit zeigte. Durch Anpassung der Molmassenverteilungen mittels einer Summe von Gauß-Funktionen im Fall der PMT-Polymere konnte die zeitliche Änderung der molaren Anteile der verschiedenen Ringspezies verfolgt werden. So wurden für Polymerkonzentrationen von 14 bis 52 Gew-% Geschwindigkeitskoeffizienten der Verschmelzung, die sich über Größenordnungen von 10^(−2) bis 10^(−6) L/mol/s erstrecken, ermittelt. Bei Verwendung von in 3-Position substituierten TZD-Derivaten wurde eine Zunahme der Anzahl verschmolzener Makrozyklen von bis zu sieben festgestellt. Die Bildung zyklischer Strukturen wurde mittels Massenspektrometrie und rasterkraftmikroskopischer (AFM) Aufnahmen gezeigt.  Neben den Homopolymerisationen wurden zyklische (AB)n-Multiblockcopolymere aus MT und PMT mit bis zu acht aus der Ringverschmelzung resultierenden Blöcken synthetisiert. Sie zeigten im Zugversuch, aufgrund der verschiedenen Topologien, im Vergleich zu linearen Diblockcopolymeren ähnlicher Zusammensetzung, deutliche Unterschiede in der maximalen Zugdehnung und der Zähigkeit.  Weiterhin wurden die eingangs erwähnten bioinspirierten Polymere durch Kombination von zyklischen und linearen Segmenten hergestellt und auf ihre mechanischen Eigenschaften untersucht. Dazu wurden zyklische (ABC)n-Multiblockcopolymere, die zusätzlich einen kurzen Block des Monomers Ethyl-2-(4-(thiiran-2-ylmethoxy)benzamido)acetat (ETBAA) enthielten, der zur Ausbildung selbstkomplementärer Wasserstoffbrückenbindungen in der Lage ist, synthetisiert. Diese Präpolymere wurden mittels 1,3-dipolarer Cycloaddition in einer Polyadditionsreaktion mit einem niedermolekularen, bifunktionellen Verknüpfungsagens oder mit monofunktionellem Poly-n-butylacrylat (PBA) bzw. Polymethylacrylat (PMA), welche mittels RAFT-Polymerisation hergestellt wurden, verknüpft. So konnte im ersten Fall eine Poly-Ringpolymer-Topologie mit bis zu 19 nachgewiesenen Wiederholeinheiten und im zweiten Fall ein Polymer mit Kette–Ring–Kette-Topologie erhalten werden.  Untersuchungen der Proben im Zugversuch zeigten beim Kette–Ring–Kette-Polymer bis auf eine höhere Elastizität keine verbesserten Materialeigenschaften im Vergleich zum linearen PMA-Präpolymer. Die Poly-Ringpolymere hingegen zeigten im Gegensatz zu den Ringpolymeren ein einzigartiges Spannungs-Dehnungsverhalten, bessere Elastizitätseigenschaften und eine Erhöhung der anwendbaren Spannung bei gleicher Dehnung. Dies wurde durch den Einfluss inter- und intramolekular ausgebildeter physikalischer Bindungen durch die enthaltenen selbstkomplementären Wasserstoffbrückenbindungsmotive hervorgerufen. Eines der untersuchten Poly-Ringpolymere zeigte aufgrund der Ausbildung eines reversiblen physikalischen Netzwerkes sogar ein Formgedächtnis und die Fähigkeit zu einer partiellen Selbstheilung.

No description available.

Carbon fiber is a lightweight, versatile material with many current and potential applications. To be able to expand the market for carbon fiber composites in other areas than special applications the production costs must be reduced. One way of accomplishing this could be to use a less expensive raw material where lignin is a good example as it can be provided at lower cost, is renewable and abundantly available compared to commercially used raw materials today. So far, the mechanical properties of lignin-based carbon fibers are inferior relative to commercial carbon fibers. For lignin-based carbon fibers to enter the commercial market more research is necessary to gain knowledge of the conversion of lignin to carbon fiber. The LightFibre project investigates the possibilities to produce carbon fibers based on a mixture of softwood kraft lignin and cellulose. The kraft lignin is isolated from black liquor in the kraft/sulfate process with the LignoBoost process. This master thesis project was conducted within in the LightFibre project and evaluated whether metal ions generally present in kraft lignin had an influence on the final carbon fiber quality in terms of mechanical properties and morphology. The mechanical properties were determined with tensile testing, the morphology by scanning electron microscopy (SEM) and the relative abundance of studied elements with electron dispersive spectroscopy (EDS). The influence of the chosen metal ions was tested by impregnation of dry-jet wet spun prefibers based on 70 wt.% softwood kraft lignin and 30 wt.% dissolving pulp cellulose. The fibers were impregnated in room temperature with solutions containing Na2SO4, K2SO4, MgSO4, FeSO4 and Al2(SO4)3 salts where the cations were the focus in these trials. The concentrations used for impregnation were 0.2 and 1M of the cations. The obtained mechanical properties of the carbon fibers of the samples impregnated with different metal ions did not deviate significantly from the reference which had a tensile strength of 870 MPa and tensile modulus of 68 GPa. The analysis of morphology with SEM showed no defects or damage of any of the fibers. Therefore, it was concluded that the impregnated metal ions: K+, Na+, Al3+, Mg2+ and Fe2+ at the obtained levels in the fibers cause no effects on the fibers during the stabilization and carbonization that affects the mechanical performance of final carbon fiber.  The amount of potassium in one of the samples was estimated to 0.1 wt.%. From the results of this study it may be suggested that the general recommendation of <0.1 wt.% ash in lignin can be exceeded, for dry-jet wet-spun kraft lignin/cellulose-based carbon fibers.

Iron-tannate dyes have been used for thousands of years and on many continents to colour materials that are now part of our cultural heritage shades of black, grey, or brown. Cellulosic and proteinaceous yarns and woven textiles have been dyed with iron-tannate dyes to form objects or components of objects for domestic and ceremonial use. Unfortunately, the longevity and useful lifetime of iron-tannate dyed objects is threatened by the dye itself which accelerates the degradation of organic materials through metal-catalysed oxidation and acid-catalysed hydrolysis. The accelerated degradation causes weakening, discolouration, and embrittlement of the organic materials at a faster rate than undyed equivalents and if left unimpeded, weakens the objects to the point that they are no longer able to be exhibited without damage. In some cases the degradation is so great that the dyed areas of the objects have crumbled to dust. At present there is no suitable chemical stabilisation method available with which to inhibit this degradation. An aqueous treatment is available for successfully stabilising paper containing iron gall ink; iron gall ink is chemically similar to iron-tannate dye. However, the aqueous nature of this treatment makes it unsuitable for weakened fibres, water soluble components, and water sensitive materials which may be part of a composite material containing iron-tannate dye. Non-aqueous treatments are therefore urgently needed in order to preserve our iron-tannate dyed cultural heritage for future generations.In this project a range of non-aqueous antioxidants and a non-aqueous deacidifier (described in Chapter 8) were tested alongside existing aqueous treatment in order to establish their ability to slow down the degradation of a range of model iron-tannate dyed textiles (Chapters 9 and 10). Model textiles were developed as part of the project (Chapters 3-5) to be substitutes for historic materials in these stabilisation studies. Validation of the model textiles for this purpose (Chapter 6) involved the comparison of the model textiles with selected historic iron-tannate dyed objects within the British Museum’s collection (Chapter 6). The historic objects and the properties of the model textiles before and after accelerated ageing (Chapters 5 and 6) and before and after treatment application (Chapters 9 and 10) have been characterised using a variety of analytical techniques (Chapter 2). In order to determine which accelerated ageing conditions were the most suitable for this project various combinations of elevated temperature and either cycling or stable relative humidity were tested for their ability to produce noticeable changes in the properties of the dyed model textiles within four weeks of ageing (Chapter 7). This project is an AHRC/EPSRC funded Science and Heritage Programme PhD in which the British Museum has been a collaborative institution. Among other wider dissemination methods, research from this project has been presented to the public on numerous occasions at gallery tours and Science Day events at the British Museum.

This thesis deals with analyses of thermoplastic welded joints. Experiments were performed, in which the not-welded specimens and specimens with cruciform welded joints were tested by tensile and three-point bending test. For these measurements, polypropylene and polyethylene specimens were used. Afterwards, the analyses of specimen models were made in the ANSYS programme. The results of the analyses were compared with figures of the analytic calculations and measurements.

This paper reviews the effects of accelerated aging with increased humidity and temperature on cellulose-based composites. The composites consist of a matrix of plastic reinforced with cellulose fibers. The company Biofiber Tech Sweden AB provided four different composites and a conventional polyolefin as reference. The aim was to examine changes in mechanical properties, chemical composition and appearance after aging, as well as variations between materials. Two different climate conditions were tested, 85% RH and <10% RH, both in 90℃. A climate chamber and an oven were used to create the extreme environmental conditions. To analyze the results, tensile testing and FTIR were performed, and color intensity and density were measured. All samples decreased in color intensity throughout aging, and dark irregularities appeared on some of the samples exposed to high humidity, which may be due to fungal formation. The tensile testing showed a general difference between high and low RH and the toughness showed a tendency to decline with aging in high humidity for many samples. The FTIR measurements also did not show any general trend. To improve the study, it would be desirable to age the material for a longer time and at a higher temperature. Overall, more samples and measurements within each characterisation technique would be needed to achieve more reliable results. Nevertheless, this study hopes to be a starting point for further research on the long-term durability of Biofiber Tech’s composites.

No description available.

<p>  </p> <p>This thesis is motivated by the author’s observation that no systematic methodology is available to characterize and model mechanical behaviors of 3D printed parts in terms of their elastic modulus and critical loading capacities. Note that the more controlled and steadier printing process is, the easier the mechanical properties parts can be predicted. This research focuses on the methods for the prediction and validation of mechanical properties of 3D printed parts, and the focus is the responses of the printed parts subjected to tensile loads. The mathematic models are derived to characterize the mechanical properties of a part along three principal directions, and the models are validated experimentally by following the American Society for Testing and Materials (ASTM) D638 testing standards. It is assumed that a unidirectional plane stress occurs to each lamina to (1) simplify a compliance matrix with a size 3 by 3 and (2) characterize the mechanical properties by the elastic modules and strengths in three principal directions. Two mathematical models are developed using the experimental data from the classical laminate theory and finite element analysis (FEA) by the SolidWorks. Both of the developed models are used to predict the ultimate tensile strength and Young’s modulus of the specimens that are printed by setting different raster angles on different layers. This thesis work aims to (1) gain a better understanding of the impact of printing parameters on the strengths of printed parts and (2) explore the feasibility of using the classical laminate theory to predict the mechanical properties of the parts printed with different raster angles and patterns. To validate the proposed mathematic models, parts by FDM are tested by following the ASTM testing standards; moreover, it testifies if the selected ASTM-D638 is suitable to test 3D printed parts by FDM. </p>

Additive manufacturing (AM) processes may introduce large residual stresses in the as-built part, in particular the laser powder bed fusion process (L-PBF). The residual stress state is an inherent consequence of the heterogeneous heating and subsequent cooling during the process. L-PBF has become renowned for its “free complexity” and rapid prototyping capabilities. However, it is vital to ensure shape stability after the component is removed from the build plate, which can be problematic due to the residual stress inducing nature of this manufacturing process. Residual stresses can be analyzed via many different characterization routes (e.g. X-ray and neutron diffraction, hole drilling, etc.), both quantitatively and qualitatively. From an industrial perspective, most of these techniques are either prohibitively expensive, complex or too slow to be implementable during the early prototyping stages of AM manufacturing. In this work a deformation based method employing a specific geometry, a so called “keyhole”-geometry, has been investigated to qualitatively evaluate the effect of different stress relief annealing routes with respect to macroscopic part deformation, mechanical properties and microstructure. Previous published work has focused on structures with open geometry, commonly referred to as bridge-like structures where the deformation required for analysis occurs during removal from the build plate. The proposed keyhole-geometry can be removed from the build plate without releasing the residual stresses required for subsequent measurement, which enables bulk manufacturing on single build plates, prior to removal and stress relief annealing.  Two L-PBF manufactured austenitic stainless steel alloys were studied, 316L and 21-6-9. Tensile specimen blanks were manufactured and the subsequent heat treatments were carried out in pairs of keyhole and tensile blank. Both a contact (micrometer measurement), and a non-contact (optical profilometry) method were employed to measure the residual stress induced deformation in the keyholes. The annealing heat treatment matrix was iteratively expanded with input from the deformation analysis to find the lowest temperature at which approximately zero deformation remained after opening the structure via wire electrical discharge machining. The lowest allowable annealing temperature was sought after to minimize strength loss.  After stress relief annealing at 900 ℃ for 1 hour, the 316L keyhole-geometry was considered shape stable. The lateral micrometer measurement yielded a length change of 1 µm, and a radius of 140 m (over the 22 mm top surface) was assigned from curve fitting the top surface height profiles. The complementary microstructural characterization revealed that this temperature corresponded to where the last remains of the cellular sub-grain structures disappears. Tensile testing showed that the specimen subjected to the 900 ℃ heat treatment had a marked reduction in yield stress (YS) compared to that of the as-built: 540 MPa → 402 MPa, whereas ultimate tensile strength (UTS) only reduced slightly: 595 MPa → 570 MPa. The ductility (4D elongation) was found to be ~13 % higher for the specimen heat treated at 900 ℃ than that of the as-built specimen, 76% and 67% respectively.  For alloy 21-6-9 the residual stress induced deformation minimum (zero measurable deformation) was found after stress relief heat treatment at 850 ℃ for 1 hour. Slight changes in the microstructure were observable through light optical microscopy when comparing the different heat treatment temperatures. The characteristic sub-grain features associated with alloy 316L were not verified for alloy 21-6-9. Similar to the results for 316L, UTS was slightly lower for the tensile specimen subjected to the heat treatment temperature required for shape stability (850 ℃) compared to the as-built specimen: 810 MPa → 775 MPa. The measured ductility (4D elongation) was found to be approximately equal for the as-built (47%), and heat treated (48%) specimen. As-built material exhibited a YS of 640 MPa while the heat treated specimen had a YS of 540 MPa. For alloy 21-6-9, the lateral micrometer deformation measurements were compared with stress relaxation testing performed at 600 ℃, 700℃ and 800 ℃. Stress relaxation results were in good agreement with the results from the lateral deformation measurements.  The study showed that for both steel alloys, the keyhole method could be successfully employed to rapidly find a suitable stress relief heat treatment route when shape stability is vital.