Untersuchungen zum Einfluss innerer Grenzflächen auf das Ermüdungsverhalten metallischer Konstruktionswerkstoffe

In dieser Arbeit wird das Ermüdungsverhalten bei hohen und sehr hohen Lastspielzahlen (bis 10⁸ Lastwechsel) zweiphasiger Konstruktionswerkstoffe am Beispiel eines Duplexstahls und einer Titanlegierung untersucht. Ein besonderes Augenmerk liegt dabei auf der stark durch die Mikrostruktur beeinflussten Schädigungsinitiierung sowie dem Wachstum kurzer Ermüdungsrisse. Es zeigt sich, dass die in der Mikrostruktur enthaltenen Phasengrenzen für beide Werkstoffe den die Wechselfestigkeit bestimmenden Beitrag liefern. Die Schädigung beginnt im Duplexstahl durch Abgleitung in der weicheren Austenitphase in Körnern mit hohem Schmidfaktor, während anschließend die überwiegende Anzahl der entstehenden Risse in Folge der elastischen und plastischen Inkompatibilität an den Phasengrenzen initiiert. Eine Definition der physikalischen Dauerfestigkeit des Werkstoffs ergibt sich aus der Barrierewirkung der Phasengrenzen, an denen Versetzungen und Risse bei kleinen Belastungsamplituden stoppen. Korngrenzen, und hier insbesondere die im Duplexstahl vorhandenen Zwillingsgrenzen, besitzen aufgrund des nicht vorhandenen Drehwinkels lediglich einen untergeordneten Einfluss auf die Ermüdungsfestigkeit. Aus der nur im Sonderfall beobachteten Rissinitiierung an herstellungsbedingten nichtmetallischen Einschlüssen wird zusätzlich eine technologische Dauerfestigkeit des Werkstoffs abgeleitet. Im Falle der Titanlegierung, die in zwei Gefügezuständen untersucht wurde, findet die Rissinitiierung vorwiegend in der sekundären Alphaphase statt. Als die die Rissausbreitung dominierenden Faktoren stellen sich die primären Gleitsysteme (basal und prismatisch) heraus, die mit einem hohen Schmidfaktor in Relation zur äußeren Belastung versehenen sind. Darüber hinaus zeigt sich, dass Risse teilweise auch normalspannungskontrolliert und interkristallin in den lamellaren Gefügebestandteilen wachsen. Die gewonnenen Ergebnisse fließen schließlich in zwei verschiedene Methoden zur Lebensdauervorhersage ein. Das für den Duplexstahl zur Anwendung gebrachte, phänomenologisch gestützte Konzept PHYBAL_LSV ist in der Lage, auf Basis von drei Ermüdungsversuchen eine zuverlässige und konservative Abschätzung der Ermüdungsfestigkeit zu liefern. Im Falle der Titanlegierung wird ein mechanismenorientierter Ansatz gewählt, der auf der Simulation der Kurzrissausbreitung in zweidimensionalen virtuellen Gefügen beruht. Da in diesem Modell die identifizierten Charakteristika des mikrostrukturbestimmten Risswachstums berücksichtigt sind, lassen sich Lebensdauern auf Basis synthetischer Wöhlerkurven auch in virtuellen Mikrostrukturen berechnen. Am Ende der Arbeit wird eine technologisch und wirtschaftlich attraktive Kombination der beiden Konzepte vorgeschlagen, die eine virtuelle Gefügeoptimierung gefolgt von der experimentell abgesicherten Lebensdauerermittlung beinhaltet.This thesis covers the fatigue behaviour of two-phased construction materials at high and very high numbers of cycles (up to 10⁸ load reversals) using the example of a duplex steel and a titanium alloy. Main emphases are put to the early stage of damage initiation and the growth of short fatigue cracks. Both phenomena are strongly dependant on the local microstructure. It becomes apparent that the phase boundaries present in both alloys determine the fatigue strength. In case of the duplex steel fatigue damage starts by slip in the softer austenite predominantly in grains exhibiting a high Schmid factor, whereas most of the cracks developing afterwards initiate at phase boundaries due to the elastic and plastic incompatibility. A definition of the physical fatigue limit results from the barrier effect of phase boundaries, where dislocations and short cracks are stopped in case of low load amplitudes. Grain boundaries, in particular twin grain boundaries present in the duplex steel, exhibit only a minor influence on the fatigue strength due to the missing twist angle. The rarely observed exception of crack initiation at non-metallic inclusions, which result from production, is used to establish a technological fatigue limit in addition. In case of the titanium alloy, which was investigated in two different microstructural modifications, crack initiation predominantly is observed in the secondary alpha phase. The crack propagation is mainly controlled by those primary slip systems (basal and prismatic), which exhibit a high Schmid factor with respect to the external load. Moreover, it can be shown that some cracks partially grow by an intercrystalline mechanism in the lamellar part of the microstructure controlled by the maximum normal stress. Furthermore, the results are used to establish two different methods for predicting the fatigue lifetime. In case of the duplex steel, this is the phenomenologically based concept of PHYBAL_LSV, which uses three fatigue experiments in order to determine a reliable and conservative estimation of the fatigue strength. A mechanism-based approach is chosen in case of the titanium alloy, which relies on the simulation of short fatigue crack growth in two-dimensional virtual microstructures. Since this model takes into account the identified characteristics of the crack growth which is depending on the microstructure, lifetimes based on synthetic Wöhler curves can be calculated using also virtual microstructures. Finally, a technologically and economically attractive combination of both concepts is proposed by using the short crack model for the optimisation of virtual microstructures followed by the experimental verification of the calculated lifetime

Terrestrial Impacts of the Central Atlantic Magmatic Province on western Pangea

Earth\u27s climate is predominantly controlled by the fluctuation of greenhouse gases, specifically CO2 and CH4, over geologic time. The late Triassic is a period of abrupt climate change that has been associated with a disruption to the global carbon cycle due the emplacement of the Central Atlantic Magmatic Province (CAMP). Evidence has shown that this global carbon cycle perturbation may be the culprit for the end-Triassic extinction. The Whitmore Point Member of the Moenave Formation is a lacustrine deposit with a disputed age of either late Triassic or early Jurassic and currently no absolute dating techniques can be applied to estimate an exact age. Therefore, I propose that identification of the CAMP carbon cycle perturbation through carbon isotope chemostratigraphy of the Whitmore Point Member will be the best current age constraint. δ13Corganic and δ13Ccarbonate were analyzed in the lacustrine deposits of the Whitmore Point Member of the Moenave Formation to construct a carbon isotope chemostratigraphic profile. Carbon isotope evidence indicates that the environmental perturbation caused by the emplacement of the CAMP is present within the Whitmore Point Member. Data was collected at two localities: 1) The Whitmore Point Reference Section (Potter Canyon, Arizona) and 2) Warner Valley, Utah. Carbon isotope data from Potter Canyon reveals a distinctive 5.5 / and 2.75 / decrease in δ13Corganic and δ13Ccarbonate, respectively, in the lower portion of the Whitmore Point Member. Warner Valley does not show a prominent negative carbon isotope excursion but has been correlated to the positive isotope excursion and main negative isotope excursion exhibited within Potter Canyon. Correlation of carbon isotope curves from different localities also helps to regionally correlate the Whitmore Point Member. The identification of the Potter Canyon negative carbon isotope excursion is the first terrestrial record of the CAMP in western Pangea and provides more compelling evidence on the global impacts of the CAMP. Carbon isotope data along with previously published conchostracan data indicates that the end-Triassic extinction is within the lower portion of the Whitmore Point Member while the Triassic - Jurassic boundary is present within the upper portion. Therefore, I propose the age of the Whitmore Point Member to be late Triassic to early Jurassic

Brennan v. Scalia, Justice or Jurisprudence? A Moderate Proposal

322 hlm.; 25 cm

Reconstructing activity patterns in prehistoric Jomon people using long bone cross-sectional geometry

Title from PDF of title page (University of Missouri--Columbia, viewed on Aug. 18, 2010).The entire thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file; a non-technical public abstract appears in the public.pdf file.Thesis advisor: Dr. Daniel Temple & Dr. Daniel Wescott.M.A. University of Missouri--Columbia 2010.This thesis uses long bone diaphyseal morphology to test hypotheses regarding behavior and functional adaptation among Jomon period hunter-gatherers from the Yoshigo site in Japan. Cross-sectional properties of Jomon femora taken at midshaft were compared with the femora of hunter-gatherers from the Aleutian Islands. Cross-sectional properties from the mid-distal shaft of the humerus were compared between the Jomon and hunter-gatherers from the Aleutian Islands, California, and Georgia Coast. Sexual dimorphism was additionally assessed between the groups. Results suggest that the Jomon share a similar pattern of femoral robusticity (J) and shape (Ix/Iy) as Aleut hunter-gatherers. This study also found that Jomon humeri are significantly more robust than all comparative samples, but humeral shape is similar between the groups. In terms of sexual dimorphism, Jomon males and females are similar in both femoral and humeral robusticity and shape relative to the comparative samples, with Jomon males being more robust than females. Jomon and Aleut femoral robusticity and shape is associated with similarity in terrestrial mobility and terrain. The greater robusticity in Jomon humeri reflects intensive bimanual activities including swimming, rowing, digging tubers and throwing and lifting of fishing nets. Similarity in shape, but differences in robusticity between the sexes suggests similar direction of loading practiced with varying intensity.Includes bibliographical reference

Pregnant Women after Physical and Sexual Abuse in Germany

Background/Aims: The aim of our study was to evaluate the prevalence of abuse among pregnant women in Germany attending our antenatal outpatient clinic and to observe whether a history of abuse had consequences for women's feelings about their pregnancy. Methods: 455 women between the 35th and 42nd weeks of gestational age were included and were asked to fill out an anonymous questionnaire concerning their pregnancy, their actual psychological state, and their history of physical/sexual abuse. 600 questionnaires were distributed (return rate 75.8%), 70 women (10.4%) were excluded because of male companionship to ensure their safety in case that they were currently in an abusive relationship with the attending man. Results: 88 women (19.3%) reported a history of sexual and/or physical abuse. Pregnant women after physical and/or sexual abuse significantly more frequently associate negative feelings with their pregnancy than nonabused women. The Hospital Anxiety Depression Scale (HADS) and the SCL-K-9 demonstrated significantly more negative feelings of depression and anxiety, strain, loneliness and less expectation of happiness for their future in abused women. Conclusion: Physical and sexual abuse are relevant problems among women in obstetric care that may complicate their pregnancies and make them feel more depressive. Copyright (C) 2009 S. Karger AG, Base

Nuclear Magnetic Resonance Study Of CO2 Capture By Fluoroalkylamines: Ammonium Ion PKa Depression Via Fluorine Modification And Thermochemistry Of Carbamylation

We are developing energy-efficient and reversible carbon capture and release (CCR) systems that mimic the Lys201 carbamylation reaction in the active site of ribulose-1,5-bisphosphate carboxylase-oxygenase (RuBisCO). The multiequilibria scenario ammonium ion Xa ⇌ amine Xb ⇌ carbamic acid Xc ⇌ carbamate Xd requires the presence of both free amine and CO2 for carbamylation and is affected by the pKa(Xa). Two fluorination strategies aimed at ammonium ion pKa depression and low pH carbamylation were analyzed with (2,2,2-trifluoroethyl) butylamine 2b and 2,2-difluoropropylamine 3b and compared to butylamine 1b. The determination of K1 and ΔG1 of the carbamylation reactions requires the solution of multiequilibria systems of equations based on initial conditions, 1H NMR measurements of carbamylation yields over a wide pH range, and knowledge of K2-K5 values. K2 and K3 describe carbonic acid acidity, and ammonium ion acidities K4 were measured experimentally. We calibrated carbamic acid acidities K5 based on the measured value K6 of aminocarbamic acid using isodesmic reactions. The proton exchange reactions were evaluated with ab initio computations at the APFD/6-311+G* level in combination with continuum solvation models and explicit solvation. The utilities of 1-3 will be discussed as they pertain to the development of fluorine-modified RuBisCO-mimetic reversible CCR systems