Stability of the cylindrical shell of variable curvature

This report is a first attempt to devise a calculation method for representing the buckling behavior of cylindrical shells of variable curvature. The problem occurs, for instance, in dimensioning wing noses, the stability of which is decisively influenced by the variability of curvature. The calculation is made possible by simplifying the stability equations (permissible for the shell of small curvature) and by assuming that the curvature 1/R as a function of the arc lengths can be represented by a very few Fourier terms. The formulas for the special case of an ellipse-like half oval with an axis ratio 1/3 ?= e ?= 1 under compression in longitudinal direction,shear, and a combination of shear and compression were evaluated. However, the results can also be applied approximately to an unsymmetrical oval-shell segment under compression, shear, and bending so that the numerical values contained in the diagrams 10 to 12 represent directly dimensioning data for the wing nose

The stresses in stiffener openings

The present study treats as a typical example a ring the center line of which is produced by the intersection of two circular cylinders of different diameter. Three load cases are analyzed: (1) Axial and circumferential stresses in both cylinders, the cylinder stresses themselves to be in the ratio conformal to the cylinders loaded under internal pressure. (2) Pure longitudinal tension in the large cylinder. (3) Pure shear (torsion) in the large cylinder. To simplify the calculation, it is assumed that the ring, compared to the shell, is very strong, so that its deformations have no perceptible effect on the stress condition in the shell. This provides an upper limit for the ring stresses actually produced in a shell design, for, according to the theory of stressed skin statics the shells, by elastic flexibility of the ring, regroup the forces deposited on it in such a manner that the ring is relieved

Behavior of a plate strip under shear and compressive stresses beyond the buckling limit

The present report is an extension of previous theoretical investigations on the elastic behavior of a plate under compression and shear in the region above the critical. The main object is the clarification of the behavior immediately above the buckling limit since no theoretical expressions for this range have thus far been found and since experimentally, too, any degree of regularity in the behavior of the plate in the range between the critical load and about three to four times the critical, is discernible only with difficulty

Synthese und bioanalytische Anwendung Lanthanid-markierter Peptide und Nucleinsäuren

Die Arbeit behandelt die Entwicklung neuer Lanthanidsonden und ihre Anwendung zur Detektion von Nucleinsäuren und Enzymen durch zeitaufgelöste Lumineszenzmessungen. Zum einen wurden dazu Lanthanidkomplex-modifizierte fluorogene Peptidsubstrate, zum anderen Chelator-modifizierte Peptidnucleinsäuren (PNAs) synthetisiert. Im funktionalisierten Peptidsubstrat wird die Lumineszenz des Lanthanidkomplexes durch einen Bis-Azo-Farbstoff (Black Hole Quencher) vollständig gelöscht. Die enzymatische Spaltung des Substrats führt zu einer räumlichen Trennung von Komplex und Quencher und so zu einem deutlichen Signalanstieg. Durch zeitaufgelöste Messung der langlebigen Lanthanidlumineszenz kann Thermolysin sehr empfindlich nachgewiesen werden. Darüber hinaus wurden die besonderen photophysikalischen Eigenschaften der Lanthanidkomplexe zur Detektion von DNA eingesetzt. An beiden Termini mit Chelatoren modifizierte Peptidnucleinsäuren wurden entwickelt und ihre Wechselwirkung mit komplementärer DNA untersucht. Diese führt zur allosterischen Destabilisierung eines zuvor gebildeten zirkularen PNA-Lanthanidkomplexes, wodurch das Metallion freigesetzt wird und mit Hilfe von Sensitizern detektiert werden kann. In einem zweiten auf Signalverstärkung beruhenden Ansatz zur Detektion von DNA fungiert ein zirkularer DNA-Zink-Komplex als Primärsonde für eine komplementäre Ziel-DNA. Auch hier wird das Metallion durch Hybridisierung freigesetzt, jedoch anschließend nicht direkt, sondern indirekt über die Aktivierung eines Zn2+-Cofaktor abhängigen Enzyms Thermolysin nachgewiesen. Eine Signalamplifikation erfolgte katalytisch über die Spaltung des oben beschriebenen fluorogenen Peptidsubstrats, welches ein starkes Lumineszenzsignal erzeugt

Sidewall Buckling of Equal-width RHS Truss X-Joints

This paper presents a new design methodology for equal-width rectangular hollow section (RHS) X-joints failing by sidewall buckling. In the new approach, a slenderness parameter is defined based on the elastic local buckling stress of the sidewall, idealized as an infinitely long plate under patch loading. A Rayleigh-Ritz approximation is thereby used to obtain a closed-form solution. The proposed design equation is verified against experimental results over a wide range of wall slenderness values obtained from the literature and complemented by a brief experimental program carried out by the authors. It is demonstrated that the new design equation yields excellent results against the experimental data. Finally, a reliability analysis is performed within the framework of both the Eurocode and the AISI standards to ensure that the proposed design equation possesses the required level of safety. The newly proposed equation strongly outperforms the current Comité International pour le Développement et l’Etude de la Construction Tubulaire (CIDECT) design rule for sidewall buckling and also further extends the range of applicability to a wall slenderness ratio of up to 50