A modeling approach for the complete ductile–brittle transition region: cohesive zone in combination with a non-local Gurson-model

The present study deals with the simulation of crack propagation in the ductile–brittle transition region on the macro-scale. In contrast to most studies in the literature, not only the ductile softening by void growth and coalescence is incorporated but also the particular material degradation by cleavage. A non-local Gurson-type model is employed together with a cohesive zone to simulate both failure mechanisms simultaneously. This consistent formulation of a boundary value problem allows arbitrary high mesh resolutions. The results show that the model captures qualitative effects of corresponding experiments such as the cleavage initiation in front of a stretch zone, the formation of secondary cracks and possible crack arrest. The influence of the temperature on the predicted toughness is reproduced in the whole ductile–brittle transition region without introducing temperature-dependent fit parameters. A comparison with experimental data shows that the shift of the ductile–brittle transition temperature associated with a lower crack-tip constraint can be predicted quantitatively.     

An anisotropic ink based on crystalline nanocellulose: Potential applications in security printing

Polymer dispersions containing crystalline nanocellulose have been used as birefringent inks. When printed onto dark paper, the letters are darker than the background if viewed without polarizers, while they are brighter than the background if viewed with crossed polarizers. This type of contrast inversion can have applications in security printing and optical authentication. © 2014 Wiley Periodicals, Inc. J. Appl. Polym. Sci. 2014 , 131, 41063.     

Studying mechanical microcontacts of fine particles with the quartz crystal microbalance

To study micromechanical adhesion, glass particles were deposited on a quartz crystal microbalance (QCM). Beforehand, a 160 nm-thick film of polystyrene (PS) had been spin-coated on the gold surface of the QCM. Shifts in the resonance frequency were monitored versus the oscillation amplitude. The aim was to analyse how QCM experiments reflect the state of adhesion. During oscillation, the motion of the particles and the induced frequency shift of the QCM are governed by a balance between inertial and contact forces. In order to vary the relative strength of the two, the diameter of the particles was varied between 5 and 20 μm. The adherence of the particles could be increased by annealing the PS film at 150 °C. Annealing led to the formation of a PS meniscus. For a semi-quantitative interpretation we have to take into account that the particles show a distribution of coupling constants.The vibration of the QCM changes the micromechanical contact between QCM surface and particles. There is an instantaneous and a long-term effect. Instantaneously, the oscillation induces partial slip. Under an oscillating load, part of the contact ruptures, which decreases the effective stiffness of the contact. In addition, there are long-term memory effects. The vibration of the QCM can lead to a consolidation and an increased coupling. However, it can also break the contact and even lead to detachment. Particles deform the PS surface and induce damage due to inertial forces.     

Moderne Fertighäuser aus Holz und Holzwerkstoffen Zweite Mitteilung: Berechnung und Festigkeit von Tafelelementen

Zusammenfassung Von den zahlreichen, bei der konstruktiven Bearbeitung des Fertighauses auftretenden Problemen k?nnen hier nur einige wenige herausgegriffen werden. Auf die Druck- und Biegebean-spruchung der Tafelelemente wird nur kurz eingegangen, wobei vor allem grunds?tzliche Fragen im Vordergrund stehen. Eingehender behandelt werden die in ihrer Ebene durch Biegekr?fte belasteten Wandtafeln (Schubbeanspruchung z. B. infolge Wind), deren Tragverhalten an Hand der durchgeführten versuche sowie mit theoretisch abgeleiteten Spannungs- und Verformungs-beziehungen beschrieben wird. Als Ma? für die Schubsteifigkeit einer Tafel wird dabei ein effektives Tr?gheitsmomentJ _eff eingeführt, das die Einflüsse der Schubkr?fte auf die Verformungen sowie des im allgemeinen clastischen Verbundes zwischen Holzrahmen und Beplankung berücksichtigt; insbesondere werden Abminderungskoeffizienten für die Scheibenwirkung von nur verbretterten Tafeln angegeben sowie der Einflu? von Querriegeln auf die mitJ _eff linear korrclierte Traglast aufgezeigt. Die Versuche zeigten, da? die aus ihnen mit 5facher Sicherheit berechnefen zul?ssigen Schublasten ann?hernd denen entsprechen, die theoretisch mit Hilfe der angegebenen Gleichungen auf der Grundlage der zul?ssigen Schubspannungen von Spanplatten abgeleitet werden k?nnen; demgegenüber werden die zul?ssigen Normalspannungen nicht ausgenützt. Im allgemeinen war der Grad der Spannungsausnutzung abh?ngig von der Art des Verbundes zwischen Rahmen und Beplankung sowie nicht zuletzt von der Beplankungsart selbst. Absehlie?end werden Fragen zur Verankerung von Schubtafeln er?rtert und im Zusammenhang damit Bemessungsvorschl?ge für Bolzenverbindungen aus neuerem Schrifttum mitgeteilt.

---

Modern Prefabricated Houses from Wood and Wood Base Materials Part II: Computation and Strength of Sheathed Frameworks

Summary Constructing prefabricated houses raises numerous problems only a few of which can be dealt with in this paper. A few basic questions concerning wall sections stressed by compression and bending forces are only briefly discussed, since the main objective of this paper was to investigate the effect of inplane bending forces (e. g. wind) by deducing theoretical formulae for stresses and deflections and by determining experimentally the loadbearing capacity of sheathed frameworks. As a measure for the shear rigidity of a panel an effective moment of inertia, denoted asJ _eff, is introduced taking into account the influence of the shear-forces on the deflections and the clastic joining between framework and sheathing; lessening coefficients for the dise-affect of merely boarded frameworks are given, and the influence of cross-bars on the load-bearing capacity, which was found to be linearly correlated toJ _eff, is indicated. Furthermore, the tests revealed that the allowable shear-loads calculated with fivefold security from the load-bearing capacity nearly correspond to those derived theoretically on the basis of the allowable shear-stresses of particle board: in contrast to this, the allowable normal stresses were not fully used. The degree of utilization of the allowable stresses generally depended on the kind of joining between framework and sheating and finally on the kind of the sheathing itself. In coaclusion, problems relerring to the mooring of shear-walls are discussed, and recent suggestions for the computation of bolt-jomings are reviewed.

     

Modified compound quadrature rules for strongly singular integrals

Computing - We show that the error term of every modified compound quadrature rule for Cauchy principal value integrals with degree of exactnesss is of optimal order of magnitude in the classesC k...     

Contributions of structural mechanics to safety and reliability of German nuclear power stations

Traditionally structural mechanics considerations have played a competent role in the design of German nuclear power stations and their fuel. Structural mechanics development and validation programs have set standards of “gooddesign practise” and established the proof of safety against catastrophic failure.     

Zum Stand der Berechnung von Behälterabstützungen und Fußkonstruktionen

Calculation of vessel supports and foot constructions . Supports of vessels often cause large strains in the wall of the container; generally the calculation of the resulting deformations and stresses turns out to be difficult. Several types of construction and the problems associated with local loadings are described, and possible methods of calculation are listed. Generally known publications are compared. Methods of series expansion are considered in more detail and their advantages as well as their limitations are shown for the example of a Fourier series expansion for a cylindrical tank. In addition two examples are considered which permit comparisons between our own calculations and usual methods and experimental results, respectively.     

Report on the Fifth Symposium on Current Trends in International Fusion Research

The Fifth Symposium on Current Trends in International Fusion Research was held on 24–29 March 2003 in Washington, USA in co-operation with the International Atomic Energy Agency (IAEA). Well-known scientists in their field of interest in fusion research were invited to present review papers. The presentations covered a broad range of fusion topics, including inertial confinement fusion, electrostatic confinement, various magnetic confinement schemes, and hybrid schemes. Each session chairman composed a session report, which John Pucadyil used to create this Report on the Fifth Symposium.