Residual stresses in aerospace structures reinforced with bonded crack retarders

Bonded crack retarder technology is an innovative concept to improve the fatigue performance of aircraft structures. Stiffening ‘straps’ are adhesively bonded to areas where potential fatigue cracking may occur. The straps retard the growth of fatigue cracks, by a combination of the local stiffening effect that reduces the crack driving force, and bridging in the wake of the crack. However, bonded crack retarder results in thermal residual stresses that may adversely affect the performance of the reinforced structure due to extensive fatigue loads in service. This is the first study where we have looked at the application of GLARE6/5 fibre-metal laminate as a bonded crack retarder onto a structural butt joint and simulated manhole mock-up assemblies containing cold-worked holes. Neutron diffraction was used for residual stress measurements. Results indicate that the strap-bonding process has no discernible effect on the magnitude of the compressive cold-working stresses. The use of bonded crack retarders should not, therefore, impair the benefits of cold working of fastener joints in aircraft structures

Dynamics of the Tippe Top via Routhian Reduction

We consider a tippe top modeled as an eccentric sphere, spinning on a horizontal table and subject to a sliding friction. Ignoring translational effects, we show that the system is reducible using a Routhian reduction technique. The reduced system is a two dimensional system of second order differential equations, that allows an elegant and compact way to retrieve the classification of tippe tops in six groups as proposed in [1] according to the existence and stability type of the steady states.Comment: 16 pages, 7 figures, added reference. Typos corrected and a forgotten term in de linearized system is adde

Dual Laser Study of Non-Degenerate Two Wavelength Upconversion Demonstrated in Sensitizer-Free NaYF4:Pr Nanoparticles

Published online: February 1, 2021Understanding the upconversion pathways of a rare-earth dopant is crucial to furthering the use of that material, either toward applications in imaging or elsewhere. This work outlines a new analysis approach that consists of using two synchronized widely-tunable laser sources to explore the properties of upconverting materials. By examining sensitizer-free rare-earth nanoparticles based on a matrix of hexagonal sodium yttrium tetrafluoride (β-NaYF4) doped with praseodymium but no ytterbium sensitizer, a “non-degenerate” two-color upconversion fluorescence at a combined excitation of 1020–850 nm is shown. This insight demonstrates the ability of this technique to locate and interrogate novel upconversion pathways. The dopant level of the nanoparticles could be modified without altering other factors, such as the particle's shape or size, that would also change optical properties and this allows investigation of the dopant-level dependency of the optical properties. The approach also allows exploration of the time delay domain between the arrival times of the two non-degenerate excitation pulses, which allows modulation of the brightness from the visible light emissions. This work opens up the parameter space for the systematic synthesis and characterization of new materials with non-degenerate upconversion emission.Thomas J. de Prinse, Afshin Karami, Jillian E. Moffatt, Thomas B. Payten, Georgios Tsiminis, Lewis Da Silva Teixeira, Jingxiu Bi, Tak W. Kee, Elizaveta Klantsataya, Christopher J. Sumby, and Nigel A. Spoone

Large-Eddy Simulations of Magnetohydrodynamic Turbulence in Heliophysics and Astrophysics

We live in an age in which high-performance computing is transforming the way we do science. Previously intractable problems are now becoming accessible by means of increasingly realistic numerical simulations. One of the most enduring and most challenging of these problems is turbulence. Yet, despite these advances, the extreme parameter regimes encountered in space physics and astrophysics (as in atmospheric and oceanic physics) still preclude direct numerical simulation. Numerical models must take a Large Eddy Simulation (LES) approach, explicitly computing only a fraction of the active dynamical scales. The success of such an approach hinges on how well the model can represent the subgrid-scales (SGS) that are not explicitly resolved. In addition to the parameter regime, heliophysical and astrophysical applications must also face an equally daunting challenge: magnetism. The presence of magnetic fields in a turbulent, electrically conducting fluid flow can dramatically alter the coupling between large and small scales, with potentially profound implications for LES/SGS modeling. In this review article, we summarize the state of the art in LES modeling of turbulent magnetohydrodynamic (MHD) ows. After discussing the nature of MHD turbulence and the small-scale processes that give rise to energy dissipation, plasma heating, and magnetic reconnection, we consider how these processes may best be captured within an LES/SGS framework. We then consider several special applications in heliophysics and astrophysics, assessing triumphs, challenges,and future directions

A practical review of shorter than excitation wavelength light emission processes

Shorter-than-excitation-wavelength (STEW) optical emissions, where photons originating in a material have higher energies than those that created them, have in the past few decades become important in science and medicine, with applications ranging from improving the efficiency of solar cells to creating new lasers and performing background-free microscopy of biological samples. Assigning and predicting the origin of STEW emissions is critical for accelerating development and applications of new processes and materials. In this review, we examine the different processes underlying STEW emissions and outline pathways to identify them using readily available experimental techniques.J. E. Moffatt, G. Tsiminis, E. Klantsataya, T. J. de Prinse, D. Ottaway and N. A. Spoone

In-fiber measurement of the erbium-doped ZBLAN 4I13/2 state energy transfer parameter

Published 13 January 2021Erbium-doped ZBLAN (Er:ZBLAN) is a commonly used glass for mid-infrared fiber lasers. Quantifying the energy dynamics of the erbium ions is important for improving the performance of mid-infrared fiber lasers. Previous studies have found a discrepancy between the strength of inter-ion energy transfer measured in bulk Er:ZBLAN and the strength required to explain current fiber laser performance. We have measured the strength of the 4 I 13 / 2 + 4 I 13 / 2 → 4 I 15 / 2 + 4 I 9 / 2 energy transfer process directly in a range of fibers for the first time, to the best of our knowledge.Jillian E. Moffatt, Georgios Tsiminis, Elizaveta Klantsataya, Ori Henderson-Sapir, Barnaby W. Smith, Nigel A. Spooner, and David J. Ottawa