Dear John

Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/68693/2/10.1177_003754976600600313.pd

Characterisation of contact pressure distribution in bolted joints

The quantification of contact area and pressure distribution in a bolted joint is essential information, as it determines the integrity of the coupling. Current bolted joint design standards are based on analytical solutions of the pressure distribution, which, because of the inherent assumptions, frequently do not accurately represent the real conditions in a joint. This study uses a nonintrusive ultrasonic technique to quantify the contact pressure distribution in a bolted connection. The advantage of this experimental technique is that the effect of actual contact conditions can be determined. An ultrasonic wave is focused onto the clamped interface, and the reflected sound signal recorded. In areas where the contact pressure is high, most of the ultrasound is transmitted, and the reflected sound signal is weak. Whereas, when the contact pressure is low, the vast majority of the ultrasound is reflected back. A parallel experimental calibration is then used to find the relationship between the reflected sound signal and contact pressure. In this way, the pressure distribution in a clamped interface is determined for a series of different bolt torques. Two different interfaces were investigated: the first consisted of two ground surfaces clamped together, and the second a turned profile pressed against a ground surface. The effect of a washer underneath the bolt head was also considered. The turned profile was found to cause the contact to spread; there was also a certain degree of fragmentation leading to higher peak pressures than in the ground interface case. With a washer positioned under the bolt head for the turned case, the clamping performance of the bolt was improved. Good agreement was found when comparing the ultrasonic measurements with previous studies, with respect to the spread of the contact pressure distribution. However, in this study, the peak contact pressure was found to occur away from the edge of the bolt hole, and to be influenced by the edge of the bolt head

Collaboration with Academia Promotes Rigorous Research

A partnership between the Naval Information Warfare Center Pacific and the Naval Postgraduate School is sending students to a new doctoral program in Information Science.The article of record may be found at https://www.onr.navy.mil/-/media/Files/ONR-Publications/Future-Force-22-Vol-6-No-4-2020.ashx?la=e

Design for limit stresses of orange fruits (Citrus sinensis) under axial and radial compression as related to transportation and storage design

This article employed the Hertz contact stress theory and the finite element method to evaluate the maximum contact pressure and the limit stresses of orange fruit under transportation and storage. The elastic properties of orange fruits subjected to axial and axial contact were measured such that elastic limit force, elastic modulus, Poisson’s ratio and bioyield stress were obtained as 18 N, 0.691 MPa, 0.367, 0.009 MPa for axial compression and for radial loading were 15.69 N, 0.645 MPa, 0.123, 0.010 MPa. The Hertz maximum contact pressure was estimated for axial and radial contacts as 0.036 MPa. The estimated limiting yield stress estimated as von Mises stresses for the induced surface stresses of the orange topologies varied from 0.005 MPa–0.03 MPa. Based on the distortion energy theory (DET) the yield strength of orange fruit is recommended as 0.03 MPa while based on the maximum shear stress theory (MSST) is 0.01 MPa for the design of orange transportation and storage system

"Dazzling Dialectics": Elizabeth Bishop's Resonating Feminist Reality

Englis

Metaphors of Innocence and Chiidhood: Parallels in Elizabeth Bishop and Three Seventeenth-century Metaphysical Poets

The vivid imagery and subtle wit of Elizabeth Bishop's poetry have intrigued me ever since I first encountered her work in an undergraduate seminar at the University of Utah. Moving from regularly anthologized poems such as "The Fish" to the more obscure "Nova Scotia" poems and then into scholarly criticism of Bishop's work, I was dismayed to discover that many critics read her poems as touching, cathartic encounters with her tragic childhood instead of deliberate pieces of fiction. Even very helpful bibliographies, such as the recent one by Barbara Page, call poems featuring child speakers "autobiographical" or discuss critics' explorations of "autobiographical" elements, without defining or proving why they are autobiographical. Finding no help in the critics, I turned to other poets and, following T. s. Eliot's lead, looked back to the imagefilled worlds of George Herbert, Andrew Marvell, and Henry Vaughan. In their poetry, I found parallel metaphors of childhood and poetic techniques that helped me modify the purely autobiographical readings of Bishop and establish her as part of a poetic tradition. This study does not try to prove that the seventeenth-century poets influenced Bishop, but instead aims to refute the autobiographical readings by establishing technical and thematic parallels.Englis

Fabrication and Testing of Low Cost 2D Carbon-Carbon Nozzle Extensions at NASA/MSFC

Subscale liquid engine tests were conducted at NASA/MSFC using a 1.2 Klbf engine with liquid oxygen (LOX) and gaseous hydrogen. Testing was performed for main-stage durations ranging from 10 to 160 seconds at a chamber pressure of 550 psia and a mixture ratio of 5.7. Operating the engine in this manner demonstrated a new and affordable test capability for evaluating subscale nozzles by exposing them to long duration tests. A series of 2D C-C nozzle extensions were manufactured, oxidation protection applied and then tested on a liquid engine test facility at NASA/MSFC. The C-C nozzle extensions had oxidation protection applied using three very distinct methods with a wide range of costs and process times: SiC via Polymer Impregnation & Pyrolysis (PIP), Air Plasma Spray (APS) and Melt Infiltration. The tested extensions were about 6" long with an exit plane ID of about 6.6". The test results, material properties and performance of the 2D C-C extensions and attachment features will be discussed

Spin tunnelling in mesoscopic systems

We study spin tunnelling in molecular magnets as an instance of a mesoscopic phenomenon, with special emphasis on the molecule Fe8. We show that the tunnel splitting between various pairs of Zeeman levels in this molecule oscillates as a function of applied magnetic field, vanishing completely at special points in the space of magnetic fields, known as diabolical points. This phenomena is explained in terms of two approaches, one based on spin-coherent-state path integrals, and the other on a generalization of the phase integral (or WKB) method to difference equations. Explicit formulas for the diabolical points are obtained for a model Hamiltonian.Comment: 13 pages, 5 figures, uses Pramana style files; conference proceedings articl