42 research outputs found
Model for the nonlinear response of a Terfenol-D-type magnetostrictive actuator
No full textA variational model of the nonlinear response of a magnetostrictive actuator to applied magnetic fields and loads, taking into account the complex behavior of the underlying domain patterns, is discussed. Magnetostriction curves for a Terfenol-D-like material in a 2D geometry are calculated exactly, and compared with experimental measurements for Terfenol- D, suggesting an explanation for the observed behavior
Multiculturalisme et marginalisation à Los Angeles. De Watts (1965) à South Central (1992)
No full textMulticulturalism and marginalization in Los Angeles. From Watts (1965) to South Central (1992), Cynthia Ghorra-Godin.
From the 1992 South Central events, the author looks on the major upheavals that have marked Los Angeles in the last two decades: the shifts in population composition since the spectacular arrival of the Hispanics, the socio-economic and inter-ethnic tensions stemming from de-industralization, the limits of political regulation. The sudden riots of 1992, just as the permanent tensions underlying urban life, reflect mainly the failure of a town planning which focused on spatial expansion and individual housing to the detriment of the development of a genuinely public space able to blend the various communities.Ghorra-Gobin Cynthia. Multiculturalisme et marginalisation à Los Angeles. De Watts (1965) à South Central (1992). In: Vingtième Siècle, revue d'histoire, n°40, octobre-décembre 1993. pp. 23-32
High Precision Form Measurement through the Use of Adaptive Structures Technology
No full textA smart solution to vibration suppression in form measuring machines is presented in which the machine's vibrations are counteracted actively. For this purpose, the machine was equipped with a sensing system, an active interface, and a special controller. This new concept has been successfully tested on a real form measuring machine
Opening Plenary
No full textWelcome from Conference Organizers Scott Redman, Executive Chair Cecilia Gobin, Program Co-Chair Julie Watson, Program Co-Chair Fran Wilshusen, Program Co-Chair Christianne Wilhelmson, Program Co-Chair Ginny Broadhurst, Salish Sea Institute Coast Salish Welcome Cecilia Gobin, Northwest Indian Fisheries Commission Coast Salish Perspectives on the Last 150 years Patti Gobin, Tulalip Tribes Patti Gobin has over 25 years of Community Development experience with the Tulalip Tribes. Presently, she is with the Natural Resource Treaty Rights office working with state, local and federal agencies regarding those issues that impact the life ways of the Tulalip Tribes. In addition to her years of experience, Ms. Gobin is a member of the Tulalip Tribes and is well versed in the culture and history of her people. Her personal goal is to invest in the future of the Coast Salish community, helping to affect a sustainable future for the next generations to come. The State of the Salish Sea Dr Isobel Pearsall and Dr Kathryn Sobocinski will give an overview about the current state of the Salish Sea. Both have led recent Salish Sea ecosystem-wide analyses – the Salish Sea Marine Survival Project and the State of the Salish Sea report, respectively. Isobel and Kathryn will each provide presentations followed by discussion with the session moderators Scott Redman, Science Program Director at the Puget Sound Partnership and Christianne Wilhelmson, Executive Director of Georgia Strait Alliance. Dr. Isobel Pearsall is the Director of the Pacific Salmon Foundation’s Marine Science Program. She co-ordinated the Canadian component of the international Salish Sea Marine Survival Project, a $24M program set to address declines in Chinook, Coho and Steelhead in the Salish Sea (2014-2019) and is continuing to work on this massive transboundary effort. Isobel holds a first class degree in Pure and Applied biology from Oxford University, a M.Sc. in Ecology from the Department of Biology at Dalhousie University, and a PhD. in Ecology from the Department of Plant Science, UBC. She was a post-doctoral fellow in ecosystem management at the Pacific Biological Station, Department of Fisheries and Oceans, Nanaimo. Since 1995, she has worked as a scientist on numerous programs for government, non-profit organizations, and private industry. She is an adjunct professor at UBC. Dr. Kathryn L. Sobocinski is an Assistant Professor in the Department of Environmental Sciences and the Marine and Coastal Science program at Western Washington University. She is the lead author of State of the Salish Sea published May 2021. Kathryn is an applied marine ecologist focusing on fishes, fish habitats, and impacts of human disturbance and climate change in coastal ecosystems. She holds a BA in Environmental Studies from Connecticut College, MS in Aquatic and Fishery Sciences from the University of Washington, and PhD in Marine Science from the Virginia Institute of Marine Science/College of William & Mary. Kathryn completed post-doctoral work at Oregon State University and NOAA-NWFSC prior to joining the WWU faculty. She resides in Bellingham, WA
Phénomènes de relaxation et frottement intérieur dans les solides vitreux
No full textSeveral mechanical relaxation phenomena are observed on glasses. The characteristics of these phenomena varry from one type of glass to another but some features seem to be common to all solids in the vitreous state. Hence, results about : — oxyde glasses, — organic glasses, — vitreous semiconductors, — metallic glasses, are recalled. Then, it is shown that there are a relaxation process about the glass transition (primary relaxation) and several relaxation processes more or less differenciated at lower temperature (secondary relaxations). The primary or α relaxation corresponds to a rapid increase of internal friction with temperature ; the Arrhenius law is not any more valid and the response of the material to stress can be non-linear. On the contrary, secondary relaxation processes are linear and obey to the Arrhenius law. Some of them can be interpreted in terms of movement of well defined structural elements (for exemple : jump of alcaly ions in silica-alcaly oxyde glasses) ; others are not clearly explained : for instance, just before the glass transition, a peak or an anomaly in the spectrum internal friction versus temperature more or less resolved from the increase of damping due to the α relaxation, is often observed. This feature seems to be associated to delayed elasticity. We propose that such a behavior corresponds to a second relaxation phenomenon (β relaxation) which is, as α relaxation, characteristic of the vitreous state. In order to have agreement between the structural models generally admitted for describing the vitreous state and the necessity to have two types of atomic arrangements for explaining the two relaxation phenomena α and β, we propose the following assumption : whatever the structural model considered, there are planar defects or boundaries in glasses. Then, the β relaxation could be due to thermally activated movements of atoms or molecules in the boundaries while the α relaxation should be the consequence of cooperative rearrangements of atoms or molecules between the boundaries. In a first step, the relaxation models well known in the case of crystalline solids are adapted to the case of glassy materials ; hence, experimental results can be interpreted at less qualitatively.Les solides vitreux présentent divers phénomènes de relaxation mécanique que l'on peut étudier par mesure de frottement intérieur. Les caractéristiques de ces phénomènes varient d'un type de solides vitreux à un autre. Néanmoins, on peut relever certains comportements qui semblent communs à l'ensemble des solides à l'état vitreux. Ainsi, le rappel de résultats concernant : — les verres minéraux, — les matériaux organiques vitreux, — les solides covalents vitreux, — les verres métalliques, fait apparaître que, dans tous les cas, il existe un processus de relaxation vers le domaine de transition vitreuse (relaxation primaire) et des processus de relaxation plus ou moins bien différenciés à plus basse température (relaxation secondaire). La relaxation primaire ou α qui se traduit généralement par une montée rapide du frottement intérieur avec la température est caractérisée par la non-validité de la loi d'Arrhénius et la non-linéarité vis-à-vis de la contrainte. Les phénomènes de relaxation secondaire, au contraire, sont linéaires et suivent la loi d'Arrhénius. Ils peuvent être nombreux et si certains peuvent être expliqués en envisageant le mouvement d'éléments structuraux bien définis (par exemple, saut des ions alcalins dans un verre silice-oxyde alcalin), d'autres donnent lieu à des anomalies de frottement intérieur dont l'interprétation n'est pas toujours clairement établie. Ainsi, un peu au-dessous du domaine de transition vitreuse, on observe souvent un pic ou une anomalie de frottement intérieur plus ou moins bien résolue de la montée de frottement intérieur lié à la relaxation α ; cette manifestation semble être associée à des effets d'élasticité retardée. Un tel comportement nous paraît correspondre à un 2e phénomène de relaxation propre à l'état vitreux (relaxation β). Pour concilier les données concernant les modèles structuraux proposés pour décrire l'état vitreux et la nécessité d'envisager 2 environnements atomiques différents pour rendre compte des phénomènes de relaxation α et β, nous proposons d'ajouter aux modèles de structure généralement admis l'hypothèse suivant laquelle existeraient des défauts de type interfaces. La relaxation β pourrait ainsi résulter du mouvement des atomes ou molécules au niveau des interfaces alors que la relaxation α serait la conséquence du mouvement coopératif des atomes ou des molécules entre les interfaces. Dans une première approche, l'adaptation des modèles de relaxation déjà connus dans le cas des solides cristallins aux solides vitreux nous permet de rendre compte, au moins qualitativement, des résultats expérimentaux
LOCALIZED LATTICE INSTABILITY RELATED TO THE NUCLEATION PROBLEM OF MARTENSITE
No full textThe generalized soft mode is not very convenient to explain the martensite nucleation process. It must be substituted by a localized soft mode approach. The starting point for this approach is the sensitivity of the mechanical stability to the strains. It is first demonstrated that calculations using second and third other elastic constants provide a good approximation to the strain producing the instability. The effects of some particular strain such as "Bain strain" or {110} in ß phase alloys are reviewed. The soft zones around some specific lattice defects like dislocations and free surfaces are then analyzed. It is shown that large lattice vibrations are localized in these soft zones. An attempt is made to explain the role of the soft zones and associate large vibration to the nucleation process
"Development of wireless fire products”
No full textThe project was to develop a radio controlled door holder system as the first in a range of radio based products for Stephenson Gobin Eng Co. Ltd. Stephenson Gobin manufacture and market a wide range of electromechanical products, including retaining devices for fire doors and smoke vents. Typical installations are in hospitals, nursing homes, shopping centers, hotels or any building open to the public. The author discusses why a radio controlled door holder system is commercially and technically viable. Various wired and Wirefree door holder systems are evaluated on merits of safety and ease of installation. Stephenson Gobin developed a bi-stable latching door holding device which consumed no current in a state that was capable of holding a fire door open. This was due to a rotating magnetic slug assembly which only drew current to latch from one state to other. The device needed to be controlled wirelessly and possible methods of communication were assessed. Communicating using the license free radio frequency spectrum was selected due to the falling costs of radio components and the huge growth in the radio communication sector. The author developed and tested the hardware and software necessary to communicate with and actuate such a device
INTERNAL FRlCTION OF SINGLE AND POLYVARIANT MARTENSITES OF Cu-Zn-A1
No full textAbstract.- The alloys which exhibit a thermoelastic martensitic transformation are characterised by a high damping in the martensitic phase.In the case of 18R faulted martensites,two explanations can be proposed:the movement of the interfaces between the variants or the movement of the partial disloca-tions present at the edge of the faults.Thesemovements can be both detected by electron microscopy.To cut between these two hypothesis,the internal friction ofa single then pblyvariant martensite has been measured.A very low internal friction is obtained in the martensite single variant whereas high internal friction is as usually obtained for the polyvariant one.This proves that the internal friction of martensite is probably due to the movement of interfaces between the ' variants
Influence du désancrage des dislocations sur l'atténuation des ondes ultrasonores dans l'aluminium
No full textUltrasonic attenuation changes have been observed during tensile test of polycristalline aluminium 99,999 %, the strain beeing always smaller than 0,006 %. The curve Δα = f(σ0) exhibits three parts wheen σ0 increases : (i) a first increase of Δα in attenuation is observed, (ii) then a constant value Δα 1 of Δα is obtained, (iii) above a stress σp attenuation increases strongly. The first increase of Δα has been interpreted in terms of breakaway of dislocations from pinning points such as impurity atoms (a simple expression is proposed to describe this increase of Δα), the second increase is attributed to dislocation multiplication. When Δα ≃ Δα 1 different effects have been observed : a tensile speed effect, a time effect when tensile test is stopped at a stress συ, and a « memory » effect associated to συ. These results are qualitatively interpreted in terms of migration of impurities towards dislocations.Nous observons la variation de l'atténuation Δα des ondes ultra-sonores dans un aluminium 99,999 % pendant l'application d'une contrainte croissante σ 0, la déformation n'excédant jamais 0,006 %. La courbe Δα = f(σ0) présente trois parties : quand σ0 croît Δα augmente tout d'abord, puis garde une valeur sensiblement constante Δα1, et enfin augmente à nouveau lorsque la contrainte dépasse une valeur notée σp. La première augmentation de Δα1 est attribuée au dépiégeage des dislocations à partir des impuretés (une relation est proposée pour décrire cette croissance de Δα), la seconde à la multiplication du nombre de boucles. Dans la partie où Δα ≃ Δα 1 nous mettons en évidence le rôle de la vitesse de mise en charge, du maintien à une contrainte quasi constante συ et un effet de « mémoire » attaché à cette contrainte. Nous interprétons qualitativement ces résultats en envisageant la migration des impuretés vers les dislocations
Amplitude and Temperature Dependence of Internal Friction in Cu-Zn-Al Alloy Measured During Very Low or Null Temperature Rate
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