Portail HAL ISAE-ENSMA
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An electro-mechanical transducer for an active anti-pulsatory system
No full textInternational audienc
Numerical and experimental study of a form of damage in plasticity.
No full textInternational audienc
Etude de la mobilité des dislocations dans le silicium monocristallin par frottement intérieur haute température
No full textLa mobilité des dislocations dans le silicium monocristallin a été étudiée par mesures isothermes de frottement intérieur. Trois pics de relaxation ont été mis en évidence à des températures croissantes, leur existence étant liée aux conditions de déformation. Le premier pic a été attribué à la migration de décrochements géométriques avec une énergie WM de 1,5 eV. Le second pic, d'énergie d'activation 1,95 eV, a été attribué à la création et à l'interaction des décrochements thermiques. Le dernier pic, d'énergie 2,4 eV, a été associé aux mouvements des décrochements thermiques dans le champ des atomes de dopant. L'énergie de formation des doubles décrochements déduite de ces essais (FDK) est de 0,9 eV
INTERNAL FRICTION TRANSIENT EFFECTS OF TITANIUM HYDROGEN SOLID SOLUTION
No full textThe internal friction of pure Ti between 500K and 700K is constant at 10-4when measured during a continuous increase of temperature. In opposite when the temperature is increased step by step, each increase of 10K induces immediatly a raising up of 4 10-4internal friction. During the following stage at the new temperature the internal friction falls slowly down to its initial value. This behaviour can be attributed to either the sudden modification of the thermodynamic equilibrium of pure titanium or the presence of a small amount of hydrogen trapped by the specimen during the experiment. This paper compares the internal friction of pure titanium and titanium containing 7 w.ppm of hydrogen. The presence of hydrogen has three consequences : - i - the internal friction background is increased from 10-4up to 30 10-4. - ii - the transient maximum of internal friction due to the temperature steps is 10 times as high as the corresponding value obtained with pure titanium. - iii - at temperatures higher than 700K large instabilities both of damping and modulus are recorded and it is not possible to reach an equilibrium value. It can be concluded that the transient maximums of internal friction are specific of the metal, the presence of hydrogen increases the amplitude of the effects