Papers by Keyword: Dislocation Damping

Abstract: Disc-shaped specimens of nickel and iron of about 30 mm diameter and a few millimeters thick were prepared by the high pressure torsion (HPT) method [1]. The produced equivalent shear strain ε linearly increased from a minimum at the centre to the periphery. The cold working process multiplied the dislocations and led to the grain fragmentation. The saturation of the grain refinement was approached at the circumference of the disk-specimens yielding a narrow distribution of the grain size with a mean value of about few hundred nanometers that depends on the material purity, temperature of the deformation [2]. The refinement of the microstructure changes the elastic properties of the material such as hardness, strength and has an influence on the attenuation and phase velocity of the ultrasound [3]. The paper reports the measurements of the longitudinal wave velocity and the attenuation in metals with polycrystalline (pc) and ultrafine (uf) microstructure.

Abstract: The relationship between acoustic emission and internal friction is investigated during cyclic deformation of copper single- and poly-crystals at intermediate amplitudes. Good agreement between these two phenomena has been demonstrated in all materials tested as long as the stress relaxation occurs uniformly within the sample whereas the difference between them becomes pronounced when strain/fracture localisation takes place. The similarity between acoustic emission and internal friction can be extended to materials deforming without appreciable plastic deformation, such as metal matrix composites where the main source of stress relaxation and strain accumulation is the particle breakage. The significance of the relation between internal friction and acoustic emission for understanding of fundamentals of AE is discussed.