Amplitude-dependent Internal Friction and Dislocation Mobility in Crystals

The amplitude-dependent internal friction due to dislocations oscillating in the lattice is described in terms of dislocation mobility. This kind of intemal friction is expressed in elementary forms in the two limiting cases, i.e. at hish and low frequencies, and with the results obtained, the behavior of relaxation peaks due to dislocations are discussed 1 INTRODUCTION The amplitude-dependent internal friction will be caused in m y cases by the dislocations oscillating in the lattice, where obstacles are dispersed. In previous papers 11-31, this kind of internal friction and the modulus defects associated with it were described in terms of dislocation mobility, and the results ccinpred with data on metals. In this paper, the behavior of relaxation peaks due to dislocations will be mainly discussed. II EXPRESSIONS IN TWO LIMITING CASES The internal friction due to dislocations oscillating in the lattice, denoted by Ap, can be expressed in elementary forms in the following two limiting cases: At high frequencies, the motion of dislocation will be determined by frictional forces, and the internal friction is expressed in a form 111 * [ : ( O ) sin0 ü.0 ,. A a. w (1) where N is the density of mobile dislocations, 00 the stress amplitude, v(a) the dislocation velccity as a function of applied stress a, o = a. sinwt, and ut = 0. At low frequencies, the frictional stress is small, and the dislocation will bow out under applied stress, to which a small frictional stress is superposed. It is a s s d that the frictional stress of is equal to the effective stress needed for the dislocation to move freely at the same velocity. That is where oe(V) is the inverse function of v(ae), the velccity as a function of effective stress a,. With this assurnption, the intenial friction is 131 ( ' ) Present adress: Nagoya Nutrition College, 2-1 Sasatsuka-cho, Nishiku, Nagoya 451 Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19851044