Hj. Christ et al., HISTORY EFFECTS IN METALS DURING CONSTANT AND VARIABLE AMPLITUDE TESTING .1. WAVY DISLOCATION GLIDE BEHAVIOR, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 201(1-2), 1995, pp. 1-12
The influence of a mechanical prehistory on the cyclic deformation beh
aviour and the fatigue life was studied on polycrystalline copper as a
material showing wavy dislocation slip character. The specimens were
predeformed monotonically either by straining in tension up to differe
nt strain values or by swaging. Subsequent fatigue testing was perform
ed at constant plastic strain in the high amplitude, low cycle fatigue
region as well as at low amplitudes. Effects of cyclic predeformation
were studied in multiple step tests with blockwise constant amplitude
s and different loading sequences. Detailed transmission electron micr
oscopy was used to characterize the dislocation arrangements formed un
der the various conditions. The results of the mechanical tests are co
mpared with constant amplitude data of samples without predeformation
in order to describe the degree of dependence on history as a function
of testing mode. Differences are interpreted and discussed on the bas
is of observed changes in the dislocation arrangement.