International Journal of Fatigue 21 (1999) S247–S253 www.elsevier.com/locate/ijfatigue Effect of texture and ramp loading on the cyclic response and dislocation substructure of copper polycrystals P. Peralta a,* , K. Obergfell b , L. Llanes c , C. Laird b , T.E. Mitchell d a Arizona State University, Department of Mechanical and Aerospace Engineering. P.O. Box 876106, Tempe, AZ 85287-6106, USA b University of Pennsylvania, Department of Materials Science and Engineering, Philadelphia, PA 19104, USA c Departamento de Ciencia de Materiales e Ingenierı ´a Metalu ´rgica, E.T.S.I.I.B. Universidad Polite ´cnica de Catalun ˜a, Barcelona 08028, Spain d Los Alamos National Laboratory, MST-CMS, Los Alamos, NM 87545, USA Abstract Fatigue tests were carried out on copper polycrystals that had a texture with strong components along directions inside the standard stereographic triangle (single slip orientations in monocrystals). The experiments showed that this “single slip” texture, ramp loading as a mechanical pretreatment and extended cycling at a given stress to insure saturation provide the conditions to obtain a plateau in the Cyclic Stress–Strain Curve (CSSC) of copper polycrystals in a reproducible fashion. Transmission Electron Microscopy (TEM) studies revealed the presence of numerous Persistent Slip Bands (PSB’s) in samples deformed within the plateau regime.  1999 Elsevier Science Ltd. All rights reserved. Keywords: Cyclic stress–strain curve; Polycrystals; Strain localization; Dislocation structures; Plateau 1. Introduction The effect of texture in the cyclic behavior of copper polycrystals has been considered secondary by some authors [1,2]; however, Llanes and his coworkers [3–5] pointed out its importance on cyclic hardening behavior and its synergism with grain size, which was confirmed in later work [6–9]. Regarding strain localization, Ras- mussen and Pedersen [10] reported a plateau, i.e., a regime wherein plastic strain can be increased at con- stant stress, in the CSSC of polycrystalline copper at a stress predicted by the Sachs model (72 MPa) using texture free samples. Wang and Laird [11] also reported the presence of a plateau in polycrystalline copper, but at a stress consistent with the Taylor model (98 MPa). They used ramp loading as a mechanical pretreatment to enhance strain localization. Despite these results, Llanes [3] did not find a plateau in copper even though he used different grain sizes and ramp loading. He con- cluded that the presence of a sharp 111–100 tex- ture in his samples was responsible for the absence of * Corresponding author. Tel.: + 1-480-965-2849; fax: + 1-480-965- 1384. E-mail address: pperalta@icarus.eas.asu.edu (P. Peralta) 0142-1123/99/$ - see front matter.  1999 Elsevier Science Ltd. All rights reserved. PII:S0142-1123(99)00095-X the plateau. Peralta et al. [7] did not find a plateau in Cu either, although the texture of their samples had components along directions inside the standard stereo- graphic triangle, i.e., single slip orientations. Morrison [8], on the other hand, obtained convincing plateaux in nickel with small and large grain size using conventional testing. Contradictory results have also been reported for other FCC materials [12,13]. These facts suggest that a systematic study of the effect of texture on fatigue is needed to understand completely the cyclic deformation of polycrystalline FCC materials. Therefore, experiments were carried out to study the effects of texture and ramp loading on the cyclic behavior of copper polycrystals with emphasis on strain localization, as represented by the presence of a plateau in the CSSC. TEM studies were also performed to correlate the cyclic response with the presence of PSB’s. 2. Experimental Cylindrical fatigue specimens of 6.35 mm diameter and 12.7 mm gauge length were machined from a 50.8 mm diameter rod of OFHC copper in such a way that the axes of the samples were tilted 15° with respect to the axis of the rod to obtain a texture different from the