Papers by Keyword: Polycrystalline Copper

Abstract: Atomic force microscopy (AFM) and focused ion beam technique (FIB) were adopted to study the early stages of surface relief evolution in 316L steel and polycrystalline copper fatigued with constant plastic strain amplitudes at different temperatures (316L steel at 93, 173 and 573 K; copper at 83, 173 and 295 K). Qualitative and quantitative data on the morphology and shape of persistent slip markings (PSMs), occurrence of extrusions and intrusions and the kinetics of extrusion growth are reported. They are discussed in relation with recent physically based theories of surface relief formation leading to fatigue crack initiation.

Abstract: Based on the crystal plasticity theory, the slip-band traces on the specimen surface of polycrystalline copper tensioned uniaxially are investigated by using the finite deformation numerical algorithm, and the statistical distributions of the inhomogeneous strain and stress in the specimen are analyzed. The tension deformation of the polycrystalline specimen is simulated by the three dimensional FEM. Through the geometric analysis of intersect-lines between the active crystallographic slip-planes and the specimen surface, the different slip-band traces of the specimen surface are calculated and discussed. According to the results, it is confirmed that the crystal plasticity theory is feasible to study the deformation of the crystalline material.

Abstract: Fatigue cracks in polycrystalline copper may originate from PSBs or grain boundaries. They usually form at the specimen surfaces, but also internal small stage I (shear) cracks have been observed with the ECC/SEM technique. They are formed together with a strongly elongated dislocation cell structure, which is reflecting in many cases localized deformation in “slip lamellae” with eventual ladder-like features, being typical of PSBs. Both, PSBs and small non-propagating cracks are initiated at cyclic stress/plastic strain amplitudes below the conventionally reported PSB threshold values, if the number of cycles exceeds a minimum, e.g. approximately 5x108 in the VHCF range. The internal small cracks are formed not only in polycrystalline electrolytic copper of 99.98% purity but also in high purity (99.999%) material.