| Autor: |
Scheele, G. |
| Přispěvatelé: |
Raabe, Dierk |
| Jazyk: |
němčina |
| Rok vydání: |
2004 |
| Předmět: |
|
| Zdroj: |
Aachen : Publikationsserver der RWTH Aachen University 162 S. : Ill., graph. Darst. (2004). = Aachen, Techn. Hochsch., Diss., 2004 |
| Popis: |
The surface topography of a bulk material is not only responsible for its optical appearance; it also has a strong influence on its physical properties like tensile strength or corrosion resistance. The topography develops during deformation due to extrinsic effects like tool-contact or due to intrinsic effects like microstructure related inhomogeneous deformation. The object of this investigation is to examine the relationship between microstructure and surface roughness during compressive and tensile deformation. The formation of the matt surface during foil rolling was taken as an example for the compressive deformation and the one-dimensional tensile test was taken as an example for the tensile deformation. The potential applicability of the crystal-plasticity finite element method was tested with regard to microstructure dependent roughness evolution. The microstructure was characterized with EBSD (electron backscattering diffraction) in a high resolution SEM with a field emission gun. The topography was measured using a white light confocal microscope. A small tensile test frame was constructed for use with the confocal microscope thus allowing in-situ surface measurements during tensile testing. The local strain distribution was calculated from the topographic dataset with a photogravimetric method. The foil rolling experiments showed an exponential relation between the roughness of the matt side and the strain. Neither the rolling velocity nor the viscosity of the rolling lubricant had a direct effect on the evolution of the matt side. An increase of the rolling force and a decrease of the viscosity of the separating lubricant reduced the roughness of the matt side because of the shift to from hydrodynamic lubrication to mixed lubrication. The homogenisation procedure after continuous casting and the modification of the chemical composition of the alloy has a strong influence on the roughness. A fine globular grain or subgrain structure has a positive effect. Such a microstructure evolves if a high volume fraction of fine particles is present. The type and fraction of precipitates was simulated with the Calphad-method. The influence of the iron, silicon, manganese and magnesium content on the roughening behaviour was investigated. Two different mechanisms were found for the roughness evolution during tensile testing. As a result of the grain structure a valley and hill structure was formed parallel to the tensile direction. In agreement with earlier publications a linear relation between roughness and strain was found. The second mechanism is based on the formation of shear bands. This leads to a surface texture, which is transverse to the tensile direction and shows an exponential relation to the strain. A method based on the classification of the localized necking of a tensile specimen was developed for the estimation of the roughening tendency of a material. With this method it is possible to make a first approximation of the roughening behaviour of an alloy during rolling without cost intensive rolling experiments. This could be advantageously used during alloy development. With a simple model the possibilities of the implementation of a crystal plasticity material law into the finite element simulation were demonstrated. The model can be used for the simulation of the orange peel effect. |
| Databáze: |
OpenAIRE |
| Externí odkaz: |
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