On the Relationship Between Deformation-Induced Surface Roughness and Plastic Strain in AA5052—Is it Really Linear?

Abstract

Three different heat treatments of aluminum alloy AA5052 were subjected to various levels of uniaxial plastic strain. The resulting surfaces were then evaluated using both scanning laser confocal microscopy (SLCM) and stylus profilometry. Three regression approaches were used to assess the quality of a linear and a curvilinear fit for the roughness data as a function of true plastic strain. While there were differences among the regression results, the analyses revealed that a linear model was more statistically appropriate for the finest grain size. As the grain size increased, the surface morphology became more complex and a quadratic model became more suitable. Since the relative area fractions of grain boundary-localized roughness and slip-induced roughness are grain size dependent, the higher order fit between the roughness and plastic strain reflects substantial changes in the ratio of these areas. The differences between the SLCM and profilometry results were attributed to the natural filtering that occurs during contact profilometry. This filtering skewed the roughness data toward the largest surface displacements, thereby reducing the measurement fidelity to the point where the only possible outcome was the linear relationship.

On the Free-Surface Roughness in Incremental Forming of a Sheet Metal: A Study from the Perspective of ISF Strain, Surface Morphology, Post-Forming Properties, and Process Conditions

“…The roughness was measured in the longitudinal direction (i.e., 2 as defined earlier) because, due to experiencing strain, this direction had greater roughness than the transverse direction. The arithmetic mean of the roughness, which has been reported to have a consistent relation with the surface deformation in the traditional forming processes [4][5][6][7][8][9], was determined using the following relation:…”

“…The arithmetic mean of the roughness adequately represents the effect of plastic deformation on free-surface roughening in the traditional forming processes [4][5][6][7][8][9]. Therefore, this measure was adopted in the current study.…”

“…Due to absence of back support, the free surfaces in metal forming endure uneven deformation, resulting in the production of rough components. This free-surface roughness consequently promotes strain localization and leads to the premature failure of components during service [4,5]. Therefore, the production of smoother surfaces has been a matter of concern for the industrial and research community [6][7][8][9].…”

“…Besides affecting the component life, the roughness also influences strain localization and, thus, the formability of a component. Therefore, it has been a worthy exercise to incorporate information from strain roughness relation (s) into deformation models in order to precisely model the process and sheet failure [4,5]. For this reason, the nature of the relationship between the ISF strain and free-surface roughness also needs to be known to be helpful later in process modeling.…”

A numerical analysis of formation of the surface relief: A single inclusion model

“…This is due to the fact that the normal stress level at the interfaces is low relative to the total stress level. However, experimental and theoretical studies (see, e.g., [8]) indicate that the surface roughness formed at an early loading stage grows almost linearly as plastic deformation develops.…”