A Study of the Fundamental Relationships between Deformation-Induced Surface Roughness and Strain Localization in AA5754

Abstract

Three-dimensional, matrix-based statistical analysis methods were developed and integrated with high-resolution topographical imaging, to assess how microstructural changes influence the evolution of plastic deformation and strain localization in a commercial AA5754-O aluminum sheet in three in-plane strain modes. Analysis of the raw surface data revealed that the general composition of the surface roughness was highly sensitive to strain mode and strain level. The microstructural conditions that promote strain localization were assessed by extending a profilebased surface roughness parameter (Rt) to matrix form. Both analyses revealed that different strain modes produce characteristic dissimilarities in the deformation at the grain level. The localization data can be well characterized with a two-parameter Weibull distribution, suggesting that strain localization is a stochastic process that can be modeled reliably with Weibull statistics. This study clearly demonstrates that an accurate and straightforward probabilistic expression that captures the microstructural subtleties produced by plastic deformation can be developed from rigorous analyses of raw topographic data. Because variations in surface morphology profoundly influence the reliability of the numerical models used to predict strain localization, incorporating expressions of this type could greatly enhance the accuracy of these models.

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

“…As shown previously, raw topographic data have a character that can generally be described with Gaussian statistics. [6,15,21,22] This is convenient since Rq is defined as one standard deviation of the normal distribution (i.e., Rq " r). [23,24] Even though it is more common in the surface roughness literature, Ra has no definitional association to the moments of the height distribution.…”

Fundamental relationships between deformation-induced surface roughness, critical strain localisation and failure in AA5754-O

“…This section is a synopsis of the procedures presented in [11] that were used to generate surface data in the various strain conditions. Sets of 30 Â 30 cm (12 Â 12 in) blanks were sheared from 1-mm thick commercially available AA5754-O sheet stock for testing.…”

“…This paper is one in a series documenting analyses of strain localisation behaviour in commercial aluminium sheet [11][12][13]. The inspiration for this research is derived from the work of Frost and Ashby [14], and others [15,16], in that changes in the microstructure or, in this case, surface morphology, can be 'mapped' with respect to the level of plastic deformation.…”

“…The inspiration for this research is derived from the work of Frost and Ashby [14], and others [15,16], in that changes in the microstructure or, in this case, surface morphology, can be 'mapped' with respect to the level of plastic deformation. Previously [11], rigorous matrix-based statistical analysis methods were developed and integrated with high-resolution topographical imaging ( Figure 1) to assess how plastic deformation and microstructure evolution influence strain localisation in aluminium sheet deformed in three in-plane strain modes. A key component of this approach involves extending the peak-to-valley surface roughness (Rt) to a matrix form, which is done for three reasons: (1) the magnitudes of the local surface extremes will change with strain to the point where they reach a value that directly reflects the onset of critical strain localisation, (2) the Rt parameter is highly sensitive to those localised changes and it is acquired through a straightforward calculation, and (3) the Rt parameter is based on a simple sum of two values, so it can be easily determined between any two nodes within a particular region in a finite element simulation, allowing for direct integration of changes in the intensity of the local surface conditions into formability models.…”

Surface topography changes in aluminum alloy sheet during large plastic straining under cyclic pure bending

“…Wilson et al (1983) found a non-linear relationship of surface roughness to strain at large strains. Stoudt et al (2009) were also skeptical of data from models assuming linear relationships between surface roughness and plastic strain. Objecting to the use of linear profiles on the assessment of roughening behavior, they proposed a statistical model based on Weibull distributions instead.…”