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

• Published in: Philosophical magazine (Abingdon, England) Vol. 89; no. 27; pp. 2403 - 2425
• Main Authors: Stoudt, Mark R., Hubbard, Joseph B.
• Format: Journal Article
• Language: English
• Published: Abingdon Taylor & Francis Group 21.09.2009; Taylor & Francis
• Subjects: aluminium alloys; Condensed matter: structure, mechanical and thermal properties; Exact sciences and technology; information theory methods; Lattice dynamics; Mechanical and acoustical properties of condensed matter; mechanical behaviour; Mechanical properties of solids; Phonons and vibrations in crystal lattices; Physics; plastic deformation; polycrystalline metals; sheet metal forming; Thermal properties of condensed matter; Thermal properties of crystalline solids; Thermodynamic properties; topological analysis; Tribology and hardness; Autocorrelation function; Vibrational modes; Roughness; Surface deformation; Eigenvalues; Stress effects; Entropy; Thermodynamic properties; Precipitates; Precursor; Surface stresses; Tribology
• ISSN: 1478-6435; 1478-6443
• DOI: 10.1080/14786430903120343

This research employs two approaches to characterise the apparent structure observed in localised strain maps constructed from surface topography data acquired from AA5754-O sheet stock that was deformed in three in-plane stretching modes. The first uses a conventional two-point autocorrelation function (ACF), while the second uses the combination of the eigenvalue spectrum associated with each map and information theory. The results from the ACF analysis are inconclusive, implying that this technique lacks the sensitivity necessary to quantify the relationships between multi-point clustering and strain localisation. The information theory-based approach reveals that the relative spectral entropy increases monotonically, attains a maximum and then decreases sharply to the failure strain. This behaviour occurs in all three strain modes and results from two competing processes: one where the formation of structure is favourable and one where it is not. The crossover point is a clear indicator of the onset of critical strain localisation and, therefore, can be regarded as a precursor to failure because once the dominant process shifts, additional strain results in the precipitate formation of a critical strain localisation event.