Publication Details

Shamdani, A. H., Khoddam, S., Thomson, P. F. & Dehghan-Manshadi, A. (2012). Microstructure and mechanical properties of IF steel deformed during plane stress local torsion. Journal of Materials Science, 47 (3), 1582-1587.


Mechanical joints are inherently vulnerable to failure because the presence of the joint hole causes a stress concentration in the vicinity of the hole. The need for improvement of material strength around a fastener hole can be satisfied by severe plastic deformation (SPD) to produce ultrafine grains. The ultrafine grained (UFG) alloys produced by SPD processing possess higher strengths than their coarse-grained counterparts as a result of the reduced grain size. However, in some circumstances such as SPD processing of Al-Zn and Al-Mg alloys the decomposition of supersaturated solid solutions competes with the Hall-Petch effect and leads to a more pronounced softening of the material [1]. Another drawback of SPD processes is that they involve bulk deformation and large energy consumption [2]. It is therefore desirable to enhance the global behaviour of the material by limiting improvement of the material property by SPD to the location at which it is needed. Localized severe plastic deformation (LSPD) techniques, such as forward spiral extrusion [3] and friction stir processing [4], involve lower energy consumption. They modify the properties of materials locally and create a gradient of grain refinement, resulting in significant improvement in the mechanical properties of the processed samples. However, these techniques cannot be used for strengthening the material around fastener holes, and thus a method for improving the strength of material around the hole is needed. To reinforce the mechanical properties of material around a hole, the plane stress local torsion (PSLT) process, which involves a plane stress axi-symmetric torsional loading, is introduced. The PSLT takes advantage of large shearing strains induced around the intended hole position, through torsional deformation [5]. As a result, the material flows plastically within a thin annular zone around the fastener hole (AZFH). Because of the limited penetration of the flow localization zone into the material, a major proportion of deformation energy is consumed within the AZFH. The PSLT therefore consumes much less energy than do bulk grain refinement techniques.

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