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In the V-bending of sheet metals using a pair of plastic punch and die manufactured by a 3D printer, the effects of two different dimensions designed with the same tool geometry on the deformation behaviors of the punch, die, and sheet were evaluated. The deformation behavior and strain distribution of the punch, die, and sheet were analyzed using a digital image correlation method. Sheets from pure aluminum to ultra-high-strength steel were bent using the two tools with different spans; one was designed on the assumption of tool steel material, and the other was designed on the assumption of plastic material. In both tools, the large compressive strain appeared around the center of the punch tip and on the corners of the die. The tools with a long span for the plastic material gave a lower bending force and small deformation of the plastic tools. The angle difference between a bent sheet at the bottom dead center and a tool was smaller for the tools with the long span, although the springback in the bent sheet appeared. It was found that the design method on the assumption of the plastic material is effective for the V-bending plastic tools. [ABSTRACT FROM AUTHOR]

Sliding wear behavior of sub-microcrystalline pure iron disks produced by high-pressure torsion (HPT) straining was studied using a ball-on-disk configuration, and the effects of the strain in the HPT process and of the duration of wear tests were investigated. It was found that the wear amount decreased with increasing number of turns during HPT, and that the specific wear rate of the initial stage was inversely proportional to the Vickers hardness of the disks. However, for long wear test times, the wear rate became very small for both non-deformed and HPT-processed specimens, because of transition from adhesive shearing wear to sliding process which was caused by (i) grain refinement at the wear-induced layer, (ii) submicron wear particles adhered to the worn surface, and (iii) surface flattening by local asperity deformation. There was no significant difference in microstructure and hardness beneath the worn surface between non-deformed and HPT-processed specimens after the wear tests. Thus HPT improved the wear resistance only at the early stage, and became less effective for long wear tests. This study is the first to show that submicron grains produced by HPT straining were further refined to a size of 100–150 nm by friction shear straining while grain refinement of iron is saturated upon further straining in HPT processing. [ABSTRACT FROM AUTHOR]

Bimodal grain structure was fabricated in a 99.99% purity aluminium by high pressure torsion at ambient temperature in reversal deformation mode at a strain amplitude Δε =1, strain rate and hydrostatic pressure P =5GPa. Enhanced boundary mobility due to the high purity of the aluminium and homologous temperature coupled with reversal simple shear deformation are found to be responsible for bimodal microstructure formation. [ABSTRACT FROM AUTHOR]

Abstract: Most of severe plastic deformation processes involve strain reversal. Till now quite big number of researches has been done on indirect study of its role, which discusses the effect of loading path in ultra-fine grained structure formation. This work is aimed to study directly the role of the strain reversal in grain refinement by severe plastic deformation. A 99.99% purity aluminum was processed by high pressure torsion up to 96° rotation (maximal equivalent strain ɛ ≈8) with two deformation modes: monotonic and reversal deformations with a step of 12° rotation (maximal equivalent strain ɛ ≈1). It was shown that strain reversal retarded the grain refinement in comparison with the monotonic deformation. This explains slower rate of the nanostructure formation of the SPD processes that involve strain reversal. [Copyright &y& Elsevier]

Abstract: The role of strain gradient on strengthening and grain refinement into nanometer scale during severe plastic deformation was studied in iron by using ball milling (BM) and high-pressure torsion (HPT) processes. Layered nanocrystalline structure with a thickness of around 100nm or less was successfully produced by these processes. The hardness obtained by BM or HPT was more than twice as high as the maximum hardness obtained by homogeneous deformation processes such as equal-channel angular pressing, accumulative roll-bonding or cold-rolling. At the center of the HPT-processed disk, where the shear strain is theoretically zero, the hardness increased with number of turns. The results of BM and HPT experiments show clearly that the strain gradient contributes significantly to strengthening and grain refinement. [Copyright &y& Elsevier]

The evolution of texture in pure aluminum subjected to monotonous and reversal deformation in high-pressure torsion was first clarified. In a low-strain regime the texture development is similar for both deformation modes, while significantly different behavior is observed at high strain levels. The monotonously deformed materials showed typical torsion textures. In contrast, strain reversal results in development of texture components not observed for simple shear deformation. [Copyright &y& Elsevier]