Papers by Keyword: Multiaxial Compression

Abstract: The paper presents the results of numerical simulations of the alternate indirect extrusion and multiaxial compression process, performed using commercial software designed for the thermomechanical analysis of plastic working processes, Forge 2009. The paper presents selected results on the distribution of deformation in the process of alternating extrusion and multiaxial compression. Examples of modifications to the shape of the die and punch, and their effect on the kinetics of the material flow as well as the likelihood of defects of materials are provided. The results confirm that suitable modifying the shape of the die and punch enables to obtain a material with no internal defects. Iterative process, alternating squeezing and multiaxial compressive strain allows the accumulation of which results in fragmentation of the microstructure.

Abstract: This article presents the results of numeric simulation obtained with commercial software for thermo-mechanical analysis of plastic forging processes, Forge 2009, of the process of alternate forced pressing and multiaxial compression. The new method of alternate forced pressing and multiaxial compression suggested by the authors is characterized by the presence in the plastically forged material of the similar states of deformations to those present in the processes of the equal channel angular pressing and cyclic extrusion compressing. From the performed preliminary tests it can be stated that as a result of combining and repeating two alternate operations: pressing and multiaxial compression, strain accumulation and development of deformation state favorable to grain crushing take place.

Abstract: Multiaxial compression (MAC) is a severe plastic deformation (SPD) method that allows sequential uniaxial compression of prismatic samples to relatively large cumulative strains. The technique involves a change in loading direction (x to y to z to x…) between successive compression passes. A high-purity α-iron containing 60 mass ppm C was thus strained using passes of ε ∼ 0.4 at room temperature (0.16 Tm) and 450 °C (0.40 Tm) to total ε ranging from 1.4 to 2.9. Both optical and electron microscopy were used to characterise the deformed microstructures. Fragmentation of the initial grain structure occurs mainly in the form of a dense, homogeneous network of low angle boundaries (LAB) delimiting subgrains of about 1 3m. The original grains are easily distinguishable and maintain a relatively equiaxed appearance even at larger strains. At room temperature, high angle boundaries (HAB) are observed within some of the initial grains, and not necessarily close to the grain boundaries. These HAB may be open or closed, and tend to align themselves at approximately 45° to the orthogonal axes, suggesting the presence of microshear bands and thus a heterogeneous deformation. Such bands of localised strain criss-cross as a result of different slip systems being activated from one pass to another. When the temperature is increased to 450 °C, grain boundary migration becomes significant owing to the lack of impurities that could otherwise provide a pinning effect. The resultant subgrain structure is coarsened to about 4 3m. Besides, the enhancement of recovery at higher temperatures also appears to discourage the generation of HAB by dislocation accumulation processes.