%0 Journal Article
%T Cumulative Effect of Pressing and Drying on Stress Generation within a Green Ceramic Compact
%A E. Vidal-Sall¨¦
%A D. Falgon
%A R. Peczalski
%A J-C. Boyer
%J Journal of Powder Technology
%D 2014
%I Hindawi Publishing Corporation
%R 10.1155/2014/674782
%X The internal stress field induced by uniaxial pressing and subsequent convective drying of a green ceramic powder was simulated by the finite element method. A density dependent elastoplastic constitutive law was used for the mechanical modeling of the compaction. A diffusive water transfer equation and a purely elastic behavior with imposed hydrostrain involving shrinkage were applied for the modeling of the drying process. The key material properties (hydrodiffusivity, hydrocontraction coefficient, Young¡¯s modulus, Poisson¡¯s ratio, and yield surface parameters) had been experimentally measured and introduced as functions of material density and water content. If residual stresses due to the compaction operation were taken into account, the maximum value of the tensile stress at the top external edge of the wheel and at the beginning of the drying process was two times higher than for a stress free green ceramic compact. Beyond the residual stress onset, the compaction operation induced density heterogeneities which had important consequences on the mechanical behavior of the compact. 1. Introduction Many factories in the mechanical industry are using grinding wheels for their finishing operations. As these wheels rotate at a high angular velocity, strong centrifugal forces can cause the wheel to break if damaged by initial precrack induced by the elaboration process. For that reason, the grinding wheel manufacturing requires a stringent product quality control. The grinding wheels dealt with in the present paper are realized with alumina based ceramic. The elaboration is composed of four steps.(1)The basic components of the wheel, that is, alumina grains with the primary and secondary binders, are mixed together.(2)The wet powder is given a shape using a single action pressing tool. The green ceramic is formed in an annular die and the compression is imposed until reaching the prescribed global density (see Figure 1).(3)The wet compact is extracted from the mold and dried with hot air in ventilated chambers at moderate temperature.(4)The dry compact is cured (vitrified) in a tunnel oven at a very high temperature; a finishing operation gives the final dimensions of the grinding wheel. Figure 1: Layout of the pressing operation as implemented with Abaqus. The punch (upper plate), the die (cylindrical wall), and the workpiece (annular compact) are drawn. The shades of grey on the compact represent the density levels (the highest density is in black). The green ceramic powder is a mix of metal oxide calibrated grains (89% of the total weight) of a
%U http://www.hindawi.com/journals/jpt/2014/674782/