4 research outputs found
Physical Properties of Sintered Alumina Doped with Different Oxides
Corundum (alpha-alumina) is a suiTab. material for usage in various industry fields owing to its chemical stability, electrical and mechanical features. It is known that properties of ceramics could be modified by addition of different oxides, as well as by changing the consolidation parameters. In this respect, alumina was doped with 1 wt.% of Cr2O3, Mn2O3 and NiO, followed by 1 hour of mechanical activation in a high-energy planetary ball mill. A sensitive dilatometer was used for sintering of powder mixtures up to 1400 degrees C and recording the obtained dilatation. The final density varied between cca. 1.9 and 3.3 g/cm(3). Microstructural changes were detected by SEM measurements. Changes in electrical permittivity and loss tangent were associated with the preparation conditions (types of additives, duration of mechanical activation). For a given mixture, the sintering increases the relative permittivity and decreases losses, exhibiting the optimal values of 8.32 and 0.027, respectively, for the sample activated 60 minutes and sintered, with the addition of MnO2. Mechanical measurements indicate significant differences in strength with the addition of different transition metal oxides. Samples with Mn and Ni, activated and sintered, with strength of 121 and 86 MPa, respectively, have a significantly higher tensile strength than the other tested samples, due to their more compact microstructures
Reduced order numerical modeling for calibration of complex constitutive models in powder pressing simulations
Numerical simulations of different ceramic production phases often involve
complex constitutive models, with difficult calibration process, relying on a
large number of experiments. Methodological developments, proposed in present
paper regarding this calibration problem can be outlined as follows:
assessment of constitutive parameters is performed through inverse analysis
procedure, centered on minimization of discrepancy function which quantifies
the difference between measurable quantities and their computed counterpart.
Resulting minimization problem is solved through genetic algorithms, while
the computational burden is made consistent with constraints of routine
industrial applications by exploiting Reduced Order Model (ROM) based on
proper orthogonal decomposition. Throughout minimization, a gradual
enrichment of designed ROM is used, by including additional simulations. Such
strategy turned out to be beneficial when applied to models with a large
number of parameters. Developed procedure seems to be effective when dealing
with complex constitutive models, that can give rise to non-continuous
discrepancy function due to the numerical instabilities. Proposed approach is
tested and experimentally validated on the calibration of modified
Drucker-Prager CAP model, frequently adopted for ceramic powder pressing
simulations. Assessed values are compared with those obtained by traditional,
time-consuming tests, performed on pressed green bodies