Reduced order numerical modeling for calibration of complex constitutive models in powder pressing simulations

Abstract

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, timeconsuming tests, performed on pressed green bodies.

Thermal and mechanical behavior of composite mortars containing natural sorptive clays and fly ash

“…These dimensional changes can be also related to the loss of humidity present in the bentonite addition. Namely, the desorption of hygroscopic water and the loosely bonded water loss takes place between 30 and 210 o C. Dehydration is fully completed up to 600 o C [41]. Also, montmorillonite structure in bentonite swiftly decomposes in short interval upon reaching 850 o C, which can be related to the 2 % shrinkage registered in the S 3 sample during 800 -900 o C interval (Tab.…”

“…The DTA curve of S 6 mortar has a series of infinitesimal effects located on the exothermic hump. The most significant is the exothermic effect at 824.50 o C. This peak is followed by another exothermic effect at 902.3 o C. In bentonite, montmorillonite structure is preserved up to 850 o C, only to swiftly decompose during the following 50 o C [41]. The peak at 824 o C marks the start of montmorillonite decomposition in the S 6 sample.…”

“…The accuracy of the models, i.e the numerical verification of the developed models was tested using coefficient of determination (r 2 ), reduced chi-square (χ 2 ), mean bias error (MBE), root mean square error (RMSE) and mean percentage error (MPE). These commonly used parameters can be calculated as follows [40,41]…”

“…its mineral heulandite, exhibits a notable endothermic effect at 120 o C as a result of single-step dehydration [40]. Similarly, bentonite main mineral -montmorillonite dehydrates at approximately 100 o C [41]. The hydration water comprised in the bentonite structure is further removed through a sequence of thermal reactions in the 100 -450 o C interval (small exothermal peak at 350 o C, endothermic valley 350 -440 o C).…”

“…The elevated water absorption in the fly ash sample can be explained by increased micro-porosity of mortar due to the application of spherical porous ash particles. Bentonite grains are less porous [41] which led to more solidified structure of the composite material. Analogously, the combination of zeolite based additives showed higher WA 28 in mortar than bentonite additives.…”