Rate-Dependent Elasto-Viscoplastic Constitutive Model for Industrial Powders. Part 2: Model Evaluation

ABSTRACT

The PSU-EVP model's constitutive parameters for alumina powder are presented. The PSU-EVP model was also used to back-predict the triaxial test data obtained for MZF and alumina powders using constitutive parameters such as the initial voids ratio (e ₀), compression index (λ), and spring-back index (κ). In the case of MZF powder, 8 out of 12 back-prediction cases had average relative difference (ARD) values below 20%. In the case of alumina powder, 7 out of 11 back-prediction cases had ARD values below 20%. Based on the back-prediction results, it was concluded that the PSU-EVP model gave fairly good results for most triaxial test data collected at 0.62 MPa/minute and 6.21 MPa/minute. However, the back-prediction results obtained at 20.7 MPa/minute had high ARD values. A sensitivity analysis was done to study the effect of changes in parameter values on the hydrostatic triaxial compression (HTC) and conventional triaxial compression (CTC) back-prediction results. From the sensitivity analysis,±10% (standard deviation variation from ±0.8σ to ±2.3σ) changes in λ and e ₀ mean values had marked effect on the HTC results. However, changes in the λ, κ, and e ₀ mean values do not produce any noticeable effect on the CTC prediction results. Overall, the PSU-EVP model can be considered to be the first step towards the development of a more robust and accurate model for prediction of stresses and strains in a dry powder compression process.

Keywords:

• PSU-EVP model
• elasto-viscoplasticity
• triaxial testing
• back-prediction

Notes

^a Measured using Micromeretics Multivolume Helium Pycnometer 1305.

^b Measured using Micromeretics 2010 ASAP analyzer with 5-point BET method for low surface area materials.

^c Particle size analysis was done using the Malvern Instruments Mastersizer light scattering equipment.

^d Determined by drying the powder under helium.

^a IP = isotropic pressure.

^b Quantity in parentheses is the COV value in %.

^a IP=isotropic pressure.

^b Quantity in parentheses is the COV value in %.

^a IP=Isotropic pressure.

^b SI=Spring-back index.

^c Quantity in parentheses is the COV value in %.

^a MP=(2*CP+UP)/3.

^b CTC value collected at confining pressure of 2.1MPa was found to be an outlier after detailed analysis, and hence was deleted from the dataset.

^a CP=confining pressure; FC=failure criterion (% value of strain difference); FS=failure stress.

^b CTC value collected at confining pressure of 2.1MPa was found to be an outlier after detailed analysis and hence was deleted from the data set.

^a CP = confining pressure.

^a CP = confining pressure.

^b The value obtained at 2.1 MPa CP was considered to be an outlier after extensive data analysis.