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 (k), and spring-back index (j). 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) backprediction results. From the sensitivity analysis, AE 10% (standard deviation variation from AE 0.8r to AE 2.3r) changes in k and e 0 mean values had marked effect on the HTC results. However, changes in the k, j, 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.

Feasibility of Relationships between Tablet Physical Quality Parameters and Mechanical Properties of Dry Powder Formulation

“…The ingredients were stored and tests were conducted in an environment controlled laboratory with temperature setting of 23 C 1 C and relative humidity setting 35% 5%. Three replications of each test were conducted (Kamath and Puri, 1997;Li and Puri, 1997;Mittal and Puri, 2005).…”

“…1) developed by Kamath and Puri (1997) and Li and Puri (1997) and modified by Mittal and Puri (2005) was used for the experiments. This CTT is capable of applying pressure on six sides of a cubical sample (powder).…”

“…equal pressure is applied on each of the six faces of the cubical sample. Parameters such as bulk modulus, compression index, and spring-back index were determined using the HTC test (Li and Puri, 1997;Mittal and Puri, 2005). All tests were conducted at pressures upto 10 MPa and loading rates of 10 and 20 MPa/min.…”

“…In CTC tests, first the sample was confined by applying same pressure on each face of the cubical sample similar to HTC tests after that deviatoric stress was applied in the top-bottom direction (also the gravity direction). Shear modulus and failure stress were determined using the CTC tests (Li and Puri, 1997;Mittal and Puri, 2005). These tests were conducted at confining pressures of 1, 2, and 3 MPa.…”