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The design challenges presented by locating high-impact noise-producing athletic spaces, such as weight rooms and gymnasia adjacent to other occupied spaces are compounded by the difficulty in conveying the resulting experience through narratives or numeric performance criteria. As auralization tools can very effectively convey experiences in room acoustics and sound isolation, that effectiveness prompted an exploration into its possible use for conveying the experiences of impact-induced noise transfer resulting from difficult adjacencies. However, realistic and accurate auralization of a structural vibration path offers far more complex challenges than typical auralizations. For example, structural modeling for building design typically does not reach the resolution required for auralizations, if performed at all. Performance data for comparative floor types typically use tapping machines to comply with the Impact Isolation Class (IIC), which does not represent the response low-frequency content induced by heavy impacts. This paper dissects a case study of a method developed to address these challenges presenting a comparative auralization between athletic and gymnasium floor underlayment systems, enabling a client to experience the relative differences to aid design decisions. This included a method of presenting structural vibration with realistic source noise components and room effects to achieve a full soundscape.

Most challenges during the development of solid dosage forms are related to the impact of any variations in raw material properties, batch size, or equipment scales on the product quality and the control of the manufacturing process. With the ever pertinent restrictions on time and resource availability versus heightened expectations to develop, optimize, and troubleshoot manufacturing processes, targeted and robust science-based process modeling platforms are essential. This review focuses on the modeling of unit operations and practices involved in batch manufacturing of solid dosage forms by direct compaction. An effort is made to highlight the key advances in the past five years, and to propose potentially beneficial future study directions.

The bulk properties of a powder are dependent on the preparation, treatment, and storage of the sample, that is, how it was handled. The particles can be packed to have a range of bulk densities and, moreover, the slightest disturbance of the powder bed may result in a changed bulk density. Thus, the bulk density of a powder is often difficult to measure with good reproducibility and, in reporting the results, it is essential to specify how the determination was made. In this article, we measured the bulk density, tapped density, and calculated the Hausner ratio of commonly used excipients with similar tapped density testers and followed the United States Pharmacopeia 30-National Formulary 25-S1 testing procedure. Based on the analysis, within lot and lot-to-lot variability and the relative errors for bulk density, tapped density, and Hausner ratio were found to be acceptable. Lot-to-lot differences were generally not measurable using this test as they were found to be within the variability of the test. The results also indicated that there was no statistically significant bias between sites for tapped density and Hausner ratio, but there was a marginally significant bias in the bulk density data set.

The mechanical behavior of powders during die compaction was investigated using the discrete element method (DEM), in which powders are modeled as discrete particles with elastoplastic material behavior. A new adhesive elastoplastic contact model that describes the force displacement behavior of contacting particles subjected to high confining conditions was introduced and implemented in DEM simulations of die compaction and uniaxial tension. The objectives of these simulations were: (1) to investigate the micromechanical behaviors of powder systems during die compaction; (2) to understand the influence of model parameters on the macroscopic behavior; and (3) to develop a methodology for the calibration of the model parameters from macroscopic experimental results. The methodology developed for the calibration of the model parameters was carried out by a combination of statistical design of experiments (DOE) and optimization techniques. The calibration methodology provided simulation results that were in good agreement with experimental results conducted on hot melt extruded (HME) copovidone powder. One of the key advantages of the calibration procedure is the need for only two experimental techniques – die compaction, and diametric compression strength tests. Furthermore, examination of the microscale behavior from simulated results revealed a connection between the level of interparticle cohesion and the corresponding level of residual wall stress of powder compacts after complete unloading in die compaction. It was found that lower levels of interparticle cohesion resulted in decreased residual wall stresses and an increase in the axial spring back from the minimum compact height at the end of compaction. These results suggest that the decrease in residual wall stress and the increase in axial spring back with lower levels of interparticle cohesion depend not only on the elastic properties of the constituent particles during unloading, but also depend on the decohesion of particle-particle contacts.

In order to improve fundamental understanding of powder flow behavior which is essential to the success of many pharmaceutical processes, this study investigates the relationship between particle-scale interactions dominated by the cohesive van der Waals force and the flow function coefficient. This study finds that the granular Bond number, defined as the ratio of the inter-particle cohesion force to particle weight, correlates well to the flow function coefficient, a metric used to assess powder flow performance and defined as the ratio of consolidation stress to unconfined yield strength. The inter-particle cohesion force was calculated by the so-called multi-asperity model which is a modification of the well-known Rumpf equation. As a major novelty, a granular Bond number is defined for multi-component mixtures (i.e. powder blends) and used to predict the flow function coefficient of binary, ternary, and quinary mixtures of a model API, acetaminophen, and two common pharmaceutical excipients, microcrystalline cellulose and pregelatinized starch. Surface modification via dry-coating was also used to alter the inter-particle force and more thoroughly investigate the effect of particle interactions on powder flow performance. Since the multi-component granular Bond number takes into account particle properties and particle interactions of all components in the powder blend, this novel approach shows good predictability for powder mixtures. Although the flow function coefficient alone is not a stringent prediction of powder flow, the modeling effort put forth in this study can be used to better guide formulation development.

The present study explores new approaches to extract Drucker–Prager/Cap (DPC) constitutive model parameters at low and high densities of compacted powders for which it is not possible to get solid, undamaged samples for model calibration purposes. Extrapolations were carried out by invoking a number of physically plausible assumptions for high density conditions and the addition of the experimental shear cell testing procedure for low density extrapolations. The effects of these extrapolations on finite element model (FEM) results of both die compaction and roller compaction were examined. The sensitivity of the extrapolated DPC parameters on compaction model results was explored by performing parametric studies for both low and high density extrapolations. Examination of die compaction model results for low density showed little sensitivity to extrapolations; however, we are able to show that extrapolations of DPC parameters to low density may have a significant effect on roller compaction modeling results. High density die compaction FEM simulations reveal a significant effect on the way in which the DPC model parameters are extrapolated to high density. A method of extrapolating the DPC model parameters to high density is presented in this work. The work presented here demonstrates the significance of properly calibrating the DPC model at low and high densities and provides the necessary guidance for this purpose.

A finite element study of the interparticle force–displacement laws on contacts of spheres at conditions corresponding to compacts pressed to high relative densities is presented here. Under these conditions, the response of a contact can be affected by the presence of neighboring contacts. Finite element simulations of axisymmetric models of equispaced and equally loaded contacts show that the force–displacement law is not unique and depends on the number of neighboring contacts. The force at a given interparticle deformation is minimum for Z = 2 but at higher coordination numbers becomes larger after a critical deformation due to the interaction of the stress fields of neighboring contacts. This difference is magnified when the local porosity closes. Furthermore, numerical simulations of periodic arrays of spheres were conducted to assess the effect of loading path and the formation of new contacts on the response of existing contacts. In both cases, it was found that, the contact response depends on the overall triaxiality of the deformation of the particle. A new deformation fabric tensor is proposed based on the deformation and direction of all contacts on a particle. The first and second invariants of this tensor are used to characterize the triaxiality of the deformation on a particle. These results form the basis for more appropriate force–displacement laws at contacts that can be implemented in discrete element simulations for high density problems.

To obtain quantitative information and mechanistic insight into the problem of sticking of acetylsalicylic acid tablets on a metallic punch. Low voltage scanning electron microscopy was used to observe punch area coverage and morphology of adhered powder on a flat punch used for a limited number of compactions. Material accumulation in terms of area coverage of the punch per compaction cycle was determined at two pressures over five compactions. The distribution of the adhered material on the punch was non-uniform with more material left on the center of the punch. The sizes of the adhered particles range from 1 to 100 μm, with 50% of the punch surface coverage from particles of an equivalent diameter > 30 μm. Three types of adhered particles were identified after the first compaction: (a) fragments of initial particles with very high aspect ratio, (b) nearly equiaxed fragments with multiple cracks, (c) heavily deformed islands of low profile. Some preliminary ideas that explain these observations are presented and discussed. The ability of SEM to provide quantitative information on sticking from few compactions presents an interesting possibility for a material sparing technique that provides insight on the propensity of sticking.

In an effort to identify the origin and the evolution of damage during the compaction/ejection cycle of powder compacts, an experimental study that compares compacts in straight and tapered dies in terms of the presence and growth of microcracks was carried out using x-ray tomography and environmental scanning electron microscopy. The results presented here document the presence of internal microcracks at high relative densities, and microcracks on the surface of the compacts. Parts compacted in tapered dies exhibit microcracks with smaller crack tip opening and have a higher axial strength than those made in a straight die. These experimental observations, together with the ideas of damage generation under compressive stresses, as well as finite element analysis of the stress field in the compact as it exits from the die, confirm the hypothesis that a two-step mechanism is responsible for damage generation in powder compacts. First, microcracking occurs during unloading within the die at high pressures and subsequently surface cracks grow under the localized stresses as the compact emerges from the die.

Amorphous solid dispersions (ASDs) consisting of acetaminophen (APAP) and copovidone were systematically studied to identify effects of drug loading and moisture content on mechanical properties, thermal properties, and tableting behavior. ASDs containing APAP at different levels were prepared by film casting and characterized by differential scanning calorimetry and nanoindentation. The glass transition temperature (Tg) continuously decreased with increasing amount of APAP, but the hardness of ASDs was increased at a low APAP content and reduced at high APAP content. This in turn significantly influenced tablet quality. Water reduced both the hardness and Tg of ASDs, and the APAP loading level corresponding to the transition to the softening mechanism was lower at a higher relative humidity. Overall, the mechanical properties, rather than the thermal properties, better represent the plasticization/antiplasticization effect of small molecule to ASDs.