Experimental and numerical simulation studies were carried out to enhance the understanding of the compaction behaviour of powder materials and to study the breakage behaviour of tablets after compaction. In order to simulate powder compaction and post compaction behaviour an appropriate constitutive model is required. To calibrate the constitutive model (e.g. a Drucker-Prager Cap model) a series of experiments were carried out including closed die compaction, uniaxial and diametrical compression tests. A newly developed apparatus consisting of a die instrumented with radial stress sensors was used to determine constitutive parameters as well as friction properties between the powder and die wall. The calibration of constitutive models requires accurate stress-strain curves. During die compaction the deformation of the powder material is determined by considering the elastic deformation (or compliance) of the system. The effect of different compliance correction methods was evaluated with regards to the accuracy of models predicting the pressing forces. A method for accounting for non-homogeneous stress states in instrumented die compaction was also developed. A complete data extraction procedure was presented. The breakage behaviour of flat and curved faced tablets was investigated and the breakage patterns of tablets were examined by X-Ray computed tomography. An empirical equation that relates the material strength to the break force was proposed. The constitutive model was implemented into the finite element package Abaqus/Standard to simulate powder compaction and breakage. A range of failure criteria have been evaluated for predicting break force of flat and curved faced tablets under diametrical compression.

Manufacture of components from powders frequently requires a compaction step. Modelling of Powder Die Compaction presents a number of case studies that have been developed to test compaction models. It will be bought by researchers involved in developing models of powder compaction as well as by those working in industry, either using powder compaction to make products or using products made by powder compaction.

The compaction of fine powders offers an attractive means of creating engineered materials; however, there are often difficulties associated with producing compacts with acceptable properties. For example, failures including lamination or capping may occur during compaction and post-compaction processes if a certain level of mechanical strength is not met. Often times, a clear understanding of the cause of the issues leading to inadequate strength is lacking, thus making it difficult to mitigate the potential for failures. There is a strong interest in the availability of tools capable of providing a deeper understanding of the mechanisms responsible for the creation of compacts with adequate strength, as well as tools that can address the criticality of potential defects, and the effect these defects have on final compact properties. The current work focuses on the following: investigating and analyzing crack formation, the development of strength in the powder compaction process, and the generation of relevant predictive models via computational modeling that will allow for process optimization. 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 was performed. Analysis of the presence and growth of microcracks was carried out using x-ray tomography and environmental scanning electron microscopy. The results show the presence of internal microcracks at high relative densities, and microcracks on the surface of the compacts. Parts compacted in tapered dies exhibited microcracks with smaller crack tip openings and had 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, confirmed the hypothesis that a two-step mechanism was 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. To further elucidate the behavior of powders in the powder compaction process and the effects that the discrete nature of damage had on strength, this work considered the discrete element method (DEM). For powders compacted to high density, it is crucial that the force-displacement behavior of contacting particles is adequately captured in order to make proper predictions related to damage and strength in compacted components. A new adhesive, elastoplastic contact model, which describes the force-displacement behavior of contacting particles compacted to high density, was introduced and implemented in the DEM. A methodology was developed for the calibration of the model parameters of the proposed model from macroscopic experimental results. This was achieved by the use of statistical design-of-experiments (DOE) and parameter optimization techniques. The proposed DEM contact model was used to assess the ability of the DEM to predict damage and the effect that damage has on strength. A validation study was conducted to assess the ability of the proposed model to adequately predict behavior of powders compacted to high density. DEM simulations of powder compacted in straight and tapered dies were performed. The validation study performed showed excellent agreement with experimental finding for the unloading and ejection of straight and tapered die compacts.

The production of compacts with complex geometries by means of powder die compaction can be a delicate task. The compression process, used in many industrial sectors, is based on the densification of a powder bed by the application of an external load to obtain compacts. In some situations, the presence of defects (for example, cracks) in the compacts can be observed following the compression process. These lead to the degradation of the mechanical properties of the compacts and therefore their properties of use, thus leading to the non-conformity of the sample. Defects in powder compacts can be mainly due to the homogeneity of the compact, the mechanical behaviour of the powder and the complexity of the geometric shape of the sample. The work of this thesis contributes to the analysis of the compaction of pharmaceutical powders on large compacts with complex geometry (presence of grooves). In particular, to further understand the impact of the geometry of the compression tools on the final state of the compacts, both experimental and numerical studies were carried out. In order to model the mechanical response of the powder in compression to an external load, the Drucker Prager Cap (DPC) model was employed. To overcome a scaling problem, a hybrid calibration method of the DPC model was introduced in this work to provide a more realistic prediction of the powder behaviour in compression. The numerical results obtained by finite element simulation were validated by means of tomographic analysis.

Particle breakage is an important process within a wide range of solids processing industries, including pharmaceuticals, food, agricultural and mining. Breakage of particles can be defined as intentional and unintentional, depending on whether it is desired or not. Through understanding of the science and underlying mechanisms behind this phenomenon, particle breakage can be either minimised or encouraged within an efficient and effective process. Particle Breakage examines particle breakage at three different length scales, ranging from single particle studies through groups of particles and looking at solid processing steps as a whole. This book is the widest ranging book in the field and includes the most up-to-date techniques such as Distinct Element Method (DEM), Monte Carlo simulations and Population Balance Equations (PBE). This handbook provides an overview of the current state-of-the- art and particle breakage. From the small scale of a single particle, to the study of whole processes for breakage; both by experimental study and mathematical modelling.* Covering a wide range of subjects and industrial applications* Allows the reader an understanding of the science behind engineered breakage processes* Giving an unrestrictive and interdisciplinary approach