Mechanical properties of agglomerates

The mechanical properties of dry and wet agglomerates are reviewed in the context of continuum solid and fluid mechanics and fracture mechanics. The focus is on practical measurements of tensile strength, yield strength, hardness and fracture toughness, and how they define the attrition behavior of agglomerates. Well-established mechanical testing methods can be applied to agglomerates, but certain limitations apply due to the nature of agglomerates being inherently non-equilibrium (glassy), anisotropic, and compressible. The mechanical response of agglomerates may vary from brittle, elastic-plastic (for most dry agglomerates) to elastoviscoplastic and fully plastic (for wet agglomerates) depending on preparation method, environment, structure and loading conditions. This transition from solid to liquid-like behavior can be followed by applying solid/fracture mechanics and rheology-based testing, respectively. It is clear that most available practical measures of agglomerate mechanical behavior are not intrinsic, i.e. independent of test specimen geometry and the manner in which stress is applied. Therefore, selection and execution of measurements must be guided by loading conditions and agglomerate size and structure from the process of concern. Micromechanical modeling addresses some of the dependence of mechanical properties on the structure of agglomerates [e.g., porosity] and the properties of their primary constituents, but it cannot describe quantitatively bulk deformation and fracture of agglomerates. For this reason, agglomerate formulations are still tailored to achieve desired performance by empirical correlation of primary particle and agglomerate structure to mechanical properties.