Effect of spherical-agglomerate strength on the distribution of force during uniaxial compression

We employ the carbon paper technique with the aim of investigating the effect of spherical-agglomerate (pellet) strength on force distributions, through confined compression of approximately 1 mm sized pellets formed from microcrystalline cellulose and polyethylene glycol. The carbon paper technique relies on the transference of imprints from compressed pellets onto white photo quality paper, which are digitised and processed via image processing software. The investigated pellets can both deform plastically and develop localised cracks in response to an applied stress, while remaining largely intact during confined compression. Our results indicate that such crack formation - henceforth referred to as fracture - has a decisive influence on force distributions. Previous work on non-fracturing systems has found that the distribution of normalized forces tends to narrow with increasing particle deformation. No narrowing is observed after the point of fracture in this study and the width of the distributions - as quantified by the standard deviation of non-normalized forces - is found to increase with the difference between non-normalized mean force and fracture force. Additional corroborative results show that spatial force-force correlations typically exhibit a marked change once the fracture force is exceeded.