Sensing, measuring and modelling the mechanical properties of sandstone

We present a hybrid framework for simulating the strength and dilation characteristics of sandstone. Where possible, the grain-scale properties of sandstone are evaluated experimentally in detail. Also, using photo-stress analysis, we sense the deviator stress (/strain) distribution at the microscale and its components along the orthogonal directions on the surface of a V-notch sandstone sample under mechanical loading. Based on this measurement and applying a grain-scale model, the optical anisotropy index K0 is inferred at the grain scale. This correlated well with the grain contact stiffness ratio K evaluated using ultrasound sensors independently. Thereafter, in addition to other experimentally characterised structural and grain-scale properties of sandstone, K is fed as an input into the discrete element modelling of fracture strength and dilation of the sandstone samples. Physical bulk scale experiments are also conducted to evaluate the load-displacement relation, dilation and bulk fracture strength characteristics of sandstone samples under compression and shear. A good level of agreement is obtained between the results of the simulations and experiments. The current generic framework could be applied to understand the internal and bulk mechanical properties of such complex opaque and heterogeneous materials more realistically in future

Correlations Between Suspension Formulation, Drying Parameters, Granule Structure, and Mechanical Properties of Spray Dried Ceramic Granules

Within this project, the correlations between internal structures of ceramic spray dried granules and resulting mechanical properties were investigated. A new method for the preparation and selective quantification of internal structure parameters based on image analysis was developed and evaluated within this project. On microstructure level the microporosity, particle distance or coordination number can be determined. The macrostructure can be characterized via shell thickness, batch composition or macroporosity determination. The mechanical properties of spray dried granules can be modified in a defined way by adjusting shell thickness and/or microporosity: Increasing fracture strength can be achieved via increasing shell thickness or reducing microporosity. Comparisons of granule properties also showed increasing fracture deformation values via increase of shell thickness and/or increase of microporosity. For the investigated granules, a dominating influence of the microstructure (microporosity) was measured. Structural changes responsible for modified mechanical properties can be achieved via suspension formulation modification regarding solid content, particle size, or suspension temperature. Furthermore, spray drying parameters like drying temperature, atomizer type, or drying kinetics influence the structure formation and therewith mechanical properties if the added polyvinyl alcohol binder is kept constant. If the additive content is modified, varied internal granule structures can be achieved, whereas the physical additive properties are decisive for the resulting mechanical granule properties