Storage and processing of granular materials are employed in numerous industries and are of interest to various branches of science and technology such as physics, chemistry, mechanics, agriculture and engineering. Agriculture and the food industry are, next to chemical and pharmaceutical industries largest producers and users of granular materials. Two basic conditions have to be fulfilled by equipment for storage and processing of granular materials: predictable and safe operations and obtaining high quality of final products.
Granular materials are distinctly different than typical forms of matter: gases, liquids and solids. Sometimes the statement is made that granular materials should be treated as an additional state of matter. Three types of effects typical for granular materials make them different from the other forms of matter: static friction between particles, non-elastic collisions and approximately zero energy of thermal movements as compared to potential energy due to the gravity. Faced with this mixture of known and unknown physical laws governing behavior of granular materials engineering practices have been developed to solve practical problems.
In recent decades increases in the number of processes and operations involving granular materials have resulted in a growing need for new theory and technology. This was accompanied with growing interest in investigations of physical properties of granular materials. Elaboration of effective design methods of technological processes requires detailed knowledge of physical properties of the processed material as well as proper understanding of their interrelations with construction materials. Development and refinement of methods for determination of physical properties of granular materials is becoming particularly important. Despite unquestionable progress in development of measurement methods mechanical properties of granular materials measured in various laboratories can vary greatly. A significant source of the wide range of results is due to the large number of measurement methods and a lack of standard experimental procedures. Moreover some influencing factors such as moisture content, bulk density, packing structure and load history remain out of control that contribute to observed variability.
Granular materials of biological origin constitute a coherent group of materials distinguished by large deformability of particles and strong dependence of their mechanical properties on moisture content. Contrary to materials of mineral origin, moisture penetrates inside grain, leading in some cases to qualitative changes in physical properties.