In the present work, a methodology for setting up virgin stress conditions in discrete element models is proposed. The developed algorithm is applicable to discrete or coupled discrete/continuum modeling of underground excavation employing the discrete element method (DEM). Since the DEM works with contact forces rather than stresses there is a need for the conversion of pre-excavation stresses to contact forces for the DEM model. Different possibilities of setting up virgin stress conditions in the DEM model are reviewed and critically assessed. Finally, a new method to obtain a discrete element model with contact forces equivalent to given macroscopic virgin stresses is proposed. The test examples presented show that good results may be obtained regardless of the shape of the DEM domain.

The evaluation of a possible application of functional shrinkable materials in thermally conductive electrical insulation elements was investigated. The effectiveness of an electron beam and gamma radiation on the crosslinking of a selected high density polyethylene grade was analyzed, both qualitatively and quantitatively. The crosslinked polymer composites filled with ceramic particles were successfully fabricated and tested. On the basis of the performed investigation, it was concluded that the selected filler, namely a boron nitride powder, is suitable for the preparation of the crosslinked polymer composites with enhanced thermal conductivity. The shape memory effect was fully observed in the crosslinked samples with a recovery factor reaching nearly 99%. There was no significant influence of the crosslinking, stretching, and recovery of the polymer composite during shape memory phenomenon on the value of thermal conductivity. The proposed boron nitride filled polyethylene composite subjected to crosslinking is a promising candidate for fabrication of thermally shrinkable material with enhanced heat dissipation functionality for application as electrically insulating components.

No abstract

ABSTRACT:Curing kinetics models used in numerical simulations describe the exothermic chemical reaction of thermosetting materials. The mathematical formula known as Kamal's model is discussed in the following paper. Traditionally, the coefficients of Kamal's equations are estimated based on differential scanning calorimetry (DSC) measurements and results from an experimental verification of such created curing kinetics model are presented. Furthermore, an inverse analysis is proposed for additional adjustment of the model. The new coefficients thus found provide better accuracy in the computer simulations. The methodology of development of the curing kinetics model is proposed as an alternative solution to the standard DSC measurements. Particularly, it could be useful for materials with a complex structure, such as composites. C

No abstract