Effect of Grain Level Anisotropy on Numerical Rock Fracture Behaviour under Dynamic Loading

The effect of rock crystal anisotropy is tested in numerical simulation of rock fracture at the laboratory sample level of scale. For this end, a numerical model based on the embedded discontinuity finite element method is applied here in simulations of uniaxial tension test on granitic rock. The rock material, consisting of Quartz (trigonal), Feldspar (triclinic) and Biotite (taken hexagonal here), is described as a linear elastic (up to fracture) heterogeneous and anisotropic material, which fails upon reaching the tensile strength of the individual constituent minerals. In the simulations of uniaxial tension test at two different levels of strain rate, the effect of averaged versus anisotropic elastic constants is tested. The results demonstrate that the effect of anisotropy is stronger at low strain rates (0.25 s-1 here), resulting in macrocrack planes at different locations for the isotropic and anisotropic material descriptions, while at higher rates (25 s-1 here) its notable effects disappear in the details of multiple macrocracks.

The Influence of Material Model of the Polyurethane Elastomer on the FEM Calculations Quality for the Various Modes of Loading

The paper presents research to verify the effectiveness of nine selected material models of elastomeric materials based on uniaxial tension test. Basing on the cyclic uniaxial tension test of elastomers sample, the stress-strain characteristic for the 18th load cycle was prepared. On the basis of the obtained characteristic, the values of material constants were calculated for the studied models (Neo-Hookean, Mooney with two and three constants, Signorini, Yeoh, Ogden, Arruda-Boyce, Gent and Marlow) and simulation of tensile, upsetting and bending processes was performed with the usage of the software MARC/Mentat. The effectiveness of the selected models was determined based on a comparison of results obtained in the experimental tensile test, upsetting test and bending test of an elastomeric samples with the results of numerical FEM calculations for each models. The research has shown that, for modeling of the elastomeric cylinder upsetting in the range of deformation of 62%, the best results with the comparison of the experiment were obtained by using the Yeoh model. In the bending process none of the analyzed models indicate a high convergence of results from an experiment. Analyzing the characteristics of the experimental and numerical tensile test it can be seen that in the entire range of punch movement (0 to 55 mm), models Signorini, Marlow, Ogden(N3) and Mooney(3) give the best results.

Modulus of Elasticity in Tension for Concrete and Fibre Reinforced Concrete

The paper deals with the determination of the modulus of elasticity in tension for cementitious composites and comparing these values with the values of modulus in compression. It describes several methods, which are usually used for determination of modulus of elasticity of concrete and fibre reinforced concrete. In the experimental program modulus of elasticity in compression and tension of various types of concrete and fibre reinforced concrete were compared. The classic test with prismatic specimens was used for determination of the modulus in compression; a new arrangement of uniaxial tension test of cementitious composites was used for determination of the modulus of elasticity in tension.