|
|
Simulace porušení betonu pomocí nelokálního modelu
Květoň, Josef ; Vořechovský, Miroslav (oponent) ; Eliáš, Jan (vedoucí práce)
Práce se zabývá numerickými simulacemi trámců v tříbodovém ohybu pomocí nelokálního modelu. Model je použit k simulaci sady zatěžovaných trámců lišících se velikostí a hloubkou zářezu. Záměrem je identifikovat pro model takové parametry, které by zajistily shodnou odezvu v porovnání s experimentální sadou zkoušek provedených na Northwestern University. Parametry materiálu a váhové funkce jsou stanoveny také na základě intenzity energie uvolňované v tělese získané z předchozích výpočtů diskrétním modelem. Odezva vypočtená pomocí nelokálního modelu je porovnána s výsledky experimentů.
|
|
|
Static and dynamic analysis of plain and fiber-reinforced concrete using discrete meso-scale model
Květoň, Josef ; Vorel,, Jan (oponent) ; Šejnoha,, Michal (oponent) ; Eliáš, Jan (vedoucí práce)
The presented thesis is devoted to mathematical modeling of concrete fracture. A special type of model called discrete particle model is used. The concrete meso-structure is simplified as a system of interconnected polyhedral particles. The particle interaction is prescribed at their contacts. Solution of discrete displacement field is obtained under the assumption of small deformations and rigid body movement of particles. Two modifications of the static version of the discrete meso-scale model are presented: (i) representation of short fiber reinforcement and (ii) implicit dynamic solver. The first main part of the thesis is devoted to modelling of short fiber reinforcement, which is used to improve poor tensile performance of concrete. This material modification leads to more efficient material use and crack width reduction. Short fibers are represented in the discrete model indirectly, taking into account the frictional forces between fiber and cement matrix. The fiber forces are applied at particle contacts working against the crack opening. This modification is able to capture the strain hardening behavior and the multiple cracking of the fiber reinforced composites. The second main part of the thesis addresses dynamic material behavior. Concrete resistance varies under different strain-rates. For slow, quasi-static loading rates, the initial micro-cracks localize into a macro-crack. For fast loading rates, the energy is not consumed by one crack only, but multiple cracking and crack branching occurs. The inertia typically dominates in fast processes. Even though the meso-scale model accounts for the inertia and the crack branching, the cracking at lower scale is not addressed. Therefore additional phenomenological rate-dependency of the constitutive law is adopted. Numerical simulations on various geometries under various loading rates are performed and compared to experimental evidence from literature.
|
|
|
Static and dynamic analysis of plain and fiber-reinforced concrete using discrete meso-scale model
Květoň, Josef ; Vorel,, Jan (oponent) ; Šejnoha,, Michal (oponent) ; Eliáš, Jan (vedoucí práce)
The presented thesis is devoted to mathematical modeling of concrete fracture. A special type of model called discrete particle model is used. The concrete meso-structure is simplified as a system of interconnected polyhedral particles. The particle interaction is prescribed at their contacts. Solution of discrete displacement field is obtained under the assumption of small deformations and rigid body movement of particles. Two modifications of the static version of the discrete meso-scale model are presented: (i) representation of short fiber reinforcement and (ii) implicit dynamic solver. The first main part of the thesis is devoted to modelling of short fiber reinforcement, which is used to improve poor tensile performance of concrete. This material modification leads to more efficient material use and crack width reduction. Short fibers are represented in the discrete model indirectly, taking into account the frictional forces between fiber and cement matrix. The fiber forces are applied at particle contacts working against the crack opening. This modification is able to capture the strain hardening behavior and the multiple cracking of the fiber reinforced composites. The second main part of the thesis addresses dynamic material behavior. Concrete resistance varies under different strain-rates. For slow, quasi-static loading rates, the initial micro-cracks localize into a macro-crack. For fast loading rates, the energy is not consumed by one crack only, but multiple cracking and crack branching occurs. The inertia typically dominates in fast processes. Even though the meso-scale model accounts for the inertia and the crack branching, the cracking at lower scale is not addressed. Therefore additional phenomenological rate-dependency of the constitutive law is adopted. Numerical simulations on various geometries under various loading rates are performed and compared to experimental evidence from literature.
|
|
|
Simulace porušení betonu pomocí nelokálního modelu
Květoň, Josef ; Vořechovský, Miroslav (oponent) ; Eliáš, Jan (vedoucí práce)
Práce se zabývá numerickými simulacemi trámců v tříbodovém ohybu pomocí nelokálního modelu. Model je použit k simulaci sady zatěžovaných trámců lišících se velikostí a hloubkou zářezu. Záměrem je identifikovat pro model takové parametry, které by zajistily shodnou odezvu v porovnání s experimentální sadou zkoušek provedených na Northwestern University. Parametry materiálu a váhové funkce jsou stanoveny také na základě intenzity energie uvolňované v tělese získané z předchozích výpočtů diskrétním modelem. Odezva vypočtená pomocí nelokálního modelu je porovnána s výsledky experimentů.
|
|
|
Numerical prediction of parasitic energy dissipation in wedge splitting tests on concrete specimens
Veselý, V. ; Holušová, Táňa ; Seitl, Stanislav
Undesirable energy dissipation taking place during wedge-splitting tests on cementitious composites and resulting in overestimation of the values of the determined fracture-mechanical characteristics of the tested materials is investigated in this paper via numerical simulations performed using a commercial finite element method tool with an implemented cohesive crack model. The rather broad range of cohesive behaviour of the studied materials was simulated through adjustments made to the corresponding characteristic length of the composite. The parasitic amount of energy is dissipated in fracture processes around the corners of the groove for the insertion of the loading platens, as these corners introduce rather strong stress concentrators to the specimen. This amount was extracted from simulated load-displacement curves and it was discovered that the amount considerably depends on the specimen proportions but its dependence on the level of material brittleness is not so significant.
|
host ::
RSS.