Numerické řešení procesu rozpojování tvrdých hornin. Část 2

This paper focuses on a numerical analysis of a hard rock (ore) disintegration process. A bit moves into the ore and subsequently disintegrates it. The disintegration (i.e. fracture of ore) is solved via a deterministic approach (FEM) and a probabilistic approach (FEM in combination with the SBRA - Simulation-Based Reliability Assessment method, i.e. Monte Carlo simulations, stochastic inputs). The ore is disintegrated by deactivating the finite elements satisfying fracture conditions. The results are compared with experiments. The application of the SBRA method is a new and innovative trend in this area. Finally, the probabilistic reliability assessment is mentioned.Článek se zaměřuje na numerickou analýzu procesu rozpojování tvrdých hornin (rud). Nůž se pohybuje do horniny a následně ji rozpojuje. Rozpojování (tj. lom rudy) je řešeno deterministickým přístupem (MKP) a pravděpodobnostním přístupem (MKP v kombinaci s metodou SBRA - Simulation-Based Reliability Assessment, tj. simulace Monte Carlo, stochastické vstupy). Ruda je rozpojována pomocí deaktivace konečných prvků, které splňují podmínky odlomení. Výsledky jsou porovnány s experimenty. Aplikace metody SBRA v této oblasti je novým a inovativním trendem. V závěru je uveden pravděpodobnostní posudek spolehlivosti

Dynamické charakteristiky nového stroje pro testování únavy železničních náprav - část 2

There were done some proposal calculations for a new testing machine. This new testing machine is determined for a dynamic fatigue testing of railway axles. The railway axles are subjected to bending and rotation (centrifugal effects). For the right proposition of a new machine is very important to know the basic dynamic characteristics of whole system. These dynamic characteristics are solved via FEM (MSC.Marc/Mentat software) in combination with SBRA (Simulation-Based Reliability Assessment) Method (probabilistic Monte Carlo approach, Anthill and Python software). The proposed dimensions and springs of a new machine for fatigue testing of railway axles were used for manufacturing. Application of the SBRA method connected with FEM in these areas is a new and innovative trend in mechanics. This paper is continuation of former work (i.e. easier deterministic approach) already presented in this journal in 2007.Byly provedeny návrhové výpočty nového zkušebního stroje. Tento nový zkušební stroj je určen pro dynamické únavové testy železničních náprav. Železniční nápravy jsou namáhány ohybem a rotací (odstředivé efekty). Pro správný návrh nového stroje je velmi důležité znát základní dynamické charakteristiky celého systému. Tyto dynamické charakteristiky jsou řešeny MKP (MSC.Marc/Mentat software) v kombinaci s metodou SBRA (Simulation-Based Reliability Assessment - pravděpodobnostní přístup Monte Carlo, Anthill a Python software). Navržené rozměry a pružiny nového stroje pro únavové testování železničních náprav byly použity pro výrobu. Aplikace metody SBRA spojené s MKP v této úloze, je novým a inovativním trendem v mechanice. Tento článek je následujícím pokračováním dřívější práce (tj. jednoduchý deterministický přístup) již prezentované v tomto časopise v r. 2007

Reliability analysis of beam on elastic nonlinear foundation

This paper is focused on the solution of simple beam continually supported by elastic (Winkler's) foundation. The foundation contains longitudinal nonlinearity. For the calculation of displacements and bending stresses are used analytical procedures (approximate solution in the form of polynomial function) and probabilistic approaches (SBRA method, Monte Carlo Simulation Method, AntHill software). Probabilistic approach includes influences of variability of load, shape and material of the beam, and variability of modulus of the foundation. Probabilistic approach is used for the reliability expertise of the beam and calculation of safety

Strength analyses of screws for femoral neck fractures

This article represents a multidisciplinary approach to biomechanics (engineering + medicine) in the field of "collum femoris" fractures. One possible treatment method for femoral neck fractures, especially for young people, is the application of cancellous (i.e. lag or femoral) screws (with full or cannulated cross-section) made of Ti6Al4V or stainless steel. This paper therefore aims to offer our own numerical model of cancellous screws together with an assessment of them. The new, simple numerical model presented here is derived together with inputs and boundary conditions and is characterized by rapid solution. The model is based on the theory of beams on an elastic foundation and on 2nd order theory (set of three differential 4th order equations, combination of pressure and bending stress-deformation states). It presents the process for calculating displacements, slopes, bending moments, stresses etc. Two examples (i.e. combinations of cancellous screws with full or cannulated cross-section made of stainless steel or Ti6Al4V material) are presented and evaluated (i.e. their displacement, slopes, bending moments, normal forces, shearing forces and stresses). Future developments and other applications are also proposed and mentioned.Web of Science38583481

O metodě centrálních diferencí aplikované na nosnících na pružném podkladu

This article is focused on the widely spread theory of straight and curved beams rested on elastic (Winkler's) foundation. For solution of these problems of mechanics, the Finite Difference Method (i.e. Central Difference Method) can be applied. The basic information about finite differences and their application are explained. This article also mentioned a new research in nonlinear behaviour of elastic foundation. Practical examples (i.e. beams with constant or variable stiffness of foundation or nonlinear foundation) are explained and solved (Matlab software).Tento článek je zaměřen na široce rozšířenou teorii přímých a křivých nosníků ležících na pružném (Winklerově) podkladu. Pro řešení těchto úloh mechaniky, může být použita metoda konečných diferencí (tj. metoda centrálních diferencí). Základní informace o konečných diferencích a jejich aplikacích jsou vysvětleny. Tento článek také zmiňuje nový výzkum v oblasti nelineárního chování pružného podloží. Praktické příklady (tj. nosníky s konstantní nebo proměnlivou tuhostí podloží nebo nelineárním podložím) jsou vysvětleny a řešeny (program Matlab)

MKP simulace napěťově-deformačních polí v kontislitku obsahujícím licí defekt během ohřevu v hlubinné peci

Round continuously cast blooms heating strategy is crucial in prevention of internal cracks initiation and propagation. Especially vanadium microalloyed Cr-Mo based steels are very sensitive to internal crack occurrence. This paper deals with two heating strategies that were realized in soaking pit. Using FEM simulation it was proved that proper heating strategy is essential to reduce internal crack propagation.Spravná strategie ohřevu kruhových kontislitků je zcela klíčová při prevenci vzniku a šíření vnitřních defektů. Obzvláště oceli mikrolegované vanadem jsou velmi náchylné ke vzniku vnitřních licích defektů. Tento článek pojednává o dvou strategiích ohřevu, které byly realizovány v hlubinné peci. Za použití MKP bylo dokázáno, že vhodná strategie ohřevu je zcela nezbytná, má-li být šíření trhliny co nejvíce omezeno

Metoda konečných diferencí použitá pro nosníky na pružném podkladu - část 2 (applications)

This article (as a continuation of the former work published in this journal), is focused on the theory and applications of beams on elastic (Winkler's) foundation. For solution of these problems of mechanics, the Finite Difference Method can be applied. Practical examples (i.e. beams with constant or variable stiffness of foundation) are explained and solved (Matlab software).Článek (jako pokračování předchozí práce publikované v tomto časopise) je zaměřen na teorii a aplikaci nosníků na pružném (Winklerově) podkladu. Pro řešení těchto úloh mechaniky, může být použita metoda konečných diferencí. Praktické příklady (tj. nosníky s konstantní nebo proměnlivou tuhostí podloží) jsou vysvětleny a řešeny (program Matlab)

Metoda konečných diferencí použitá pro nosníky na pružném podkladu - část 1 (teorie)

This article is focused on the theory of straight and curved beams on elastic (Winkler's) foundation. For solution of these problems of mechanics, the Finite Difference Method (i.e. Central Difference Method) can be applied. The basic information about finite differences and their application are explained.Článek je zaměřen na teorii přímých a křivých nosníků na pružném (Winklerově) podkladu. Pro řešení těchto úloh mechaniky, může být použita metoda konečných diferencí (tj. metoda centrálních diferencí). Základní informace o konečných diferencích a jejich aplikacích jsou vysvětleny

Experimental research of a new generation of support systems for the transport of mineral raw materials

Within the transportation of materials in mining using the belt conveyor systems, a conveyor belt is particularly the component with the highest wear rate. The development trends in the field of conveyor belt wear, in terms of disruption damage, are mostly focused on the innovation of damping components of buffer beds with impact rubber bars. Impact bars are an essential component of innovative buffer beds suitable for several types of belt conveyors. In mining, these bars are also used in buffer beds of bucket wheel excavator used for the extraction of overlying soils. The most important attribute of this support system is the impact resistance. Therefore, the output of the present paper is the determination of the limit impact dynamic loading based on the quantification of the force effect. The buffer bed eliminates the shortcomings of classic constructions, above all a point contact, and it allows better sealing-off of the whole place of an impact if required. Construction of the buffer bed should provide sufficient stiffness, flexibility, ability to direct conveyor belts at the direction of conveying, absorb the kinetic energy of the transported material, and ensure a surface contact between the material and the conveyor belt by increasing the surface friction drag. This paper deals with the experimental measurement of three kinds of impact rubber bars with different frameworks. Impact characteristics of the bars are significantly affected by the material and the type of metallic framework. The examined impact bars were exposed to the effects of the dynamic impact loading that is of great importance and facilitates the simulation of the belt conveyor system operation. The entire loading process was documented and impact load curves in time were analysed. The depth of penetration and the values of impact load were determined.Web of Science22438537

Analysis of locking self-taping bone screws for angularly stable plates

Paper focuses on biomechanics, specifically on locking cortical bone screws in angularly stable plates used for the treatment of bone fractures in the medical fields of traumatology and orthopaedics. During extraction of titanium-alloy implants, problems are encountered in an effort to loosen some locking bone screws from the locking holes of an angularly stable plate and the subsequent stripping of the internal hexagon of the screw head. The self-locking of the screw-plate threaded joint was verified by calculation and the effect of the angle of the thread on the head of the locking cortical bone screw on self-locking was evaluated. The magnitude of the torque, causing the stripping of the internal hexagon (the Inbus type head) of a locking cortical bone screw with a shank diameter of 3.5 mm from Ti6Al4 V titanium alloy to ISO 5832-3, was determined experimentally. Also, it was experimentally found that the rotation of the screwdriver end with a hexagonal tip inside the locking cortical bone screw head during stripping of the internal hexagon causes strain of the screw head perimeter and thereby an increase of thread friction. The effect of tightening torque on the possibility of loosening of the locking cortical bone screw from the locking hole of an angularly stable plate was assessed experimentally. From the evaluation of five alternative shapes of locking cortical bone screw heads in terms of the acting stress and generated strains, it follows that the best screw is the screw with the Torx type head, which demonstrates the lowest values of reduced stress and equivalent plastic strain. Based on experiments and simulations the authors recommend that all global producers of locking cortical bone screws for locking holes of angularly stable plates use the Torx type heads, and not heads of the Inbus type or the Square, PH, PZ types.Web of Science37462561