Wyniki wyszukiwania - BazTech

1

Deformation failure analysis and identification method of zoning type of actual tunnel surrounding rock

Jing Wei, Gao Yunlong, Jin Rencai, Jing Laiwang

Archives of Civil Engineering

|

2023

|

Vol. 69, nr 4

549--571

EN

The research on deformation zoning mechanism of tunnel surrounding rock is of great significance for ensuring safe production and disaster prevention in coal mines. However, the traditional deformation zoning theory of tunnel surrounding rock uses the ideal strain softening model as the criterion for judging the zoning type of all tunnel surrounding rock, ignoring the difference between the deformation zoning type of a specific actual tunnel and the basic zoning type of surrounding rock. In order to study the method for determining the actual deformation zoning type of tunnel surrounding rock, the formation mechanism of the actual deformation zoning of tunnel surrounding rock has been revealed. Combined with engineering examples, a method for determining the actual deformation zoning type and boundary stress of specific tunnel surrounding rock has been proposed. The results show that the boundary stress and position of the actual deformation zone are determined by the peak strength fitting line, residual strength fitting line, support strength line, and the position of the circumferential and radial stress relationship lines of each deformation zone. The actual boundary stress of each zone of tunnel surrounding rock is ultimately only related to the basic mechanical properties of the tunnel surrounding rock and the in-situ stress field. The research results can provide reference for disaster management of underground engineering, stability evaluation of surrounding rock, and support scheme design.

2

Stress evolution of rock breakages by a disc cutter assisted by pre-cuts

Liu Jie, Chen Wei, Liu Taoying, Peng Di

Archives of Civil and Mechanical Engineering

|

2023

|

Vol. 23, no. 2

art. no. e115, 2023

EN

To study the rock breakage mechanism by constant cross-section cutters assisted by pre-cuts, the present study first performed small-scaled linear cutting tests on sandstone specimens containing pre-cuts. The laboratory tests indicate that the sufficiently large penetration, causing successful internal and surface crack incisions, is essential for large chip formation. In addition, the small pre-cut depth may fail to form large chips. The numerical results agree well with laboratory tests in fracture patterns. More importantly, the numerical analysis indicates that the increases in rolling force frequently result in stress concentrations. When the stresses concentrate to critical values, fracture propagation occurs. The fracture propagation causes stress dissipation and the decrease in rolling force. Thus, the relation between cutting load fluctuations and crack propagation is revealed. Moreover, the influence of penetration on crack propagation is analyzed. By analyzing the stress fields at typical peak points of the rolling force, the crack propagation direction is predicted, and the influence of pre-cut depth on fracture propagation is studied.

3

Evaluation of continuous filament mat influence on the bending behaviour of GFRP pultruded material via Electronic Speckle Pattern Interferometry

Benfratello S., Fiore V., Palizzolo L., Scalici T.

Archives of Civil and Mechanical Engineering

|

2017

|

Vol. 17, no. 1

169--177

EN

Pultrusion is a process allowing the production of unidirectional (roving) fibre-reinforced polymer (FRP) structural elements with constant cross section. Recently, also civil engineers focused their attention on pultruded composite materials as alternative to traditional ones (e.g., concrete, steel). Furthermore, to improve the transverse strength and stiffness with respect to the fibres direction, continuous filament mat (CFM) is often placed within the stacking sequence. The CFM influence on the global mechanical behaviour is not considered by appropriate actual international standards. In this paper, the influence of the CFM layers on the mechanical behaviour of glass fibres pultruded composite material is investigated. In particular, the bending behaviour is analyzed by performing a four-point bending test on specimens extracted from an H-shape member. The experimental analysis was carried out via Electronic Speckle-Pattern Interferometry (ESPI) (handled by phase-stepping technique) to obtain a full-field displacement map and to numerically achieve the longitudinal strains. By imposing the equilibrium conditions and assuming the compression and tensile roving Young's moduli as constant, the CFM Young's moduli are determined. Finally, the mean stress acting on the material is obtained showing that CFM layers have to be considered to correctly evaluate the maximum stress and to optimize the design phase.

4

Kryterium energetyczne wzrostu krzywoliniowej trajektorii szczeliny

Mróz K., Doliński K.

Zeszyty Naukowe. Mechanika / Politechnika Opolska

|

2011

|

z. 99

117-119

EN

In the presentation the analysis of crack curving or instability under mode I loading conditions will be discussed. The simplified approach is used, namely the MK-criterion [7,8,9] based on the linear elastic fracture mechanics (LEFM). In the criterion it is assumed that crack growth follows the direction of minimum distortion energy density at a distance corresponding to specified value of dilatation energy.

5

Modelowanie numeryczne pola naprężenia w górotworze naruszonym wielopokładową eksploatacją węgla kamiennego w warunkach silnego zagrożenia sejsmicznego

Pilecki Z.

Zeszyty Naukowe Instytutu Gospodarki Surowcami Mineralnymi i Energią PAN

|

2011

|

nr 80

93-102

PL

Przedstawiono numeryczną dwuwymiarową symulację pola naprężenia wytworzonego w wyniku wielopokładowej eksploatacji węgla kamiennego, prowadzonej w trudnych warunkach zagrożenia sejsmicznego, w jednej z kopalń Górnośląskiego Zagłębia Węglowego. Obliczono wpływ projektowanej eksploatacji w dwóch wariantach na zmianę pola naprężenia w górotworze. Dokonaną eksploatację symulowano w kolejności chronologicznej, w okresach kwartalnych. Obliczenia przeprowadzono dla dwóch wybranych przekrojów geologicznych, w przybliżeniu prostopadłych do siebie. Przemieszczenia pionowe w modelu kontrolowano na podstawie wyników pomiarów geodezyjnych obniżenia powierzchni terenu. Obliczenia wykonano w ośrodku sprężysto-plastycznym z kryterium wytrzymałościowym Coulomba-Mohra za pomocą programu FLAC ver. 5.0. Generalnie, analiza numeryczna pokazała, że projektowana eksploatacja w zależności od wariantów w zróżnicowany sposób zmieniła pole naprężeń w analizowanej partii górotworu. Podkreślono, że duży wpływ na kształtowanie się zagrożenia sejsmicznego miały koncentracje naprężeń, zwłaszcza w strefie uskokowej, grubych warstwach skalnych i w rejonie krawędzi eksploatacyjnych.

EN

Numerical simulation of stress field influenced by multi-seam hard coal mining, in difficult geological and mining conditions, in one of the coal mine of Upper Silesian Basin has been presented. The changes of stress field in rock mass, as a result of up to date mining and planned mining in different variants, have been calculated. Simulation has been carried out for two geological cross-sections, perpendicular each other approximately, in direction of N-S and W-E. In the model, vertical displacements have been controlled by results of geodetic measurements of terrain surface subsidence. Calculation has been done in elastic-plastic medium with Mohr-Coulomb criterion with the help FLAC v. 5.0 system. These numerical analysis enables to estimate the influence of planned mining on stress field, and as well seismic threat. Generally, obtained results showed, that planned mining in analyzed variants may cause different stress changes, especially in fault zone, thick geological layers, and close to neighboring seam edges, and finally different seismic threat forming.

6

On the singularities at the tips of orthotropic wedges in plane elasticity. Part 2

Blinowski A., Wieromiej-Ostrowska A.

Technical Sciences / University of Warmia and Mazury in Olsztyn

|

2006

|

nr 9

65-72

EN

Part Two of the present paper contains more detailed studies of the subject, including cases of arbitrary symmetry. The order of singularity λ changes with the change in the properties of at least one material as well as with the wedge rotation angle y and its opening angle φ. Relations λ - φ for different sets of elastic constants corresponding to composites of epoxy resin and kevlar fiber, epoxy resin and boron fiber and real metallic cubic crystal (aluminum and tungsten) were studied. For some cases of arbitrary symmetry, modes of stress distribution for different values of λ were determined. It was found that the real solutions for λ are solitary in a complex plane. No complex solutions corresponding to finite elastic energy in the vicinity of a wedge tip (0 ≤ Re λ ≤ 2) were found.

PL

W niniejszej pracy rozpatrzono przypadek klina niesymetrycznego, zorientowanego niezgodnie z osiami ortotropii. Zbadano przebiegi zmienności rzędu osobliwości λ ze zmianą kąta obrotu ψ jednego materiału przy kątach rozwarcia klina φ=φ/2 i φ=φ/3 dla różnych kombinacji stałych sprężystych odpowiadających takim materiałom, jak: kompozyt żywicy epoksydowej i włókna kewlarowego, kompozyt żywicy epoksydowej i włókna borowego i rzeczywisty kryształ metaliczny w układzie regularnym (aluminium i wolfram). Poszukiwano rozwiązań pierwiastków rzeczywistych i zespolonych. Otrzymane rozwiązania są izolowanymi punktami na płaszczyźnie zespolonej, nie znaleziono rozwiązań zespolonych w obszararze (0 ≤ Re λ ≤ 2) odpowiadających skończonym wartościom energii sprężystej w otoczeniu wierzchołka klina. Dla wybranego przypadku niesymetrycznego znaleziono rozkłady naprężeń odpowiadających wartościom λ. Rozkłady te nie wykazywały ani symetrii, ani antysymetrii.