The paper presents research results on the selection of parameters for the asymmetric rolling process of bimetallic plates 10CrMo9-10 + X2CrNiMo17-12-2. They consisted in determining the optimum parameters of the process, which would be ensured to obtain straight bands. Such deformation method introduces in the band the deformations resulting from shear stress, which affect changes in the microstructure. But their effect on the structure is more complicated than in the case of homogeneous materials. It has been shown that the introduction of asymmetric conditions into the rolling process results in greater grain refinement in the so-called hard layer. There was no negative effect on the structural changes in the soft layer observed.
Many precision devices, especially measuring devices, must maintain their technical parameters in variable ambient conditions, particularly at varying temperatures. Examples of such devices may be super precise balances that must keep stability and accuracy of the readings in varying ambient temperatures. Due to that fact, there is a problem of measuring the impact of temperature changes, mainly on geometrical dimensions of fundamental constructional elements of these devices. In the paper a new system for measuring micro-displacements of chosen points of a constructional element of balance with a resolution of single nanometres and accuracy at a level of fractions of micrometres has been proposed.
Coal mining activities carried out for 200 years in Upper Silesia have had a negative effect on buildings. T his impact is in all cases related with continuous deformations of the surface and in certain cases with discontinuous deformations (mostly cave-ins), changes in water relations and mining tremors. T he paper presents an evaluation of the impact of a mining activity on a building situated in the Upper Silesian Coal Basin. T he building was affected by continuous deformations and mining tremors. Calculations were made of the values of deformation rates by means of Budryk–Knothe’s theory, which were partly verified on the basis of the results from geodetic measurements. An analysis of the velocity and acceleration of basement vibrations caused by mining-induced tremors was also conducted. T he conclusions included a high consistency between the results obtained on the basis of calculations and the values obtained by means of PGA and PGV measurements. In the case of tremors with the highest energy in the hipocentrum, there an empirical formula allowing for calculation of PGA value in given geological and mining conditions was also proposed. T he application range of the formula mentioned above is obviously limited only to the conditions in consideration. The presented conclusions indicate that at present, sufficiently precise methods, allowing for calculations for practical purposes, not only of deformation indices’ values, but also of PGV and PGA values, presently exist.
An analysis of the impact of mining with caving on the surface shows that a type of rock mass strata seems to be one of the critical factors affecting the process. Correlating the values of mining-induced surface deformation with the rock mass structure and the state of its disturbance is of crucial importance. Therefore, if other mining conditions are left unaffected, then those factors exert the key influence on a course and distribution of subsidence and rock mass deformation. A proper description of rock mass type and properties also seems rational for a proper determination of prediction parameters, especially in the case of a multi-seam coal mining, and/or the exploitation carried out at considerable depths. A general outcome of the study discussed in this paper is the development of the methodology and model practices for determining the rock mass type and, as a result, for selecting the optimal values of parameters for predicting the values of surface subsidence in relation to particular geological and mining conditions. The study proves that the type of rock mass may be described by such factors as the influence of overburden strata, the influence of Carboniferous layers, the disturbance of rock mass and the depth of exploitation.
Deriving the formulas for strain components, we are assuming, that cross-section of a rod being rotated in space during deformation does not need to be perpendicular to deformed centroid line. This not a quite intuitive assumption allows for more compact and easier formulas for strain tensor or equilibrium equations. Derived transformations between actual and initial coordinate system, components of strain tensor and virtual works principle for investigated spatially curved beams of bisymmetric cross-section are shown in this paper. Conformity with other models from referenced literature is also shown.
Underground mining extraction causes the displacement and changes of stress fields in the surrounding rock mass. The determination of the changes is extremely important when the mining activity takes place in the proximity of post-flotation tailing ponds, which may affect the stability of the tailing dams. The deterministic modeling based on principles of continuum mechanics with the use of numerical methods, e.g. finite element method (FEM) should be used in all problems of predicting rock mass displacements and changes of stress field, particularly in cases of complex geology and complex mining methods. The accuracy of FEM solutions depends mainly on the quality of geomechanical parameters of the geological strata. The parameters, e.g. young modulus of elasticity, may require verification through a comparison with measured surface deformations using geodetic methods. This paper presents application of FEM in predicting effects of underground mining on the surface displacements in the area of the KGHM safety pillar of the tailing pond of the OUOW Żelazny Most. The area has been affected by room and pillar mining with roof bending in the years 2008-2016 and will be further exposed to room-and-pillar extraction with hydraulic filling in the years 2017–2019.
The article is focused on the most recent investigations of glaciotectonic structures in high escarpment exposures of the Vistula valley from Dobrzyń to Kuzki in the western part of the Płock Basin. Deformations involve Neogene and occasionally the Lower Pleistocene deposits and they are not expressed as landforms. Structural investigations and analysis of archival geological data provided new information on the origin of large-scale shear structures. Results obtained are clearly contrary to the concept of Brykczyński (1982) regarding valley-side glaciotectonics in the Płock Basin. An emergence of the extensive zone of serial thrust structures of significant amplitude (up to 100–150 m) was found to have not been controlled by a palaeovalley. A driving mechanism is interpreted as a gravity spreading in front of ice sheets advancing from north-northeast during the South Polish Complex (Dorst-Elsterian).
The sodium expansion and creep strain of semi-graphitic cathodes are investigated using a modified Rapoport apparatus. To further understanding of the sodium and bath penetration damage processes, the impact of external stress fluence on the carbon cathode microstructure has been defined with XRD analysis, Raman spectroscopy and scanning electron microscope (SEM). Graphite atoms fracture into smaller fragments that are less directional than the pristine platelets, which allows for a possible filling of the cracks that thus develop by the sodium and bath during aluminum electrolysis. The average microcrystalline size (calculated by Raman spectroscopy) is reduced by the deformation. The decreased intensity and widened ‘G’ and ‘D’ peaks in the analysis indicate the poor order of the sheets along the stacking direction while the consistent layered graphite structure is sustained.
A total number of 156 palaeomagnetic specimens of metacarbonates from 9 sites in Blomstrandhalvøya and Lovénøyane (Kongsfjorden, western Spitsbergen) and an additional 77 specimens of unmetamorphosed sediments infilling fractures (4 sites) within the Caledonian metamorphic basement of Blomstrandhalvøya were demagnetized. No relicts of pre-metamorphic magnetization were identified. The Natural Remanent Magnetization (NRM) pattern of metacarbonates is dominated by Caledonian (sensu lato) – Svalbardian and Late Mesozoic/Cenozoic secondary magnetic overprints carried by the pyrrhotite and magnetite/maghemite phases, respectively. The NRM of unmetamorphosed sediments infilling the karstic/tectonic fractures is dominated by hematite carrier. It revealed three stages of magnetization: Caledonian sensu lato, Carboniferous and Late Mesozoic/Cenozoic, which can be related to their initial fracturing, karstification and sedimentation or reactivation. As the majority of the palaeopoles calculated for the Kongsfjorden sites fit the 430 – 0 Ma sector of Laurussia reference path in an in situ orientation these results support the hypothesis that Blomstrandhalvøya and Lovénøyane escaped main Eurekan deformations. The potential rotation of the Kongsfjorden basement by any west dipping listric fault activity rotating the succession accompanying the opening of North Atlantic Ocean was not documented by the palaeomagnetic data presented here.
Geodesic measurements of mining area deformations indicate that their description fails to be regular, as opposed to what the predictions based on the relationships of the geometric-integral theory suggest. The Knothe theory, most commonly applied in that case, considers such parameters as the exploitation coefficient a and the angle of the main influences range tgβ, describing the geomechanical properties of the medium, as well as the mining conditions. The study shows that the values of the parameters a = 0.8 and tgβ = 2.0, most commonly adopted for the prediction of surface deformation, are not entirely adequate in describing each and every mining situation in the analysed rock mass. Therefore, the paper aims to propose methodology for determining the value of exploitation coefficient a, which allows to predict the values of surface subsidence caused by underground coal mining with roof caving, depending on geological and mining conditions. The characteristics of the analysed areas show that the following factors affect surface subsidence: thickness of overburden, type of overburden strata, type of Carboniferous strata, rock mass disturbance and depth of exploitation. These factors may allow to determine the exploitation coefficient a, used in the Knothe theory for surface deformation prediction.
The paper presents a new geotechnical solution indicating a possibility of effective building structures protection. The presented solutions enable minimization of negative effects of underground mining operations. Results of numerical modelling have been presented for an example of design of preventive ditches reducing the influence of mining operations on the ground surface. To minimize the mining damage or to reduce its reach it is reasonable to look for technical solutions, which would enable effective protection of building structures. So far authors concentrated primarily on the development of building structure protection methods to minimize the damage caused by the underground mining. The application of geotechnical methods, which could protect building structures against the mining damage, was not considered so far in scientific papers. It should be noticed that relatively few publications are directly related to those issues and there are no practical examples of effective geotechnical protection. This paper presents a geotechnical solution indicating a possibility of effective protection of building structures. The presented solutions enable minimization of negative effects of underground mining operations. Results of numerical modelling have been presented for an example of design of preventive ditches reducing the influence of mining operations on the ground surface. The calculations were carried out in the Abaqus software, based on the finite element method.
Entries in steeply pitching seams have a more complex stress environment than those in flat seams. This study targets techniques for maintaining the surrounding rock mass stability of entries in steep seams through a case study of a steep-seam entry at a mine in southern China. An in-depth study of the deformation and instability mechanisms of the entry is conducted, employing field measurement, physical simulation experiment, numerical simulation, and theoretical analysis. The study results show that the surrounding rock mass of the entry is characterised by asymmetrical stress distribution, deformation, and failure. Specifically, 1) the entry deformation is characterised by a pattern of floor heaving and roof subsidence; 2) broken rock zones in the two entry walls are larger than those in the roof and floor, and the broken rock zone in the seam-floor side wall is larger than that in the seam-roof side wall; 3) rock bolts in the middle-bottom part of the seam-floor side wall of the entry are prone to failure due to tensile stress; and 4) rock bolts in the seam-roof side wall experience relatively even load and relatively small tensile stress. Through analysis, disturbances were found to occur in both temporal and spatial dimensions. Specifically, in the initial mining stage, the asymmetrical rock structure and stress distribution cause entry deformation and instability; during multiple-seam multiple-panel mining operations, a wedge-shaped rock mass and a quasi-arc cut rock stratum formed in the mining space may cause subsidence in the seam-floor side wall of the entry and inter-stratum transpression, deformation, and instability of the entry roof and floor. The principles for controlling the stability of the surrounding rock mass of the entry are proposed. In addition, an improved asymmetrical coupled support structure design for the entry is proposed to demonstrate the effective control of entry deformation.
Two strength-age hardening aluminum-lithium alloys: Al-2.3wt%Li and Al-2.2wt%Li-0.1wt%Zr in two different heat treatment conditions: solution state (S) and additionally in aging state (A) were severely plastically deformed by rolling with cyclic movement of rolls (RCMR) method to produce ultrafine – grained structure. Two thermo-mechanical treatments were used: (S+A+RCMR) and (S+RCMR+A+RCMR). To investigate the combined effect of plastic deformation and heat treatment, tensile tests were performed. Microstructural observations were undertaken using scanning transmission electron microscopy (STEM), and scanning transmission electron microscopy (SEM) equipped with electron backscattering diffraction detector (EBSD). Based on the obtained results, it can be deduced that maximum mechanical properties as: yield strength (YS) and ultimate tensile strength (UTS) could be achieved when the microstructure of alloys is in (S+A+RCMR) state. For samples in (S+RCMR+A+RCMR) state, ductility is higher than for (S+A+RCMR) state. The microstructural results shows that the favourable conditions for decreasing grain size of alloys is (S+A+RCMR) state. Additionally, in this state is much greater dislocation density than for (S+RCMR+A+RCMR) state. The microstructure of alloys in (S+RCMR+A+RCMR) state is characterized by grains/subgrains with higher average diameter and with higher misorientation angles compared with (S+A+RCMR) state.
Microstructure and texture of the CuCr0.6 alloy processed by rolling with cyclic movement of rolls (RCMR) at room temperature were investigated. The RCMR processing was applied for the samples in different initial conditions in the solid solution followed by quenching into iced water at 1000oC for 3 h and in aging treatment conditions performed at 500oC for 2 h and at 700oC for 24 h. Application of the solution and aging processes prior to RCMR deformation results in the partial dissolution of Cr particles into the Cu matrix and precipitation of the second phase particles. RCMR processing with value of the total effective strain (εft) of 5 was introduced to the material. It was found that the RCMR method is effective in texture weakening. The obtained results revealed that there is a large similarity in texture orientations after RCMR processing independently of heat treatment conditions. Cyclic character of deformation leads to an incomplete transition of LAB to HAB.
The paper has presented the results of theoretical studies and experimental tests of the plastic deformation of multi-layered Ti/Al/Mg specimens. Theoretical studies were carried out using the Forge2011® computer program. Physical modeling, on the other hand, was performed using the Gleeble3800 simulator. Cuboidal specimens were cut off from the plates obtained in the explosive welding method. Based on the obtained investigation results it has been found non uniform deformation of the particular layer as a result their different value of flow stress.
Influenced by the dynamic pressure of the front abutment pressure and the lateral abutment pressure, large deformation of surrounding rock occurs advancing working face in the entry heading adjacent to the active longwall mining face. Based on the cause analysis of entry large deformation, a new technology was put forward to solve the problem, and the designing method of drilling hole parameters for directional hydraulic fracturing was formed. Holes are drilled in the entry or in the high drainage entry to a certain rock layer over the adjacent working face, hydraulic cutting or slotting at the bottom of a borehole were also applied in advance to guide the hydraulic fractures extend in expected direction, through which the hard roof above the coal pillar can be cut off directionally. As a result, the stress concentration around the entry was transferred, and the entry was located in a destressing area. The field test at Majialiang coal mine indicates that the propagation length of cracks in single borehole is more than 15 m. After hydraulic fracturing, the large deformation range of the entry is reduced by 45 m, the average floor heave is reduced by 70%, and the average convergence of the entry’s two sides is reduced by 65%. Directional hydraulic fracturing has a better performance to control the large deformation of the dynamic pressure of the entry heading adjacent to the advancing coal face. Besides, it can improve the performance of the safety production.