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The article presents an original method for determining the modulus of elasticity of natural materials. A studied solution was based on vibrations of non-uniform circular cross-section cantilevers solved using Bessel functions. The derived equations, together with experimental tests, allowed for calculating the material’s properties. Assessments were based on the measurement of the free-end oscillations in time using the Digital Image Correlation (DIC) method. They were induced manually and positioned at the end of a cantilever and monitored in time using a fast Vision Research Phantom v12.1 Camera with 1000 fps. GOM Correlate software tools were then used to find increments of deflection on a free end in every frame. It provided us with the ability to make diagrams containing a displacement–time relation. To find natural vibration frequencies, fast Fourier transform (FFT) analyses were conducted. The correctness of the proposed method was compared with a three-point bending test performed on a Zwick/Roell Z2.5 testing machine. The presented solution generates trustworthy results and can provide a method to confirm the elastic properties of natural materials obtained in various experimental tests.

The paper presents the results of numerical simulation of brittle material fracture initiated by Griffith's crack situated at any angle with respect to the load direction. The simulations were performed with the Simulia Abaqus FEA system using the X-FEM method. The direction of the crack propagation was determined using the user's subroutine written in Fortran, implemented in the Abaqus system. The authors programmed several conditions for the direction of the fracture propagation: maximum principal stress criterion, Ottosen-Podgórski criterion, three criteria based on displacements around the crack tip, and the MTS criterion, which is based on stress intensity factors. For the purposes of this study, two shapes of the crack tip were analyzed - sharp and blunted. The relationship between the direction of the initial fracture and the direction of crack propagation was found. The simulations were carried out for the angles of the initial crack from 0° to 90°, every 10°. A theoretical analysis of the implemented criteria was also carried out and compared to numerical results. The influence of the shape of the crack tip on the simulation result was analyzed. It was shown that the simulation results closest to the theoretical results were obtained for the own implementation of the stress-based criteria. It has also been proven that the shape of the crack tip has little effect on the result if the finite element mesh is properly densified. However, the sharp crack has a disadvantage for small initial crack angles. The Author’s method of predicting the crack propagation has been proven correct and effective. This work is also the basis for the further development of the described method.

This article presents the results of the computer simulations of a four-point bending test of a concrete single-edge notched beam. In this publication, the authors compared the X-FEM method of simulating the crack in the Abaqus FEA system. The paper also contains the results obtained with the Abaqus subroutine recently developed by the authors, used for defining the direction of the crack and the failure criterion. The publication explains the way of working of this algorithm. The described calculations show that computer analysis gives unrealistic results in terms of the destructive force. SEN-beam is an interesting laboratory test in which a lot of factors influence the results. It is especially important to study what phenomena occur in the final phase of the study, when the crack tip is near the opposite side.

The article describes a computer analysis of the pull-out test used to calculate the force needed to pull out a rock fragment and determine the shape of this broken fragment. The analyzed material is sandstone and porphyry. The analysis included the first approach to using own subroutine in the Simulia Abaqus system, that is, which task is undertaken to accurately determine the crack path of the Finite Element Method model. The work also contains a description of laboratory tests and analytical considerations.

This paper presents a study on wind flow in the passage between the walls of a bell tower. The bell tower, raised above the church roof, consisted of two walls with the horizontal angle between them equal to 100°. Computational fluid dynamics (CFD) simulations were performed for 3D models of the entire church structure. Two opposite inflow wind directions, which corresponded to diverging and converging wall layouts, were used. Amplification factors of the wind velocity along the passage were calculated. Additionally, full-scale measurements were conducted using three ultrasonic anemometers and three cup anemometers placed along the horizontal centreline of the bell tower walls. The CFD results were validated with the use of in-situ data. Wind velocity amplification or reduction observed in CFD simulations and full-scale measurements were of the same order. The biggest amplification of the wind velocity behind the passage was obtained for diverging walls, whereas the biggest reduction occurred in the front of the contraction for converging walls. The influence of geometry simplification and changes in the description of the wind flow were also analysed. Considerable differences in CFD simulations results were caused by small changes in the geometry of the model rather than by changes in the terrain category, including the roughness of the terrain.

This paper presents experimental, theoretical and numerical studies of wood-CFRP beams bonded with polyurethane (PUR) adhesive. The analyses include two types of CFRP (carbon fibre-reinforced polymer) strengthening configurations and pure glue laminated timber beams as a reference. Through detailed analyses of a double-lap connection on blocks with and without CFRP strips, the authors state that neglecting the cohesive stiffness of adhesive layers may lead to an overestimation of an overall beam&rsquo, s stiffness. This is significant with wood&ndash, CFRP connections, which showed values two times lower than with wood&ndash, wood connections. Theoretical modelling of the equivalent area used in a theory of composites provided much stiffer behaviour of the beams than in laboratory experiments. It proves that a PUR glue eliminates the possibility of using simple models that assume a perfect connection between bonded parts. These conclusions led the authors to use the finite element method (FEM) to take into account the cohesive stiffness. The FEM, based on the properties obtained from a double-lap joint analysis, allowed for the precise prediction of the elastic stiffness of the beams.

The paper presents numerical and experimental research on glulam delamination in a double lap connection with predominant shear stresses. Laboratory tests and wide literature survey enabled to determine timber and glue joint parameters. Cohesive zone theory, generally used for epoxy matrix and fiber reinforced composites, was adopted to modelling glue layer delamination in glulam elements. Numerical models were validated with laboratory tests.

Structural designing of reinforced concrete structures consists in determination of the cross section height and amount of the vertical and horizontal reinforcement on the basis of the internal forces. These forces are not determined correctly without considering the structure deformation. It means that the geometric type nonlinearity should be regarded at least. In the case of compression the buckling and the so called “second order effects” should be taken into account. The EC2-1-1 code gives the general rules for such effects, but they are described in details only for columns and buildings. Therefore the aim of this paper is to formulate recommendations which will be useful for reinforced concrete cylindrical tanks for liquids and particulate solids compressed vertically (meridional compression) and horizontally (hoop compression). These recommendations are formulated on the basis of nonlinear FEM analysis, which is preceded by analysis of expressions describing the critical stress of cylinders, formulated by theory of elasticity.

The paper describes an approach to model glue laminated timber (GLT) made of pinewood (softwood), taking into account damage processes in timber and adhesive layers. An example of a pre-cracked beam has been presented. Obtaining necessary material properties has been supported by several finite elements models (FEM), laboratory tests and a wide literature survey. The authors have taken into consideration an orthotropic material with damage for timber lamellas and isotropic traction separation law for bonding layers. Both plane stress CPS8R and COH2D4 finite elements from the Simulia ABAQUS system or mesh density, used in the numerical analyses, have been carefully chosen and tested. The GLT beam model has been verified on the basis of several values, using two types of testing techniques&mdash, MTS 809 machine measurements and digital image correlation (DIC). Additional results revision has been provided by measuring a crack shear displacement (CSD), using the original laboratory test setup by the authors&rsquo, idea. Finally, some conclusions and introductory recommendations for modelling a glue laminated timber in a plane stress have been formulated. The paper is a part of a wider research on timber-polymer composites, which is still under development.

The paper presents an approach to natural plant stems numerical modelling in a three-point bending test. Introduced subject was connected with elaborating more efficient systems for harvesting energetic plants. There were modelled, and laboratory tested two types of stems – sida hermaphrodita and miscanthus giganteus. Course of proceedings for obtaining natural cross-sectional dimensions with graphical data processing was described in detail. Basing on dozens of stems slices from random parts of plants, three different cross-section approximations were proposed and computationally implemented – a circular pipe, an elliptical pipe (symmetrical cross-section) and a sine-cosine series pipe (asymmetrical cross-section). Analytical formulas for calculating a cross-sectional area and moments of inertia for each approximation were given. Basic material parameters as an elastic modulus and yielding stress was obtained from simply supported beam theory and laboratory force – the deflexion relation. FEM models were created in Simulia Abaqus software using C3D20R elements. Preliminary approach to modelling damage with perfect plasticity was done basing on several samples bended to failure in laboratory tests. Conclusions for future work with numerical modelling natural plant stems were drawn.

This paper describes a method of predicting the direction of crack propagation implemented by user subroutines in the Simulia-Abaqus FEA system with the use of the extended finite element method (X-FEM). This method is based on displacements and stresses according to Westergaard’s solution of Griffith’s crack problem. During the calculations, in each crack increment, the algorithm reads the stresses and displacements in the model around the crack tip, calculates the criterion values at the read points, reduces them to a unit distance from the crack tip, fits a polynomial to these points, and finds the minimum of the function closest to the last propagation angle. The algorithm also decides when the crack grows, depending on a chosen criterion. Four criteria have been implemented to predict the direction of failure propagation: the maximum principal stress criterion, the Ottosen–Podgórski criterion, the new criterion described here based on the minimum component values of the displacement vector, and the maximum circumferential tensile stress (MTS). These criteria were verified in two tests: the three-point bending test of the notched beam and the anchor pull-out test. For these tests, the criterion built into Simulia Abaqus does not correctly define the crack path, which causes the crack propagation direction to “rotate” when simulating the fracture. The criteria developed here, in most cases, determine the crack path and the maximum force very well compared to real laboratory tests.

Measurements of the Linke turbidity factor (LTF) were performed at Belsk (20.78°E, 51.83°N), Poland, since 1964. This data is used to retrieve broadband aerosol optical thickness normalized to the air mass equal to 2 (BAOT2). A linear analysis of the BAOT2 changes reveals an upward trend of 0.023±0.017(2σ) in the 1964–1975 period, a downward trend of–0.051±0.017(2σ) in the 1976–1991 period, and afterwards a statistically insignificant trend of–0.009 ± 0.014(2σ). Such pattern may be related to the economic changes in Poland (changing emissions and environmental policies). The elevated BAOT2 values, excluded from the trend, are found in 1984 and 1992 due to the volcanic eruptions of El Chichon and Mt. Pinatubo, respectively. Past AOT values at 340 and 500 nm are reconstructed using a linear relationship found between AOT and BAOT2. The reconstructed data is used by the radiative transfer models to estimate a response of the total solar and erythemal radiation to the changes in the atmospheric aerosols at Belsk.

This paper presents an attempt of using a finite element method for predicting delamination of a glue laminated timber beam through a cohesive layer. There were used cohesive finite elements, quadratic stress damage initiation criterion and mixed mode energy release rate failure model. Finite element damage was equal to its complete stiffness degradation. Timber material was considered to be an orthotropic with plastic behaviour after reaching bending limit.This paper presents an attempt of using a finite element method for predicting delamination of a glue laminated timber beam through a cohesive layer. There were used cohesive finite elements, quadratic stress damage initiation criterion and mixed mode energy release rate failure model. Finite element damage was equal to its complete stiffness degradation. Timber material was considered to be an orthotropic with plastic behaviour after reaching bending limit.

This paper describes the computer analysis of the pull-out test for determining the force needed to pull out a rock fragment, and the shape of this fractured fragment. The material analysed is sandstone. The analysis included a comparison of the various crack propagation methods in computer program using the Finite Element Method. The work also contains a description of performed laboratory tests and analytical considerations.

Measurements of erythemal irradiance have been carried out continuously at Belsk since May 1975. We present a homogenization procedure of the UV time series for the period of 1976–2008. Long-term oscillations discovered in the homogenized data set agree with those extracted from the reconstructed UV data for all-sky and clear-sky conditions. The UV climatology was established and the UV variability was determined. Positive UV trends were found for the period of 1976-2008 in the annual mean (5.6±0.9% per decade), in the seasonal mean for the warm subperiod of the year (April–October, 5.5±1.0% per decade), and in monthly means (∼2–9% per decade). A satisfactory agreement between the trend extracted from the homogenized ground-based data and that found in satellite UV data for Belsk (1979–2008) supports the reliability of satellite trend analyses over wider areas during snowless periods.

Eruption of Eyjafjallajokull volcano took place on 13-14 April 2010, and created an ash cloud moving towards densely populated areas in Europe. Dispersion models show that the cloud appeared over Poland at noon on 16 April. Measurements of optical properties of the atmospheric aerosols by the Cimel Sun Photometer (optical thickness and volume size distribution) and lidar (backscatter coefficient) at Belsk (52° N, 21° E) for the period 15-26 April 2010 are examined to find volcanic ash in the atmosphere over the site. Thin aerosol clouds, linked to the volcanic eruption, were found below 5 km, and their optical thickness (at 500 nm) varied only slightly in the range of a few hundredths. The optical depth of the aerosol clouds in the 5-7.5 km layer was less than 0.01.

The lidar ratios at 500 and 1020 nm were derived from POM 01L sun-sky scanning photometer measurements taken at Belsk Geophysical Observatory (long. 20°47′, lat. 51°50′) in the period from 2002 to 2006. The most frequently occurring lidar ratio values for the study period are 50 sr and 30 sr at 500 nm and 1020 nm, respectively. Calculations of lidar ratios for summer and winter seasons have been made as well. Back trajectory analysis was also performed to final aerosol source of origin.

This paper deals with the problem of vibration that occurs in many industrial buildings. It covers the complete procedure of handling such tasks. Two buildings in a “Lubelski Wegiel S.A.” coal mine were examined in 2003 – 2005. Some years after building vibration of floors appeared (Figs 2-3). It was caused probably by modification in the building structures or improper maintenance of machines. Measurements and numerical simulations (Figs 4-5 and Tab. 1) showed that resonance appeared. It was stated that main elements of the structure were not in danger and vibration concern the floors only. Necessary modifications of the structures were designed (Figs 6-7). Testing measurements after bringing them into effect were conducted (Figs 8-11).

In this paper, the results of the finite elements method simulations of loosening of rock by special design ripping head [F. Eichbaum, Schneidend- brechende Gewinnung mit der Schneidscheibe. Experimentell und theoretische Untersuchungen. Gluckauf- Betriebsbucher, Band 22, Verlag Gluckauf GMBH Essen, 1980] have been presented. The influence of friction factor rock and ripping tool on trajectory of loosing of rock has been investigated. It is important to obtain wide range loosing of rock in mining technology. This makes getting a thick excavated material possible and guarantees more energy-saving excavating process. The results show that increase of friction angle results in growth of crack propagation range, so loosing rock pieces are bigger. Numerical studies were carried out for an angle varying from 0° to 24°. Calculations done using finite elements method determine mechanical conditions necessary for optimization and improvement of experimental head for future research. In crack propagation analysis, loosing element method and Podgorski’s plasticity condition were utilized [J. Podgorski, Journal of Mining Science 38 (4) (2002) 374–380, July; J. Podgorski, Journal of Engineering Mechanics 111 (2) (1985) 188–201] .

The influence exerted by three types of failure criterion on the shape and direction of crack propagation in the brittle material is considered. The crack development was simulated by the finite-element method. The Huber - Mises, Drucker - Prager, and PJ failure criteria were applied to the materials whose characteristics corresponded to concrete or rocks.

Presented paper contains results of fracture analysis of brittle composite materials with a random distribution of grains. The composite structure has been modelled as an isotropic matrix that surrounds circular grains with random diameters and space position. Analyses were preformed for the rectangular “numerical sample” by finite element method. FE mesh for the examples were generated using the authors’ computer program RandomGrain. Fracture analyses were accomplished with the authors’ computer program CrackPath3 executing the “fine mesh window” technique. Calculations were preformed in 2D space assuming the plane stress state. Current efforts focus on brittle materials such as rocks or concrete.

The history of ozone observations at Belsk (51.84°N, 20.79°E) is shortly described and the results of a novel statistical model are presented to show various aspects of the long-term variability of Belsk’s ozone in the period 1963–2012. The model stems from previous experiences of the Department of the Atmospheric Physics, Institute of Geophysics, Polish Academy of Sciences (IGF PAS), in the statistical modeling of the ozone layer. The analysis corroborates our earlier finding of the first stage of the ozone recovery over Belsk, i.e., a weakening of the negative ozone trend there. The second stage of the ozone recovery, i.e., an appearance of the statistically significant positive trend in series having had removed the “natural variability”, could not be yet announced. Generally, the long-term variability of the Belsk’s total ozone follows the anthropogenic trend, which is forced by changes of the man-made ozone depleting substances concentration in the mid-stratosphere. It provides a strong support for the effectiveness of the Montreal Protocol 1987 (and its subsequent amendments) regulations for protection of the ozone layer. The slowing down of the ozone recovery and the first sign of returning back to the negative tendency, which previously existed in the period 1980–1996, are found in the Belsk’s ozone time series since 2005, especially in the summer data. Such changes in the ozone layer are of special interest as they will induce an increase of the ground level solar UV-B intensity in the season of the naturally high UV radiation and frequent outdoor activity. Thus, in spite of evidence of the ongoing ozone recovery over the globe, the ozone issue, especially its local aspect, still needs attention of both scientists and public.

Over a period of several years tests and analyses have been conducted on cutting tools with various tip designs with the aim of improving understanding of the mechanics of rock cutting. The ultimate purpose of this investigation is to design a cutting tool that will minimize both the loss of energy due to friction between the tool and the rock mass and the effect of crushing in the contact area between the tool and the rock. An additional objective is to determine the cutting tool tip loading and the energy consumption of the cutting process so as to optimize the choice of ripping head motor for a given machine.1,2,3 Hitherto large differences have been found between analysis (which often employs simplifying assumptions) and practice.4 More advanced analysis of the problem has been attempted using fracture mechanics.5,6 Ingraffea and coworkers analysed the conditions for crack initiation from the components of the forces acting on the rock mass (Fig. 1).5 Whittaker and co-workers drew on the work of Evans3 to model crack propagation on the assumption of continuous and homogeneous rock loading from the cutting tool tip (Fig. 2 ).6 These analyses involved considerable simplifications of the stress transfer from the tool tip to the rock mass and also disregarded friction between the tool tip and the rock mass

The process of rock cutting, during which the layer of crushed material is formed in the vicinity of the cutting tool, is examined by means of finite-element method. Different combinations of elasticity and plasticity states are analyzed for the layer and rock; the causes of possible wear of the cutting edge are established.

The subject of paper was a research on mechanical system with pneumatic coupling, consisting of a compressor turbine (T I ) and of so-called free driving turbine (T II ). The purpose of the tests is to determine the applicability of Empirical Mode Decomposition (EMD) algorithm to identify operating parameters of the mechanical system, which is necessary to build a system for structure condition monitoring with use of vibroacoustic method. There has been assumed possibility of easy separation of working frequencies of these components on order to estimate amplitudes generated by them.

A general failure criterion dependent on three stress tensor invariants is proposed. It is applicable to a rather large class of materials including, metals, rocks, concrete and soils. The classical failure criteria and some recently proposed criteria are particular cases of this general criterion. The condition presented permits the uniform description of different groups of materials for which quite different forms of the failure criteria have been applied to date. A general form is applied to formulate failure criteria for plain concrete and sand. These criteria, to which smooth (conical for sand or paraboloidal for concrete) surfaces correspond, provide good agreement between predicted values of failure stresses and experimental results. This was possible due to the introduction of a new two‐parameter function describing the deviatoric cross section of the failure surface. Two cross sectional shape characteristic ratios, λ and θ, defined in this paper, make possible the systematic analysis of differen...

The two longest cable-stayed bridges in Poland (230m and 250m main span lengths) have been subjected to the aerodynamic analyses. This paper presents the main topics in these calculation processes: modal analysis, estimation of internal forces generated by the static load action, analysis of vibrations excited by the atmospheric turbulence and feedbacks, determination of bridge vibrations generated by the vortex excitation, calculation of stresses produced with the dynamic wind action. The dynamic structure response has been calculated using the quasi-steady method, which allowed analysis of just a few representative mode shapes, with the results precision acceptable in the engineering practice. Finally, both bridges have been found safe and resistant to the dynamic wind action, however the Warsaw bridge is more susceptible to the aerodynamic influence, especially its deck.