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The mechanical properties of wood show a very high dependence on the moisture content (MC). A consideration of MC in numerical simulations increases the applicability of such prediction with respect to application and moisture states of the wood material. The goal of this work is to develop an accurate orthotropic elasto-plastic model for oak wood (Quercus robur L.) at two different MC levels applicable for finite element analysis (FEA). To achieve this goal, the following steps were carried out: (a) in-house standard specimens tests in compression, tension, and shear and in all three orthogonal directions, followed by three-point bending, where all specimens were conditioned to a 12 and 25.6% MC, prior to the mechanical test; (b) integration of all obtained material characteristics into the consistent numerical material models; (c) validation of the developed material models by comparing the numerically predicted values with the experimental ones; and (d) iterative calibration of the material models by adjusting the individual material characteristics to minimize error using a reference. Material models were successfully developed with the following mean relative errors: 5.2% for 12% MC and 5.8% for 25.6% MC, respectively. Both numerical material models consistently predicted the oak elasto-plastic response that can be easily integrated into any FEA.

The wood-water interactions of modified beech wood (Fagus sylvatica L.) were studied. Specimens were thermally modified at 180 (TM1), 200 (TM2) and 220 °C (TM3), acetylated (Acet), and melamine formaldehyde (MF) resin (Mel) modified. Afterwards, the water vapour characteristics, i.e. water vapour sorption isotherms, equilibrium moisture content (EMC), dimensional stability of specimens conditioned at 30, 65 and 90% RH and liquid water characteristics, i.e. water absorption, maximum moisture content (MC), leachability and swelling kinetics, were determined and the results compared with reference (Ref) specimens. From the results, it is evident that the scale of wood-water interactions was highly dependent on the thermal modification temperature and type of chemical modification. The water vapour isotherms of thermally modified wood decreased, whereas more severe treatment exhibited more distinct reduction. The EMC values of the Mel and TM1 specimens decreased only at high RH, whereas the most significant decrease, within the whole range of observation, was found in the Acet group. The maximum MC reduction was achieved by acetylation. As a consequence of swelling reduction, dimensional stability expressed as anti-swelling efficiency (ASE) was considerably improved. A relatively high initial linear-phase swelling rate was found for the Ref specimens, whereas modified wood exhibited comparatively slow and gradual swelling.

The effects of microwave and steam treatment were analyzed relative to the immediate (thermo-hygro-plasticity) and post-assessed (permanent changes) properties of wood. The study was conducted using European beech (Fagus sylvatica L.) standard and 1.5 times up-scaled (only for microwave-heated and reference samples) bending specimens tested in a static three-point loading mode. The specimens were plasticized by heat and moisture (1) separately and (2) simultaneously by heating moist specimens using (i) various microwave regimes in continuous mode, and (ii) heated saturated steam in discontinuous mode. Oven-dried specimens tested at 20 degrees C served as references. The thermo-hygro-plasticity was studied immediately after treatment, whereas the permanent changes were assessed after oven-drying of plasticized specimens to 0% moisture content. Permanent structural changes were analyzed using scanning electron microscopy. Microwave treatment increased the plasticity of wood (decreasing the modulus of elasticityby 70%) comparably to steam treatment, when the output moisture content was 30% or higher. A similar degree of plasticity was found in up-scaled specimens heated by microwaves. Further analyses confirmed that microwave treatment did not cause any permanent damage to wood structure or reduce mechanical performance. The results showed that microwave treatment is an efficient alternative to steaming when plasticizing moist wood.

Thermal modification of wood is an environment-friendly method, which, among others, enhances wood water related properties, whereas the use of hot oil as a heating medium generally leads to better performance. In this study, European beech wood was hemp oil-impregnated, thermally modified at 200 °C and both ways of treatment were combined. Analysis of the treated wood included the determination of the change in important wood characteristics—colour, hygroscopicity, dimensional stability, bending properties, and decay resistance against white rot. The results indicate that heat treatment combined with oil has influenced the properties of beech wood more than heat treatment itself. In certain cases, the high effectiveness is only relative with regard to mass increase caused by high oil retention.

One-sided surface charring of beech wood (Fagus sylvatica L.) was analyzed. Specimens were charred on one surface using contact heating system with a hot plate, at a temperature of 220 °C and atmospheric pressure for 15 or 40 min. Surface charring was applied on the radial or tangential surface. Spectrophotometric chemical analysis was carried out to determine the total amount of soluble carbohydrates and phenolic compounds beneath the surface in order to evaluate the depth (within 1, 2, 3 and 4 mm) of the degradation affected by the charring. Specimens of dimensions 14 × 14 × 14 mm were used to determine the moisture behavior of charred specimens. The equilibrium moisture content (EMC) of specimens was calculated at a temperature of 20 °C and 65% relative humidity. Water absorption (WA) was recorded during the water immersion for 240 h at various intervals. Finally, the three-point bending tests were undertaken and modulus of rupture (MOR) and modulus of elasticity were calculated. Degradation of the main wood compounds due to chemical changes occurred during the surface charring is closely associated with a mass loss (3.5–5.5%) and further related to the severity of process and orientation of specimens to heat flow. Application of surface charring resulted in the significant reduction in EMC (~ 20%) as a result of a decrease in hydroxyl groups, an increase in cellulose crystallinity as well as further cross-linking of lignin. Furthermore, the WA of one-sided surface-charred wood considerably decreased (15%) when compared to that of the control specimens. A significant increase in soluble carbohydrates as well as phenolic compounds was found, and it can be stated that one-sided charring affected wood properties to depth 2–3 mm from the surface. Significant differences (14–24%) of bending strength MOR results are most likely due to improved sorption behavior of wood. The results show that beech wood charring improved moisture-related characteristics and consequently led to better mechanical behavior, but more studies are needed to exploit the potential of surface charring method for future use.

Despite continual development of the tree pulling test, there is no systematic study on the interaction of stem and root-plate stiffness in relation to tree assessment results. New methods involving numerical modelling and optical techniques provide tools for effective and deeper understanding of the interaction of stem and root-plate stiffness. Within this study, a finite element (FE) model of the tree response to static loading was developed, and the interaction between the stem and root-plate stiffness was analysed on three levels: longitudinal stem strains, root-plate inclinations and stem deflection curve. The model was validated at all three levels by comparison with experiment. Sensitivity analysis of the validated model showed a significant correlation of root-plate stiffness represented by the root volume and soil elastic modulus to the tree response. By analysing the defects in tree response, the importance of proper location for detection of strains and inclinations was demonstrated, especially regarding asymmetrical defects. A numerical estimate of the second derivative of displacement based on the Taylor approximation, was used to analyse the stem deflection curve.

This article focuses on the interconnection of class and race with capitalism. First it presents a definition of capitalism and its attitude towards civil statuses and exploitation. Secondly, it analyzes the origins of racism in capitalism despite its emphasis on freedom and equality, and its indifference to the social identities of the people it exploits. Consequently, it examines racial oppression as a strategy for capitalist control of the laboring class. In the end it focuses on the very important distinction between oppression and exploitation. These distinct relations also have very different impact on the behavior of social agents and groups, their life opportunities and forms of social conflict. If we want to understand how racial hierarchies reproduce capitalist class relations, we have to understand the basic requirements of class relations and capitalist reproduction itself.

This work employs the acoustic emission (AE) method for material state monitoring. AE presents a non-destructive evaluation technique, which could be used for detection of microstructural changes in composite material. Work describes the process of acquisition of AE in tensile loading of carbon composite materials. In course of tensile stress, the composite was monitored with optical method, applying principles of digital image correction (DIC). Optical stereovision method enables calculation of field shift and field of proportional deformation at composite surface. The objective is analysis of damage in carbon composite materials and employ the methodology of AE signal processing for facilitation of early damage diagnostics and prediction of structural failure. For this purpose, the experimental setup was designed to obtain results from 50 nominally identical composite samples in tensile loading test. Force load applied on samples was synchronically recorded along with AE and image data. Experimental data were subsequently analysed in a way enabling the description of typical phenomena in course of every measurement. Results show that observation of AE sources could be employed in facilitation of early damage diagnostics and establishment of failure prognosis. It is about internal changes in composite material. info:eu-repo/semantics/openAccess

The hardwood is a natural composite, which finds applications in many fields such as an important building material. Attention was paid to the accurate description of the European beech wood under high strain rates in order to constitute a reliable input for the finite element method. It was done on the basis of split Hopkinson tensile bar tests, taking also into consideration the previously reported pressure bar tests to capture the tensile–compressive failure asymmetry, which was incorporated through the stress triaxiality. Strains measured on the steel bars for specimens oriented in all principal loading directions were used to calibrate the fully orthotropic behaviour of elasticity, plasticity and fracture. The concept of continuum damage mechanics was applied to the damage accumulation in order to simulate the crack propagation within explicit finite elements realistically.

This paper presents theoretical and experimental assessment of full-scale traditional dowel-type connections in tension parallel to grain made of Norway spruce ( Picea abies L. Karst.) and English oak ( Quercus robur L.). The joint dimensions were derived from the nominal dowel diameter d = {12, 16, 20, 24} mm according to the European standards EN 383 and EN 26891. Determination of the total joints displacement and surface strain distribution on the dowels was carried out using digital image correlation (DIC) technique. The theoretical and experimental approaches were focused on the determination of the load-slip joints moduli ( K ) and the dowel load-carrying capacity ( P y ) for various dowel diameters with the same length/diameter ratio equal to 3. The theoretical solution of the load-slip joints stiffness was carried out according to the Beam on Elastic Foundation (BEF) theory and the dowel load-carrying capacity according to Johansen's yield theory based on the European yield model (EYM). The theoretical results correlated with experimental values quite well. The theoretical solution proved to be a proper way for the design of the wooden dowel-type joints from the safety perspectives.

Norway spruce (Picea abies L. Karst.) and European beech (Fagus sylvatica L.) samples were loaded in shear mode aimed at testing their elastic material characteristics applicable in finite element analysis (FEA). More precisely, experimental and numerical analyses of uniaxial tensile test parallel to grain in longitudinal-radial (LR) or longitudinal-tangential (LT) shear of plane are described. The elastic material models in the FEA are based on own experimental data and those of the literature. The verification of material characteristics was performed by 3D numerical models with the same parameters as for the experimental tests. The fully orthotropic elastic material model was applied in the uniaxial tensile tests. The digital image correlation (DIC) method served for verification of the numerical models with proposed elastic material characteristics. Good correlation was found between numerically predicted and experimentally measured data. The minor differences between the two data sets could be mainly attributed to certain natural wood characteristics, which were neglected in the proposed models, i.e. especially variation of earlywood and latewood density. The proposed elastic material models offer general data sets for the evaluation of mechanical response of timber structures and especially in timber connexions.

Failure of a tree can be caused by a stem breakage, tree uprooting, or branch failure. While the pulling test is used for assessing the first two cases, there is no device-supported method to assess branch failure. A combination of the optical technique, pulling test, and deflection curve analysis could provide a device-supported tool for this kind of assessment. The aim of the work was to perform a structural analysis of branch response to static mechanical loading. The analyses were carried out by finite element simulations in ANSYS using beam tapered elements of elliptical cross-sections. The numerical analyses were verified by the pulling test combined with a sophisticated optical assessment of deflection evaluation. The Probabilistic Design System was used to find the parameters that influence branch mechanical response to loading considering the use of cantilever beam deflection for stability analysis. The difference in the branch’s deflection between the simulation and the experiment is 0.5% to 26%. The high variability may be explained by the variable modulus of the elasticity of branches. The finite element (FE) sensitivity analysis showed a higher significance of geometry parameters (diameter, length, tapering, elliptical cross-section) than material properties (elastic moduli). The anchorage rotation was found to be significant, implying that this parameter may affect the outcome in mechanical analysis of branch behavior. The branch anchorage can influence the deflection of the whole branch, which should be considered in stability assessment.

Experimental and numerical analyses are presented concerning of compression tests parallel and perpendicular to the grain, three-point bending, and double-shear joints in compliance with the relevant test standards (ASTM D2395, BS 373, EN 383 and EN 26891). Woods of Norway spruce (Picea abies L. Karst.) and European beech (Fagus sylvatica L.) were tested to describe their non-linear behavior. Elasto-plastic material models were the basis for the finite-element (FE) analyses with the input of own experimental data and those of the literature. The elasto-plastic material model with non-linear isotropic hardening was applied based on the Hill yield criterion in regions of uniaxial compression. The material characteristics were first optimized and validated by means of basic 3D FE models under the same conditions as applied for the experiments. Afterwards, the validated material models were implemented into the solver with more complex numerical analyses of wooden dowel joints. Concurrently, the digital image correlation (DIC) served for verification of the numerical wooden joint models. A good agreement (with a relative error up to 16%) was found between numerically predicted and experimentally measured data. The differences may be mainly attributed to some natural characteristics of wood which were not considered in the proposed material models. The proposed elasto-plastic material models are capable of predicting the wood’s ultimate strength, and therefore could contribute to a more reliable design of wood structures and their performance.

The hardwood, as a natural composite, may be subjected to the dynamic loading in many applications, such as the high-speed disintegration or structural collapses. The correct material description is needed for finite element modelling that can take place in the design stages of wood manufacturing processes or building the wooden structures. The split Hopkinson pressure (Kolsky) bar test provides the data for high strain rates. The experiments were carried out on the European beech wood in all the principal loading directions. The tests were repeated computationally in order to obtain the material constants of the complex material model, which covered the anisotropy of elasticity, plasticity as well as fracture behaviour. Moreover, the failure was considered non-symmetric with respect to the tension and compression. This was achieved by incorporating the stress triaxiality dependency into the failure model. The crack initiation and propagation were realized through the element deletion technique within LS-DYNA code. The real behaviour was captured quite well including the pulses in the incident and transmission bars.

Abrupt changes of climate have intensified during the last few decades, bringing higher risks from tree failures by either uprooting or stem breakage. To eliminate the risks, many techniques of tree assessment are being used. In the presented work, an optical technique based on 3D Digital Image Correlation (3D-DIC) was investigated as one of the tools to be used in identification of tree defects. Within the work, two ash trees were examined by pulling tests coupling 3D-DIC and standard techniques. The trees were measured in five consecutive steps of artificially made defects of two kinds - root and stem damage. We hypothesized defects can be identified using full-field strains and displacements. Results indicated that 3D-DIC provides comparable strains as standard semi-destructive extensometers. Statistical tests (α = 0.05) showed the 3D-DIC technique method is capable of identifying changes of displacements and strains after creating artificial defects in trees. However, despite the statistical differences, the practical arboricultural considerations of findings are still limited due to low absolute differences. The study also suggests there might exist path-dependency of the defect creation order when evaluating stiffness/strains from extensometers of two different positions. This could have impact on a practical assessment of tree stability in the future, but it must be further tested on larger data sets due to the proof-of-concept character of this work. In general, 3D-DIC brings extensive improvement in data acquisition quality and quantity, especially from the perspective of natural variability and heterogeneity in trees and wood. info:eu-repo/semantics/openAccess

The reinforcement of timber and concrete load bearing beams is increasingly utilized. The most promising effect can be achieved by CFRP (carbon fibre reinforced polymer). However, the difference in mechanical properties of the materials used may be so vast that the two components slip from each other at high stresses. This study deals with the delamination of CFRP from a beam. Design of corrugated reinforced surface is presented. It is based on area enlargement, which leads to a higher applied force needed for CFRP delamination during 4-point bending. Moreover, the corrugated shape comes to synergy with the timber beam which deforms during the flexural load and cyclic humidity. Corrugated CFRP is able to adapt to transverse dimensional changes and vice-versa increases the bending stiffness in the longitudinal direction. All in all, the corrugated shape of CFRP constrains the delamination and seems to be applicable for long-term reinforcement.

This article presents an analyses of democracy and capitalism from the point of view of Political Marxism, particularly Ellen Meiksins Wood. It distinguishes between two conceptions of democracy: the ancient Athenian democracy which conferred a civic status on subordinate classes, creating the unique social class, the peasant-citizen and contemporary elitist liberal capitalist democracy. Consequently it shows that the former was first and only workers democracy in history. Further it compares these two democracies and their influence on economy, particularly class relations and issues of exploitation. It finishes by presentation of limits of modern democracy and proposes possible solution.

In this paper, static bending (modulus of rupture, MOR, and modulus of elasticity, MOE) and compression strength parallel to grain (Σc??) of black alder wood (Alnus glutinosa Gaertn.) were investigated. For experimental testing, we used black alder wood from two different areas: Crni Jarci, Croatia, and Malá Byst?ice, Czech Republic. Experimental tests were carried out according to the Czech national standards: ?SN 49 0115 and ?SN 49 0116 for static bending and ?SN 49 0110 for compression strength. The samples from Malá Byst?ice showed lower values of MOR (~14%), MOE (~30%), and Σc?? (~4%), when compared to the samples from Crni Jarci. The relationship between density and strength was investigated. The difference between the studied groups at the 0.05 significance level was confirmed. The average linear correlation was found between density and the observed mechanical properties (for Σc??). The average density was 5491397645907kg m-3 for samples from Crni Jarci and 469 kg m-3 for samples from Malá Byst?ice. The results were compared with values indicated in similar studies.

The goal of the study is to investigate the non-standard deformation behaviour of wood loaded by compression parallel to the grain. This is represented as a negative increment of strain in the range of plastic deformations when the load continues to increase. The objectives of this study are to point out this problem and to provide its description based on the deformation fields that have been analysed using three approaches: a) full-field optical technique based on digital image correlation (DIC); b) “clip on” extensometer and its virtual analogy, and c) crosshead displacement method. Further, the negative strain phenomenon was studied depending on the sample length. The samples were made from the European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L. Karst.). Based on the strain analysis, it can be concluded that the deformation field consists of three sub-regions exhibiting different stiffness values (three-spring model). The failure of less stiff zones near the compression plates during the “non-standard” compression behaviour causes almost zero compression deformation of the stiffer middle zone or even leads to its expansion. The three-zone heterogeneity of deformation field induces a deviation of the displacement and strain measured by the proposed approaches. This phenomenon substantially influences the resulting longitudinal Young’s modulus and, therefore, should be of concern when measuring wood in such mode.

Gaseous ammonia treatment in combination with densification of wood has been known for several decades, but these days there is no industrial production of materials modified in this way; also, little has been published in this area of wood science. In this study, selected physical and mechanical properties, i.e. density profile, bending strength, hardness and moisture absorption were investigated for Lignamon (1), which was obtained from the Czech industrial production. Selected properties were also investigated using steam-densified beech (2) and native beech (3) and compared with each other. Densitometry of Lignamon showed a large variability in the density profile compared to that of only densified beech. It is affected by the degree of densification, temperature and moisture gradients, and their relationship to the glass transition of the wood cell wall. Modulus of elasticity, hardness, moisture exclusion and anti-swelling efficiency of Lignamon are enhanced compared to densified beech. The enhanced dimensional stability and lower hygroscopicity of Lignamon are probably caused by heat treatment during the process. Further investigation will be carried out with self-produced Lignamon samples.

The review presents the twentieth International Conference on Critical Theory ‘Philosophy and Social Science’ which took place in Prague in May 2012. The review briefly summarizes some of the delivered talks, for example, a lecture ‘Beyond toleration’ by C. Taylor, ‘Can society be commodities all the way down?’ by N. Fraser, ‘On the will, voice and eyes of the people’ by A. Ferrara and his colleagues, ‘Authoritarian versus critical theory’ by M. Hrubec, ‘Theorizing violence’ by M.P. Lara, and other ones. The conference is an annual international event focusing on important social and political issues from the point of view of critical theory, but it is open to other interpretations as well. The conference is hosted by the Institute of Philosophy at the Academy of Sciences, Prague, Czech Republic, especially its Centre of Global Studies.

This article analyzes crisis as part of deeper trends determined in historical development from the perspective of two important theoretical streams: firstly, Analytical Marxism, and secondly, the Critical Theory of Society (the Frankfurt School). It shows both general determinants of historical development and pathological determinants of historical development. Examining Analytical Marxism and its theory of technological determinism, the article explains crisis in respect of situations of systemic changes mainly from the perspective of the relationship between forces of production and relations of production. Examining the Critical Theory, the article clarifies the role of the pathological determinants of instrumental rationality in human history in relation to efforts at human emancipation. In the article, crisis is seen as the superficial appearance of the historical developmental trends where there are inherent permanent tendencies to crisis. Crisis is a temporary eruption of the deeper contradictory development of the capitalist mode of production and other systems within the history of human civilization. The article discusses an issue of determinism as a necessary framework for the interpretation of crisis, and offers an interpretation of the preconditions of crisis not only from the economic point of view, but also, on a deeper level, in a civilizational sense.

An alternative assessment procedure for the mechanical performance of thermally modified timber is presented. Non-defect beech wood (Fagus sylvatica L.) specimens were thermally modified at 180°C and 200°C and subjected to static three-point bending load. Based on the full-field strain data acquired during the tests, the neutral axis (NA) at a 50 % level of maximal loading force was identified and localized within the specimen height by means of image processing methods. The NA in specimens mildly thermally modified moved toward the tensile zone when compared to the control specimens, whereas the position of NA within the specimens severely thermally modified was comparable with the NA position in control specimens. The proposed procedure proved to be applicable for the assessment of the mechanical performance; however, in the present study, the NA movements caused by thermal modification were not found to be statistically significant.

A new sandwich composite structure was prepared that utilizes classic wood-based composites as the core and face materials. Particleboards were used as faces, which covered a plywood-made iso-grid core. A new type of core-face fixation was suggested and assessed. The sandwich panels can be regarded as lightweight, as their density was below 400 kg/m3. Digital image correlation (DIC) was used to determine Poisson’s ratios and obtain additional insight into the deformation behavior of the sandwich panel. DIC was also employed to assess the core-face bonding, which was based on imprinted grooves on one side of the particleboard face. The results include strength in edgewise and flatwise compression and flexural properties. The latter were determined through three-point bending tests. Comparable strength properties were found relative to the literature, which means that this new type of sandwich panel demonstrates a competitive property profile. It was concluded that the developed sandwich panel is versatile, and the hollow spaces in the core can be filled with insulation materials such as fibers or foams. Surfaces can also be covered with some overlay, delivering improved bending performance.

Tree root system belongs to a key factor of the tree stability because it provides the anchorage point to the ground/soil, beside its physiological purpose. Therefore, to assess the tree stability with a certainty, it is needed to have information about tree root-plate, ie. to know roots health state, its geometrical distribution in a space with respect to a tree and surrounding objects, to know properties of the ground (soil) and to know material properties of roots. This work assessed 10 oak trees in terms of their reaction to bending induced by a standard pulling test accompanied with optical technique based on digital image correlation to obtain displacement at various locations of tree. Trees were tested in both intact state and with soil removed from the surface of the root plate. Results showed that performed soil removal did not have statistically significant effect on apparent tree stiffness. The same conclusions were found based on data provided by both inclinometers and digital camera.