Fracture mechanics studies of non-yielding materials like concrete : modelling of tensile fracture and applied strength analyses

Fracture mechanics studies of non-yielding materials are presented. The studies are based on theoretical models for the macroscopical mechanical behaviour of materials during tensile stress induced fracture. A number of applied numercal analysis are indicated. Fracture models and strength relations are discussed also from a few more general and fundamental points of view. A number of comparisons are made to test results from literature. The applications concern materials such as concrete, reinforced concrete, mortar and wood. Most numerical calculations are carried out by means of finite element methods. The fracture mechanics model called the fictìtious crack model is emphasized. This model gives a.description of gradual and localized fracture-softening in a single discrete tensile fracture process region. 0ther models dealt with: linear elastic fracture mechanics, Weibull-model, un-limited plasticity, conventional maximum stress theory and a few more special models. Specimens dealt with during numerical calculations: beams in bending, fracture mechanics tests specimens, tensile test specimens, pipes in bending and crushing, specimens with a re-entrant corner and longitudinally reinforced concrete beams in shear. According to the results obtained, it seems to be theoretically consistent and often of great practical importance to take into account the gradual and localized fracture-softening during strength analysis of specimens and structural elements

Legal Statutes of Arab Refugees

The recently developed particle filter offers a general numerical tool to approximate the state a posteriori density in nonlinear and non-Gaussian filtering problems with arbitrary accuracy. Because the particle filter is fairly easy to implement and tune, it has quickly become a popular tool in signal processing applications. Its main drawback is that it is quite computer intensive. For a given filtering accuracy, the computational complexity increases quickly with the state dimension. One remedy to this problem is what in statistics is called Rao-Blackwellization, where states appearing linearly in the dynamics are marginalized out. This leads to that a Kalman filter is attached to each particle. Our main contribution here is to sort out when marginalization is possible for state space models, and to point out the implications in some typical signal processing applications. The methodology and impact in practice is illustrated on terrain navigation for aircrafts. The marginalized particle filter for a state-space model with nine states is evaluated on real aircraft data, and the result is that very good accuracy is achieved with quite reasonable complexity

Finger-Joints and Laminated Wood. Final Report for the BFR-project

This report gives an overview and summary of research on wood-adhesive bonds performed during several years in a number of separate studies. These studies concern the mechanical testing, numerical analysis and constitutive modelling of wood-adhesive bonds in timber engineering. Applications such as finger-joints and glued-laminated timber are considered. The experimental studies include the testing of the fracture characteristics of wood-adhesive bonds. The numerical studies relate to the strength of finger-joints and laminated beams.In the experimental studies, the complete stress-displacement response of small specimens, particularly their fracture softening behaviour beyond peak stress, was recorded. A major outcome from the experiments is that wood-adhesive bonds can behave in a fracture-softening manner, and that it is possible to record this under stable conditions.In one of the numerical studies the finite element method was employed to analyse the stress distribution around zones of low stiffness in a laminated beam. A fracture mechanics analysis was also performed of the delamination of a laminated beam. The results show that the often made assumption of a stress redistribution taking place around weak zones is not necessarily true. Another finding is that the delamination of an initially cracked glulam beam tends to be increasingly dominated by mode II failure as the lamination thickness decreases.In another study, also related to finger-joints and laminated beams, the finger-joint failure in a glulam beam was simulated using a nonlinear fictitious crack model with stochastic properties. The results show the proposed approach to be able to account for such phenomena as the size effect and the laminating effect. Another observation is that finger-joint fracture energy, i.e. the ductility, has a major influence on lamination and beam strength. The influence of bondline defects on the tensile strength of a finger-joint was also investigated. It was demonstrated that even a small defect in the form of a glueline void, can have a relatively strong influence on the tensile strength. It was also demonstrated that the strength of finger-joints is largely inuenced by the outermost finger.Finally, an interface model based on damage mechanics is suggested for the modelling of wood-adhesive interfaces. This model accounts for joint dilatation and post-cracking friction. Also, a homogenisation scheme is presented for combining the proposed model with ordinary plasticity models for the adhesive bulk. This homogenisation procedure is based on assumptions regarding the stress and strain gradients typical of thin bondlines

Distribution and structure of Capercaillie (Tetrao urogallus) leks in a Scandinavian mountain range area

The Capercaillie (Tetrao urogallus) is distributed along the whole Scandinavian mountain range, but so far few studies exist about habitat selection, reproductive success, survival rate, lek structure and distribution, etc. of Capercaillie in this region. In this study, I searched for Capercaillie leks during the years 2003-2007 in valleys of the Scandinavian Mountain Range near the village of Tärnaby, Västerbotten County. In total, 20 lek sites were discovered, their locations in the landscape described, and the numbers of territorial males at each lek counted. Within the study area, the influence by forestry so far is small, compared to the situation on lower elevations and in more central part of the boreal forest region where most capercaillie studies have been performed. Observation of Capercaillie males in the study area suggests that the distribution of leks and the number of attending Capercaillie males is different than in other parts of Fennnoscandia. The lek sites were typically found in the upper parts of the coniferous forest, in the edge between the spruce and birch vegetation belts, or in forests mixed with Norway spruce (Picea abies) and birch (Betula pubescens ssp. Czerepanovii). The height of the forest varied from 0 to 25 m, but tree height of 10 to 18 m was preferred in areas of the leks. In lower parts of the valley, leks were also found in broader belts of coniferous forest

Influence of Plastic Dissipation on Apparent Fracture Energy Determined by a Three-Point Beding Test

A three-point bending test used for determining the fracture energy in modus I for wood perpendicular to the grain is studied, If the height of the specimen is varied, the results show a size effect, The specimens used in testing have been analyzed by finite element calculations with an anisotropic elasto-plastic material model in order to determine the influence of plastic dissipation. Analysis has been performed for three sizes of specimens where the height and length have been varied. The computational results are compared with experimental results

Experimental and numerical determination of the hygroscopic warping of cross-laminated solid wood panels

The moisture-induced warping of three-layered cross-laminated solid wood panels made of Norway spruce was studied. The panels were exposed to different climate conditions at 65% and 100% relative humidity at the two panel faces. The results showed increasing cup deformation with an increasing relative thickness of the outer layers. The annual growth ring orientation was found to have a significant influence on the magnitude of the cup deformation. Measurements and numerical simulations of the moisture distribution within the panel were made in order to provide data for numerical simulations of the warping. A distinctive moisture profile with a conspicuous influence of the adhesive bond lines was found. The coefficient of diffusion of the adhesive bond lines was determined from the measurements and simulations. The mechanical material model used for the warping simulations takes into account elastic strain, moisture-induced swelling, and mechano-sorptive strain. The simulations showed good agreement with the warping test results. The most important material parameters for the cup deformation, which were identified in a parametric study of a panel with vertically oriented annual rings, are the moduli of elasticity and the swelling coefficients in the longitudinal and radial direction. Furthermore, the mechano-sorptive coefficient in radial direction was found to have a significant influence on war

Experimental study on innovative connections for large span timber truss structures

This paper summarizes an experimental investigation on several innovative reinforcing techniques for the “Single Large Diameter Dowel Connection”, SLDDC in timber truss structures. Besides lateral reinforcing or prestressing, also steel plates glued on two sides of the glulam specimens were used as reinforcing measure. To study the efficiency of these techniques, 15 full-scale quasi-static tensile tests on glulam members with a SLDDC on either ends of each member were performed. It was found that the reinforcement significantly enhanced the bearing capacity of the SLDDCs. All of the reinforcing techniques showed a satisfactory efficiency, preventing splitting of wood. Moreover, most of the specimens remains showed a remarkable post failure strength

Chemistry of supported palladium nanoparticles during methane oxidation

Time-resolved in situ energy-dispersive X-ray absorption spectroscopy and mass spectrometry are used to correlate changes in chemical state of alumina and ceria supported palladium nanoparticles with changes in activity and selectivity for methane oxidation. Specifically, modulation excitation spectroscopy experiments are carried out by periodically cycling between net-reducing and net-oxidizing reaction conditions. The XANES and EXAFS data show that the palladium nanoparticles are readily bulk oxidized when exposed to oxygen, forming a PdO-like phase, and reduced back to a reduced (metal) phase when oxygen is removed from the feed. The difference between the two support materials is most noticeable at the switches between net-oxidizing and net-reducing reaction conditions. Here, a brief reduction in conversion is observed for the alumina supported catalyst, but for the ceria this reduction in conversion is minor or not observed at all. This difference is attributed to differences in the oxidation kinetics and the oxygen storage capability of ceria