Density profile and microstructural analysis of densified beech wood (<Emphasis Type="Italic">Fagus sylvatica</Emphasis> L.) plasticized by microwave treatment

This study was carried out in order to determine the efficacy of microwave (MW) plasticization for wood densification purposes. The plasticization process was carried out using a continuous feed laboratory MW at a frequency of 2.45 GHz. European beech (Fagus sylvatica L.) specimens measuring 50 mm?×?40 mm?×?8 mm were MW treated (plasticized) with an output of 3.5 kW at a conveyor speed of 0.4 m/min. Afterwards, MW plasticized specimens were densified with a ratio of 50%. Microscopic structure changes of densified wood were detected using a scanning electron microscope (SEM) and density profiles were measured using the X-ray densitography. An average density of 677 kg m^?3 and 771 kg m^?3 increased significantly to 951 kg m^?3 for radially densified and to 1194 kg m^?3 for tangentially densified specimens. X-ray densitography results show uniformity of density profiles through specimen thickness, which confirmed the evenly plasticized volume of wood. Microscopic structure observation revealed that the MW plasticization was not accompanied by any fractures, and deformations present in the densified wood were due to viscoelastic buckling of cell walls without crack propagation. Therefore, MW treatment can be considered as an effective method for wood plasticization.     

Reducing the moisture sensitivity of linear friction welded birch (Betula pendula L.) wood through thermal modification

Linear friction welding of wood is a bonding process applied to wood and during which a stiff bond line is formed by the softening and rehardening of wood components to form a composite material composed mainly of wood fibres embedded in a modified lignin matrix. Unfortunately, the bonds tend to spontaneously delaminate or lose their strength when exposed to moist conditions. Some approaches were previously applied to overcome this problem, but so far a suitable solution has not been found. This paper presents results of applying post-welding thermal modification to reduce the moisture sensitivity of welded wood. The experiments included welding of birch wood, thermal modification under superheated steam at atmospheric pressure, internal bond (IB) and tensile-shear strength testing and soaking tests. As supposed, the non-modified reference specimens performed poorly after the seven days soaking test (on average 0.33 MPa IB strength), whereas the thermally modified specimens yielded almost the same IB strength in dry and wet condition (on average e.g. 1.15 and 0.93 MPa, respectively). Such a similar load bearing capacity in very different moisture conditions was previously reported only in the case of paduk wood. Similar to the reduction of IB strength occurred during the soaking test, also delamination was observed more clearly in non-modified reference specimens (e.g. 4 vs. 0 total delaminations after seven days soaking). Therefore, the authors suggest that post-welding thermal modification could provide a suitable bond-stabilisation method against moisture, although the process parameters must be optimised in further research, for instance, to ensure scalability.     

Quantitative phase analysis of metastable structure in a laser melted Fe-C alloy

Quantitative X-ray diffraction phase analysis was utilized to investigate the structure of a Fe-3.5 wt% C alloy after laser melting. The measurements were taken on surfaces modified by a series of equidistant laser tracks with overlappings k = 0.25, 0.50 and 0.75, and the results were extrapolated to the non-interfering tracks. On the same samples, the microstructure was observed by scanning electron microscopy. The structure of the rapidly solidified surface layers consists of -Fe (ferrite and martensite), -Fe (retained austenite) and cementite. The results of X-ray diffraction point to a very high amount of carbide indicating a non-stoichiometric composition of cementite. Besides, the volume fraction of -Fe increases with increasing coefficient of overlapping k. At the same time, the volume fraction of cementite decreases while the content of -Fe remains nearly constant. The changes are attributed to decomposition of the metastable carbide due to tempering of the former tracks by the following laser passes. This thermal effect was quantified on the base of the heat-transfer model of moving Gaussian beam.     

Polygonization of implicit surfaces with sharp features by edge-spinning

This paper presents an adaptive approach for polygonization of implicit surfaces. The algorithm generates a well-shaped triangular mesh with respect to a given approximation error. The error is proportional to a local surface curvature estimation. Polygonization of surfaces of high curvature, as well as surfaces with sharp features, is possible using a simple technique combined with a particle system approach. The algorithm is based on a surface tracking scheme, and it is compared with other algorithms based on a similar principle, such as the marching cube and the marching triangle algorithms.     

Analysis of Äspö Pillar Stability Experiment: Continuous thermo-mechanical model development and calibration

The paper describes an analysis of thermo-mechanical (TM) processes appearing during the Äspö Pillar Stability Experiment (APSE). This analysis is based on finite elements with elasticity, plasticity and damage mechanics models of rock behaviour and some least squares calibration techniques. The main aim is to examine the capability of continuous mechanics models to predict brittle damage behaviour of granite rocks. The performed simulations use an in-house finite element software GEM and self-developed experimental continuum damage MATLAB code. The main contributions are twofold. First, it is an inverse analysis, which is used for (1) verification of an initial stress measurement by back analysis of convergence measurement during construction of the access tunnel and (2) identification of heat transfer rock mass properties by an inverse method based on the known heat sources and temperature measurements. Second, three different hierarchically built models are used to estimate the pillar damage zones, i.e. elastic model with Drucker–Prager strength criterion, elasto-plastic model with the same yield limit and a combination of elasto-plasticity with continuum damage mechanics. The damage mechanics model is also used to simulate uniaxial and triaxial compressive strength tests on the Äspö granite.     

Swelling kinetics of thermally modified wood

European Journal of Wood and Wood Products - The swelling kinetics of native and thermally modified wood was studied. Norway spruce, Scots pine, European beech, and English oak specimens of...     

Photo-conductivity and Hall mobility of holes at polypyrrole–diamond interface

Surface of intrinsic monocrystalline diamoncd is selectively terminated by hydrogen and oxygen atoms to create electrically conductive microscopic square with contact leads in corners. Polypyrrole (PPy) film is then electrochemically deposited onto the H-terminated square. The resulting PPy-diamond system is characterized under a broad-band light illumination by four probe resistivity and Hall mobility measurements and the in-plane transport properties of holes at the PPy-diamond interface are evaluated. We also discuss applicability of these techniques on this specific heterosystem.     

Selecting Manufacturing Technology: A Knowledge Modelling Approach

This paper describes the development of a knowledge based system for selecting the technology for manufacturing machine parts. The problem is formally specified and analysed. The problem solving method is modelled by instantiating two Generic Task Models (GTM) in the domain of bulk metal forming. Both technological and economical criteria are considered. Static knowledge is represented as domain ontologies. The system has been implemented and experimentally tested.     

Early stage of diamond growth at low temperature

We investigate the first stages of nanocrystalline diamond (NCD) thin film growth at low substrate temperature. NCD films were grown on silicon substrates by microwave plasma enhanced chemical vapor deposition (CVD) for 0–300 min at a temperature of 410 °C. Si substrates were ultrasonically seeded in suspension of detonation nanocrystalline diamond powder. The seeding density approached values up to 1 ⁎ 10¹² cm^− 2, which allows growth of ultra-thin fully closed layers. Stagnation of the AFM roughness indicates that the low temperature NCD growth is a) delayed due to the surface contamination of the used nanodiamond powder and b) possibly dominated by the growth in the lateral direction. XPS measurements showed that the measured surface exhibits changes from a multi-phase composite (seeding layer) to single-phase one (NCD layer).