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Abstract: In this study, the mechanical properties of bonded single-lap joints are analysed by tensile lap shear tests on beech wood. A one-component polyurethane adhesive was used, and three different methods of surface preparation were applied: planing, sanding along the grain, and sanding perpendicular to the grain. Prior to bonding, the wooden lamellae underwent laser scanning to obtain surface profiles, which were then analysed for surface roughness. Scanned surface topographies with their features were integrated into the finite element analysis (FEA) software COMSOL Multiphysics to simulate the lap shear bonding area for different surface profiles and roughness. The FEA model implements linear material models, which represent the adherend and thin adhesive layer, combined with a modified local cohesive zone model for the adhesive bond interfacial forces. The experimental tests were conducted in a dry environment, where a higher surface roughness achieved by sanding correlated with a higher tensile shear strength. This increased surface roughness was attributed to the enhanced mechanical interlocking mechanism. This finding aligns with the FE analysis, which showed that increased surface roughness, micropillars and indentations, led to variations in stress concentration and distribution compared to a smooth surface bond.
Keywords: beech wood, mechanical interlocking, surface modification, polyurethane, finite element modeling
Published in DiRROS: 11.08.2025; Views: 464; Downloads: 212
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Abstract: Cessation of xylem formation or wood growth (CWG) and onset of foliar senescence (OFS) are key autumn phenological events in temperate deciduous trees. Their timing is fundamental for development and survival of trees, ecosystem nutrient cycling, the seasonal exchange of matter and energy between the biosphere and atmosphere and affect the impact and feedback of forests to global change. A large-scale experimental effort and improved observational methods have allowed us to compare the timing of CWG and OFS for different deciduous tree species in Western Europe, in particularly silver birch, a pioneer species, and European beech, a late-succession species, at stands of different latitudes, of different levels of site fertility, and for two years with contrasting meteorological and drought conditions i.e., the low-moderately dry 2017 and the extremely dry 2018. Specifically, we tested whether foliar senescence started before, after or concurrently with CWG. OFS and CWG occurred generally between late September and early November, with larger differences across species and sites for OFS. Foliar senescence started concurrently with CWG in most cases, except for the drier 2018 and, for beech, at the coldest site, where OFS occurred significantly later than CWG. Behavior of beech in Spain, the southern edge of its European distribution, was unclear, with no CWG, but very low wood growth at the time of OFS. Our study suggests that OFS is generally triggered by the same drivers of CWG or when wood growth decreases in late summer, indicating an overarching mechanism of sink limitation as a possible regulator of the timing of foliar senescence.
Keywords: autumn phenology, xylem formation, foliar senescence, cambium, chlorophyll, radial growth, wood, decidiuous trees, common aspen, common beech, pedunculate oak, silver birch
Published in DiRROS: 10.06.2020; Views: 3091; Downloads: 2032
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Abstract: An inventory of tree microhabitats was done in two unmanaged forests (Kobile and Ravna gora forest reserves) and one managed beech forest in SE Slovenia. The purpose of this study was to determine the influence of forest management, natural disturbances, and tree characteristics on microhabitat patterns. Forest structure and microhabitats were recorded in systematically placed plots (500 m2 in size) across each area. In total, we inventoried 849 trees on 54 plots and 1833 tree microhabitats. The results showed that forest management had no significant influence on the abundance of microhabitats per tree, but there were differences regarding microhabitat type between managed and unmanaged sites. There were substantially more microhabitats related to standing dead and live habitat trees in unmanaged forest (e.g. woodpecker cavities, insect galleries and bore holes, branch holes, dead branches and fruiting bodies of fungi), whereas in managed forests there were more tree microhabitats related to management (e.g. exposed heartwood, coarse bark, and epiphytic plants). The results also indicate that disturbance, tree diameter, vitality, and species influence the density, diversity, and occurrence of tree microhabitats.
Keywords: forest management, biodiversity, tree microhabitats, beech forests, old-growth, veteran tree, natural disturbance, dead wood
Published in DiRROS: 08.07.2019; Views: 8792; Downloads: 3870
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Keywords: Kočevska, Slovenia, dead wood, coarse woody debris, beech, undergrowth, diversity, virgin forest remnant
Published in DiRROS: 12.07.2017; Views: 5852; Downloads: 2401
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