Characterization of wood-adhesive bonds in wet conditions by means of nanoindentation and tensile shear strength

The performance of adhesive-hardwood bonds can often be sensitive to humidity and temperature variation. Therefore, it is frequently challenging to achieve standard requirements for structural applications. To gain a better understanding of the wood-adhesive bond, the properties of the individual constituents as well as the local interface of European beech (Fagus sylvatica L.) wood cell walls in contact with structural adhesives were analyzed by means of nanoindentation. These results are compared to classical lap-shear strength. As adhesives two different one-component polyurethane adhesives (1C PUR) and a phenol resorcinol formaldehyde adhesive (PRF) were used. In one case, the beech wood was additionally pre-treated with an adhesion-promoting agent (primer) prior to bonding with 1C PUR. Beech wood joints were analyzed subsequent to several treatments, namely standard climate, after wet storage and in re-dried conditions. In addition, the influence of the primer on the hydroxyl accessibility of beech wood was investigated with dynamic vapor sorption (DVS). The lap-shear strength revealed good performance in dry and re-dried conditions for all adhesives on beech. Both polyurethane adhesives obtained deficits when tested in wet conditions. The use of a primer significantly improved the PUR performance in wet condition. DVS experiment demonstrated a decrease in hydroxyl group accessibility when using a high primer concentration. As novelty, nanoindentation was used for the first time to characterize the local wood–adhesive-interface properties in wet conditions. Nanoindentation showed that all tested 1C PUR perform quite similar in room climate, while PRF achieves considerable higher values for reduced E-modulus and hardness. Wet storage led to a considerable reduction in mechanical properties for all adhesives, while the highest relative change was observed for PRF. After re-drying, the adhesives re-gained a large part of their original mechanical properties in room climate. No distinct effect of the primer on the local micromechanical properties could be detected with nanoindentation in terms of specific work of indentation

Gait and Force Analysis of Provoked Pig Gait on Clean and Fouled Concrete Surfaces

Gait and force analysis have proven to be useful methods in linking claw injuries to surface material conditions. To determine the relationship between claw disorder and floor properties such as friction and surface abrasiveness, the factors controlling gait must be characterised. The effects of fouled concrete floor conditions on the gait of 10 pigs walking in a curve, using kinematics and kinetics to record gait parameters and slip frequency are described and compared with clean conditions. Pigs adapted to fouled floor conditions by reducing their walking speed and stride length, using a higher number of 3-foot support phases and by lowering diagonality. This adaption produced lower vertical forces, a twofold reduction in propulsion and outward stabilisation force and a threefold increase in braking force, without reducing the peak utilised coefficient of friction (UCOF). The UCOF values for both limbs of the curve walking pigs exceeded the recorded dynamic coefficient of friction and the corresponding UCOF values for pigs walking a straight line in fouled floor condition. As UCOF increased and available friction from the fouled floor surface decreased, this resulted in higher forward and backward slip frequency in both limbs for pigs walking in a curve. Pigs provoked to walk in a curve can adapt to fouled floor condition, but if the floor is heavily fouled this adaption is not sufficient to ensure safe walking

Om straffmätning vid upprepad brottslighed

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Smart manufacturing of curved mass timber components by self-shaping

With the rise of complex and free-form timber architecture enabled by digital design and fabrication, timber manufacturing companies increasingly need to produce curved components. In this thesis, a novel approach for the manufacturing of curved timber building components is proposed and analyzed. Following biological role models such as the bending of pine cone scales, a smart way to curve wood at large-scale is given by the biomimetic concept of bi-layered laminated wood. This principle enables large programmed material deformations upon controlled moisture content change. The main objectives of this thesis are the in-depth understanding of the mechanics of self-shaping wood bilayers and the up-scaling of the already known principle from the laboratory to the industrial scale in order to enable an application as form-stable curved elements in architecture. Hereby, the main challenges addressed are the accurate prediction of shape-change in terms of the natural variability in wood material parameters, the scale-dependent impact of moisture gradients on mechanical behavior, and the influence of wood-specific time- and moisture-dependent deformation mechanisms such as creep or mechano-sorption in the shaping process. Major impacts of these aspects on the shaping behavior could be demonstrated by the use of continuum-mechanical material models adapted to wood, both in the form of analytical and numerical models. Based on the gained insight, the up-scaling process to industrial manufacturing was successfully made possible. A collaborative project realized in 2019, the 14 m high Urbach tower, is presented as a proof of concept for application and competitiveness of the novel biomimetic method for production of curved mass timber components. Furthermore, next to self-shaping by bending to single-curved components, possibilities and limitations for achieving double-curved structures using wood bilayers in a gridshell configuration are analyzed and discussed

En komparativ studie av VaR-modeller

Historiskt sett har oftast den avkastning som en kapitalförvaltare genererat varit av intresse. Risken som förknippats med den aktuella investeringen har ofta kommit i skymundan. I början på 1990-talet inträffade ett antal olika finansiella kriser och detta medförde att riskmedvetenheten ökade. Nu var inte enbart den erhållna avkastningen intressant. Även den risk som förknippades med investeringen var av stor vikt. Företag började ta fram system för att mäta risk och ofta arbetade man med så kallade Value at Risk (VaR) som definieras som ”den med viss sannolikhet förväntade förlusten från ogynnsamma marknadsrörelser över en definierad tidsperiod”. Den tidigare forskningen som har bedrivits inom VaR har ofta koncentrerats till att testa om modellen håller statistiskt. Däremot tas ingen hänsyn till den beräknade förlusten. Syftet med denna uppsats är att undersöka fyra olika VaR-modeller, Equally weighted moving average (MA), GARCH, RiskMetrics och historisk simulering. Vi utför ett tvåstegs-test där vi först klargör om modellerna kan anses statistiskt signifikanta. Därefter beräknar vi förlusten med en Loss-funktion. Resultaten i vår studie visar att flertalet av VaR-modellerna godkänns i det första testet som vi genomför. I en tidigare studie genomförd av Sarma et.al (2001) godkändes endast två av VaR-modellerna, deras studie bygger dock på andra index än OMX som vi använder oss av. Vi anser dock att VaR är ett adekvat riskmått under de förutsättningar som vi genomför vår studie på

Mobbning: Ett homogent eller heterogent studieområde? : En inventering av studentuppsatser

Enligt viss svensk forskning råder stor homogenitet gällande forskning kring mobbning. Denna påpekar att endast ett fåtal forskare figurerar i de flesta vetenskapliga artiklar som fokuserat på mobbning. Syftet med föreliggande studie var att undersöka huruvida denna homogenitet stod att finna i uppsatser skrivna på Högskolan i Gävle, skrivna inom samma ämnesområde. Detta genomfördes genom en inventering där uppsatserna analyserades och kategoriserades efter relevanta ämnesområden. Resultatet visade att det fanns stor homogenitet på flera punkter. Bland annat återkom tre forskare och en ickevetenskaplig källa frekvent i de flesta uppsatsernas definition av mobbning. Studien visade också att majoriteten av uppsatserna var skrivna av blivande lärare inom lärarprogrammet samt att det inom andra utbildningsprogram endast fanns ett fåtal uppsatser skrivna om mobbning.     Nyckelord: heterogenitet, homogenitet, inventering, mobbning, uppsatser

Om partiella finska reformer rörande unga förbrytare

Föredrag hållet vid Kriminalistföreningens i Finland möte den 3 november 1975