Cyclic impulsive compression loading along the radial and tangential wood directions causes localized fatigue

Abstract

We report for the first time on the existence of a localized reduction in elasticity caused by repeated compression impaction applied along the tangential wood direction. Previous research indicates that localized strain profiles are generated by such cyclic impacting on wood along its radial direction. This finding is significant for the paper/board-making industry where wood is exposed to cyclic unipolar compression during grinding. However, the effect of the impacting direction, with respect to the orientation of the annual rings, on the localization phenomenon is unknown. In addition, the shape of the developing fatigue layer is unclear. We revisit the localization phenomenon with a focus on tangential impacting. We employed ultrasonics and x-ray tomography to quantify the induced fatigue. An interlacing technique increased the precision of the ultrasonic stiffness depth profiling technique. We studied both radial and tangential wood annual ring geometries. We used ultrasound to quantify the drop in shear modulus resulting from impacting. Both radial and tangential geometries featured strain localization, but the shape of the fatigued layer was different in the radial and tangential wood geometries (steeper profile in the radial geometry). The fatiguing reduced the shear modulus. These results tell us about the ratio of the number of hits that need to be delivered along the radial and tangential direction of the ground wood, respectively. This insight may translate into a design pattern for an energy saving grind stone surface.

Introduction of shock wave technology to fir wood preservation

“…Partly missing torus or damaged pits could be seen in SEM with shockwave and standard pressure-vacuum samples (Figure 3) which indicates a pathway for the Aniline Blue solution. While cyclic impulsive compression loads along the radial and tangential wood directions causes localized fatigue (Salmi et al 2012), in our test cell wall integrity is locally collapsed and cracks appear at the end grain and along the cell middle lamella.

Figure 3 SEM images of Abies grandis conditions of pits in fir sapwood (A) Control sample with intact pits (arrow) (B) Vacuum-Pressure-Treatment sample possible opened pits (arrow) (C) Cracks on shock wave sample (D) Wave-like deformation of shock wave sample.

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“…Partly missing torus or damaged pits could be seen in SEM with shockwave and standard pressure-vacuum samples (Figure 3) which indicates a pathway for the Aniline Blue solution. While cyclic impulsive compression loads along the radial and tangential wood directions causes localized fatigue (Salmi et al 2012), in our test cell wall integrity is locally collapsed and cracks appear at the end grain and along the cell middle lamella.…”

Avaliação do efeito da fadiga no módulo de elasticidade na flexão de painéis de madeira compensada

“…Para estruturas submetidas a cargas dinâmicas ou cíclicas, como pontes, viadutos e silos, deve-se levar em conta o efeito de fadiga no material [16,17,18,19]. Em ambas as normas brasileiras apresentadas, não há requisitos normativos para considerar o efeito de fadiga nas propriedades mecânicas do material, o que motiva o desenvolvimento de pesquisas nessa temática.…”

Defibration mechanisms and energy consumption in the grinding zone – a lab scale equipment and method to evaluate groundwood pulping tools

“…In studies aimed at increasing the understanding of the grinding processes, lab scale tests are thus attractive as these avoid the use of full-scale equipment and tools and allow better control of the test conditions. Research using small grinders have been performed previously, investigating e. g. the effects of temperature (Steenberg and Nordstrand 1962) and atmospheric pressure (Atack et al 1981), modification of conventional grinding stones (Lucander et al 1985, Björkqvist and Lucander 2001, Nurminen et al 2018, grit morphology (Enström et al 1990, Sandås and Lönnberg 1990, Sandås 1991a, 1991b, Lönnberg et al 1996, Tuovinen et al 2008, Tuovinen and Fardim 2015, fatigue pretreatment (Salmi et al 2012a), differences between heartwood and sapwood (Bengs and Lönnberg 1994), glass transition (Blechschmidt et al 1986) and wood alignment A) The pressure chamber with the miniature lathe inside, holding a cylindrical wood specimen, and the heated water container in the bottom. B) An illustration of the tool holder mechanism.…”