The influences of moisture content variation, number and width of gaps on the withdrawal resistance of self tapping screws inserted in cross laminated timber

A large experimental campaign comprised of 470 withdrawal tests was carried out, aiming to quantify the withdrawal resistance of self-tapping screws (STS) inserted in the side face of cross laminated timber (CLT) elements. In order to deeply understand the “CLT-STS” composite model, the experimental tests considered two main parameters: (i) simple and cyclic changes on moisture content (MC) and (ii) number and width of gaps. Regarding (i), three individual groups of test specimens were stabilized with 8%, 12% and 18% of moisture content and one group was submitted to a six month RH cycle (between 30% and 90% RH). Concerning (ii), different test configurations with 0 (REF), 1, 2 and 3 gaps, and widths equal to 0mm (GAP0) or 4mm (GAP4), were tested. The influences of MC and number of gaps were modeled by means of least square method. Moreover, a revision of a prediction model developed by Uibel and Blaß (2007) was proposed. The main findings of the experimental campaign were: the decrease of withdrawal resistance for specimens tested with MC=18% in most configurations; the unexpected increase of withdrawal resistance as the number of gaps with 0mm increased; and, the surprising increase of withdrawal resistance for REF specimens submitted to the RH cycle.The development of the present work was possible only thanks to the financial support of the 391 Portuguese Science Foundation (Fundação de Ciência e Tecnologia, FCT), through PhD grant SFRH / BD17392 / 79972 / 2011. Further, the valuable partnerships with the Institute of Timber Engineering and Wood393 Technology, at Graz University of Technology (Austria), and Rusticasa are gratefully acknowledged

Effect of thermal modification on properties and milling behaviour of African padauk (Pterocarpus soyauxii Taub.) wood

The purpose of this study was to analyze the effect of thermal treatment on chemical changes, mechanical properties and machining behavior of African padauk wood. Thermal modification of padauk wood was carried out at 3 different temperatures (160 degrees C, 180 degrees, and 210 degrees). Effect of modification temperature on chemical constituents and bending proper-ties of padauk wood were ascertained. Thermally modified and un-modified samples were subjected to milling operation with combination of various processing parameters such as cutting speed (20, 30, 40 m/s), feed speed (4, 8, 11 m/min) and rake angle (15 degrees, 20 degrees, 25 degrees), to obtain the optimum combination in terms superior surface quality (surface roughness and surface waviness) and minimum energy consumption. Cellulose and lignin proportion increased while hemicellulose proportion reduced significantly following thermal modifi-cation. Modification temperature, particularly 210 degrees, had significant effect on the chemical constituents and bending strength of padauk wood. Modification up to 180 degrees did not cause any significant loss in bending strength and bending stiffness, but the strength and stiff-ness loss was significant when samples were modified at 210 degrees. Best surface quality with minimum energy consumption was obtained in African padauk wood thermally modified at 210 degrees and milled with a cutting speed of 20 m/s, rake angle of 20 degrees and feed rate of 4 m/min. (C) 2020 The Authors. Published by Elsevier B.V