PEER-REVIEWED ARTICLE bioresources.com Gaff et al. (2016). “Impact bending strength,” BioResources 11(4), 9880-9895. 9880 Impact Bending Strength as a Function of Selected Factors Milan Gaff, Daniel Ruman,* Vlastimil Borůvka, and Vladimír Záborský This article examines the influence of selected factors (wood species, densification, thickness, glue type, and number of cycles) on the impact bending strength (IBS) of solid and laminated wood. The evaluated properties were measured on samples of European beech (Fagus sylvatica L.) and common aspen (Populus tremula L.). Two types of glues were used for laminated wood: polyvinyl acetate (PVAc) and polyurethane (PUR). The highest IBS values were recorded in laminated beech specimens glued with polyvinyl acetate glue that were not subjected to cyclical loading. Keywords: Impact bending strength; Cyclic loading; Laminated wood; Densification Contact information: Department of Wood Processing, Czech University of Life Sciences in Prague, Kamýcká 1176, Prague 6 - Suchdol, 165 21 Czech Republic; *Corresponding author: dano.ruman@gmail.com INTRODUCTION Wood is a unique natural material demonstrating both positive and undesirable natural properties (Bodig and Jayne 1982). In the wood processing industry, new possibilities for eliminating its undesirable properties are constantly being sought, as are various modifications to improve its physical and mechanical properties. Such modifications include wood densification (Kurjatko et al. 2010). Each wood species is characterized by a specific density influencing its physical and mechanical properties. Higher density woods are firmer, harder, and more resistant than those with lower densities (Požgaj et al. 1993). Densification can increase the densities of woods with lower initial densities, thereby expanding the range of their possible uses. Various densification methods have been used to increase wood density and improve its mechanical properties (Kollmann et al. 1975; Higashihara et al. 2000; Navi and Heger 2004; Boonstra and Blomberg 2007; Fukuta et al. 2008; Gabrielli and Kamke 2008; Fang et al. 2011; Fang et al. 2012). Wood densification techniques have been applied to wood for various purposes, such as, for example, to increase the adhesion of glue through the mechanical activation of the glued surface (Aydin 2004; Bekhta et al. 2009). Densification depends on many factors such as the wood species, density, and anisotropy (the direction of loading in pressure perpendicularly to the grain, radial or tangential) (Easterling et al. 1982; Morsing 2000; Nairn 2006), and is most frequently carried out by pressing. Knowledge about the dynamic strength of densified wood is minimal, and for this reason was included in the experimental part of our study. Wood properties can also be modified by gluing together individual lamellas, resulting in the formation of so-called laminated materials. Phenol-formaldehyde (PF) glues are most frequently used for the industrial production of laminated veneer lumber (LVL) and other components (Adams 2005). PF glues are toxic, however, and thus the use