Fatigue behavior of beech and pine wood modified with low molecular weight phenol-formaldehyde resin

• Published in: Holzforschung Vol. 75; no. 1; pp. 37 - 47
• Main Authors: Pečnik, Jaka Gašper, Kutnar, Andreja, Militz, Holger, Schwarzkopf, Matthew, Schwager, Hannes
• Format: Journal Article
• Language: English
• Published: Berlin De Gruyter 01.01.2021; Walter de Gruyter GmbH
• Subjects: Beech; Competitive materials; Creep rate; Cyclic loads; Environmental impact; Fagus sylvatica; Fatigue; Fatigue strength; Formaldehyde; Heat treating; Low molecular weights; Modulus of rupture; Molecular weight; phenol formaldehyde; Phenol formaldehyde resins; Phenols; Pine; Pine trees; Pinus sylvestris; Reduction; stress level; Wood; Wood construction; wood modification
• DOI: 10.1515/hf-2020-0015
• ISSN: 0018-3830

Modification of wood improves certain properties of natural wood and presents competitive alternatives to synthetic materials that may have larger environmental impacts. One aspect of modified wood that is currently not fully understood is the dynamic performance and how it is affected by the modification process. In this study, low-molecular weight phenol formaldehyde (PF) resin was applied to Scots pine ( L.) and European beech ( L.) wood. The effect of this modification was evaluated using a three-point bending test undergoing cyclic loading. Compared to reference samples, modified wood showed higher static performance but revealed a reduction in cyclic fatigue strength (9% for pine and 14% for beech). Cyclic fatigue strength of unmodified wood was found to be 67% of the static modulus of rupture for both species. With PF resin modification, the fatigue strength dropped to 58% for pine and 53% for beech. While fatigue strength decreased, there was no reduction in cyclic modulus or change in the creep rate within the stationary creep phase. It is important to consider the reduction in fatigue strength when using PF modified wood for any construction purposes with expected cyclic loading conditions.