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A b s t r a c t. This work provides the values of both the static and the kinetic friction coefficients for chestnut (Castanea sativa Mill.) of Spanish origin. Knowledge concerning these coefficients has its main application in the study of agroindustrial structures and machinery with timber members in contact. This determination was developed taking into account the timber anisotropy to establish surfaces and directions of slipping. A modified direct shear test device was used to conduct the tests and reproduce the tribological system. This procedure was functional and reliable and considered suitable for standardizing the friction measurement between timber surfaces, since this device is widely distributed in geotechnical and materials laboratories and the European codes do not specify a procedure or device to carry it out. The average values obtained were 0.46 for the static coefficient and 0.33 for the kinetic one, without considering the surfaces and directions of slipping. These values ranged between 0.36 and 0.55 for the static friction coefficient and between 0.28 and 0.39 for the kinetic friction coefficient depending on the direction considered and also taking into account the anisotropy of the timber. A good correlation was obtained between both coefficients, thus allowing for the estimation of the kinetic coefficient from the static one.K e y w o r d s: wood, mechanical properties, friction coefficient, direct shear test

This study focuses on the friction characteristics of chestnut sawn timber (Castanea sativa Mill.) of Spanish origin. The values of both the static and dynamic friction coefficients were determined, as this knowledge is of interest for the numerical simulation of the stress transmission in joints of timber structures. Therefore, two sets of tests were carried out combining different orthotropic orientations. Firstly, timber-to-timber tests were assessed to obtain the coefficients applicable to carpentry joints; secondly, timber-to-steel friction was also evaluated to determine the coefficients needed for mechanical joints with metal plates and dowels. The results presented a conventional behavior of friction, i.e., a maximum static value before sliding and a subsequent decrease. For timber-to-timber tests, global mean values of μs = 0.47 and μk = 0.36 were found, and the results were slightly higher than those obtained between pieces with the same orthotropic orientation and sliding direction. Regarding timber-to-steel tests, the resulting friction coefficients, as well as the difference existing between the static and dynamic values were lower (μs = 0.19 and μk = 0.17) compared to the timber-to-timber sets. The use of these results in numerical studies would allow for closer simulations in which chestnut wood is involved in friction. In addition, the values provided herein could be included as new data in standards that already consider other wood species.

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