Residual strength of thermally modified Scots pine after fatigue testing in flexure

Scots pine (Pinus sylvestris) was thermally modified and its residual strength after cyclic bending was tested. Asymmetric sinusoidal cyclic oscillations at 20 Hz frequency and load ratio p = 0.3 were conducted. The variables of the experiment were the thermal treatment temperature (160, 190 and 220 °C), the number of bending oscillations (103, 505 × 103 and 106) and the equilibrium moisture content at target climates of 20 °C and 35, 65 and 95 % relative humidity (RH). The results showed that all input variables were insignificant for the residual modulus of elasticity. The initial moisture content of the specimens before fatigue testing and the maximum thermal modification temperature were identified as main influence on the residual modulus of rupture. The cyclic creep deflection significantly increased with increasing number of loading and initial specimen moisture content.