Fatigue properties of jointed wood composites part I - Statistical analysis, fatigue master curves and constant life diagrams

摘要

The primary aim of this work was to assess the fatigue performance of scarf-jointed laminated wood composites used to manufacture wind turbine blades and establish simple fatigue design procedures. Laminates made from poplar (Populus canadensis/serotina), Khaya (Khaya ivorensis) and beech (Fagus sylvatica), incorporating typical scarf joints, were assessed under reversed loading (R=-1). Scarf joints were found to be great equalizers of fatigue performance for wood species with different static strengths. Poplar was investigated at several other R ratios ( +3, -3, -0.84 and 0.33). The application of 95% survival probability limits derived from pooled data increases the statistical reliability of sigma-N curves and gives an improved estimate of a material's minimum performance. The sigma-N curves derived for all th ree wood species at R=-1 were normalized with respect to ultimate compressive strength values and found to be practically coincidental. This allowed the derivation of a master curve for a generic scarf-jointed wood laminate under reversed load conditions. This relationship was verified using data from the literature and found to be a good predictor of fatigue performance. The construction of simple triangulated constant life diagrams based on static tensile and compressive tests and fatigue testing at R=-1 brings about a rapid assessment of the overall fatigue performance of any wood composite. These can then be used in the fatigue design or life prediction of wood composites under cyclic loading. (C) 1998 Kluwer Academic Publishers. [References: 40]