Axial Fatigue Properties of Pinus Tabulaeformis Root

The axial fatigue properties test were carried out on pinus tabulaeformis root indoor,simulating cyclic loading leading to soil erosion in nature. Results showed that root tensile force and tensile strength of pinus tabulaeformis after fatigued cycle 100 times and 1000 times were both significantly higher than those of root under monotonic loading. The fatigue stress-strain hysteretic curve of root showed obvious cycle features. At initial stage,"hysteretic loop" was a plump shape of "spindle" with a better capacity of plastic deformation and energy dissipation,and was arranged for "sparse" but not close. With increasing cycle number,hysteretic loop spacing was more and more intensive which tended to be stable. "Hysteretic loop" of loading section and unloading section were both fit by quadratic function,The fitting parameter A,B and C of "Hysteretic loop" varied smoothly with increasing cycle number in addition to the smaller diameter roots. Total deformation of hysteresis curve included elastic deformation and plastic deformation. With 20th cycle for boundaries,total strain was divided into two stages: rapid growth stage and slow growth stage.