Objective  Oil tree peony is a unique woody oil tree species in China, which belongs to the perennial shrub. To harvesting the fruit, stem cutting can be an efficient way, but the mechanism of efficient cutting of shrub stem has been one of the difficult problems in forestry production. It is of great significance to study the dynamic mechanical properties of shrub stem under different strain rates and establish its constitutive model for stem cutting.

  Method  In this paper, a quasi-static tensile test of peony stems and a dynamic tensile test were established to investigate the characteristics of plastic deformation during stem fracture. Then, based on the experiment, Johnson-Cook model was used to be the constitutive equation of peony stem cutting, and the model parameters were obtained by experimental fitting according to the physical meaning of the model parameters. Finally, a finite simulation was carried out by ANSYS/LS-DYNA software and the result was compared with experimental result.

  Result  The results of quasi-static tensile test showed that there was obvious strain hardening phenomenon in the process of stem fracture. The results of dynamic tensile test showed that there was a significant strain rate effect on stem fracture, and the tensile strength increased with the increase of strain rate. Based on the experiment results, the material parameter values of Johnson-Cook model were obtained. According to the comparison of simulation and experiment results, there was no significant difference between the simulation and experiment result of cutting force and cutting energy, which verified the accuracy of the constitutive equation and parameter determination.

  Conclusion  In this paper, based on the Johnson-Cook model, the constitutive equation of peony stem cutting was established and its reliability was verified, which provided a basis for the numerical simulation of cutting properties of oil tree peony stem and the design of cutter of harvesting machine.