Abstract:In order to investigate the stress relaxation characteristics of litchi as well as the damage patterns induced in the relaxation condition, a compression stress relaxation test and statistical analysis on the associated damage were carried out under different experimental conditions. The stress relaxation model was confirmed, and the influence of experimental factors on model parameters and litchi damage was analyzed. The results indicated that the stress relaxation characteristics of litchi could be described by a five-element generalized Maxwell model with a coefficient determination (R2) of 0.98. Within the test range, deformation did not significantly affect the elastic modulus of the model, but loading direction had a significant impact. All of the experimental factors affected the relaxation time and viscosity coefficient of the model, and although the elastic moduli and relaxation time were not significantly correlated, each factor showed a significant correlation independently. The prominent damage factors were in the order of compression deformation, loading direction, loading rate, and relaxation time. For the increment of 1 mm in deformation, 10 s in relaxation time, and 10 mm/s in load rate, the average increase of the absorbed energy in litchi were 3.3 mJ, 0.26 mJ, and 0.2 mJ, respectively. The viscosity coefficient was not significantly correlated with the absorbed energy in litchi. With the increase of compression deformation, absorbed energy and the damage degree of litchi also increased; there was an approximate quadratic relationship between damage degree and absorbed energy in litchi.
