荔枝应力松弛特性及其损伤的试验研究

Experimental Study on Stress Relaxation Characteristics and Associated Damage of Litchi

为探讨荔枝的应力松弛特性及其在压缩松弛条件下的损伤规律,对其进行了不同试验条件的压缩应力松弛和损伤统计试验,确定了荔枝应力松弛模型并分析了试验因素对模型参数和荔枝损伤的影响等。结果表明:荔枝的应力松弛特性可用五元件Maxwell模型描述,模型拟合R2达到0.98;试验范围内,变形量对模型弹性模量影响不显著,而加载方向对其影响最大;试验因素均影响模型松弛时间和粘性系数;模型弹性模量与松弛时间之间无显著相关,但各自都显著相关;对损伤影响显著的因素依次为压缩变形量、加载方向、松弛时间和加载速率;变形量、松弛时间和加载速率分别每增加1 mm、10 s和10 mm/s,荔枝吸收的能量分别平均增加3.3 m J、0.26 m J和0.2 m J;荔枝的粘性系数与其吸收的能量无显著相关;随着压缩变形量增加,荔枝吸收的能量和损伤度也不断增加;荔枝损伤度与其吸收的能量近似二次曲线关系。

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 m J, 0.26 m J, and 0.2 m J, 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.