稻谷吸湿过程中内部应力峰值分析

Analysis of Peak Stress in Rice Kernel during Moisture Absorption

使用空间轴对称有限元方法 ,将稻谷颗粒视为由 3种材料组成的 3层旋转椭球体 ,在不同初始湿度M0 、温度 T和相对湿度 RH 条件下 ,对内部的湿度 M、温度 T进行了数值模拟 ,应用所得结果对吸湿应力场进行了数值计算 ,分析了胚乳中截面的应力分布随时间的变化。计算结果表明 ,拉伸应力峰值出现在谷粒中心 ,垂直于中截面。由于此峰值应力对裂纹的产生有直接的影响 ,本文着重研究了 M0 、RH 和颗粒吸湿量对中心轴向应力峰值及其出现时间的影响。

Moisture absorption of long grain rice and absorption induced stresses were studied using axisymmetrical finite element method. The rough rice kernel was treated as a 3 layer ellipsoid, which consists of hull, bran, and endosperm. Moisture ( M ) diffusion and temperature ( T ) conduction in the kernel were analyzed first. M and T in the kernel were studied at different rice initial moisture content ( M 0 ) and air relative moisture content ( R H ) levels. With the obtained M and T data under each level, the viscoelastic stresses caused by absorption in the endosperm of the kernel were computed. The material of the endosperm was considered as a linear viscoelastic. The distribution of axial stress on mid section of endosperm and the change of the stresses during absorption were obtained. The peak tensional stress was found at center of the kernel, which is consistent with the observation of fissuring originated from the center. As its importance for fissuring control, the peak stress was studied for different M 0 and R H , and a family of contour lines of the peak stress were drawn in M 0R H plane which may be used to estimate the possibility of rice grain fissuring in different absorption conditions. The results obtained in this paper lay the foundation for improving drying quality of rice.