Effect of low temperature on tensile mechanical properties of wheat bran

Abstract: The cryogenic ultrafine grinding technology has the advantages of narrow particle size distribution, high grinding efficiency, no deterioration and low energy consumption. It is an important technical means to improve the nutritional composition and economic value of wheat bran. In order to reveal the influence of temperature on wheat bran grinding performance, a dynamic thermomechanical analyzer (DMA) was used to test the tensile failure of wheat bran samples in the temperature range from (80 ℃ to 30 ℃. On this basis, the effects of temperature on the mechanical properties of wheat bran, such as Young's modulus, ultimate stress and ultimate strain, as well as on energy consumption parameters such as crushing energy and refrigerant consumption, were studied. The results showed that with the decrease of temperature, the plasticity of wheat bran decreased and the brittleness increased, gradually changing from elastic-plastic material to brittle material. When the temperature is (80 ℃, the linear fitting coefficient of stress-strain curve is 99.95%, approaching 100%. It can be considered that the glass transition temperature of wheat bran is (80 ℃. The crushing energy of wheat bran decreases significantly with the decrease of temperature. Compared with the room temperature (30 ℃), the crushing energy of wheat bran decreases by nearly 70% at (80 ℃, which fully shows the low energy consumption advantage of low temperature embrittlement. The Young's modulus increased significantly with the decrease of temperature, and increased 93.14% at (80 ℃. The ultimate stress seems to be insensitive to temperature change, with a small increase of about 14.58% in the whole varied range of temperature. The ultimate strain decreases with the decrease of temperature. Within the whole varied range of temperature, the ultimate strain decreases by 66.68%, and which is basically consistent with the change of crushing energy. Their sensitivity to temperature ranges from high to low in order of Young's modulus > ultimate strain > ultimate stress. It is also found that there are great differences among the experimental data of mechanical properties at the same temperature, which may be mainly related to the inherent difference between wheat bran samples. The consumption of liquid nitrogen increases linearly with the decrease of temperature. The consumption of liquid nitrogen at (80 ℃ is 1.74 times as much as that at (40 ℃ and 2.94 times as much as that at (10 ℃. At the same time, it is found that there is a local minimum in Young's modulus, ultimate stress, ultimate strain and liquid nitrogen consumption near (10 ℃. If the grinding temperature is (10 ℃, it will be helpful to improve the economy of cryogenic grinding for wheat bran. Considering comprehensively the economy between the cryogenic mechanical properties of wheat bran and the refrigerant consumption, the suitable temperature range for cryogenic ultrafine grinding of wheat bran should be from (40 to 0 ℃. Based on the experimental and identification results, the linear and non-linear functional relationships between Young's modulus, ultimate stress, ultimate strain and temperature difference are given respectively, and the linear functional relationships between liquid nitrogen consumption and temperature difference are also given. In conclusion, the effect of temperature on the mechanical properties of wheat bran is significant. The use of low temperature embrittlement characteristics can improve the grinding performance of wheat bran, but attention should be paid to the economic problems caused by refrigerant consumption. The results of this study preliminarily reveal the effect of low temperature embrittlement on the mechanical properties of wheat bran, which can provide a reference for the selection of grinding temperature for ultra-fine grinding of wheat bran at low temperature.