糙米正面破碎特性与裂纹扩展规律

Front fracture characteristics and crack propagation of brown rice

目的:研究碾米室中糙米破碎特性。方法:利用万能材料试验机进行糙米力学试验,通过数字显微镜观察糙米中裂纹及其扩展变化。结果:糙米受力时会经历屈服阶段与强化阶段的交替过程,直至断裂;在挤压载荷作用下,内部微孔洞处产生裂纹,裂纹的快速扩展造成了米粒破碎或断裂,在三点弯曲和剪切载荷下,糙米从支撑端底面产生裂纹,并扩展至正面;糙米的抗挤压变形能力最大、抗三点弯曲变形能力次之、抗剪切变形能力最小;与挤压载荷相比,糙米在三点弯曲和剪切载荷下的破碎强度和破碎能较小。结论:在对碾米机结构进行设计时,要尽量减少弯曲、剪切作用对糙米的影响;同等条件下,粳型糙米的力学特性优于籼型糙米。

Objective: Study on broken characteristics of brown rice in rice milling chamber. Methods: The mechanical tests of brown rice were carried out by universal material testing machine, and the breaking cracks were observed by digital microscope. Results: Brown rice will undergo the alternating process of yield stage and strengthening stage until fracture. Under the action of extrusion load, cracks were generated at the internal microvoids, and the rapid propagation of cracks caused the breakage or fracture of rice grains. Under three-point bending and shear loads, cracks were generated from the bottom of the support end and extended to the front. The compressive deformation resistance of brown rice was the largest, followed by the three-point bending deformation resistance, and the shear deformation resistance were the smallest. Compared with extrusion load, the breaking strength and breaking energy of brown rice under three-point bending and shear load were smaller. Conclusion: When designing the structure of rice mill, the influence of bending and shearing on brown rice should be minimized. Mechanical properties of japonica brown rice are better than indica brown rice under the same conditions.