声发射法无损检测稻谷籽粒应力裂纹  

Non-destructive detection of stress cracking in rice kernel by acoustic emission

作　　者：吴中华[1,2] 康宁 董晓林 赵丽娟 张忠杰[3] Wu Zhonghua;Kang Ning;Dong Xiaolin;Zhao Lijuan;Zhang Zhongjie(College of Mechanical Engineering,Tianjin University of Science and Technology,Tianjin 300222,China;International Joint Research Center of Low-Carbon Green Process Equipment,Tianjin 300222,China;Academy of State Administration of Grain,Beijing 100037,China)

机构地区：[1]天津科技大学机械工程学院,天津300222 [2]天津市绿色低碳过程装备国际联合研究中心,天津300222 [3]国家粮食局科学研究院,北京100037

出　　处：《农业工程学报》2018年第16期274-280,共7页Transactions of the Chinese Society of Agricultural Engineering

基　　金：国家自然科学基金(31471618);国家重点研发计划子课题(2017YFD0400904-4)

摘　　要：针对目前稻谷应力裂纹缺乏有效研究手段的难题,该文提出利用声发射法研究应力裂纹的设想。以天优3301籼型感温三系杂交稻谷为物料,建立稻谷干燥和机械压缩试验声发射检测装置,测量并分析了稻谷干燥、应力和声发射信号之间关联。结果表明:谷粒在干燥和受载过程产生的声发射信号能够被有效检测;干燥过程中声发射信号时序特征与稻谷干燥特性、典型干燥现象关联密切。湿基含水率为22%稻谷籽粒在60℃条件下,在干燥初始加热期0~7 min,稻谷因内部温度梯度形成的应力而释放少量声发射信号;在7~40 min声发射信号伴随温度梯度减弱而消失;在干燥40 min后,声发射信号受水分梯度影响而重新出现,并且信号密集区和水分梯度最大值时间重合,均出现稻谷湿基含水率干燥到14%附近;30~80℃自然冷却中稻谷声发射信号急剧增加,与高温干燥冷却段爆腰率快速上升现象相对应。湿基含水率为20%谷粒在30 N压载过程中声发射信号峰值与应力屈服8 MPa均出现在100 s。该文研究表明声发射法可为研究稻谷应力裂纹提供一种新的方法和途径。Rice kernels after being harvested would encounter various stresses in its sequent operations such as drying,milling.These stresses easily cause the stress cracks.Stress cracks are classified into micro cracks,meso cracks and macro cracks.The stress cracks are generally propagated from micro to meso cracks,and even to macro ones,which are called fissuring.Rice fissuring would reduce the head rice yield and thus the economic value of rice.However,there is no effective method to study stress cracks.In this work,the acoustic emission method was first proposed to investigate the cracks.The hot air drying and mechanical compression experiment were performed.The experimental material was the Tianyou 3301 indica hybrid rice with an initial moisture content of 22%.The acoustic emission(AE)pulse signals generated by the stress cracking inside the rice kernel during the drying and mechanical compression processes were monitored by AE instrument respectively.The relationships between drying,stress and strain,AE pulse signal of the rice kernel were analyzed based on the rice drying experimental and numerical results,and AE results.Experimental results show that the AE signals in the drying and mechanical compression processes can be measured effectively.In the air drying process,the timing sequence property of the AE signals generated in the rice kernel agreed well with the drying characteristics and some typical drying phenomena.In the case of the rice kernel with an initial 22%moisture content dried at 60℃,the AE signals were active in the initial heating stage of 0-7 min and these signals were believed to be caused by the temperature gradient.In the 7-40 min,the AE signals were weak because the temperature gradient diminished but the moisture gradient increased gradually.The AE signals became active again after 40 min,which was expected to be caused by the moisture content gradient.It was observed that their peaks were corresponding to the maximum moisture content gradient.In the sequent cooling process,the intensive AE

关 键 词：干燥 应力分析 声发射 稻谷 应力裂纹 爆腰 

分 类 号：TQ028.6[化学工程]