| 香梨静压接触应力测量及损伤预测 |
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| 引用本文： | 吴 杰,李 凡,葛 云,胡 蓉.香梨静压接触应力测量及损伤预测[J].农业工程学报,2013,29(6):261-266. |
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| 作者姓名： | 吴 杰 李 凡 葛 云 胡 蓉 |
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| 作者单位： | 石河子大学机械电气工程学院,教育部绿洲特色经济作物生产机械化工程研究中心,石河子 832003 |
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| 基金项目： | 国家自然科学基金资助项目（31160335） |
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| 摘 要： | 为了实现香梨果实静压损伤面积的准确评估和预测,该文采用Prescale感压胶片对香梨不同静压水平下的接触应力分布进行测量分析和有限元模拟。研究结果表明,当香梨50～200N静压时,50N时香梨无肉眼可辨的损伤,感压胶片测量的峰值应力0.5～0.6MPa,其应力面积在香梨损伤面积中所占很小;感压胶片测量的接触应力分布中只有≥0.2MPa范围的应力面积非常接近香梨损伤面积,因此可作为香梨损伤面积的应力阈限。当该应力阈限用于香梨静压有限元模拟的损伤面积预测时,100和150N压力下的相对误差率约6%,200N压力下的预测误差为13%,这说明有限元法能够较准确地预测香梨静压损伤面积,从而可为今后香梨采收、分级和包装装置的减损结构优化设计提供依据。
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| 关 键 词： | 有限元方法 损伤检测 压力传感器 静压 接触应力 库尔勒香梨 |
| 收稿时间： | 2012/8/27 0:00:00 |
| 修稿时间： | 2013/1/10 0:00:00 |
Measurement of contact pressure of Korla pear under compression and bruising predication using finite element analysis |
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| Wu Jie,Li Fan,Ge Yun and Hu Rong.Measurement of contact pressure of Korla pear under compression and bruising predication using finite element analysis[J].Transactions of the Chinese Society of Agricultural Engineering,2013,29(6):261-266. |
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| Authors: | Wu Jie Li Fan Ge Yun and Hu Rong |
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| Institution: | (Research Center of Oasis Agricultural Mechanization,Ministry of Education,College of Mechanical and Electrical Engineering,Shihezi University,Shihezi 832003,China) |
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| Abstract: | Abstract: Bruise of Korla pears due to mechanical damage caused by static loading is considered as a significant problem during orchard harvest and transportation. In practice, there is a greater interest in damage area for visible bruising assessed by commercial operators and consumers. In this respect, bruise area is essentially related to contact pressure. Experimentally, the contact pressures are difficult to measure as fruit exhibit both anisotropic properties and viscoelastic behavior. It is worth noting that a non-invasive pressure-sensitive film is now used to study the contact area and pressure of fruit due to its ease of application. Additionally, an alternative approach is to estimate stresses using finite element analysis (FEA), which provides a user-friendly format in interpreting bruise formation of fruit. However, the output from FEA is very difficult to interpret and compare. Therefore, the objectives of this work were to study static contacts for Korla pear compressed at different loads using a novel pressure sensitive film technique. The film measurements were then used to validate the analytical results of FEA aiming to accurately predicate the bruise area of Korla pear under compression. In this study, the pear samples were compressed at loads of 50, 100, 150, 200 and 250 N by two parallel plates. The Prescale(r) film (Fuji Film Corporation, Japan) for ultra super low pressure was placed between the sample and the upper plate to measure contact pressure and contact area. When the force was loaded on the film, microcapsules were broken to release their color-forming material at a density that corresponds to the specific level of applied pressure. A prescale pressure graphic system (FPD-8010E), composed of a scanner, was used to evaluate multicolor of results and obtain the data of contact. Meanwhile, the model geometry of a real Korla pear was developed using the 'Spline" option and imported into ANSYS software to create a mesh with hexahedral elements. Assuming that a pear was a linear elastic material, the FEA simulation was run to obtain equivalent stress that followed the Von Mises stress criteria for failure. The film measurements showed that the maximum pressure in the pear contacts remained at a level of 05-0.6 MPa for all loads. Although the film presented the contact pressure area when the load was 50 N, this load did not cause any visible discoloration. The contact area for load ranged from 100 to 200 N was larger than actual bruise area. Only the area occupied by the pressure greater than 0.2 MPa was well correlated to the bruising area (R2=0.83), so this data was applied to determine an appropriate stress area of pear model for estimation of bruise area. As a result, the relative error rate of bruise predications with FEA in pear compressions was around 6% for 100N and 150 N while it was 13% for 200 N. This shows that the use of FEA can comparatively precisely predicate the bruise area of Korla pear. Thus, this approach will help for design of harvesting and sorting equipment and packaging media in reducing likelihood of pear bruising resulting from static loads. |
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| Keywords: | finite element method damage detection pressure sensors compression contact pressure Korla pear |
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