Evaluation of litchi impact damage degree and damage susceptibility
Evaluation of litchi impact damage degree and damage susceptibility
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荔枝冲击损伤程度及损伤敏感性评价
DOI：
10.1016/j.compag.2020.105409
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发表时间：
2020-06
影响因子：
8.3
通讯作者：
Yang Zhou
中科院分区：
文献类型：
--
作者：
Wang Weizu;Zhang Shuangming;Fu Han;Lu Huazhong;Yang Zhou
荔枝果实在摇动采收或运输过程中受到冲击而产生的机械损伤，降低了荔枝果实的品质，缩短了货架期。本文以'糯米刺'和'桂味'荔枝为试材，采用一种新的测试方法，研究了荔枝果实与刚性平板的碰撞行为，旨在探索评价荔枝果实损伤程度和抗损伤能力的方法。在摆锤装置上进行冲击试验，用力传感器和高速摄像机记录冲击力、压缩深度和接触长度。在此基础上，提出了一种计算任意时刻接触面积、平均表面压力和压缩体积的方法。对冲击过程的分析表明，在所有情况下，变形阶段的结束是水果在冲击过程中最危险的时刻。随着跌落高度从200 mm增加到800 mm，两个品种的吸能百分率、最大接触面积和受害程度均增加，而接触时间则减少。当跌落高度在400 ~ 800 mm范围内时，最大表面压力保持稳定，表面压力不是影响损伤程度的主要因素。在200 mm处，“桂味”和“糯米刺”的受害率分别为13.34%和13.27%;在800 mm处，受害率分别为27.89%和23.74%。在400 mm处，损伤程度分别为70%和79%。荔枝品种差异对接触面积和接触时间的影响较小，但对600 mm和800 mm高度下的受害程度影响显著。基于弹性理论，采用决定系数较高的幂函数模型，成功地拟合了两个品种的冲击能与压缩深度之间的关系。结合压缩体积与损伤程度之间良好的线性拟合关系，利用冲击能量预测损伤程度。引入损伤敏感度（DS）来描述荔枝果实对冲击损伤的敏感性。结果表明，随着跌落高度的增加，DS减小。在600 ~ 800 mm的跌落高度范围内，'糯米刺'的抗冲击能力强于'桂味'。本研究提出的新方法可用于荔枝果实损伤程度的评估和荔枝振动筛的优化设计。
Mechanical damage induced by impact during shaking harvesting or transportation debases the quantity and shortens the shelf life of litchi fruit. In this paper, ‘Nuomici’ and ‘Guiwei’ litchis were used to study the impact behavior between fruit and a rigid plate with a new measuring method in order to achieve an approach to evaluate the damage degree and the damage resistance. Impact tests were conducted on a pendulum device and the impact force, compressed depth and contact length were recorded with a force sensor and a high-speed camera. Based on these data, a method was introduced to calculate the contact area, average surface pressure and compressed volume at any given moment of the impact. Analysis of the impact process indicated that the end of deformation phase was the most dangerous moment for a fruit during the impact in all cases. For both cultivars, as the drop height increased from 200 mm to 800 mm, the percentage of absorbed energy, the maximum contact area and the damage degree increased, while the contact time decreased. The maximum surface pressure remained stable as the drop height ranged from 400 mm to 800 mm, so that surface pressure was not a main factor affecting the damage degree. The damage degree of ‘Guiwei’ and ‘Nuomici’ were 13.34% and 13.27% at drop height of 200 mm and 27.89% and 23.74% at 800 mm. Respectively, 70% and 79% damage degree happened at drop height of 400 mm. The difference of litchi cultivar has low effect on contact area and contact time, but significant effect on damage degree when drop height was 600 mm and 800 mm. Based on elastic theory, power models with high coefficient of determination were successfully used to fitting the relationship between impact energy and compressed depth for both cultivars. Combined with the good linear fittings between compressed volume and damage degree, the damage degree could then be predicted with impact energy. Furthermore, the damage susceptibility (DS) was introduced to describe the susceptibility of impact damage of litchi fruit. The results show thatDSdecreased with the increase of drop height. ‘Nuomici’ was more resist to impact damage than ‘Guiwei’ as drop height changed from 600 mm to 800 mm. The new method presented in this study can be used to evaluate the damage of litchi fruit and optimize the design of litchi shakers.
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