科研之友
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摘要
For viscoelastic products such as fruit, the major mechanical damage is usually not direct splitting but rather local bruising caused by dropping impacts during harvesting, handling, packaging, and transportation. It is necessary to develop engineering approaches to control the fruit's local bruise volume and bruise ratio, which is the ratio of bruise volume to whole volume of the fruit. As an extension of conventional product fragility and damage boundary, the concept of dropping bruise fragility and bruise boundary was proposed and defined in this study. In view of the limitations of conventional testing methods (ASTM D3332 Standard Test Methods for Mechanical Shock Fragility of Products), the method and procedure for determining dropping bruise fragility and bruise boundary of fruit were also established by adapting free-fall dropping tests. Free-fall dropping tests with a series of drop heights were conducted on fresh 'Gala' apples. The dropping impact acceleration, velocity, and deformation change during contact at varies drop heights were obtained. The relationship between bruising deformation and theoretical deformation of the samples was determined. The dropping bruise fragilities and bruise boundaries of 'Gala' apples at different bruise ratios were determined by a combination of tests and theoretical analysis. The results showed that there were obvious differences between dropping bruise boundary of apples and conventional damage boundary of products. Even if the dropping impact velocity approached zero, the fruit could be bruised as long as the impact acceleration exceeded a certain value. Moreover, a series of dropping bruise fragilities and dropping bruise boundaries can be established for different levels of bruise ratios.
