跌落损伤脆值及损伤边界

提出了跌落损伤脆值与跌落损伤边界的新概念,并提出了测定获取跌落冲击损伤脆值与跌落损伤边界曲线的技术过程与方法.以嘎拉苹果为研究对象,设计多组高度对嘎拉苹果进行自由跌落刚性冲击试验.在测试获得冲击力-时间数据的基础上,通过理论分析计算,得到加速度-时间、变形量-时间等动态关系曲线,获得了嘎拉苹果跌落损伤脆值;构造了嘎拉苹果跌落损伤边界曲线.结果表明,跌落损伤边界曲线与传统产品跌落破损边界曲线存在较大差异.对应果品类产品,即使速度很小,只要产品瞬时加速度达到一定值,也将产生冲击损伤;对应不同的损伤率,可构造相应的多条损伤边界曲线.提出的概念及研究结果为控制果品类产品的跌落损伤、合理地进行缓冲包装设计提供了新的理论基础.

Dropping bruise fragility and bruise boundary

For the 'viscoelastic' products such as fruits,the major mechanical damages usually are not direct split but local bruise caused by dropping impact during distribution,packaging and transportation.It is worthier to control the local bruise volume and bruise ratio of fruits in engineering.As an extension of traditional product fragility and damage boundary,the concept of dropping bruise fragility and bruise boundary was developed in this paper.In view of the limitations for traditional testing methods,the method and procedure for determining dropping bruise fragility and bruise boundary were also established by adopting free-fall dropping tests.Taking 'Gala' apples as study objects,the free-fall dropping impact tests with different drop heights are made.The dropping bruise fragilities and bruise boundaries of 'Gala' apples at different bruise ratios were determined by means of test results and theoretical analysis.The results showed that,there were obvious differences between dropping bruise boundary and traditional damage boundary of products.Even if the velocity was low enough the fruits would be bruised as long as acceleration of products exceeded a certain value.Moreover,to different bruise ratios,a series dropping bruise boundaries can be established correspondingly.