单自由度模型苹果脆值的预测

目的 以苹果为研究对象，建立一种易操作的脆值测定方案对苹果进行缓冲包装设计和分析。 方法 通过静态压缩试验测得苹果的线刚度，通过跌落试验测出破损临界跌落高度，进而基于单自由度理论模型计算出苹果脆值。根据苹果的脆值和缓冲材料的静态缓冲系数设计出最优包装方案。最后，模拟公路随机振动和跌落试验评价上述缓冲方案的可行性。结果 无泡沫网苹果的破损临界跌落高度为 5 cm，线刚度为106.59 kN/m，固有频率为109.79 Hz；带泡沫网苹果破损临界跌落高度为10 cm，线刚度为104.48 kN/m，固有频率为106.58 Hz，临界脆值Gc约为96.28。据此，按照80 cm的搬运跌落高度设计时，缓冲材料EPE厚度需要达到1.98 cm。结论 建立的脆值测定方案具有精准度高，且较传统脆值测定方法对仪器依赖度低，具有操作简便易行、普适性强等优点，易于推广到其他类型包装件脆值的测定。

Predicting the Fragility of an Apple Based on a Single Freedom Degree Model

The work aims to develop a fragility measurement scheme easy to operate for the cushioning packaging design and analysis of apples, with the apples as study object. The elastic stiffness of apples was determined by the static compression test. The critical drop height of damage was obtained by the drop test. Furthermore, the fragility of apples was calculated on the basis of single freedom theoretical model. Then, an optimal packaging scheme was designed according to the apple fragility and static cushioning coefficient of the cushioning materials. Finally, the road random vibration test and drop test were simulated to evaluate the feasibility of the above-mentioned cushioning scheme. For apples with mesh-foam protection, the critical drop height of damage was 5 cm, the elastic stiffness was 106.59 kN/m, and the natural frequency was 109.79 Hz, while those without mesh-foam protection were 10 cm, 104.48 kN/m and 106.58 Hz, respectively, and the fragility Gc was about 96. In view of the above, as for the design according to the 80 cm handling drop height, the cushioning material EPE should be 1.98 cm thick. The fragility measurement scheme developed has high precision and it has such advantages as low demand on the instruments, good handle ability and generalization, compared with the traditional fragility measurement method. It is easy to apply the fragility measurement scheme in the fragility measurement of other types of packages.