Study On Compressive And Creep Characteristics Of Watermelon

Watermelon is easily damaged in the process of collecting, storage, transportation. Therefore, it's necessary to do quantitative analysis on watermelon's biomechanics and load capacity to ensure the reliability and rationality of processing and design. One hand, it's favorable to understand watermelon's mechanics and its laws, to guide watermelon grading with mechanical properties, to improve the evaluation system of watermelon's quality. On the other hand, since watermelon's mechanics are more intensively researched and broken mechanism was revealed, which can conduct watermelon's sorting, collecting and transporting.According to the problems on declining watermelon quality caused by storage and transportation currently, and the shortcomings of study on mechanical damage of watermelon at home and abroad, a new evaluation method was put forward in this paper: the intact watermelon under the natural status was studied by a compression test and creep test, and the relation between creep characteristics and quality with the variation of storage time, as well as mechanical properties of the watermelon were analyzed with Finite element method through test and theoretical analysis. The following conclusions were drawn:1. Deformation-force curves about ellipsesolid body of intact watermelon under quasi -static loading were developed and analyzed under different temperature and hardness, different loading rate. The curve reflects two visible feature points: biological yield point and the rupture point. In addition, the curve shows that rupture force compressed in perpendicular direction is greater than horizontal bearing's watermelon.2. Compressive parameters had been acquired by the curve and fitness the curve under different conditions, such as biological yield force, deformation energy, rupture force, rupture energy. The scope of stiffness of horizontal and perpendicular bearing's water melon is 20.6~42.5 N/ mm and 27.9~62.3 N/mm; the scope of rupture force is 845~1940 N and 1077~2432 N; the scope of rupture energy were 8.3~60.4 N?m and 16.4~68.7 N?m.It provide theoretical guidance and data support for watermelon harvest, storage, transportation and design of processing machinery. 3. The effect and variance about temperature, speed and hardness against the compressive parameters was analyzed. It can be concluded that the compressive parameters were all significantly affected by the effective factors (significant probability Sig.Value<0.01). Statistic analysis indicated that there is a significant positive correlation among compression parameters presented.4. The damage principle of watermelon was analyzed. For horizontal bearing's watermelon, its maximum force position is in the epidermis of equatorial plane, along the direction of meridian direction. Perpendicular bearing's watermelon stem, its cracks is along the meridian direction. The study results show that the damage of watermelon was caused by the maximum force under the compression load. Therefore the maximum force can be used to explain the mechanism of watermelon macro damage.5. Two Mathematical models were set up: (1) compression parameters forecast watermelon damage volume; (2) compression parameters forecast watermelon quality.The model which was set is meaningful through the analysis of ANOVA. Study result show that parameters of compression can predict injury and quality of watermelon.6. The mechanics model of compressing watermelon was established by the finite element method, and its horizontal bearing's simulation value of carrying capacity was compared with experimental data, which showed that maximal difference between simulation and experiment is 10.0%. At last, the characteristics of carrying compressing capacity in perpendicularity and horizon of watermelon stem was studied, and the simulation numerical solution was confirmed by comparing with the experiment data. It can be concluded that perpendicularl bearing's watermelon stem strain and the stress was less than the horizontal bearing under the same pressure. The study will provide the theory basis to watermelon's storing, transporting and processing and so on.7. The creep curve and the corresponding creep parameters of watermelon (γ0,γ1, Trel,η2) were acquired in different load, temperatures and hardness. At the same time a watermelon creep model was established as the four components Burgers model, and the corresponding constitutive equation: D tFFetFt. It is found that the new model well describes the full creep procedure of watermelon. by a different load, and temperature and hardness of watermelon creep curve, parameters of creep, creep parameters on the creep and creep curve of the correlation between parameters. The effect on temperature, hardness and loading force against the creep curve and parameters, on creep parameters against creep curve, and correlation about creep parameter with itself was analyzed. The parameters of the creep equations are calculated and the forecast curves are drawn. In comparison with the experimental curves, the theory results are proved, within the error of 5 percent. The rheological parameters of the creep equations are calculated and the forecast curves are drawn. In comprison with the experimental curves, the theorial results are proved, within the error of 5 percent.8. The creep rate and deformation of watermelon are different in different load. The greater load, the sooner the creep rate and the greater corresponding deformation is. The reason of creep damage was deformation values in excess of threshhold. It is feasible for explaining the mechanism of injury creep to use critical deformation.9.Watermelon quality(TSS, PH etc.)curve, creep curve and the corresponding creep parameters with different storage time was acquired under different temperature, hardness and different load, and their changeable ressons were analyzed. Two mathematical models were set up: (1) the creep parameters change with the storage time; (2) creep parameter forecast watermelon quality. The relevance of creep parameters and texture of watermelon was analyzed to realize non-destructive assessment watermelon texture and improve product quality, and reduce the watermelon injury.