In this paper, a novel control-loop concept is presented to investigate the viscoelastic properties of different pome fruits. Repeated mechanical effects are one of the most important risk factors during the postharvest procedures, so our work aimed to expand knowledge in the field. The actual investigations involved Golden Delicious apples and Packham pears. The developed model is based on the Poynting–Thomson body and, during the validating dynamic creep tests, different repeated compressive loads were applied. The examined frequencies were chosen from the most common components of the frequency distribution during the transportation process; the given range is responsible for the highest volume of fruit damage and the most extensive losses. The identified mathematical system determines the viscoelastic model parameters with the best fit to the measured creep data. The model properties of the tested fruit textures are compared in six different frequency setups, with the inspected pome species showing different elastic and viscous responses for the adjusted load conditions. The custom testing device with variable load functions and the proposed solution allow system identification with a wide range of setup possibilities. The resulted viscoelastic parameters can be used for further failure analysis and for the comparison of different pome fruit materials.
In this paper, the multiple linear regression model of mechanical properties related to the failure mechanism of apple tissue under repeated compressive load was investigated. More refined failure characteristics may lead to improved processing and logistics aspects of the given fruits. For our study, the following failure-related factors are considered during the cyclic measurements of Golden Delicious apples: the viscoelastic parameters, the dissipated energy, and the rupture point of the cell-structure, which is described with the time to failure parameter (TTF). For the determination of viscoelastic components, the three element Poynting-Thomson body was applied, and a closed-loop control system is identified with the measured creep data. From the hysteresis loop – in each cycle of the force-deformation parametric curve – the dissipated energy can be calculated with a numeric integration method. The rupture point of the fruit tissue – where the measuring pin is breaking through the peel and the cortex – is observed with a high-framerate video analysis, so that the time index of the failure point can be evaluated. The focus is to define the influence of the mentioned factors to the TTF parameter of the examined fruit material. During the statistical evaluation of the resulted data, the failure of time can be successfully determined with a multiple lienar regression model of the determined viscoelastic and dissipated energy variables. With the resulted equation, the failure time of Golden Delicious apples can be predicted based on the measured failure-related parameters obtained during the compressive load tests.
One of the most significant phenomena in the processing of horticultural crops, leading to the damaging of the fruit, is fatigue due to repeated mechanical stress, which endangers the integrity of the produce, especially during transport. In the event of such damages, the immediate environment of the damaged fruit, or even the entire batch of crops may be in danger, as the biological processes leading to spoilage are not limited to the individual crop damaged. In the case of repeated effects, a force less than the static limit value is sufficient to cause spoilage, but in addition to the load, the material properties of the given crop, as well as the energy balance observed during damage play important roles in determining the mechanical resistance. Accordingly, in our work, a description of the spoilage process is built on the material models most characteristic of the selected crops, on the dissipated energy indicators measured during repeated loads, and on the definition and determination of the spoilage time. In the experiments, the fatigue indices of Golden Delicious apples, making up most of the apple production of the European Union, and of long shelflife Packham pears are compared by setting up linear regression models.
The mechanical investigations on hammer mills and the connected theoretical research is one of the projects carrying on for several years at our Department. The generalization of the results gained until now is still an actual problem that is effected at present, according to the analytical objectives with applying the up-to-date instrumentation and measurement techniques. To the investigations, such a laboratory measurement system has been elaborated and designed that is capable of determining the performance and energy consumption (power requirement) of the mill, the product quality as well as other machine and operating (process) properties with an acceptable accuracy, using not too great sample masses in tests. The investigation was carried out with different cereal grains. The data processing was effected by an own computer software utilizing which a standard model has been developed for handling the measured data. That provides the possibly widest description of the conditions of comminution process according to the present knowledge. ÖsszefoglalóA kalapácsos aprítógépek géptani vizsgálata és az ezzel kapcsolatos elméleti kutatás sok éve folyó program Tanszékünkön. Az eddig elért eredmények kiterjesztése ma is folyik, most célzottan a legújabb műszerezési és számítógépes méréstechnika alkalmazásával. Vizsgálatainkhoz olyan laboratóriumi mérőrendszert dolgoztunk ki, amely lehetővé teszi az aprítógép teljesítőképességének, energiafelhasználásának és a termék (őrlemény)minőségének, valamint más gép-és üzemi jellemzők nagyságának kielégítően pontos meghatározását különböző anyagok ill. anyagállapotok esetén, nem túl nagy mintatömegek felhasználásával. A kísérleteket szemes gabonafélékkel végeztük. Az adatfeldolgozást számítógépre vittük, s ezt kihasználva, egységes modellt dolgoztunk ki a mérési adatok kezelésére, amely lehetővé teszi az aprítási viszonyok a jelenlegi ismeretek szerint lehetséges legszélesebb körű leírását.
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