The Mechanical Mechanism Of Temperature-Induced Cracking In Greenhouse Tomato

Tomatoes are one of the most widely planted and consumed fruit and vegetable in the world.However,tomato fruits pericarp cracking often occur during growth,which seriously affects the yield and quality of tomatoes.tomatoes are generally exposed to a fluctuating environmental temperature(0-40 ℃)throughout growth.Due to there is very little information on anti-cracking capacity of the tomato pericarp under different environmental temperature condition.This research gap impedes the accurate assessment of a tomato crop variety’s anti-cracking ability and restricts the inverse rapid search for a pericarp phenotypic indicator for locating the control gene to enhance anti-crack breeding.In this study,tomato fruit was taken as the main research object to investigate the specific relationship between temperature and fruit cracking by measuring the cracking characteristics of tomato fruit under different growth environment temperatures.On the basis of experiments,a three-point bending finite element model and a thermally coupled finite element model of tomato pericarp were constructed using the finite element analysis software Abaqus to explore the thermodynamic characteristics of tomato fruit cracking.In addition,a regression model was established based on the simulation results to predict the cracking resistance of tomato fruit.The main research contents and results are as follows:(1)In order to explore the environmental factors that induce tomato fruit cracking,this study provided different environmental growth temperatures for tomato fruit through bagging.The results showed that there were significant differences in the ambient temperature of fruit growth between the sunny and shady sides of the greenhouse.The growth temperature of tomato fruit under daytime bagging treatment was much higher than the normal growth temperature of tomato in the greenhouse,while the difference between the growth temperature of tomato fruit under nighttime bagging treatment and the normal growth temperature of tomato in the greenhouse was not significant.The cracking rate of tomato fruit treated with bagging is much higher than that of tomato fruit grown under normal conditions.At the same time,the cracking rate of sunny tomato fruit is greater than that of shady tomato fruit.When the humidity is about 50 %RH,and the temperature of the fruit growing environment exceeds30 ℃ and the temperature difference between day and night is greater than 20 ℃,the fruit is more prone to cracking.In addition,the higher the maturity,the easier the tomato fruit is to crack,and the faster the crack propagation speed is.Growth environment temperature and whether the fruit cracks have no significant impact on the mesocarp thickness of tomato fruit,while growth environment temperature has no significant impact on the exocarp thickness of tomato fruit,but whether the fruit cracks has a significant impact on the exocarp thickness of tomato fruit.(2)In this study,a three-point bending extended finite element(XFEM)model including five parts: a loading probe,exocarp,mesocarp,pre-crack,and two rigid fixed support points was developed for investigating the cracking susceptibility of pericarp during fruit development and postharvest handling.During pericarp cracking simulation,a displacement load of the probe was applied over a cuboid pericarp sample to replace the increasing turgor pressure of mesocarp cells.The XFEM based three-point bending model with average tissue mechanical data was found to be able to reproduce the probe loading force-pericarp deflection behavior and the crack propagation length-pericarp deflection behavior in the three-point bending test up to 6 mm tomato pericarp deflection deformation with an average relative error of about 7.8 % and 5.2 %,respectively.The XFEM model’s crack propagation area and volume were affected by environmental temperature,exocarp and mesocarp thickness.Three multiple linear regression mathematical models were established for quantitatively predicting the tomato pericarp cracking susceptibility.It was found that the factors affecting the cracking susceptibility of pericarp in descending order include exocarp thickness,pericarp deflection,mesocarp thickness,and temperature.(3)The thermo-biomechanical coupling three-point bending FE analysis in the tomato pericarp sample was performed.Results showed that the established FE model was capable of reproducing the experimental probe loading force-pericarp deflection and the crack propagation length-pericarp deflection curves in deflection deformation up to 6 mm,with average relative errors of 3.0 % and 4.3 %,respectively.The propagation area and volume of the crack in pericarp model were gradually sensitive to the temperature gradient acting on the exocarp surface and fruit ripeness.Three obtained linear mathematical models can quantitatively predict the cracking status of the pericarp under different temperature gradient levels when the sunlight caused a uniform temperature increase on the exocarp surface.The tomato had a better anti-cracking ability when the sunlight caused a non-uniform temperature increase on the exocarp surface.This study provides a basis for preventing the cracking of tomato fruit during development by controlling the environme.