Contact Pressure Analysis Of Drop Impact For Korla Pear And Bruising Predication Using Finite Element Analysis

In this paper the contact pressure was measured by pressure-sensitive film for Korla pear drop impactdifferent counterfaces at a series of dropping heights. Then, these results were compared with calculationsby Hertz equation to analysis the applicability of Hertz equation on contact pressure area. The bruise areacould be accurately assessed and predicted by finite element method based on the relationship betweencontact pressure area and bruise area. This approach will help for design of harvesting and sortingequipment. The main results are as follows:(1) In the Korla pear drop experiment, the change law of bruise area and bruise threshold for Korlapear drop impact on steel board, rubber board, HDPE board, corrugated board and pear from differentheights were analyzed. The contact pressure was measured with pressure sensitive film to establish therelationship between contact pressure area and bruise area. The results showed that the bruise area changedexponentially with drop heights when Korla pears impacted against different counterfaces (R2≥0.90). Thebruise thresholds of Korla pear, i.e. the corresponding heights, were in order of steel board, pear, rubberboard, HDPE board and corrugated board from low to high. For Korla pear impact against the steel board,rubber board, HDPE board and pear, the total pressure area was closed to the bruise area. The averagerelative error was4.84%,1.83%,3.21%,6.38%. But when Korla pears impacted against corrugated board,the pressure area over than0.2MPa was well correlated to the bruise area. The average relative error was6.81%.(2) The contact pressure area of calculations with Hertz equation and measurements withpressure-sensitive film were compared and analyzed for Korla pear drop impact the vast counterfaces. Theresult showed that the calculations with Hertz equation was close to the measurements by thepressure-sensitive film when Korla pear drop impact steel board, rubber board, HDPE board at the lowheight. With the increases of the drop height, the calculations with Hertz equation of contact area showedlarger deviation. When Korla pear drop impact corrugated board at low height, the Hertz equation is notsuitable for calculating the contact pressure. However, when the drop height was above the cushionthreshold of corrugated board, the calculations with Hertz equation was close to measurements by thepressure sensitive film. For the Korla pear drop impact Korla pear, the impact display mainly elasticdeformation instead of plastic deformation within height, so the value of Hertz equation is close to themeasurements by the pressure-sensitive film.(3) According to the relationship between the contact pressure area and the bruise area, the finiteelement method was used to simulate Korla pear drop impact different counterfaces to predicate thedamage. The results showed that the finite element method can predict exactly the damage size for Korlapear drop impact counterfaces. The predicted bruise area is little higher than the actual bruise area. WhenKorla pear drop impact the steel board, rubber board, HDPE board and Korla pear, the relative error were 12.72%,6.33%,4.91%and5.62%. For the corrugated board, the relative error is about16.74%.