青香蕉多次敲击力学特性及易损性评估

Mechanical properties and bruise susceptibility of green bananas under repeated impacts

香蕉通常在绿硬期(即青香蕉)进行采运,在此过程中果指与作业部件和果指与果指之间易发生反复碰撞。为探明果指的机械性质,减少香蕉采运过程中的碰撞损伤,该研究针对不同生长位置的果指进行了敲击试验。通过方差分析检验了敲击次数、敲击能量和生长位置对果指力学特性(加速度峰值和恢复系数)及易损性(损伤尺寸和敏感度)的影响。结果表明,敲击能量越高,加速度越大,恢复系数越小,损伤尺寸和敏感度越大,果指越易损伤;在果指塑性变形对应的敲击能量阈值内,加速度、恢复系数与损伤尺寸随次数以非线性方式增加,但增量主要集中在初始5次,而损伤敏感度则以非线性方式递减,随着敲击次数的增加,果指的易损性呈非线性降低。越靠近果轴底端且在内排生长的果指,越易损伤。该研究成果可为香蕉采运等过程中的防护措施与风险因素的管理提供依据。

Banana fruits are typically harvested and transported while still green and hard,referred to as green bananas.However,frequent collisions often occur between fruit fingers,working parts,and adjacent fruit fingers during this stage.This study aims to investigate the mechanical properties of fruit fingers at different growth positions.The experimental material was selected as the finger of the banana plant(Musa spp.)on a supporting platform created by 3D printing technology.A complete factorial experiment was performed using a pendulum method.The test conditions included three impact energies(0.27,0.52,and 0.88 J)and three repeated times(1,5,and 10)across three growth positions(the inner rows of the first and second nodes,the outer rows of the first and second nodes,and the inner and outer rows of the last nodes)within a green banana bunch.Mechanical parameters were calculated,such as peak acceleration,coefficient of restitution(CoR),bruise area(BA),bruise volume(BV),and bruise susceptibility(BS).Among them,the BS represented the ratio of BV to the total absorbed impact energy.A multi-way analysis of variance was also conducted at a significance level of 5%to determine the statistical significance of the mean values of the parameters.The results demonstrated that there was a strong positive correlation between peak acceleration and bruise sizes,and a strong negative correlation between the CoR and BS.Specifically,the higher peak acceleration resulted in the more severe damage to the fruit fingers,whereas the smaller CoR made the green bananas more susceptible to damage.Moreover,the impact energy,repeated times,their interaction,and the location of banana growth significantly dominated the mechanical parameters of the BA,BV,and BS.The higher impact energy led to the greater peak acceleration,BA,BV,and BS,whereas,the lower CoR was observed.Consequently,the higher impact energy tended to increase the susceptibility of banana fruit to damage.Once the impact energy was below the threshold for the plastic deformation of green bananas,the peak acceleration and CoR were improved non-linearly with each impact up to the first five impacts,after which the increment decreased progressively for each subsequent impact.Similar trends were observed for the BA and BV,while the opposite was true for the BS.Therefore,the susceptibility of banana fruit decreased with the increasing impacts.It is challenging for the reduced number of impacts to less than five during production.Fruit damage can be minimized to reduce the energy required to hit the banana fingers.Once the impact energy exceeded the threshold,an initial increase in the peak acceleration and CoR was followed by a decrease,due to the plastic deformation and ductile fracture of the banana finger from continued impacts.Both BV and the rate of increase were enhanced with the number of repetitions.Furthermore,the BS of banana fingers in the outer row was generally smaller than that in the inner row,indicating that the inner row was more susceptible to impact-induced bruise damage.These findings can provide a strong reference to managing the protective measures and risk factors during banana harvesting and transportation.