A multiscale computation study on bruise susceptibility of blueberries from mechanical impact

Abstract

Impact bruising is a prevalent form of mechanical damage that occurs in blueberries during harvesting and postharvest handling processes. The accurate quantification of bruising remains a challenging task, primarily due to the limitations of available technologies. To address this issue, herein, the data-enabled computational method was employed to evaluate the bruise susceptibility of blueberries under various free drop scenarios. A multiscale computational model, comprising the skin, flesh, and seeds, was constructed based on the anatomical structures of blueberries. The mechanical properties were obtained through compression tests, and free drop experiments were conducted to validate the computational model. A total of 120 cases were simulated, considering various drop heights, impact angles, and contact surface materials. Based on simulation results, empirical models to predict bruise susceptibility were developed specifically for each contact surface material using the response surface methods. The results revealed that mechanical behavior of blueberries subjected to compressive loading was adequately described using a linear elastic-plastic model, with Young’s modulus, tangent modulus, and yielding strain being 0.339 MPa, 0.166 MPa, and 0.185, respectively. The equivalent plastic strain (PEEQ) metric from simulations effectively captured bruising distribution in drop impacts with a bruising threshold value set at 0.1. Bruise susceptibility was influenced by the modulus ratios between the contact surface material and blueberry, and exhibited a linear positive relationship with drop heights. In addition, the effect of impact angle was contingent on the drop height. At lower drop heights, greater bruising occurred at vertical impact angles. As the drop height increased, the blueberries became more susceptible to bruising at the horizontal impact angles. The specific transition in drop height varied among different contact surface materials. These results demonstrate the capability of the multiscale computational model to simulate drop scenarios and assess the bruise susceptibility of blueberries. The theoretical insights provided by this study offer valuable guidance for optimizing fresh-market blueberry mechanical harvesting machine design and postharvest handling processes for longer shelf-life.