Finite element modeling of apple tissue mechanics: A comparative study of elastic and elastoplastic behavior across ripening stages

The mechanical properties of apple tissues vary significantly with ripening, influencing their susceptibility to bruising during handling. This study developed and validated finite element models (FEM) to simulate the mechanical behavior of ‘Chopin’ apples at three ripening stages: development, ripening, and senescence. Two modeling approaches, elastic and elastoplastic, were calibrated using experimental stress–strain data obtained from uniaxial compression and tensile tests. Model validation was performed by comparing simulated force–displacement curves and contact pressure distributions with empirical measurements.

Elastic models showed strong agreement with modified experimental data, achieving fit values between 87 % and 91 %, particularly in early-stage fruit. However, their performance declined when applied to unprocessed data that included permanent deformation, with fit values decreasing to 79–83 %. In contrast, elastoplastic models delivered superior accuracy across all ripening stages, with fit values ranging from 91 % to 96 %, and effectively reproduced nonlinear behaviors such as yield and localized tissue failure. Contact area predictions further supported the enhanced performance of elastoplastic models, particularly in capturing shifts in pressure distribution during loading.

These findings highlight the limitations of simplified elastic assumptions in modeling biological tissues and underscore the advantages of elastoplastic formulations in capturing irreversible mechanical responses. Although computational time increased by 20–39 %, the improvement in predictive realism justifies their application in bruise prediction, robotic fruit handling, and postharvest process optimization.