Numerical and experimental performance evaluation of ventilated packages

[摘要] ENGLISH ABSTRACT: Packaging serves a crucial role in reducing postharvest losses, particularly in the handling of fresh horticultural produce, and would be difficult to do without. Packaging protects the produce against mechanical hazards such as compression, impact, drop or vibration during distribution, ensuring its safe delivery to the consumers in a sound condition, at a minimum cost. Ventilated corrugated paperboard (VCP) packaging is being used extensively for handling fresh produce due to its capability to promote uniform and rapid cooling. However, the presence of ventilation openings jeopardises the strength of the package which could result in produce damage. As it is of utmost importance to ensure that the produce reaches its final destination without damage, continuous improvement in the package strength is paramount. Hence, this project aimed to gain a better understanding of the structural performance of VCP packaging to enhance the development of better and improved package designs.Firstly, a validated finite element analysis (FEA) model was developed to study the structural performance of an existing VCP package. This model incorporated some geometrical nonlinearities of the package. Paper and paperboard characterisations were done to determine the tensile properties, edge compression resistance and flat crush resistance. The tensile properties were used as input parameters in the model. The model was able to predict the compression strength of the package, and showed good agreement with experimental results, within 10%. Package liner thickness had a linear relationship with the compression strength. The stress in the package was found to be concentrated and a maximum at the corners.Subsequently, the FEA model was used to assess the strength of different package designs with emphasis on the influence of different geometrical configuration. The model was validated with experimental results. Increasing the vent area of the package reduced its compression strength. Packages manufactured with double-walled corrugated board performed better than single-walled board irrespective of the design, with the difference in strength as high as 72%. This study showed the importance of knowing the paperboard properties in the design of a package to improve its strength.Furthermore, the creep behaviour of different package designs was evaluated, and results showed load and environment conditions as significant factors affecting the creep rate. Increasing the applied load and relative humidity (RH) as well as reducing the temperature, accelerated the creep rate of the package. Also, package configuration also had a significant effect on the creep rate.Finally, to understand the deformation phenomenon of packages subjected to compression load, the displacement field of different designs was studied using digital image correlation (DIC), a full-field non-contact optical measurement technique. Findings showed that the distribution of the package displacement islargely heterogeneous. The displacement field in the out-of-plane direction was the largest while that in the horizontal direction was the smallest. Buckling was found to be a predominant phenomenon occurring at the centre of the package panels.Overall, this study provided empirical and numerical evidence for the design of improved packages, balancing the need for adequate structural performance and optimum cooling functionalities of the package.

[发布机构] Stellenbosch University