Numerical and experimental performance evaluation of ventilated packages

Fadiji, Tobi Samuel (2019-04)

Thesis (PhD)--Stellenbosch University, 2019.

Thesis

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 is largely 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.

AFRIKAANSE OPSOMMING: Verpakking speel 'n deurslaggewende rol in die vermindering van na-oesverliese, veral in die hantering van vars tuinbouprodukte, en dit sal moeilik wees om daar sonder klaar te kom. Verpakking beskerm die produk teen meganiese skade as gevolg van druk, impak, val of vibrasie tydens verspreiding. Dit verseker die veilige aflewering van die produk, in ‘n veilige toestand en teen minimum koste, aan die verbruiker. Geventileerde gegolfde karton (GGK) verpakking word omvattend gebruik vir die hantering van vars produkte as gevolg van sy vermoë om uniforme en vinnige verkoeling te bevorder. Die teenwoordigheid van ventilasie openinge belemmer egter die sterkte van die verpakking wat tot skade aan die produk kan lei. Aangesien dit van uiterste belang is om te verseker dat die produk sy eindbestemming sonder skade bereik, is voortdurende verbetering in die verpakkig se sterkte van die grootste belang. Daarom was die doel van hierdie proefskrif om 'n beter begrip van die strukturele vermoeë van GGK verpakking te verkry en om sodoende die ontwikkeling van beter verpakking te bevorder. Eerstens is 'n gevalideerde eindige element-analise (EEA) model ontwikkel om die strukturele vermoeë van bestaande GGK-verpakking te bestudeer. Hierdie model het sommige geometriese nie-lineariteite van die verpakking ingesluit. Papier- en kartonkarakterisasie is gedoen om die trek eienskappe, rand drukweerstand en plat breekweerstand te bepaal. Die trek eienskappe is gebruik as invoer veranderlikes in die model. Die model was in staat om die druksterkte van die verpakking te voorspel en het binne 10% goeie ooreenkoms met eksperimentele resultate getoon. Die dikte van die verpakkingvoering het 'n lineêre verband met die druksterkte gehad. Die spanning in die verpakking was gekonsentreer en ‘n maksimum in die hoeke. Vervolgens is die EEA-model gebruik om die sterkte van verskillende verpakkingsontwerpe te bepaal, met die klem op die invloed van verskillende geometriese konfigurasies. Die model is gevalideer met eksperimentele resultate. Verhoging van die ventilasie area van die verpakking het die druksterkte verlaag. Verpakking wat met dubbelwandige golfkarton vervaardig is, het beter gevaar as enkelwandige karton, ongeag die ontwerp, met 'n verskil in sterkte van tot 72%. Hierdie studie het getoon dat dit belangrik is om die karton-eienskappe te weet gedurende die ontwerp van verpakking om sodeoende sy sterkte te verbeter. Verder is die kruipgedrag van verskillende verpakkingsontwerpe geëvalueer, en resultate het las- en omgewingsomstandighede as belangrike faktore wat die kruipkoers beïnvloed, getoon. Verhoging van die aangewende las en relatiewe humiditeit (RH) asook die verlaging van die temperatuur, versnel die kruipkoers van die verpakking. Verpakkingskonfigurasie het ook 'n beduidende uitwerking op die kruipkoers gehad. Ten slotte, om die vervormingsverskynsel van verpakking onder druklas te verstaan, is die verplasingsveld van verskillende ontwerpe bestudeer aan die hand van digitale beeldkorrelasie (DBK), 'n nie-kontak optiese metingstegniek. Bevindinge het getoon dat die verdeling van die verpakking se verplasing hoofsaaklik heterogeen is. Die verplasingsveld in die uit-vlak rigting was die grootste terwyl dit in die horisontale rigting die kleinste was. Daar was gevind dat knik ‘n oorheersende fenomeen in die middel van die verpakkingpanele was. In die algemeen het hierdie studie empiriese en numeriese bewyse verskaf vir die ontwerp van verbeterde verpakking, wat die behoefte aan voldoende strukturele vermoeë en optimale afkoelfunksies van die verpakking balanseer.

Please refer to this item in SUNScholar by using the following persistent URL: http://hdl.handle.net/10019.1/106165
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