DMIMPT - Development of methods for the identification of mechanical properties in tissues of plant origin

Skin appearance and cracking is one of major causes of fruit value decrease and losses. It is well recognised that fruit skin (FS) is subjected to a complex stress field during fruit growth, harvesting, storage and transportation. Furthermore, FS has a complex mechanical behaviour, rendering the identification of its constitutive laws a challenging issue from both theoretical and experimental points of view. Understanding the relationships between the composition and morphology of FS and its mechanical behaviour is an important research topic, with a clear economic impact in the agro-food industry.

In the literature, the majority of works address material parameters of fruits and fruit skin (such as rupture force, rupture energy and firmness) with conventional approaches and try to relate them with production and post-harvesting factors. The experimental and data reduction methods used in those works did not allow the identification of intrinsic mechanical properties of FS, which can be used in numerical simulations of fruit behaviour. Considering this, we intend to develop direct and inverse methods, based on numerical simulations and full-field displacement measurements, to identify the hyperelastic constitutive behaviour of FS. With this approach, the relationships between mechanical properties and material composition and morphology can be accessed in a rational way.

It is worth mentioning that the global objective of the research team (RT) is to develop methods based on an inverse approach for the identification of the entire properties package in fruits from a single mechanical test. The achievement of this objective is attainable in three main steps. The first one involves the development of a set of methods to characterize the mechanical behaviour of each anatomical structure (exocarp, mesocarp and endocarp). The second one regards the development of numerical tools to generate the geometry of the referred fruit structures. The third one involves the conception of inverse methods to estimate material properties based on a single test at the fruit (organ) scale. For this exploratory work the RT will be focused on one major component, i.e., the skin (or exocarp). Apple will be used as the fruit model in this work, due to its importance in the deployment region (University, UTAD) as well as to the Portuguese agro-based economy. It is worth mentioning that the proposed methodology can be applied to other materials. Despite the importance of the agro-industry to the Portuguese gross value added, there is still a lack of knowledge among the Portuguese research community dedicated to the plant tissue biomechanics. Hence, besides the scientific objectives, this work will contribute to develop the research skills of CITAB in the domain of plant tissue biomechanics.