Numerical Models for Adhesion and Fracture of Biological and Bio-inspired Composite Structures

Today, the industry still relies on chemical adhesives for most applications. Adhesive tapes and glues are now used in aeronautics, robotics, and other innovative fields. The global adhesive and sealant market is constantly growing due to the versatility of these tools, such as adhesive tapes and glues. However, these products are afflicted by fundamental flaws: they are non-recyclable, disposable tools, of which the manufacturing generates highly toxic chemical waste, both in liquid and aeriform state. The same pattern is also found in the materials for the construction sector. This approach is in strong opposition to what is observable in nature, which employs complex geometrical structure to achieve extreme mechanical properties, as for example vertical locomotion, while using only few families of building blocks, e.g., minerals, proteins. This thesis provides insights around biological and bio-inspired materials, investigating how we can analyse the behaviour of bioadhesives or predict the resistance of polymeric composites thanks to the implementation of numerical models. Unification of single and double peeling theories for tape adhesion illustrates the basis of contact mechanics and tape adhesion, before introducing three dimensional contacts. These contacts, while based on an elementary double branched structure, can span a wide range of adhesive forces by varying the angles describing the structure. The results presented here show how nature can thus achieve tunability using simple architectures and are compared with numerical and empirical tests. To further explore the range of bioadhesives, we need however to analyse the full behaviour of bidimensional adhesive contacts, such as the tips of the animal pads or spider anchorages. To do so, in A theoretical-numerical model for the peeling of elastic membranes we introduce a numerical framework which is based on the Lattice Spring Model and the Cohesive Zone Model. The model, which has been verified by comparing its numerical results to continuum mechanics and adhesion theories, is employed to investigate the influence of mechanical and geometrical parameters, as the surface aspect ratio or the adhesive energy per area, on the overall performances of the adhesives. This newly acquired knowledge is then applied to spider anchorages, heterogeneous silk-based adhesives, in Strong tunability and high adhesion in spider anchorages, where we analyse in detail the interaction between pulling angles and pull-off forces in three different spider species, uncovering the presence of a softer region which allows the rotation of the stiffer parts of the anchorage and thus enhances the pull-off forces for a wide range of pulling angles. Finally, a first possible application of the model to the prediction and development of new materials is presented in An investigation on the mechanical properties of Single Polymer Composites, where Single Polymer Composites, i.e. composites where the fibre and the matrix are both composed of the same polymer or of polymers belonging to the same type, are investigated through a parametric study, which analyses the influence of fibres arrangements, fibres scales and interface properties on the strength and toughness of the reinforced material. The results and theories presented in this work, together with the new manufacturing techniques now available, can lead to the development of new optimized composite materials and composite adhesives, with specific goals and tunable properties.