Parametric modelling of mechanical performance of fibrous networks

Fibrous networks are ubiquitous in natural materials (such as in human eyes, collagen tissues, tendons), and engineered materials (such as nonwovens, reinforced carbon fibre composites). They are used in many areas from hygiene and health care to civil engineering. Hence, understanding of their deformation behaviours is essential to design new fibrous networks tailored for specific applications and to improve the mechanical performance of existing materials.

Many attempts have been made to understand the mechanical behaviour of fibrous networks using analytical and numerical models. However, the numerical modelling is challenging due to the complex microstructure composed of randomly distributed and curved fibres. Models have been limited by the few modelling parameters used, so, they do not provide us with a complete picture. Therefore, a 3D multi-scale parametric computational model was developed to simulate compression, tension, and flow performances of fibrous networks. Randomly distributed fibres with fibre-to-fibre contact interactions were implemented into a novel computational model as these interactions along with the orientation of the fibres are the key deformation mechanisms of compression in transmitting the load from fibre to fibre.

The effect of model size on tensile and compressive responses of a fibrous network was numerically studied to find an optimum model size. The novel model enabled the

simulation of through-thickness compression response as well as tensile response. This newly developed model was used in parametric investigations. Meanwhile, a method

was developed to compute the number of fibre-to-fibre contacts. It was observed that the optimum model size depends on the microstructure of the fibrous network. As a

geometric parameter was altered, a new sensitivity analysis should be performed to assess an optimum model size for the new modelling parameters. Also, tensile and

compressive responses of a fibrous network depend on modelling parameters, such as fibre diameter, fibre alignments and fibre-to-fibre interactions. In the validation of the FE model with experimental tensile tests, a soft mechanical response was observed in the experiment, opposite to the simulations. This behaviour was attributed to the temperature- and time-dependent nature of polymer fibres.

The effect of compression on flow properties including air permeability was also investigated using FE and CFD analyses and this behaviour was verified by existing

analytical and empirical models. Solid volume fraction and fibre diameter were the main parameters controlling the permeability of the fibrous network. Also, orientation

distribution of fibres influenced the permeability. A fibrous network with more aligned fibres showed the highest air permeability.

The proposed parametric computational model can be extended for simulation of damage and fracture behaviour of fibrous networks. Also, it can be extended for other

fibrous networks such as point bonded nonwovens.