Composite laminates are an important subject of modern technology and engineering. The most common mode of failure in these materials is probably interlaminar fracture (delamination). Delamination growth under applied fatigue loads usually leads to structural integrity loss of the composite laminate, and hence its catastrophic failure. It is known that several parameters can affect the fatigue fracture performance of laminates. These include the constituent material properties, composite geometry, fatigue load variables or environmental factors. The knowledge about effects of these parameters on fatigue delamination growth can lead to a better understanding of composite fatigue fracture behaviour. Effects of some of these parameters can be elucidated by undertaking appropriate sensitivity analysis combined with the finite element method (FEM) and related software. The purpose of this work was three-fold. The first goal was the elaboration and computational implementation of FEM-based numerical strategies for the sensitivity analysis of interface fatigue crack propagation in elastic composite laminates. The second goal of this work was the numerical determination and investigation of displacement and stress fields near the crack tip, contact pressures along crack surfaces, mixed mode angle, energy release rate and the number of cumulative fatigue cycles. The third aim of the present study was to use the developed strategies to evaluate numerically the sensitivity gradients of the total energy release rate and fatigue life with respect to design variables of the curved boron/epoxy-aluminium (B/Ep-Al) composite laminate in two different material configurations under cyclic shear of constant amplitude. This study provided novel strategies for undertaking sensitivity analysis of the delamination growth under fatigue loads for elastic composite laminates using the package ANSYS. The numerical results of the work shed more light on mechanisms of interfacial crack propagation under cyclic shear in the case of a curved B/Ep-Al composite laminate. Moreover, the outcome of the sensitivity gradients demonstrated some advantages for using the sensitivity analysis to pinpoint directions for the optimisation of fatigue fracture performance of elastic laminates. The strategies proposed in this work can be used to study the sensitivity of the interface fatigue crack propagation in other elastic laminates, if the crack propagates at the interface between the elastic and isotropic components. However, the strategies can be potentially extended to composites with interfacial cracks propagating between two non-isotropic constituents under a constant amplitude fatigue load. Finally, the strategies can also be used to undertake the sensitivity analysis of composite fatigue life with respect to variables of fatigue load.

Stimuli-sensitive hydrogels are polymeric materials, which are able to reversibly swell in water in response to evironmental changes. Relevant stimuli include variations of pH, temperature, concentration of specific ions etc. Stacked layers composed of multiple thin hydrogels - also referred to as hydrogel-layer composites - combine the distinct sensing properties of different hydrogels. This approach enables the development of sophisticated micro uidic devices such as bisensitive valves or uid-sensitive de ectors. In order to numerically simulate the swelling of a polyelectrolyte hydrogel in response to an ion concentration change the multifield theory is adopted. The set of partial differential equations - including the description of the chemical, the electrical and the mechanical field - are solved using the Finite Element Method. Simulations are carried out on a twodimensional domain in order to capture interactions between the different fields. In the present work, the ion transport is governed by diffusive and migrative uxes. The distribution of ions in the gel and the solution bath result in an osmotic pressure difference, which is responsible for the mechanical deformation of the hydrogel-layer composite. The realized numerical investigation gives an insight into the evolution of the displacement field, the distribution of ions and the electric potential within the bulk material and the interface between gel and solution bath. The predicted behavior of the relevant field variables is in excellent agreement with results available in the literature.

Composite laminates are an important subject of modern technology and engineering. The most common mode of failure in these materials is probably interlaminar fracture (delamination). Delamination growth under applied fatigue loads usually leads to structural integrity loss of the composite laminate, and hence its catastrophic failure. It is known that several parameters can affect the fatigue fracture performance of laminates. These include the constituent material properties, composite geometry, fatigue load variables or environmental factors. The knowledge about effects of these parameters on fatigue delamination growth can lead to a better understanding of composite fatigue fracture behaviour. Effects of some of these parameters can be elucidated by undertaking appropriate sensitivity analysis combined with the finite element method (FEM) and related software. The purpose of this work was three-fold. The first goal was the elaboration and computational implementation of FEM-based numerical strategies for the sensitivity analysis of interface fatigue crack propagation in elastic composite laminates. The second goal of this work was the numerical determination and investigation of displacement and stress fields near the crack tip, contact pressures along crack surfaces, mixed mode angle, energy release rate and the number of cumulative fatigue cycles. The third aim of the present study was to use the developed strategies to evaluate numerically the sensitivity gradients of the total energy release rate and fatigue life with respect to design variables of the curved boron/epoxy-aluminium (B/Ep-Al) composite laminate in two different material configurations under cyclic shear of constant amplitude. This study provided novel strategies for undertaking sensitivity analysis of the delamination growth under fatigue loads for elastic composite laminates using the package ANSYS. The numerical results of the work shed more light on mechanisms of interfacial crack propagation under cyclic shear in the case of a curved B/Ep-Al composite laminate. Moreover, the outcome of the sensitivity gradients demonstrated some advantages for using the sensitivity analysis to pinpoint directions for the optimisation of fatigue fracture performance of elastic laminates. The strategies proposed in this work can be used to study the sensitivity of the interface fatigue crack propagation in other elastic laminates, if the crack propagates at the interface between the elastic and isotropic components. However, the strategies can be potentially extended to composites with interfacial cracks propagating between two non-isotropic constituents under a constant amplitude fatigue load. Finally, the strategies can also be used to undertake the sensitivity analysis of composite fatigue life with respect to variables of fatigue load.