The increasing use of composite materials in aerospace is driven by their high strength-to-weight ratio, but manufacturing these structures represents a large energy footprint and consumption of auxiliary materials. Thermoplastic composites consolidated with Induction heating offers a sustainable alternative to autoclave produced thermosetting composites, eliminating the need for prepreg refrigeration along with most auxiliary materials and a reduction in cycle time and energy consumption. Induction heating, however, is difficult and expensive to test and prototype and therefore there is a need for a way to predict tool behavior.

This thesis develops and builds on a finite element simulation framework in COMSOL Multiphysics to model induction heating of a tool for a C cross-section composite spar, using both, stationary and transient simulations- the latter of which incorporate temperature-dependent material properties - to analyze heating behavior in the tool and the effect of various parameters on the temperature distribution. The simulation model is validated through coil inductance measurements as well as heat surveys on an existing subscale tool.

Design guidelines for tool dimensions, coil placement are derived from simulations and tested virtually on a hypothetical tool geometry. A parametric modeling framework is created in the simulation software package itself, enabling rapid iterations of tool designs, streamlining development. Results demonstrate strong agreement between simulations and experiments with the stationary models predicting the variation in temperatures over the tool better while the transient model calculating the absolute temperatures more accurately. A combination of both these models in conjunction with tool design guidelines presented in this thesis can be potentially used for efficient, first-time-right tooling design for induction heated press consolidation tools.

Fibre-reinforced polymer (FRP) composites have become indispensable in aerospace engineering over the past two decades, driving the need for efficient and standardized testing protocols to certify their reliability. However, no standardized protocol currently exists for fatigue testing of FRPs, particularly due to fibre bridging—a phenomenon prominent in testing but rarely encountered in real-world applications. This study investigates existing fatigue data processing techniques, with a primary focus on a regression-based approach that could standardize fatigue data analysis. Current fatigue delamination characterization methods often rely on single-parameter empirical models, which struggle to capture the complex interaction between cyclic and monotonic load components, expressed as ∆√G and Gmax, respectively. This study demonstrates that the regression method’s zero-bridging technique effectively incorporates both parameters, offering a comprehensive view of delamination growth by isolating it from fibre bridging effects. This approach suggests a shift away from the traditional 2D analysis to a 3D framework, which considers both Gmax and ∆√G, enabling a more accurate depiction of delamination behaviour across various stress ratios. Notably, the results reveal that zero-bridging data align on a common plane under consistent stress ratios, shifting as stress ratios increase. Additionally, fibre orientation influences data clustering, with similar orientations exhibiting stronger convergence than dissimilar ones. Comparison of this regression-based method with the modified Paris law reveals significant discrepancies in its current implementation, suggesting alternative approaches to address these limitations. This study also highlights the impact of data size and selection on the model behaviour, stressing their importance in accurate model representation. This research validates the regression method as a promising candidate for standardizing fatigue data processing, improving the precision and reliability of post-test analysis for fibre-reinforced polymer composites.

The development of novel materials has been of great interest to the aerospace industry in the pursuit of efficiency and cost reduction. Fibre-steered variable stiffness laminates have promising characteristics due to the ability to better tailor designs for expected loading, as the fibre orientation can be varied within a layer. This thesis was created to develop a fibre placement planning algorithm for fibre-steered layers on moderately curved open shells for a given fibre angle distribution.

The fibre-steered layers are to be produced by Automated Fibre Placement (AFP) without any course overlaps, which means that several manufacturing defects have to be considered. Gaps between courses are inevitable due to course shifting in combination with the prescribed fibre paths, and tow cuts run the risk of tow straightening due to loss of steering control of the AFP roller head. Furthermore, steering limits have to be observed to prevent tow buckling.

The thesis objective was approached by dividing it in three parts. Firstly, the geometry of the mould and the course paths was defined parametrically in the form of NURBS surfaces and curves. These have been widely used in Computer Aided Modelling (CAM) and have extensive support in terms of existing algorithms and documented work. Additionally, performing most operations in the parametric space allows for greater accuracy compared to general finite element methods.

Secondly, the fibre angle distribution was converted into a fibre layer. This was initiated by generating initial course centre lines, which were then fit onto the parametric surface. Representations of tow courses were made by geodesically offsetting the course centre lines in the binormal direction. A curve-curve intersection algorithm was then used to accurately detect tow overlaps, which were handled according to the tow placement strategy. Two tow placement strategies have been developed, one for general use and one to specifically prevent tow straightening. In addition, curvature of the course centre line was registered to check for tow buckling, and the minimum cut length was enforced by evaluating the length of tow segments.

Lastly, fitness criteria for fibre-steered layers were defined. Layers were evaluated for gap percentage, fibre angle error and number of cuts. These can be used to objectively grade layers against each other, or to assess the effects of fibre steering against conventional laminates.

Delamination is one of the common failure types in the fiber composites. The trailing edge in the wind turbine blades, for example, is one of the structural components where the delamination is driven by mode III under predominantly flapwise loading. There has been an extensive effort in developing test procedures and test specimens for determination of the delamination toughness in mode I and mode II delamination while the mode III is neglected due to its complexity, on the one hand, and the lack of a reliable test procedure and numerical model for the mode III delamination toughness testing on the other hand. Therefore, the cur- rent project aims for developing an experimental test specimen capable of extracting cohesive laws using the J integral approach. To this end, the FEM is utilized for the analyses of various parameters.

Delamination can be modeled using Progressive Failure Analysis where the crack initia- tion and crack evolution are studied. The present thesis covers both aspects of the Progressive Failure Analysis in the unidirectional fiber composites. Before starting the mode III, mode I and II test specimens are analyzed to establish requirements for proper three-dimensional simulation. The reliable numerical model from this step is the fundamental model for the mode III delamination analysis. In the first part of the project, the Double Cantilever Beam cross-section is optimized to give the pure mode III. LEFM is invoked for the analyses of this section (Small Fracture Process Zone). The results have shown that the pure mode III cannot be accomplished and there always exists an induced coupling mode II under anti-plane load- ing. Furthermore, the results suggest higher mesh density is required at the free surface to further investigate the 1/√r-singularity at this location.
The second part of the thesis covers the Cohesive Zone Modeling (Large Fracture Process Zone) whereby the crack evolution is simulated by the cohesive elements. The implemented cohesive law is validated by the J integral. The bilinear cohesive law has been successful in simulating the crack extension for Large-Scale Bridging condition. The traction-separation law has been validated through the resistance curve generated by the FEM and derivation of the resistance w.r.t the tangential end-opening.

The commercial code, ABAQUS, is utilized in this study for the Finite Element Analyses.

A numerical fatigue delamination model is validated by means of experimental tests. Delamination is initiated on the skin-stiffener interface which, under cyclic compressive loading and in the post-buckling regime, grows at a decreasing rate. A cohesive zone formulation is used to model the static and fatigue delamination growth, good agreement is found in terms of delamination shape. Further investigation is required, using improved material inputs, for the model to be validated in terms of delamination magnitude. The numerical model shows promising characteristics, which may be employed for future damage tolerant composite structural designs.

A proposed future mode of mass transit is the hyperloop system, in which magnetically levitating passenger pods travel at high speed through a tube held at low pressure. This thesis will investigate the dynamics of such a system, and determine the influence of various parameters on the dynamic response of the system. The tube has been modelled using an implicit dynamic finite element model, coupled to a vehicle model based on rigid body dynamics by a PID controlled force, which simulates the magnetic suspension. The influence of several vehicle and infrastructure parameters on the overall dynamics has been determined, and several interesting resonance and cancellation cases have been observed. The results prove the hyperloop concept is feasible from a dynamics point of view, while the methodology is readily adapted for use with more realistic vehicle models for future hyperloop design work.

A composite wind turbine blade is partially thick-walled to comply with high strength criteria. When the manufacturer’s recommended cure cycle (MRCC), which is designed for thin-walled components, is used for thick-walled components it can lead to high levels of residual stress. This experimental research investigates different cure cycles for thick-walled glass-fibre epoxy composites made by vacuum infusion with the objective of minimising residual stresses and cycle time. It is found that a two-dwell cure cycle with a low second dwell temperature will significantly decreases the exothermic peak temperature, increases the maximum shear stress, decreases the acoustic emission activity and reduces time compared to the single dwell MRCC.

Besides building ultra-lightweight sportscars, Donkervoort Automobielen B.V. is developing a novel core material to be applied in complex shaped composite sandwich structures. This material goes by the name of X-Core and has the unique capability of generating the pressure required for facesheet consolidation, enabling a one-shot manufacturing process for the first time. The present research has focused on the phenomena present during the manufacturing process of the foam. In-situ temperature measurements have been carried out to gain a deeper understanding of the thermal behaviour of the material. A numerical model, based on a transient finite difference method, was then constructed to predict the temperature distribution in the material during its cure under different processing conditions, material compositions and cure cycles. The proposed model can now be applied in fine-tuning cure-cycles required to attain certain desirable X-Core properties.

As the demand on new lightweight materials increases due to economic and environmental reasons, fiber reinforced plastics seem an interesting solution. In order to maximize their potential, ways have to be found to introduce damage tolerant designs. To this end, in the present exercise, the damage caused by cyclic loading is investigated.
Cyclic loading causes loss of stiffness and strength of composite structures. In the present work a progressive damage analysis model has been built. Damage is tracked by a macroscopic failure criterion. Failure occurring at levels below the macroscopic level are captured by a degradation theory which requires S-N curves as input. An attempt is made to use S-N curves derived from static tests only. Stress solutions are obtained using a finite element package. In order to bring the macroscopic damage, degradation and stress solution parts together, a cycle jumping algorithm has been developed which minimizes the amount of FEM stress solutions required and the required amount of function evaluations.
In its current form, the model is able to properly predict the trend of stiffness and strength behavior. Showing that a model like this has potential. For the proper predictions of mag- nitudes, additional failure modes should be modeled and the usage of S-N curves obtained from large specimens for applying on smaller geometries (elements) should be reconsidered.

The dutch government plans to build a vast amount of offshore wind turbines. Therefore, it will be necessary to decrease the costs of the transportation, installation and maintenance of these wind turbines. Jules Dock tries to achieve this by replacing the steel design of the next generation 10MW wind turbine tower by a flexible composite design.
Damping is an important parameter of flexible structures, therefore a research thesis has been set up to determine the damping properties of the composite tower. In order to determine the material damping of the tower, DMA measurements have been conducted and a viscoelastic damping model has been created. According to this model, the damping loss factors are approximately 71% higher than the damping loss factors of a steel tower with the same dimensions, which results in an increase of the fatigue life. Also the tower’s material damping can be considered temperature and frequency independent.