Enhanced characterization of tow gaps in fiber steered laminates: Advanced specimen design for better representation of defects in structures

The thesis aimed to characterize the effects of manufacturing-induced defects, particularly gaps in variable stiffness laminates. The primary focus centered on designing a specimen capable of accurately characterizing gap effects. A refined, element-level specimen design featuring a controlled gauge zone was developed, based on pre-defined...

A Fibre-Path Generation Algorithm for Fibre-Steered Variable Stiffness Laminates

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...

Experimental and numerical study of bending-induced buckling of stiffened composite plate assemblies

Despite their importance in benchmarking numerical simulations, buckling tests still feature compromises between component-level and high-fidelity large-scale tests. For example, compression-induced buckling tests cannot capture the through-thickness or span-wise stress gradients in wing skins. Consequently, the results obtained often require...

Experimental quality assessment of thermoplastic composite corner regions manufactured using laser-assisted tape placement

Over the past 25 years, interest in thermoplastic composites in aircraft has steadily increased. Combining winding and laser-assisted tape placement is a promising method to manufacture thermoplastic structures using in-situ consolidation, as shown recently by manufacturing a variable stiffness, unitized, integrated-stiffener thermoplastic...

Reflectivity and emissivity analysis of thermoplastic CFRP for optimising Xenon heating and thermographic measurements

The demand for efficient composite production processes is growing as the proportion of composites in modern aircraft increases. Particularly, thermoplastic composites are interesting for sustainability and cost efficiency. They can be manufactured using deposition methods, which involve heating by radiation in the visible and near-infrared...

The effects of local fibre steering: Reducing gaps and overlaps by compensating for tow width fluctuation in automated fibre placement

The aerospace industry increasingly uses fibre-reinforced plastics that are manufactured using automated fibre placement (AFP). A common problem in AFP is the occurrence of gaps and overlaps that affect the structural perfromance of laminates. Tow width fluctuation is an important cause of gaps and overlaps. Two developments in manufacturing are...

Imaging sensor data modelling and evaluation based on optical composite characteristics: Investigation of data quality for inline inspection

Automated Fibre Placement is a common manufacturing technique for composite parts in the aero-space industry. Therefore, a visual part inspection is required which often covers up to 50% of the actual production time. Moreover, the inspection quality of this manual step fluctuates significantly. A camera-based automated inline inspection is...

Influence of repass treatment on carbon fibre-reinforced PEEK composites manufactured using laser-assisted automatic tape placement

Laser-assisted automated tape placement (LATP) in-situ consolidation of thermoplastic composites offers an efficient solution for production of large, high performance composite structures. The present work investigates laser repass treatment as a method of enhancing surface roughness and mechanical properties of LATP processed CF/PEEK...

In-line variable spreading of carbon fibre/thermoplastic pre-preg tapes for application in automatic tape placement

This study investigates a device for in-line continuous spreading of carbon fibre/thermoplastic pre-preg tape for potential application in the Laser-Assisted Automatic Tape Placement (LATP) laminate manufacturing process. The spreading device allows variable tape width to be achieved locally during lay-up. Integration of this device in the...

Properties of a thermoplastic composite skin-stiffener interface in a stiffened structure manufactured by laser-assisted tape placement with in situ consolidation

A critically important consideration of stiffened structural panels is the interfacial properties between skin and stiffener. In the present study a novel implementation of laser-assisted tape placement (LATP) was used to produce a representative skin-stiffener of a wingbox from carbon fibre reinforced PEEK. First, a stiffener is manufactured...

Online non-destructive evaluation in automated fibre placement

The strict quality requirements for aerospace composite structures give rise to costly quality control procedures. In automated fibre placement (AFP) these procedures rely heavily on manualwork and inspection. This research aims at performing preventative non-destructive evaluation of composite laminate quality based on an online geometric...

Optimum lay-up design of variable stiffness composite structures

Advancements in automated fibre-placement (AFP) technology make it possible to take laminate tailoring further than just stacking sequence optimisation; they enable the designer to vary the fibre orientation angle spatially within each ply. Spatial variation of fibre orientation angles results in a variable stiffness (VS) laminate. The work...

Damage and Failure of Non-Conventional Composite Laminates

For a long time, the application of composite materials was restricted to military aircraft and secondary structures of commercial aircraft. Furthermore, the design possibilities offered by composite laminates were narrowed to quasi-isotropic configurations due to their closer behaviour with monolithic materials, hence with a more predictable...