This master thesis research investigates the possibility to repair carbon fiber thermoplastic aircraft
structures using induction welding. Carbon fiber is conductive and heats up when placed inside an
alternating magnetic field. A generator, coil, and pressure frame are needed to perform induction
welding. The support plates needed to pressurize the carbon fiber parts need to be non-conductive,
non-magnetic, temperature resistant, stiff at high temperatures, and thermally insulating.
The material used is five harness satin weave carbon fiber PPS supplied in pre-consolidated plates
and unconsolidated semi-preg. Three different joint geometries are used in this investigation: a conventional
scarf, a continuous scarf, and a stepped lap joint. The stepped lap joint and the conventional
scarf are milled using a CNC machine. The continuous scarf is produced in a press using specialized
tooling and a press program prescribed by TenCate.
Of each type two specimens are produced: an induction welded specimen and a press joined specimen.
The specimens are tested in tension to determine the tensile strength and stiffness. This gives
the performance of the induction welded joints with respect to the press joined specimens. Additionally,
both of the welded specimens are compared to the pristine specimens.
By measuring the temperature along the weld-line of multiple test specimens, an induction welding
program is obtained for each joint type. Achieving a consistent temperature along the weld-line is
challenging due to the thermal conductivity of carbon fibers and other effects inside the laminate. Similar
to the continuous scarfed specimens, the press joined specimens are created using specialized tooling.
Before testing the specimens in tension, they are scanned using a C-scan. The press bonded
specimens show no flaws, whereas the induction welded specimens do not return the signal to the
transducer. Micrography of the specimens shows similar results as the C-scan. The press joined
specimens show little to no flaws and the induction welded specimens show a significant amount of
voids and small unjoined sections near the tips for the continuous scarf and stepped lap specimen.
The tensile tests show that all induction welded joints perform less than the press joined specimens
with a percentage of about 73-78%. The conventional scarf and the continuous scarf result in a similar
failure strength recovery of about 44% of the pristine failure strength for the press joined specimens.
Both the conventional scarf and the continuous scarf show similar behavior in welding and the tensile
testing, but the continuous scarf is more difficult to produce. Therefore the conventional scarf joint is
preferred over the continuous scarf joint. The stepped lap joint has the best performance, recovering
about 59% of the pristine stiffness. The stiffness of all tested specimens is between 92%-99% of the
pristine stiffness.
Inspection using digital image correlation and finite element modeling indicates the failure initiates
inside the PPS matrix in between the parts at the location of the first or last step. Finite element modeling
also suggests that a smaller angle for the scarf joint or a longer overlap for the stepped lap joint would
increase failure strength.

EX-CORE, a novel foam core material developed by Donkervoort Automobielen B.V., allows the creation of complexly shaped sandwich structures in a one-shot out-of-autoclave manufacturing process. Products with small tolerances and high surface quality on all surfaces can be obtained. The EX-CORE technology has achieved its intended goal at Donkervoort of saving cost and time for the production of sandwich structures for their cars. Now Donkervoort has the ambition to further develop EX-CORE for larger scale automotive manufacturing. To make the EX-CORE technology competitive with other composite production processes, the cycle time of several hours should be reduced to several minutes. The present work contributes to this development by re-engineering the EX-CORE foam composition such that cure cycle time reductions can be achieved.

This report shows that animal glue from porcine skins can be used to make thin films with reproducible properties. It shows that the tensile strength of the film relates linearly to the bloom strength, while the stiffness remains constant for temperatures lower than the glass transition temperature. The report continues to show how Differential Scanning Calorimetry (DSC), Fourier Infra-red Spectroscopy (FTIR), and X-ray Diffraction (XRD) can be used to predict the strength of an animal glue film. The test results show that XRD is the easiest method to obtain a reasonable prediction of the mechanical properties. Meanwhile, DSC holds additional information on the internal stress state of the sample, which may promise better predictions of the mechanical properties once the analysis has been optimized.

X-core is a novel foam core material developed by Donkervoort Automobielen, it enables a unique one-shot process for seamless composite sandwich structures with mould-defined features all-around. The foam is co-cured to carbon fibre/epoxy prepregs, in this form the process is currently used to make car components for the Donkervoort D8 GTO RS. One of the main challenges that is faced in the manufacture of these ‘bare carbon’ components is the visible presence of surface defects. In this research a variety of process variables are primarily correlated to the surface porosity content of the laminate. Processing guidelines pertaining to the cure cycle, core material composition, moulding and type of prepreg are formulated based on these relations. The main causes for surface porosity are identified and it is found that the process is especially sensitive to the laminate composition: Variations in stacking sequence and fibre aerial weight.