2Hollow glass fiber reinforced epoxy matrix composites were produced to study whether the damage development can be followed and the self-repair can triggered by filling the fibers with suitable additives. Composite plates were manufactured by the hand layup and vacuum assisted resin transfer molding techniques. To detect subcritical transverse impact damage, hollow fibers were filled with an ultraviolet fluorescent dye, whereas for selfrepair, they were filled with a polyester resin along with the corresponding accelerator. The healing process was induced at different temperatures and continued for different durations. It was demonstrated that the targeted damage detection and self-repair can be achieved using thin (10-13 µm outer diameter) reinforcing hollow fibers. The selfrepairing ability was demonstrated in three point bending tests and the healing was confirmed by inspection with scanning electron microscopy.

Comparative analyses have been completed on hollow and solid E-type glass fibers. Single fiber tensile tests were performed and correlations have been determined between the geometry and the tensile strength of the fibers. The flexural properties of the solid and the hollow fibers have been determined with deflection tests. The hollow glass fibers showed higher tensile strength and flexural rigidity than the solid glass fibers in the case of similar outer diameter. The hollow fibers were filled with the help of capillary effect, and the filling process was examined as a function of the viscosity and the contact angle between glass and fluids. Relationship has been detected between fiber filling speed and the inner diameter of the fibers, and the filling speed was increased by the lower viscosity and contact angle.

The geometry and mechanical properties of solid and hollow carbon fibres were investigated by light-and scanning electron microscopy, and by single fibre tensile tests. The hollowness factor of fibres was determined by their external and internal diameter. The tensile strength was determined by single fibre tensile break tests. It was shown that the bigger the diameter of the fibres the lower the mechanical properties is. It was found that the hollow carbon fibres are suitable for preparation of a self-repairing composite with the advantage over other solutions because of their geometrical and mechanical properties.

Bending moduli of solid and hollow glass fibres were determined by means of fibre deflection tests. The test method was modified by measuring both the vertical and horizontal displacements of the end of the deflected fibre without increasing the number of tested fibres in order to reduce the high scatter of the conventional test results obtained by measuring only the vertical displacement. Upper and lower boundary curves of the fibre end displacements were determined to filter out the inaccurate measurements e.g. when the neutral line of the fibre is not a plane but a spatial curve. Mean and coefficient of variation of the fibre bending modulus were estimated from the recorded coordinates of the fibre ends applying two newly developed statistical evaluation methods based on the individual coordinates or on their average. After comparing several evaluation methods it was demonstrated that the individual coordinate based method provided the least relative error of the average.