I. De Baere

Strain Monitoring in Thermoplastic Composites with Optical Fiber Sensors: Embedding Process, Visualization with Micro-tomography, and Fatigue Results:

This study investigates the possibility of using optical fibers with Bragg gratings for measurements under fatigue loading conditions. Detailed information is given on the principle of optical fiber measurements, the embedding process, and the fatigue tests. To verify the strain derived from the optical fiber, the strain is compared with extensometer measurements. A special design of the blades of the extensometer is presented, since the standard blades suffer from a loss of grip on the surface of the specimen. Furthermore, X-ray micro-tomography is discussed and used for the visualization of the optical fibers and damage in the composite material. The material used for this study is a carbon fiber-reinforced polyphenylene sulfide. It can be concluded that the optical fiber survives over half a million loading cycles, without de-bonding of the fiber. Furthermore, the resolution of the microtomography is high enough to visualize not only the optical fiber, but also damage in the material.

Feasibility Study of Fusion Bonding for Carbon Fabric Reinforced Polyphenylene Sulphide by Hot-Tool Welding

In recent years, there is a growing interest in joining techniques for thermoplastic composites as an alternative to adhesive bonding. In this article, a fusion bonding process called hot-tool welding is investigated for this purpose and the used material is a carbon fabric reinforced polyphenylene sulphide. The welds are first observed through a microscope, after which the quality is experimentally assessed using a short three-point bending setup. A comparison is made between the welded specimens and the equivalent hot pressed specimens. It can be concluded that the hot-tool welding process is very promising for the welding of material under study and that the short three-point bending setup proves interesting for evaluating bonds between composite specimens.

The use of rivets for electrical resistance measurement on carbon fibre-reinforced thermoplastics

The use of fibre-reinforced thermoplastics, for example in the aeronautical industry, is increasing rapidly. Therefore, there is an increasing need for in situ monitoring tools, which preferably have limited influence on the behaviour of the material and which are easy to use. Furthermore, in the aeronautical industry composites are very often attached with rivets. In this study, the possibility of the use of rivets as contact electrodes for electrical resistance measurement is explored. The material used is a carbon fibre-reinforced polyphenylene sulphide. First, the set-up used is discussed. Then, static tensile tests on the laminate are performed. The possible influence of an extensometer on the measurements is examined. Furthermore, failure predictability is assessed. It may be concluded that the proposed set-up with the rivets can be used for electrical resistance measurement, with the ability to predict failure, and that the extensometer has a negative influence on the resistance measurement.

Analysis of the Numerical and Geometrical Parameters Influencing the Simulation of Mode I and Mode II Delamination Growth in Unidirectional and Textile Composites

The reliability of composite structures depends, among other damage mechanisms, on their ability to withstand delaminations. In order to have a better understanding of the cohesive zone method technique for delamination simulations, a complete analysis of the multiple parameters influencing the results is necessary. In this paper the work is concentrated on the cohesive zone method using cohesive elements. First a summary of the theory of the cohesive zone method is given. A numerical investigation on the multiple parameters influencing the numerical simulation of the mode I and mode II delamination tests has been performed. The parameters such as the stabilization method, the output frequency, the friction and the computational efficiency have been taken into account. The results will be compared to an analytical solution obtained by linear elastic fracture mechanics. Additionally the numerical simulation results will be compared to the experimental results of a glass-fibre reinforced composite material for the mode I Double Cantilever Beam (DCB) and to a carbon fibre 5-harness satin weave reinforced polyphenylene sulphide composite for the mode I DCB and mode II End Notched Flexure (ENF).