Up until today, mode-I fatigue delamination testing has not been standardized, because no consensus exists on best practices to reduce the observed scatter in data, and on the proper parameter describing similitude. A dominant contributor to the scatter seems the fibre bridging observed in the tests. This paper proposes a straightforward experimental and analysis approach to derive zero-bridging delamination resistance curves from each tested specimen without requiring a theoretical model.

The use of composite materials, like glass- and carbon- fiber reinforced polymers, is expected to increase exponentially in the coming years. Consequently, in order to monitor the structural health of these materials, the development of new sensing devices is rapidly accelerating. For this purpose, our research groups have recently developed new ultra-thin polymer waveguide sensors which can be exploited to measure both uni- and multi-axial strains occurring in composite components. These sensing foils are manufactured by creating Bragg gratings in waveguides realized in flat polymeric substrates, which makes their placement and alignment easier compared to traditional fiber optic sensors. Moreover, using a non-straight waveguide it is possible to spatially multiplex the sensing gratings in such a way that an optical strain rosette can be created. This paper investigates the suitability of the proposed polymer waveguide sensors for the estimation of the modal parameters of composite components.

In this paper, the MLMM modal parameter estimation method (Maximum Likelihood estimation of a Modal Model) and its new variant will be introduced. The MLMM method tackles some of the remaining challenges in modal analysis (e.g. modal analysis of highly-damped cases where a large amount of excitation locations is needed such as the modal analysis of a trimmed car body). Another big advantage of the MLMM method is its capability to fully integrate, within the estimated modal model, some important physical constraints, which are required for the intended applications, e. g. realness of the mode shape and FRFs reciprocity. More classical modal parameter estimation methods have rarely the possibility to fully integrate these constraints and the obtained modal parameters are typically altered in a subsequent step to satisfy the desired constraints. It is obvious that this may lead to sub-optimal results. The MLMM method uses the Levenberg-Marquardt optimization scheme to directly fit the modal model to the measured FRFs. The applicability of MLMM to estimate an accurate constrained modal model will be demonstrated using two challenging industrial applications.

A long-term SCC crack growth kinetics study, using precracked WOL samples, was performed. The samples were exposed in a mild steel storage tank containing a solution with high levels of ammonium and carbonate ions. Some samples were fully immersed in the tank content, while in other cases, intermittent drying took place in the tank upper regions. At short times, the highest (intergranular) crack growth rates were obtained at immersed regions and initially, the region with intermittent drying showed considerably slower growth rates. With pronounced exposure times, the trend however reversed and the growth in the intermittent drying region accelerated while the samples in the immersed location experienced a retardation in the SCC growth velocities. It was found that the SCC mechanism progressed through a process where small cracks first formed at the fatigue crack front and thereafter merged to form a continuous SCC crack front.

For the prediction of long term behavior several methods are known. This paper focuses on creep in dynamic mechanical analysis (DMA) and in a tensile setup. The investigated material was Polyamide 6 (PA6). As a pre-study for the DMA, Polypropylene (PP) was tested considering five different factors. To determine the significant influences, the results were interpreted statistically.