Macro-mechanical and microscopic study of the fatigue damage behaviour of a carbon fabric/PPS thermoplastic composite

This manuscript elaborates on the tension-tension fatigue behaviour of a carbon fabric reinforced polyphenylene sulphide. The damage behaviour will be investigated by (i) conducting fatigue experiments, in order to determine the macroscopic behaviour such as permanent deformation and stiffness degradation and (ii) a microscopic investigation using both optical and scanning electron (SEM) microscopy. It may be concluded that for the [(0°,90°)]4s stacking sequence the material does not show significant stiffness reduction and that only limited permanent deformation is present. Furthermore, the material shows very brittle failure behaviour. For the [(+45°,-45°)]4s stacking sequence, however, a different behaviour manifests itself. Stiffness reduction does occur and there is a significant permanent deformation, in combination with a high rise in temperature, above the softening temperature of the matrix

Effective use of transient vibration damping results for non-destructive measurements of fibre-matrix adhesion of fibre-reinforced flax and carbon composites

Fibre-matrix adhesion affects fibre-reinforced composites' mechanical properties, a process which can be improved by applying appropriate sizing on the fibre. Transverse bending tests and Scanning Electron Microscopy (SEM) can help quantify this effect This paper investigates if modal damping measurements are a reliable alternative for quantifying fibre-matrix adhesion. When a composite sample is vibrating, part of the dissipated energy is due to the internal friction. More internal friction and slipping at the fibre-matrix interface is expected with a weaker fibre-matrix bond, hence increasing the amount of dissipated energy, which in turn is proportional to the modal damping value. This paper researches two different cases to validate this hypothesis. In the first case, we will use two composite samples of flax fibre, one with and one without sizing. In the second case, we will compare flax and carbon fibre laminates. If the only variable is fibre sizing, better adhesion is related to significantly lower damping and higher resonance frequencies. If composite laminates with different fibre and matrix type are compared, lower adhesion is not necessarily related to increased damping and lower resonance frequencies. However, when combining the damping result with SEM microscopy, it is possible to assess the relative contribution to the internal energy dissipation of the fibre, the matrix and the fibre-matrix interface individually. (C) 2016 Elsevier Ltd. All rights reserved

Texture comparison between cold rolled and cryogenically rolled pure copper

Nowadays, there is a considerable scientific interest in bulk ultrafine grained materials, due to their potential for superior mechanical properties. One of the possible formation methods of nano-grained materials is cryogenic rolling. The influence of rolling at cryogenic temperatures has been investigated. Significant differences in the textures and the microstructures can be observed between the cryogenically rolled copper and conventionally cold rolled copper, reduced to the same thickness

Influence of grain size on the electrochemical behavior of pure copper

Despite numerous research works a thorough understanding on how grain size influences the electrochemical behavior of metals is still lacking due to the inability to decouple grain size effects from other microstructural characteristics. In this work, the combination of potentiodynamic polarization measurements and the gold-nanoplating technique was used on high purity copper to further explore this relationship. The high purity copper was thermomechanically processed in such a way that three samples were produced with markedly different average grain sizes, namely 1.4, 48 and 191 A mu m. All other parameters influencing the electrochemical behavior, such as internal stresses and texture were kept constant; microstructural characterization was performed by electron backscatter diffraction. In 0.1 M HCl, the anodic polarization curves demonstrate that for the smaller the grain size a lower corrosion potential and higher corrosion current density is observed. The gold-nanoplating experiments show that the material with the smallest grain size is corroding more uniformly than the samples with the larger grain sizes. In the sample with the medium grain size, the higher electrochemical activity of the grain boundaries is demonstrated. In the largest grain size sample, both the grain boundaries as well as some of the grain interiors are covered with gold