A statistical study of railway fastening insulating plates from various points of the Spanish territory reveals that high responsibility structural components injected with a hygroscopic material such as polyamide (PA) reinforced with short fiberglass can absorb varying amounts of water, depending on the working environment. This hygroscopic nature of PA6 means that the mechanical behavior of the matrix, and thus of the component as a whole, is heavily dependent on the content of water retained. This article studies the absorption and diffusion of water in the core of PA6. To verify the effects of humidity on the mechanical properties of reinforced PA6, the material was conditioned, that is, it was assigned a precise humidity content. The results obtained show that the interphase between the fiber and the matrix is a preferential way for the water advance in the composite. The diffusion of water in the PA core was carried out according to Fick's Second Law and the diffusion coefficient responds to an Arrhenius exponential law. The material behavior was experimentally validated and so it can be applied to quantify the humidity content of a component in a specific environment of temperature and exposure. POLYM. COMPOS., 26:580 -586, 2005.

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The aim of the present research is to determine the influence of the calcification of human mitral valves on the mechanical properties of their marginal chordae tendineae. The study was performed on marginal chords obtained from thirteen human mitral valves, explanted at surgery, including six non-calcified, four moderately calcified and three strongly calcified valves. The mechanical response of the chords from the non-calcified and moderately calcified valves was determined by means of quasi-static tensile tests (the poor condition of the strongly calcified valves prevented them from being mechanically characterised). The material parameters that were obtained and analysed (the Young's modulus, the secant modulus, the proportional limit stress, the ultimate strength, the strain at fracture and the density of energy stored up to maximum load) revealed noticeable differences in mechanical behaviour between the two groups of mitral chordae tendineae. Large scatter was obtained in all cases, nevertheless, considering the mean values, it was observed that the normal chords are between three and seven times stiffer or more resistant than the moderately calcified ones. On the contrary, the results obtained for the strain at fracture showed a rather different picture as, in this case, no significant differences were observed between the two families of chords. A scanning electron microscopy study was conducted in order to find out the relevant features of the calcium deposits present in the calcified chordae tendineae. In addition, the general aspects appreciated in the stress vs. strain curves were correlated with the collagen morphological evidences determined microscopically. Finally, the calcium content present in the three groups of chords was quantitatively determined through atomic absorption spectroscopy; then, the relation between the mechanical properties of normal and moderately calcified chords as a function of its calcium content was obtained. This analysis confirmed the existence of a strong correlation between calcium content and stiffness or resistance whereas the influence on the ductility seems to be negligible.

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In recent years, great advances have been made in non‐destructive or quasi‐non‐destructive test techniques for the determination of fracture toughness. One of the most interesting of these techniques is the one known as Small Punch, in which a punch acts on a small plane specimen, deforming it until fracture. From the continuous records of force and displacement of the punch taken during the test, it is possible to quantify the energy absorbed and then to determine the classic parameters of fracture mechanics such as ductile‐to‐brittle transition temperature or even the fracture toughness of the material. In this paper, fundamental aspects of the interpretation of the results of this kind of test have been studied. The effect of specimen thickness has been analysed. Moreover, a study has been carried out with the aim of clarifying the relation between the orientations in which it is possible to machine Small Punch specimens and the orientations of traditional specimens used in the determination of fracture toughness.

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