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In this work, some mechanical properties of natural and treated bamboo fibers used as reinforcement in green polymeric composites have been evaluated. The physical and chemical treatments improve slightly the mean stiffness and the mean tensile strength but also increase their average spread. However, the failure strain presented an inverse behaviour. Observations made by SEM reveal some modifications of the microstructure of their fundamental cells at the surface of the fibers, making possible a better adhesion between fiber and polymeric matrix. [ABSTRACT FROM AUTHOR]

The 3D microstructure of dentinal tissue, the main tissue of the tooth, is the subject of an increasingly comprehensive body of knowledge. The relationship between this microstructure and the mechanical behaviour of dentinal tissue remains, nonetheless, under question. This article proposes an original SEM analysis of dentin microstructure, accounting for lateral branches, and a mechanical model based on these findings. An interesting observation is that lateral branches have a dense collar, as do tubules. The diameter of these branches as well as a percentage area are quantified all along the depth of a dentin sample. We use these unprecedented data to build an orthotropic homogenized model of dentin. The heterogeneities of microstructure are taken into account using level-set functions. The results reveal that the lateral branches slightly influence the global homogenized elastic behavior of the dentin tissue, albeit creating stress concentration areas that are highly influenced by the inclination of the traction with respect to the tubule and branches. Image 1 [ABSTRACT FROM AUTHOR]

Abstract Cold uniaxial pressed PTFE compacts were subjected to thermal cycles of increasing maximum temperature below melting temperature, and thermal expansion was followed in both the compaction and transverse directions. The measurements reveal that thermal expansion consists of two distinct contributions: i) an irreversible part that is controlled only by the maximum temperature experienced by the sample, and ii) a reversible, or thermo-elastic, part that is observed while cycling below the maximum temperature. Moreover, both of these thermal strains exhibit marked anisotropy, resulting from the cold oedometric compaction of the sample. A quantitative analysis of these eigenstrains is proposed, following a formal analogy with elasto-plasticity. Finally, it is shown that such behavior is specific to cold-pressed compacts as sintered samples exhibit isotropic and purely reversible thermo-elastic behavior. Highlights • Thermal expansion of cold pressed PTFE compacts contains two anisotropic contributions, one reversible and one irreversible. • Dilatometric measurements during repeated cycles of increasing amplitude allows these two contributions to be distinguished. • The irreversible part of the thermal expansion is controlled solely by the maximum temperature experienced by the sample. [ABSTRACT FROM AUTHOR]

The manufacturing of polytetrafluoroethylene products is usually carried out by cold isostatic and/or uniaxial pressing of the powdered polymer, followed by sintering of the “green” parts. During pressing, the air initially present in the loose powder leads to the formation of defects in the material, but the mechanisms involved are not entirely understood. The aim of this study was to better understand the role played by the entrapped air during the cold pressing of polytetrafluoroethylene powder. Observation of the microstructure and determination of some mechanical properties of green and sintered samples, manufactured with different quantities of entrapped air by the cold isostatic pressing process, were carried out. The analysis indicated that defects are formed when the entrapped air pressure in the pressed part leads to internal stresses exceeding the intergranular cohesion resistance of the green part. These defects remain in the microstructure even after sintering, considerably reducing the mechanical strength. [ABSTRACT FROM AUTHOR]

PTFE presents an original secondary crystallization that appears to be independent of the primary one. The conjunction of differential scanning calorimetry and dilatometry experiments has offered complementary data to study both crystallization melted compacted powder and of recrystallized samples. The primary crystallization is responsible for the crystallinity content variation with the cooling rate. It preserves the anisotropy induced by previous compaction that can be observed by dilatometry. Conversely, the secondary crystallization appears to be instantaneous, reversible, kinetic-free and isotropic. It occurs over a wide temperature range between 250°C and 310°C. • Two independent crystallization mechanisms for PTFE are proposed. • The rate-limited primary crystallization sets the final crystallinity content. • It inherits from uniaxial pressing of an anisotropy revealed in dilatometry. • In contrast, the secondary crystallization is instantaneous and fully reversible. • The secondary crystallization appears to be isotropic. [ABSTRACT FROM AUTHOR]