Molecular orientation behavior of mesomorphic isotactic polypropylene under uniaxial and biaxial deformation

The molecular orientation behavior of mesomorphic isotactic polypropylene films under biaxial extension was investigated at room temperature. The birefringence was measured not only for drawn films but also simultaneously with biaxial stresses. It was found that there exists a yield point at which the neck is initiated on the biaxial deformed films and necking occurred and propagated in only one stretching direction, resulting in mosaic structures consisting of necked blocks. POLYM. ENG. SCI., 2011. © 2010 Society of Plastics Engineers     

Characterization and Mechanical Properties of Flexible Dimethylsiloxane-Based Inorganic/Organic Hybrid Sheets

Flexible large sheets of dimethylsiloxane-based inorganic/organic hybrids with sizes of ∼200 mm × 290 mm and ∼1.5 mm thickness have been fabricated from poly(dimethylsiloxane) (PDMS) and metal alkoxides of Zr and Ta. The hybrid sheets were characterized by XPS, EXAFS, FT-IR, HRTEM, and SAXS. The inorganic components derived from metal alkoxides in the dimethylsiloxane-based hybrid sheets were found to be present as oxide-like clusters with sizes of 2–3 nm or below, which were chemically attached to PDMS via M–O–Si bonds. The hybrid sheets showed high elongation, strength, and thermal stability. A high elongation of about 100% was observed in the hybrid sheets fabricated in Zr(OBuⁿ)₄/PDMS = 2 at 180°C and a high tensile strength of about 3.0 MPa was observed in those fabricated in Zr(OBuⁿ)₄/PDMS = 4 at 180°C. The flexibility of the hybrid sheets was kept at least to 200°C for 100 h in N₂. These features are thought to come from the inorganic components derived from metal alkoxides, which are close to the molecular-level size and behave as a strong cross-linking agent of PDMS chains.     

3‐D numerical analysis on the mixing performance for assemblies with filled zone of right‐handed and left‐handed double‐flighted screws and kneading blocks in twin‐screw extruders

We have calculated and visualized numerically the mixing performances of four kinds of assemblies in twin‐screw extruders that were composed of right‐handed or left‐handed double‐flighted full flight screws and neutral or left‐handed stagger angle kneading blocks, taking into consideration industrial usage. We have found that the mixing performance of a kneading block interposed between full flighted screws is strongly influenced by the flow of full flighted screws, in particular that of a neutral kneading block. Furthermore, we have proposed the simple mixing indices, which could describe both uniform mixing and heterogeneous mixing, and also applied them to our marker tracking results of four kinds of assemblies. We found that more uniform mixing is obtained for the assembly that has a neutral kneading block before the right‐handed full flight screw, and a more enhanced heterogeneous mixing is obtained for the assembly that has a left‐handed kneading block before the left‐handed full flight screw. The reason for the latter mixing ability will relate to the quasi‐channels of the left‐handed kneading block, through which marker clusters flow while elongating.     

Hydrogen storage in trimethylamine hydrate: Thermodynamic stability and hydrogen storage capacity of hydrogen+trimethylamine mixed semi-clathrate hydrate

The thermodynamic stability and hydrogen occupancy for the hydrogen+trimethylamine mixed semi-clathrate hydrate system were investigated by means of phase equilibrium (pressure–temperature) measurements and Raman spectroscopic analyses. The hydrogen molecule gradually advanced to occupy the empty small cage of trimethylamine hydrate in proportion to pressure increase. Almost all small cages were filled up with the hydrogen molecules at about 80 MPa. Isothermal Raman spectroscopic analysis showed that the absorption-rate of hydrogen to the pre-treated trimethylamine hydrate was comparable to those of tetrahydrofuran hydrate. Only one hydrogen molecule was enclosed with one small cage at the equilibrium state in pre-treated trimethylamine hydrate.     

Strain-induced martensitic transformation near twin boundaries in a biomedical Co–Cr–Mo alloy with negative stacking fault energy

Biomedical Co–Cr–Mo (CCM) alloys have been commonly used for artificial hip and knee joint prostheses, but a need to improve their biomedical inertness and wear resistance has become widely recognized. The mechanical behavior of CCM alloys is dominated by strain-induced martensitic transformation (SIMT), which causes crack initiation during plastic deformation but dramatically enhances the wear resistance in practical use. To develop more reliable CCM alloys it is essential to clarify the factors affecting the occurrence of SIMT. In the present study we have focused on the effect of annealing twin boundaries (ATBs) on SIMT behavior. We have analyzed in detail the substructures near a parallel pair of ATBs after deformation under a stress preferential for slip parallel to the ATBs. Preferential formation of ε-hexagonal close-packed (HCP) phase at ATBs in metastable γ-face-centered cubic (FCC) phase was found by both scanning electron microscopy with electron backscattered diffraction (EBSD) analysis and transmission electron microscopy (TEM). High resolution TEM images indicated that thickening of the ε-HCP phase does not proceed regularly on every second atomic plane, which would form perfect ε-phase HCP structure, but irregularly leaving a high density of stacking faults. Furthermore, the thickness of the ε-HCP phase was found to be different at ATBs on the two sides of the twin. The difference was attributed to the internal stress due to strain incompatibility at the ATBs on the basis of residual stress analysis by the EBSD–Wilkinson method and phase-field simulation of solute segregation at ATBs.