SiC matrix composites in which Si-M(=Ti, Zr)-C-O fiber is used as the reinforcing fiber are materials with superior heat capability and damage tolerance. It is known that the fiber’s oxidation and thermal decomposition characteristics have a significant influence on the durability of Si-M-C-O/SiC. We measured the weight change, oxide layer thickness, and crystallite size of Si-M-C-O fiber, and the X-ray absorption fine structure (XAFS) of Si-Zr-Cr-O fiber, when exposed in an ambient atmosphere and in a vacuum. We determined the thermal decomposition of the fiber exposed in an ambient atmosphere, and we analyzed the influence of the added metal elements (M=Ti, Zr) and the oxygen content on thermal decomposition based on the difference in thermal decomposition behavior due to the type of fiber and the exposure environment. The results indicated that, when in a vacuum, the oxygen content of the fiber had a significant influence on the thermal decomposition of the Si-M-C-O fiber and the nucleation of ZrC in the Si-Zr-C-O fiber. On the other hand, when in the ambient atmosphere, in comparison with the behavior of ZrC in Si-Zr-C-O (1), TiC in Si-Ti-C-O (2) was formed at a lower temperature in a shorter time, indicating that resistance to thermal decomposition is greatly influenced by the type of metal added.
CO2 was absorbed into C60-C70 binary solids at room temperature using a commercially available autoclave. The solids were then immersed in liquid CO2 for 24 h at a gas pressure of 5 to 6 MPa, and the degree of CO2 storage was evaluated by infrared (IR) spectroscopy and X-ray diffraction (XRD). CO2 was detected in pure C60 by IR measurement, and the stoichiometry was estimated to be C60(CO2)0.34 based on the increase in the lattice parameter. Although no trace of CO2 storage was detected for pure C70, the addition of C70 to C60 at a mole fraction of up to 0.16 did not appreciably degrade the storage capacity of CO2 from that in pure C60. The stability of CO2 trapped in solid fullerenes is explained in terms of geometrical considerations based on hard-sphere packing at octahedral sites.
In this paper we showed that stress-strain curves of strain-aged specimen of low carbon steel can be predicted by computer simulation based on the constitutive equations which have been proposed in order to explain the yield point phenomena. In the theory two internal stresses are supposed: the one, Yint is the stress which is work-hardened, and the other, Yir the stress work-softened and age-hardened. It was supposed that strain aging influences two internal stresses in following way: the work-hardening rate of Yint and the value of Yir are both increased with increase in aging time. This supposition was formulated as functions of aging temperature and aging time. The simulated stress-strain curves showed a good agreement with the experimental ones, which means that the constitutive equations used in the simulation are reliable.
Stress-strain curve of low carbon steel tested at room temperature shows the yield point phenomenon at first and then is followed by smooth work-hardening behavior, but in blue-shortness temperature range it shows irregular and/or serrated form. In this paper we tried to simulate these curves based on a constitutive equation. Results of computer calculation suggested that following assumptions are necessary for simulated curves to fit in with experimental ones: 1. Strain rate is determined by effective stress which is defined as the difference between applied stress and internal stress. 2. The internal stress consists of two terms; the one is ordinary internal stress which is work-hardened, and the other is the cause of yield point phenomena, which is work-softened and age-hardened. 3. A deformed region (element) in specimen exerts a kind of interaction stress on neighboring one if there is “strain difference” between both regions. At room temperature the strain difference means the difference in total strain, but in the blue-shortness temperature range we must use a different term “corresponding strain” in place of total strain. And the corresponding strain is defined as a function increased with strain and decreased with time.