It is considered that the heat island phenomenon is generated by temperature rise due to heat release from urban structures which have a high heat absorptance and are warmed by solar radiation during the daytime. Applying solar heat high reflectance paint to the exterior surfaces of urban structures would suppress the increase in temperature, and make it possible to mitigate the heat island phenomenon. This paper describes the influence of solar reflectance and transmittance characteristics of top coat with the change of film thickness and the reflectance characteristic of the under coat on the solar reflectance of paint system, while aiming to establish a design method of solar heat high reflectance paint system. The conclusions obtained from this study are as follows : (1) It has a linear relation between log T that is indicated in a logarithm of film thickness T(μm) and solar transmittance τe1 (%). (2) It has been confirmed that the solar reflectance of the paint system is influenced by the solar reflectance of the under coat. (3) It is possible to show the solar reflectance of the paint system as the sum of total solar reflectance (ρe1) of the top coat and solar reflectance (ρe2) which is transmitted by solar radiation considering the reflection on the surface of the under coat.
Fiber Bragg grating (FBG) is an optical fiber device that selectively reflects only those light signals with the wavelength matched to the grating period of refractive index modulation. When two FBGs with identical index modulation period are concatenated in series, the signal light reflected by the FBGs may interfere with itself by the process of multiple reflections between adjacent FBGs, and the reflection spectrum may behave in a complicated manner with spectrum completely different from that of a single FBG. This paper analyzes the optical spectrum reflected by the concatenated FBGs both experimentally and theoretically, and demonstrates how the spectrum varies depending on which is larger between coherency length of the light signal and separation distance of the concatenated FBGs.
In this study, the optical and mechanical properties of cyclo-olefin polymers (COPs) which were added several kinds of polysilane or silicone were investigated. When adding low molecular weight polysilane (PMPS) into COPs upto 20wt%, the transparency of the COP blends was maintained and, at the same time, their refractive index values increased with an increase of PMPS content. On the other hand, when adding polysilane with high molecular weigh or silicone into COPs, those films became cloudy even with 10wt% of the additives, indicating that they cannot be dispersed homogeneously. Besides the glass-transition temperature (Tg) of COPs can be controlled by adding PMPS, and its decline ratio of Tg was almost proportional to the PMPS content. This result indicated that PMPS can play the role of plasticizer for COP materials. For the molecular motion in the glassy state of COPs, however, the activation energy of their enthalpy relaxation increased by adding PMPS, indicating that PMPS hinders enthalpy relaxation.
A study was conducted on the combustion product gases generated when polyurethane, other polymeric materials, and wood are burnt, and their safety. Compared to other materials, the ignition and combustion times of PU were short, which showed that it is a highly combustible material. Regarding its toxicity during combustion, CO and HCN etc. of isocyanate group origin are particularly viewed as problematic. From the results of the examination of the risk factors during fires, the lengths of time for the most influential risk factor in each sample to reach the fatal dose were in the order of PU foam, wood, PA66, PP, PC, and PU. In the case of PU, the emission of CO and HCN, which are considered particularly problematic during fires, was not great even when compared to PP, PC, and PA66 etc. often used in daily life. However, the risk increases when it is in the state of foam because the combustion speed is faster.
The mechanical and thermal properties of epoxy resin used for electronic parts are changed by thermal load in manufacturing processes and prolonged use, and these properties make defective of electronic devices. In this report, warp behavior of a two-layer-laminated body consisting of epoxy resin and steel caused by thermal load were examined from both sides of experiment and theory. As a result, it was clarified that viscoelastic properties of epoxy resin, such as storage modulus, loss modulus, loss tangent and glass transition temperature were changed by thermal load, and that warp behavior could be predicted by thermo-viscoelastic analysis based on linear thermo-viscoelastic theory by using these viscoelastic properties.
It has become common to apply thermal barrier coatings (TBC) to hot gas path parts in gas turbines to increase thermal efficiency. However, some uncertainty about the delamination life prediction method for TBC still remains. The influences of mechanical parameters on delamination behavior were investigated through thermo-mechanical fatigue (TMF) tests to improve TBC delamination life prediction. The parameters investigated were loading pattern, strain range, ceramic coating thickness, and high temperature exposure processing prior to TMF tests. Delamination behavior with a simulated loading pattern seemed to better correspond to behavior under out-of-phase (OP) loading than that with in-phase (IP) loading. The OP loading pattern was better for evaluating delamination lives because of its shorter test period. The delamination lives became shorter under larger strain ranges. Of the specimens tested, the specimen with a 0.9-mm-thick ceramic coating had the shortest delamination life. The specimen with a 0.6-mm-thick coating had almost the same or longer life than the specimen with a 0.3-mm-thick coating. These results strongly suggest that an optimum ceramic coating thickness keeps the cooling performance consistent with delamination strength. Thermally grown oxides (TGO) are generally thought to be the main cause of TBC degradation in long-term operated gas turbine blades. The growth behavior of TGO was observed by exposing specimens to a high-temperature environment and it was suggested that the Larson-Miller parameter (LMP) could predict TGO thickness well. In addition, some specimens were exposed to high-temperature environments prior to TMF tests to evaluate the effect of TGO thickness on delamination lives. This high temperature pre-exposure seemed to accelerate the delamination growth rate due to sintering and TGO.
Rotating bending fatigue tests were carried out for a squeeze cast Al alloy, AC4CH-T6, to investigate the effect of flow forming on fatigue strength. By flow forming, the microstructure was crush down to the forming direction. The increase in fatigue strength was confirmed by flow forming. The effect of flow forming on the increase in fatigue strength was mainly caused by the increase in resistance to a crack growth. However the increase in fatigue strength was very small and there was no or little improvement in the scatter of fatigue strength, meaning that the application of flow forming to squeeze cast Al alloy should be considered from viewpoints of cost, equipment and so on. This was caused from that the alloy squeeze cast was essentially refined the microstructures and reduced the defects like a void.
The shear mode propagation and threshold behaviors of small, semi-elliptical fatigue cracks were investigated in the JIS-SUJ2 bearing steel. Fully-reversed torsional loading was combined with a static axial compressive load to obtain crack growth in the longitudinal direction of cylindrical specimens. Non-propagating cracks smaller than ≅1mm in size were obtained (i) by decreasing the stress amplitude in tests using notched specimens, and (ii) by using smooth specimens in constant stress amplitude tests. The Mode II and Mode III threshold stress intensity factor ranges, ΔKIIth and ΔKIIIth, were estimated from the shapes and dimensions of non-propagating cracks. The threshold values decreased with a decrease in crack size, and there was no significant difference between ΔKIIth and ΔKIIIth. Wear on the crack faces was inferred by a powder and also by changes in microstructure in the wake of a crack. The ΔKIIth in the absence of interference of crack faces was estimated to be approximately 13MPa·m1/2 for a 1mm long crack.
In order to investigate fatigue properties of maraging steel at elevated temperature, rotating bending fatigue tests were carried out at room temperature, 473K and 673K in ambient air. Fatigue strength at elevated temperature was higher than that at room temperature, though static strength was decreased at elevated temperature. Endurance ratio σw/σB (σw : fatigue limit, σB : tensile strength) was increased with increasing temperature. Crack growth resistance was hardly influenced by temperature. Hardness of specimen after fatigue test was increased and the hardness was large with increasing fatigue life. That is, the high fatigue strength at elevated temperature may be explained by age hardening yielded at fatigue process at elevated temperature. This phenomena was confirmed from the results that the steel double-aged at 673K corresponding to the fatigue tested condition showed high static and fatigue strengths.
In order to investigate the effect of humidity on initiation and propagation properties of a fatigue crack of 18%Ni maraging steels with different grain size and hardness, rotating bending fatigue tests were carried out in relative humidity of 25% and 85%. Fatigue strength was largely decreased by high humidity and the decrease in fatigue strength due to high humidity was increased with increases in grain size and specimen hardness. In high humidity, both of initiation and propagation of a crack were accelerated. The acceleration of a crack growth was caused by intergranular crack. Although the proportional relation between fatigue limit and hardness held up to HV600 in high humidity of 85%, the limiting hardness in the relation increased to HV 750 in low humidity of 25%. The decrease in fatigue strength due to high humidity was suppressed by double aging, which was aged at 673K for 3.6Ks after aging at 753K for 150ks.