The pressure effects on thermal inactivation of subtilisin BPN' (S-BPN') and its pressure inactivation have been studied by measuring the rate of hydrolysis of succinyl-l-alanyl-l-alanyl-l-prolyl-l-phenylalanine-p-nitroanilide (SAAPFpNA) catalyzed by S-BPN' in the temperature range of 15-67.5°C and at the pressures up to 700MPa. The apparent rate of hydrolysis decreased with time above a certain temperature and pressure. The decrease is due to the decrease in S-BPN' activity. The enthalpy change of the thermal inactivation was 100-220kJ·mol-1, and the volume change of this process was 18--4cm3·mol-1. While S-BPN' was inactivated in the pressure range of 500-700MPa at 15-45°C, the corresponding volume change was -13--22cm3·mol-1.
Pressure and concentration dependences of viscosity for aqueous KCl and Csl solutions were examined at 298.2K and compared with those for aqueous NaCl and CsCl solutions. The viscosity minimum, observed for pure water with increasing pressure, became shallow or disappeared by adding alkali halides. The Jones-Dole B coefficients for Na+, K+, Cs+, Cl-, and I- increased with increasing pressure and then decreased after having a maximum. These results are discussed in terms of water structure and dielectric friction effect.
Calcium silicate briquettes were hydrothermally made from the raw materials of waste coal ash which were activated by pretreating with 0.05mol/l-HCl solution or 0.1mol/l-NaOH solution at 80°C for 4 hours. After curing for 72 hours, the briquette consisted of hydrogarnet, C-S-H, and tobermorite. The briquette made from the pretreated coal ash had lower bending strength and lower bulk density than those made from untreated coal ash. To improve the strength, waste silica containing 85wt% α-quartz was added with the pretreated coal ash. The pretreatment of coal ash indirectly improved the reactivity of waste silica, since hydrothermal solution easily invaded into the briquette through pore developed by the reaction of coal ash. The briquettes having bending strength of 18.7MPa and bulk density of 1.42Mg/m3 were obtained.
Differential scanning calorimetry (DSC), X-ray diffraction and probe microscopy were used to study the annealing behavior of an aromatic copolyester with bulky side group. A transition from one crystalline state to another was observed in the thermal analyses. However, no transition was found in the X-ray diffraction patterns. The phenomenon was explained by the model based on the molecular structure. The material used in this study has a cylindrical projection due to the conformational freedom in a repeat unit which contains phenylene groups and a couple of ester linkages. Such molecules are likely to aggregate in the manner of the closed packing and generate comformationally disordered crystals. The thermal treatment promotes the molecular segments to settle in the most stable conformation which is free of steric hindrance, and hence the shrinkage of the unit cell takes place. The diameter of the crystal is as small as 10-20nm. The morphological change due to the thermal treatment was observed as the generation of constricted part in the cylindrical crystals.
The activation energy for the crystallization of an aromatic copolyester with bulky side group was obtained by using a differential scanning calorimeter (DSC). The results of non-isothermal crystallization experiments indicate that there are two crystallization processes; the fast process and the slow process. The crystallization during cooling is controlled by diffusion. The activation energy for the slow process is quite large because of difficulty in diffusion of a molecule due to the rigid rod structure. On the other hand, the isothermal crystallization takes place by nucleation and growth. The activation energy based on kinetic data was 645kJ·mol-1. The value is somewhat larger than those of flexible polymers because of the large energy barrier in molecular movement due to the rigid backbone and bulky side groups. The equilibrium melting temperature and heat of fusion were determined, and the equilibrium entropy change of 0.63J·mol-1·K-1 was calculated from the thermodynamical relationship, ΔSf°=ΔHf°/Tm°. Compared to the literature values for flexible polymers such as polyethylene (9.88J·mol-1·K-1) and polypropylene (15.1J·mol-1·K-1), the obtained value is rather small. This is because the transition from nematic melt to crystals induces less entropy change than that from isotropic melt to crystals.
The influence of parameters in the Gurson's constitutive equation for porous plastic materials on ductile fracture at an interface crack under mixed mode loading is discussed based on a comparison of computational and experimental results. A simple method to estimate the parameters using the deformation data of tensile specimens and the Kalman filter is proposed. A finite element simulation is performed to demonstrate the usefulness of the proposal method. It is suggested that two different specimens (e.g., one is a rectangular plate with a center hole and the other is a side notched plate) are necessary to guarantee a correct estimation.
Recently, a concept of pseudo stable phenomenon (PSP) was proposed by theoretical considerations.The PSP is a phenomenon that crack extension occurs before the load reaches the maximum, Pmax, and it appears in conventional fracture toughness tests for crack-rate sensitive, perfectly brittle materials. The crack extension due to PSP depends on the initial crack length, a0, the testing machine compliance, Λ*, and the crack-rate sensitivity, m*, of crack resistance force. In the theoretical considerations, a method of numerical simulation was proposed by Nojima and Nakai. In the present paper, a series of three point bending tests was carried out on soda-lime glass to examine the PSP experimentally. For the tests, a testing equipment with large machine compliance and specimens with different initial crack lengths were used. The experimental data were compared with the results of numerical simulation. It was found by both experiments and numerical simulations that the amount of crack extension due to PSP becomes maximum when x0≈0.16 (x0=a0/W, W: specimen width) and that the fracture toughness obtained from Pmax, and x0 is always understimated.
Ferritic cast iron with spheroidal graphite for cask was in this study. The material was separated into five parts along the radius direction of the vessel, and the relation between microstructure and Charpy impact behavior was investigated. The results obtained are summarized as follows; (1) The size of graphite and the distance between graphite nodules increased near the center in the section of the vessel, and the number of graphite nodules inversely decreased. (2) Fast Fourier Transforming treatment used to analyse the absorbed energy was effective on the estimation of impact characteristics of cast irons. (3) The difference in impact energy of the materials collected from different parts of the vessel along the radius direction was not recognized. It was found that the dectile-brittle transition temperature was about 270K. (4) Above the transition temperature, the absorbed energy was dependent on the ferrite grain size, section area rate of the ferrite phase and the ductility of it. Below the transition temperature, graphite nodules were found to arrest the brittle crack propagation.
For evaluating the creep damage of 2.25Cr1Mo steel (JIS STPA24) welded joint, degradation mechanism and non-destructive analytical methods (Ultrasonic test noise analysis methods: UT noise analysis) were studied on the welded joint creep specimens interrupted at various test periods. Degradation of the heat affected zone (HAZ) prior to the base metal degradation was calculated from the simplified computation formulae simulating the stress relaxation curve. Creep void formation was remarkable in the middle of HAZ of the specimen, rather than near the surface, followed by the formation of linkage called Type IV cracking. UT noise analysis method, especially effective for detecting fine defects, could be used to measure the degradation of the welded joint HAZ. The measured results of welded joint in fossil power plant indicated the usefulness of UT noise analysis method.
Polyetherimide (PEI) resin has more excellent characteristics in mechanical, thermal, and electrical and in crack resistance, in comparison with other engineering plastics. Because of this advantage, PEI resin applications have been extending as a material for use in precise mechanical devices and medical equipment.In these applications, different kinds of cleaning should be implemented. Especially, in the area of medical care, the severe cleaning and disinfection by irradiation is repeatedly provided to medical tools after their use to disinfect them from bacteria. It is, therefore, believed that a systematic appreciation of the degradation behavior of PEI resin under various environmental factors is essential. From these view points, we have tried to identify the degradation behavior under such environmental factors as water absorption, ozone water absorption, ultraviolet (UV) ray irradiation, and the coexistence of water absorption and UV ray irradiation, using analytic methods with chemical devices. We also studied how those degradation behaviors influence fatigue characteristics. As a result, it became clear that strength against fatigue was deteriorated by disintegration of the principal chain structure under the coexistent environment of water absorption and UV ray irradiation.
Fatigue crack propagation was investigated in fiber metal laminates which have been developed as the aerospace materials. Two kinds of fiber metal laminates were prepared for the fatigue crack propagation test. One was the laminates in which an unidirectional aramid fiber/epoxy prepreg was sandwiched between aluminum alloy sheets, and another was the laminates of a glass fiber/epoxy prepreg and aluminum alloy sheets. The fatigue crack growth in aluminum alloy sheets is strongly influenced by the bridging behavior of unbroken fibers. The effects of difference in reinforcing fiber, initial notch length and pre-stretching were investigated. In comparison with conventional aluminum alloy sheet, the crack propagation rate was extremely small and the decrease in propagation rate was observed in spite of the K increasing test, depending on the initial notch length and the stress ratio. The glass fiber/aluminum alloy laminates showed the noticeable effect of pre-stretching on crack growth rate. The mechanism for the improvement in fatigue crack propagation was also investigated on the basis of the compliance variation with crack propagation and the stress distribution analysis of infrared spectra.
In order to predict service load from fatigue fracture surface, the use of striation spacing (s) and the ratio of striantion height (H) to s, H/s is proposed. It is well known that s is correlated with the crack growth rate da/dN. However, since the crack growth curve da/dN-ΔK depends on the stress ratio R (=Pmin/Pmax=Kmin/Kmax), it is not possible to determine the minimum service load Pmin and the maximum service load Pmax only from da/dN-ΔK or s-ΔK relationship. In the previous paper, the authors found that there existed one-to-one correspondence between H/s and the stress ratio R for 2017-T4 aluminum alloy and SUS304. Thus, the key to evaluate the stress ratio R in service load is an acurate determination of H/s. The method used in the previous paper to measure H of striations is composed of several procedures such as cutting, embedding in plastics and finally sectioning specimens by a microtome (a special cutting machine). In this paper, an improved method of sectioning the fracture surface directly by the microtome is developed. By the new method, an increased number of accurate data of H/s become available and the histogram indicating the scatter of H/s values specific to a definite R ratio can be obtained. Three materials, 2017-T4 aluminum alloy, SUS304 and a high Mn steel, were investigated in order to study the effect of material properties on the relationship between H/s and R. It was found that the mean value of the upper twenty data of 100 measured values of H/s was a unique function of R for all three materials. This result implies, with a high degree of plausibility, the existence of one-to-one correspondence between H/s and R regardless of materials. Thus, the master curve (H/s-R relationship) obtained in this study may be used for the failure analysis of various structures of different materials.
In this paper, we present a method for monitoring fatigue damage of steel specimens non-contactly using a laser speckle sensor. This method is based on the phenomenon whereby the intensity distribution of laser speckle changes depending on surface profile change invoked by fatigue damage. Analysis of the laser speckle distribution can be made quantitatively using an image processing system. The distribution of speckle intensity was observed under cyclic tensile load with a constant stress amplitude. The intensity distribution of laser speckle was found to expand with the occurrence of slipbands due to fatigue. The experiment was also made for plate specimens with a circular hole. The result showed that the distribution of laser speckle at the hole edge changes with the number of loading cycles and the detection of fatigue damage is possible in the case that plastic strain is not localized in a very small region.