Numerical simulation of the excavation damaged zone around an opening in brittle rock

The micromechanics-based damage model proposed by Golshani et al. [A micromechanical model for brittle failure of rock and its relation to crack growth observed in triaxial compression tests of granite. Mech Mater 2006;38:287–303] is extended so that time-dependent behavior of brittle material can be taken into account, with special attention to the numerical analysis of an excavation damaged zone (EDZ) around an opening, which is a major concern in assessing the safety of underground repositories. The present model is capable of reproducing the three characteristic stages of creep behavior (i.e., primary, secondary, and tertiary creep) commonly observed in the laboratory creep tests. The sub-critical microcrack growth parameters (i.e., n and A) can be determined for Inada granite by fitting the numerical results of elapse time to failure versus the creep stress ratio curve with the experimental data under both dry and wet conditions. It is found that moisture has a significant influence on the parameter A rather than the parameter n. Use of the extended model makes it possible to analyze not only the extension of microcrack length, but also the development of EDZ around an opening as a function of time. The damaged zones mainly develop in the sidewalls of the opening in the case that the vertical stress σ₂₂ is larger than the horizontal stress σ₁₁.     

Evaluation of apparent viscosity of liquid-containing porous particles by the intrusion method using a conical rotor

The apparent viscosity of a wet powder consisting of porous silica particles and a viscous liquid was evaluated by means of a newly developed powder rheometer in which a rotating conical rotor with grooves on the surface intrudes semi-statically into the powder bed. Using this rheometer, the relationship between the shear torque and the depth of intrusion, i.e., the torque characteristic curve, was measured under various conditions. The shear force acting on a contact point between the particles was estimated from the torque characteristic curve. Above the critical liquid amount in which the pores of the particles were filled with the liquid, the shear force increased with an increase in the thickness of the liquid film formed on the particle surface regardless of the pore volume. From the change of shear force with the physical properties of the liquid, it was clear that the shear force is closely related to the liquid bridge force acting on the contact points between the particles. The apparent viscosity coefficient of the wet powder was determined from the shear rate dependence of the shear force. At the relatively high liquid amounts corresponding to funicular and capillary states, the apparent viscosity coefficient increased sharply with the thickness of the liquid film since the viscosity of the liquid strongly affected the shear flow of the wet powder. Subtle changes of the apparent viscosity due to the liquid amount and the physical properties of the liquid can be sensitively detected by using the rotary-intrusion method.     

Photoelectrochemical study of lanthanide titanium oxides, Ln2Ti2O7 (Ln = La, Sm, and Gd)

Photocatalytic activities for hydrogen evolution of lanthanide titanium oxides, Ln₂Ti₂O₇ (Ln = La, Pr, Nd, Sm, Gd, Dy, Ho, Er, and Yb) prepared by a solid-state reaction were studied. Hydrogen gas was clearly evolved in distilled water suspension of La₂Ti₂O₇ and Sm₂Ti₂O₇. From the photoelectrochemical measurements, the values of the flat band potential were estimated to be −0.04, −0.02, +0.27 eV for La₂Ti₂O₇, Sm₂Ti₂O₇, Gd₂Ti₂O₇, respectively, versus the normal hydrogen electrode (NHE). The values of the band gap energy were calculated to be about 3.29, 2.79, 2.82 eV for La₂Ti₂O₇, Sm₂Ti₂O₇, Gd₂Ti₂O₇, respectively. The photocatalytic activities of Ln₂Ti₂O₇ (La, Sm, and Gd) were discussed along with detailed band structures estimated in this study. From the band structures, Sm₂Ti₂O₇ is a possible candidate of photocatalyst responding to visible light.     

A study on three-dimensional (spatio-temporal) noisecharacteristics of letterbox EDTV

The difference between the three-dimensional noise characteristics of the current NTSC and that of the letterbox EDTV has been studied. We have shown that when the letterbox EDTV pictures (main panel) are displayed in the 16:9 aspect area with the same picture height as that of NTSC pictures (4:3), and when the signal levels are the same, the three-dimensional noise power spectrum of the main panel of letterbox EDTV is transformed into a low spatial frequency region with high density, and the total noise power remains unchanged both in NTSC and EDTV. The helper signals which are multiplexed onto the black bands in the top and bottom portions of the screen, generally, increase the total noise power of decoded EDTV signals even if the amplitude of the helper signals is large enough. By applying a three-dimensional weighting function, it is shown that the weighted noise power of the letterbox EDTV becomes larger than that of NTSC. Hence, in order to retain the existing service area after introducing the EDTV broadcasting service, it will be necessary to install noise suppressing measures in the EDTV system     

Studies of the chemical degradation of polysiloxanes by hydrofluoric acid: 1. Poly (tetramethyl-p-silphenylene siloxane)

Hydrofluoric acid solution selectively degrades poly (tetramethyl-p-silphenylene siloxane) (TMpS) through scission of the Si---O bonds. The crystallinity of self-seeded single crystals of TMpS is significantly enhanced on degradation as the fold surfaces are removed. For 48% HF at 30°C the crystallinity change is from 73 to 95%. This corresponds to removal of two or more monomeric units from each crystal surface. Acid concentration and treatment temperature are very significant factors in the degradation reactions. The observed molecular weight change with time also depends on these details. The molecular weight distribution of a fraction at first broadens and then narrows with degradation time. At relatively long reaction times, the molecular weight (by g.p.c.) is reduced by more than an order of magnitude over that of the starting polymer fraction. In the early stages of chemical degradation the reaction is heterogeneous presumably because of poor wetting of the siloxane polymer by the HF reagent.     

Craze yielding and fracture mechanism in PE/PS/PE laminated films

Mechanical behaviour of laminated films of PS and PE, especially the altered mechanical properties of PS in the laminated state, were studied as functions of PE volume fraction. It was observed that crazing in PS can be modified by laminating layers of PE to both sides. Elongation at break and hence fracture energy increased conspicuously when PE volume fraction increased. Craze yielding stress in PS layers also increased with increasing PE volume fraction because craze formations in PS layers were suppressed by the reduction of tensile stress concentration effect at craze tips. Craze initiations were always found at the free side edges of the laminated films, which can be correlated with the transverse interlaminar shear stress concentrations existing at the edges of the laminated films caused by the difference in Poisson's ratios between PS and PE.     

Thermolysis and hydrogenolysis of polyethylene under steam pressure

Thermolysis and hydrogenolysis of polyethylene under steam pressure were carried out by batchwise autoclave in the recovery of liquid petrochemical resources from waste polymers. Thermolysis of polyethylene under steam pressure occurred in the temperature range 400–475°C and reaction pressures up to 213 bar. The presence of steam is advantageous for an increase in liquid products and 450°C is an appropriate temperature for the formation of low molecular aromatic compounds. Hydrogenolysis of polyethylene was studied at 450°C and initial hydrogen pressure range of 10–100 bar under steam pressure. Over 80 wt % of the low-boiling product was converted to saturated hydrocarbons at 40 bar hydrogen pressure, which corresponds to 1 mole hydrogen to 1 mole monomeric unit of polyethylene. The schemes for the thermolysis and the hydrogenolysis, especially the aromatization, are discussed.     

Effects of focusing on the resolution characteristics of integral photography

The effects of focusing on the resolution characteristics of integral photography (IP) are analyzed. First, there is an attempt to obtain the resolution characteristics of capture and display systems as the product of their modulation transfer functions (MTFs). Next, the relationship between this overall MTF and focusing during the capture is studied. The results show that, with focusing set at infinity, IP can provide three-dimensional images without remarkable resolution degradation over a wide range of depth.