Evaluation of creep damage in heat affected zone of thick welded joint for Mod.9Cr–1Mo steel

Mod.9Cr–1Mo steel has been used for boiler components in ultra-supercritical (USC) thermal power plants. The creep strength of welded joint of this steel decreases due to the formation of Type IV cracking in heat affected zone (HAZ) at higher temperatures. The present paper aims to clarify the damage processes and mechanisms of the welded joint for Mod.9Cr–1Mo steel. Long-term creep tests of base metal, welded joint and simulated fine- grained HAZ were conducted at 550, 600 and 650 °C. Creep tests using thick plate welded joint specimen were interrupted at several time steps, and evolutions and distributions of creep damages were measured quantitatively using laser microscope. It is found that creep voids initiate at early stage of creep life (0.2 of life), the number of creep voids increases until 0.7 of life, and then voids coalesced into the macro crack at the later stage of life (0.8 of life). Creep damages concentrate mostly at a quarter depths of the plate thickness within the fine-grained HAZ of the present welded joint. The experimental creep damage distributions were compared with the computed results by using the FEM analysis. Both creep strain concentration and high stress triaxiality in fine-grained HAZ of welded joint are considered to accelerate the creep void formation and growth.     

Oxidative Degradation of Bisphenol A by Fruit Homogenates

ABSTRACT: The oxidative degradation of bisphenol A (BPA) by several fruit homogenates was investigated. Their homogenates were incubated with BPA at 25 °C for 0 to 120 min, and the acetone extracts were analyzed by high-performance liquid chromatography (HPLC) with a photodiode array detector (200 to 650 nm). The 2 degradation products (UK-1 and UK-2) from BPA were detected on HPLC chromatograms (280 nm). UK-1 and UK-2 were identified to be 2-(3,4-dihydroxyphenyl)-2-(4-ydroxyphenyl) propane, (3-OH-BPA) and 4-[1-(3,4-dihydroxyphenyl)-isopropyl]benzene-1,2-diol, (3,3'-diOH-BPA), respectively, by HPLC-MassPectrometry (LC-MS). In the process of incubation, the peak of 3-OH-BPA attained the maximum value in the 1st 20 min, and that of 3,3'-diOH-BPA increased more slowly, attaining the maximum in 50 min. On the other hand, incubation of 3-OH-BPA (instead of BPA) with grape homogenates gave the maximum peak of 3,3'-diOH-BPA in only 10 min. 3, 3'-diOH-BPA was a polyphenol compound that contained 4 hydroxyl groups. These results suggested that BPA would be degraded (converted) to brown pigments through the compounds of 3-OH-BPA and 3, 3'-diOH-BPA in some fruit homogenates.     

Improvement in Fatigue Strength of Biomedical β-type Ti–Nb–Ta–Zr Alloy While Maintaining Low Young’s Modulus Through Optimizing ω-Phase Precipitation

The improvement in fatigue strength, with maintenance of a low Young’s modulus, in a biomedical β-type titanium alloy, Ti–29Nb–13Ta–4.6Zr (TNTZ), by thermomechanical treatment was investigated. A short aging time at an ω-phase-forming temperature combined with severe cold rolling was employed. A fine ω phase is observed in TNTZ subjected to this thermomechanical treatment. Because the rolling texture of β phase is formed by cold rolling, such as the ω phase may be preferentially oriented to a direction that is effective for inhibiting the increase in Young’s modulus. The samples aged at 573 K (300 °C) for 3.6 ks and 10.8 ks after cold rolling exhibit a good balance between a high tensile strength and low Young’s modulus. In the case of the sample aged for 3.6 ks, the tensile strength is improved, although the fatigue strength is not improved significantly. Both the tensile strength and the fatigue strength of the sample aged for 10.8 ks are improved. This fatigue strength is the highest among the TNTZ samples used in the current and in previous studies with Young’s moduli less than 80 GPa.     

An adaptive method for the determination of the order of element for acquiring the desired accuracy in 3D elastostatic FEM analysis

An adaptive method for the determination of the order of element (or element order) was developed for the finite element analysis of 3D elastostatic problems. Here the order of element means the order of polynomial function, which interpolates the displacement distribution in the element. This method was based on acquiring the desired accuracy for each finite element. From the numerical experiments, the relationship ξ=k(1/p)^β was deduced, where ξ is the error of the result of the finite element analysis relative to the exact value, p is the order of element, and k and β are constants. Applying this relationship to the two results of computations with different orders of element, the order of element for the third computation was deduced. A computer program using this adaptive determination method for the order of element was developed and applied to several 3D elastostatic problems of various shapes. The usefulness of the method was illustrated by these application results.     

Prediction of gas‐liquid two‐phase mixture flow in a vertical pipe with a sudden expansion in diameter

The principle of gas‐lift pumps is applied to vacuum‐decarburization with the RH (Ruhrstahl Heraeus) process to circulate molten steel. Gas‐lift pumps are also applicable to the transportation of molten iron/steel between different refining processes. This paper treats theoretical analysis of steady‐state flow characteristics of gas‐liquid two‐phase mixtures rising in a vertical pipe with an abrupt expansion of its diameter. The system of governing equations is based upon a one‐dimensional multi‐fluid model. Flow pattern transitions are taken into consideration. A new numerical procedure to predict the flow characteristics at the sudden expansion has been proposed. Experiments have also been performed for several conditions to confirm the applicability as well as the validity of the present numerical model. It has been found that the predictions agree reasonably well with the experimental data. Next, the effect of the sudden expansion of pipe diameter on the pump performance was investigated numerically. As a result, it has been confirmed that the sudden expansion of pipe diameter contributes to improve the pump efficiency.     

Characterization of incubation time on creep crack growth for weldments of P92

Most structures are mainly fabricated by welding which are likely to be regions of crack initiation and propagation. In such weldment, it is known that the multi-axial stress fields appear due to the plastic constraint induced by the differences in material micro-structure between the weld metal, heat affected zone (HAZ) and base metal. In the present study, the experiments of creep crack growth tests and the structural mechanical analyses of weldment were conducted to understand the effects of stress multi-axiality of weldment on the characteristics of creep crack growth, creep deformation and creep ductility. Additionally, to characterize the time of creep crack initiation up to the start of a brittle type creep crack growth, the distribution of stress multi-axiality (TF) through the base metal, fine-grain HAZ, coarse-grain HAZ to weld metal were investigated.     

Gait control for redundant legged biped robot at constant velocity and constant height of the waist

In this paper, we propose a gait control method for redundant legged biped robot based on leg center of mass (COM) position control at constant velocity and constant height of the waist. The developed biped robot has redundant legs, which have four degrees of freedoms (DOFs) on each in the sagittal plane. The redundant DOF enables movement of its leg tip position and its leg COM position independently. Therefore, the proposed robot has structural capability to control the leg COM position for maintaining the projection of the total COM inside the support polygon without upper body motion. Such capability enables the stable static walk in the arbitrarily desired velocity and height of the waist motion. The validity of the proposed method for the static walk at constant velocity and constant height of the waist in the leg COM position control for redundant legged biped robot is confirmed by several results of simulation and experiment. © 2006 Wiley Periodicals, Inc. Electr Eng Jpn, 156(4): 51–59, 2006; Published online in Wiley InterScience ( www.interscience.wiley.com ). DOI 10.1002/eej.20357     

Qualitative analysis of the fast brittle fracture

The energy balance equation of the fast brittle fracture is extended in such a way that the fracture surface roughness effect is taken into account. Experimental results of Takahashi and Arakawa [1–3] are analyzed using the extended energy balance equation. It is found that our analysis qualitatively agrees with it in regard to the acceleration and deceleration of the crack propagation. The crack branching condition is also discussed.