Steel conveying rollers used in hot rolling mills must be exchanged frequently at great cost because hot conveyed strips induce wear and deterioration on the surface of roller in short periods. In this study, new roller structure is considered which has a ceramics sleeve connected with two short steel shafts at both ends by shrink fitting. Here, the ceramics sleeve may provide a longer life and reduce the cost for the maintenance. However, after used for a period the steel shaft has to be pulled out for exchange. Simply, heating outside surface and cooling inside surface of the shaft are necessary for separation. However, attention should be paid to the maximum thermal stress of the ceramics sleeve in the process of separation. In this paper, finite element method analysis is applied to the structure and thermal stress has been calculated with the varying dimensions of the structure. Also several effects on thermal stress have been investigated, such as the effect of shrink fitting ratio, outside diameter, the fitted length, thickness of shaft, materials and so on. Finally the most appropriate thermal conditions have been discussed to reduce maximum stress and make separation easy, which is very useful for designing of new rollers.

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The effect of hydrogen exposure on high strength steel, SCM435, based on a sharp notched specimen was investigated. Tensile tests were carried out in hydrogen gas and helium gas environments. In the hydrogen gas environment, specimens that were not exposed to hydrogen gas and specimens that were exposed to hydrogen gas for 48 h were used. As the result of the tensile tests with specimens of various notch depths, the tensile strengths of the hydrogen-gas-exposed specimens were higher than that of the non-exposed specimens. The tensile strength increases with the exposure time in hydrogen gas until hydrogen homogeneously diffuses in the entire specimen for the notched specimens of t =1.0 mm. The fracture surfaces of the specimens in hydrogen gas showed an intergranular fracture near the notch root while the specimens in helium gas showed a fracture mode of microvoid coalescence. The crack initiation stress of the non-exposed specimen was lower than that of the 48h-hydrogen-exposed specimen.

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Simplified inelastic design procedures have been required to reduce simulation cost and to shorten the development period for the modern high temperature machines and structures. Stress redistribution locus (SRL) method has been proposed to provide a reasonable solution employing both the elastic Finite Element (FE) analysis and a unique hyperbolic curve. In the SRL method, dimensionless stress and strain that were normalized using the inelastic stress/strain and the corresponding elastic stress/strain were introduced. This methodology is based on the fact that the stress distribution in well deformed or in high temperature components changes with deformation or time and that the dimensionless stress-strain relation traces a kind of the elastic follow-up locus in spite of the constitutive equation of the material. In this paper, FE analyses incorporating plasticity and creep were performed for a tapered nozzle of a reactor vessel under some thermal transient loads. The dimensionless stress-strain relation was compared with a conventional and newly proposed SRL curves. FE analysis results showed there to be a critical point in the tapered nozzle due to the thermal transient load dependant on a descending rate of temperature from the higher temperature in the operation cycle. Whenever a certain amount of inelastic strain in the nozzle is produced in a restricted area, the dimensionless stress-strain relation is depicted inside the presently proposed SRL curve. Thus the appropriate coefficient in the SRL method is found to be greater than the proposed one, and the present criterion guarantees robust structures for complicated components involving inelastic deformation.

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The effects of the nominal diameter of pipe flange connections with non-asbestos spiral wound gaskets(SWG) under internal pressure on the mechanical characteristics such as the contact gasket stress distribution which governs the sealing performance, the load factor and the hub stress of the connections were evaluated. The stresses in the connections with the nominal diameters from 3” to 24” under internal pressure are analyzed using the elasto-plastic(EP) FEM analysis taking account the hysteresis and non-linearity of deformation behavior of the non-asbestos SWG. As a result, it is found that the variations in the contact gasket stress distributions are substantial due to the flange rotation in the connections with the larger nominal diameter. Leakage tests were conducted to measure the axial bolt forces (the load factor) and the hub stress. The results obtained from the EP-FEM analyses are fairly consistent with the experimental results concerning the variation in the axial bolt forces (the load factor) and the hub stress. Using the obtained contact gasket stress distributions and the fundamental relationship between the amount of leakage and the contact gasket stress, the amount of the leakage of the connections is estimated. It is observed that the sealing performance of the connections with larger nominal diameter is worse than that of the connection with smaller nominal diameter because of the flange rotation. The estimated results are in a fairly good agreement with the measured results. The difference in the hub stress between the EP-FEM and ASME code is demonstrated and the differences in the load factor and the sealing performance of the connections are shown between the asbestos and non-asbestos gaskets.

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The technique for rapid evaluation of fatigue limit using infrared thermography has been developed and paid much attention recently. However, the enhancement of reliability of this technique is demanded for practical application in industries. This study is conducted to verify the effect of stress concentration on fatigue limit evaluation through numerical simulation. Temperature evolutions of stainless steel specimens with different notches are simulated by 3D elasto-plastic finite element analysis. It has been shown that the fatigue limit evaluation based on the temperature evolution is essentially explained by plastic energy dissipation, and that the temperature evolution should be measured after a sufficiently large number of cycles so that plastic shakedown is achieved. It has been remarked that the fatigue limit is overestimated if the spatial resolution of infrared thermography is not fine enough to measure the temperature evolution at the stress concentration site.

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Poly(L-lactic acid) (PLLA) was toughened by blending with three different ductile biopolymers such as poly (ε-caprolactone) (PCL), poly(butylene succinate-co-e-caprolactone) (PBSC), poly (butylene succinate-co-L-lactate) (PBSL). The blend ratio was fixed to 50:50. Lysine triisocyanate (LTI) was added to the blends as a compatibilizer. Characterizations such as Fourier transform infra-red (FT-IR) spectroscopy, field-emission electron microscope (FE-SEM), and mode I fracture test were used to characterize the effectiveness of LTI on the mechanical and morphological properties of various PLLA blends. It was found that PLLA/PCL blend shows the highest toughness energy among the binary blends. On the other hand, addition of LTI in PLLA/PBSC blend exhibits the best toughness property. Based on the FE-SEM observation, fractured surfaces of PLLA blends with LTI indicate ductile fracture with dense elongated fibrils. The largest damage zone is generated in the vicinity of crack-trip, suggesting that high energy dissipation occurred in the crack-trip region. FT-IR analysis also suggested that the NCO groups of LTI were acted as a compatibilizer, as the results of interaction between the two phases of the polymer blends.

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