[en] This study investigates the correlation between the microstructural change and fracture characteristics in the coarse-grained heat-affected zones (CGHAZs) of the newly developed quenching, lamellarizing and tempering (QLT)-processed 9% Ni steel. The microscopic fracture behaviors of the various sub-zones within the HAZs including local brittle zone (LBZ) were estimated using simulated HAZ specimens. Both results of Charpy impact tests and in situ scanning electron microscopy (SEM) observations on simulated CGHAZ specimens show that the inter-critically reheated coarse-grained HAZ (IC CGHAZ) is a primary LBZ of this steel at cryogenic temperature, but not at room temperature. Microstructural analysis suggests that, unlike in other studies, the cryogenic LBZ phenomenon of the IC CGHAZs cannot be explained simply by the amount of martensite-austenite (M-A) constituents, but is mainly associated with the carbon contents in them. From all results obtained, a mechanism for microscopic toughness change among the CGHAZs is proposed and discussed

[en] Electronic speckle-pattern interferometry (ESPI) was applied for noncontact, real-time evaluation of thermal deformation in a flip-chip package. The spatial resolution of ESPI was increased to submicron scale by magnifying the areas studied in order to measure the deformation of such small-scale components as the solder in the flip-chip package. Thermal deformation in the horizontal and vertical directions around the solder joints was measured as two-dimensional mappings during heating from 25 to 125 deg. C. ESPI was successful in obtaining information on the complicated deformation field around the solder joints. Furthermore, the shear strain could also be calculated using the measured thermal deformation around each solder joint. The applicability of ESPI to flip-chip packages was verified by comparing the ESPI results with those of finite-element analysis (FEA)

[en] Notch effect and loading rate dependency on fracture toughness were considered when evaluating fracture toughness of small notched specimens using the instrumented impact test. Notch effect was analyzed into stress redistribution effect and stress relaxation with a viewpoint of stress triaxiality. Stress redistribution effect was corrected by introducing effective crack length, which was the sum of actual crack length and plastic zone size. Stress relaxation effect was also corrected using elastic stress concentration factor, which would decrease if plastic deformation occurred. As a result, corrected fracture toughness of the notched specimen was very consistent with the reference fracture toughness obtained using precracked specimen. In addition, limiting notch root radius, below which fracture toughness was independent of notch radius, was observed and discussed. Loading rate dependency on fracture toughness, which was obtained from the static three point bending test and the instrumented impact test, was also discussed with stress field in plastic zone ahead of a notch and fracture based on stress control mechanism. (author)

[en] Small punch test is used to assess the reliability of industrial facilities such as fusion reactor structures and power generation systems. Conventional small punch tests evaluate transition temperature and fracture strain by analyzing the load-deflection curves and deformation behaviors, respectively. However, previous research did not consider fracture mechanical concepts such as flaw, stress analysis and fracture toughness. In this study, to obtain more reliable fracture characteristics based on linear elastic fracture mechanics in small punch tests, a pre-crack was introduced to small punch specimen. Stress and deformation behaviors near the crack tip were analyzed and the stress intensity factor was derived. Using the load at crack initiation point, the fracture toughness of SA 508 C1.3 steel was successfully evaluated

[en] In a welded joint, the formation of residual stress is inevitable. The stress can result in decrease of fatigue life in a welded structure under superimposed external stress. On this account it is important to evaluate the residual stress in use of structural steel. But conventional residual stress evaluating methods have difficulties of the derivation of residual stress free state in the field and destructive or lab-scale experiments. In this study, new residual stress evaluating model was suggested using continuous indentation technique. We theoretically induced load-depth curve for residual stress free state from the hardness and strength of the material. From the curve, we evaluated the residual stress in a welded joint using the difference from residual stress state. And we used invariant contact area because it is uniform value regardless of residual stress in the material or plastic deformation at the indentation test. The residual stress results from continuous indentation technique showed good agreement with conventional methods such as hole-drilling and saw cutting methods for API X65 and SS400. Therefore, this method has possibilities in actual application of industrial field