In this study, linear friction welding (LFW) is used to join high carbon steel such as S55C (JIS G 4051) because it controls the maximum temperature during the joining process. The effect of LFW ...conditions on Charpy absorbed energy is studied. The thickness of a rectangular parallelepiped shape is 14 mm, the width is 20 mm, and the length is 64 mm. The applied pressure (P) controls the maximum temperature. Under high-temperature conditions, P is 100 MPa. Under middle-temperatures conditions, P is between 250 and 350 MPa. Under low-temperature conditions, P is between 400 and 450 MPa. Under all condi-tions, joints are cooled to room temperature.The microstructure and hardness of LFW joints are examined. The toughness is determined using a 300 J instrumented Charpy tester. The absorbed energy is estimated using two methods. The first method uses the potential energy difference, and the second involves calculating the area surrounded by the stroke–load relationship. With an increase in P, the microstructure changes from martensite to ferrite and microcementite. In addition, the maximum hardness at the interface decreases from 500 HV–700 HV to 400 HV. The maximum absorbed energy is confirmed at 400 MPa using the potential energy method and at P of 450 MPa using the area method. Energies absorbed before and after the maximum load are assumed to be crack initiation and propagation (Ep) energies, respectively. The maximum ener-gy is due to an increase in Ep, which is enhanced when the microstructure changes from martensite to ferrite and microcementite.
Under heavy traffic conditions, some fatigue cracks have been found at welding joints between U-shaped ribs “trough ribs” and deck plates. Fatigue cracks along thickness direction of deck plate from ...root tip are important because visual crack detection from outside is limited. In this paper, new functional steel plates with initiation resistance of fatigue crack at weldment and propagation resistance at base material are applied to deck plate to evaluate improvement of fatigue life. We conducted fixed-point fatigue tests with real scale partial models consisted with one trough rib and a transverse girder, and the elastic FEM (Finite Element Method) analysis corresponding to the fatigue test specimen. Based on these results, we studied the fatigue properties which focused on the difference between conventional steel plates and newly developed steel plates, FCA (Fatigue Crack Arrester). Fatigue cracks were initiated from root tip of welded joints between a trough rib and a deck plate. It is clarified that FCA steel plates instead of conventional steel plates can improve the fatigue life under the same welding conditions. This improvement effect becomes much clearer in the high cycle region, which is noticeable at the operation and management stage of bridges.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
It is important to consider the interaction between multiple cracks for evaluating the reliability of structures. In this study, the stress intensity factor (K value) calculated from finite element ...method is used for evaluation of interacting surface crack. For simplification, it is assumed that neighboring two cracks with various aspect ratios have same dimension and located parallel. Interaction criterion for coalescence of two cracks is set as 10% amount of rise of maximum value of K value. As a result of investigation about the interaction criterion of located parameter, it is confirmed that the criterion is much affected with aspect ratio of cracks. Finally, simple criteria as functions of aspect ratio are obtained.
To reduce the weight of connecting structures, welding is usually used. In the case of welding thin plates, fatigue cracks often propagate in the heat affected zone (HAZ) rather than base metals. ...Therefore, it is important to investigate the extension behavior of fatigue crack in HAZ of welding joint. In this study, four-point bending fatigue tests for two high strength steels, an ordinary shipbuilding steel K36A and a shipbuilding steel K36 with low carbon contents by TMCP, were carried out under the stress ratios (R) of 0.1 and 0.8. The specimen with HAZ introduced by thermal cycle simulating the temperature history of HAZ was prepared. The crack extension rate of K36A HAZ specimen is lower than that of the corresponding base metals, especially at small repeating range of stress intensity factor. For R = 0.8 tests imitating tensile residual stress, the crack extension rate much greater than that of R = 0.1.
Adhesively bonded joints will fail under comparatively low stress by addition of unexpected peel loads to shear loads. Thus, it is essential to evaluate the strength of adhesively bonded joints under ...the mixed mode conditions consisting of peel loads and shear loads. However, evaluation methods for thin adherends under mixed mode conditions have not been establised. In this study, a biaxial loading apparatus and multilayer specimens are developed to evaluate static strength and fatigue strength of adhesive joints. This method is applied in adhesive tests of metallic coatings. As a result of the evaluation tests, the static fracture standard can be described by a quarter-ellipse which is subjected to pure shear strength and pure peel strength. The fatigue strength can be predicted if the static fracture standards and the voids caused by peel loads are considered. The adhesion strength of galvanized steel under the mixed mode can be evaluated in liquid nitrogen.
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