Papers by Keyword: Roller Working

Abstract: In this study, fatigue tests have been performed using two kinds of specimens made of 25 steel. One is pre-strained specimen with pre-strain ratio changing from 2% to 8% by tension, the other is roller worked with deformation of 0.5 mm and 1.0 mm in diameter direction. In the case of pre-strained specimen, the fatigue limit increases according to increase of tensile pre-strain, the fatigue limit of 8% pre-strained specimen is 25% higher than that of non-pre-strained one; in the case of roller worked specimen, the fatigue limit of R05 and R10 is 126% and 143% to that of non-roller worked specimen, respectively. These remarkable improvements of fatigue limit would be caused by the existence of compressive residual stress, work-hardening and the elongated microscopic structures.

Abstract: In this study, the authors have investigated and compared the effects of roller working and ion nitriding on fatigue properties of eutectoid steel. Five kinds of roller worked and two kinds of ion nitrided specimens were used in this test. The fatigue test was performed using a rotating bending fatigue testing machine to evaluate the fatigue strength of roller worked and ion nitrided eutectoid steel. The fatigue test result shows that roller working is more effective on improving the fatigue strength of the material than ion nitriding. On the other hand, the ion nitriding can much greatly increase the surface hardness than the roller working. In the case of roller working, the fatigue properties are improved by the three main factors which are compressive residual stress, work hardening and fiberized micro-structure.

Abstract: Three kinds of materials, pure aluminum (Al1050), carbon steel (S25C) and eutectoid steel (NHH) with V-notch are used in this study to compare the effect of roller working on the fatigue properties among the test materials. As the result, all of the fatigue strengths are improved after roller working and the optimum deformation values exist for every test materials. Fiberized microstructure at the notch bottom, work hardening and compressive residual stress caused by roller working are considered as the main reasons for the fatigue strength improvement. The highest fatigue strength improvement of Al1050, S25C and NHH was 30%, 118% and 155%, respectively. The optimum fatigue improvement of NHH is the highest and it is much higher than that of Al1050, and the optimum deformation value of Al1050 is much lower than that of the other materials. Moreover, the roller working effect is much remarkable for the materials with better hardenability.

Abstract: In order to study the effect of plastic deformation on fatigue behaviors of plastically deformed specimen, bending fatigue tests had been performed on notched deformed stainless steel specimens. Also pulsating fatigue tests were done on notched non-deformed specimens to evaluate the influence of mean stress on fatigue behavior of notched non-deformed specimens. The result showed that according to increase of deformation value, the fatigue limits of these specimens also significantly increase. Fatigue limit of rolled specimen does not linearly increase with increase in plastic deformation value. Based on fatigue limit diagram, the effect of compressive residual stress on fatigue limit improvement of stainless steel is higher than that of work-hardening. In case of non-deformed specimen, when the compressive mean stress increases, the fatigue limit and the number of cycles to failure increase. In case of tensile mean stress, this kind of mean stress decreases the fatigue limit.

Abstract: The fatigue strength have been investigated about the plastic deformed specimens by roller working in Ti-6Al-4V alloy with a notch by 4 kinds of plastic deformation ratio. The plastic deformation values (Δ t) are employed 0.05, 0.1, 0.25 and 0.4 mm on notched specimens of Ti-6Al-4V alloy by roller-working. The hardness test, fatigue test and SEM observation was carried out on non-roller worked specimens and roller-worked specimens at room temperature. Based on the results of these tests, Though the hardness number of roller worked materials are higher than those of non-deformed Ti-6Al-4V alloy, the fatigue limit of roller worked materials becomes deteriorated in spite of roller working. Fatigue fracture had occurred in the non- deformed area where tensile residual stress exists. From the results of the SEM observation, stepped defect could be notch effect for reducing the fatigue strength of Ti-6Al-4V alloy.

Abstract: About 90% of steel structure™s failure was induced from the notched parts due to the stress concentration. Therefore it was very important to research how to improve the fatigue property of notched parts when the stainless steel was used as structural material. Rotating bending fatigue test was preformed to investigate the effect of different notch-machining process (Conventional lathe-machining, Combination of lathe-machining and roller-working) on fatigue strength of the typical austenitic stainless steel SUS304. Fatigue limit of roller-worked specimen was improved to 285% compared to that of lathe-machined specimen. It was found that, work hardening effect induced in roller-working process played an important role to improve the fatigue strength. In addition, the residual compressive stress and the fibriform structure in the specimen surface-layer induced by roller-working were also effective to improve the fatigue strength. Non-propagating fatigue crack was observed in the notch surface of the roller-worked SUS304 for the first time.