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Volume 38 (2000)
- Issue 6 Pages 342-
- Issue 5 Pages 262-
- Issue 4 Pages 198-
- Issue 3 Pages 124-
- Issue 2 Pages 68-
- Issue 1 Pages 4-
Predecessor
Volume 38, Issue 4
Displaying 1-5 of 5 articles from this issue
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Yasuo OTOGURO, Katsukuni HASHIMOTO, Masao INOUE, Kazuteru OHISHI, Yuki ...2000 Volume 38 Issue 4 Pages 198-204
Published: July 25, 2000
Released on J-STAGE: August 05, 2010
JOURNAL FREE ACCESSHardness distribution, micrographs, and chemical analysis of the nitrided surface layer under various conditions were investigated for a 2.25Cr-1Mo steel. Moreover, relationships between nitriding conditions and creep rupture properties were examined.
The results obtained are as follows:
1) The hardness of the nitrided surface layer increased and nitrogen diffused inside deeper with increasing nitriding time.
2) Nitride on the surface spalled or decomposed to diffuse inside as solved nitrogen during heat treatment after nitriding.
3) Nitriding increased markedly creep rupture strength but nitriding for longer time decreased rupture ductility.
4) Combination of high creep rupture strength and good ductility were achieved by nitriding for relatively short period.View full abstractDownload PDF (4482K) -
Hideyuki Ishigami, Katsuyuki Matsui, Akira Tange, Kotoji Ando2000 Volume 38 Issue 4 Pages 205-215
Published: July 25, 2000
Released on J-STAGE: August 05, 2010
JOURNAL FREE ACCESSFatigue fracture processes are divided into 7 stages. Fatigue promotive and defensive factors of each stage were considered systematically. Based on this consideration, new methodology to increase fatigue limit of components which subjected to cyclic load of stress ratio R≥0 was proposed. That is: (a) To increase the Vickers Hardness of the component as high as possible. (b) To introduce high compressive residual stress as high as possible. (c) To fine a grain size as fine as possible. To achieve this condition, new surface treatment methods were developed by authors and the methods were applied to coil spring and gear. By using these methods, fatigue life of coil spring was increased by about 10 times and fatigue limit of gear was also increased up to 250%, successfully and economically.View full abstractDownload PDF (1358K) -
Akira TANGE, Kotoji ANDO2000 Volume 38 Issue 4 Pages 216-223
Published: July 25, 2000
Released on J-STAGE: August 05, 2010
JOURNAL FREE ACCESSAutomotive Coil Spring is always required to increase fatigue strength for the weight-saving. There are mainly two methods to increase fatigue strength. (a) to increase vickers hardness, (b) to increase compressive residual stress. For the method (a), since the present vickers hardness, HV is very high around 600HV, it is difficult to increase the hardness further. On the other hand, if the HV is increased further, spring will become too sensitive for corrosion fatigue and hydrogen embrittlement. For the method (b), shot peening is a very popular technique to apply compressive residual stress. Based on the above background, we studied on the following subjects,
(1) Stress intensity factor of surface cracks by compressive residual stress are calculated. By using the calculated results, it was considered what is the most suitable compressive stress to increase the fatiguelife of coil spring.
(2) To apply the most suitable residual stress in coil spring, following four shot-peening techniques were studied, systematically, (2.1) Double shot-peening, (2.2) Stress shot-peening, (2.3) Warm shot peeling, and (2.4) Combined shotpeening above.
(3) Fatigue tests were carried out on coil springs which were processed under the above shot-peening techniques. It was found, that (a) the compressive residualstress has significant effect on fatigue strength and optimum stress distribution can be predicted, (b) proposed combined shot-peening an excellent effect on increasing the fatigue strength of coil spring.View full abstractDownload PDF (3372K) -
Yochiaki TAMURA2000 Volume 38 Issue 4 Pages 224-233
Published: July 25, 2000
Released on J-STAGE: August 05, 2010
JOURNAL FREE ACCESSDownload PDF (1462K) -
Tadashi Ishikawa2000 Volume 38 Issue 4 Pages 234-242
Published: July 25, 2000
Released on J-STAGE: August 05, 2010
JOURNAL FREE ACCESSA steel plate with remarkably improved fracture propagation arrest capability (crack arrestability) has been developed to minimize damage to a steel structures by preventing the propagation of cracks which may initiate due to unexpected accidents or the like. The steel plate is a hybrid-type steel plate (with multi-layer structure in its thickness direction) whose surface layer has remarkably high resistance to brittle fracture. The surface layer consists of ultra-fine grains of 1 to 3μm. The level of grain size has been realized on an industrial basis for the first time in the world. Even if a brittle crack propagates in the plate, the surface layers may not fracture or fracture in a ductile manner absorbing crack propagation energy (forming so-called “shearlip”) so that the brittle crack arrestability is remarkably improved.
This paper describes mechanical properties and performances against brittle fracture and fatigue fracture included large-scale fracture test results. Structure integrity concept in which the steel with high crack arrestability is utilized and its actual application to large ships are also demonstrated.View full abstractDownload PDF (8332K)
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