Effect of Stress States on Creep Fracture Modes of an Austenitic Steel with High Ductility.

Niu, Li-Bin; Nakamura, Masayuki; Futamura, Asahiko; Kobayashi, Mitsuyuki

doi:10.2355/isijinternational.40.511

Cited by 11 publications

(13 citation statements)

References 14 publications

(18 reference statements)

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“…7,15,16) In the present torsional creep rupture tests, as stated above, all of the specimens exhibited a ductile transgranular creep fracture of shear type. And larger creep deformations with many micro-voids were observed near the fracture surfaces.…”

Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 96%

“…On the other hand, authors have discussed the creep fracture modes of the smooth specimens ruptured in tension. 7) It has been reported that at higher stresses (meanwhile larger s m ) a ductile fracture caused due to the larger deformation, which restrained the growth of creep voids. But at lower stresses a brittle intergranular fracture occurred due to the sufficient growth of voids with slower creep deformations.…”

Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 99%

“…Generally, it has been assumed that the von Mises equivalent stress s controls creep rate and governs the nucleation of creep voids but does not contribute to their growth, 7,13,14) while the mean stress s m promotes the growth of the creep voids or cracks. 7,15,16) In the present torsional creep rupture tests, as stated above, all of the specimens exhibited a ductile transgranular creep fracture of shear type.…”

Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 99%

“…[3][4][5] It has been known that the creep rupture properties of materials under multi-axial stress conditions are influenced by the multi-axial stress components, such as the maximum principal stress s 1 , the von Mises equivalent stress s and the mean stress s m . 6,7) However, effects of these multi-axial stress components and material characteristics on the multiaxial creep rupture properties have not been made clear.…”

Section: Introductionmentioning

confidence: 99%

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Creep Rupture Properties of an Austenitic Steel with High Ductility under Multi-axial Stresses.

2002

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Using tubular specimens of austenitic steel SUS310S with high ductility, creep rupture tests are conducted in tension, torsion and combined tension-torsion stress states at 700°C. It is found that the maximum principal stress determines the multi-axial creep rupture life of the steel. The reasons are assumed to be that many voids nucleated in the early stages of creep, and that at any creep stress states this steel showed larger deformations and continuous nucleating of voids during creep testing. Furthermore, by observing on the scanning electron micrographs, the specimens ruptured at various stresses are found to exhibit different fracture modes. These creep fracture modes and their formatting factors are discussed in detail. It is assumed that at a multi-axial stress state, the von Mises equivalent stress promotes creep deformation and nucleation of creep voids, meanwhile the growth of the voids should be restrained by the large creep deformation. It is further suggested that in a specimen with existing of the mean stress and a smaller equivalent stress, a brittle intergranular fracture should occur easily.KEY WORDS: creep; multi-axial stress; creep rupture life; fracture; ductility. Table 1. Mechanical properties of the steel used. ly. These tests were performed in air using a tensile-torsional creep test machine. The temperature was kept at 700Ϯ 1°C and was monitored with a thermocouple attached on the external surface of each specimen. Tensile creep elongation and torsional creep rotation angle were measured continuously, using a dial gauge and a rotary encoder device, respectively.For the ruptured specimens, creep fracture surfaces and their longitudinal sections were observed with a scanning electron microscope (SEM). Results Creep Rupture LivesThe von Mises effective strain e¯of the tubular specimens was calculated from the tensile elongation and the torsional rotation angle measured during creep testing. Creep curves of the steel at 4 stress states (torsional, tensile and combined stress states), showing the relation of the effective strain and time, are plotted in Fig. 2. It is found that the torsional creep specimens exhibited larger creep deformations than the others. And at each stress state, the effective strain to rupture showed a decrease tendency with decreasing the applied stress. The relation between the effective strain and time to rupture is clearly shown in Fig. 3. Among the 4 stress states, the effective strain to rupture exhibited larger values in torsion and smaller values in tension. Creep Fracture ModesBy observing the creep fracture surfaces with SEM, the creep fracture modes were examined in detail. It was found that different fractures were exhibited in the specimens under different stress conditions. Regardless of the fracture modes, it was also found that creep voids formed homogeneously in every ruptured specimen by observing its longitudinal section.Firstly, all of the present specimens in torsional creep were found to exhibit a ductile transgranular fracture in a shear mode. ...

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Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 96%

Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 99%

Section: Creep Fracture Modes Under Multi-axial Stressesmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Creep Rupture Properties of an Austenitic Steel with High Ductility under Multi-axial Stresses.

2002

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“…[5][6][7][8] And it is strongly influenced by the multiaxial stress components, such as the von Mises equivalent stress, the mean stress and so on. 9,10) However, the initiation and growth behavior of creep voids, which is closely related with the creep rupture life, has not been made clear for the materials with different characteristics under multi-axial stresses. So, it is necessary to clarify the effects of the multi-axial stress components and the material characteristics on the initiation and growth behavior of creep voids.…”

Section: Introductionmentioning

confidence: 99%

Initiation and Growth Behavior of Creep Voids in an Austenitic Steel with High Ductility under Multi-axial Stresses.

et al. 2003

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This study aims mainly to clarify the effects of the multi-axial stress components on the initiation and growth behavior of creep voids. For this purpose, creep tests, particularly creep interrupt tests are conducted in tension, torsion and in combined tension-torsion stress states at 700°C, using tubular specimens of the austenitic steel SUS310S with high ductility. Creep voids formed in the specimens are examined in detail by observation with the scanning electron micrographs. It is found that creep voids in the torsional creep specimens form easily to a certain size in the primary creep, but they grow difficultly to rupture. While from torsional stress state to tensile one, creep voids become easy to grow. The initiation and growth behaviors of creep voids under the multi-axial stress conditions are discussed. It is further suggested that the von Mises equivalent stress is a dominant component for the initiation of creep voids, and the mean stress component strongly promotes their growth.KEY WORDS: creep; creep interrupt test; void; initiation and growth; multi-axial stress; fracture. creep fracture mechanisms, creep tests were conducted in tension, torsion and in combined tension-torsion stress states using the tubular specimens. In the combined tension-torsion stress states, the ratios of applied tensile stress s to applied shear stress t on the external surface of specimen are 1 : 1 and 2 : 1. These tests were performed in air using a tensile-torsional creep test machine. The test temperature was kept at 700Ϯ1°C and monitored with a thermoelectric couple attached on the external surface of each specimen. Tensile creep elongation and torsional creep rotation angle were measured continuously, using a dial gauge and a rotary encoder device respectively. Thus, the von Mises effective strain of the specimen at any time can be calculated by where e and g are the nominal tensile strain and the nominal shear strain, respectively. To investigate the effects of multi-axial stress components on the initiation and growth behavior of creep voids, 2 kinds of the creep interrupt tests for the specimens loaded at a given maximum principal stress s 1 were carried out: (1) The creep tests were interrupted at the initial and final stages of steady state creep. (2) The creep tests were interrupted as their effective strains reached the same.For the tested specimens, longitudinal sections were etched with the chemical solution (25vol%HNO 3 ϩ50vol% HClϩ25vol%Glycerin) after mechanical polishing. The specimens were then observed in detail with a scanning electron microscope (SEM). The "fraction of creep voids on grain boundary lines", 11) i.e., a fraction of total length of creep void areas on the grain boundary lines, was measured on the SEM micrographs. Also, the "average diameter of creep voids" was calculated. Because each void area observed on the longitudinal sections was just only a cutting plane of a spherical void, in this work the average diameter of the spherical creep voids was calculated approximately from these cut...

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Creep and creep fracture/damage finite element modelling of engineering materials and structures: an addendum

Mackerle¹

2004

International Journal of Pressure Vessels and Piping

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Effect of Stress States on Creep Fracture Modes of an Austenitic Steel with High Ductility.

Cited by 11 publications

References 14 publications

Creep Rupture Properties of an Austenitic Steel with High Ductility under Multi-axial Stresses.

Creep Rupture Properties of an Austenitic Steel with High Ductility under Multi-axial Stresses.

Initiation and Growth Behavior of Creep Voids in an Austenitic Steel with High Ductility under Multi-axial Stresses.

Creep and creep fracture/damage finite element modelling of engineering materials and structures: an addendum

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