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Investigation of low cycle fatigue behaviour of building structural steels under earthquake loading
258
Fatigue Abstracts
Measurement of fluid flow rates through cracks. Clarke, L.V., Bainbridge, H., Beck, S.B.M. and Yates, J.R. btternational Journal of Pressure Vessels and Piping (1997) 71(1), 71-75
The preferred combination of primary and critical slip during cyclic deformation is also discussed in terms of dislocation reactions. Graphs, 40 ref.
An experimental study has been performed into leak rates through a series of cracked specimens. Semi-elliptic fatigue cracks were grown through aluminium plates and the flow of water was measured as a function of crack length and crack opening. Two relationships were found between volumtric flow rate and crack opening in the region of flow studied. For larger crack openings theoretical results obtained by modelling laminar flow between parallel planes corresponded well to the experimental data. At smaller crack openings, agreement was found with theoretical results obtained by modelling the pressure drop due to bends and changes in area. It was also found that below a threshold value of crack opening no flow occurred. Graphs, 16 ref.
The importance of uniformity in the application of the shot peening treatment. Straub. J. Shot Peener (1997) 11(1), 10 12
Fatigue crack growth of Ni3AI(CrB) single crystals at ambient and elevated temperatures. Zhang, G.P., Wang, Z.G. and Li, G.Y. Acre Materialia (1997) 45,(4), 1705 1714 Fatigue crack propagation behaviour of compact tension specimens of Ni3AI(CrB) single crystals has been examined at room temperature and elevated temperature. The results indicated that crystallographic cracking occurs on two or more { I l l / planes simultaneously at room temperature. With increasing temperature, the cube slip plane becomes active and plays an important role in determining the cracking path. Orientation and temperature dependence of the fatigue crack initiation threshold from the notch root exists. Similar to the flow stress, the crack initiation threshold increases with temperature, and the threshold for (100)[010] orientation is higher than that for (110)[110]. Both orientation and temperature affect the fatigue crack growth rates (FCGRs). The FCGRs of (00)[010] are higher than that of (110)[110] in the Paris regime. A crystallographic relationship between the primary crack plane and the secondary slip plane ahead of the crack tip is suggested to explain the dependence of FCGRs on orientation. The oxidation embrittlement at the crack tip and the activated cube slip should be responsible for the acceleration of FCGRs in the Paris regime and the oxide-induced crack closure has a significant effect on the deceleration of FCGRs in the near-threshold regime at elevated temperatures. Both the relationship of orientations between octahedrat slip planes and the applied load axis and the increasing activity of the cube slip plane with temperature determine the significant variation of fracture path with temperature. Graphs, photomicrographs, 26 ref,
Cyclic deformation behaviour and dislocation structures of [001] copper single crystals. II. Characteristics of dislocation structures. Wang, Z., Gong, B. and Wang, Z. Acre Materialia (1997) 45(4), 1379-1391 The dislocation structure of [001] Cu single crystals developed in cyclic deformation has been systematically studied with transmission electron microscopy and related to the mechanical behaviour presented previously. The dislocation configuration for this orientation is characterized by labyrinth structures over all the strain amplitudes investigated. At high strain amplitudes (3'p~= 1.8 x 10 ~-3.0 x 10 3), additional structures such as exclusive walls and strips were observed. The strips are parallel to {111} slip planes and are associated with macro-deformation bands reported previously. At low strain amplutudes ('Ypt< = 2.4 x 10-4), however, labyrinth becomes irregular in geometrical shape. Labyrinth structures consist of two types of perpendicular walls: one is always parallel to (00t) plane and the other may be (100), (210) or (120). The characteristic dimension of labyrinths, such as channel width, increases with decreasing applied strain amplitude. The nature of dislocations in labyrinth structures was identified to be mainly primary and critical dislocations. The role of labyrinth structures in cyclic deformation was discussed in terms of geometrical considerations. It has been shown that labyrinth structures are more favourable to cyclic deformation by promoting multiple slip and cross slip. Finally, the cyclic saturation stress was quantitatively correlated with the microparameter of labyrinth structures. Photomicrographs, 35 ref.
Cyclic deformation behaviour and dislocation structures of [001] copper single crystals. I. Cyclic stress-strain response and surface feature. Wang, Zh., Gong, B. and Wang, Z. Acta Materialia (1997) 45(4), 1365-1377 Cyclic deformation behaviour of [001] copper single crystals was investigated in symmetrical pull-push fatigue tests at the ambient temperature and with constant plastic shear strain amplitudes (Tp0 in the range of 1.0× 10-4 to 3.0 × 10 3. The formation and development of surface slip bands (SBs) were examined in situ by a light microscope. A rapid initial hardening stage followed by a pronounced overshooting or significant softening was found with the crystals tested at "Ypr> = 4 . 8 x 10 4. The cyclic stress-strain curve of [001] crystals does not show any plateau behaviour, instead it follows, if corrected with the Taylor factor the power law function for copper polycrystals. The fatigue limit, defined as the critical strain amplitude below which SBs do not form, was found to be ~1.7 x 10-4, a value much higher than that for single slip oriented crystals, but very close to that for polycrystals modified by the Taylor factor. In situ observation revealed that the primary SBs appeared at the very beginning of cyclic deformation and frequently they were not persistent. The secondary (critical) SBs usually formed at the overshooting stage after rapid hardening. Deformation bands with the characteristics of kink bands were detected in the final stage of the cyclic deformation. Analysis indicated that the rapid initial cyclic hardening is caused by the formation of L o m e ~ Cottrell locks, while the overshooting/softening behaviour is related to the operation of secondary slip or the formation of dislocation labyrinth structure.
The effects of shot peening uniformity on fatigue life were investigated on specimens of 9260 steel. Unpeened specimens were compared in bend tests with specimens peened using only whole shot and with both whole and broken shot. Fatigue life was practically unchanged by peening with broken shot after peening with whole shot; also fatigue life was greater for a group of specimens peened with whole shot than for a group peened with the same arc height and coverage but with broken shot. Graphs.
Investigation of low cycle fatigue behaviour of building structural steels under earthquake loading. Sheng, G.M. and Gong, S.H. Acre Metallurgica Sinica (English Letters) (1997) 10(1), 51-55 Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fatigue test are carried out. The experimental results showed that microalloying of V, Ti and Nb can improve the anti-seismic properties of steel bars. In the high strain and short life range, both the static strength and ductility of steels are very important to increasing the low cycle fatigue resistance of steels. Graphs, photomicrographs, 4 refs.
Rolling contact fatigue damage in TiC- and TiN-coated steels. Mivoshi, Y., Ogura, K. and Kido, K. Journal ~[' the Society of Materials Science, Japan (1997), 46( 1), 77-83 The rolling contact fatigue of TiC- and TiN-coated steels (SKH51) was investigated. The damage was observed with a Scanning Acoustic Microscope (SAM). Measurements of X-ray residual stress and surface leaky wave velocity were also made to evaluate the damage. The SAM observation was useful to reveal the behaviour of delamination and crack propagation below the surface. The results obtained are as follows. (I) In the TiC-coated steel, cracks initiated at micro pits generated in the CVD process and propagated in a parallel direction to the rolling direction of balls at the interface between TiC film and the substrate. This resulted in the delamination and finally the peeling of TiC film. (2) In the TiN-coated steel, micro delamination appeared at spherical defects between the film and the substrate, and grew into macro delamination. The delamination expanded and finally TiN film on the delamination peeled off the substrate. (3) Both TiC and TiN films had an extremely large compressive residual stress. The progress of the film delamination caused an addtional compressive stress in the tangential direction of the rolling direction. The residuat stress measurement by X-ray was found to be effective for the evaluation of the contact fatigue damage of TiC- and TiN-coated steels. Graphs, photomicrographs, 9 ref.
Prediction of crack initiation life of converter shell based on stress analysis. Miyahara, M., Toyama, K. Tokimasa, K. and Kurihara, S. Journal of the Society of Materials Science, Jupan (1997) 46(I), 47-52 In order to clarify effective measures to extend a life converter shell in a steel production plant, the thermal fatigue crack initiation life was predicted by the strain range partitioning method. A three-dimensional FEM model of the converter which is composed of a shell and bricks was established. An inelastic strain of the shell caused by a thermal cycle during operation was evaluated by an elastic plastic-creep analysis. Since the thermal expansion of bricks is partly absorbed by a gap between bricks, the inelastic strain of the shell is affected by the gap size. Therefore, in the FEM model the hyperelastic element was used in order to describe the deformation behaviour of bricks and gaps, and the stress analysis was conducted taking the gap size into consideration. Based on the analytical results and creep-fatigue properties of the shell material, the crack initiation life of the shell was predicted. The relationship between the shell life and cooling conditions at the outer surface of the shell and the relationship between the shell life and the gap size were examined. The following results were obtained. (1) The predicted shell life corresponded well with that in the actual converter. (2) It is possible to extend the shell life by decreasing the maximum shell temperature which can be attained by increasing the film coefficient of cooling at the outer surface of the shell. (3) It is also possible to extend the shell life by increasing the gap size. Furthermore, the larger the gap size is, the decrease of shell temperature becomes more effective for the shell life extension. Shell material was a low alloy steel. Graphs. 12 ref.
Measurement of the distribution of cavities on grain boundary and evaluation of damage parameters of SUS304 stainless steel under creepfatigue condition. Tada, N., Fukuta, T,, Kitamura, T. and Ohtani, R. Journal of the Socie~' of Materials Science, Japan (1997) 46(I), 39-46 Creep-fatigue tests of SUS304 stainless steel were conducted and creep cavities initiated along grain boundaries inside the specimen were observed on the longitudinal cross-section by means of a scanning laser microscope. The results obtained were as follows. (i) The shape of cavities was almost spherical when they were small. (ii) There was no preferential direction of grain boundaries for the cavity initiation. (iii) Since cavities preferentially grew and coalesced along grain boundaries perpendicular to the stress axis direction, the shape
Fatigue Abstracts
Measurement of fluid flow rates through cracks. Clarke, L.V., Bainbridge, H., Beck, S.B.M. and Yates, J.R. btternational Journal of Pressure Vessels and Piping (1997) 71(1), 71-75
The preferred combination of primary and critical slip during cyclic deformation is also discussed in terms of dislocation reactions. Graphs, 40 ref.
An experimental study has been performed into leak rates through a series of cracked specimens. Semi-elliptic fatigue cracks were grown through aluminium plates and the flow of water was measured as a function of crack length and crack opening. Two relationships were found between volumtric flow rate and crack opening in the region of flow studied. For larger crack openings theoretical results obtained by modelling laminar flow between parallel planes corresponded well to the experimental data. At smaller crack openings, agreement was found with theoretical results obtained by modelling the pressure drop due to bends and changes in area. It was also found that below a threshold value of crack opening no flow occurred. Graphs, 16 ref.
The importance of uniformity in the application of the shot peening treatment. Straub. J. Shot Peener (1997) 11(1), 10 12
Fatigue crack growth of Ni3AI(CrB) single crystals at ambient and elevated temperatures. Zhang, G.P., Wang, Z.G. and Li, G.Y. Acre Materialia (1997) 45,(4), 1705 1714 Fatigue crack propagation behaviour of compact tension specimens of Ni3AI(CrB) single crystals has been examined at room temperature and elevated temperature. The results indicated that crystallographic cracking occurs on two or more { I l l / planes simultaneously at room temperature. With increasing temperature, the cube slip plane becomes active and plays an important role in determining the cracking path. Orientation and temperature dependence of the fatigue crack initiation threshold from the notch root exists. Similar to the flow stress, the crack initiation threshold increases with temperature, and the threshold for (100)[010] orientation is higher than that for (110)[110]. Both orientation and temperature affect the fatigue crack growth rates (FCGRs). The FCGRs of (00)[010] are higher than that of (110)[110] in the Paris regime. A crystallographic relationship between the primary crack plane and the secondary slip plane ahead of the crack tip is suggested to explain the dependence of FCGRs on orientation. The oxidation embrittlement at the crack tip and the activated cube slip should be responsible for the acceleration of FCGRs in the Paris regime and the oxide-induced crack closure has a significant effect on the deceleration of FCGRs in the near-threshold regime at elevated temperatures. Both the relationship of orientations between octahedrat slip planes and the applied load axis and the increasing activity of the cube slip plane with temperature determine the significant variation of fracture path with temperature. Graphs, photomicrographs, 26 ref,
Cyclic deformation behaviour and dislocation structures of [001] copper single crystals. II. Characteristics of dislocation structures. Wang, Z., Gong, B. and Wang, Z. Acre Materialia (1997) 45(4), 1379-1391 The dislocation structure of [001] Cu single crystals developed in cyclic deformation has been systematically studied with transmission electron microscopy and related to the mechanical behaviour presented previously. The dislocation configuration for this orientation is characterized by labyrinth structures over all the strain amplitudes investigated. At high strain amplitudes (3'p~= 1.8 x 10 ~-3.0 x 10 3), additional structures such as exclusive walls and strips were observed. The strips are parallel to {111} slip planes and are associated with macro-deformation bands reported previously. At low strain amplutudes ('Ypt< = 2.4 x 10-4), however, labyrinth becomes irregular in geometrical shape. Labyrinth structures consist of two types of perpendicular walls: one is always parallel to (00t) plane and the other may be (100), (210) or (120). The characteristic dimension of labyrinths, such as channel width, increases with decreasing applied strain amplitude. The nature of dislocations in labyrinth structures was identified to be mainly primary and critical dislocations. The role of labyrinth structures in cyclic deformation was discussed in terms of geometrical considerations. It has been shown that labyrinth structures are more favourable to cyclic deformation by promoting multiple slip and cross slip. Finally, the cyclic saturation stress was quantitatively correlated with the microparameter of labyrinth structures. Photomicrographs, 35 ref.
Cyclic deformation behaviour and dislocation structures of [001] copper single crystals. I. Cyclic stress-strain response and surface feature. Wang, Zh., Gong, B. and Wang, Z. Acta Materialia (1997) 45(4), 1365-1377 Cyclic deformation behaviour of [001] copper single crystals was investigated in symmetrical pull-push fatigue tests at the ambient temperature and with constant plastic shear strain amplitudes (Tp0 in the range of 1.0× 10-4 to 3.0 × 10 3. The formation and development of surface slip bands (SBs) were examined in situ by a light microscope. A rapid initial hardening stage followed by a pronounced overshooting or significant softening was found with the crystals tested at "Ypr> = 4 . 8 x 10 4. The cyclic stress-strain curve of [001] crystals does not show any plateau behaviour, instead it follows, if corrected with the Taylor factor the power law function for copper polycrystals. The fatigue limit, defined as the critical strain amplitude below which SBs do not form, was found to be ~1.7 x 10-4, a value much higher than that for single slip oriented crystals, but very close to that for polycrystals modified by the Taylor factor. In situ observation revealed that the primary SBs appeared at the very beginning of cyclic deformation and frequently they were not persistent. The secondary (critical) SBs usually formed at the overshooting stage after rapid hardening. Deformation bands with the characteristics of kink bands were detected in the final stage of the cyclic deformation. Analysis indicated that the rapid initial cyclic hardening is caused by the formation of L o m e ~ Cottrell locks, while the overshooting/softening behaviour is related to the operation of secondary slip or the formation of dislocation labyrinth structure.
The effects of shot peening uniformity on fatigue life were investigated on specimens of 9260 steel. Unpeened specimens were compared in bend tests with specimens peened using only whole shot and with both whole and broken shot. Fatigue life was practically unchanged by peening with broken shot after peening with whole shot; also fatigue life was greater for a group of specimens peened with whole shot than for a group peened with the same arc height and coverage but with broken shot. Graphs.
Investigation of low cycle fatigue behaviour of building structural steels under earthquake loading. Sheng, G.M. and Gong, S.H. Acre Metallurgica Sinica (English Letters) (1997) 10(1), 51-55 Based on the failure model of building structural steels under earthquake loading, the low cycle fatigue test at constant strain, the stochastical fatigue test under real earthquake load spectrum and the structural fatigue test are carried out. The experimental results showed that microalloying of V, Ti and Nb can improve the anti-seismic properties of steel bars. In the high strain and short life range, both the static strength and ductility of steels are very important to increasing the low cycle fatigue resistance of steels. Graphs, photomicrographs, 4 refs.
Rolling contact fatigue damage in TiC- and TiN-coated steels. Mivoshi, Y., Ogura, K. and Kido, K. Journal ~[' the Society of Materials Science, Japan (1997), 46( 1), 77-83 The rolling contact fatigue of TiC- and TiN-coated steels (SKH51) was investigated. The damage was observed with a Scanning Acoustic Microscope (SAM). Measurements of X-ray residual stress and surface leaky wave velocity were also made to evaluate the damage. The SAM observation was useful to reveal the behaviour of delamination and crack propagation below the surface. The results obtained are as follows. (I) In the TiC-coated steel, cracks initiated at micro pits generated in the CVD process and propagated in a parallel direction to the rolling direction of balls at the interface between TiC film and the substrate. This resulted in the delamination and finally the peeling of TiC film. (2) In the TiN-coated steel, micro delamination appeared at spherical defects between the film and the substrate, and grew into macro delamination. The delamination expanded and finally TiN film on the delamination peeled off the substrate. (3) Both TiC and TiN films had an extremely large compressive residual stress. The progress of the film delamination caused an addtional compressive stress in the tangential direction of the rolling direction. The residuat stress measurement by X-ray was found to be effective for the evaluation of the contact fatigue damage of TiC- and TiN-coated steels. Graphs, photomicrographs, 9 ref.
Prediction of crack initiation life of converter shell based on stress analysis. Miyahara, M., Toyama, K. Tokimasa, K. and Kurihara, S. Journal of the Society of Materials Science, Jupan (1997) 46(I), 47-52 In order to clarify effective measures to extend a life converter shell in a steel production plant, the thermal fatigue crack initiation life was predicted by the strain range partitioning method. A three-dimensional FEM model of the converter which is composed of a shell and bricks was established. An inelastic strain of the shell caused by a thermal cycle during operation was evaluated by an elastic plastic-creep analysis. Since the thermal expansion of bricks is partly absorbed by a gap between bricks, the inelastic strain of the shell is affected by the gap size. Therefore, in the FEM model the hyperelastic element was used in order to describe the deformation behaviour of bricks and gaps, and the stress analysis was conducted taking the gap size into consideration. Based on the analytical results and creep-fatigue properties of the shell material, the crack initiation life of the shell was predicted. The relationship between the shell life and cooling conditions at the outer surface of the shell and the relationship between the shell life and the gap size were examined. The following results were obtained. (1) The predicted shell life corresponded well with that in the actual converter. (2) It is possible to extend the shell life by decreasing the maximum shell temperature which can be attained by increasing the film coefficient of cooling at the outer surface of the shell. (3) It is also possible to extend the shell life by increasing the gap size. Furthermore, the larger the gap size is, the decrease of shell temperature becomes more effective for the shell life extension. Shell material was a low alloy steel. Graphs. 12 ref.
Measurement of the distribution of cavities on grain boundary and evaluation of damage parameters of SUS304 stainless steel under creepfatigue condition. Tada, N., Fukuta, T,, Kitamura, T. and Ohtani, R. Journal of the Socie~' of Materials Science, Japan (1997) 46(I), 39-46 Creep-fatigue tests of SUS304 stainless steel were conducted and creep cavities initiated along grain boundaries inside the specimen were observed on the longitudinal cross-section by means of a scanning laser microscope. The results obtained were as follows. (i) The shape of cavities was almost spherical when they were small. (ii) There was no preferential direction of grain boundaries for the cavity initiation. (iii) Since cavities preferentially grew and coalesced along grain boundaries perpendicular to the stress axis direction, the shape