- Email: [email protected]
Dislocation structure and corduroy contrast in a 316L alloy fatigued at (0.3–0.5) Tm
Fatigue Abstracts impact loading theoretically derived. 35CrMoV and 20Cr2Ni4A steels are discussed. Graphs, 8 ref. Creep and fatigue properties in modified IMI 834 high-temperature titanium alloy. Matsumoto, T. Kobe Res Dev (Apr 1993) 43 (2), 103-106 (in Japanese)
By replacing niobium in IMI 834, one of the most advanced high-temperature titanium alloys with lwt% tantalum, creep strengths tested up to 6(100C were greatly improved. This new Ti alloy also showed equal or superior high-cycle and low-cycle fatigue strength compared to IMI 834. One possibility suggested is that the new alloy, including IMI 834, may be improved in fatigue strength by lowering carbon to an appropriate content in consideration of creep strength. Graphs, photomicrographs, 4 ref. Dynamical model of the wall structure in persistent slip bands of fatigued metals. I. Dynamical model of edge dislocation walls. Differt, K. and Essmann, U. Mater Sci Eng A (30 May 1993) A164 (1-2), 295-299 A set of partial non-linear differential equations is suggested which describe the dislocation walls in persistent slip bands of fatigued metals. The stationary solution yields the shape of the walls, which consist of well-separated edge dislocation dipoles. The distribution function of the dipole heights is calculated. There exists a solitary solution, which can be associated with the movement of the walls. Graphs, 15 ref. Dislocation structure and corduroy contrast in a 316I, alloy fatigued at (0.3-0.5) T~. Gerland, M., Mendez, J., Lepinoux, J. and Violan, P. Mater Sci Eng A (30 May 1993) A164 (1-2) 226-229 An austenitic stainless steel 316L was fatigued under vacuum at intermediate temperatures. At 300 °C the fatigue life of this alloy is much higher than at room temperature or at 60&C. This behaviour is associated with the occurrence of the Portevin-LeChatelier effect and with the presence of a corduroy contrast and a corduroy dislocation microstructure. These different features are described and a coherent explanation is proposed. Graphs, photomicrographs, 13 ref. Transformation of dislocation patterns in fatigued copper single crystals. Holzwarth, U. and Essmann, U. Mater Sci Eng A (30 May 1993) A164 (1-2), 206-210
The transition from the so-called matrix to persistent slip bands (PSBs) during the fatigue of copper single crystals and the transition of the dislocation arrangement of PSBs formed at 300 K to that characteristic for a deformation temperature of 77 K have been investigaged by cyclic deformation tests and transmission electron microscopy. Strain localization occurs well before the first fragments of the typical ladder-like dislocation arrangement of PSBs can be identified. The results indicate that the motion of dislocation walls plays an important role in establishing the ladder-like dislocation arrangement. After a sharp decrease of the deformation temperature at constant amplitude of resolved plastic shear strain, only a certain volume fraction of the PSBs remains active, but with a larger intrinsic amplitude of plastic shear strain. Photomicrographs, graphs, 24 ref. Intrinsic fatigue crack growth rates for AI-LI-Cu-Mg alloys in vacuum. Slavik, D.C., Starke, E.A. Jr, Gangloff, R.P. and Blankemhip, C.P. Jr Metall Trans A (Aug 1993) 24A (8) 1807-1817 The influences of microstructure and deformation mode on inert environment intrinsic fatigue crack propagation were investigated for A I - L i - C u - M g alloys AA2090, AA8090 and X2095, compared to AA2024. The amount of coherent shearable A' (A13Li) precipitates and extent of localized planar slip deformation were reduced by composition (increased Cu/Li in X2095) and heat treatment (double ageing of AA8090). Intrinsic growth rates, obtained at high constant K,,~, to minimize crack closure and in vacuum to eliminate any environmental effect, were alloy dependent; da/dN varied up to tenfold based on applied AK or Ak/E. When compared based on a crack tip cyclic strain or opening displacement parameter (AK/(cry~ Et)), growth rates were equivalent for all alloys except X2095-T8, which exhibited unique fatigue crack growth resistance. Tortuous fatigue crack profiles and large fracture surface facets were observed for each AI-Li alloy independent of the
302
Fatigue, 1994, Vol 16, June
precipitates present, particularly A', and the localized slip deformation structure. Reduced fatigue crack propagation rates for X2095 in vacuum are not explained by either residual crack closure or slip reversibility arguments; the origin of apparent slip band facets in a homogeneous slip alloy is unclear. Better understanding of crack tip damage accumulation and fracture surface facet crystallography is required for A1-Li alloys with varying slip localization. Photomicrographs, graphs, 52 ref. Small fatigue crack behavior in 7075-T651 aluminum as monitored with Rayleigh wave reflection. Hirao, M., Tojo, K. and Fukuoka, H. Metall Trans A (Aug 1993) 24A (8), 1773-1783 Small fatigue crack growth in 7075-T651 aluminium is periodically monitored with an ultrasonic Rayleigh wave technique. The wideband reflection signals are digitized and stored in the computer memory to permit signal processing in the frequency domain. With the help of the constructed three-dimensional reflection coefficient, the reflection amplitude spectra yield the measurements of the crack depth, if >0.062 mm, and the crack closure stress. Acoustically obtained da/dN-AK~ff relations describe the anomalous growth behaviour of small surface cracks, extending from the late small crack regime to the large crack regime passing through the minimum growth rate. The split spectrum processing proves to be useful in removing the grain noises to illuminate the target echoes, which is necessary to detect the nucleation and characterize cracks < 0.1 mm in depth. Discussions on the computer-controfled, automated, in situ monitoring system are provided. Photomicrographs, spectra, graphs, 29 ref. The cyclic deformation and fatigue behaviour of the low carbon steel SAE 1045 in the temperature regime of dynamic strain ageing. Weisse, M.,
Wamukwamba, C.K. Christ, H.-J. and Mughrabi, H. Acta Metall Mater (July 1993) 41 (7), 2227-2233 The cyclic deformation behaviour of normalized SAE 1045 steel (German steel grade Ck 45) has been investigated over a range of temperatures between 20 and 375°C. Special attention has been paid to the effects of dynamic strain ageing, which are most pronounced at approx 300~C. Different types of deformation tests (tension tests, incremental step tests, and constant amplitude cyclic deformation tests under stress control with a stress amplitude of 400 MPa as well as under plastic strain control with a plastic strain amplitude of 0.5%) were performed to observe the influence of temperature on the macroscopic mechanical behaviour. These tests were followed by TEM studies on microstructural features. In the temperature range of maximum dynamic strain ageing, the material was found to show maximum strength in unidirectional as well as in cyclic deformation tests. While the fatigue life is maximum at the temperature of maximum dynamic strain ageing in stress-controlled tests, it is minimum in plastic strain controlled tests. At the temperature of maximum dynamic strain ageing, approx 3000C, the dislocations are arranged in dense dislocation tangles and parallel dislocation walls, whereas at room and at higher temperatures (375°C) mainly dislocation cell structures are observed. Graphs, photomicrographs, 18 ref. Structural failures: causes, prevention, and misinterpretation. Barsom, J.M. Mater Charact (July 1993) 31 (1), 19-32
Observations on causes and prevention of failures in structural and equipment components are presented that are related to the initiation and propagation of fatigue cracks. Some of these observations are illustrated by using actual failures. A discussion of some common misconceptions and misinterpretations that have led to incorrect conclusions in failure investigations is outlined. A36 and A572 Gr.50 steels and an aluminium alloy are discussed. Photomicrographs, graphs, 9 ref. Gulliver among the atoms. Gillan, M. New Scientist (Apr 1993) 138 (1867), 34-37
By using the basic laws of quantum mechanics to create computed simulations of matter on the atomic scale, realistic electron's-eye views of solids and liquids may be created. An imaginary cluster of approx 50 atoms is enough to initiate the properties of real substances. Modern parallel computing techniques have simulated a system of 400 atoms the 7 × 7 reconstruction on the surface of silicon. As parallel computers are developed, simulations on thousands of atoms will become possible, allowing studies of such processes as metal fatigue and catalysis on Pt.
By replacing niobium in IMI 834, one of the most advanced high-temperature titanium alloys with lwt% tantalum, creep strengths tested up to 6(100C were greatly improved. This new Ti alloy also showed equal or superior high-cycle and low-cycle fatigue strength compared to IMI 834. One possibility suggested is that the new alloy, including IMI 834, may be improved in fatigue strength by lowering carbon to an appropriate content in consideration of creep strength. Graphs, photomicrographs, 4 ref. Dynamical model of the wall structure in persistent slip bands of fatigued metals. I. Dynamical model of edge dislocation walls. Differt, K. and Essmann, U. Mater Sci Eng A (30 May 1993) A164 (1-2), 295-299 A set of partial non-linear differential equations is suggested which describe the dislocation walls in persistent slip bands of fatigued metals. The stationary solution yields the shape of the walls, which consist of well-separated edge dislocation dipoles. The distribution function of the dipole heights is calculated. There exists a solitary solution, which can be associated with the movement of the walls. Graphs, 15 ref. Dislocation structure and corduroy contrast in a 316I, alloy fatigued at (0.3-0.5) T~. Gerland, M., Mendez, J., Lepinoux, J. and Violan, P. Mater Sci Eng A (30 May 1993) A164 (1-2) 226-229 An austenitic stainless steel 316L was fatigued under vacuum at intermediate temperatures. At 300 °C the fatigue life of this alloy is much higher than at room temperature or at 60&C. This behaviour is associated with the occurrence of the Portevin-LeChatelier effect and with the presence of a corduroy contrast and a corduroy dislocation microstructure. These different features are described and a coherent explanation is proposed. Graphs, photomicrographs, 13 ref. Transformation of dislocation patterns in fatigued copper single crystals. Holzwarth, U. and Essmann, U. Mater Sci Eng A (30 May 1993) A164 (1-2), 206-210
The transition from the so-called matrix to persistent slip bands (PSBs) during the fatigue of copper single crystals and the transition of the dislocation arrangement of PSBs formed at 300 K to that characteristic for a deformation temperature of 77 K have been investigaged by cyclic deformation tests and transmission electron microscopy. Strain localization occurs well before the first fragments of the typical ladder-like dislocation arrangement of PSBs can be identified. The results indicate that the motion of dislocation walls plays an important role in establishing the ladder-like dislocation arrangement. After a sharp decrease of the deformation temperature at constant amplitude of resolved plastic shear strain, only a certain volume fraction of the PSBs remains active, but with a larger intrinsic amplitude of plastic shear strain. Photomicrographs, graphs, 24 ref. Intrinsic fatigue crack growth rates for AI-LI-Cu-Mg alloys in vacuum. Slavik, D.C., Starke, E.A. Jr, Gangloff, R.P. and Blankemhip, C.P. Jr Metall Trans A (Aug 1993) 24A (8) 1807-1817 The influences of microstructure and deformation mode on inert environment intrinsic fatigue crack propagation were investigated for A I - L i - C u - M g alloys AA2090, AA8090 and X2095, compared to AA2024. The amount of coherent shearable A' (A13Li) precipitates and extent of localized planar slip deformation were reduced by composition (increased Cu/Li in X2095) and heat treatment (double ageing of AA8090). Intrinsic growth rates, obtained at high constant K,,~, to minimize crack closure and in vacuum to eliminate any environmental effect, were alloy dependent; da/dN varied up to tenfold based on applied AK or Ak/E. When compared based on a crack tip cyclic strain or opening displacement parameter (AK/(cry~ Et)), growth rates were equivalent for all alloys except X2095-T8, which exhibited unique fatigue crack growth resistance. Tortuous fatigue crack profiles and large fracture surface facets were observed for each AI-Li alloy independent of the
302
Fatigue, 1994, Vol 16, June
precipitates present, particularly A', and the localized slip deformation structure. Reduced fatigue crack propagation rates for X2095 in vacuum are not explained by either residual crack closure or slip reversibility arguments; the origin of apparent slip band facets in a homogeneous slip alloy is unclear. Better understanding of crack tip damage accumulation and fracture surface facet crystallography is required for A1-Li alloys with varying slip localization. Photomicrographs, graphs, 52 ref. Small fatigue crack behavior in 7075-T651 aluminum as monitored with Rayleigh wave reflection. Hirao, M., Tojo, K. and Fukuoka, H. Metall Trans A (Aug 1993) 24A (8), 1773-1783 Small fatigue crack growth in 7075-T651 aluminium is periodically monitored with an ultrasonic Rayleigh wave technique. The wideband reflection signals are digitized and stored in the computer memory to permit signal processing in the frequency domain. With the help of the constructed three-dimensional reflection coefficient, the reflection amplitude spectra yield the measurements of the crack depth, if >0.062 mm, and the crack closure stress. Acoustically obtained da/dN-AK~ff relations describe the anomalous growth behaviour of small surface cracks, extending from the late small crack regime to the large crack regime passing through the minimum growth rate. The split spectrum processing proves to be useful in removing the grain noises to illuminate the target echoes, which is necessary to detect the nucleation and characterize cracks < 0.1 mm in depth. Discussions on the computer-controfled, automated, in situ monitoring system are provided. Photomicrographs, spectra, graphs, 29 ref. The cyclic deformation and fatigue behaviour of the low carbon steel SAE 1045 in the temperature regime of dynamic strain ageing. Weisse, M.,
Wamukwamba, C.K. Christ, H.-J. and Mughrabi, H. Acta Metall Mater (July 1993) 41 (7), 2227-2233 The cyclic deformation behaviour of normalized SAE 1045 steel (German steel grade Ck 45) has been investigated over a range of temperatures between 20 and 375°C. Special attention has been paid to the effects of dynamic strain ageing, which are most pronounced at approx 300~C. Different types of deformation tests (tension tests, incremental step tests, and constant amplitude cyclic deformation tests under stress control with a stress amplitude of 400 MPa as well as under plastic strain control with a plastic strain amplitude of 0.5%) were performed to observe the influence of temperature on the macroscopic mechanical behaviour. These tests were followed by TEM studies on microstructural features. In the temperature range of maximum dynamic strain ageing, the material was found to show maximum strength in unidirectional as well as in cyclic deformation tests. While the fatigue life is maximum at the temperature of maximum dynamic strain ageing in stress-controlled tests, it is minimum in plastic strain controlled tests. At the temperature of maximum dynamic strain ageing, approx 3000C, the dislocations are arranged in dense dislocation tangles and parallel dislocation walls, whereas at room and at higher temperatures (375°C) mainly dislocation cell structures are observed. Graphs, photomicrographs, 18 ref. Structural failures: causes, prevention, and misinterpretation. Barsom, J.M. Mater Charact (July 1993) 31 (1), 19-32
Observations on causes and prevention of failures in structural and equipment components are presented that are related to the initiation and propagation of fatigue cracks. Some of these observations are illustrated by using actual failures. A discussion of some common misconceptions and misinterpretations that have led to incorrect conclusions in failure investigations is outlined. A36 and A572 Gr.50 steels and an aluminium alloy are discussed. Photomicrographs, graphs, 9 ref. Gulliver among the atoms. Gillan, M. New Scientist (Apr 1993) 138 (1867), 34-37
By using the basic laws of quantum mechanics to create computed simulations of matter on the atomic scale, realistic electron's-eye views of solids and liquids may be created. An imaginary cluster of approx 50 atoms is enough to initiate the properties of real substances. Modern parallel computing techniques have simulated a system of 400 atoms the 7 × 7 reconstruction on the surface of silicon. As parallel computers are developed, simulations on thousands of atoms will become possible, allowing studies of such processes as metal fatigue and catalysis on Pt.