| 1. |
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| 2. |
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| 3. |
- Ahlström, Johan, 1969, et al.
(author)
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Fatigue behaviour of rail steel - a comparison between strain and stress controlled loading
- 2005
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In: Wear. - : Elsevier BV. - 0043-1648. ; 258:7-8, s. 1187-1193
-
Journal article (peer-reviewed)abstract
- Strain and stress-controlled fatigue testing of rail material UIC grade 900A has been performed. The tests were carried out in uniaxial, constant amplitude push-pull loading on polished test bars. Strain-controlled experiments were performed at 0.4, 0.6 and 1.0% total strain amplitude. Two identical tests at each strain level were made and the results show very little spread:
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| 4. |
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| 5. |
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| 6. |
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| 7. |
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| 8. |
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| 9. |
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| 10. |
- Ahlström, Johan, 1969, et al.
(author)
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Modified Railway Wheel Steels: Production and Evaluation of Mechanical Properties with Emphasis on Low-Cycle Fatigue Behavior
- 2009
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In: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 40A:7, s. 1557-1567
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Journal article (peer-reviewed)abstract
- Railway wheels are exposed to high mechanical and thermal loads. The objective of this study has been to develop wheels that are more resistant to damage from these loads. Fourteen different materials have been produced in the form of full-scale railway wheels. Parameters that have been varied include the chemical composition, production processes, and heat treatment. The materials have been investigated microstructurally and by hardness, tensile, and impact toughness testing. In addition, the low-cycle fatigue (LCF) behavior has been characterized at room temperature and at subzero temperatures. The results indicate improvement in microstructure and mechanical properties for some materials and it is probable that these materials would endure better in service. © The Minerals, Metals & Materials Society and ASM International 2009.
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| 11. |
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| 12. |
- Ahlström, Johan, 1969, et al.
(author)
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Short-time tempering kinetics of quench hardened pearlitic steels
- 2010
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In: Conference proceedings ICTPMCS-2010, 31 May – 2 June 2010, Shanghai, China. ; , s. 6 pp-
-
Conference paper (peer-reviewed)abstract
- In many industrial processes such as welding, and operating environments like railway wheel/rail contact, certain material volumes are exposed to very short temperature pulses that endure for times of the order of 1 s or shorter. When pearlitic steel is exposed to temperatures above the effective austenitisation temperature, martensite forms upon rapid cooling. In the current work tempering of a martensitic carbon steel was performed, with a laser heat source to create short time top-hat temperature pulses, and also with conventional salt bath experiments for longer tempering times. Temperatures were varied in the range of 500 to 700°C, and times between 0.05 to 3000 s. It was found that the martensitic test samples showed a very rapid initial softening upon tempering. During the first 0.1 second the hardness decrease was measured to 35-55% in the tested temperature range. Thereafter the additional hardness decrease was limited to ~10-15% of the original hardness, even after 30 min of tempering. Thus the use of time-temperature models for predicting tempering properties, that relies on constant or linear dependence of the activation energy cannot be extrapolated to very short time processes.
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| 13. |
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| 14. |
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| 15. |
- Cao, Yu, 1969, et al.
(author)
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Mechanical Behaviour of a Rephosphorized Steel for Car Body Applications — Effects of Temperature, Strain Rate and Pre-treatment
- 2011
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In: Journal of Engineering Materials and Technology, Transactions of the ASME. - : ASME International. - 1528-8889 .- 0094-4289. ; 133:2, s. 021019-1 - 021019-11-
-
Journal article (peer-reviewed)abstract
- Temperature and strain rate effects on the mechanical behaviour of a commercial rephosphorized, interstitial free steel have been investigated by uniaxial tensile testing, covering applicable temperatures (-60 – +100°C) and strain rates (1•10-4 – 1•102 s-1) experienced in automotive crash situations. The effect of prestraining to 3.5 % with or without successive annealing at 180°C for 30 min has also been evaluated. These treatments were used to simulate pressing of the plates and the paint-bake cycle in the production of car bodies. Yield and ultimate tensile strengths, ductility including uniform and total elongation and area reduction, thermal softening effect at high strain rate and strain rate sensitivity of stress were determined and discussed in all cases. It was found that the Voce equation [σ = σs- (σs -σ0) exp (ε/ε0)] can be fitted to the experimental true stress-true plastic strain data with good precision. The parameter values in this equation were evaluated and discussed. Furthermore, temperature and strain rate effects were examined in terms of thermal and athermal components of the flow stresses. Finally, a thermal activation analysis was performed.
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| 16. |
- Cao, Yu, 1969, et al.
(author)
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Temperature and strain rate effects on the mechanical behavior of dual phase steel
- 2015
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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 636, s. 124-132
-
Journal article (peer-reviewed)abstract
- The effect of temperature and strain rate on the mechanical behavior of a commercial dual phase steel (DP 800) has been investigated experimentally by uniaxial tensile tests in this study, covering temperatures (−60 °C to 100 °C) and strain rates (1×10–4 to 1×10+2 s−1) encompassing conditions experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity have been determined and discussed. It was found that the Voce equation [σ=σs−(σs−σ0)exp(−εθ0/σs))] can be satisfactorily applied to describe the tensile flow curves by means of a modified Kocks–Mecking model. In this model the parameter θ0 is fixed, whereas both σ0 and σs consist of athermal and thermal stress components. The athermal component is only weakly dependent on temperature through the elastic shear modulus μ. The thermal stress component is governed by temperature and strain rate. Statistical analysis based on the experimental data has allowed all parameters in the Voce equation to be quantified.
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| 17. |
- Cao, Yu, 1969, et al.
(author)
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The influence of temperatures and strain rates on the mechanical behavior of dual phase steel in different conditions
- 2015
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In: Journal of Materials Research and Technology. - : Elsevier BV. - 2238-7854. ; 4:1, s. 68-74
-
Journal article (peer-reviewed)abstract
- This study deals with the mechanical behavior of DP steel. A commercial dual phase steel (DP 800) was strained to 3.5% followed by annealing at 180 degrees C for 30 min to simulate the pressing of the plates and the paint bake cycle involved in the manufacturing process of automobile body structures. The effect of temperarure and strain rate on the machanical behavior of this material was investigated by uniaxial tensile tests, covering applicable temperatures (-60 degree C to +100 degree C) and strain rates (1x10exp-4 s-1 to 1x10exp+2 s-1) experienced in automotive crash situations. Yield and ultimate tensile strength, ductility, temperature effects and strain rate sensitivity as well as strain rate hardening rate have been determined and discussed.
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| 18. |
- Cvetkovski, Krste, 1983, et al.
(author)
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Influence of short heat pulses on properties of martensite in medium carbon steels
- 2013
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In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 561, s. 321-328
-
Journal article (peer-reviewed)abstract
- The process of tempering a martensitic medium carbon steel was investigated with the aim to study resulting material properties. The experimental results were used to model residual stresses caused by local heating, with the finite element method. Tempering was followed for times from 0.1 s up to 1 h by using laser heating and conventional salt bath furnace treatments within the temperature interval 500–700 °C. In addition, the thermal expansion was evaluated using dilatometry. Experiments showed that the initial stages of martensite decomposition, associated with loss of crystal tetragonality, proceed almost instantly. An initial large decrease of hardness within the first tenth of a second of the tempering process was measured, followed by only limited further softening with increased tempering time. Thus for the current material the tempering time had limited influence on hardness, governed primarily by the peak temperature during the heating process. Finite element modelling of rapid local heating and cooling showed that the tempering behaviour and associated dilatation effects yield a peak temperature dependent residual stress field with a broad tensile stress distribution for the case of un-tempered martensite. However, for tempered martensite the residual stress field depends primarily on the heating rate and peak temperature and shows large gradients with tensile stresses in the surface and compressive below. Thereby, for both cases, residual stresses were obtained but with completely different residual stress gradients.
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| 19. |
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| 20. |
- Cvetkovski, Krste, 1983, et al.
(author)
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Monotonic and cyclic deformation of a high silicon pearlitic wheel steel
- 2011
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In: Wear. - : Elsevier BV. - 0043-1648. ; 271:1-2, s. 382-387
-
Journal article (peer-reviewed)abstract
- The development of railway wheel steel grades has gone towards higher strength to enhance rolling contact fatigue resistance and ability to withstand thermally induced damage throughout the service lifetime. In this study a recently developed wheel steel material for passenger trains containing high levels of manganese and silicon, approximately 1 wt% of each, was tested in low cycle fatigue at different total strain amplitudes. In addition, monotonic tensile and Charpy V-notch impact testings in the temperature range −60 °C to 180 °C were performed. The results were compared to another steel grade commonly used in Europe for railway wheels. The low cycle fatigue results show similar cyclic lifetime Nf, and fatigue stress amplitude development for both materials, but the highly alloyed steel exhibits reduced cyclic softening and hardening during the fatigue life and is in this respect more stable in its behaviour. As is typical for pearlitic–ferritic steels both materials show a pronounced monotonic strain hardening. It was concluded that the increased levels of manganese and silicon have minor effects on monotonic behaviour but substantial influence on cyclic behaviour at ambient temperatures. At increased temperatures, though, there are indications of additional effects on monotonic behaviour. However, the high temperature properties have to be investigated further to gain full understanding of mechanisms and effects.
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| 21. |
- Cvetkovski, Krste, 1983, et al.
(author)
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Thermal degradation of pearlitic steels: influence on mechanical properties including fatigue behaviour
- 2011
-
In: Materials Science and Technology. - 1743-2847 .- 0267-0836. ; 27:3, s. 648-654
-
Journal article (peer-reviewed)abstract
- With the aim to predict the durability of railway wheels, thermomechanical damage was studiedfor two steels with different alloying levels of silicon and manganese in the temperature range of500–725uC. Softening caused by cementite spheroidisation in pearlite leads to changes in themechanical behaviour and an accompanying decrease in fatigue lifetimes. It was found thathigher contents of Si and Mn lead to better resistance to softening of both virgin and plasticallydeformed material. Correspondingly, the high Si–Mn alloyed steel loses much less in fatiguelifetime than the lower alloyed steel.
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| 22. |
- Cvetkovski, Krste, 1983, et al.
(author)
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Thermal softening of fine pearlitic steel and its effect on the fatigue behaviour
- 2010
-
In: Procedia Engineering: 10th International Fatigue Congress, FATIGUE 2010; Prague; Czech Republic; 6 June 2010 through 11 June 2010. - : Elsevier BV. - 1877-7058. ; 2:1, s. 541-545
-
Conference paper (peer-reviewed)abstract
- Associated with the durability of railway wheelsets, thermal damage was studied for two different steels in the temperature range 500 °C to 725 °C. Softening caused by cementite spheroidisation in the pearlitic materials leads to changes in the mechanical behaviour. It was found that higher contents of silicon and manganese leads to better resistance to softening. Correspondingly, softening leads to loss in fatigue life times at given stress amplitudes as read out from Wöhler curves. However the higher alloyed steel looses much less in fatigue life time than the less alloyed steel.
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| 23. |
- Dahlström, Gunnar, et al.
(author)
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FÖR HJÄRTAT OCH SNILLET - om Kungl. Samhällets emblem
- 2012
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In: KVVS Årsbok 2012, pp. 119-128. - 0436-113X. ; , s. 119-128
-
Journal article (other academic/artistic)abstract
- Emblem och sigill har förekommit i Kungl. Samhället från dess tillblivelse på 1770-talet. Minnespenningar och minnesmedaljer var ofta förekommande under akademiens tidigare år för att därefter bli alltmer ovanliga. Under de senaste årtiondena har emblem åter kommit i mer omfattande bruk, i samklang med det övriga samhällets tilltagande intresse av emblem och logotyper. I uppsatsen med tyngdpunkten på de senaste 25 åren beskrivs Kungl. Samhällets emblem, minnesmedalj, ledamotnål och ordförandekedja. De språkvarianter som här förekommer är svenska, latin och runor, men märkligt nog inte engelska.
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| 24. |
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| 25. |
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| 26. |
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| 27. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Influence of overloading on fatigue durability and stability of the residual stresses in shot peened normalized steel
- 2011
-
In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; 528:24, s. 7323-7330
-
Journal article (peer-reviewed)abstract
- The present investigation deals with the effect of overloads on the stress relaxation and fatigue life time of shot-peened near-pearlitic steels. Single cycles with a total strain amplitude of 0.6 % with start in tension or compression were exerted either at the very beginning or after 1000 cycles and superimposed on the constant total strain amplitude test at 0.3 %. The results were compared with the constant amplitude test data. It was shown that such overloading can reduce the fatigue life time by 25%-60% of the life time obtained in constant amplitude tests. Maximum amount of reduction was obtained in overloading histories started with straining in tension. The stress amplitudes and corresponding mean stress development after overloading were also recorded and used to interpret the effects of overloads on the fatigue life times. In addition the residual stress relaxation throughout the whole lifetime was followed.
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| 28. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Influence of shot peening on fatigue durability of decarburized spring steels
- 2011
-
In: Proceeding of international shot peening conference (ICSP 11). - 9780615497235 ; , s. 183-188
-
Conference paper (peer-reviewed)abstract
- The influence of shot peening on high cycle fatigue behaviour of spring steel was investi-gated. The material studied was a quenched and tempered carbon steel 51SiCr7 (0.55 C, 1.9 Si and 0.9 Mn). Three series of fatigue specimens with zero, 0.15 and 0.45 mm depth of decarburization were produced. Half of the specimens from each series were shot peened, leading to a thickness of the compressed surface layer of about 0.25 mm. The specimens were tested in bending fatigue. A 45% improvement in fatigue limit of the decarburized series was achieved after shot peening. The detail of relaxation of the residual stresses was followed and compared for different series of specimens.
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| 29. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Influence of shot peening on fatigue durability of normalized steel subjected to variable amplitude loading
- 2012
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In: International Journal of Fatigue. - : Elsevier BV. - 0142-1123. ; 38:May 2012, s. 75-83
-
Journal article (peer-reviewed)abstract
- The influence of shot peening on the fatigue durability of normalized carbon steels subjected to variable amplitude loading has been investigated. The relaxation of residual stresses was recorded during the fatigue life time. Strain amplitude spectra were extracted from real spectra recorded from components in service. The results were compared with data achieved from constant amplitude testing. In both types of tests parallel studies were made on both peened and unpeened specimens. Shot peening leads to pronounced increase in life time, especially for smaller amplitudes. For both variable and constant amplitude loading shot peened specimens exhibit longer life provided the residual stresses during fatigue loading do not relax more than to about 60% of their initial value. To get an improvement in life time of at least a factor two for peened specimens, the stress amplitude in constant amplitude loading or the maximum stress amplitude in variable amplitude history must not be more than 20% larger than the magnitude of the initial residual stresses. This limit corresponds to 1.2 times the yield strength of the unaffected material.
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| 30. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Stability of Residual Stresses Created by Shot Peening in Monotonic Loading and at the Presence of Load Reversals - Experiments and Modeling
- 2012
-
In: Journal of Engineering Materials and Technology, Transactions of the ASME. - : ASME International. - 1528-8889 .- 0094-4289. ; 134:2, s. 021010-
-
Journal article (peer-reviewed)abstract
- As a method for mechanical surface treatment, shot peening has been widely used to improve the fatigue strength of materials. However, the influence of residual stresses introduced by shot peening depends on their stability. The stability of residual stresses during fatigue may be studied in two stages: the first cycle and successive cyclic loading. In this study the stability and development of the residual stresses during the first cycle of strain controlled fatigue of normalized steel was investigated. The influence of total strain amplitude and the loading direction was studied. The residual stresses were obtained using the x-ray diffraction technique. It was shown that the stability and relaxation of the residual stresses depend both on the amount and the direction of the loading stresses. Finite element modeling (FEM) was used to rationalize the experimental data. Very good agreement between the experimental and FEM results were observed
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| 31. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Stability of Residual stresses Created by Shot Peening of Pearlitic Steel and Their Influence on Fatigue Behaviour
- 2010
-
In: 10th International Fatigue Congress, FATIGUE 2010; Prague; Czech Republic; 6 June 2010 through 11 June 2010. - : Elsevier BV. - 1877-7058. ; 2:2, s. 613-622
-
Conference paper (peer-reviewed)abstract
- In this study the effect of shot peening on the fatigue lifetime of a near pearlitic microalloyed steel was investigated. The fatigue tests were run in strain control with parallel recording of stress relaxation and recovery of the work hardened surface zone at different total strain amplitudes exerted to the test specimens. These relaxation processes were followed versus cycle number up to half of the fatigue life time (N=Nf/2). Provided that the global plastic strain amplitude is lower than about 0.08 % a noticeable increase in life time is seen. Lower plastic strain amplitude increases the life time. At small plastic strain amplitudes it was found that the fatigue life time could be increased more than tenfold by the shot peening process.
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| 32. |
- Dalaei, Kamellia, 1975, et al.
(author)
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Stability of shot peening induced residual stresses and their influence on fatigue lifetime
- 2011
-
In: Materials science and engineering A. - : Elsevier BV. - 0921-5093. ; 528:3, s. 1008-1015
-
Journal article (peer-reviewed)abstract
- Mechanical surface treatment methods such as shot peening may improve the fatigue strength of materials. In this study, the effect of shot peening on strain controlled constant amplitude fatigue loading of a near pearlitic microalloyed steel was investigated. The stress amplitudes throughout the whole lifetime were followed, in addition to detailed recording of stress-strain hysteresis loops, particularly at small cycle numbers. The detailed relaxation of residual stresses and the changes in full width of half maximum (FWHM) of the X-ray peak at the surface and in depth as function of the number of cycles and plastic strain were recorded. By these techniques, the onset as well as the rate of relaxation of residual stresses could be followed at different strain amplitudes. Pronounced increase in lifetime of the shot peened specimens tested at total strain amplitude smaller than 0.3% (corresponding to 0.034% plastic strain amplitude) was achieved. This coincides with reasonably stable residual stresses at the surface and in depth. © 2010 Elsevier B.V.
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| 33. |
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| 34. |
- Hosseini, Seyed, 1981, et al.
(author)
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Determination of Stresses and Retained Austenite in Carbon Steels by X-rays - A Round Robin Study
- 2011
-
In: Experimental Mechanics. - : Springer Science and Business Media LLC. - 1741-2765 .- 0014-4851. ; 51:1, s. 59-69
-
Journal article (peer-reviewed)abstract
- Residual stresses and retained austenite are twoimportant process-related parameters which need to becontrolled and monitored carefully during production andheat treatment of products. X-ray diffraction techniques arenormally used in this context, and the purpose of thepresent study was to investigate the reproducibility andaccuracy of these methods for medium and high carbonsteels. The work was carried out as a round robin studyincluding nine different laboratories in Sweden and Finland.Stress measurements were carried out on three specimens etched to three different depths, 0 μm, 230 μm and 515 μm. Retained austenite measurements were carried out on three specimens containing approximately 11, 17 and 30 vol.-% of this phase. The stress measurements showed good reproducibility with standard deviations of typically 4% on flat and smooth surfaces and not more than about 8% on etched surfaces. Estimations revealed that specimen misalignment and improper X-ray spot location were the main sources behind the variation in the stress recordings. The determination of retained austenite showed a standard deviation of typically 15% between the different contributors. However, by using identical evaluation methodsfor all raw data, the data spread could be narrowed by afactor of 3 to 4 despite the fact that different experimental settings were used in the individual laboratories.
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| 35. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(author)
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Development of the unloading stiffness during cyclic plastic deformation of a high-strength aluminium alloy in different tempers
- 2007
-
In: International Journal of Materials Research. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 98:11, s. 1115-1123
-
Journal article (peer-reviewed)abstract
- The development of stiffness during unloading from peak stress during cyclic plastic deformation (low cycle fatigue) was studied in a high-strength Al-5.4Zn-1.2Mg alloy, both in naturally aged and peak aged conditions. A phenomenological model based on a 2nd order stress–strain relationship was developed using data from detailed recordings of the stress-strain hysteresis loops. Three stages of the parameter values were identified: an initial transition part of the fatigue life time, a major stationary stage shifting over to the final stage where failure modes become prominent. The nonlinear stiffness was found to be asymmetric with respect to tension and compression. Further, the naturally aged material generally shows larger stiffness for both positive and negative stresses than does the peak aged material. Finally, the stiffness for the naturally aged condition exhibits larger scatter compared to the peak aged materials, interpreted as inferior averaging in the dislocation structures.
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| 36. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(author)
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Dynamic strain ageing and dynamic precipitation in AA7030 during cyclic deformation
- 2010
-
In: Procedia Engineering. - : Elsevier BV. - 1877-7058 .- 1877-7058. ; 2:1, s. 265-273
-
Conference paper (peer-reviewed)abstract
- The effects of dynamic strain ageing (DSA) and dynamic precipitation (DP) on the stress-strain response during low-cycle fatigue of naturally aged (NA) and peak-aged (PA) AA7030 alloy at different temperatures was investigated. The results show that the PA temper is largely unaffected by DSA/DP, and the cyclic deformation behavior is controlled by the accumulation of dislocations and strain localization due to repeated shearing of precipitates. In the NA temper, on the other hand, the effect of temperature on DSA and DP is the main mechanism controlling the stress-strain response. At temperature above room temperature, DP in the intense slip bands inhibits cyclic softening and the samples harden until the on-set of crack growth. At lower temperatures, the rate of DP is too slow to compensate for the softening in the slip bands and the stress amplitude saturates or decreases. The stress amplitude development is shown to primarily be a result of the evolution of the effective stress associated with dislocation-precipitate interactions.
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| 37. |
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| 38. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(author)
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Effect of heat treatment on the strain hardening behaviour of an Al-Zn-Mg alloy
- 2009
-
In: International Journal of Materials Research. - : Walter de Gruyter GmbH. - 1862-5282 .- 2195-8556. ; 100:11, s. 1574 - 1581
-
Journal article (peer-reviewed)abstract
- The strain hardening of the Al-5.2Zn-1.2Mg alloy AA7030 in different conditions has been investigated. The dislocation related strengthening was described by the Voce equation and the quantitative effects of different superposition laws have been studied. All tempers, except the over-aged, suffer from plastic instability before the geometric Considère condition is reached. This was attributed primarily to the occurrence of shear failure due to dynamic strain ageing effects. For plastic strain levels below approximately 8 %, preceding the plastic instability, the results show that the saturation stress in the under and peak-aged tempers is independent of heat treatment, whereas the kinetics of structure formation differs. Using a linear superposition law in the under and peak aged tempers has negligible effects, whereas the use of Pythagorean addition for the over-aged temper significantly decreases the goodness-of-fit, although not to unacceptable levels. Furthermore, the naturally aged temper shows strong influence of dynamic precipitation.
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| 39. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(author)
-
Influence of Heat Treatment on the Cyclic Deformation Properties of Aluminium Alloy AA7030
- 2008
-
In: Materials Science & Engineering A: Structural Materials: Properties, Microstructure and Processing. - : Elsevier BV. - 0921-5093. ; A479:1-2, s. 345-355
-
Journal article (peer-reviewed)abstract
- An extruded AA7030 alloy (Al-5.4Zn-1.2Mg) was tested in low-cycle fatigue at different total strain amplitudes to determine the cyclic deformation and fracture behaviour and to investigate the effect of heat treatment-natural ageing (NA) or peak ageing (PA). The results show that the fatigue life is longer in the NA temper at a given plastic strain amplitude. The fatigue life can be described by a total strain amplitude approach, where both NA and PA fall on the same straight line. The NA temper shows continuous cyclic hardening until the onset of fatal crack growth while the PA temper hardens during the first 20-30% of the fatigue life and then softens due to crack growth. The crack propagation mechanisms are different between the tempers, where NA favours transgranular cracking while intergranular propagation prevails in PA. Finally, a tension/compression stress asymmetry was observed under symmetric straining.
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| 40. |
- Hörnqvist Colliander, Magnus, 1979, et al.
(author)
-
Temperature and strain rate dependence of the dynamic strain ageing effect in an Al-Zn-Mg alloy
- 2006
-
In: Materials Science and Technology. - 1743-2847 .- 0267-0836. ; 22:2, s. 213-222
-
Journal article (peer-reviewed)abstract
- An AA7030 alloy (Al-5·4Zn-1·2Mg) was tested for evidence of dynamic strain aging in naturally aged and peak aged condition and under varying conditions in terms of strain rate and temperature. Clear evidence in terms of strain rate sensitivity, serrated yielding (Portevin-Le Chatelier effect) and propagative plastic instabilities was observed in the naturally aged temper while the peak aged temper only showed serrated yielding. Further evidence of dynamic strain aging was the temperature and strain dependence of the strain rate sensitivity, which can be explained by the additional dislocation activation energy resulting from solute pinning. Investigation of the specimen surfaces was carried out to reveal an orange peel structure with pronounced glide bands. Small cracks within individual grains rather than grain boundary cracking could be observed. © 2006 Institute of Materials, Minerals and Mining.
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| 41. |
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| 42. |
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| 43. |
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| 44. |
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| 45. |
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| 46. |
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| 47. |
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| 48. |
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| 49. |
- Lundstrom, Dennis, et al.
(author)
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Anisotropy in Thermal Transport Properties of Cast γ-TiAl Alloys
- 2022
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In: International Journal of Materials Research. - 1862-5282. ; 92:11, s. 1203-1212
-
Journal article (peer-reviewed)abstract
- The thermal transport properties have been determined for titanium aluminide with nominal composition Ti-48Al-2W-0.5Si (at.%), cast to cylindrical bars with different gamma/(gamma + alpha(2)) microstructures. The amount of phases and the orientation of the lamellar plates vary from the core to the rim in each of the bars. Differences in the thermal conductivity of the two phases lead to anisotropy in the thermal transport properties, but with cylindrical symmetry in the bars. A newly developed, high-precision technique, the so-called transient plane source (TPS) technique, was used to resolve the anisotropy in a wide temperature range. Typically, the conductivity increases monotonously from about 12- 14 W/m center dot K at room temperature up to about 20-22 W/m center dot K at 700 degrees C for the different materials. The anisotropy in both conductivity and diffusivity is about 15% at all temperatures, but with fundamental differences between the different materials. The anisotropy of the transport properties is explained in terms of amounts of phases and directionality of the lamellar plates.
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| 50. |
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