共查询到20条相似文献,搜索用时 31 毫秒
1.
G. V. Prasad Reddy R. Sandhya M. Valsan K. Bhanu Sankara Rao S. Sankaran 《Transactions of the Indian Institute of Metals》2010,63(2-3):505-510
In this paper, Low cycle fatigue (LCF) behavior of 316LN austenitic stainless steel alloyed with 0.078 and 0.22 wt% nitrogen, designated as N078 and N022 steels respectively, is compared in the temperature range 300–873 K by strain controlled fatigue tests at ± 0.6% strain amplitude. Interestingly, N022 steel showed continuous decrease in fatigue life with temperature in contrast to N078 steel which showed maximum in fatigue life at 573 K. Drastic reduction in fatigue life is observed in both the steels in the temperature range 673–873 K and has been attributed to the occurrence of dynamic strain aging. Both steels exhibited manifestations (for ex.: decrease in plastic strain and anomalous stress response with increase in temperature) corresponding to the occurrence of Dynamic Strain Ageing (DSA) in the above temperature range. Under all testing conditions, fracture surfaces revealed transgranular crack initiation and transgranular crack propagation. 相似文献
2.
The ferritic steel 16Mo3 is commonly used for heat exchangers and steam generators. The temperature loading conditions for these applications range typically from 200 to 500°C. For a basic characterization of the steel 16Mo3, the properties were determined by means of tensile tests with different strain rates. At 200 and 300°C, a negative strain‐rate sensitivity was observed which is due to dynamic strain ageing (Portevin–LeChâtelier effect). To characterize the low cycle fatigue (LCF) behavior of this steel, isothermal strain‐controlled LCF tests were carried out at 200 and 500°C at different strain amplitudes. The cyclic stress response curves are showing principally different courses at the investigated temperatures. The stress relaxation behavior was obtained by cyclic load enhancement tests at various strain amplitudes with dwell times of 30 and 120 s. 相似文献
3.
Low cycle fatigue behavior of TWIP (twinning induced plasticity) steel was investigated in axial symmetric tension-compression cyclic loading pattern. Fracture surfaces and microstructures were examined by optical, scanning electron and transmission electron microscopes. It was found that the fatigue life at the strain amplitude of 0.4 % is up to 15 000 cycles, which is much longer than TRIP780 and HSLAS00 steels. The strain hardening and softening features are significant until the strain amplitude comes to 1.25 ~. Persistent slip bands and tiny mechanical twinning layers were observed after fatigue deformation. Deformation mechanism of TWIP steel at low cycle fatigue process is not only twinning, but a complex of both twinning and persistent slip bands. 相似文献
4.
Fully reversed low-cyclic fatigue (LCF) tests were conducted on [001], [012], [-112], [011], and [-114] oriented single crystals
of nickel-based superalloy DD3 with different cyclic strain rates at 950°C. The cyclic strain rates were chosen as 1.0×10−2, 1.33×10−3 and 0.33×10−3 s−1. The octahedral slip systems were confirmed to be activated on all the specimens. The experimental result shows that the
fatigue behavior depends on the crystallographic orientation and cyclic strain rate. Except [001] orientation specimens, it
is found from the scanning electron microscopy (SEM) examination that there are typical fatigue striations on the fracture
surfaces. These fatigue striations are made up of cracks. The width of the fatigue striations depends on the crystallographic
orientation and varies with the total strain range. A simple linear relationship exists between the width and total shear
strain range modified by an orientation and strain rate parameter. The nonconformity to the Schmid law of tensile/compressive
flow stress and plastic behavior existed at 950°C, and an orientation and strain rate modified Lall-Chin-Pope (LCP) model
was derived for the nonconformity. The influence of crystallographic orientation and cyclic strain rate on the LCF behavior
can be predicted satisfactorily by the model. In terms of an orientation and strain rate modified total strain range, a model
for fatigue life was proposed and used successfully to correlate the fatigue lives studied in this article. 相似文献
5.
K. Bhanu Sankara Rao H. Schiffers H. Schuster G. R. Halford 《Metallurgical and Materials Transactions A》1996,27(2):255-267
The effects of strain rate (4 × 10-6 to 4 × 10-3 s-1) and temperature on the low-cycle fatigue (LCF) behavior of alloy 800H have been evaluated in the range 750 ° to 950 °. Total
axial strain controlled LCF tests were conducted in air at a strain amplitude of ± 0.30 pct. Low-cycle fatigue life decreased
with decreasing strain rate and increasing temperature. The cyclic stress response behavior showed a marked variation with
temperature and strain rate. The time- and temperature-dependent processes which influence the cyclic stress response and
life have been identified and their relative importance assessed. Dynamic strain aging, time-dependent deformation, precipitation
of parallel platelets of M23C6on grain boundaries and incoherent ledges of twins, and oxidation were found to operate depending on the test conditions.
The largest effect on life was shown by oxidation processes.
On leave from the Indira Gandhi Centre for Atomic Research, Kalpakkam 603102, India. 相似文献
6.
采用径向应变控制研究了Z3CN20-09M奥氏体不锈钢在室温和350℃高温下的低周疲劳行为.Z3CN20-09M不锈钢表现为先硬化后软化的循环特性,但硬化的程度取决于温度和应变幅.随着应变幅的增加,Z3CN20-09M钢的低周疲劳循环寿命逐渐减短,而相同循环次数下应力幅也随之提高.温度对Z3CN20-09M钢的低周疲劳行为影响较大,与室温相比高温下的循环硬化程度更高,相同应变幅下高温的低周疲劳寿命也高于常温下的寿命.通过疲劳实验的原位观察发现,奥氏体内的滑移面、夹杂物及奥氏体和铁素体两相的界面是疲劳裂纹可能的形核位置,奥氏体和铁素体两相的不协调变形使相界处产生应力集中,导致疲劳裂纹容易沿两相界面扩展. 相似文献
7.
8.
Kenneth S. Vecchio Michael D. Fitzpatrick Dwaine Klarstrom 《Metallurgical and Materials Transactions A》1995,26(3):673-689
Strain-controlled low-cycle fatigue tests have been conducted in air at elevated temperature to determine the influence of
subsolvus thermomechanical processing on the low-cycle fatigue (LCF) behavior of HAYNES 230 alloy. A series of tests at various
strain ranges was conducted on material experimentally processed at 1121 °C, which is below the M23C6 carbide solvus temperature, and on material fully solution annealed at 1232 °C. A comparative strain-life analysis was performed
on the LCF results, and the cyclic hardening/softening characteristics were examined. At 760 °C and 871 °C, the fatigue life
of the experimental 230/1121 material was improved relative to the standard 230/1232 material up to a factor of 3. The fatigue
life advantage of the experimental material was related primarily to a lower plastic (inelastic) strain amplitude response
for a given imposed total strain range. It appears the increase in monotonic flow stress exhibited by the finer grain size
experimental material has been translated into an increase in cyclic flow stress at the 760 °C and 871 °C test temperatures.
Both materials exhibited entirely transgranular fatigue crack initiation and propagation modes at these temperatures. The
LCF performance of the experimental material in tests performed at 982 °C was improved relative to the standard material up
to a factor as high as 2. The life advantage of the 230/1121 material occurred despite having a larger plastic strain amplitude
than the standard 230/1232 material for a given total strain range. Though not fully understood at present, it is suspected
that this behavior is related to the deleterious influence of grain boundaries in the fatigue crack initiations of the standard
processed material relative to the experimental material, and ultimately to differences in carbide morphology as a result
of thermomechanical processing.
Formerly Graduate Student, University of California, San Diego, La Jolla, is Senior Material Engineer, Solar Turbines Inc.,
San Diego, CA 92186-5376. 相似文献
9.
F. M. Yang X. F. Sun H. R. Guan Z. Q. Hu 《Metallurgical and Materials Transactions A》2003,34(4):979-986
An investigation was made on the strain-controlled low-cycle fatigue (LCF) of K40S cobalt-base superalloy at 900 °C in ambient
atmosphere. The results show that K40S alloy possesses high LCF resistance in comparison with X-40 alloy. Under the testing
conditions in this study, K40S alloy exhibits a cyclic stress response of initial hardening followed by softening. The cyclic
stress response behavior has been attributed to dislocation-dislocation interactions and dislocation-precipitate interactions.
The high response stress can lead to a large stress concentration at locations where inelastic strains of high amplitude accumulate,
which account for the decreasing fatigue life with increasing strain rate. The well-distributed carbide particles are the
“secondary” crack initiation sites. The secondary crack initiation relaxes the stress concentration at the crack tip, reducing
the driving force of crack propagation. High-temperature LCF failure of K40S alloy results from the interaction of the mechanical
fatigue and environmental oxidation. 相似文献
10.
Vakil Singh 《Transactions of the Indian Institute of Metals》2010,63(2-3):167-172
This paper gives a brief review of the efforts made to study the effects of cold rolling on low cycle fatigue (LCF) behavior of stainless steels, titanium alloy Timetal 834 and Ni-Fe based Super alloy IN 718 at different temperatures and different strain amplitudes. Low Cycle Fatigue tests on cold worked 316L stainless steel at various temperatures from room temperature to 923K have been reported. In all tests the effect of 20% prior cold work(PCW) on LCF behavior of type 316L (N) stainless steel had been studied at 873K under total axial strain controlled mode in air at strain amplitudes from ±0.25% to ±1.0%. Fatigue life in the solution annealed condition was similar to that of the PCW material at higher strain amplitudes (≥0.5%) while at lower strain amplitudes the PCW material exhibited longer life. The influence of PCW on LCF behavior of type 304 and AISI 304LN stainless steel was studied at various temperatures and it was observed that the fatigue life was strongly dependent on prior cold work, temperature, and strain amplitude employed. Cold rolling of the titanium alloy Timetal 834 and age hardenable Ni-Fe-based superalloy IN 718 has been found to cause marked enhancement in LCF life at low strain amplitude and eliminate the bilinearity from the Coffin-Manson(C-M) relationship. Work carried on this aspect, however is very limited particularly in the case of Titanium alloys and Ni-Fe based Superalloy IN 718 相似文献
11.
采用轴向应变幅控制的低周疲劳试验研究了总应变幅对4Cr5MoSiV1热作模具钢700 ℃低周疲劳行为的影响,包括循环应力响应行为、循环应力应变行为、循环迟滞回线和应变疲劳寿命行为等。结果表明:随着总应变幅从0.2%增大到0.6%,4Cr5MoSiV1钢在700 ℃时循环应力响应均表现为先循环硬化再循环软化的特性,并且应力幅最大值从220 MPa增大到308 MPa。同时,随着总应变幅的增大,4Cr5MoSiV1钢在700 ℃下的低周疲劳寿命由6750循环周次降低到210循环周次,且其过渡寿命约为1313循环周次。疲劳断口形貌分析结果显示,高温低周疲劳过程中裂纹主要萌生于试样表面处,且随着应变幅增大,裂纹源逐渐增多,疲劳条纹间距变宽,其断裂方式由韧性断裂转变为脆性断裂。透射电镜分析结果显示,循环软化可能与板条结构转变为胞状结构、基体发生位错湮灭、碳化物的析出和粗化有关。 相似文献
12.
Govind R. Chanani Stephen D. Antolovich 《Metallurgical and Materials Transactions B》1974,5(1):217-229
The low cycle fatigue (LCF) behavior of a high strength, metastable austenitic steel called TRIP steel has been studied. High strain LCF experiments on cylindrical, well-polished specimens under diametral strain control were carried out. To study the effect of a mixed austenite-martensite matrix, LCF tests were also done on the TRIP steel after inducing significant amounts of martensite in the austenite matrix by means of a very high unidirectional prestrain. To establish the role played by the martensite transformation, tests were also run above the MD. The amount of martensite induced was magnetically measured by means of a “permeameter” built specifically for this purpose. It was found that the LCF life of the TRIP steel, both at room temperature (in the presence of martensitic transformation) and at 200°C (in the absence of the transformation), was related to the plastic strain range, εPR, by the Manson-Coffin law. Either cyclic hardening or softening occurred at room temperature, depending primarily upon the plastic strain range used in cycling. Hardening was observed below 3 pct plastic strain range. For LCF tests at 200°C, cyclic softening was observed in all cases. The hardening and softening behavior has been found to depend on the martensitic transformation taking place in these steels during cycling. However, the LCF life correlated best to the percent reduction in area, independent of the extent of the martensite transformation. 相似文献
13.
Fully reversed low-cyclic fatigue (LCF) tests were conducted on [001], [012],
, [011], and
oriented single crystals of nickel-based superalloy DD3 with different cyclic strain rates at 950 °C. The cyclic strain rates
were chosen as 1.0 × 10−2, 1.33 × 10−3, and 0.33 × 10−3 s−1. The octahedral slip systems were confirmed to be activated on all the specimens. The experimental result shows that the
fatigue behavior depends on the crystallographic orientation and cyclic strain rate. Except [001] orientation specimens, it
is found from the scanning electron microscopy (SEM) examination that there are typical fatigue striations on the fracture
surfaces. These fatigue striations are made up of cracks. The width of the fatigue striations depends on the crystallographic
orientation and varies with the total strain range. A simple linear relationship exists between the width and total shear
strain range modified by an orientation and strain rate parameter. The nonconformity to the Schmid law of tensile/compressive
flow stress and plastic behavior existed at 950 °C, and an orientation and strain rate modified Lall-Chin-Pope (LCP) model
was derived for the nonconformity. The influence of crystallographic orientation and cyclic strain rate on the LCF behavior
can be predicted statisfactorily by the model. In terms of an orientation and strain rate modified total strain range, a model
for fatigue life was proposed and used successfully to correlate the fatigue lives studied in this article. 相似文献
14.
Y. Umakoshi H. Y. Yasuda T. Nakano K. Ikeda 《Metallurgical and Materials Transactions A》1998,29(13):943-950
The temperature and orientation dependence of cyclic deformation, fatigue life, and fracture behavior in TiAl polysynthetically
twinned (PST) crystals were investigated, focusing on the change of plastic strain energy and deformation mode in the γ domains.
Stress-controlled fatigue tests were performed at 1 or 10 Hz using the same stress amplitude in tension and compression (R=−1) over a temperature range from −196 °C to 700 °C. The fatigue strength at ϕ=45 deg (ϕ being the angle between the loading
axis and lamellar planes) decreased monotonically with increasing temperature. At ϕ=0 deg, the fatigue strength was high up
to 500 °C, but the fatigue life decreased rapidly above 600°C because of dynamic recovery and interlamellar separation. The
plastic strain energy—stress amplitude curves in specimens fatigued with ϕ=45 deg increased monotonically with stress amplitude
for all temperatures and for higher temperatures with ϕ=0 deg. At 25 °C and −196 °C with ϕ=0 deg, three regions in the plastic
strain energy—stress amplitude curves were observed. This anomalous change in the plastic strain energy at lower temperatures
was due to a transition in primary deformation mode between twinning and slip by ordinary dislocations in some domain orientations.
This article is based on a presentation made in the symposium “Fundamentals of Gamma Titanium Aluminides,” presented at the
TMS Annual Meeting, February 10–12, 1997, Orlando, Florida, under the auspices of the ASM/MSD Flow & Fracture and Phase Transformations
Committees. 相似文献
15.
M. Valsan D. H. Sastry K. Bhanu sankara Rao S. L. Mannan 《Metallurgical and Materials Transactions A》1994,25(1):159-171
Strain-rate effects on the low-cycle fatigue (LCF) behavior of a NIMONIC PE-16 superalloy have been evaluated in the temperature
range of 523 to 923 K. Total-strain-controlled fatigue tests were performed at a strain amplitude of ±0.6 pct on samples possessing
two different prior microstructures: microstructure A, in the solution-annealed condition (free of γ′ and carbides); and microstructure
B, in a double-aged condition with γ′ of 18-nm diameter and M23C6 carbides. The cyclic stress response behavior of the alloy was found to depend on the prior microstructure, testing temperature,
and strain rate. A softening regime was found to be associated with shearing of ordered γ′ that were either formed during
testing or present in the prior microstructure. Various manifestations of dynamic strain aging (DSA) included negative strain
rate-stress response, serrations on the stress-strain hysteresis loops, and increased work-hardening rate. The calculated
activation energy matched well with that for self-diffusion of Al and Ti in the matrix. Fatigue life increased with an increase
in strain rate from 3 × 10-5 to 3 × 10-3 s-1, but decreased with further increases in strain rate. At 723 and 823 K and low strain rates, DSA influenced the deformation
and fracture behavior of the alloy. Dynamic strain aging increased the strain localization in planar slip bands, and impingement
of these bands caused internal grain-boundary cracks and reduced fatigue life. However, at 923 K and low strain rates, fatigue
crack initiation and propagation were accelerated by high-temperature oxidation, and the reduced fatigue life was attributed
to oxidation-fatigue interaction. Fatigue life was maximum at the intermediate strain rates, where strain localization was
lower. Strain localization as a function of strain rate and temperature was quantified by optical and scanning electron microscopy
and correlated with fatigue life. 相似文献
16.
17.
K. Bhanu Sankara Rao M. Valsan R. Sandhya S. L. Mannan P. Rodriguez 《Metallurgical and Materials Transactions A》1993,24(4):913-924
The influence of prior cold work (PCW) on low-cycle fatigue (LCF) behavior of type 304 stainless steel has been studied at
300, 823, 923, and 1023 K by conducting total axial strain-controlled tests in solution annealed (SA, 0 pct PCW) condition
and on specimens having three levels of PCW, namely, 10, 20, and 30 pct. A triangular waveform with a constant frequency of
0.1 Hz was employed for all of the tests performed over strain amplitudes in the range of ±0.25 to ± 1.25 pct. These studies
have revealed that fatigue life is strongly dependent on PCW, temperature, and strain amplitude employed in testing. The SA
material generally displayed better endurance in terms of total and plastic strain amplitudes than the material in 10, 20,
and 30 pct PCW conditions at all of the temperatures. However, at 300 K at very low strain amplitudes, PCW material exhibited
better total strain fatigue resistance. At 823 K, LCF life decreased with increasing PCW, whereas at 923 K, 10 pct PCW displayed
the lowest life. An improvement in life occurred for prior deformations exceeding 10 pct at all strain amplitudes at 923 K.
Fatigue life showed a noticeable decrease with increasing temperature up to 1023 K in PCW state. On the other hand, SA material
displayed a minimum in fatigue life at 923 K. The fatigue life results of SA as well as all of the PCW conditions obeyed the
Basquin and Coffin-Manson relationships at 300, 823, and 923 K. The constants and exponents in these equations were found
to depend on the test temperature and prior metallurgical state of the material. A study is made of cyclic stress-strain behavior
in SA and PCW states and the relationship between the cyclic strain-hardening exponent and fatigue behavior at different temperatures
has been explored. The influence of environment on fatigue crack initiation and propagation behavior has been examined. 相似文献
18.
利用Gleeble1500热模拟试验机对H13模具钢在650-800℃温度范围,0.1-20s-1应变速率下的热压缩变形行为进行了研究,并得到了该材料在20-650℃范围内的弹性模量,建立了H13钢的有限元模型;通过高温拉伸实验和通用斜率法建立了H13钢的应变-低周疲劳寿命关系;结合有限元方法提出了一种预测H13钢制铝型材挤压模具低周疲劳寿命的方法,并在此基础上得到了工艺和结构参数对模具疲劳行为的影响规律。结果表明:疲劳应变损伤值随着挤压速度的增加以及模桥根部圆角半径的减小而增大,其中结构参数为关键影响因素。最后通过生产实际验证了该方法的可靠性。 相似文献
19.
用全反向恒应变幅试验方法,研究了C-Mn轨钢珠光体及回火索氏体的应变疲劳行为,探讨了塑性应变在应变疲劳中的作用。试验结果表明,轨钢的疲劳是塑性应变控制过程。大应变幅时,疲劳寿命的急剧缩短与塑性应变幅的快速增长有关,减小片间距会降低塑性应变幅在总应变幅中所占比例;抗拉强度相等时,因循环软化而致的塑性应变幅增大及较小的可允许应变范围是回火索氏体疲劳寿命低于珠光体的主要原因。 相似文献
20.
R. Kannan V. S. Srinivasan M. Valsan K. Bhanu Sankara Rao 《Transactions of the Indian Institute of Metals》2010,63(2-3):571-574
Modified 9Cr-1Mo steel is being used extensively as structural material for steam generator components of liquid metal cooled fast breeder reactor and fossil fired power plants. The selection of this material is primarily based on a good combination of mechanical properties, high thermal conductivity, low thermal expansion coefficient and good resistance to stress corrosion cracking in water-steam and sodium environment systems compared to austenitic stainless steels. A further improvement of the thermal efficiency of modern steam turbines can be achieved by increasing the steam operating temperature. It has been found that the substitution of W for Mo enhances the high temperature tensile strength, fracture toughness and creep strength. This had led to the development of P92 Steel. The components of the steam generators are often subjected to repeated thermal stresses as a result of temperature gradients that occur on heating and cooling during start-ups and shut-downs or during temperature transients. This leads to low cycle fatigue (LCF) damage in the component. However, the data on LCF properties of the W added 9Cr steel (designated as P92 steel) is scarce and this paper aims in understanding the high temperature low cycle fatigue behaviour of P92 Steel. Total axial strain controlled low cycle fatigue tests have been conducted in air in the temperature range 823 and 873 K to ascertain the influence of temperature on the LCF behaviour of the steel. A constant ramp rate of 3 × 10?3 s?1 was employed for all the tests. The alloy exhibited a continuous softening before the final load drop that occurred due to the propagation of macro fatigue cracks. The softening rate is more for the tests conducted at higher strain amplitudes compared to that of lower strain amplitudes. Fatigue life decreased with increasing temperature and strain amplitude. In this paper the observed LCF results have been explained based on the detailed metallography and fractography conducted on the failed samples. 相似文献