Strain-Based Fatigue Test and Reliability Research of 42CrMo Alloy Steel

2010 ◽  
Vol 97-101 ◽  
pp. 856-860
Author(s):  
Nan Xu ◽  
Xiu Hua Ren ◽  
Wei Qiang Wang
Keyword(s):  
Fatigue Test ◽  
Alloy Steel ◽  
Strain Range ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Range Data ◽  
Stress Range ◽  
Probability Models ◽  
Total Strain Range

The strain-based fatigue tests of 42CrMo alloy steel were conducted by controlling six sets of total strain range, and stress range data was obtained under each strain range. The results of fatigue test revealed that fatigue performance of 42CrMo alloy steel was of tremendous dispersivity all though materials were strictly chosen, heat-treated and machined. Cyclic stress-strain (CSS) curves were compared with monotonic tensile curve, which showed that 42CrMo alloy steel quenched and tempered was a kind of cyclic softening material. Evaluation results revealed that LND was the best probability function to describe cyclic stress of strain fatigue for 42CrMo steel. Cyclic stress range under the median and high probability was evaluated by means of stochastic performance probability models.

Cyclic Softening and Over-Softening of a 1 Percent Cr-Mo-V Steel at Elevated Temperature

1981 ◽  
Vol 23 (6) ◽  
pp. 305-308
Author(s):  
T. Gardiner
Keyword(s):  
Shear Stress ◽  
High Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Stress Range ◽  
Continuous Cycling ◽  
History Effect ◽  
Initial Cycle ◽  
Range Variation ◽  
Total Shear

Detailed results are presented of shear stress range variation during cycling of 1 per cent Cr-Mo-V test specimens within controlled total shear strain limits at 565°C. The cyclic softening induced during continuous and two-step cycling are compared. A saw-toothed pattern for the strain was maintained for each cycle giving a constant straining rate. Normal cyclic softening was found throughout the tests but another phenomenon of over-softening occurred during the two-step tests when high strain cycles took place first. A permanent history effect had been produced within the steel. This over-softening did not depend on the straining rate of the cycling or the magnitude of the initial cycle ratio. The generally accepted method of determining cyclic stress-strain curves using continuous cycling is shown to be invalid when over-softening is present.

A LIFE ASSESSMENT FOR STEAM TURBINE CASING USING INELASTIC ANALYSIS

2008 ◽  
Vol 22 (11) ◽  
pp. 1141-1146 ◽  
Author(s):  
WOOSUNG CHOI ◽  
JUNGSEOB HYUN
Keyword(s):  
Steam Turbine ◽  
Thermal Stresses ◽  
Strain Range ◽  
Cyclic Stress ◽  
Life Assessment ◽  
Total Strain Range ◽  
Unsteady Temperature ◽  
Inelastic Analysis ◽  
Life Consumption ◽  
Start Ups

An important characteristic of a fossil power plant is its ability to maintain reliability and safety of the plant against frequent start-ups and load changes. Unstable states arising during start-ups, shutdowns and load changes give rise to unsteady temperature distribution with time in steam turbine innercasing (HP/IP), which results in non-uniform strain and stress distribution. The rapid increase of temperature during starts-ups, especially, causes susceptible to failure and reduction of expected life for steam turbine components. Thus accurate knowledge of thermal stresses is required for the integrity and lifetime assessment for the turbine components. In this paper, the fatigue damage is calculated of steam turbine inner casing was calculated by combining the stress analysis based procedure and Neuber's rule. By substituting the material cyclic stress-strain relationship into the Neuber equation, the inelastic total strain range was obtained. Using this study, life consumption of steam turbine inner-casing can be obtained and a guideline for effective maintenance was proposed.

Part 3: Predictions of Deformation and Life under Fatigue/Creep Conditions

1976 ◽  
Vol 190 (1) ◽  
pp. 339-348 ◽  
Author(s):  
A. J. F. Paterson ◽  
E. G. Ellison
Keyword(s):  
Life Prediction ◽  
Strain Curve ◽  
Strain Range ◽  
Cyclic Strain ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Virgin Material ◽  
Creep Data ◽  
Stress Strain Curve ◽  
Material Conditions

Predictions of the behaviour of a 1 Cr Mo V steel at 565 °C under cyclic strain plus dwell conditions have been carried out. The strain hardening mechanical equation of state appears to be useful under virgin material conditions but the presence of cyclic softening can cause major errors. Reasonable success was obtained in predicting “softened creep” curves from the virgin creep data and the cyclic stress strain curve. Both strain and time are important in life prediction and a method is proposed which combines the strain range partitioning approach and a modified form of cumulative damage method. Predictions under various combinations of tensile and compressive dwell have been presented.

Effect of Creep in Low-Cycle Fatigue of Pressure Vessel Steel

1970 ◽  
Vol 92 (1) ◽  
pp. 67-73 ◽  
Author(s):  
J. Dubuc ◽  
A. Biron
Keyword(s):  
Pressure Vessel ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Fatigue Tests ◽  
Pressure Vessel Steel ◽  
Cycle Fatigue ◽  
Total Strain Range ◽  
Vessel Steel ◽  
The Mean ◽  
Mean Strain

Low-cycle fatigue tests have been carried out at 2 cpm on a pressure vessel steel at 350 deg C (662 deg F). The total strain range was fixed for each test and the minimum (or mean) strain in some cases was constant (zero minimum value), in others increased uniformly in time at a predetermined rate. It was found that variations in the mean strain up to 0.5 percent/hour had no significant influence on the results.

Cyclic Deformation of a Modern TiAl Alloy at High Temperatures

2014 ◽  
Vol 891-892 ◽  
pp. 1131-1136 ◽  
Author(s):  
Tomáš Kruml ◽  
Alice Chlupová ◽  
Karel Obrtlík
Keyword(s):  
Lamellar Structure ◽  
Tial Alloy ◽  
Low Cycle Fatigue ◽  
Lamellar Microstructure ◽  
Strain Curve ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Tensile Curve ◽  
Cyclic Straining

Ternary TiAl alloy with 8 at.% Nb and lamellar microstructure is subjected to low cycle fatigue tests at temperatures ranging from room temperature to 800 °C. The aim of the study is to find limit conditions when the microstructure is still stable and to study mechanisms of microstructural degradation when this limit is exceeded. Up to 750 °C, no cyclic softening or hardening is observed and cyclic stress-strain curve follows the tensile curve. Cyclic softening is characteristic for 800 °C. The TEM observation did not reveal any substantial changes in the microstructure due to the cycling up to 700°C. The lamellar structure is altered by cyclic straining at 750 °C and, to a higher extent, at 800°C. In specimens cycled to fracture at 800 °C, the domains without lamellar structure cover about 10% of volume and are almost dislocation free. The destruction of lamellar microstructure is the reason for the marked cyclic softening at 800 °C.

Low-Cycled Fatigue Life of S30408 Stainless Steel at Liquid-Nitrogen Temperature

2018 ◽  
Author(s):  
Yingzhe Wu ◽  
Huaijian Xu ◽  
Qunjie Lu ◽  
Jinyang Zheng ◽  
Ping Xu
Keyword(s):  
Stainless Steel ◽  
Fatigue Life ◽  
Liquid Nitrogen ◽  
Strain Amplitude ◽  
Hysteresis Loops ◽  
Cyclic Strain ◽  
Liquid Nitrogen Temperature ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests

This paper is concerned with the low-cycled fatigue life of S30408 austenitic stainless steel at 77 K. Strain-controlled low-cycled fatigue tests were performed in a liquid-nitrogen bath covering a strain-amplitude range of 0.4%–1.0%. The role of the reduced temperature is examined during the low-cycled fatigue tests by comparing the fatigue performance to the one at ambient temperature that was obtained in our previous work. It is found that the cryogenic low-cycled fatigue life is significantly improved by a factor of 5–10 in the low strain-amplitude range of 0.4%–0.5%, resulting from the pronounced hardening effect due to the low temperature. However, the cryogenic improvement gradually reduces with the increasing strain-amplitude. At 77 K, the cyclic stress amplitude increases rapidly at the beginning of the fatigue test, and no cyclic softening is found due to the cryogenically constrained movement of the dislocations. The fatigue hysteresis loops and fatigue stress-strain curves shows that the cyclic plastic strain at cryogenic temperature accounts for a limited proportion in the total cyclic strain, and the damage may occurs explosively at the beginning of the cyclic load at 77 K.

Short-life fatigue under combined stresses

1967 ◽  
Vol 2 (1) ◽  
pp. 91-95 ◽  
Author(s):  
G Z Libertiny
Keyword(s):  
Fatigue Test ◽  
Strain Range ◽  
Cyclic Strain ◽  
Equivalent Strain ◽  
Fatigue Tests ◽  
Short Life ◽  
Strain Parameter ◽  
Dependent Parameter ◽  
Experimental Findings ◽  
Stress Dependent

Most of the short-life fatigue tests have been carried out in push-pull or in reversed bending. Many machine parts and structural elements, however, are subjected to combined rather than uniaxial fatigue loads. This work is intended to demonstrate a possible approach to solving the problem of short-life fatigue failures due to a multiaxial stress-strain system. The paper includes a review of the available literature relevant to the problem. The more important experimental findings are summarized and presented in the form of diagrams. Various approaches toward the solution of the problems are discussed, and a new approach is proposed. It is demonstrated in this paper that the use of an ‘equivalent-strain parameter’ calculated from the Mises law is not suitable in the description of the problem. It was found that when the strain Δ∊ in the direction of the maximum stress is adopted as a strain parameter and a stress-dependent parameter L is introduced, all of the results can be described by the following equation:         Δ∊ Na = C where n = f( np, L) and C = f( Cp, L),     Δ∊ = cyclic strain range,      N = number of cycles to failure,      np = slope of the log ∊-log N curve which represents a push-pull fatigue test,      L = stress parameter,      Cp = constant in the log ∊-log N curve which represents a push-pull fatigue test. These functions have been determined approximately. It is recognized that, because of lack of experimental data, the present work can indicate only a possible and somewhat speculative approach and that there is a great need for further experimental work.

Cyclic Softening of Cu-Ni-Si Alloy Single Crystals under Low-Cycle Fatigue

2010 ◽  
Vol 654-656 ◽  
pp. 1287-1290 ◽  
Author(s):  
Toshiyuki Fujii ◽  
Hiroshi Kamio ◽  
Yoshifumi Sugisawa ◽  
Susumu Onaka ◽  
Masaharu Kato
Keyword(s):  
Plastic Strain ◽  
Single Crystals ◽  
Low Cycle Fatigue ◽  
Strain Curve ◽  
Electron Microscopic Observation ◽  
Cyclic Hardening ◽  
Cyclic Stress ◽  
Cyclic Softening ◽  
Fatigue Tests ◽  
Electron Microscopic

Cu-2.2wt%Ni-0.5wt%Si alloy single crystals were grown by the Bridgman method and aged at 723 K for 10 h to form Ni2Si precipitates. Fully reversed tension-compression fatigue tests were conducted on the aged single crystals with a single slip orientation under constant plastic-strain amplitudes at room temperature. Cyclic softening occurred at plastic-strain amplitudes between 2.5x10-4 and 2.5x10-2. Using the maximum stress amplitude in each cyclic hardening/softening curve, a pseudo cyclic stress-strain curve (CSSC) was obtained. The CSSC was found to exhibit a plateau region with a stress level of about 167 MPa. Transmission electron microscopic observation revealed the formation of persistent slip bands (PSBs) in the plateau regime. It was found that the Ni2Si precipitate particles were intensively sheared by glide dislocations within the PSBs and were eventually re-dissolved into the Cu matrix. The macroscopic cyclic softening can be attributed to the local softening induced by the re-dissolution of the Ni2Si particles in the PSBs.

HIGH TEMPERATURE LOW CYCLE FATIGUE AND FRACTURE CHARACTERISTIC IN TWO SINGLE CRYSTAL SUPERALLOYS

2010 ◽  
Vol 24 (15n16) ◽  
pp. 2892-2897
Author(s):  
J. J. YU ◽  
Z. H. WANG ◽  
X. F. SUN ◽  
T. JIN ◽  
H. R. GUAN ◽  
...  
Keyword(s):  
Stress Amplitude ◽  
Low Cycle Fatigue ◽  
Strain Range ◽  
Fatigue Tests ◽  
Total Strain ◽  
Stress Axis ◽  
Cycle Fatigue ◽  
Total Strain Range ◽  
Refractory Elements ◽  
Fatigue And Fracture

Total strain controlled low cycle fatigue tests were conducted at 1173K for DD32 and SRR99 alloys. With the increase of total strain range, the stress amplitude of DD32 alloy improved more fleetly than that of SRR99 alloy. At total strain ranges less than or equal to 1.0%, the low cycle fatigue life of DD32 alloy was greater than that of SRR99 alloy. It was shown that the higher content of refractory elements in DD32 alloy resulted in a remarkable improvement of LCF properties compared to SRR99 alloy. The crack propagation perpendicular to the stress axis occurred in transgranular mode in both alloys. DD32 alloy presented more ductile character than SRR99 alloy.

Low Cycle Fatigue Behavior of Alloy 800H Base Metal and Weldments at 700°C

2018 ◽  
Author(s):  
Seon-Jin Kim ◽  
Rando Tungga Dewa ◽  
Woo-Gon Kim ◽  
Eung-Seon Kim
Keyword(s):  
Base Metal ◽  
Deformation Behavior ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Strain Range ◽  
Fatigue Tests ◽  
Total Strain ◽  
Cycle Fatigue ◽  
Alloy 800H ◽  
Total Strain Range

Alloy 800H is currently being considered as one of the near-term candidate materials for design and construction of some major high temperature components of a very high temperature reactor (VHTR). System start-ups and shut-downs as well as power transients will produce low-cycle fatigue loadings of components. The aim of this work is to study the low cycle fatigue behavior of Alloy 800H base metal and weldments at 700°C. The weldment specimens were machined from gas tungsten arc welding (GTAW) butt-welded plate such that the loading direction was oriented transverse to the welding direction. Fully reversed total-strain controlled low-cycle fatigue tests have been performed at total strain ranges of 0.6, 0.9, 1.2 and 1.5%. For all the low-cycle fatigue tests, triangular test waveforms with a constant strain rate of 10−3/s were applied. Low-cycle fatigue testing was conducted in accordance with ASTM Standard E606 on servo-hydraulic test machines. And also, creep-fatigue experiments were carried out at 700°C employing 0.6% total strain range and 10−3/s strain rate using trapezoidal waveform with tension hold time. The main focus is to characterize the low-cycle fatigue properties for Alloy 800H weldment specimens from the cyclic deformation behavior and fatigue fracture behavior. The cyclic deformation behavior was influenced by total strain range and material property. The fatigue life was decreased with increasing the total strain range for both base metal and weldment. However, the lives of weldment specimens have a longer life than that of base metal at lower total strain ranges. It was also observed that creep effects play a significant role in fatigue life reduction.

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