scholarly journals Kinetic equation of stable growth for low cycle fatigue cracks

2015 ◽  
pp. 18
Author(s):  
N. V. Tumanov
Keyword(s):  
Kinetic Equation ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cycle Fatigue ◽  
Stable Growth

Computational and fractographic study of the stable growth of low cycle fatigue cracks in the disk of an aircraft engine turbine under complex loading cycles

2021 ◽  
Vol 87 (4) ◽  
pp. 52-60
Author(s):  
N. V. Tumanov ◽  
N. A. Vorobjeva ◽  
A. I. Kalashnikova ◽  
E. P. Kuz’min ◽  
M. A. Lavrentyeva ◽  
...  
Keyword(s):  
Crack Growth ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Complex Loading ◽  
Aircraft Engine ◽  
Cycle Fatigue ◽  
Turbine Engine ◽  
Steady Growth ◽  
Calculation Methodology ◽  
Stable Growth

The results of a comprehensive computational and experimental study of the kinetics of low-cycle fatigue cracks (LCF) in a turbine disk made of EP741NP granular nickel alloy of an aircraft gas turbine engine under complex loading cycles (CLC) are presented. The configuration of crack fronts was reconstructed using light microscopy. Steps of the blocks of fatigue striations characterizing the crack increment under CLC at the stage of steady crack growth are measured using scanning electron microscopy during microfractographic analysis. The period of LCF crack steady growth is estimated and the reproducibility of the regularities of steady growth is demonstrated which testifies the capability of reliable prediction for LCF crack steady growth. The finite element modeling of the reconstructed crack fronts has been carried out. The values?? of the range of stress intensity factor at each crack front in the area of measuring the pitch of the striation blocks were calculated for the subcycles of complex loading cycles. Using the previously developed physically grounded mathematical model and calculation methodology, forecasting of stable growth of the LCF crack was carried out. The results of forecasting match the data of micro-fractographic analysis unlike the results of LCF crack growth prediction based on Paris law which differ significantly from experimental data.

Low-Cycle Fatigue Behaviour of Gas Turbine Alloys

1974 ◽  
Vol 188 (1) ◽  
pp. 321-328 ◽  
Author(s):  
W. J. Evans ◽  
G. P. Tilly
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
High Stress ◽  
Cyclic Creep ◽  
Fatigue Curve ◽  
Fatigue Behaviour ◽  
Material Surface ◽  
Tension Stress ◽  
Cycle Fatigue ◽  
Stress Tests

The low-cycle fatigue characteristics of an 11 per cent chromium steel, two nickel alloys and two titanium alloys have been studied in the range 20° to 500°C. For repeated-tension stress tests on all the materials, there was a sharp break in the stress-endurance curve between 103 and 104 cycles. The high stress failures were attributed to cyclic creep contributing to the development of internal cavities. At lower stresses, failures occurred through the growth of fatigue cracks initiated at the material surface. The whole fatigue curve could be represented by an expression developed from linear damage assumptions. Data for different temperatures and types of stress concentration were correlated by expressing stress as a fraction of the static strength. Repeated-tensile strain cycling data were represented on a stress-endurance diagram and it was shown that they correlated with push-pull stress cycles at high stresses and repeated-tension at low stresses. In general, the compressive phase tended to accentuate cyclic creep so that ductile failures occurred at proportionally lower stresses. Changes in frequency from 1 to 100 cycle/min were shown to have no significant effect on low-cycle fatigue behaviour.

Short Crack Initiation during Low-Cycle Fatigue in SAF 2507 Duplex Stainless Steel

2007 ◽  
Vol 345-346 ◽  
pp. 343-346 ◽  
Author(s):  
M.C. Marinelli ◽  
Suzanne Degallaix ◽  
I. Alvarez-Armas
Keyword(s):  
Stainless Steel ◽  
Duplex Stainless Steel ◽  
Room Temperature ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Surface Strain ◽  
The Other ◽  
Cycle Fatigue ◽  
Cyclic Tests ◽  
Characteristic Microstructure

In this work, the formation of fatigue cracks is considered as a nucleation process due to the development of a characteristic microstructure formed just beneath the specimen surface. Strain controlled cyclic tests were carried out at room temperature at total strain ranges εt = 0.8 and 1.2% in flat specimens of SAF 2507 Duplex Stainless Steel (DSS). The results show that for this DSS, at εt = 0.8%, the correlation between phases (Kurdjumov-Sacks crystallographic relation) plays an important role in the formation of microcracks. On the other hand, at εt = 1.2%, microcracks initiate in the ferritic phase and the K-S relation does not seem to affect the formation of the cracks.

Using CFRP to Repair the Steel Pipe with Fatigue Cracks

2010 ◽  
Vol 146-147 ◽  
pp. 1086-1089 ◽  
Author(s):  
Hong Tao Zhang ◽  
Xiao Xiang Xue ◽  
Yan Zheng ◽  
Peng Feng
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Fiber Reinforced Polymer ◽  
Steel Pipe ◽  
Carbon Fiber Reinforced Polymer ◽  
Cycle Fatigue ◽  
Safe Operation ◽  
Reinforced Polymer ◽  
Pressure Pipeline ◽  
Crack Defect

This paper provides a new method to repair the steel pipe with fatigue cracks by using carbon fiber reinforced polymer (CFRP). Cracks may arise in Pressure pipeline in service because of low cycle fatigue. Crack defect is the biggest problem, because crack will gradually propagate and seriously threaten the safe operation of pipeline. This paper provides a repair and calculation method for pressure pipeline with fatigue cracks, and some specific engineering cases are given based on this method.

A Study on the Low Cycle Fatigue Behavior of the Steel for Shipbuilding Industry

2005 ◽  
Vol 297-300 ◽  
pp. 10-15 ◽  
Author(s):  
Kyung Su Kim ◽  
Byung Ok Kim ◽  
Young Kwan Kim ◽  
Chang Hwan Lee ◽  
Sung Won Lee
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Published Data ◽  
Cycle Fatigue ◽  
Maritime Industry ◽  
Shipbuilding Industry ◽  
Design Procedures ◽  
Calculation Results ◽  
Good Agreement

Recently, most of fatigue cracks in ship structures are reported within a few years after delivery. This type of fatigue characteristics cannot be explained adequately by the S-N curve based on high cycle fatigue. Calculation results under critical loading conditions reveal that stress magnitude higher than three times the yield stress occurs at some critical locations. It shows the fatigue cracks are related to low cycle fatigue. But the existing recommended design procedures in maritime industry do not properly cover low cycle fatigue problems. This work represents the first step in an effort to develop a design code that addresses low cycle fatigue problems. Low cycle fatigue test for uniform round specimen made of base/weld metal and for cruciform welded joint are carried out under constant amplitude alternating load, controlled by strain. Strain-cycle curves for the base metal and weld joints show good agreement with published data as well as some code recommended design curves.

Effect of Fiber Volume Fraction on Low Cycle Fatigue Behavior of Al2O3f/Al-Si Composites

2012 ◽  
Vol 268-270 ◽  
pp. 87-91
Author(s):  
Jian Jun Cui ◽  
Bing Chao Li ◽  
Guo Hua Zhang ◽  
Jian Xin Zhang ◽  
Zuo Shan Wei ◽  
...  
Keyword(s):  
Volume Fraction ◽  
Low Cycle Fatigue ◽  
Fatigue Behavior ◽  
Fatigue Cracks ◽  
Fatigue Tests ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Short Fibers ◽  
Fiber Volume ◽  
Large Size

The tensile and low cycle fatigue tests were carried out on alumina short fibers reinforced Al-Si piston alloy composites (Al-Si MMCs). Three Al-Si MMCs reinforced with 10, 17 and 25 vol.% of alumina short fibers were prepared to investigate the effects of volume fraction on tensile and low cycle fatigue properties at room temperature (RT) and 350°C. The results showed that the tensile strength decreased with the increasing of volume fraction of fibers at RT and was slight different at 350°C. Among the three MMCs, the 17%-MMCs showed highest stress level under the low cycle fatigue tests. The fatigue cracks were usually initiated from the clustered and large size fibers near the surface of specimen, propagated along the fiber/matrix interface at RT and grew rapidly by means of broken the fibers at 350°C.

scholarly journals Evaluation of Low Cycle Fatigue Performance of Selective Laser Melted Titanium Alloy Ti–6Al–4V

Metals ◽  
2019 ◽  
Vol 9 (10) ◽  
pp. 1041 ◽  
Author(s):  
Peng Zhang ◽  
Allen Naihui He ◽  
Fei Liu ◽  
Kaifei Zhang ◽  
Junjie Jiang ◽  
...  
Keyword(s):  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Cyclic Stress ◽  
Fatigue Properties ◽  
Cycle Fatigue ◽  
Low Carbon ◽  
Specific Strength ◽  
Material Fatigue ◽  
Lower Strain ◽  
High Degree

The material of Ti–6Al–4V has been widely applied in various industries, such as automobile, aerospace, and medical due to its high specific strength, superior thermal stability and strong corrosion resistance. In the recent decades, selective laser melting (SLM) has become an attractive method to fabricate Ti–6Al–4V parts, thanks to its significant advantages in low material consumption, the high degree of freedom in design, low carbon footprint, etc. Predictability of SLM material fatigue properties is especially important for the safety-critical structures under dynamic load cases. The present research is aimed at evaluating the low cycle fatigue (LCF) performance of SLM Ti–6Al–4V under high loading states. LCF tests were performed for as-built and annealed SLM Ti–6Al–4V. Comparison between LCF properties of SLM Ti–6Al–4V and the wrought Ti–6Al–4V was also made. It was found that as-built SLM Ti–6Al–4V demonstrated a comparable LCF performance with the wrought material. The LCF life of as-built SLM Ti–6Al–4V was longer than that of wrought Ti–6Al–4V at lower strain amplitudes. However, the wrought Ti–6Al–4V had better LCF performance at higher strain amplitudes. The results revealed that the porosity in the as-built SLM material exerted much more impact on the degradation of the material at high strain amplitudes. Annealing deteriorated the LCF performance of SLM Ti–6Al–4V material due to the formation of coarser grains. The cyclic Ramberg–Osgood and the Basquin–Coffin–Manson models were fitted to depict the cyclic stress–strain and the strain–life curves for the SLM Ti–6Al–4V, based on which the LCF performance parameters were determined. In addition, the fatigue fracture surfaces were observed by using scanning electron microscopy (SEM), and the results indicated that fatigue cracks originated from the surface or subsurface defects.

Study of the damage to 12Cr18Ni10Ti steel samples under low cycle fatigue using methods of nondestructive control

2021 ◽  
Vol 87 (5) ◽  
pp. 61-67
Author(s):  
A. A. Khlybov ◽  
Yu. G. Kabaldin ◽  
D. A. Ryabov ◽  
M. S. Anosov ◽  
D. A. Shatagin
Keyword(s):  
Structural Changes ◽  
Residual Life ◽  
Low Cycle Fatigue ◽  
Fatigue Cracks ◽  
Operating Time ◽  
Test Material ◽  
Magnetic Characteristics ◽  
Propagation Time ◽  
Cycle Fatigue ◽  
Number Of Cycles

The possibility of determining the degree of damage to flat samples in the area of low-cycle fatigue at the stage of accumulation of scattered damage before the appearance of a macroscopic crack is demonstrated. Flat samples were tested for cantilever bending at room temperature with a constant loading amplitude until a fatigue crack appeared. Austenitic steel 12Cr18Ni10Ti was used as a test material. The velocity (propagation time) of elastic waves in the material and the coercive force were measured upon testing at intervals of 500 cycles. The zone of damage development was analyzed and value of hardening (based on microhardness measurements) was determined within 15 mm of the developed crack. The analysis of the images of the alloy microstructures in the zone of the most likely crack propagation was performed following different number of cycles at the same point on the sample surface. The structural changes (γ – α transition (formation of martensite deformation)) that occur during cyclic loading, as well as nucleation and development of damage, followed by the formation of fatigue cracks, inevitably lead to changes in the elastic and magnetic properties of the material. At the initial stages of loading, we observed changes in the initial (both acoustic and magnetic) characteristics of the material, which later became stable or changed slightly. When operating time exceeded 80 % of the number of cycles before failure, a significant change in the measured parameters occurred. The obtained dependences of the acoustic and magnetic characteristics of the material provide reliable information about the current damage and can be used in estimating the residual life of the structures made of 12Cr18Ni10Ti steel.

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