Effect of stress levels on compressive low-cycle fatigue behaviour of softwood

Holzforschung ◽  
2005 ◽  
Vol 59 (6) ◽  
pp. 662-668 ◽  
Author(s):  
Meng Gong ◽  
Ian Smith
Keyword(s):  
Mathematical Model ◽  
Creep Strain ◽  
Stress Level ◽  
Low Cycle Fatigue ◽  
Total Duration ◽  
Peak Stress ◽  
Cyclic Creep ◽  
Cycle Fatigue ◽  
Creep Tests ◽  
Stress Levels

Abstract Low-cycle fatigue (LCF) of spruce under parallel-to-grain compression was investigated to simulate the damage that occurs during extreme events such as hurricanes. Load control was used, with peak stress levels of 75%, 85% and 95% of static compressive strength (C max). Changes in the residual cyclic modulus, cyclic creep strain and modified work density were correlated with the number of load cycles to assess their suitability as damage indicators. Creep tests were also carried out and the strain compared with cyclic creep strain under LCF load. Fatigue and creep tests had a total duration of 10 min. A three-element mathematical model was used to predict the cyclic creep strain. Some key findings were that: (1) the residual cyclic modulus varies with the number of load cycles at a given stress level and decreases with an increase in stress level; (2) cyclic creep strain and pure creep strain are strongly influenced by the peak stress level; and creep specimens fail but fatigue specimens do not at a 95% peak stress level; and (3) the three-element mathematical model is appropriate for predicting cyclic creep strain.

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.

Evaluation of the Heat Treatment Role for Light Aluminum Alloys Subjected to Creep and Low Cycle Fatigue

2010 ◽  
Vol 638-642 ◽  
pp. 455-460 ◽  
Author(s):  
A. Rutecka ◽  
L. Dietrich ◽  
Zbigniew L. Kowalewski
Keyword(s):  
Mechanical Properties ◽  
Heat Treatment ◽  
Low Cycle Fatigue ◽  
Numerical Models ◽  
Cyclic Hardening ◽  
Fatigue Tests ◽  
Cycle Fatigue ◽  
Lower Stress ◽  
Creep Tests ◽  
Different Temperatures

The AlSi8Cu3 and AlSi7MgCu0.5 cast aluminium alloys of different composition and heat treatment were investigated to verify their applicability as cylinder heads in the car engines [1]. Creep tests under the step-increased stresses at different temperatures, and low cycle fatigue (LCF) tests for a range of strain amplitudes and temperatures were carried out. The results exhibit a significant influence of the heat treatment on the mechanical properties of the AlSi8Cu3 and AlSi7MgCu0.5. An interesting fact is that the properties strongly depend on the type of quenching. Lower creep resistance (higher strain rates) and lower stress response during fatigue tests were observed for the air quenched materials in comparison to those in the water quenched. Cyclic hardening/softening were also observed during the LCF tests due to the heat treatment applied. The mechanical properties determined during the tests can be used to identify new constitutive equations and to verify existing numerical models.

A Kt-Based Method for Calculating LCF Life of Notched Specimens

1994 ◽  
Vol 116 (4) ◽  
pp. 403-408 ◽  
Author(s):  
N. Merah ◽  
T. Bui-Quoc ◽  
M. Bernard
Keyword(s):  
Fatigue Life ◽  
Stress Concentration ◽  
Stress Level ◽  
Stress Concentration Factor ◽  
Concentration Factor ◽  
Low Cycle Fatigue ◽  
Cyclic Hardening ◽  
Cycle Fatigue ◽  
Unnotched Specimen ◽  
Stress Raisers

Under cyclic loading, the effect of stress raisers on the fatigue life depends upon several parameters, the most important being the stress concentration factor, the stress level, and the material notch sensitivity. In particular, in the low-cycle fatigue region, a number of procedures are currently used, but additional developments are required for improvement of the life prediction capabilities. In this paper, a method is proposed for calculating notched specimen low-cycle fatigue life from unnotched specimen data using as the main parameter the stress concentration factor combined with the applied stress level and the cyclic-hardening properties of the material. The proposed method is then applied to several materials with a variety of notch geometries to obtain the predicted lives. The correlation between the calculated lives and the experimental data is discussed in connection with the predictions obtained from Neuber’s and Zwicky’s relations.

scholarly journals Durability of MAR-247 and IN-713C Nickel Superalloys under Cyclic Creep Conditions

2015 ◽  
Vol 15 (4) ◽  
pp. 17-20
Author(s):  
M. Cieśla ◽  
F. Binczyk ◽  
G. Junak ◽  
M. Mańka ◽  
P. Gradoń
Keyword(s):  
Heat Treatment ◽  
Low Cycle Fatigue ◽  
Solution Treatment ◽  
Cyclic Creep ◽  
Constant Load ◽  
Creep Process ◽  
Cycle Fatigue ◽  
Subsequent Aging ◽  
Fine Grained ◽  
Test Conditions

Abstract Paper presents the assessment of impact of heat treatment on durability in low-cycle fatigue conditions (under constant load) in castings made using post-production scrap of MAR-247 and IN-713C superalloys. Castings were obtained using modification and filtration methods. Additionally, casting made of MAR-247 were subjected to heat treatment consisting of solution treatment and subsequent aging. During low-cycle fatigue test the cyclic creep process were observed. It was demonstrated that the fine-grained samples have significantly higher durability in test conditions and , at the same time, lower values of plastic deformation to rupture Δϵpl. It has been also proven that durability of fine-grained MAR-247 samples can be further raised by about 60% using aforementioned heat treatment.

scholarly journals Experimental Study on the Short-Term Uniaxial Creep Characteristics of Sandstone-Coal Composite Samples

Minerals ◽  
2021 ◽  
Vol 11 (12) ◽  
pp. 1398
Author(s):  
Dawei Yin ◽  
Feng Wang ◽  
Jicheng Zhang ◽  
Faxin Li ◽  
Chun Zhu ◽  
...  
Keyword(s):  
Creep Strain ◽  
Stress Level ◽  
Creep Strength ◽  
Creep Deformation ◽  
Shear Failure ◽  
Composite Sample ◽  
Short Term ◽  
Creep Failure ◽  
Creep Tests ◽  
Composite Samples

In this investigation, the uniaxial short-term creep tests with multi-step loading were conducted on the sandstone-coal composite samples, and the characteristics of creep strength, creep deformation, acoustic emission (AE), and creep failure of composite samples were studied, respectively. The creep strength of the composite sample decreased with the stress-level duration, which was mainly determined by the coal and influenced by the interactions with the sandstone. The creep deformation and damage of sandstone weakened the deformation and damage accumulation within the coal, resulting in the larger strength for the composite sample compared with the pure coal sample. The axial creep strain of composite sample generally increased with the stress-level or the stress-level duration under same conditions. The AE characteristics of composite sample were related to the creep strain rate, the stress level, the stress level duration, and the local failure or fracture during creep loading. The micro or macro failure and fracture within the composite sample caused the rise in the axial creep strains and the frequency and intensity of AE signals, especially the macro failure and fracture. The creep failures of composite samples mainly occurred within the coal with the splitting ejection failure accompanied by the local shear failure, and no obvious failures were found within the sandstone. The coal in the composite sample became more broken with the stress-level duration.

An Investigation of a Heat Exchanger Tubesheet Crack Caused by a Process Upset

2004 ◽  
Author(s):  
Trevor G. Seipp ◽  
Shiju V. P. George
Keyword(s):  
Heat Exchanger ◽  
Residual Stresses ◽  
Crack Propagation ◽  
Low Cycle Fatigue ◽  
Peak Stress ◽  
Propagation Mechanism ◽  
Cycle Fatigue ◽  
Tube Rolling ◽  
Initiation Mechanism ◽  
Crack Propagation Mechanism

A heat exchanger tubesheet experienced cracks in the ligaments between tube holes. This paper describes the analyses that were performed in order to determine the cause of the crack. The first analysis examined the residual stresses in the tubesheet caused by the tube-rolling. It showed that the residual stresses caused by a typical rolling operation would be negligible. The second analysis examined the steady-state operating condition. It indicated that a tensile stress field existed on the surface of the tubesheet — a potential crack propagation driving force. The third analysis examined a thermal transient caused by a process upset. This transient created high peak stress intensities. However, a fatigue analysis indicated that the stress intensities were inadequate to initiate a crack in the low-cycle fatigue regime. The results of these analyses pinpoint the locations of the cracks accurately, and indicated that while a crack propagation mechanism existed, a crack initiation mechanism did not. Therefore, it was concluded that the crack may have been caused in the manufacturing process.

scholarly journals Analysis of Fatigue Life of PMMA at Different Frequencies Based on a New Damage Mechanics Model

2014 ◽  
Vol 2014 ◽  
pp. 1-8 ◽  
Author(s):  
Aifeng Huang ◽  
Weixing Yao ◽  
Fang Chen
Keyword(s):  
Fatigue Life ◽  
Damage Mechanics ◽  
Low Cycle Fatigue ◽  
Low Frequency ◽  
Creep Damage ◽  
Cyclic Creep ◽  
Continuum Damage Mechanics ◽  
Creep Tests ◽  
Damage Evolution Equation ◽  
Load Rate

Low-cycle fatigue tests at different frequencies and creep tests under different stress levels of Plexiglas Resist 45 were conducted. Correspondingly, the creep fracture time,S-Ncurves, cyclic creep, and hysteresis loop were obtained. These results showed that the fatigue life increases with frequency at low frequency domain. After analysis, it was found that fatigue life is dependent on the load rate and is affected by the creep damage. In addition, a new continuum damage mechanics (CDM) model was established to analyze creep-fatigue life, where the damage increment nonlinear summation rule was proposed and the frequency modification was made on the fatigue damage evolution equation. Differential evolution (DE) algorithm was employed to determine the parameters within the model. The proposed model described fatigue life under different frequencies, and the calculated results agreed well with the experimental results.

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