CONVERTING CONSTANT AMPLITUDE LOADING OF PRESTRESSED CONCRETE SLEEPER (PCS) FROM VARIABLE AMPLITUDE

2015 ◽  
Vol 76 (11) ◽  
Author(s):  
Sharul Nizam I. ◽  
Afidah A.B. ◽  
Siti Hawa H. ◽  
Mohd Ikmal Fazlan R.
Keyword(s):  
Fatigue Life ◽  
Prestressed Concrete ◽  
Constant Amplitude ◽  
Variable Loading ◽  
Study Variable ◽  
Variable Amplitude ◽  
Railway System ◽  
Rainflow Cycle Counting ◽  
Number Of Cycles ◽  
Stress Block

Prestressed Concrete Sleepers are structures that support railway system and absorb variable loading from the train that pass along the rail. In this study, variable amplitude loading from PCS taken from site measurement was converted into constant amplitude loading. Therefore the number of cycles and frequency are also important to be determined. There are various method for counting the number of cycles and the best adoptive method was Rainflow Cycle Counting. Once the number of cycles is obtained as well as the constant amplitude stress in a series of stress block, the prediction of fatigue life of PCS can be analyzed by further research in the laboratory work. However the limitation of this study is only to obtain the constant amplitude loading of PCS and also counting the number of cycles in various series of stress blocks.

CONSTANT AMPLITUDE SPECTRUM OF THREE COACHES TRAIN AND CYCLIC COUNTING ON PRESTRESSED CONCRETE SLEEPERS (PCS)

2015 ◽  
Vol 76 (11) ◽  
Author(s):  
Mohd Ikmal Fazlan R. ◽  
Sharul Nizam I. ◽  
Afidah A.B. ◽  
Siti Hawa H.
Keyword(s):  
Prestressed Concrete ◽  
Constant Amplitude ◽  
Counting Method ◽  
Loading Test ◽  
Freight Train ◽  
Variable Amplitude ◽  
Amplitude Data ◽  
Strain Data ◽  
Rainflow Cycle Counting ◽  
Current Loading

The raw strain data collected from Keretapi Tanah Melayu Berhad (KTMB) railway are in variable amplitude. This paper discovers how the variable amplitude data can be changed to the constant amplitude data. It is found that the raw strain data is not suitable for fatigue and strength testing on Prestressed Concrete Sleepers (PCS). Apart from that, the most suitable method in determining the numbers of cycles is Rainflow Cycle Counting Method. Through rainflow cycle counting method, the number of cycles is determined. The numbers of cycles are used to simplify the laboratory test such as fatigue and strength test for the PCS. The frequencies of dynamic loading test on the PCS are set based the numbers of cycles. The constant strain data are also converted into constant loading data using the relationship of stress-strain and loading-stress. Constant amplitude loading will again simplify the laboratory testing. The goal is to show that the designs used in PCS are appropriate based on current loading demand. Then, a comparison of constant amplitude data is made between different numbers of coaches and freight train. The maximum data from the comparison shows that the higher loadings are obtained from freight train.

Effect of Cycle-Counting Methods on Effective Stress Range and Number of Stress Cycles for Fatigue-Prone Details

2000 ◽  
Vol 1740 (1) ◽  
pp. 49-60 ◽  
Author(s):  
Shima Najem Clarke ◽  
David W. Goodpasture ◽  
Richard M. Bennett ◽  
J. Harold Deatherage ◽  
Edwin G. Burdette
Keyword(s):  
Fatigue Life ◽  
Effective Stress ◽  
Stress Range ◽  
Variable Amplitude ◽  
Counting Methods ◽  
Rainflow Cycle Counting ◽  
The Mean ◽  
Stress Cycles ◽  
Number Of Cycles ◽  
Two Parameters

Two important parameters in fatigue life evaluations of existing steel highway bridges are the number of stress cycles experienced and the effective stress range. The inaccuracies in predicting remaining fatigue life can be attributed to either one of these two parameters. However, the AASHTO guide specification has no provisions for the cycle-counting methods to be used to determine these two parameters. A sensitivity analysis that addresses the effects of cycle-counting methods on the effective stress range and the number of cycles for various fatigue-prone details in both main and secondary bridge members is described. A comparison of five cycle-counting methods (level-crossing counting, peak counting, simple-range counting, mean-crossing-peak counting, and rain-flow counting) by using a simple variable-amplitude strain-time history showed that both the stress range and the number of cycles are sensitive to cycle-counting methods. Two of the most commonly used cycle-counting techniques for highway bridge variable-amplitude loading are the mean-crossing-peak and the rainflow cycle-counting methods. A comparison of the two methods by using field data taken under normal traffic showed that the rainflow cycle-counting method is more conservative than the mean-crossing-peak method. The relationship between the mean-crossing-peak and the rainflow cycle-counting methods was determined in the form of a correlation coefficient and a linear regression line. There is a nearly perfect positive correlation between the two methods. Therefore, values obtained for the effective stress range and the number of cycles by the mean-crossing-peak method can be converted to values for the rainflow method.

The Effect of Crack Growth Retardation when Comparing Constant Amplitude to Variable Amplitude Loading in an Aluminium Alloy

2014 ◽  
Vol 891-892 ◽  
pp. 948-954 ◽  
Author(s):  
Madeleine Burchill ◽  
Simon A. Barter ◽  
Michael Jones
Keyword(s):  
Growth Rate ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Retardation ◽  
Crack Front ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Growth Increments ◽  
Crack Growth Retardation

It has often been observed that the growth of short fatigue cracks under variable amplitude (VA) cyclic loading is not well predicted when utilising standard constant amplitude (CA) crack growth rate/stress intensity data (da/dN v DK). This paper outlines a coupon fatigue test program and analyses, investigating a possible cause of crack growth retardation from CA-only testing. Various test loading spectra were developed with sub-blocks of VA and CA cycles, then using quantitative fractography (QF) the sub-block crack growth increments were measured. Comparison of these results found that, after establishing a consistent uniform crack front using a VA load sequence, the average crack growth rate then progressively slowed down with the number of subsequent CA load cycles applied. Further fractographic investigation of the fracture surface at the end of each CA and VA sub-block crack growth, identified significant crack front morphology differences. Thus it is postulated that a variation or deviation from an efficient crack path is a driver of local retardation in short crack growth during CA loading. This may be a source of error in analytical predictions of crack growth under VA spectra loading that may need to be considered in addition to other potential effects such asless closure whilst cracks are small. For aircraft designers, using solely CA data for fatigue life predictions this may result in non-conservative estimates of total crack fatigue life, producing unexpected failures or an increased maintenance burden.

Applicability of Equivalent Constant Amplitude Loading for Assessing the Fatigue Life of Pipelines and Risers and the Influence of Compressive Stress Cycles

2013 ◽  
Vol 135 (2) ◽  
Author(s):  
Mohammad Iranpour ◽  
Farid Taheri
Keyword(s):  
Experimental Investigation ◽  
Fatigue Life ◽  
Compressive Stress ◽  
Time History ◽  
Life Assessment ◽  
Constant Amplitude ◽  
Safety Factors ◽  
Variable Amplitude ◽  
Fatigue Life Assessment ◽  
Stress Cycles

Fatigue life assessment of pipelines and risers is a complex process, involving various uncertainties. The selection of an appropriate fatigue model is important for establishing the inspection intervals and maintenance criteria. In offshore structures, the vortex-induced vibration (VIV) could cause severe fatigue damage in risers and pipelines, resulting in leakage or even catastrophic failure. The industry has customarily used simple fatigue models for fatigue life assessment of pipelines and risers (such as the Paris or Walker models); however, these models were developed based on constant amplitude loading scenarios. In contrast, VIV-induced stress-time history has a variable amplitude nature. The use of the simplified approach (which is inherently non conservative), has necessitated the implementation of large safety factors for fatigue design of pipelines and risers. Moreover, most of the experimental investigations conducted to date with the aim of characterizing the fatigue response of pipelines and risers have been done based on incorporation of constant amplitude loading (CAL) scenarios (which is unrealistic), or converting the variable amplitude loading (VAL) scenarios to an equivalent CAL. This study demonstrates that the use of such approaches would not be lead to accurate assessment of the fatigue response of risers subject to VIV-induced VAL. The experimental investigation performed in this study will also clarify the underlying reasons for the use of large safety factors by the industry when assessing the fatigue life of pipelines and risers. In addition, an experimental investigation was also conducted to highlight the influence of the compressive portion of VIV stress-time history on the fatigue life of such components. It is shown that the compressive stress cycles significantly influence the fatigue crack growth response of risers, and their presence should not be ignored.

scholarly journals Fatigue Performance of Natural and Synthetic Rattan Strips Subjected to Cyclic Tensile Loading

Forests ◽  
2022 ◽  
Vol 13 (1) ◽  
pp. 76
Author(s):  
Yanting Gu ◽  
Jilei Zhang
Keyword(s):  
Tensile Strength ◽  
Fatigue Life ◽  
Ultimate Tensile Strength ◽  
Applied Stress ◽  
Stress Level ◽  
Tensile Loading ◽  
Constant Amplitude ◽  
Tensile Fatigue ◽  
Number Of Cycles ◽  
Cycles To Failure

Tensile fatigue performances of selected natural rattan strips (NRSs) and synthetic rattan strips (SRSs) were evaluated by subjecting them to zero-to-maximum constant amplitude cyclic tensile loading. Experimental results indicated that a fatigue life of 25,000 cycles began at the stress level of 50% of rattan material ultimate tensile strength (UTS) value for NRSs evaluated. Rattan core strips’ fatigue life of 100,000 cycles started at the stress level of 30% of its UTS value. Rattan bast strips could start a fatigue life of 100,000 cycles at a stress level below 30% of material UTS value. SRSs didn’t reach the fatigue life of 25,000 cycles until the applied stress level reduced to 40% of material UTS value and reached the fatigue life of 100,000 cycles at the stress level of 40% of material UTS value. It was found that NRSs’ S-N curves (applied nominal stress versus log number of cycles to failure) could be approximated by S=σou(1−H×log10⋅Nf). The constant H values in the equation were 0.10 and 0.08 for bast and core materials, respectively.

Microstructural Behaviour Study and FEA-Based Fatigue Simulation on Parabolic Leaf Spring

2011 ◽  
Vol 462-463 ◽  
pp. 419-424
Author(s):  
Fayyadh Nakhaie Ahmad Refngah ◽  
Shahrum Abdullah ◽  
Azman Jalar ◽  
L.B. Chua
Keyword(s):  
Fatigue Life ◽  
Fatigue Test ◽  
Leaf Spring ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Fea Model ◽  
Fracture Area ◽  
Tension And Compression ◽  
Behaviour Study ◽  
Parabolic Leaf Spring

It is compulsory to have a good fatigue life to a component that is heavily subjected to cyclic loading. One of the good examples is parabolic spring, which is one of the components in suspension system for large vehicles. It serves to absorb, store and release back the damping energy due to road irregularity, bump and holes. These activities involve a lot of camber deflection that caused by the tension and compression loads. In reality, the loading that subjected to parabolic spring is variable amplitude loading, but most of the manufacturer used constant amplitude (CA) loading for the fatigue test. The objective of this paper is to relate the simulation result with the microstructure behaviour of the leaf spring that failed due to fatigue. A full scale fatigue test was carried out until that parabolic spring meet failure. In order to investigate the fatigue life, CA signal was generated based on an actual fatigue test on the parabolic spring, and it was then analysed using the FEA-based fatigue simulation. A microstructure study was then performed for both fracture and non-fracture area. From the FEA-based simulation, it gave the prediction on damage that occurred at the critical area and also the prediction on the lowest cycle with respect to the FEA model. In the actual fatigue test, the failure was occurred at the centre part of the spring, which is at bolt join of assembly hole. The microstructure analysis showed that the grain at the fracture area indicated some different from the non-fracture area in term of size, phase and precipitation of carbon.

Corrosion Fatigue of AZ91E-T6 Cast Magnesium Alloy in a 3.5 Percent NaCl Aqueous Environment

1995 ◽  
Vol 117 (3) ◽  
pp. 293-298 ◽  
Author(s):  
R. I. Stephens ◽  
C. D. Schrader ◽  
K. B. Lease
Keyword(s):  
Fatigue Life ◽  
Magnesium Alloy ◽  
Fatigue Behavior ◽  
Fatigue Tests ◽  
Mean Stress ◽  
Constant Amplitude ◽  
Variable Amplitude ◽  
Cast Magnesium Alloy ◽  
Cast Magnesium ◽  
Variable Amplitude Fatigue

The objective of this research was to obtain and compare constant and variable amplitude fatigue behavior of AZ91E-T6 cast magnesium alloy in both an air and 3.5 percent NaCl aqueous corrosive environment. An additional objective was to determine if commonly used models that describe fatigue behavior and fatigue life are applicable to this material and test environment. Fatigue tests included constant amplitude strain-controlled low cycle fatigue with strain ratio, R, equal to 0, −1 and −2, Region II constant amplitude fatigue crack growth with load ratio, R, equal to 0.05 and 0.5 and variable amplitude fatigue tests using keyhole notched specimens. In all fatigue tests, the corrosion environment was significantly detrimental relative to the air environment. Mean strains influenced fatigue life only if accompanied by significant mean stress. The Morrow and Smith, Watson, and Topper mean stress models provided both accurate and inaccurate fatigue life calculations. Likewise, variable amplitude fatigue life calculations using the local strain approach and based upon the formation ofal mm crack at the keyhole notch were both accurate and fairly inaccurate depending on the specific model used.

Influence of the Selected Fatigue Characteristics of the Material on Calculated Fatigue Life under Variable Amplitude Loading

2011 ◽  
Vol 104 ◽  
pp. 197-205 ◽  
Author(s):  
Adam Niesłony ◽  
Andrzej Kurek
Keyword(s):  
Fatigue Life ◽  
Energy Parameter ◽  
Correct Selection ◽  
Constant Amplitude ◽  
Random Loading ◽  
Data Set ◽  
Variable Amplitude ◽  
Comparison Results ◽  
Machine Elements ◽  
Fatigue Characteristics

The algorithm of fatigue life determination for machine elements subjected to random loading uses fatigue characteristics of the material determined under constant-amplitude loading. They are usually stress or strain characteristics as well as characteristics using the energy parameter. Their correct selection influences correctness of the obtained results related to the experimental data. The paper presents analysis of convergence of the calculated fatigue lives of some constructional materials subjected to random loading under uniaxial loading state. For calculations concerning one material the same loading state was assumed and fatigue characteristics were determined on the basis of one data set obtained under constant strain amplitude tests. Calculated fatigue lives based on different fatigue characteristics were compared and their convergences were tested. It has been proved that convergences are different depending on the material. The comparison results were presented in form of graphs.

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