Development of Fatigue Detecting Sensor

2004 ◽  
Vol 261-263 ◽  
pp. 1313-1318 ◽  
Author(s):  
T. Kobayashi ◽  
O. Muragishi ◽  
K. Nihei
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Sampling Period ◽  
Growth Characteristics ◽  
Life Assessment ◽  
Metal Foil

A fatigue detecting sensor that enables easy and precise estimation of fatigue damage of machines and structures was developed, based on the crack growth characteristics of metal. The sensor is composed of a metal foil with a single edge notch and a base metal foil. The two metal foils are bonded at the both far ends. The sensor is attached with an adhesive to the surface of structural member which is subjected to cyclic loads. The fatigue damage of the member is detected as the fatigue crack initiation from the notch tip of the sensor. The fatigue crack growth rate is independent of the crack length. The metal foil of the sensor is given pre-tension, so the sensor has stable crack growth characteristics independent of the average strain. The crack growth length is measured in a certain period after the installation. The length is converted to the fatigue damage of the member during the sampling period of sensor installation. Since no measuring instrument and signal wiring is necessary, the diagnosis procedure becomes easy and the cost for structural health monitoring could be reduced. With such small size of the sensor as conventional strain gages, the pin-pointed application of the sensor to the hot spot of structural stress concentration, where is important for the fatigue strength estimation of welded structures, is possible. Therefore, precise fatigue remaining life assessment could be carried out. Sensors with several strain ranges were developed, so application to vast strain range is possible. Even such a small strain range as 1/10000 is able to be detected. The sensors have been applied to various products like steel bridges, rolling stocks, ships, etc.

Fatigue Life Assessment for Variable Strain in a Mixing Tee by Use of Effective Strain Range

2021 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Fatigue Life ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Effective Strain ◽  
Strain Range ◽  
Life Assessment ◽  
Miner’S Rule ◽  
Loading Sequence ◽  
Miner's Rule

Abstract Mixing flow causes fluctuations in fluid temperature near a pipe wall and may result in fatigue crack initiation. Movement of the hot spot, at which the pipe inner surface was heated by hot flow from the branch pipe, causes thermal stress fluctuations. In this study, the effect of the loading sequence on thermal fatigue in a mixing tee was investigated. In addition, the prediction method of the fatigue life for the variable thermal strain in the mixing tee was discussed. The time histories of the strain around the hot spot were estimated by finite element analysis for which the temperature condition was determined by wall temperature measured in a mock-up test. The accumulated fatigue damage around the hot spot obtained by Miner's rule was less than 1.0. Since the strain around the hot spot had waveforms with periodic overload, the loading sequence with periodic overload caused reduction of the fatigue life around the hot spot. Crack growth tests showed that a single overload decreased crack opening strain and increased the effective strain range. The increment of the effective strain range accelerated the crack growth rate after the overload. The accumulated fatigue damage for the strain in the mixing tee was calculated using Miner's rule and the strain ranges which added the maximum increment of the effective strain range. The accumulated fatigue damage was larger than 1.0 under most conditions. The proposed procedure is suitable to predict the conservative fatigue life in a mixing tee.

Modeling of Fatigue Crack Propagation

2004 ◽  
Vol 126 (1) ◽  
pp. 77-86 ◽  
Author(s):  
Yanyao Jiang ◽  
Miaolin Feng
Keyword(s):  
Fatigue Crack ◽  
Fatigue Crack Growth ◽  
Crack Initiation ◽  
Crack Propagation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Fatigue Crack Propagation ◽  
Fatigue Crack Initiation ◽  
Cyclic Plasticity ◽  
R Ratio

Fatigue crack propagation was modeled by using the cyclic plasticity material properties and fatigue constants for crack initiation. The cyclic elastic-plastic stress-strain field near the crack tip was analyzed using the finite element method with the implementation of a robust cyclic plasticity theory. An incremental multiaxial fatigue criterion was employed to determine the fatigue damage. A straightforward method was developed to determine the fatigue crack growth rate. Crack propagation behavior of a material was obtained without any additional assumptions or fitting. Benchmark Mode I fatigue crack growth experiments were conducted using 1070 steel at room temperature. The approach developed was able to quantitatively capture all the important fatigue crack propagation behaviors including the overload and the R-ratio effects on crack propagation and threshold. The models provide a new perspective for the R-ratio effects. The results support the notion that the fatigue crack initiation and propagation behaviors are governed by the same fatigue damage mechanisms. Crack growth can be treated as a process of continuous crack nucleation.

Fatigue Crack Initiation and Growth Observation for 316 Stainless Steel Subjected to Equi-Biaxial Cyclic Loading

2015 ◽  
Author(s):  
Satoshi Iida ◽  
Shigeki Abe ◽  
Takao Nakamura ◽  
Masayuki Kamaya
Keyword(s):  
Fatigue Crack ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Equivalent Stress ◽  
Fatigue Crack Initiation ◽  
Biaxial Stress ◽  
Fluid Temperature ◽  
Plant Design ◽  
Cracking Behavior ◽  
Thermal Transients

Fatigue accumulation is one of the ageing phenomena considered in the plant design and maintenance. The degree of fatigue damage is evaluated by cumulative usage factor using design fatigue curve, which is determined from results of uniaxial fatigue tests. The stress caused by thermal transients is generally equibiaxial, not uniaxial. Fluid temperature fluctuation due to changes in plant conditions, such as plant start-up and shutdown, is the primary cause of fatigue damage. For accurate fatigue damage evaluation, it is important to be conducted under equi-biaxial condition. In this study, pressurized disc fatigue test was conducted in order to simulate the cyclic equi-biaxial stress. In order to clarify how the crack initiates and grows under the equi-biaxial stress condition. Cracking behavior was examined by replica observation method. The crack growth rates were identified by the change in the crack length. It was shown that the fatigue crack growth rate under equi-biaxial stress was faster than that under uniaxial stress for the same equivalent stress intensify factor. It was concluded that the reduction in the fatigue life under equi-biaxial stress was brought about by the accelerated crack growth.

Fatigue Life Prediction for Variable Strain at a Mixing Tee by Use of Effective Strain Amplitude

2020 ◽  
Author(s):  
Koji Miyoshi ◽  
Masayuki Kamaya
Keyword(s):  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Hot Spot ◽  
Effective Strain ◽  
Single Overload ◽  
Loading Sequence

Abstract Mixing flow causes fluid temperature fluctuations near the pipe walls and may result in fatigue crack initiation. The authors have previously reported the loading sequence effect on thermal fatigue in a mixing tee. The fatigue damage around the hot spot, which was heated by the hot jet flow from the branch pipe, obtained by Miner’s rule was less than 1.0. Since the strain around the hot spot had waveforms with periodic overload, the loading sequence with periodic overload caused reduction of the fatigue life around the hot spot. In this study, the effect of a single overload on the fatigue crack growth rate was investigated in order to clarify the reduction of the fatigue life at the mixing tee due to strain with periodic overload. In addition, the prediction method of the fatigue life for the variable thermal strain at the mixing tee was discussed. It was shown the crack growth rate increased after an overload for both cases of tensile and compressive overloads. The effective strain amplitude increased after the application of a single overload. The fatigue life curve was modified by considering the increment of the effective strain range. The fatigue damage recalculated using the modified fatigue life curve was larger than 1.0 except in a few cases. The fatigue life could be assessed conservatively for variable strain at the mixing tee using the developed fatigue curve and Miner’s rule.

Mechanisms of fatigue crack initiation in annealed, quenched and tempered 4340 steel

2000 ◽  
Vol 214 (9) ◽  
pp. 1151-1161 ◽  
Author(s):  
F Yang ◽  
A Saxena
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Fatigue Damage ◽  
Fatigue Crack Initiation ◽  
Strain Range ◽  
Remaining Life ◽  
Structural Components ◽  
Atomic Force ◽  
Slip Bands ◽  
4340 Steel

The mechanisms of fatigue crack initiation in annealed and quenched and tempered 4340 steel were characterized. Several axial fatigue specimens were tested at a strain range of 1.5 per cent to various fractions of fatigue life. The tested specimens were thoroughly examined using a scanning electron microscope (SEM) and an atomic force microscope (AFM). The latter technique provides a better resolution and is also capable of providing quantitative surface topographical information. In annealed 4340 steel, the initial fatigue damage is shown to accumulate in the form of steps between ferrite and cementite laths in the pearlitic microstructure. Subsequent damage accumulation occurs by formation of slip bands which are formed by joining several adjoining steps. Cracks initiate from the slip bands. In quenched and tempered steels, the fatigue damage accumulates at discontinuities at a more rapid rate than in the remaining regions of the specimen, leading to crack initiation and growth emanating primarily from the discontinuities. The roughness of the specimen surface increases with fatigue damage in both microstructures, as demonstrated from the measurements obtained from AFM studies. Such correlations may be useful in predicting the remaining life of cyclically loaded structural components.

scholarly journals Microstructural mechanisms of cyclic deformation, fatigue crack initiation and early crack growth

2015 ◽  
Vol 373 (2038) ◽  
pp. 20140132 ◽  
Author(s):  
Haël Mughrabi
Keyword(s):  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Cyclic Deformation ◽  
Damage Evolution ◽  
Fatigue Cracks ◽  
Fatigue Crack Initiation ◽  
Cycle Fatigue ◽  
Cubic Metals

In this survey, the origin of fatigue crack initiation and damage evolution in different metallic materials is discussed with emphasis on the responsible microstructural mechanisms. After a historical introduction, the stages of cyclic deformation which precede the onset of fatigue damage are reviewed. Different types of cyclic slip irreversibilities in the bulk that eventually lead to the initiation of fatigue cracks are discussed. Examples of trans- and intercrystalline fatigue damage evolution in the low cycle, high cycle and ultrahigh cycle fatigue regimes in mono- and polycrystalline face-centred cubic and body-centred cubic metals and alloys and in different engineering materials are presented, and some microstructural models of fatigue crack initiation and early crack growth are discussed. The basic difficulties in defining the transition from the initiation to the growth of fatigue cracks are emphasized. In ultrahigh cycle fatigue at very low loading amplitudes, the initiation of fatigue cracks generally occupies a major fraction of fatigue life and is hence life controlling.

An experimental study of initial flaws in thin sheets of 2024 aircraft aluminium alloy

2014 ◽  
Vol 5 (2) ◽  
pp. 120-128 ◽  
Author(s):  
Wyman Zhuang ◽  
Qianchu Liu ◽  
Cathy Smith
Keyword(s):  
Experimental Study ◽  
Fatigue Crack ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Optical Microscope ◽  
Life Assessment ◽  
Content Type ◽  
Essential Input ◽  
Surface Discontinuities

Purpose – One of the challenges in the prediction of fatigue crack growth is to identify representative initial flaws and defects that can cause fatigue crack initiation and subsequent crack growth. Representative initial flaws identified from this experimental study provided an essential input for the fatigue life assessment programme of the PC-9/A training aircraft currently in service. The paper aims to discuss these issues. Design/methodology/approach – This paper addresses this challenge with a critical literature review and experimental assessment of initial flaw types that may cause fatigue crack initiation, by fatigue testing and fractography analysis using optical microscope and scanning electron microscopy (SEM). Findings – With a focus on aluminium alloy (AA) 2024-T3 thin sheet, the results cover various discontinuities from microstructural constituent particles inherent from the material process to macrostructural defects and surface discontinuities (such as burrs and machining marks) introduced during the production of airframes. It was found that most fatigue cracks originated from the bore surface discontinuities of rivet holes in the PC-9 vertical stabiliser thin panels rather than microstructural material defects of AA2024-T3 inherent from the material process. Research limitations/implications – The experimental study has found that quantifying fatigue initial flaw sizes which resulted from poorly finished fastener holes with arbitrary discontinuities at the surface is a challenging topic. This topic is under the current investigation using a statistics based analysis of initial flaws in the prediction of fatigue crack growth. Practical implications – The results obtained from this experimental study provided an essential input for the empennage and aft fuselage recertification and life assessment programme for the PC-9/A training aircraft currently in service. Originality/value – This experimental study examined AA2024-T3 thin skin panels from two different PC-9/A aircraft. The post-test failure analysis using optical microscope and SEM found that machining defects dominate fatigue crack initiation that can result in subsequent crack propagation.

Analysis of Black Hawk Main Transmission Support Beam In-Service Fatigue Crack

2014 ◽  
Vol 891-892 ◽  
pp. 708-713
Author(s):  
John Vine ◽  
Phil Jackson ◽  
Wei Ping Hu
Keyword(s):  
Fatigue Crack ◽  
Service Life ◽  
Stress Analysis ◽  
Crack Growth ◽  
Fatigue Damage ◽  
Primary Structure ◽  
Fatigue Cracking ◽  
Growth Characteristics ◽  
Fractographic Analysis ◽  
Methods And Techniques

The Australian Defence Science and Technology Organisation (DSTO) was recently tasked with evaluating an in-service fatigue crack discovered in the primary structure of an Australian Army Black Hawk helicopter. This crack, discovered early in the affected components service life, was quite large and subsequent fractographic analysis generated substantial information with respect to its growth characteristics. Consequently, it was decided to use this in-service fatigue crack to test the ability of those methods and technologies being developed at DSTO to model and assess a ‘real’ example of helicopter airframe fatigue cracking. This paper details the process of analysing an in-service fatigue crack using methods and technologies developed and/or improved at DSTO in the areas of visualisation, fatigue spectra generation, load and stress analysis, and crack growth prediction. Results will highlight the effectiveness of the methods and techniques in modelling the observed fatigue damage and areas where further improvements are required.

Fatigue Crack Growth of Alloy 7050-T7451 Plate in L-S Orientation

2012 ◽  
Vol 525-526 ◽  
pp. 221-224
Author(s):  
Rui Bao ◽  
Xiao Chen Zhao ◽  
Ting Zhang ◽  
Jian Yu Zhang
Keyword(s):  
Growth Rate ◽  
Stress Intensity Factor ◽  
Fatigue Crack ◽  
Stress Intensity ◽  
Crack Growth Rate ◽  
Crack Growth ◽  
Growth Characteristics ◽  
Stress Intensity Factor Range ◽  
Constant Amplitude ◽  
Stress Ratios

Experiments have been conducted to investigate the crack growth characteristics of 7050-T7451 aluminium plate in L-S orientation. Two loading conditions are selected, i.e. constant amplitude and constant stress intensity factor range (ΔK). The effects of ΔK-levels and stress ratios (R) on crack splitting are studied. Test data shows that crack splitting could result in the reverse of crack growth rate trend with the increasing R ratio at high ΔK-level. The appearance of crack splitting depends on both ΔK and R.

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