Detection Of Fatigue Damage Research Articles

Improvement of damage detection methods based on experimental modal parameters

The objective of this paper is to introduce a new method for structural damage detection based on experimentally obtained modal parameters. The new method is suitable for detection of fatigue damage occurring in an aluminium cantilever beam. The damage has been practically realised as saw cuts of different sizes and at different locations. The first step of analysis included an attempt of damage identification with the most often used damage indicators based on measured modal parameters. For that purpose special signal processing technique has been proposed improving the effectiveness of indicators tested. However the results obtained have not been satisfactory. That was the motivation for defining new damage indicators (frequency change based damage indicator, Hybrid Damage Detection method), utilising the change of natural frequencies and any mode shape (measured or modelled) as the measurement of frequencies is much less time consuming in comparison to total mode shape measurement. It has been shown that the proposed technique is suitable for damage localisation in beam-like structures.

Design of Impedance Spectroscopy Based Structural Health Monitoring Sensors for Fatigue Damage Detection in Aluminum Beams

Piezoelectric sensors have been previously used for continuous structural health monitoring using impedance spectroscopy. However, three important issues still remain to be investigated for efficient design of such sensors, namely (i) the effect of sensor geometry on sensitivity of impedance based damage detection, (ii) the selection of frequency band for continuous health monitoring, and (iii) identification of damage quantification metric. In this study, we address these issues and report the results on aluminum beam subjected to mechanical fatigue. A commercially available Materials Testing Machine was used in order to perform a load controlled fatigue test (250–1350 lbs @ 20 cycles/sec) on a notched aluminum beam. Sensor geometry was optimized with the help of damage index metric based health monitoring. Next, optimized geometry was selected to further study the selection of frequency band with a new approach based on number of peaks in the impedance signature under identical testing conditions. The results of this study provide a benchmark for designing the sensors for structural health monitoring.

A stochastic fatigue damage model for composite single lap shear joints based on Markov chains and thermoelastic stress analysis

ABSTRACTQuantitative damage detection in composite single lap joints during fatigue is difficult and not practical with many traditional experimental methods. The objective of this study is to combine a new experimental analysis method with existing stochastic models that is capable of taking the scatter inherent in composite fatigue data into account for better representation of damage evolution in single‐lap joints. This study presents a new quantitative approach where thermoelastic stress analysis (TSA), a remote sensing and non‐destructive evaluation technique, is used for in situ continuous monitoring for fatigue damage detection of Fibre Reinfoced Polymeric (FRP) S2‐glass/E733FR single‐lap joints. Image analysis algorithms are developed to capture the debonding fronts, and Markov Chain models (MCMs) are developed to capture the fatigue damage evolution in composite lap‐joints based on the experimental analysis. The TSA damage index at the last fatigue cycle is used to calibrate the MCMs, and damage predictions using the MCMs are then examined at different fatigue cycles. Methods to construct a predictive stochastic S–N curve utilizing the MCMs are discussed. The proposed IR‐TSA with MCMs is shown to be very effective in predicting the damage evolution and allowed constructing S–N curves that take the variability into account for damage in composite single‐lap joints.

Optimum inspection planning for minimizing fatigue damage detection delay of ship hull structures

Fatigue is one of the main factors which can produce cracks, and lead to failure of ships. For these structures, damage occurrence and propagation due to fatigue are affected by the action of sea water waves and the sea environment as well as operation, fabrication, and modeling of ship structures under uncertainties. In order to efficiently maintain the safety of ship structures, an optimum inspection plan should be made by considering these uncertainties using a probabilistic approach. In this paper, such an approach is presented and applied to ship hull structures subjected to fatigue. The resulting inspection plan is the solution of an optimization problem based on the minimization of expected fatigue damage detection delay. Damage detection delay will produce the maintenance delay which, in turn, is likely to endanger the serviceability and even the survival of the structure. The formulation of the expected damage detection delay includes uncertainties associated with damage occurrence, propagation, and detection. The effects of the quality and number of inspections on the optimum inspection planning are investigated. A well-balanced inspection planning is considered as a solution of an optimization problem with two conflicting criteria. This well-balanced inspection planning provides optimum inspection types and times. Furthermore, the cost-effective inspection plans are designed to provide the optimum strategy either by considering a single type or multiple types of inspections.

Digital Image Correlation technique: Application to early fatigue damage detection in stainless steel

In the context of development of a numerical model, to accurately predict the fatigue life of a structural component, it is fundamental to consider both the initiation stage and the propagation stage of micro-cracks. Such a development requires dedicated experimental tools both to provide the physical understanding needed for designing models and to validate the proposed approaches and models. Thus, this paper presents the experimental means that need to be used for such a purpose. The approach is based on the analysis of displacement field measurements by digital image correlation (DIC) during low-cycle fatigue tests. A specific filtering tool is also presented to minimize the committed errors when derivative operation is performed for strain calculation. Therefore, in this quite recent application of DIC, the reproducibility of the method has to be questioned and validated, with help of some more conventional strain measurements devices. It seems that the experimental conditions have to be carefully controlled, so that the results can be interpreted in terms of mechanical phenomena.

In Service Detection of 45 Steel’s Rotary Bending Fatigue Damage Based on Metal Magnetic Memory Technique

In order to study the relation between metal fatigue damage and the associated magnetic memory signals, the detection theory was studied based on magneto mechanical effect, and the rotating bending fatigue experiments on 45 steel were carried out combined with on-line data collecting system. The magnetic signals along axis at prefab defects in the fatigue process were studied. Experimental results show that the characteristics of the magnetic signals are different at every different stage of the fatigue process, in particular the magnetic signal changing faster in the late fatigue process, which indicates that it is feasible to detect fatigue damage using metal magnetic memory technique. Accordingly, the method is proposed to detect the rotation-bending fatigue damage for specimens in service by magnetic signals.

S0305-4-2 地震荷重を受けた原子力用鋼の低サイクル疲労特性とAE挙動([S0305-4]計測・疲労強度)

It is important to expand knowledge for low-cycle fatigue properties of pre-strained nuclear component materials and nondestructive inspection (NDI) techniques for fatigue damage detection when considering resumption of nuclear power plant subjected seismic load. As acoustic emission (AE) monitoring can be applied during fatigue test and operation of plants, we conducted AE monitoring during low-cycle fatigue test. The AE monitoring results showed that reduction of fatigue life by applied high pre-strain was caused by shorten of fatigue crack initiation life. The result also showed that the possibility to use AE monitoring for online monitoring of fatigue damage detection.

1715 原子力用鋼の低サイクル疲労試験中におけるAE発生挙動(OS17-4 低サイクル疲労とその応用-き裂進展評価・モニタリング-)

It is important to expand knowledge for low-cycle fatigue properties of pre-strained nuclear component materials and nondestructive inspection (NDI) techniques for fatigue damage detection when considering resumption of nuclear power plant subjected veiy large load which caused plastic deformation, such as seismic load. As acoustic emission (AE) monitoring can be applied during fatigue test and operation of plants, we conducted AE monitoring during low-cycle fatigue test of austenitic stainless steel. The AE monitoring results showed that reduction of fatigue life by applied high pre-strain was caused by shorten of fatigue crack initiation life. The result also showed that the possibility to use AE monitoring for fatigue damage detection of nuclear power plants.

1704 塑性予ひずみ検出のための電気化学的手法の研究と適用性の検討(OS17-1 低サイクル疲労とその応用-予ひずみ、変動荷重の影響-)

1704 塑性予ひずみ検出のための電気化学的手法の研究と適用性の検討(OS17-1 低サイクル疲労とその応用-予ひずみ、変動荷重の影響-)

A New Wireless Smart Sensor for Fatigue Damage Detection of a Single Steel Bar

In this study, a new wireless smart sensor for fatigue damage detection of a single steel bar is proposed. A modified stress intensity factor is used to introduce a master curve of fatigue crack growth. Acoustic Emission signals are also measured and incorporated in the procedure for the structural health monitoring.

Detecting fatigue damage in 2.25Cr–1Mo steel with scanning SQUID gradiometry

In order to develop a new method for detecting fatigue damage nondestructively in 2.25Cr–1Mo steel, which is used in high temperature steam piping of fossil power plants and petroleum chemical facilities, fractured and interrupted samples in low-cycle fatigue (LCF) tests were investigated using scanning superconducting quantum interference device (SQUID) gradiometer. High temperature LCF experiments on 2.25Cr–1Mo steel were conducted to obtain various fatigue damage ratio, D f . Simultaneously, we also examined the fatigued samples by optical microscopy, electron back scatter diffraction pattern, magnetic force microscopy and hardness measurements to analyze the damage level. Except for a couple of samples, SQUID integrated intensity decreased with increasing D f , suggesting the potential of SQUID to evaluate fatigue damage in 2.25Cr–1Mo steel.

Heat dissipation measurements in low stress cyclic loading of metallic materials: From internal friction to micro-plasticity

The present paper deals with a procedure to measure the very small quantities of heat generated during the very first cycles of mechanical loading on metallic specimens. A dedicated procedure is presented to reach the required sensitivity in terms of heat sources with some original features with respect to the present state of the art, assuming that the heat sources are uniformly distributed within the specimen as such low strain levels. Then steel (cold rolled and annealed) and aluminium specimens were tested at two different aspect ratios ( R σ = 0.1 and R σ = - 1 ). It was shown that for small stress levels, the heat generated was more or less constant with cycle number. This energy was associated to visco-elastic behaviour (internal friction) and it was shown that the same energy could be measured with the two stress ratios when plotted against strain rate (stress amplitude at constant frequency, here 15 Hz). Then, after a certain stress level, an initial outburst of energy was evidenced over about 10–15 cycles before a constant level was reached again. This was associated to micro-plastic adaptation. This procedure provides an advanced tool to tackle the problem of very early fatigue damage detection and is aimed at providing some physical justification to the procedures of rapid fatigue limit detection by self-heating tests.

10204 表面ひずみ測定による回転曲げの疲労損傷検出(強度特性と評価,一般講演)

10204 表面ひずみ測定による回転曲げの疲労損傷検出(強度特性と評価,一般講演)

Statistical pattern analysis of ultrasonic signals for fatigue damage detection in mechanical structures

This paper addresses online monitoring of fatigue damage in polycrystalline alloy structures based on statistical pattern analysis of ultrasonic sensor signals. The real-time data-driven method for fatigue damage monitoring is based on the concepts derived from statistical mechanics, symbolic dynamics and statistical pattern identification. The underlying concept is detection and identification of small changes in statistical patterns of ultrasonic data streams due to gradual evolution of anomalies (i.e., deviations from the nominal behavior) in material structures. The statistical patterns in terms of the escort distributions from statistical mechanics are derived from symbol sequences that, in turn, are generated from ultrasonic sensors installed on the structures under stress cycles. The resulting information of evolving fatigue damage would provide early warnings of forthcoming failures, possibly, due to widespread crack propagation. The damage monitoring method has been validated by laboratory experimentation in real time on a computer-controlled fatigue damage testing apparatus which is equipped with a variety of measuring instruments including an optical travelling microscope and an ultrasonic flaw detector.

1508 発振回路法を用いたひずみ計測の疲労損傷検出への適用性(S10-2 非破壊評価とモニタリングII,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

1508 発振回路法を用いたひずみ計測の疲労損傷検出への適用性(S10-2 非破壊評価とモニタリングII,21世紀地球環境革命の機械工学:人・マイクロナノ・エネルギー・環境)

A study of a fatigue management system for long LNG carriers using a new fatigue damage sensor

A pro-active safety management system for ship structures that quantifies the aging effect such as by fatigue and corrosion on the ship's structural integrity is proposed as a new approach to the ship's structural surveys that have conventionally been made according to a more passive management system. Some of the authors have developed a compact fatigue damage sensor that can detect accumulated fatigue damage in welded structures by attachment to the member and inspection after a certain period. The authors have applied this sensor to the hull structures of an LNG carrier for experimental purposes, ascertained its long-term durability under the severe environment to which the ship was exposed and obtained quantitative data on the accumulated fatigue damage. In this paper, the authors propose a fatigue management system using this sensor called the Hull Aging Management System and propose it as a pro-active safety management system for LNG carrier hull structural aging and introduce a method to improve the accuracy of accumulated fatigue damage detection by using this sensor.

On the non-destructive detection of fatigue damage in industrial aluminium alloys by positron annihilation

The average positron lifetime has been determined non-destructively and in-situ during fully symmetric push-pull fatigue experiments in the bulk material of the aluminium alloys 2024 T3 and 7075 T6 using a servo-hydraulic fatigue testing system equipped with a mobile positron beam produced by a 72Se/72As generator (initial activity of ≈ 0.9 MBq; average positron penetration depth ≥1 mm). Contrary to earlier investigations on stainless steel using the same experimental approach, no variation of the average positron lifetime could be observed during fatigue and neither early nor late stages of fatigue damage could be revealed. It is concluded that fatigue induced changes of the defect spectra in technologically relevant aluminium alloys are masked for the present method by saturation trapping in precipitates. A sufficiently high increase of the dislocation density and the creation of vacancy clusters must be confined to the vicinity of propagating fatigue cracks or the fatal fatigue crack. Therefore the zone with sufficient detectable fatigue damage has not enough statistical weight to modify the average positron lifetime of the aluminium alloy bulk material.

2233 磁気特性変化を用いたSUS304鋼の疲労損傷検出(S15-2 実験力学と材料評価(2),S15 実験力学と材料評価)

For the detection of fatigue damage before crack initiation in an austenitic stainless steel,SUS304, we investigated the possibility of the fatigue damage detection and evaluation from the change in the magnetization. Fatigue tests and measurements of magnetization conducted under the stress ration, R, of -1. The experimental results showed that the location, where the maximum changes in the value of the changes in the leakage magnetic flux density B_z observed, coincided with the location of the stress concentration, where the crack was formed, and the value of B_z rapidly increased before crack initiation. When no crack was found, increasing rate of B_z decreased with increasing the number of cycles, and the value of B_z was saturated to a certain value. It was found that fatigue damage before crack initiation can be detected from the change in the magnetization in SUS304 steel.

OS3-3-1 Fatigue Damage Evaluation of SUS304 Steel Using Magnetism Change in Fatigue Process

For the detection of fatigue damage before crack initiation in an austenitic stainless steel, SUS304, we investigated the possibility of the fatigue damage detection and evaluation from the change in the magnetization. The changes in the magnetization before the fatigue crack initiation were observed in the fatigue process at several stress amplitude and stress ratio. It was found that the changes in the leakage magnetic flux density B_z were observed before crack initiation and the location, where the maximum changes in the value of B_z observed, coincided with the location of the stress concentration, where the crack was formed. The experimental results obtained by fatigue tests conducted under the stress ration, R, of -1, and 0.1 showed that the change in the magnetization of SUS304 specimen was depended on the stress ratio. Under either stress ratio, the value of B_z rapidly increased just before crack initiation. When no crack was found, increasing rate of B_z decreased with increasing the number of cycles, and the value of B_z was saturated to a certain value. It was found that fatigue damage before crack initiation can be detected from the change in the magnetization in SUS304 steel.

704 発振回路法を用いたひずみ計測による疲労損傷検出の可能性(計測・制御II)

704 発振回路法を用いたひずみ計測による疲労損傷検出の可能性(計測・制御II)