scholarly journals On the probability of an undetected surface-breaking crack

2008 ◽  
Vol 35 (1-3) ◽  
pp. 1-10
Author(s):  
J.D. Achenbach ◽  
S.S. Kulkarni
Keyword(s):  
Crack Detection ◽  
Fatigue Cracks ◽  
Crack Depth ◽  
Critical Value ◽  
Stress Fields ◽  
Cyclic Loads ◽  
Paris Law ◽  
Number Of Cycles ◽  
Damage Tolerant ◽  
Surface Breaking Crack

Surface-breaking fatigue cracks are common defects in metal components subjected to cyclic loads. Such cracks tend to propagate in stress fields that are below the critical stress level for static loading. An important part of a damage tolerant design philosophy is the requirement that surface-breaking cracks should be detectable before they reach a critical depth. In this paper, we consider a surface-breaking crack in a two-dimensional geometry, whose original depth is defined by a probability density function. The increase of the crack depth with number of cycles is governed by Paris law, and the detectability depends on a probability of crack detection (POD). Based on this information we determine the probability that the crack depth will have exceeded a prescribed critical value at a specified number of cycles.

Rotordynamic Crack Diagnosis: Distinguishing Crack Depth and Location

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
Philip Varney ◽  
Itzhak Green
Keyword(s):  
Condition Monitoring ◽  
Crack Detection ◽  
Fatigue Cracks ◽  
Equations Of Motion ◽  
Crack Depth ◽  
Forced Response ◽  
Contour Plot ◽  
Crack Model ◽  
Finite Width ◽  
Shaft Speed

The goal of this work is to establish simple condition monitoring principles for diagnosing the depth and location of transverse fatigue cracks in a rotordynamic system. The success of an on-line crack diagnosis regimen hinges on the accuracy of the crack model, which should account for the crack's depth and location. Two gaping crack models are presented; the first emulates a finite-width notch typically manufactured for experimental purposes, while the second models a gaping fatigue crack. The rotordynamic model used herein is based upon an available overhung rotordynamic test rig that was originally constructed to monitor the dynamics of a mechanical face seal. Four degree-of-freedom, linear equations of motion for both crack models are presented and discussed. Free and forced response analyses are presented, emphasizing results applicable to condition monitoring and, particularly, to diagnosing the crack parameters. The results demonstrate that two identifiers are required to diagnose the crack parameters: the 2X resonance shaft speed and the magnitude of the angular 2X subharmonic resonance. First, a contour plot of the 2X resonance shaft speed versus crack depth and location is generated. The magnitude of the 2X resonance along the desired 2X frequency contour is then obtained, narrowing the possible pairs of crack location and depth to either one or two possibilities. Practical aspects of the suggested diagnostic procedure are discussed, as well as qualitative observations concerning crack detection.

scholarly journals Mechanical structural health prognosis with nonlinear mixed frequency ultrasonic signal analysis

2021 ◽  
Vol 268 ◽  
pp. 01075
Author(s):  
Hanxin Chen ◽  
Mingming Liu ◽  
Zhenyu Hu ◽  
Menglong Li ◽  
Sen Li
Keyword(s):  
Crack Detection ◽  
Prediction Models ◽  
Fatigue Cracks ◽  
Crack Depth ◽  
Research Work ◽  
Nonlinear Coefficient ◽  
Difference Frequency ◽  
Average Error ◽  
Sum Frequency ◽  
The Difference

In order to detect the early fatigue crack of mechanical components simply, this paper puts forward the ultrasonic testing technology of different side collinear mixing. Firstly, based on the nonlinear ultrasonic theory, the method of calculating the difference frequency and sum frequency nonlinear coefficients of mixing ultrasonic is deduced. Then, the ram-5000 SINAP ultrasonic system is used to detect the aluminum alloy specimens with five different depth fatigue cracks, and the corresponding spectrum diagram is drawn. From the experimental results, we get that the crack depth is positively correlated with the nonlinear coefficients of difference frequency and sum frequency within a certain crack depth. Finally, by analyzing and fitting the experimental data, the prediction models of the difference frequency and sum frequency nonlinear coefficients on the crack depth are established. Through the analysis and combination of the above two prediction models, the prediction model of the mixing relative nonlinear coefficient is established, and the average error of the three prediction models is compared. The results show that the mixing relative nonlinear model has better results. The research work in this paper makes a useful exploration for crack detection and crack depth prediction.

Assessment of thermal behavior of a cooling system to reduce thermal fatigue cracks in aluminum injection molds

2020 ◽  
pp. 75-86
Author(s):  
Sergio Antonio Camargo ◽  
Lauro Correa Romeiro ◽  
Carlos Alberto Mendes Moraes
Keyword(s):  
Thermal Fatigue ◽  
Cooling System ◽  
Fatigue Cracks ◽  
Cooling Water ◽  
Thermal Conditions ◽  
Thermal Gradients ◽  
Ansys Software ◽  
Cooling Systems ◽  
Thermal Fatigue Cracks ◽  
Number Of Cycles

The present article aimed to test changes in cooling water temperatures of males, present in aluminum injection molds, to reduce failures due to thermal fatigue. In order to carry out this work, cooling systems were studied, including their geometries, thermal gradients and the expected theoretical durability in relation to fatigue failure. The cooling system tests were developed with the aid of simulations in the ANSYS software and with fatigue calculations, using the method of Goodman. The study of the cooling system included its geometries, flow and temperature of this fluid. The results pointed to a significant increase in fatigue life of the mold component for the thermal conditions that were proposed, with a significant increase in the number of cycles, to happen failures due to thermal fatigue.

Fatigue crack detection method using analysis of vibration signal

2017 ◽  
Vol 1 (20) ◽  
pp. 63-74 ◽  
Author(s):  
Arkadiusz Rychlik ◽  
Krzysztof Ligier
Keyword(s):  
Crack Detection ◽  
Fatigue Cracks ◽  
Fatigue Cracking ◽  
Vibration Signal ◽  
Technical Condition ◽  
Visual Methods ◽  
Signal Characteristics ◽  
Fatigue Crack Detection ◽  
Sample Structure ◽  
Change Identification

This paper discusses the method used to identify the process involving fatigue cracking of samples on the basis of selected vibration signal characteristics. Acceleration of vibrations has been chosen as a diagnostic signal in the analysis of sample cross section. Signal characteristics in form of change in vibration amplitudes and corresponding changes in FFT spectrum have been indicated for the acceleration. The tests were performed on a designed setup, where destruction process was caused by the force of inertia of the sample. Based on the conducted tests, it was found that the demonstrated sample structure change identification method may be applied to identify the technical condition of the structure in the aspect of loss of its continuity and its properties (e.g.: mechanical and fatigue cracks). The vibration analysis results have been verified by penetration and visual methods, using a scanning electron microscope.

scholarly journals Monitoring a sudden crack of beam-like bridge during earthquake excitation

2013 ◽  
Vol 35 (3) ◽  
Author(s):  
Nguyen Viet Khoa
Keyword(s):  
Fourier Transform ◽  
Crack Detection ◽  
Crack Depth ◽  
Sudden Change ◽  
Wavelet Spectrum ◽  
Cracked Beam ◽  
Earthquake Excitation ◽  
Time Frequency ◽  
Short Time ◽  
Time Information

This paper presents a wavelet spectrum technique for monitoring a sudden crack of a beam-like bridge structure during earthquake excitation. When there is a sudden crack caused by earthquake excitation the stiffness of the structure is changed leading to a sudden change in natural frequencies during vibration. It is difficult to monitor this sudden change in the frequency using conventional approaches such as Fourier transform because in Fourier transform the time information is lost so that it is impossible to analyse short time events. To overcome this disadvantage, wavelet spectrum, a time-frequency analysis, is used for monitoring a sudden change in frequency duringearthquake excitation for crack detection. In this study, a model of 3D crack is applied. The derivation of the stiffness matrix of a 3D cracked beam element with rectangular section adopted from fracture mechanics is presented. Numerical results showed that the sudden occurrence of the crack during earthquake excitation can be detected by the sudden change in frequency using wavelet power spectrum. When the crack depth increases, the instantaneous frequency (IF) of the structure is decreased.

Dynamic Behaviour and Crack Detection of a Multi Cracked Rotating Shaft using Adaptive Neuro-Fuzzy-Inference System

2016 ◽  
Vol 6 (4) ◽  
pp. 1-10 ◽  
Author(s):  
Rajeev Ranjan
Keyword(s):  
Finite Element ◽  
Fuzzy Inference System ◽  
Crack Detection ◽  
Fuzzy Inference ◽  
Crack Depth ◽  
Multiple Cracks ◽  
Rotating Shaft ◽  
Element Analysis ◽  
Inference System ◽  
Neuro Fuzzy

The presence of crack changes the physical characteristics of a structure which in turn alter its dynamic response characteristics. So it is important to understand dynamics of cracked structures. Crack depth and location are the main parameters influencing the vibration characteristics of the rotating shaft. In the present study, a technique based on the measurement of change of natural frequencies has been employed to detect the multiple cracks in rotating shaft. The model of shaft was generated using Finite Element Method. In Finite Element Analysis, the natural frequency of the shaft was calculated by modal analysis using the software ANSYS. The Numerical data were obtained from FEA, then used to train through Adaptive Neuro-Fuzzy-Inference System. Then simulations were carried out to test the performance and accuracy of the trained networks. The simulation results show that the proposed ANFIS estimate the locations and depth of cracks precisely.

Electrical Resistance Method for Fatigue Crack Detection of Steel Deck

2013 ◽  
Vol 361-363 ◽  
pp. 1397-1401 ◽  
Author(s):  
Zhou Zhi Yuan Yuan ◽  
Bo Hai Ji ◽  
Zhong Qiu Fu ◽  
Rong Liu ◽  
Miao Cheng
Keyword(s):  
Fatigue Crack ◽  
Electrical Resistance ◽  
Crack Detection ◽  
Crack Depth ◽  
Influential Factors ◽  
Element Analysis ◽  
Resistance Method ◽  
Electrode Space ◽  
Fatigue Crack Detection ◽  
Steel Deck

The present study employs an electrical resistance method for fatigue crack detection in steel deck. The detection influential factors are analyzed via the finite element analysis under different electrode space and deck width. As a result, the electrode space influenced on detecting precision, and the smaller the better. The resistance measurement method is presented, and the formula of fracture damage ratio and the equivalent crack depth are established. It is proved by fatigue crack detection experiment of U-rib specimen, which shows that using electrical resistance method to detect fatigue crack is feasible.

scholarly journals Detection of Micro-Cracks in Metals Using Modulation of PZT-Induced Lamb Waves

Materials ◽  
2020 ◽  
Vol 13 (17) ◽  
pp. 3823
Author(s):  
Sang Eon Lee ◽  
Jung-Wuk Hong
Keyword(s):  
Quantitative Analysis ◽  
Crack Length ◽  
Crack Detection ◽  
Lamb Waves ◽  
Early Stage ◽  
Fatigue Cracks ◽  
Excitation Frequency ◽  
High Sensitivity ◽  
Detection Algorithm ◽  
Modulated Waves

The ultrasonic modulation technique, developed by inspecting the nonlinearity from the interactions of crack surfaces, has been considered very effective in detecting fatigue cracks in the early stage of the crack development due to its high sensitivity. The wave modulation is the frequency shift of a wave passing through a crack and does not occur in intact specimens. Various parameters affect the modulation of the wave, but quantitative analysis for each variable has not been comprehensively conducted due to the complicated interaction of irregular crack surfaces. In this study, specimens with a constant crack width are manufactured, and the effects of various excitation parameters on modulated wave generation are analyzed. Based on the analysis, an effective crack detection algorithm is proposed and verified by applying the algorithm to fatigue cracks. For the quantitative analysis, tests are repeatedly conducted by varying parameters. As a result, the excitation intensity shows a strong linear relationship with the amount of modulated waves, and the increase of modulated wave is expected as crack length increases. However, the change in the dynamic characteristics of the specimen with the crack length is more dominant in the results. The excitation frequency is the most dominant variable to generate the modulated waves, but a direct correlation is not observed as it is difficult to measure the interaction of crack surfaces. A numerical analysis technique is developed to accurately simulate the movement and interaction of the crack surface. The crack detection algorithm, improved by using the observations from the quantitative analyses, can distinguish the occurrence of modulated waves from the ambient noises, and the state of the specimens is determined by using two nonlinear indexes.

Buried Crack Detection in Aircraft Multi-Layer Structure Based on Pulsed Eddy Current

2013 ◽  
Vol 330 ◽  
pp. 536-541
Author(s):  
Sheng Lai ◽  
Hu Chen ◽  
Yue Wen Fu
Keyword(s):  
Crack Detection ◽  
Layer Structure ◽  
Fatigue Cracks ◽  
Low Frequency ◽  
Time Domain Analysis ◽  
Dynamic Imaging ◽  
Pulsed Eddy Current ◽  
Electromagnetic Detection ◽  
Electromagnetic Testing ◽  
Dual Polarity

The fatigue cracks of key parts, as one of the main damages of multilayer structure in aircraft, are important objects for aircraft structural health monitoring. Conventional electromagnetic testing which uses sinusoidal signal is high sensitive to surface cracks, but it is typically difficult to measure or predict embedding cracks. A novel electromagnetic detection technique is proposed in this paper, and dual polarity low-frequency pulse is used to excite the coil. A time-domain analysis method called time-slice is utilized to obtain the transient amplitude matrix from array signal. Good results have been presented by such dynamic imaging of simulating buried cracks in multi-layer riveted structure. Experimental results show that the new electromagnetic testing has the advantages of hidden defects detection and rapid detection, and it can effectively detect buried defects in multilayer structures of aircraft, and determine damage position.

scholarly journals Research on coalescence and probabilistic failure physics modeling of coplanar semiellipse cracks

2018 ◽  
Vol 169 ◽  
pp. 01032
Author(s):  
Sufen Li ◽  
Yufeng Sun ◽  
Weiwei Hu ◽  
Zhaoxia Liu
Keyword(s):  
Fatigue Cracks ◽  
Simulation Method ◽  
Small Sample ◽  
Uncertain Parameters ◽  
Engineering Structures ◽  
Great Loss ◽  
Paris Law ◽  
Physics Modeling ◽  
Environment Stress ◽  
Failure Life

Multiple fatigue cracks, causing transient fatigue fracture and resulting in great loss of life and property, are very commen in engineering structures. In order to predict the fatigue life of engineering alloys more accurately, the interaction and coalescence of adjacent cracks was investigated and the four stages of cracks growth were discussed in this paper. The SIF(stress intensity factor) value was found to growth rapidly in the ligament failure, and simulation method was used to find out the coalescence point. Then, the Paris’ law was chosen to discribe the crack growth process. Taking random factors like structure size, material properties, environment stress parameter into account, the probability physical of failure model of alloys can predict the failure life more accurate. Accordingly, the uncertain parameters of the Paris’ law were updated via Bayesian update method. The posterior distributions of uncertain parameters were obtained by the MCMC-Gibbs sampling. Finally, the probabilistic failure life models before and after coalescence were established by Monte Carlo simulation method. The probabilistic modeling method, which can greatly reduces the historical data or experimental data needed for the reliability evaluation of small sample products, can also be applied to other aspect of physic of failure , effectively saving time and cost.

Sign in / Sign up

Export Citation Format

Share Document