Online fatigue crack prognosis using nonlinear ultrasonic modulation

2019 ◽  
Vol 18 (5-6) ◽  
pp. 1889-1902 ◽  
Author(s):  
Hyung Jin Lim ◽  
Hoon Sohn
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Power Function ◽  
Estimation Method ◽  
Target Structure ◽  
Fatigue Index ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Nonlinear Ultrasonic ◽  
Remaining Fatigue Life

This article presents an online remaining fatigue life estimation (prognosis) technique using nonlinear ultrasonic modulation. When two ultrasonic inputs at two distinct frequencies are introduced to a structure with a fatigue crack, modulation components at the sum and difference of input frequencies are generated owing to crack opening and closing. First, a fatigue index is defined for prognosis and extracted from nonlinear ultrasonic modulation measurement. Subsequently, it is shown that the fatigue index is expressed as a simple power function of loading cycles applied to a target structure based on the Nazarov–Sutin and Paris–Erdogan theories. Then, the real-time remaining fatigue life estimation method is proposed by fitting the power function to online data obtained from the target structure. The performance of the proposed prognosis technique is evaluated using either notched or welded aluminum (6061-T6) plate specimens.

scholarly journals A fatigue crack initiation and growth life estimation method in single-bolted connections

2019 ◽  
Vol 54 (2) ◽  
pp. 79-94 ◽  
Author(s):  
Arash P Jirandehi ◽  
TN Chakherlou
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Initiation ◽  
Crack Growth ◽  
Fatigue Crack Initiation ◽  
Multiaxial Fatigue ◽  
Estimation Accuracy ◽  
Life Estimation ◽  
Lower Error ◽  
Fatigue Life Estimation

Fatigue life estimation accuracy of mechanical parts and assemblies has always been the source of concern in different industries. The main contribution of this article lies in a study on the accuracy of different multiaxial fatigue criteria, proposing and investigating the accuracy of four optimized fatigue crack initiation life estimation methods—volume, weighted volume, surface and point, thereby improving the multiaxial fatigue life estimation accuracy. In order to achieve the goal, the fatigue lives of bolt clamped specimens, previously tested under defined experimental conditions, were estimated during fatigue crack initiation and fatigue crack growth and then summed together. In the fatigue crack initiation part, a code was written and used in the MATLAB software environment based on critical plane approach and the different multiaxial fatigue criteria. Besides the AFGROW software was utilized to estimate the crack growth share of fatigue life. Experimental and numerical results showed to be in agreement. Furthermore, detailed study and comparison of the results with the available experimental data showed that a combination of Smith–Watson–Topper approach and volume method results in lower error values, while a combination of Fatemi–Socie criterion and surface or point method presents estimated lives with lower error values. In addition, the numerical proposed procedure resulted in a good prediction of the location of fatigue crack initiation.

Fatigue Life Estimation for HFMI-Treated Weldments Considering Weld Toe Magnification Factors

2020 ◽  
Vol 142 (6) ◽  
Author(s):  
Dong-Yub Kim ◽  
Myung-Hyun Kim
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Estimation Method ◽  
Magnification Factor ◽  
Life Estimation ◽  
Positive Effects ◽  
Magnification Factors ◽  
Fatigue Life Estimation ◽  
Weld Toe ◽  
Explicit Consideration

Abstract High-frequency mechanical impact (HFMI) post-treatment is a proven method to improve the fatigue life of welded structures. The positive effects of HFMI treatment are influenced by the weld toe geometries and residual stresses. This study investigates the effect of geometric and mechanical improvements by HFMI treatment on fatigue strength with explicit consideration of the weld toe magnification factor. General fatigue life estimation method is based on experiment data, and residual stress may be considered in addition. In terms of HFMI-treated structures, geometric improvement also affects the fatigue life. Thus, a more efficient method is suggested by considering the weld toe magnification factor to assess the effects of HFMI treatment. First, the weld toe magnification factor in HFMI-treated conditions is calculated to consider the geometrical effect of HFMI treatment at the weld toe region. Second, a stress ratio model is introduced to consider the compressive residual stress by HFMI treatment based on the Paris equation. The results were validated by comparing them with the estimated fatigue life from previous studies on HFMI-treated welded specimens.

The Fatigue Life Estimation Method From the Stress Concentration Region With Zero Defect: An Application to the Fatigue Crack Growth Simulation Code “FLARP” for the In-Plane Gusset Welded Joint

2004 ◽  
Author(s):  
Masahiro Toyosada ◽  
Koji Gotoh ◽  
Keitaro Konuma ◽  
Akira Sueda
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Crack Opening ◽  
Simulation Code ◽  
Growth Simulation ◽  
Life Estimation ◽  
Crack Growth Simulation ◽  
Fatigue Life Estimation

In-plane gusset welded joints are very popular and used in many steel constructed structures. Fatigue life estimations for this type of joint have been performed by applying the fatigue crack growth simulation code “FLARP” developed by the authors. The fatigue crack shows the typical opening/closing behavior during fatigue crack growth. The plastic deformed layer in the crack wake, which represents the loading history indirectly, contributes to the behavior. The consideration of crack closure is essential in the estimation of the fatigue life. FLARP enables the quantitative simulation of the fatigue crack opening/closing. By considering the cyclic plastic behavior ahead of a fatigue crack tip, the improved effective stress intensity factor range (ΔKRPG) to denote the fatigue crack propagation law, which is formulated by replacing the crack opening load with the Retensile Plastic zone Generating load (RPG load), was defined. ΔKRPG is adopted as the parameter for the fatigue life estimation by FLARP. The validity of the fatigue life estimation by FLARP is confirmed by comparing the estimated S-N curves with the experimental results for the in-plane gusset welded joints.

Improvement of Pipeline Fatigue Life Estimation

2016 ◽  
Author(s):  
Sanjay Tiku ◽  
Aaron Dinovitzer ◽  
Vlad Semiga ◽  
Mark Piazza ◽  
Tom Jones
Keyword(s):  
Numerical Simulation ◽  
Growth Rate ◽  
Fatigue Crack ◽  
Fatigue Life ◽  
Crack Growth Rate ◽  
Fatigue Crack Growth ◽  
Crack Growth ◽  
Fatigue Crack Growth Rate ◽  
Life Estimation ◽  
Fatigue Life Estimation

Fracture mechanics methodologies for calculating fatigue lives have been successfully applied by pipeline operators to estimate integrity reassessment intervals. Their application in the definition of pipeline system fatigue lives has been overly conservative in actual practice. The source and magnitude of the conservatism inherent in the calculated fatigue life estimates needs to be identified so operators have a better indicator of when reassessments should take place. The pipe life estimation is especially critical for Electric Resistance Weld (ERW) and Electric Flash Weld (EFW) pipeline systems with longitudinally oriented defects. Prior work on improving fatigue life was initiated through studies completed by Pipeline Research Council International, Inc. (PRCI) to evaluate the sources of differences between fatigue life estimates produced by industry fatigue analysis software and different metallurgists. Two significant sources of conservatism in the fatigue life estimation process were identified: the fatigue crack growth rate (da/dN) and the bulging correction factor applied to axial surface flaws. The experimental and numerical simulation techniques considering the impact of these factors on rate of fatigue crack growth of pipeline axially oriented defects are described in this paper. Finite element modeling was used to simulate pipe bulging in the presence of axial flaws. The effect of the pipe thickness, diameter and flaw geometry was compared with treatments included in existing defect assessment standards. The results illustrate that for longer and deeper flaws existing treatments over represent the local bending due to pipe wall bulging. This results in unnecessarily conservative (shorter) fatigue life estimates. The crack growth rate (da/dN) was measured in a compact tension specimen material fatigue testing program. The test results included a range of ERW and EFW pipe materials with varying vintages and grades. The measured fatigue crack growth rate for the materials tested was found to be lower than that recommended by existing industry standards. This adds to the over conservatism of current approaches. The numerical simulation and materials testing results and related recommendations presented in this paper are compared to existing codified treatments to quantify the level of conservatism inherent in the current state of practice. Recommendations are provided to enhance the precision and better manage conservatism in fatigue crack growth rate calculations. Increased accuracy serves to improve integrity management and would be of interest to pipeline operators, consultants and regulators.

Identification of Variable Amplitude Fatigue Loading Based on Bivariate Probability Mass Functions

2019 ◽  
Author(s):  
Hewenxuan Li ◽  
David Chelidze
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Temporal Dynamics ◽  
Variable Amplitude ◽  
Life Estimation ◽  
Fatigue Life Estimation ◽  
Time Histories ◽  
Probability Mass ◽  
Bivariate Probability ◽  
Mass Functions

Abstract Fatigue life estimation under variable amplitude (VA) loading remains one of the major unresolved engineering problems. When engineering structures experience VA loading, the corresponding load at the crack front will be highly non-stationary. Under such conditions, the load interaction effects greatly affect fatigue crack propagation rate and can cause significant variation in the corresponding fatigue life. Existing characterization methods focus on single overload effect and their extensions to sequence of overloads which does not reflect the irregularity of the realistic loading. In this paper, numerical simulations were used to compare the fatigue life under various synthetic load time histories. The resulting time to failure estimation, concerning statistically and spectrally identical deterministic loads and their stochastic surrogates, exhibits drastic difference which reflects the corresponding differences in the temporal structure of the loads, which are not differentiated by their linear characteristics. This indicates that the temporal dynamics of the load time histories have considerable influence on fatigue crack propagation and fracture. In order to differentiate temporal dynamics of the synthetic loading, new bivariate probability mass functions (BPMFs) are proposed. They can capture and preserve the underlying temporal dynamics of locally non-stationary variable amplitude load-time histories with identical linear statistics. And qualitative explanations of the potential of this proposed method for fatigue life estimation under VA loading are discussed.

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