Thermographic Determination of Fatigue Damage

1978 ◽  
Vol 100 (2) ◽  
pp. 200-203 ◽  
Author(s):  
J. A. Charles ◽  
F. J. Appl ◽  
J. E. Francis
Keyword(s):  
Fatigue Life ◽  
Mild Steel ◽  
Surface Temperature ◽  
Fatigue Damage ◽  
Fatigue Cracks ◽  
Temperature Distributions ◽  
Fatigue Failures

The energy released due to hysteresis effects in cyclically loaded materials can be used to predict where fatigue cracks are likely to initiate and to determine the stage of fatigue life. In the present study, thermography is used to monitor the surface temperature distributions on a series of double-notched, mild steel fatigue specimens cyclically loaded in bending. The results indicate that the fatigue life of the material encompasses three thermal stages, each of which is indicative of the fatigue damage the material has sustained. This information can be used to avoid in-service fatigue failures.

Fatigue Assessment of Existing Riveted Bridges

2018 ◽  
Author(s):  
Henrik Mehlsen
Keyword(s):  
Fatigue Life ◽  
Fatigue Failure ◽  
Visual Inspection ◽  
Fatigue Cracks ◽  
Repeated Loading ◽  
Fe Modelling ◽  
Railway Bridges ◽  
Loading And Unloading ◽  
Fatigue Failures ◽  
Thick Layers

Fatigue failure of bridges occurs after repeated loading and unloading and hence fatigue becomes more and more severe with time. A majority of all existing riveted bridges are not explicitly designed for fatigue failures. Bridge owners should therefore have focus on fatigue life of riveted bridges. It can be difficult to discover fatigue cracks by visual inspection due to thick layers of paint and the fact that the rivets themselves may hide the cracks. Hence, it may be necessary to determine critical joints and possible fatigue cracks by using FE-modelling. Identification of critical joints may also target future inspection efforts and highlight hidden details, which may call for special inspection measures to be implemented. This paper describes a fatigue study of 11 riveted railway bridges in Denmark that includes both visual inspections and FE-modelling of bridges.

A novel method to improve fatigue behaviors of holed structures based on electromagnetic force

2022 ◽  
pp. 095440622110641
Author(s):  
Guo Zheng ◽  
Zengqiang Cao ◽  
Minghao Zhang
Keyword(s):  
Residual Stress ◽  
Fatigue Life ◽  
Electromagnetic Force ◽  
Stress Measurement ◽  
Fatigue Cracks ◽  
Axial Direction ◽  
Novel Method ◽  
Fatigue Life Enhancement ◽  
Fatigue Failures ◽  
Improve Fatigue

In this study, a novel method stress wave strengthening (SWS) process based on electromagnetic force was proposed to improve the fatigue life of holed structures. Corresponding tests were carried out to explore the fatigue performance of SWS. Cold expansion (CE) was also investigated for comparison. The fatigue life of SWS and CE samples were evaluated, moreover, the mechanisms of fatigue failures and life enhancements were also discussed. Results showed that double-side SWS extended fatigue life significantly and reduced stiffness degradation more effectively with respect to CE process. Moreover, fatigue cracks commonly appeared at mid-planes of hole surfaces and horizontally grew in SWS samples, which differed a lot from CE samples. Through the residual stress measurement, it is seen that more uniform residual stress along axial direction can be obtained by SWS compared to CE, which can explain the fatigue life enhancement and failure mechanism of SWS method.

Energy-based damage descriptions to assess fatigue life of steel samples undergoing various multiaxial loading spectra

2017 ◽  
Vol 28 (1) ◽  
pp. 35-57 ◽  
Author(s):  
GR Ahmadzadeh ◽  
A Varvani-Farahani
Keyword(s):  
Fatigue Life ◽  
Mild Steel ◽  
Fatigue Damage ◽  
Hysteresis Loops ◽  
Growth Stress ◽  
Principal Strain ◽  
Stress Strain ◽  
Damage Models ◽  
Maximum Principal Strain ◽  
Loading Spectrum

The present study evaluates fatigue damage of four steel alloys, mild steel, SS347, SNCM439, and SNCM630, by means of Socie, Ellyin, and Varvani-Farahani damage models. The Socie model assesses fatigue damage through product of maximum principal strain amplitude and maximum normal stress on the maximum principal strain plane. Damage description by Ellyin was developed as both elastic and plastic strain energies over loading spectrum were integrated. The elastic–plastic response of materials is evaluated through use of Garud’s constitutive plasticity model to achieve components of stress/ strain and corresponding stress–strain hysteresis loops. Based on the Varvani-Farahani model, components of stress and strain calculated from largest Mohr’s circles over peak-valley events are employed to assess fatigue damage. Overall damage was calculated on the basis of energy-based models from counted reversals over entire loading blocks and related to fatigue life. The Socie approach overpredicted lives for steel samples. Predicted life data for mild steel and SS347 samples fell below the midline based on the Ellyin’s model. Both Ellyin and Varvani-Farahani models showed a good agreement of predicted lives for steel samples within factors ±3 as compared with experimental data. The choice of damage assessment was highly related to consistency of damage descriptions to crack formation and early growth, stress/strain components, material properties, and loading spectrum.

A Model for the Determination of Residual Fatigue Life of a Nickel-Based Superalloy

2008 ◽  
Vol 130 (3) ◽  
Author(s):  
Duyi Ye ◽  
Jinyang Zheng
Keyword(s):  
High Temperature ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Strain Energy ◽  
Damage Mechanics ◽  
Residual Fatigue Life ◽  
Mechanics Model ◽  
Plastic Strain Energy ◽  
Residual Fatigue

In this paper, both the dissipation of the plastic-strain energy and the exhaustion of the static toughness during high-temperature low-cycle fatigue of GH4145/SQ superalloy were investigated. Together with the analysis of the microscopic aspects of the material, an energy-based damage mechanics model was developed for the prediction of the residual fatigue life of the high-temperature fastened parts in power plant. Experimental results show that the static toughness is a parameter that is highly sensitive to the fatigue damage process. The deterioration of the static toughness during fatigue process reveals the exhaustion of the materials’s ability to absorb energy, which is essentially associated with the irreversible energy dissipation process of the fatigue failure. Based on the dissipation of the plastic-strain energy and the exhaustion of the static toughness during fatigue, a damage variable is defined that is consistent with the fatigue damage mechanism. The variable is sensitive to the fatigue process and can be measured with a simple experimental procedure. A fatigue damage evolution equation is derived on the basis of Lemaitre’s potential of dissipation in the framework of continuum damage mechanics. Furthermore, an equation for the determination of the residual fatigue life is deduced. The fatigue damage mechanics model is verified by comparing the predicted results with the experimental observations. The fatigue damage mechanics model developed may provide a feasible approach to determining the residual fatigue life of the high-temperature fastened parts in power plant.

Fatigue Life Extension Procedure for Subsea Wells Based on Pressure Testing

2021 ◽  
Author(s):  
Arne Fjeldstad ◽  
Torfinn Hørte ◽  
Gudfinnur Sigurdsson ◽  
Anders Wormsen ◽  
Espen Berg ◽  
...  
Keyword(s):  
Fatigue Crack ◽  
Fatigue Life ◽  
Fatigue Damage ◽  
Hot Spots ◽  
Fatigue Cracks ◽  
Load Test ◽  
Life Extension ◽  
Case Examples ◽  
Pressure Test ◽  
Number Of Cycles

Abstract This article presents a fatigue life extension procedure for subsea wells based on fracture mechanics. It makes use of the outcome of an internal pressure test to determine a safe period for drilling and completion. The pressure test is used as a load test and can only reveal deep fatigue cracks. The safe operational period is estimated as the number of cycles required to grow a fatigue crack from the largest fatigue crack that remains stable after the pressure test until it becomes unstable due to an accidental load. The procedure takes into account the probability of the presence of the fatigue crack that can be revealed by the pressure test. This is used to determine design fatigue factors for the procedure. The design fatigue factor is formulated in terms of the (S-N based) accumulated fatigue damage for historical operations. The procedure is illustrated with two case examples (fatigue hot spots) for illustrating the procedure in more detail: wellhead extension girth weld and wellhead profile. Conditions for use are given at the end of the article.

FACTORS INFLUENCING THE DETERMINATION OF MAXIMUM SURFACE TEMPERATURE FOR EXPLOSION-PROOF LUMINAIRES

2017 ◽  
Vol 16 (6) ◽  
pp. 1309-1316 ◽  
Author(s):  
Lucian Moldovan ◽  
Sorin Burian ◽  
Mihai Magyari ◽  
Marius Darie ◽  
Dragos Fotau
Keyword(s):  
Surface Temperature ◽  
Maximum Surface ◽  
Factors Influencing ◽  
Maximum Surface Temperature
Sign in / Sign up

Export Citation Format

Share Document