What is Fatigue analysis: Definition and 16 Discussions

In materials science, fatigue is the initiation and propagation of cracks in a material due to cyclic loading. Once a fatigue crack has initiated, it grows a small amount with each loading cycle, typically producing striations on some parts of the fracture surface. The crack will continue to grow until it reaches a critical size, which occurs when the stress intensity factor of the crack exceeds the fracture toughness of the material, producing rapid propagation and typically complete fracture of the structure.
Fatigue has traditionally been associated with the failure of metal components which led to the term metal fatigue. In the nineteenth century, the sudden failing of metal railway axles was thought to be caused by the metal crystallising because of the brittle appearance of the fracture surface, but this has since been disproved. Most materials seem to experience some sort of fatigue-related failure such as composites, plastics and ceramics.To aid in predicting the fatigue life of a component, fatigue tests are carried out using coupons to measure the rate of crack growth by applying constant amplitude cyclic loading and averaging the measured growth of a crack over thousands of cycles. However, there are also a number of special cases that need to be considered where the rate of crack growth is significantly different compared to that obtained from constant amplitude testing. Such as: the reduced rate of growth that occurs for small loads near the threshold or after the application of an overload; and the increased rate of crack growth associated with short cracks or after the application of an underload.If the loads are above a certain threshold, microscopic cracks will begin to initiate at stress concentrations such as holes, persistent slip bands (PSBs), composite interfaces or grain boundaries in metals. The stress values that cause fatigue damage are typically much less than the yield strength strength of the material.

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  1. FEAnalyst

    Fatigue life of a simple beam

    Hi, some time ago I wondered if it's possible to calculate fatigue life (number of cycles to failure) for complex models analytically, based on static FEA results: https://www.physicsforums.com/threads/fatigue-life-hand-calculations-based-on-static-fea-results.994264/ Unfortunately, it seems...
  2. Ridzuan

    Fatigue analysis with JIS standard book

    Dear guys can somebody explain, what is actually the following terms, used in fatigue analysis: 1. Mean stress correction factor 2. Plate thickness correction factor 3. Redundancy factor Thanks guys. you are the best...
  3. D

    Fatigue analysis in the frequency domain

    Assuming that a TLP platform is examined and the wave forces acting on the tendons of the mooring lines are presented in RAOs (as a function of wave frequency). Using Jonswap spectra for North sea (i.e peakness factor equal to 3.3) we can obtain Hs (significant wave height); Tp (peak period) and...
  4. K

    Time History Fatigue Analysis - Ansys Static Structural Quer

    I'm testing a part for fatigue, and I got a time series of Forces and Moments on three different parts of the body (A wind turbine hub). From the static structural fatigue analysis, I noticed that you need a von mises stress input - that's not a problem. My problem is, how do I place different...
  5. K

    Variable Amplitude Fatigue Analysis - Super Confused on how

    Hey everyone I'd be really grateful if anyone could help me out here, been going round in circles for two weeks now and I need to get going soon. Jumping right to the point, here's my problem: We are currently working on a student project and designing a Wind Turbine for future opensource use...
  6. Ravi Singh choudhary

    Fatigue Analysis: Maximum & Minimum Stress

    Whether we are using Soderberg or Goodman line; it is two dimensional Cartesian coordinate system in which x-axis is the mean stress and y-axis is stress amplitude. For them to calculate we have two values one is maximum stress and other is minimum; I found on Quora.com that they are not...
  7. S

    Mean stress with miner's rule in fatigue analysis

    Hi I was wondering how you would account for mean stress (such as using with goodman equation) using von mises with miners rule due to variable loading Thank you
  8. S

    What stress to use for fatigue analysis

    Hi, I was wondering which stress values from a finite element program to use for fatigue analysis, (von mises, principal, tresca). I was leaning towards principal stresses but then would my stress range be σ11 from load case 1 (LC1) to σ11 of LC2, or would i need to do σ11-σ33 first and then...
  9. salwacheg

    Fatigue Vibration with Fe-Safe

    Hello everybody , I am student in mechanical enginnering. I have to evaluate the solution Fe-Safe. i am working on two subjects: Harmonic and PSD Vibrations. The modal analysis are done in Abaqus. I would like to understand how Fe-Safe computes Life Fatigue in case of harmonic analysis. What...
  10. R

    Fatigue Analysis - Factor of safety

    Homework Statement Hey everyone, I'm trying to do this question and have no idea where to go with it. http://dl.dropbox.com/u/630750/Screen%20Shot%202011-11-02%20at%2014.17.42.png Homework Equations See below. The Attempt at a Solution Here is my attempt/thinking so far...
  11. D

    Fatigue Analysis Using Rainflow Counting & S-N Curves

    Hi, For a fatigue analysis assignment I am working with rainflow counting and S-N curves.The given data is a plot of the stresses in a wingbox during a single flight. I have already derived the S-N curves, did the rainflow analysis and stored the (half) cycles (including the residu) in a...
  12. B

    Pressure vessel fatigue analysis

    Hi, I am wondering if there is any guideline and examples of design and analysis according to EN13445.
  13. G

    Analyzing Fatigue Failure in a Shaft Under Bending and Bearing Loads

    hello, im trying to do a fatigue analysis on a shaft but keep getting that it will never brake, which is impossible , because of various cases that it did after something like 3.5 years the shaft is made of Al-6061 and a divided force of 700N is working on him. the linear speed at the edge...
  14. E

    How can we solve the fatigue problem in a more efficient way?

    Hi everyone. I'm working with a project about Fatigue Analysis now. I got some questions I'm stuck with at the moment. So I'm wondering if you have any idea about them. The method people usually use to solve the fatigue problem at the moment is like this: The first six plots shows...
  15. C

    Designing Coaxial Output Shafts: Fatigue Analysis

    Part of my design project requires that I design two coaxial output shafts. I've gone through and calculated the inner shaft based on deflection and Goodman fatigue criterion. The problem now is this: the other output shaft must be a hollow shaft that shares its axis with the interior shaft. All...
  16. C

    Fatigue analysis from market data

    I am working on a project for a company to analyse the fatigue life of a component. There is an existing component that the company manufactures and the component fails by fatigue on the average 540 days. The component is a tube made of low carbon steel of yield 260N/sqmm and ultimate of...