What is Fatigue: Definition and 95 Discussions

Fatigue is a feeling of tiredness. It may be sudden or gradual in onset. It is a normal phenomenon if it follows prolonged physical or mental activity, and resolves completely with rest. However, it may be a symptom of a medical condition if it is prolonged, severe, progressive, or occurs without provocation.
Physical fatigue is the transient inability of muscles to maintain optimal physical performance, and is made more severe by intense physical exercise. Mental fatigue is a transient decrease in maximal cognitive performance resulting from prolonged periods of cognitive activity. Mental fatigue can manifest as somnolence, lethargy, or directed attention fatigue.Fatigue and 'feelings of fatigue' are sometimes confused. Unlike weakness, fatigue can usually be alleviated by periods of rest.

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  1. F

    Fatigue limits of leaf springs

    Hi to all. How would I go about calculating the fatigue limit of leaf springs? Is there an equation out there in the form of N, cycles to failure= f(variables, material properties) Or will I have to use the Stress equations for leaf springs and use that stress value and then...
  2. A

    Effect of resonance on Fatigue Life

    I'm doing a research project which aims to develop a mathematical correlation for fatigue life prediction at resonance frequency. An experimental setup is also to be created which would be used to carry out the experiment, cyclic loading cycles until failure. For this a Cussons linear vibrator...
  3. F

    Medical Ego Depletion and Decision Fatigue

    So I've become aware that the more "good" choices we make, the easier it is to make a "bad" choice, e.g. if you're on a diet for a couple of months, its very easy to slip and have a piece of chocolate cake, that sort of thing. Here's the wikipedia. http://en.wikipedia.org/wiki/Ego_depletion So...
  4. 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...
  5. 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...
  6. B

    Fatigue Properties of Duplex Stainless Steel

    Hello All, I'm hoping someone can assist me in locating a stress amplitude vs. cycles curve (S N curve) for a Duplex Stainless Steel. The particular material I'm using is SAF 2205. I have been searching far and wide, including the Atlas of Fatigue Curves, but I have not been able to find...
  7. E

    Uncovering the Mystery of Fatigue Cracks: Sources, Detection & Prevention

    what are fatigue cracks? what are the major sources of fatigue withing the fuselage? how can fatigue cracks be detected during inspection? how can the risk of fatigue cracks in the fuselage be reduced? why are they dangerous? what is their origin? I've tried to find answers for these...
  8. G

    Piano Wire Fatigue Experiment: Calculating Stress and Modulus"

    Hi All I am the new at the forum and would be very grateful for help about my Lab. I am doing the postgraduate course of Biomedical Engineering. We had a Lab about the fatigue of piano wire, as a part of materials science module. During the experiment, high strength piano wire was tested by...
  9. C

    John & Susan's Leg Bone Fatigue: Examining an SN Curve

    For human bone the constant n has a value of 6. Two people embark on a fitness regime. John runs 6,000 steps per day (subjecting his leg bones to a stress range of 40MPa) and walks 20,000 steps per day (at a stress range of 15MPa). Susan walks 10,000 steps per day (at 15MPa) and does 200 jumps...
  10. R

    Calculating Fatigue Life for Variable Stress in Cast Aluminum

    Hello How can I calculate the fatigue life of a variable stress between 0 and 90 MPa in cast aluminum? Do I use the mean stress and compare it with the wohler curve? what is the logic of using the mean stress? Why not the maximum stress? Do I have to use the Goodman or Gerber diagram...
  11. R

    Aluminum consumed fatigue life

    How to determine in a cast aluminum part its consumed fatigue life? Lets imagine I get a cast aluminum part that looks good, but I have no idea for how many km it has been used (automotive). Which kind of non destructive tests or methods could I use to determine the consumed fatigue life, and...
  12. L

    Literature regarding appearence of cracks. Thermal, pressure fatigue

    Hello! I am wondering if anyone could recommend som literature for me to get my hands on. If there is any literature regarding how the appereance of a crack in a piece of thin metal (~0,4mm - 1mm) could be related to pressure fatigue or thermal fatigue. Does the crack due to thermal fatigue...
  13. S

    Fatigue analysis:frequency domain vs time domain

    I have read a lot of paper about fatigue damage, in some fields it is particularly used the time domain approach while in others the frequency domain approach, but I haven't understood when it is better to use frequency approach respect time domain approach. May you help me to understand better...
  14. B

    Pressure vessel fatigue analysis

    Hi, I am wondering if there is any guideline and examples of design and analysis according to EN13445.
  15. 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...
  16. 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...
  17. F

    Pole Fatigue Calc for Key West: AASHTO Spec & Vc of 45mph

    I was asked by the CE to do a fatigue calc for a speaker pole going up in key west. I am using AASHTO standard spec for structural supports for highway signs, luminaires, and traffic signals. he said to assume a Vc of 45mph, an importance factor of 1.0 (from category I-lights in the...
  18. H

    Principal Stress, VonMises Stress , Fatigue

    1. I didnt understand why some people extracting Principal stress for aluminum material which is subjected to dynamic loads(acceleration).Why not Von Mises? 2. Which has more advantages in predicting Fatigue Life and how? 3. How will you distinguish between tensile and compressive...
  19. J

    Surface Finish vs. Fatigue strength?

    Does anyone have access to a chart shown surface finish vs. impact of fatigue strength at 10^6 for various matals? In our company we limit the surface finishes to 63 Ra max for highly stressed areas. But where did that value come from? The best way to find out is to see a chart showing the...
  20. Z

    Improve Fatigue Life with Shot Peening: Compressive Stress Benefits

    How does shot peening help improve fatigue life, or rather, how does the compressive surface stress imposed help improve fatigue life? How does materials having high elastic moduli and large grain size prevent creep?
  21. B

    Fatigue Failure on Turbine Blade(large subsonic aircraft)

    I am doing a project on the subject above, and i am selecting one type of material that is currently popular used in gas turbine, but i found it difficult to select the material as there are too many nickel-based alloy that can be use for this application. Can anyone direct me with a suggestion...
  22. Q_Goest

    Fatigue strength of 304, cold worked versus annealed

    This web page: http://www.hghouston.com/ss_cwp.html states: The web page also shows that fatigue strength can be improved dramatically by cold working. Endurance limit is listed as: 304 annealed = 35 ksi 304 3/4 hard = 92 ksi I'm in the process of designing something that will be...
  23. V

    Fatigue Properties of Chinese steel

    Hi everyone, I just joined and was wondering if anyone could help me in finding the cyclic fatigue properties of Chinese steel, specifically 30Mn2? I need to perform a fatigue life analysis on a Chinese truck spindle, but cannot find the properties anywhere. I have tried to match the chemical...
  24. Q_Goest

    What is the maximum mean stress in a bolted joint?

    There's a common belief that for any given bolted joint, the higher the preload, the longer the fatigue life. I’d like to challenge that preconception and suggest that increasing preload above that needed to keep the joint together and acting as a pair is generally a bad thing and results in...
  25. S

    Methods of laboratory fatigue testing?

    Methods of laboratory fatigue testing?? I have had a try at this question but don't think the answer was enough. Can someone please check it and give me the correct answer. Question Outline the methods of laboratory fatigue testing and the results likely to be obtained. (10 marks)...
  26. D

    Dynamic Creep & Fatigue: Defined & Tested

    What is the difference between dynamic creep and fatigue? How are they tested?
  27. M

    Aluminum Alloy Fatigue Information

    Hey guys, I'm working on a project and am looking for some fatigue data for aluminum alloys, A356-T6 in particular. I've looked through the MIL-5 and Aerospace (Cindas) handbooks and haven't found any decent information. The textbook I have "Mechanical Engineering Design" by Shigley and...
  28. A

    Fatigue strength of vascomax 350

    Hi, I need to calculate the fatigue strength of vascomax 350 material. I have referred Machine design Hand book, Author-Shigley The data provided and example calculation is for material having Ultimate strength less than 200ksi. The Ultimate strength of vascomax 350 is 350ksi . Please...
  29. A

    Calculating Fatigue Factor for Vascomax 350 CVM Material

    Hi, What is fatigue factor? How do we calculate? Books / sites for reference? We have a bolt made of Vascomax 350 CVM material. I want to know the fatigue factor that should be used for calculation. The yield strength of the material is 335 ksi and ultimate strength is 340 ksi...
  30. A

    Calculate Fatigue Life of Custom Bolt

    Hi All, We have manufactured a custom bolt (similar to standard bolt). Now we need to calculate the fatigue life of the bolt. Could you please guide me in calculating the fatigue life? Thanks, Ana
  31. rohanprabhu

    Doesn't Alternating current cause fatigue?

    Take the case of a lamp bulb. When applied an Alternating current across it.. it basically goes on and off 50 times in a second [in India atleast.. we get 50Hz]. Now, it means that the filament gets hold and cold continuously. From wikipedia: so.. is alternating current more damaging for...
  32. 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...
  33. wolram

    Medical Vitamin B12 & Folic Acid Deficiency: Causes of Fatigue & Weakness

    Would a lack of vitimin b12 and folic acid make some one very tired?
  34. S

    Creep and Fatigue stress from power plan components

    Hi, I'm new here, and I'm not really sure where this thread goes, so please feel free to move it Homework Statement basically, I'm doing a project involving converting raw data on pressure and temperature (and time) in a power plant situation (mainly the pipes carrying the steam) here is...
  35. B

    Calculating Fatigue Breaking Point of Steel Hollow Shaft

    I have some calculations I would like to make, though I am having trouble finding information. I have a circular hollow shaft made of steel. I would like to calculate the breaking point of said shaft at 1000 cycles and 1000000 cycles. What kind of information/properties of the metal needs to...
  36. T

    Speedy Pressure Vessel Fatigue Cycling

    Gents, I am looking for a design modification to accomplish 250,000 cycles of pressure loading in a short time period. We are going from 0 (1atm) to 10psi but currently only getting 10 cycles in 120 seconds. Enclosed is a diagram of the system. Details: Rate goal is 3hz Power Source is...
  37. W

    Shaft diameter, Fatigue, etc.

    Hi, I have been atempting this is a question for a week now and I've been struggling on the final part. The question is below in bold. The tension in a flat belt pulley is 1250N when stationary. Calculate the tension in each side, and the power transmitted, when the belt is on the point of...
  38. C

    Solving Fatigue Law Problem: Calculate # Flights

    Im having a problem with the following question and my understanding of it... An aluminium alloy obeys the fatigue law S = 895N^-0.12, where S is the stress amplitude and N is the number of cycles. An airdraft componentfabricated from this alloy, undergoes the following stress amplitude...
  39. R

    Creep and Static Fatigue: What's the Distinction?

    What is the difference between these two phenomena? Or are they the same thing? I have heard both terms used in different classes, but they seem to be the same or similar.
  40. Mk

    Medical Stress & Fatigue: Causes, Effects & Solutions

    I was watching the Amazing Race last night, on CBS, and I watched this girl freak out, after so much stress (the Amazing Race is a show where a team goes around the world and has to get back to America before anyone else to get $1 million). And I was thinking... Stress is such a terrible...
  41. N

    WTC Metal Fatigue. How Did Building 7 Fall?

    Building 7 was hit by no aircraft or debris. It had several small fires and amazingly collapsed in symmetrical fashion at free fall speeds. We saw in Madrid a building burn at intense levels for MANY hours but not collapse. Is there any scientific explanation for such a catastrophic...
  42. T

    Table of fatigue strengths for different steels

    I'm looking at a table of fatigue strengths for different steels. I would like to know what the figures mean. For instance, for S235 under streching/pressure it says 0\pm160 and 130\pm130. I believe the values are supposed to be average tension pluss/minus amplitude tension, but I'm not sure...
  43. C

    How can I estimate the fatigue life of a component subjected to a rotating cam?

    I am working on a physics problem in a project to estimate fatigue life of a component. There is a cam rotating with an offset of 10mm rotating at an rpm of 230. The component is a cantilever fixed at one end is getting hit by this cam while it is rotating. The cam is at the other end of...
  44. 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...
  45. A

    What do the symbols in da/dN=A(^K)m represent in material fatigue and stress?

    Could you please explain what each of the following symbols stand for: da/dN=A(^K)m I have worked out that da is the crack length i have worked out that dN is the number of cycles Are both of these correct? Thanks
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