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. Syed7777777

    Random Vibration Fatigue Analysis

    Hi Everyone, I'm trying to do a "Random Vibration Fatigue Analysis" on a bracket assembly that is mounted on the headboard of a pickup truck. BACKGROUND: The bracket assembly is mounted on the headboard of the truck using 2xbolts (1 per each mount). The truck regularly travels on a rough...
  2. L

    Understanding fatigue and ultimate loading

    Some basic background before i ask the question. I have been using openFAST, am opensource software to simulate a 5MW wind turbine. I then use the data from openFAST, and run it through its counter partner Mlife, to calculate fatigue and time to failure. Below is the data that Mlife dumped to...
  3. S

    Is Thermal Expansion Fatigue a Concern for Aluminum Alloy Motorcycle Frames?

    Hello, assuming to keep an aluminum alloy motorcycle frame not in use, still, will the daily temperature variations cause thermal fatigue due to the continuous expansions and retractions or is the force developed by a few degrees of variations not sufficient to create microstructural dislocations?
  4. J

    A Fatigue Failure in Structural Elements: Axial, Shear & Torsional Loads

    "The stresses acting on a structural element subjected to axial, shear or torsional loads are constant and do not change sign throughout the loading cycle. Therefore, alternating stresses, which cause fatigue, do not occur in these cases. On the other hand, in a beam subjected to bending load...
  5. Pipsqueakalchemist

    Engineering (material science) Fatigue life prediction using integral

    So for this question, I understand the math but just wanted to be clear on a few things. So I had this question on my midterm but instead of tensile and compressive stresses, it was tensile and tensile stress. I initially thought that the delta sigma in the integral was the maximum stress so in...
  6. A

    Fatigue Testing: Calculating ΔK vs da/dN from R & Max Stress

    Hello Everybody, Im doing my lab report on Fatigue testing for a Single Edge Notched Tension (SENT) sample and need to plot ΔK vs da/dN for a series of a vs N readings at different R and maximum stress values (attached in the picture). I've just been given one equation for Ki and told that I...
  7. T

    Medical Universal Virus? - mononucleosis, chronic fatigue, multiple sclerosis....

    forget about chronic fatigue, I remembered it has been tracked to gut bacteria! Epstein-Barr virus seems to be associated with many conditions. "Associated" is the operative there because almost everyone is a host for Epstein-Barr. Science News has a somewhat long but quite readable article...
  8. mktsgm

    What Triggers Fatigue During Illness: Understanding the Pathophysiology?

    What is the mechanism of Fatigue what events initiate it and how? The trigger of a fever, called a pyrogen, results in the release of prostaglandin E2 (PGE2) Generally just as a pyrogen such as PGE2 (or LPS) sets thermogenesis in motion, leading to a fever, what kind of events are triggered in...
  9. U

    Engineering Can Fatigue Failure of Material be Demonstrated at Home Using Everyday Items?

    What are some creative ways to display fatigue failure of material due to axial, bending, torsional loading using common household items? This is an experiment I have to do at home, I need help with some ideas
  10. 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...
  11. FEAnalyst

    Fatigue life hand calculations based on static FEA results

    Hi, advanced FEA programs allow their users to perform fatigue analyses. However, there are still many programs where such simulations can't be performed. I've heard that in such case one can use results obtained from regular linear static FEA to calculate fatigue life manually. Theoretically...
  12. E

    Difference between brittle fracture and fatigue crack growth

    My question here is regarding fracture of materials. I have problems in understanding some concepts. Now, for static loading, there is a property called KIC (fracture toughness). By equating our stress from the static load to this KIC, we get the maximum length of the crack which does not...
  13. K

    A Fatigue stress concentration factor (Kf)

    Hi, I had been reading about the fatigue stress concentration factor (Kf) which is reduced compared to the geometric stress concentration factor (Kt). The reduction in turn dpends upon the material's sensitivity to notches...
  14. K

    Endurance limit / fatigue strength at high temperatures

    Hello All, I had been reading a book on Machine Design. I understand that at high temperatures, yield strength of the material drops. The behaviour of the fatigue strength i.e. the drop in fatigue strength may at times be taken to be of same proportion as that of yield strength. It is also...
  15. R

    One Ball fatigue failure at Deep Groove Ball bearing

    I am working on finding a solution for a gear box field failure. Failure description: In the deep groove ball bearing only one rolling element has a pre-mature fatigue failure (Image-6.jpg) and rest of the all ball is in good condition (image-05.jpg). Do anyone has seen the same kind of...
  16. 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...
  17. F

    Medical Understanding ATP, Fatigue, and Sleep: The Role of Cell Energy and Rest

    When our body cells are full of ATP (fuel from our mitochrondria), they are supposed to energize our biological systems.. but why do we feel fatigue when we don't sleep when we still have sufficient or ample supplies of ATP? What really cause fatigue?
  18. Saumya Kar

    Automotive Random Vibration and PSD spectrum profiles

    I am starting work on structural durability area for after treatment systems and deal with Random Vibration and PSD profiles quite often. However there are few fundamental questions about PSD profiles that I could not get answer to after a lot of search on internet. So finally decided to write...
  19. Grinkle

    I Question about expansion and photon fatigue

    @phinds noted in a recent thread that energy is not conserved on a cosmological scale, which hadn't occurred to me before, so I did some reading and happily the concepts were easy to digest and things I already understood but just hadn't connected the dots myself on regarding the implications...
  20. George Zucas

    Modifying Sharp Edges for Fatigue

    Hello all, I was wondering, for modifying the sharp edges of a shaft, which one of the cases attached is better? Why? My guess would be the one with the radius since there are more materials remaining than the other but there should be a reason for the other case since that is also frequently...
  21. S

    Fatigue of a Rotor: Predicting Life Expectancy with Variable Cyclic Stresses

    I have a fast rotating rotor spinning over 2 axis (over its main axis and over an external axis - the two axis are perpendicular to each other). Easiest to imagine this is like a windturbine yawing as it follows the wind direction.Each of the two rotations obviously causes a distinct centripetal...
  22. 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...
  23. 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...
  24. T

    How to tell if a spring is fatigue, creep or degrade?

    I'm doing some spring endurance test. If the spring is exceeding its cycles limit and causes fatigue failure, how normally the spring constant changes? For example, after the expected limit cycles (lets say 2million load-unload cycles), will the spring constant gradually decreases? or...
  25. 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...
  26. 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...
  27. N

    Low cycle fatigue, Coffin's law

    Homework Statement Hi, I require some assistance using coffin's law. I have the strain range and cycles to failure but need coffins slope- 'c'. C2 can then be found after the other values are known.Homework Equations Δε^pl=C2/N^c Where Δε^pl is plastic strain range, N is the cycles to failure...
  28. S

    Door Hinge axial fatigue testing equipment

    Well some one have any experence related to axial fatigue testing equipment designing? Have to discuss some concepts and need the feedback.
  29. B

    Abaqus Fatigue Algorithm

    Hi all, I'm hoping there's someone here who can give me a little help. So I've run a large number of fatigue tests, both stress and strain controlled, and using the data from these I've calibrated material constants for the chaboche model in Abaqus and run the simulations getting fairly similar...
  30. 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
  31. Marie Cailey

    Could I use this as a factor that affects muscle fatigue

    Could I use "The intensity of muscle contractions" as a factory that may affect how quickly muscles become fatigued? I'm doing an experiment, but is this a legitimate idea? Would my hypothesis be "The intensity of muscle contractions in the body affects how quickly muscles become fatigued"?
  32. 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...
  33. O

    Dang Van multiaxial fatigue criterion

    Hello everyone, I am trying to find a difference between two versions of the Dang Van criterion on multiaxial fatigue. Let's say that Dang Van 1 is the one that uses a critical plane and Dang Van 2 the one that uses the Tresca criterion (which means no critical plane) I assume that the only...
  34. S

    Fatigue Life of 0.10mm SS304 Sheet | Sathish Rosario

    Dear All, I would like to calculate fatigue life for the following: A SS430F metal component is repeatedly hitting at 0.10mm SS304 sheet with 1 Kg load from 0.20 mm distance. Assume, Area of hitting: 5.5mm X 16mm = 88 Sq.mm. Hitting load = 1 Kg Tensile strength of 0.10mm SS304 sheet is 515...
  35. T

    List of Metals or Alloys With Fatigue Limits?

    I know that steel and titanium have fatigue limits. Just to clarify, metals or alloys with fatigue limits are metals that - as long as they experience pressures that lower than the limits - can last "indefinitely". Aluminum, for example, does NOT have a fatigue limit. No matter how small the...
  36. T

    List of metals or alloys with fatigue limit

    I know that steel and titanium have fatigue limits. Just to clarify, metals or alloys with fatigue limits are metals that - as long as they experience pressures that lower than the limits - can last "indefinitely". Aluminum, for example, does NOT have a fatigue limit. No matter how small the...
  37. R

    Thermal fatigue for heat exchanger cycle test comparison

    I have a heat exchanger with water/air as medium and we test it in a facility where we cycle the water temperature between 25 to 95 degrees Celcius with a cycle time of 5 minutes for thermal fatigue. Our customer require the testing to be between 5 to 95 degrees instead with 3 minute long...
  38. Saumya Kar

    Von Mises stress Vs Principle stress

    Hello Folks, May be I am bring up the old topic again., but I've lost enough sleep over this topic. I understand that we use Von-Mises criteria for ductile material failure by comparing to yield limit and max principal stress is used to check failure for brittle materials. My question is bit...
  39. 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...
  40. steves1080

    Calculate drag force on a temperature probe inserted in a water pipe

    I'd like to add a temperature probe to a 4" water pipe downstream of a centrifugal fill pump, but I am afraid of the probe shearing from being subjected to a constant force from the upstream pump (which pumps at about 400 gal/min). Naturally, my thought was to use the drag force equation, but I...
  41. Q

    Carbon steel fatigue and temperature properties

    Hi everyone, I need some specific mechanical properties of A516 carbon steel, but as yet I am unable to find it online. Can you help me find the fatigue limit and the relation between yield strength and temperature? Are there tabulated values for this? Thanks! Mark edit: found it! seems i...
  42. A

    Doubt on Fatigue Strength S-N diagrams

    A standard way of plotting an S-N (fatigue strength vs no of cycles) graph is to start off by taking a value of Sm (for N=1000) cycles and joining it to the point depicting Se(Endurance Limit). Now we commonly take Sm= 0.9Sut for steels. Now I was wandering, before you actually get to use the...
  43. 1

    Calculating Fatigue Limit | STRESS vs. Stress Amplitude | Homework Help

    Homework Statement First of all, fatigue limit is defined in terms of STRESS, NOT stress amplitude, right? Calculate the fatigue limit based on the given data (see my attempt for data). Homework Equations N/A The Attempt at a Solution Here is a link to the data + my graph...
  44. I

    Wire With Greatest Bending Fatigue Resistance

    I need to add flexibility to this joint (where the arrow is pointing) and I was thinking about using a method I saw on this flexible clamp. I ripped it apart and it looks like they used copper wire as the flex material. What would be the best wire to use? I'm worried that perhaps it could...
  45. C

    Calculating Critical Surface Edge Crack for Fatigue Life of Material

    Homework Statement Compute the crtitical surface edge crack if the fatigue life = 8000000 cycles and maximum tensile stress is 21000 psi. m=3.5 and A= 0.00000000004 in ksi and in. units. Initial crack edge is 0.120 in. Y= 1.15 Homework Equations The equation is given in the attached file...
  46. S

    What is the Effect of Low Frequency Fatigue on Structural Damage?

    fatigue: low frequency and structural damage Hi all, I have a measured loading history and I need to calculate the structural damage through the Miner rules. The signal is measured on a rod element of a plough. As you can see from the load PSD, the signal has a verly low frequency component...
  47. T

    Fatigue calculations for stainless steel seamless tubing

    Looking to understand Fatigue calculations for stainless steel seamless tubing Problem: Material: 304 Stainless Steel tubing (.375 OD, .072 wall) per ASTM specifications used at 158F degrees maximum Ambient UTS 515 MPa, YTS 205 MPA, temperature de-rated per MIL-HDBK-5J to UTS 473.8 MPa, YTS...
  48. W

    How to calculate fatigue life in the creep realm?

    I am looking for some information on how to calculate fatigue life for materials at temperatures elevated into the creep realm. ASME Sec 8 Div 2 describes how to do this for carbon steel below 700F and stainless below 800F, but I am interested in temperatures > 1000F. I am performing an FEA...
  49. D

    Centrifugal Fan Fatigue Question

    Homework Statement I have a question concerning the desig of high-velocity, high-pressure industrial blowers. The company wants to avoid welding the blades to the impeller sides as welding causes the blades to deform slightly, and dynamic balancing of the impeller is difficult because of weld...
  50. F

    Analysis of Fatigue due to random vibration

    Hi! I'm trying to find a good way to predict fatigue caused by a random vibration (given PSD). I know at least 2 ways of doing it but I'm questioning them both. One of them is using the rain flow count algorithm at a simulated acceleration/time signal to generate a certain amount of...
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