Wednesday, 5 August 2015

SOLIDWORKS Simulation - “Durability Analysis for Random Vibration”

What is Random Vibration Fatigue?

  • Structures or Mechanical components are subjected to random form of loading.
  • Wind Loads, Wave Loads, Car engine operating on different moving roads are such examples.
  • Random loading changes over time.
  • Random vibration involves dynamic loading conditions.

Random Vibration Fatigue

  • Three methods to compute the expected damage ratio due to random loading Fatigue.
    •   Narrow Band Method
    •   Steinberg Method
    •   Wirsching Method
  • Loading and response are random processes
  • Frequency based fatigue is required for such loading conditions.
  • They use statistical measures for solutions.
  • Requires a Dynamic random vibration study run for Fatigue calculation.
  • New Fatigue study involves stress PSD(Power Spectral Density)

What are Dynamic Loads ?

  • Dynamic loads are classified to deterministic or non deterministic.
  • Deterministic loads defined are functions of time and predicted precisely.
  • They are harmonic, periodic or non periodic.
  • Non deterministic loads cannot be defined as functions of time.
X Axis -  Frequency(Hertz)
Y Axis -  PSD (Amplitude²/ Frequency)

Benefits for Fatigue Analysis

  • Calculates the Fatigue Strength Reduction Factor(Kf).
  • The calculation takes place when the corrected alternating stress is less than the endurance limit.


  • Life will provide the Time for Fatigue Failure
  • Damage will provide the percentage of Life during the Random Vibration Loading conditions.


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