Thursday, 27 August 2015
Wednesday, 5 August 2015
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.