durability analysis for random vibration
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SOLIDWORKS Simulation
“Durability Analysis for Random Vibration”
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Random Vibration Loading
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.
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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.
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Random Vibration Fatigue
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)
X Axis - Frequency(Hertz)Y Axis - PSD (Amplitude²/ Frequency)
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Computation Methods
Three methods to compute the expected damage ratio due to random loading Fatigue. Narrow Band Method Steinberg Method Wirsching Method
Calculates the Fatigue Strength Reduction Factor(Kf).
The calculation takes place when the corrected alternating stress is less than the endurance limit.
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Performing a Random Vibration Fatigue Study
Add In the Simulation and Drop Down the New Study
Setup and run a linear dynamic random vibration study initially.
Select Fatigue > Random Vibration – Fatigue for Random Vibration
Fatigue Study tree > Add Event by right clicking on the Loading(Random Vibration).
Fatigue event > associate the Random Vibration study.
Under Duration select the time duration of the random loading input for the model applied.
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Performing a Random Vibration Fatigue Study
Apply/Edit Fatigue Data to add S-N curve for the material.For Stress variation from the maximum cycle to the minimum cycle, Multiple data points can be entered.
Type of computational method(Narrow Band, Steinberg or Wirsching), if necessary. The Narrow Band method mostly provide conservative results.
Final step is to Run the Study to estimate the Life and Damage as Results.
Life will provide the Time for Fatigue FailureDamage will provide the percentage of Life during the Random Vibration Loading conditions.
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