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Durability engineering videos

Durability engineering videos

Random Vibration Fatigue Capabilities in nCode DesignLife

Vibration Fatigue is a failure mode that can affect many components and assemblies under repeated loading. Such vibration loading inputs can activate resonance conditions which require estimation of stresses from a dynamic FE run. In nCode DesignLife, these dynamic stresses can be paired with random PSD excitations in the frequency domain to obtain fatigue answers. In addition to stress-life analysis, nCode DesignLife also covers strain-life, spot weld and seam weld analysis in the frequency domain.

In this webinar we will look at:

  • Overview of vibration Fatigue capabilities in nCode DesignLife and focus on random vibration capabilities in particular
  • Simulating a shaker table test virtually in nCode DesignLife for better test-CAE correlation
  • Multiaxis PSD capabilities for analyzing components that are subjected to multiaxial vibrations simultaneously in real life
  • Application to both parent metal and welds

Originally presented on April 16, 2020

Notes from the presenter

Thanks for watching – we hope you got an overview of vibration fatigue capabilities in nCode DesignLife with particular focus on random vibration. The webinar led to a lot of questions (50+ questions) and some of those were not addressed in the webinar due to paucity of time. I’d like to answer a few common questions and highlight a few points here that were not covered:

  • How is a PSD created and does nCode have tools to create PSD from any time history data ? Yes, we have capability to convert time series to PSD in nCode. The DSP Glyph Palette in nCode has a frequency spectrum glyph that enables time history to PSD conversion. Essentially this glyph is performing the Fast Fourier Transformation (FFT) calculations. It is important to highlight here that NOT every time series data is eligible for a PSD conversion. PSD assumes the time series data is meeting meet random, gaussian and stationarity requirements. Stationarity means characteristics not changing with time.
  • What mean stress correction options are available in SN and EN when static stresses and FRF results are combined? We talked about the ability to bring pre-stress/isothermal temperature or constant stress load cases that need to be combined with FRFs. Since the Generally the dynamic results don’t tell us much about preload, bolt up, residual stress, etc. and such results are brought in separately as a static load case. nCode offers various mean stress corrections in SN like Goodman, Gerber, FKM, Walker etc. and in EN we offer Morrow and Smith Watson Topper (SWT) options.
  • Accuracy of modal FRF approach against direct FRF approach: The benefits of using modal FRF approach over the direct FRF approach was highlighted in the one of the slides in the webinar. Modal FRF setup benefits include reduced FE file sizes and lower FE solve times compared to direct FRF setup. This led to many questions on the accuracy of the modal FRF approach against the traditional widely used direct FRF. As long as the frequency resolution (frequency steps) between the modal FRF setup and direct FRF is the same, there is very minimal difference between the two approaches.
  • Tutorial files on the webinar demo examples: All of the examples highlighted in the webinar (except the exhaust manifold model) are available in the worked example 10 of DesignLife worked examples. This is available with the software installation and the examples data and nCode .flo files can be found in the nCode installation directory. The PDF documentation are located in the manuals tab of the nCode home screen (bottom left option).

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