Simulation for Designers - Part 7

Simulation for Designers - Part 7

Simulation for Designers - Part 7

Safety Factor Plots

I frequently get told that safety factor plots results within Nastran In-CAD are not correct. The reason for this is that safety factor values are calculated in a slightly different way. 

This is best explained by the following example. I will use 200MPa for yield limit for comparison purposes

Safety factor calculation based on average stress at location A is 20.51

Average Stress value = (10+12+9+8)/4 = 9.75

Safety Factor = 200/9.75 = 20.51

Safety factor calculation based on how Nastran In-CAD displays plots at Location A is 20.97.

Safety Factor for Element 1 = 200/10 = 20

Safety Factor for Element 2 = 200/12 = 16.667

Safety Factor for Element 3 = 200/9 = 22.222

Safety Factor for Element 4 = 200/8 = 25

Average Safety Factor = (20+16.667+22.222+25)/4 = 20.97

So, this is the reason why there is slight difference in the safety factor results. Both results are correct as they have been calculated in slightly different ways. It is entirely up to you which value you take.

Here a safety factor display is showing a minimum value of 21.11.

Note changing Data Type to Corner or Centroidal will yield the same safety factor result.

So, for the same model and results if we display the average centroidal results the maximum stress value becomes 9.4381MPa.

So, based on this value the factor of safety (hand calculation) is 21.19.

This is very close to the Safety Factor plot value of 21.11 with a difference of less than 0.5%. 

There is also a great article on “Safety factor is not correctly reconciled in Autodesk Nastran In-CAD” by John Holtz from Autodesk which you may find very useful. (Available here)

NB: If you cannot wait and would like to learn more about Nastran In-CAD now then I would recommend the 'Up and Running with Autodesk Nastran In-CAD 2019' book available from Amazon worldwide.

If you would to watch some of the videos I have created around Autodesk Simulation then please take a look at our Simulation webinar library.


AI, Automation & the Future of AEC: The 2025 Outlook

30 March 2025

Bluebeam teamed up with Hanover Research to produce the AEC Technology Outlook 2025 report. Conducted in summer 2024, the study examines how global AEC firms are adopting AI, prioritizing sustainability, and integrating digital workflows. Read more!

Paths to Net Zero: Insights for Sustainable AEC

10 December 2024

As the built environment sector accounts for nearly 40% of global CO₂ emissions, achieving net-zero carbon has evolved from aspiration to necessity. In response, Symetri hosted the Paths to Net Zero: Insights, Technologies, and Solutions webinar series in September 2024. This article distils key takeaways from the series, offering a snapshot of challenges, trends, and impactful approaches shaping the future of decarbonization in the AEC industry.