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[wangbb]

Hi,

I perform a implicit static analysis and use *DATABASE_BINARY_D3MAX/*DATABASE_MAX_SOLID_SET to output the maximum stress of a target solid element set, and then perform post-processing in LSPP. 

The issue I encounter is that, for the same set, the location and value of the maximum stress from d3max and d3plot are different:

- In d3max, the maximum stress is 853 MPa, with element ID = 19651.

- In d3plot, the maximum stress is 932 MPa, with element ID = 19114.

I would like to know what causes this discrepancy.

Thank you very much.

[Nanda]

Hello Wang,

The difference in maximum stress values and associated element IDs reported in the d3max and d3plot files for the same solid element set in an LS-DYNA implicit static analysis is primarily due to the way each file records and stores stress data.

Key Differences on how they both work:

1. d3max File
   • Records the maximum (or minimum) stress value reached by each element throughout the entire analysis.
   • Updates results at intervals controlled by the DTCHECK parameter.
   • Tracks the peak stress experienced by an element, regardless of the time step at which it occurred.
   • Therefore, d3max is intended to capture the absolute extreme stress values over the complete simulation.
2. d3plot File
   • Stores stress and strain results only at discrete output states (time steps) specified for post-processing.
   • The maximum stress reported from d3plot is the highest value observed among the saved states.
   • If the true peak stress occurs between two output states, it may not be captured in the d3plot database.
   • Consequently, the reported maximum stress and its associated element ID may differ from those found in d3max.

You can reduce this discrepancy, by outputting d3plot's at a higher frequency, this can be done by decreasing the DT.

Regards,

Nanda.

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[wangbb]

Hello Nenda,

Thanks for your feedback.

Additional questions are as follows:

1. I can understand that the different methods used by d3max and d3plot to collect data which lead to different locations and values for the maximum stress. 
However, what confuses me is why the result from d3max is smaller than that from d3plot.  As you mentioned, “d3max is intended to capture the absolute extreme stress values over the complete simulation,” so I would naturally expect d3max to give larger values, not smaller. 
Therefore, I would like to confirm whether the stresses in d3max and d3plot are calculated using the exact same method.

2. Between d3max and d3plot, which one is more reliable (or more trustworthy)?

3. By the way, which keyword should I use to output the mass of the assigned part?

Thank you in advance.

[Nanda]

Hello Wang,

Please do the below checks:

1. In LS-PrePost, identify exactly what stress quantity is plotted in d3max and d3plot. Are both same quantities (VM-stress/x-stress/etc)?
2. Turn off/on averaging, and see if it helps.
3. Verify whether integration-point output is enabled (Refer to NINTSLD under *DATABASE_EXTENT_BINARY).
4. Plot time histories for both elements (19114 and 19651) and compare the stress definition being used.

My suspicion:

Because the d3plot value (932 MPa) exceeds the d3max value (853 MPa), the most likely explanation is that you are not comparing the same stress measure or the same integration-point representation between the two databases. This is much more common than a database-output issue itself.

Also, which version of LS-PrePost you use? Could you upgrade to the latest one?

Between d3max and d3plot, that depends on how your output controls are setup. If d3max is requested for all elements, I would rely on d3max more.

You can get this information in LS-PrePost itself:

In the output files, check for d3hsp, the mass summary is written by default. Look for keywords like "summary of mass" in the d3hsp file.

Regards,

Nanda

[wangbb]

Hello Nanda,

The problem was resolved after upgrading LSPP to 4.12.

[wangbb]

Hello Nanda,

I am currently using LS-PREPOST version 4.7.20. I will upgrade to the latest version and check again.

Thank you.

[wangbb]

Hello Nanda,

Regarding the mass, the situation is, I need to set a constraint on the mass in HyperStudy, so I need to invoke a output file (such as binout) to input the mass.

However, I don't know which keyword can generate the mass into output file.

[Nanda]

Hello Wang,

That's refreshing to hear. As far as the mass part, I'm not sure if it can be outputted in any separate file. What is HyperStudy? What kind of inputs does HyperStudy accept?

Is d3hsp file not helping?

Regards,

Nanda