## General Mechanical

#### Nonlinear Shock Analysis – help

• canoztrk
Subscriber

Hello everyone!

I am simulating a structure with a shock of 40g shock wave for a given time like 11 ms.

Firstly when i encountered with this project I've used modal+transient(Mode superposition) and our customer responded our report with  "

 Material data is unsufficient for shock analyses since only the linear elastic material properties are used. Nonlinear material parameters must be handled for these type analyses. "

So my question is what type of material data that I need and is it really differenciate results between nonlinear transient and modesuper position transient analysis? (I'm questioning I read equ. stress with MSUP is 0,5 Mpa but if i perform nonlinear transient would I see like 100 Mpa??) btw my model contains composite material too.

• peteroznewman
Subscriber

For the Modal Analysis

1. What is the frequency of the first mode of the structure?
2. What was the highest frequency you requested in the Modal analysis?
3. Did you look at the Cumulative Mass Participation in each direction?

For the Transient Analysis

• What was the smallest margin of safety for all the materials in the model?
• How did you evaluate the margin of safey of the composite material?
• If all the materials stayed in the linear elastic range, then you wouldn't expect a different result by adding nonlinear material properties.
• canoztrk
Subscriber

For modal Analysis

1- 28 Hz

2- 577 Hz

3- it is 1 for all rotxyz and translationxyz

For the Transient Analysis

1- 70

2- Tsai Hill and IRF value is 0,12

• peteroznewman
Subscriber

An 11 ms shock excites a natural frequency at 45 Hz while your Modal analysis recovered frequencies up to 577 Hz so that is plenty high enough.

It seems like all the materials stayed in the elastic range, so there is no need to have nonlinear material properties for this model.

One difference between a MSUP Transient and a full nonlinear Transient is when there is frictional contact in the model. Since Modal must convert nonlinear contacts into linear contact, frictional contact will behave differently in a MSUP Transient than a full Transient. For example, gaps cannot open up in a MSUP Transient in frictional contacts.