Force~Time history

[Hussain2339]

Dear all,

I am simulating the Impact of Timber Projectile on an Aluminum Panel.

The value of maximum deflection I get is quite close to experimental but the time is almost 10 times (See the pic attached).

 

[FEA way]

How do you simulate this - do you use initial velocity applied to the projectile, gravity load or another approach ?

 

[Hussain2339]

I assigned velocity to projectile

 

[Hussain2339]

In Abaqus, I applied velocity to the projectile. In the Experiment, It was a drop weight test of Timber projectile, due to gravity

 

[FEA way]

And you placed the projectile right above the target (initially in contact) ? Make sure that the value of the initial velocity is correct. Can you share some screenshots of the model and the results (possibly a few frames from the deformed shape contour plot) ?

 

[Hussain2339]

 

[Hussain2339]

 

[Hussain2339]

 

[Hussain2339]

I know the reason for difference in permanent deflection, Just wandering about the time of Impact

 

[NRP99]

You need to consider the calculation of time required to complete the distance maintained between the timbre and panel. Distance/Initial velocity gives the time it will take to travel timbre to impact the panel. If you adjust the distance, the impact time will be exact.

How experiment is done? If its gravity based then apply gravity maintaining the same distance between the two to achieve the exact velocity and time point of impact.

 

[Hussain2339]

How can we apply gravity load to the dynamic tests? It won't hit the plate

 

[NRP99]

Drop analysis can be done like free fall experiment. No strings attached. Do not apply any constraints or free constraints in the direction of gravity. And make it free fall from the same distance as experiment is done.

The gravity will make the velocity increase as the timbre travels towards the panel and at just before impact, velocity will be v=√2gh where h is distance between timbre and panel.

 

[FEA way]

In most cases, it’s better to run drop simulation with initial velocity instead of free fall under gravity. Especially since you can’t account for air resistance this way and the simulation of free fall will be approximate. It would be better to modify the results from the experiment used for comparison with FEA so that they start from the beginning of the impact, not from the beginning of the fall. But if you don’t want to do this and you prefer to do the direct comparison then you can simulate the free fall using the aforementioned approach. Either way, you have to make sure that the results from the simulation and the ones from the experiment cover the same range of events.

 

[NRP99]

@FEA way
How much would be the impact of air resistance on velocity of free falling object? Negligible, I guess.

Yes it can save time of the analysis if impact is made with initial velocity of √2gh and placing the timbre just before fractional mm of the impact location.

 

[Hussain2339]

@FEA and NRP

Thank you very much for your response.

I am using velocity to the projectile and comparing from the point of impact. The difference of time period is almost 10 times.

 

[FEA way]

So basically the whole impact and following effects such as rebound happen too fast in the analysis ? Double-check all the settings of the simulation including unit consistency. Something must be way off if there is such a difference.

 

[NRP99]

Can you share velocity vs time plot for both experiment and your simulation? That would make clear what is going wrong.

 

[Hussain2339]

I repeated the test and also tried different boundary conditions.

This is the closest I could achieve.