Learning Forum

[SONGYANG]

Hi, guys, I'm doing a feline landing simulation using Explicit Dynamics, the basic setting is as follow.

1. A cat forefoot, including soft tissue, bones, and cartilages was used.
2. All the contacts between bones and cartilages, between bones, cartilages, and the internal surface of soft tissue are bonded, the contact between the soft tissue and the plate below is set as body interaction with a friction coefficient of 0.6.
3. The initial velocity is set as 2.405m/s.
4. the end time in the analysis settings is set as 0.008 s since only 5mm landing is simulated, and all other setting is the default.
5. A standard earth gravity is also added.
6. The plate is set as Fixed support.

[Ashish Khemka]

Please see if the following discussion helps:

Time step too small error in Explicit Dynamics ÔÇö Ansys Learning Forum

Regards Ashish Khemka

[Chris Quan]

After a point mass has been added to the model, the total mass of the system is increased. This will increase the total momentum of the system, which can result in higher stresses and larger strains in the foot materials during the drop impact.
Time step will drop if an element has been severely distorted due to higher stresses and larger strains.
You need to make sure Erosion is activated under Analysis Settings -> Erosion Controls to remove the distorted elements and thus prevent the drop of time step.
You also need to check material models of the foot to make sure they are realistic. For example, the materials may not behave as linear elastic under the higher momentum so material plasticity and failure need to be taken into account of in their material models.
Material plasticity and failure models can be added to materials in Engineering Data.

[SONGYANG]

Dear cxquan Sorry for the delayed reply.
Could you talk more about the material plasticity and failure models? As I can find from the Engineering Data, there are various models in the Plasticity, could you tell me which one should I choose for my model? And could you provide me with some references for the value settings? such as for human bones and soft tissue?
Thank you so much.

[SONGYANG]

Dear Ashish Khemka Thank you for the recommendation, but unfortunately it didn't solve my problem, do you know any information about what Mr cxquan said?