Usually for automobile metal structures, we assume a failure to be identified, when we see plastic strain crossing around 10%.
Showing posts with label LS Dyna. Show all posts
Showing posts with label LS Dyna. Show all posts
Tuesday, November 12, 2013
What ELFORM do you use for different elements and Why? in the context of LS-Dyna
In terms of speed and robustness I would rank shell formulations as follows:
1. type 2
2. type 2 with BWC warping stiffness and full projection (see BWC and PROJ in *CONTROL_SHELL)
3. type 10
4. type 16 (Type 16 shells require approximately 2.5 times more CPU than type 2 shells.)
5. type 7
6. type 6 [1]
The last 3 formulations listed above are fully-integrated (4 in-plane integration points) and thus do not suffer from hourglass modes [2]. Generally speaking, the underintegrated elements tend to be a little too soft. By using stiffness-based hourglass control (HG type 4) and a reduced hourglass coefficient (say, .03 to .05), the behavior is stiffened slightly and so this hourglass combination is generally recommended for most applications of the underintegrated shells. For very high velocity/rate problems, viscosity-based hourglass control is recommended.
Accuracy:
From an accuracy standpoint, shell type 16 is preferred over the underintegrated formulations provided the following are true:
- initial element shape is reasonable
- element does not distort unreasonably during the simulation
- Used together with hourglass control type 8, the type 16 shell will give the correct solution for warped geometries.
1. type 2
2. type 2 with BWC warping stiffness and full projection (see BWC and PROJ in *CONTROL_SHELL)
3. type 10
4. type 16 (Type 16 shells require approximately 2.5 times more CPU than type 2 shells.)
5. type 7
6. type 6 [1]
The last 3 formulations listed above are fully-integrated (4 in-plane integration points) and thus do not suffer from hourglass modes [2]. Generally speaking, the underintegrated elements tend to be a little too soft. By using stiffness-based hourglass control (HG type 4) and a reduced hourglass coefficient (say, .03 to .05), the behavior is stiffened slightly and so this hourglass combination is generally recommended for most applications of the underintegrated shells. For very high velocity/rate problems, viscosity-based hourglass control is recommended.
Accuracy:
From an accuracy standpoint, shell type 16 is preferred over the underintegrated formulations provided the following are true:
- initial element shape is reasonable
- element does not distort unreasonably during the simulation
- Used together with hourglass control type 8, the type 16 shell will give the correct solution for warped geometries.
Thursday, November 7, 2013
What is Hourglass energy? IQ3
1st order reduced-integration elements (which happen to be the very type of elements generally used in explicit solvers) suffer from hourglassing. These elements only have one integration point; because of this the elements can shear without introducing any energies. FEA codes which rely on 1st order reduced integration elements counter this by introducing hourglass energy. In situations where these elements would otherwise shear, this augmented energy keeps this from happening. This is reflected in your reported hourglass energy values. High hourglassing energy is often a sign that mesh issues may need to be addressed.
Subscribe to:
Posts (Atom)