Flanagan-Belytschko hex element with hourglass control.

[zhouxinwei]

We recently found that the default hourglass stiffness parameter is too high for the Flanagan-Belytschko hex element with single integration point. Our users have reported that this could lead to unreasonable hardening for metal plasticity.

Before version 2017.08.32, the default value is approximately 0.01K, where K is the bulk modulus; since version 2017.08.32, the default value is changed to 0.0008G, where G is the shear modulus. Also since version 2017.08.32, there is a scaling factor the user can adjust this stiffness parameter.

The default behavior of this element will be different (i.e. the same old input will give different results with version 2017.08.32+), the user can use keyword HourglassStiffnessBasedOnBulkModulus to retrieve the old hourglass stiffness.

Please refer to the manual for more details.