I have several questions related to swelling.
1. According to the documentation, swelling is only available as a User Programmable Feature (UPF), USERSW. Is that true?
2. Is USERSW limited to isotropic materials?
3. Is USERSW available for SOLID226/227. If not, can it be made so?
The concept of swelling in ANSYS means different things to different people. Historically, irradiation induced swelling was all that was available. In recent years, questions have come in concerning other forms of swelling, such as hygrothermal growth in concrete and composites.
In the beginning, ANSYS had irradiation induced swelling capability. The capability was removed in 1986 and replace with user swelling. If you look through the documentation, you will find references to swelling, but in all cases, that reference is to user swelling. And user swelling is only available for core ANSYS elements, such as PLANE42, SOLID45, LINK8, etc. The swelling equation currently used as the demonstration coding for USERSW is not the same as any of the irradiation induced swelling equations removed in 1986. User swelling is NOT available for the 18x family of elements. Implementation of swelling for the 18x elements will require the use of USERMAT. At present, there are no material non-linearities in elements 226 and 227 and if that does occur, it will likely follow the 18x element implementation.
In addition to the limitation on elements, user swelling is also limited to isotropic materials and only 1 strain value is permitted. That strain value is appended as a single value to the end of the thermal strain record on the .rst file. This is more for historic reason than for anything else. A single value is probably okay for irradiation induced strain but may not be appropriate for any other type of swelling, such as hygrothermal swelling of concrete or composite materials.
Irradiation induced swelling is similar in behavior to thermal expansion except for the time part; swelling doesn't go down when the fluence goes down. There is an incremental component that continues to grow so long as fluence is available. The user could make swelling do the same thing with a little thought and planning. There are no known examples of the latter and it won't work easily if other temperature dependent behaviors are also present.
USERSW is available in the customize/user directory and is attached here for convenience. Also attached is a sample problem from the ANSYS regression set.