RHS in VUEL

[Supratik]

I am presently developing a VUEL in abaqus. I have some problems defining RHS for a 3-D brick element (C3D8). As per the abaqus documentation,
RHS gives the element internal force vector; for a simple one dimensional truss problem, The RHS is as follows (I am quoting from the subroutine reference manual example):

c assemble internal load in RHS
rhs(kblock,1) = -forceTra
rhs(kblock,4) = forceTra

The above is for a single truss element , where forceTra = k*(u2-u1) and -forceTra = k*(u1-u2).

However, I cound not find out what will be the form of RHS vector for a full 3-D brick element (C3D8 for full integration or C3D8R for a single intergation point). I would be eagerly awaiting for somebody to help.

Regards,

Supratik

[matsgd]

The internal force vector of a solid element is given by
F=integral(BL^T*sigma)dV

where BL is the linear strain displacement matrix, and sigma is the stress tensor. In a UL formulation, BL is with respect to the current configuration and sigma is Cauchy stress. In a TL formulation, BL is with respect to the initial configuration and the stress is the second Piola-Kirchhoff stress. Cf. Bathe's "Finite element procedures" or Belytschko, et al., "Nonlinear finite elements for continua and structures".

Mats