I just attended USNCCM11, and heard from a presentation that there should be free code for polymer viscoplasticity model from M.C. Boyce.Unfortunately, I googled from half an hour and dowloaded nothing this afternoon. Can anybody give more info ?

Thanks in advance !

I have an idea: In abaqus, I want to simulate crack propagation by XFEM, and meanwhile I also want to define the stress update algorithm by writing a UMAT.
Anybody wants to share related experiences?

Hi, friends,

Now, I am implementing the non-local continuum theory in ABAQUS through UMAT programming.

Unfortunately, I have been obstacled by the following question:

On one hand, in non-local continuum theory, the non-local strain of every particular integration point is determined by the global strain field all over the specimen.

In all textbooks, when iteration methods are introduced, the iterative formula is always H(x)x+f=0, where f is the external force applied on the system. All methods are stated when f is fixed.

These methods cann't be used directly to the displacement-controlled case, unfortunately. The reason is that the external force f keeps changing during the iteration. In this case, f is determined due to both the controlled displaement and the instant system stiffness, of which the former is fixed but the latter keeps changing during the iteration. As a result, the external force f is not fixed.

Recently, I find that definitions of secant stiffness and tangent stiffness in many books seem pretty confused.Therefore, here I am giving the definitions I think correct, then give my questions on them.

Consider the equation

H(x)x+f=0

(1) Definition of tangent stiffness. As for the above equation, what is the tangent stiffness for some particular value x0?

Let's give the definition according basic knowledge of advanced mathematics. Let's consider the curve H(x)x~x. For this curve, y=H(x)x, so the tangent at x0 is

A question has arised when I read a book about fracture mechanics recently.

This question is about the calculation of potential energy in "fixed-grips" (prescribed displacement) and "dead-load" (prescribed displacement).

Opinions in the book: In the condition of prescribed displacement, the potential energy is equal to the area between the displacement axis and the curve of load .vs. displacement, and has a positive value. In the condition of prescribed loading, the potential energy is equal to the area between the load axis and the curve of load .vs. displacement, and has a negative value.

Anyone can explain the above conclusion for me please?

Thank you!