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# Liu Jinxing's blog

## Look for free-code UMAT on polymer viscoplasticity model of M.C. Boyce

Wed, 2011-08-10 12:09 - Liu JinxingI 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 !

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## How to combine XFEM and UMAT in ABAQUS?

Wed, 2010-11-10 03:21 - Liu JinxingI 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?

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## A question on UMAT implementation of non-local theory

Sat, 2009-11-14 13:42 - Liu Jinxing

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.

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## Question on non-linear iteration in cases of force-controlled loading and displacement-controlled loading

Fri, 2009-10-30 01:34 - Liu JinxingIn 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.

## Question on the definitions of secant stiffness and tangent stiffness in iterative methods for non-linear problems

Fri, 2009-10-30 01:23 - Liu JinxingRecently, 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

## Calculation of potential energy in conditions of prescribed displacement and prescribed loading

Mon, 2009-06-01 23:48 - Liu JinxingA 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).

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