Should the user make a subroutine to calculate the rotation matrix in Abaqus VUMAT?

11 November 2016 1 5K Report

Dear all,

I am making a VUMAT subroutine based on Abaqus/Explicit. I have to use the rotation matrix [R] to define the material constitutive relation. However, VUMAT does not provide it directly. I am wondering whether I have to make my own codes to calculate it according to [F]=[R][U]. If yes, is LU decomposition method suitable for this case? Note that: [F], [R] and [U] are 3 by 3 matrices. Or do I have other ways to obtain it?

Many thanks

Shuai

Shuai Chen

Hi Rober,

Thanks for your answer. I am dealing with 3D elements. Ordinary algorithm was used to calculate [R] = [F] [U]^-1. But it seems unstable same time. Maybe I have to try the explicit expression of [R] to avoid performing the inverse calculation of [U]. However, it may need a bit work to calculate tensor invariants and then I am able to use this explicit method, since Abaqus/Explicit does not provided functions in its library to calculate tensor invariants.

Many thanks

Shuai

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