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Constitutive law

Question about implicit creep subroutine in Abaqus

The implicit implementation of creep in abaqus requires dh/d(\delta \epsilon_c ) as Jacobian in Newton-Raphson's iteration. The derivative can be expanded as shown in the figure attached. The term dh/dq, the one underlined by a green stroke, is expected to be provided by users through specifying DECRA, whereas the term dq/d(\delta \epsilon), underlined by a red one, is confusing me. It seems that that term is computed by Abaqus but I have no idea how it is done. The same question applies to the last derivative on the right hand side.

Abaqus, UMAT, Constitutive law, Powder

Dear all,


I have several questions about how to use existing constitutive law of material to code UMAT in Abaqus. I have carried out experiment for several powder materials, including metal, ceramic, polymer powders. The powder aggregate is compacted in a cylindrical die. After the compaction, relationships between axial stress and axial strain, radial stress and axial strain are obtained. The material under such condition is always treated as elastic plastic material.

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