SUBROUTINE UMAT(stress,statev,ddsdde,sse,spd,scd,
1 rpl, ddsddt, drplde, drpldt,
2 stran,dstran,time,dtime,temp,dtemp,predef,dpred,cmname,
3 ndi,nshr,ntens,nstatv,props,nprops,coords,drot,pnewdt,
4 celent,dfgrd0,dfgrd1,noel,npt,layer,kspt,kstep,kinc)
c WRITE (6,*) '
c NOTE: MODIFICATIONS TO *UMAT FOR ABAQUS VERSION 5.3 (14 APR '94) c
c (1) The list of variables above defining the *UMAT subroutine,
c an
d th
e first (standard) block o
f variables dimensioned below,
c have variable names adde
d compared to earlier ABAQUS versions.
c
c (2) The statement: include 'aba_param.inc' must be adde
d as below.
c
c (3) As of version 5.3, ABAQUS files use double precision only.
c The file aba_param.inc has a line "implicit real*8" and, since
c it is include
d in th
e main subroutine, it will define the variables
c there as double precision. But other subroutines still nee
d the
c definition "implicit real*8" since there may be variables that are
c not passe
d to them through th
e list or common block.
c
c (4) This is current as of version 5.6 of ABAQUS.
c
c (5) Note adde
d by J. W. Kysar (4 November 1997). This UMAT has been
c modifie
d to keep track of th
e cumulative shear strain in each
c individual slip system. This information is neede
d to correct an
c error in the implementation of the Bassani an
d Wu hardening law.
c Any line of code which has been adde
d or modified is preceded
c immediately by a line beginning CFIXA an
d succeeded by a line
c beginning CFIXB. Any comment line adde
d or modified will begin
c with CFIX.
c
c The hardening law by Bassani an
d Wu was implemented incorrectly.
c This law is a function of both hyperbolic secant square
d and hyperbolic
c tangent. However, the arguments of sech an
d tanh ar
e related to the *total*
c slip on individual slip systems. Formerly, the UMAT implemente
d this
c hardening law by using the *current* slip on each slip system. Therein
c lay the problem. The UMAT di
d not restrict th
e current slip to be a
c positive value. So when a slip with a negative sign was encountered, the
c term containing tanh le
d to a negativ
e hardening rate (since tanh is an
c od
d function).
c The UMA T has been fixe
d by adding stat
e variables to keep track o
f the
c *total* slip on each slip system by integrating up the absolute value
