Dear all,
I am currently implementing my own fatigue crack growth behavior within an Abaqus Cohesive Zone Element via a combination of URDFIL, UEXTERNALDB and ofcourse UMAT. I could go into the intent of all the different routines, but this is beyond the point for this question since they seem to work fine.
What I am strugling with is the time incrementation. During the calculations within the UMAT I obtain information on convenient time steps to efficiently simulate the model. I tried enforcing these from the same UMAT using the variable PNEWDT, however, although the time incrementation is set to automatic, e.g.:
[tt]*STATIC
0.01, 1., 1e-5, 0.1[/tt]
I obtain the behavior which according to the manual corresponds to fixed time incrementation. Specifically, the expected effect is only present when[tt] PNEWDT=1.0d0[/tt]. (I should note this is merely a test, in general the PNEWDT would not be a prescibed value but be dependent on for example damage rate.) In the situation where [tt]PNEWDT[/tt] has a value > 1 the value is ignored and the usual automatic time increments are enforced (going from 0.01 to 0.1 magnitude steps), whilst for [tt]PNEWDT[/tt] values < 1 the job terminates.
Any ideas why this happends or how I can make this work? Alternative approaches are also welcome ofcourse.
Any help would be very much appreciated.
I am currently implementing my own fatigue crack growth behavior within an Abaqus Cohesive Zone Element via a combination of URDFIL, UEXTERNALDB and ofcourse UMAT. I could go into the intent of all the different routines, but this is beyond the point for this question since they seem to work fine.
What I am strugling with is the time incrementation. During the calculations within the UMAT I obtain information on convenient time steps to efficiently simulate the model. I tried enforcing these from the same UMAT using the variable PNEWDT, however, although the time incrementation is set to automatic, e.g.:
[tt]*STATIC
0.01, 1., 1e-5, 0.1[/tt]
I obtain the behavior which according to the manual corresponds to fixed time incrementation. Specifically, the expected effect is only present when[tt] PNEWDT=1.0d0[/tt]. (I should note this is merely a test, in general the PNEWDT would not be a prescibed value but be dependent on for example damage rate.) In the situation where [tt]PNEWDT[/tt] has a value > 1 the value is ignored and the usual automatic time increments are enforced (going from 0.01 to 0.1 magnitude steps), whilst for [tt]PNEWDT[/tt] values < 1 the job terminates.
Any ideas why this happends or how I can make this work? Alternative approaches are also welcome ofcourse.
Any help would be very much appreciated.