Hi all,
I am implementing the constitutive behaviour of two-crystal CuAlNi shape memory alloy during uniaxial loading using UMAT. My aim is to pass single crystal to polycrystal model. So, I am trying two-crystal problem firstly. I have no trouble with implementing two-crystal (one crystal has no rotation, other crystal has 10 degree rotation). However, when I implement two crystal ( one crystal has no rotation, other crystal has 30 degree rotation), there is an convergence problem. I think this problem is a result of defining of the crystal boundaries. I use two C3D8 element and I define rotation in UMAT like that:
! ELEMENT 1:: 30 DEGREE
IF (NOEL.EQ.1.) THEN
ROTATE(1,1)=0.866025403
ROTATE(1,2)=0.5
ROTATE(2,1)=-0.5
ROTATE(2,2)=0.866025403
ROTATE(3,3)=1.
! ELEMENT 2:: 0 DEGREE
ELSE
ROTATE(1,1)=1.
ROTATE(2,2)=1.
ROTATE(3,3)=1.
END IF
I transform our transformation strain using these rotate tensors.According to our constitutive equations; the difference between the crystals which have different orientations is only transformation strain. When two crystal have close rotations, there is no problem but when difference between the rotations increases, I can not get results because the shared nodes of the elements have very different values in finite element and I think it is a problem.
Nazım Babacan
I am implementing the constitutive behaviour of two-crystal CuAlNi shape memory alloy during uniaxial loading using UMAT. My aim is to pass single crystal to polycrystal model. So, I am trying two-crystal problem firstly. I have no trouble with implementing two-crystal (one crystal has no rotation, other crystal has 10 degree rotation). However, when I implement two crystal ( one crystal has no rotation, other crystal has 30 degree rotation), there is an convergence problem. I think this problem is a result of defining of the crystal boundaries. I use two C3D8 element and I define rotation in UMAT like that:
! ELEMENT 1:: 30 DEGREE
IF (NOEL.EQ.1.) THEN
ROTATE(1,1)=0.866025403
ROTATE(1,2)=0.5
ROTATE(2,1)=-0.5
ROTATE(2,2)=0.866025403
ROTATE(3,3)=1.
! ELEMENT 2:: 0 DEGREE
ELSE
ROTATE(1,1)=1.
ROTATE(2,2)=1.
ROTATE(3,3)=1.
END IF
I transform our transformation strain using these rotate tensors.According to our constitutive equations; the difference between the crystals which have different orientations is only transformation strain. When two crystal have close rotations, there is no problem but when difference between the rotations increases, I can not get results because the shared nodes of the elements have very different values in finite element and I think it is a problem.
Nazım Babacan
