fixed symmetry handling
- ort not tested, no examples, no documentation => removed - aP is the opposite of isotropic => removed isostropic materials can be easily specified as cI or cF, using C_44 = 1/2 * (C_11 - C_12). Acceptable extra effort for special use case orthorhombic can be easily implemented if needed, but needs test, documentation, and examples
This commit is contained in:
parent
ab070a3c13
commit
40698740aa
2
PRIVATE
2
PRIVATE
|
@ -1 +1 @@
|
|||
Subproject commit 37b19666872a67acdc3c70c270335fd21f11986e
|
||||
Subproject commit 14e754308e81545a231220f9d993fb4571729ced
|
|
@ -1,7 +1,7 @@
|
|||
TWIP_Steel_FeMnC:
|
||||
lattice: cF
|
||||
mechanical:
|
||||
elastic: {type: hooke, C_11: 175.0e9, C_12: 115.0e9, C_44: 135.0e9}
|
||||
elastic: {type: Hooke, C_11: 175.0e9, C_12: 115.0e9, C_44: 135.0e9}
|
||||
plastic:
|
||||
type: dislotwin
|
||||
output: [rho_mob, rho_dip, gamma_sl, Lambda_sl, tau_pass, f_tw, Lambda_tw, tau_hat_tw, f_tr]
|
||||
|
|
|
@ -1,7 +1,7 @@
|
|||
Tungsten:
|
||||
lattice: cI
|
||||
mechanical:
|
||||
elastic: {type: hooke, C_11: 523.0e9, C_12: 202.0e9, C_44: 161.0e9} # Marinica et al. Journal of Physics: Condensed Matter(2013)
|
||||
elastic: {type: Hooke, C_11: 523.0e9, C_12: 202.0e9, C_44: 161.0e9} # Marinica et al. Journal of Physics: Condensed Matter(2013)
|
||||
plastic:
|
||||
type: dislotwin
|
||||
D: 2.0e-5 # Average grain size / m
|
||||
|
|
|
@ -1,16 +0,0 @@
|
|||
# Kuo, J. C., Mikrostrukturmechanik von Bikristallen mit Kippkorngrenzen. Shaker-Verlag 2004. http://edoc.mpg.de/204079
|
||||
Aluminum:
|
||||
lattice: aP
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p]
|
||||
elastic: {type: hooke, C_11: 110.9e9, C_12: 58.34e9}
|
||||
plastic:
|
||||
type: isotropic
|
||||
output: [xi]
|
||||
xi_0: 31e6
|
||||
xi_inf: 63e6
|
||||
dot_gamma_0: 0.001
|
||||
n: 20
|
||||
M: 3
|
||||
h_0: 75e6
|
||||
a: 2.25
|
|
@ -1,8 +1,8 @@
|
|||
FreeSurface:
|
||||
lattice: aP
|
||||
lattice: cI
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p]
|
||||
elastic: {type: hooke, C_11: 1e8, C_12: 1e6}
|
||||
elastic: {type: Hooke, C_11: 1e8, C_12: 1e6, C_44: 4.95e7}
|
||||
plastic:
|
||||
type: isotropic
|
||||
output: [xi]
|
||||
|
|
|
@ -2,7 +2,7 @@ Aluminum:
|
|||
lattice: cF
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
|
|
@ -4,7 +4,7 @@
|
|||
Ferrite:
|
||||
lattice: cI
|
||||
mechanical:
|
||||
elastic: {C_11: 233.3e9, C_12: 135.5e9, C_44: 118.0e9, type: hooke}
|
||||
elastic: {C_11: 233.3e9, C_12: 135.5e9, C_44: 118.0e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12, 12]
|
||||
a_sl: 2.0
|
||||
|
|
|
@ -4,7 +4,7 @@
|
|||
Martensite:
|
||||
lattice: cI
|
||||
mechanical:
|
||||
elastic: {C_11: 417.4e9, C_12: 242.4e9, C_44: 211.1e9, type: hooke}
|
||||
elastic: {C_11: 417.4e9, C_12: 242.4e9, C_44: 211.1e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12, 12]
|
||||
a_sl: 2.0
|
||||
|
|
|
@ -4,7 +4,7 @@ Magnesium:
|
|||
c/a: 1.62350
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 59.3e9, C_12: 25.7e9, C_13: 21.4e9, C_33: 61.5e9, C_44: 16.4e9, type: hooke}
|
||||
elastic: {C_11: 59.3e9, C_12: 25.7e9, C_13: 21.4e9, C_33: 61.5e9, C_44: 16.4e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [3, 3, 0, 6, 0, 6]
|
||||
N_tw: [6, 0, 0, 6]
|
||||
|
|
|
@ -6,7 +6,7 @@ cpTi:
|
|||
c/a: 1.587
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 160.0e9, C_12: 90.0e9, C_13: 66.0e9, C_33: 181.7e9, C_44: 46.5e9, type: hooke}
|
||||
elastic: {C_11: 160.0e9, C_12: 90.0e9, C_13: 66.0e9, C_33: 181.7e9, C_44: 46.5e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [3, 3, 0, 6, 12]
|
||||
a_sl: 2.0
|
||||
|
|
|
@ -1,5 +1,5 @@
|
|||
references:
|
||||
- www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html
|
||||
- www.engineeringtoolbox.com/specific-heat-metals-d_152.html
|
||||
c_p: 910.0
|
||||
C_p: 910.0
|
||||
K_11: 236.0
|
||||
|
|
|
@ -1,4 +1,4 @@
|
|||
references:
|
||||
- de.wikipedia.org/wiki/Gold
|
||||
c_p: 128.0
|
||||
C_p: 128.0
|
||||
K_11: 320.0
|
||||
|
|
|
@ -1,4 +1,4 @@
|
|||
references:
|
||||
- www.mit.edu/~6.777/matprops/copper.htm
|
||||
c_p: 385.0
|
||||
C_p: 385.0
|
||||
K_11: 401.0
|
||||
|
|
|
@ -1,5 +1,5 @@
|
|||
references:
|
||||
- www.engineeringtoolbox.com/thermal-conductivity-metals-d_858.html
|
||||
- www.engineeringtoolbox.com/specific-heat-metals-d_152.html
|
||||
c_p: 490.0
|
||||
C_p: 490.0
|
||||
K_11: 54.0
|
||||
|
|
|
@ -1,4 +1,4 @@
|
|||
references:
|
||||
- www.mit.edu/~6.777/matprops/tungsten.htm
|
||||
c_p: 132.51
|
||||
C_p: 132.51
|
||||
K_11: 178.0
|
||||
|
|
|
@ -1,4 +1,4 @@
|
|||
c_p: 1
|
||||
C_p: 1
|
||||
K_11: 0
|
||||
K_22: 0
|
||||
K_33: 0
|
||||
|
|
|
@ -1,4 +1,4 @@
|
|||
c_p: 1
|
||||
C_p: 1
|
||||
K_11: 1e30
|
||||
K_22: 1e30
|
||||
K_33: 1e30
|
||||
|
|
|
@ -36,9 +36,9 @@ phase:
|
|||
lattice: cF
|
||||
mechanics:
|
||||
output: [F, P, F_e, F_p, L_p]
|
||||
elasticity: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elasticity: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
Steel:
|
||||
lattice: cI
|
||||
mechanics:
|
||||
output: [F, P, F_e, F_p, L_p]
|
||||
elasticity: {C_11: 233.3e9, C_12: 135.5e9, C_44: 118.0e9, type: hooke}
|
||||
elasticity: {C_11: 233.3e9, C_12: 135.5e9, C_44: 118.0e9, type: Hooke}
|
||||
|
|
|
@ -9,7 +9,7 @@ phase:
|
|||
lattice: cF
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
@ -26,7 +26,7 @@ phase:
|
|||
lattice: cI
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
|
|
@ -641,7 +641,7 @@ phase:
|
|||
lattice: cF
|
||||
mechanical:
|
||||
output: [F, F_e, F_p, L_p]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
@ -658,7 +658,7 @@ phase:
|
|||
lattice: cI
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
@ -675,4 +675,4 @@ phase:
|
|||
lattice: cI
|
||||
mechanical:
|
||||
output: [F]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
|
|
|
@ -9,7 +9,7 @@ phase:
|
|||
lattice: cF
|
||||
mechanical:
|
||||
output: [F, P, F_e, F_p, L_p, O]
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: hooke}
|
||||
elastic: {C_11: 106.75e9, C_12: 60.41e9, C_44: 28.34e9, type: Hooke}
|
||||
plastic:
|
||||
N_sl: [12]
|
||||
a_sl: 2.25
|
||||
|
|
|
@ -296,7 +296,6 @@ module lattice
|
|||
integer, parameter :: &
|
||||
BCT_NSLIP = sum(BCT_NSLIPSYSTEM) !< total # of slip systems for bct
|
||||
|
||||
|
||||
real(pReal), dimension(3+3,BCT_NSLIP), parameter :: &
|
||||
BCT_SYSTEMSLIP = reshape(real([&
|
||||
! {100)<001] systems
|
||||
|
@ -366,30 +365,13 @@ module lattice
|
|||
1, 1, 1, 1,-2, 1 &
|
||||
],pReal),shape(BCT_SYSTEMSLIP)) !< bct slip systems for c/a = 0.5456 (Sn), sorted by Bieler 2009 (https://doi.org/10.1007/s11664-009-0909-x)
|
||||
|
||||
!--------------------------------------------------------------------------------------------------
|
||||
! orthorhombic primitive (oP)
|
||||
integer, dimension(*), parameter :: &
|
||||
ORT_NCLEAVAGESYSTEM = [1, 1, 1] !< # of cleavage systems per family for orthorhombic primitive
|
||||
|
||||
integer, parameter :: &
|
||||
ORT_NCLEAVAGE = sum(ORT_NCLEAVAGESYSTEM) !< total # of cleavage systems for orthorhombic primitive
|
||||
|
||||
real(pReal), dimension(3+3,ORT_NCLEAVAGE), parameter :: &
|
||||
ORT_SYSTEMCLEAVAGE = reshape(real([&
|
||||
0, 1, 0, 1, 0, 0, &
|
||||
0, 0, 1, 0, 1, 0, &
|
||||
1, 0, 0, 0, 0, 1 &
|
||||
],pReal),shape(ORT_SYSTEMCLEAVAGE)) !< orthorhombic primitive cleavage systems
|
||||
|
||||
|
||||
enum, bind(c); enumerator :: &
|
||||
lattice_UNDEFINED_ID, &
|
||||
lattice_ISO_ID, &
|
||||
lattice_FCC_ID, &
|
||||
lattice_BCC_ID, &
|
||||
lattice_BCT_ID, &
|
||||
lattice_HEX_ID, &
|
||||
lattice_ORT_ID
|
||||
lattice_BCT_ID
|
||||
end enum
|
||||
|
||||
! SHOULD NOT BE PART OF LATTICE BEGIN
|
||||
|
@ -414,12 +396,10 @@ module lattice
|
|||
|
||||
public :: &
|
||||
lattice_init, &
|
||||
lattice_ISO_ID, &
|
||||
lattice_FCC_ID, &
|
||||
lattice_BCC_ID, &
|
||||
lattice_BCT_ID, &
|
||||
lattice_HEX_ID, &
|
||||
lattice_ORT_ID, &
|
||||
lattice_BCT_ID, &
|
||||
lattice_equivalent_nu, &
|
||||
lattice_equivalent_mu, &
|
||||
lattice_applyLatticeSymmetry33, &
|
||||
|
@ -479,12 +459,12 @@ subroutine lattice_init
|
|||
elasticity => mech%get('elastic')
|
||||
lattice_C66(1,1,ph) = elasticity%get_asFloat('C_11')
|
||||
lattice_C66(1,2,ph) = elasticity%get_asFloat('C_12')
|
||||
lattice_C66(4,4,ph) = elasticity%get_asFloat('C_44')
|
||||
|
||||
lattice_C66(1,3,ph) = elasticity%get_asFloat('C_13',defaultVal=0.0_pReal)
|
||||
lattice_C66(2,2,ph) = elasticity%get_asFloat('C_22',defaultVal=0.0_pReal)
|
||||
lattice_C66(2,3,ph) = elasticity%get_asFloat('C_23',defaultVal=0.0_pReal)
|
||||
lattice_C66(3,3,ph) = elasticity%get_asFloat('C_33',defaultVal=0.0_pReal)
|
||||
lattice_C66(4,4,ph) = elasticity%get_asFloat('C_44',defaultVal=0.0_pReal)
|
||||
lattice_C66(5,5,ph) = elasticity%get_asFloat('C_55',defaultVal=0.0_pReal)
|
||||
lattice_C66(6,6,ph) = elasticity%get_asFloat('C_66',defaultVal=0.0_pReal)
|
||||
|
||||
|
@ -497,10 +477,6 @@ subroutine lattice_init
|
|||
lattice_structure(ph) = lattice_HEX_ID
|
||||
case('tI')
|
||||
lattice_structure(ph) = lattice_BCT_ID
|
||||
case('oP')
|
||||
lattice_structure(ph) = lattice_ORT_ID
|
||||
case('aP')
|
||||
lattice_structure(ph) = lattice_ISO_ID
|
||||
case default
|
||||
call IO_error(130,ext_msg='lattice_init: '//phase%get_asString('lattice'))
|
||||
end select
|
||||
|
@ -1565,9 +1541,6 @@ function lattice_SchmidMatrix_cleavage(Ncleavage,structure,cOverA) result(Schmid
|
|||
integer :: i
|
||||
|
||||
select case(structure)
|
||||
case('oP')
|
||||
NcleavageMax = ORT_NCLEAVAGESYSTEM
|
||||
cleavageSystems = ORT_SYSTEMCLEAVAGE
|
||||
case('cF')
|
||||
NcleavageMax = FCC_NCLEAVAGESYSTEM
|
||||
cleavageSystems = FCC_SYSTEMCLEAVAGE
|
||||
|
@ -1705,15 +1678,15 @@ function lattice_applyLatticeSymmetry33(T,structure) result(T_sym)
|
|||
T_sym = 0.0_pReal
|
||||
|
||||
select case(structure)
|
||||
case('aP','cF','cI')
|
||||
case('cF','cI')
|
||||
do k=1,3
|
||||
T_sym(k,k) = T(1,1)
|
||||
enddo
|
||||
case('hP')
|
||||
case('hP') ! MD TODO: I think that 'tI' has the same symmetry as 'hP' for 2nd order tensors
|
||||
T_sym(1,1) = T(1,1)
|
||||
T_sym(2,2) = T(1,1)
|
||||
T_sym(3,3) = T(3,3)
|
||||
case('oP','tI')
|
||||
case('tI')
|
||||
T_sym(1,1) = T(1,1)
|
||||
T_sym(2,2) = T(2,2)
|
||||
T_sym(3,3) = T(3,3)
|
||||
|
@ -1740,21 +1713,13 @@ function applyLatticeSymmetryC66(C66,structure) result(C66_sym)
|
|||
C66_sym = 0.0_pReal
|
||||
|
||||
select case(structure)
|
||||
case ('aP')
|
||||
do k=1,3
|
||||
do j=1,3
|
||||
C66_sym(k,j) = C66(1,2)
|
||||
enddo
|
||||
C66_sym(k,k) = C66(1,1)
|
||||
C66_sym(k+3,k+3) = 0.5_pReal*(C66(1,1)-C66(1,2))
|
||||
enddo
|
||||
case ('cF','cI')
|
||||
do k=1,3
|
||||
do j=1,3
|
||||
C66_sym(k,j) = C66(1,2)
|
||||
enddo
|
||||
C66_sym(k,k) = C66(1,1)
|
||||
C66_sym(k+3,k+3) = C66(4,4)
|
||||
C66_sym(k+3,k+3) = C66(4,4) ! isotropic C_44 = .5*(C_11-C_12)
|
||||
enddo
|
||||
case ('hP')
|
||||
C66_sym(1,1) = C66(1,1)
|
||||
|
@ -1769,19 +1734,6 @@ function applyLatticeSymmetryC66(C66,structure) result(C66_sym)
|
|||
C66_sym(4,4) = C66(4,4)
|
||||
C66_sym(5,5) = C66(4,4)
|
||||
C66_sym(6,6) = 0.5_pReal*(C66(1,1)-C66(1,2))
|
||||
case ('oP')
|
||||
C66_sym(1,1) = C66(1,1)
|
||||
C66_sym(2,2) = C66(2,2)
|
||||
C66_sym(3,3) = C66(3,3)
|
||||
C66_sym(1,2) = C66(1,2)
|
||||
C66_sym(2,1) = C66(1,2)
|
||||
C66_sym(1,3) = C66(1,3)
|
||||
C66_sym(3,1) = C66(1,3)
|
||||
C66_sym(2,3) = C66(2,3)
|
||||
C66_sym(3,2) = C66(2,3)
|
||||
C66_sym(4,4) = C66(4,4)
|
||||
C66_sym(5,5) = C66(5,5)
|
||||
C66_sym(6,6) = C66(6,6)
|
||||
case ('tI')
|
||||
C66_sym(1,1) = C66(1,1)
|
||||
C66_sym(2,2) = C66(1,1)
|
||||
|
@ -2012,7 +1964,7 @@ function buildCoordinateSystem(active,potential,system,structure,cOverA)
|
|||
|
||||
select case(structure)
|
||||
|
||||
case ('cF','cI','aP','oP','tI')
|
||||
case ('cF','cI','tI')
|
||||
direction = system(1:3,p)
|
||||
normal = system(4:6,p)
|
||||
|
||||
|
@ -2247,7 +2199,6 @@ function lattice_equivalent_nu(C,assumption) result(nu)
|
|||
/ (S(1,1)+S(2,2)+S(3,3) +2.0_pReal*(S(1,2)+S(2,3)+S(1,3)))
|
||||
else
|
||||
error stop 'invalid assumption'
|
||||
K = 0.0_pReal
|
||||
endif
|
||||
|
||||
mu = lattice_equivalent_mu(C,assumption)
|
||||
|
@ -2280,7 +2231,6 @@ function lattice_equivalent_mu(C,assumption) result(mu)
|
|||
/ (4.0_pReal*(S(1,1)+S(2,2)+S(3,3)) -4.0_pReal*(S(1,2)+S(2,3)+S(1,3)) +3.0_pReal*(S(4,4)+S(5,5)+S(6,6)))
|
||||
else
|
||||
error stop 'invalid assumption'
|
||||
mu = 0.0_pReal
|
||||
endif
|
||||
|
||||
end function lattice_equivalent_mu
|
||||
|
@ -2298,6 +2248,7 @@ subroutine selfTest
|
|||
real(pReal), dimension(2) :: r
|
||||
real(pReal) :: lambda
|
||||
|
||||
|
||||
call random_number(r)
|
||||
|
||||
system = reshape([1.0_pReal+r(1),0.0_pReal,0.0_pReal, 0.0_pReal,1.0_pReal+r(2),0.0_pReal],[6,1])
|
||||
|
@ -2305,10 +2256,11 @@ subroutine selfTest
|
|||
if(any(dNeq(CoSy(1:3,1:3,1),math_I3))) error stop 'buildCoordinateSystem'
|
||||
|
||||
call random_number(C)
|
||||
C(1,1) = C(1,1) + 1.0_pReal
|
||||
C = applyLatticeSymmetryC66(C,'aP')
|
||||
if(dNeq(C(6,6),lattice_equivalent_mu(C,'voigt'),1.0e-12_pReal)) error stop 'equivalent_mu/voigt'
|
||||
if(dNeq(C(6,6),lattice_equivalent_mu(C,'voigt'),1.0e-12_pReal)) error stop 'equivalent_mu/reuss'
|
||||
C(1,1) = C(1,1) + C(1,2) + 0.1_pReal
|
||||
C(4,4) = 0.5_pReal * (C(1,1) - C(1,2))
|
||||
C = applyLatticeSymmetryC66(C,'cI')
|
||||
if(dNeq(C(4,4),lattice_equivalent_mu(C,'voigt'),1.0e-12_pReal)) error stop 'equivalent_mu/voigt'
|
||||
if(dNeq(C(4,4),lattice_equivalent_mu(C,'reuss'),1.0e-12_pReal)) error stop 'equivalent_mu/reuss'
|
||||
|
||||
lambda = C(1,2)
|
||||
if(dNeq(lambda*0.5_pReal/(lambda+lattice_equivalent_mu(C,'voigt')), &
|
||||
|
|
|
@ -947,18 +947,14 @@ subroutine crystallite_results(group,ph)
|
|||
'second Piola-Kirchhoff stress','Pa')
|
||||
case('O')
|
||||
select case(lattice_structure(ph))
|
||||
case(lattice_ISO_ID)
|
||||
structureLabel = 'aP'
|
||||
case(lattice_FCC_ID)
|
||||
structureLabel = 'cF'
|
||||
case(lattice_BCC_ID)
|
||||
structureLabel = 'cI'
|
||||
case(lattice_BCT_ID)
|
||||
structureLabel = 'tI'
|
||||
case(lattice_HEX_ID)
|
||||
structureLabel = 'hP'
|
||||
case(lattice_ORT_ID)
|
||||
structureLabel = 'oP'
|
||||
case(lattice_BCT_ID)
|
||||
structureLabel = 'tI'
|
||||
end select
|
||||
selected_rotations = select_rotations(crystallite_orientation,ph)
|
||||
call results_writeDataset(group//'/mechanical',selected_rotations,output_constituent(ph)%label(ou),&
|
||||
|
|
Loading…
Reference in New Issue