If I didn't need any of the intermediate matrices I'd make a User Defined Function and just pass the barest number of parameters and do all the heavy lifting internal to the UDF


This isn't finished but you'd just use

=StiffnessMatrixOrient(151.7, 10.3, 0.25, 3.6, 55)

or

StiffnessMatrixOrient(a7, a8, a9, a11, a23)


in the worksheet


I couldn't figure out if you were returning a single number or a matrix, but the UDF could do either


Option Explicit

Sub drv()
    Dim v3x3 As Variant
    
    v3x3 = StiffnessMatrixOrient(151.7, 10.3, 0.25, 3.6, 55)
End Sub
 

Function StiffnessMatrixOrient(E1 As Double, E2 As Double, V12 As Double, G12 As Double, OrientationDegrees As Double) As Variant
    Const cPI As Double = 3.14159265358979
    
    Dim T(1 To 3, 1 To 3) As Double, T_Inverse As Variant, T_Transpose As Variant
    Dim R(1 To 3, 1 To 3) As Double, R_Inverse As Variant, R_Transpose As Variant
    Dim C(1 To 3, 1 To 3) As Double, S(1 To 3, 1 To 3) As Double
    
    Dim SinRad As Double, CosRad As Double, v21 As Double
    
    SinRad = Sin(OrientationDegrees * cPI / 180#)
    CosRad = Cos(OrientationDegrees * cPI / 180#)
    
    'T matrix
    T(1, 1) = CosRad ^ 2
    T(1, 2) = SinRad ^ 2
    T(1, 3) = 2 * SinRad * CosRad
    T(2, 1) = SinRad ^ 2
    T(2, 2) = CosRad ^ 2
    T(2, 3) = -2 * SinRad * CosRad
    T(3, 1) = -SinRad * CosRad
    T(3, 2) = SinRad * CosRad
    T(3, 3) = CosRad ^ 2 - SinRad ^ 2
    T_Inverse = Application.WorksheetFunction.MInverse(T())
    T_Transpose = Application.WorksheetFunction.Transpose(T_Inverse)

    'R matrix
    R(1, 1) = 1#
    R(1, 2) = 0#
    R(1, 3) = 0#
    R(2, 1) = 0#
    R(2, 2) = 1#
    R(2, 3) = 0#
    R(3, 1) = 0#
    R(3, 2) = 0#
    R(3, 3) = 2#
    R_Inverse = Application.WorksheetFunction.MInverse(R())
    R_Transpose = Application.WorksheetFunction.Transpose(R_Inverse)

    'C matrix
    v21 = (E2 / E1) * V12
    
    C(1, 1) = E1 / (1 - V12 * v21)
    C(1, 2) = V12 * E2 / (1 - V12 * v21)
    C(1, 3) = 0#
    C(2, 1) = v21 * E1 / (1 - V12 * v21)
    C(2, 2) = E2 / (1 - V12 * v21)
    C(2, 3) = 0#
    C(3, 1) = 0#
    C(3, 2) = 0#
    C(3, 3) = G12
 
 

    Stop    '   to check
End Function