Material-dependent mass and stiffness damping (MP,ALPD and MP,BETD) is an additional method of including damping for dynamic analyses and is useful when different parts of the model have different damping values.
ALPD and BETD are not assumed to be temperature dependent and are always evaluated at T = 0.0. Special-purpose elements, such as MATRIX27 and FLUID29, generally do not require damping. If you specify material property ALPD and BETD for these elements, however, the program uses the value to create the damping matrix at solution time.
Constant material damping coefficient (MP,DMPS) is a material-dependent structural damping coefficient that is constant with respect to the excitation frequency in harmonic analysis and is useful when different parts of the model have different damping values (see Damping Matrices in the Mechanical APDL Theory Reference). DMPS is not temperature-dependent and is always evaluated at T = 0.0.
Damping for composite materials:
For composite elements, MAT specifies a single material (the element material) and SECDATA defines additional composite materials/layers. Generally, Mechanical APDL considers only element material damping (MP,ALPD, MP,BETD, or MP,DMPS) defined with the element material and applies it to the element as a whole (ignoring element material damping defined with additional composite materials).
If you require different Rayleigh damping coefficients for different composite materials/layers, however, issue the corresponding data-table commands (TB,SDAMP,,,,ALPD, TB,SDAMP,,,,BETD); for more information about this option and supported elements, see Defining Rayleigh Damping via TB.
See Damping Matrices in the Mechanical APDL Theory Reference for more details about the damping formulation.
See Damping in the Structural Analysis Guide for more information.