Regarding CTE (coefficient of thermal expansion):

Definitions of CTE (there are 3) and conversions are given in 
http://ftp.lstc.com/anonymous/outgoing/jday/thermal_expansion.pdf

Except as noted below, LS-DYNA uses the tangent CTE.

Per Art (8/28/09), MAT_106 lets you use alpha-s (secant CTE) by setting the parameter LCALPH
negative and defining TREF. I thought this was also going to be implemented for
MAT_ADD_THERMAL_EXPANSION but did not see any code changes yet.

_______________________________________________________________________
It seems that mat_255 also has this option of  using alpha-s (secant CTE) rather than alpha-t (tangent CTE).
See also notes on mat_189.

___________________________________________________________
Thomas implemented a new `orthotropic`
option in *mat_add_thermal_expansion,
so that different coefficients of thermal expansion can be defined along
the a-b-c directions for any orthotropic
material model (in the same fashion as *mat_021).
3/29/2010