  This article proposes a coupled thermomechanical finite element model
tailored to the macroscale simulation of metal additive manufacturing processes
such as selective laser melting. A first focus lies on the derivation of a
consistent constitutive law on basis of a Voigt-type spatial homogenization
procedure across the relevant phases, powder, melt and solid. The proposed
constitutive law accounts for the irreversibility of phase change and
consistently represents thermally induced residual stresses. In particular, the
incorporation of a reference strain term, formulated in rate form, allows to
consistently enforce a stress-free configuration for newly solidifying material
at melt temperature. Application to elementary test cases demonstrates the
validity of the proposed constitutive law and allows for a comparison with
analytical and reference solutions. Moreover, these elementary solidification
scenarios give detailed insights and foster understanding of basic mechanisms
of residual stress generation in melting and solidification problems with
localized, moving heat sources. As a second methodological aspect, dual mortar
mesh tying strategies are proposed for the coupling of successively applied
powder layers. This approach allows for very flexible mesh generation for
complex geometries. As compared to collocation-type coupling schemes, e.g.,
based on hanging nodes, these mortar methods enforce the coupling conditions
between non-matching meshes in an $L^2$-optimal manner. The combination of the
proposed constitutive law and mortar mesh tying approach is validated on
realistic three-dimensional examples, representing a first step towards
part-scale predictions.
