Residual stresses are generated in thermoplastic composite parts produced using extrusion-based additive manufacturing (AM). The layer-by-layer deposition of molten thermoplastic composite material and the subsequent cooldown results in the differential thermal contraction of the deposited layers, giving rise to residual stress in the additively manufactured parts. These residual stresses depend on the material properties of the polymer composite and the processing parameters used during the AM process. The residual stresses affect the mechanical performance and the final printed shape of the manufactured part. Efficient numerical modeling methods can predict residual stresses for AM parts and hence help design geometrically accurate and mechanically reliable parts. However, large-scale AM introduces computational challenges for evaluating residual stresses due to the large number of degrees of freedom in the numerical models. This research work explores the use of an explicit thermal model and a mesh merging technique to expedite the numerical analysis of thermal history and residual stresses in large-scale additively manufactured thermoplastic composite parts. The goal of the research is to develop an efficient modeling method for aiding the design of AM polymer composite parts.