This investigation presents and discusses the influence of impedance mismatch on the explosive expansion of multi-layer armature tubes, as an adjunct to helical flux-compression generator research at the University of Missouri-Rolla, directly affecting the understanding of flux cut-off and high strain-rate changes in generator armatures. A previous investigation, reported elsewhere, studied longitudinal fractures that characteristically developed in single-layer armatures at smaller expansion ratios than predicted by classical analysis. The current study examines shock-produced tensile stresses in the armature skin, and the effects on those tensile stresses caused by density variations within layers of multi-layer armatures. In the original investigation, these tensile stresses produced cracks that occurred within two diameters of the detonator end of the armature, but did not extend when the tubing expanded under explosive pressurization. Such cracks appear to cause magnetic flux cut-off, and flux losses seriously affect energy conversion efficiency. The current study utilizes a two-dimensional Lagrangian finite-difference numerical model, classical impedance-matching calculations, and explosives-loaded multi-layer armature testing to analyze the effect of detonation waves on multi-layer armatures of different compositions. As an extension of the original work, this study further isolates shock wave effects during armature expansion