On the influence of material non-linearities in geometric modeling of kink band instabilities in unidirectional fiber composites

Author-Highlights
• Analytical (post)buckling model of axially compressed UD composites using the Potential Energy concept.
• Non-linear material behaviour considered consistently in all corresponding strain energy terms.
• A non-linear material was derived allowing to solve the equations analytically.
• Comparisons with experimental data are improved over previously achieved.
• Non-linearities relevant in matrix shearing and axial compression and negligible for other contributions.

The axial compressive failure of aligned fiber composites triggered by kink band instabilities is the topic of investigation herein. Particular emphasis is put on the accurate prediction of the post-failure regime, where fiber composites are known to exhibit substantial post-failure strength. In this regard, a previous analytical model, based on geometric relationships and energy principles, is enhanced by consistently taking into account material non-linearities. Therefore, a non-linear constitutive law is introduced herein based on a newly developed exponential formulation. This non-linear constitutive law is subsequently implemented into the stress–strain response in interlaminar shearing as well as the compression response. The model enhancements are validated against published experimental data yielding excellent comparisons. Furthermore, the relevance of modeling non-linear material behavior in interlaminar dilation and bending is assessed using a bilinear constitutive law. However, implementing non-linear material behavior does not yield any improvements and can therefore be neglected.