  Hygro-responsive materials exhibit a complex structure-to-property
relationship. The interactions of water within these materials under varying
hygric and mechanical loads play a crucial role in their macroscopic
deformation and final application. While multiple models are available in
literature, many lack a comprehensive physical understanding of these
phenomena. In this study, we introduce a novel Stick-Slip Fiber Bundle Model
that captures the fundamental behaviors of hygro-responsive materials. We
incorporate moisture-dependent elements and rules governing the initiation and
relaxation of slip strains as well as failure to the statistical approach
offered by Fiber Bundle Models. The additional features are based on
well-founded interpretations of the structure-to-property relationship in
cellulosic materials. Slip strains are triggered by changes in load and
moisture, as well as by creep deformations. When subjected to moisture cycles,
the model accumulates slip strains, resulting in mechanosorptive behavior. When
the load is removed, slip strains are partially relaxed, and subsequent
moisture cycles trigger further relaxation, as expected from observations with
mechanosorptive material. Importantly, these slip strains are not considered
plastic strains; instead, they are unified, non-linear frozen strains,
activated by various stimuli. Failure of fibers is defined by a critical number
of slip events allowing for an integrated simulation from intact, via damaged,
failed states. We investigate the transition between these regimes upon changes
in the hygric and mechanical loading history for relevant parameter ranges. Our
enhanced Stick-Slip Fiber Bundle Model increases the understanding of the
intricate behavior of hygro-responsive materials and contributes to a more
robust framework for analyzing and interpreting their properties.

Soft Condensed Matter;Materials Science