  Polyurethane adhesives are extensively used in manufacturing of the
lightweight components. These adhesives are hygroscopic in nature causing the
material to degrade their mechanical properties due to ageing under
environmental conditions. Polyurethane adhesive shows non-linear rate-dependent
behaviour due to viscoelastic properties and assumes nearly incompressible
deformation. Finite-strain viscoelastic model is formulated based on the
continuum rheological model by combining spring and Maxwell elements in
parallel. Nearly incompressible property is considered by decomposing the
mechanical free energy into volumetric and isochoric parts. This work focuses
on the investigation of the influence of moisture on the fracture behaviour.
Phase-field damage model proved to be an efficient method to investigate the
fracture behaviour. Therefore, the finite-strain viscoelastic material model is
coupled with the phase-field model to investigate fracture behaviour. Material
is assumed to be isotropic, therefore the total mechanical energy is considered
for bulk degradation. Experiments are conducted on the samples aged for
different humid conditions to understand tear strength. These test results are
used to identify the phase-field damage material parameters from numerical
investigation.
