Constitutive modeling of a graded porous polymer based on X-ray computed tomography

This work focuses on the constitutive modeling of a graded porous polymer pipeline coating based on X-ray micro computed tomography (XRMCT). Previous work has revealed that finite element (FE) models generated from XRMCT scans of cylindrical coating specimens reproduce their response in uniaxial compression accurately. In this work, we use FE models generated from XRMCT scans to study the pressure-sensitive yield strength of the porous coating. Since the coating is known to have a graded pore structure through its thickness, data from an XRMCT scan of a full coating sample is divided into twenty-four sublayers across the coating thickness, from which FE models are generated. These FE models are used to perform numerical limit analyses to map the yield locus for each sublayer, which are utilized to calibrate an analytical yield surface. A strong correlation is found between the fitted yield surface parameters and the average porosity of the sublayers. This observation is used to propose a constitutive model where the yield strength depends on the porosity and its evolution with deformation. The constitutive model is implemented as a user subroutine in a commercial explicit FE solver and validated against experimental component tests, showing good agreement.