Computational coupling of moisture diffusion and mechanical deformation in polymer matrix composites

Abstract

A computationally efficient multiscale-multiphysics model aimed at predicting mechanical response of thermoplastic composites subjected to different levels of moisture was developed. The mathematical model of the coupled moisture-diffusion-mechanical-deformation phenomenon was stated at the microscale, based on the observed experimental data, and then upscaled using a mathematical homogenization approach. A two-way coupling between moisture diffusion and mechanical deformation was introduced by which diffusivity was enhanced by hydrostatic strain, whereas strength and stiffness were assumed to degrade because of moisture ingression, which also gives rise to swelling. The computational complexity of analyzing the two coupled physical processes at multiple scales was reduced via a model reduction scheme for multiple physical processes. The model was validated for 30% by weight filled glass fiber and carbon fiber reinforced thermoplastic composites. The moisture conditioning and uniaxial tension experiments were utilized to identify diffusion and mechanical properties at a fine scale. The identified properties were then used to validate the formulation in the three-point bending test. motor oil, brake fluid, gasoline, and battery acid) has often resulted in overdesign and thus limited their insertion in load bearing components because the overdesigned component may not yield any mass advantages. There are two main reasons for this state of affairs: (1) existence of multiple spatial scales and multiple coupled physical processes, such as thermal, mechanical, and moisture diffusion; and (2) costly environmental degradation experiments that require long time exposure of the test specimens to varied levels of humidity and temperature conditions. Among the various thermoplastic composites, short fiber thermoplastics have been increasingly used in the automotive industry. Their usage is intended to fill the gap in the mechanical properties between continuous-long fiber composites, primarily used as structural members, and unreinforced polymers, used as non-load bearing members. Glass and carbon short fibers are primarily used as reinforcements in polyamides (PA/nylon) or polyphthalamides. The main applications are in body parts, such as door panels, hoods, bonnets, and bumpers, and engine parts including cam covers, engine mounts, fuel tanks, fuel cells, and interior trims including molded seats. These materials are in demand because of their manufacturing ease, versatility, low cost, corrosion resistance, and superior mechanical, thermal, and electrical properties.Polyamides of semi-crystalline composition are known to absorb moisture because of their chemical structure. Experimental studies of PA-6, PA-66, and PA-46 polyamides report an equilibrium moisture content varying in the range from 1.2 to 2.5 wt.% of water at 50% relative humidity (RH) and 23 ı C temperatures and about 8-9 wt.% upon reaching saturation conditions [6][7][8][9]. The moisture is first absorbed in the microcracks and macrocracks/voids, if present, ...

A convection–diffusion porous media model for moisture transport in polymer composites: Model development and validation

“…It would be of great interest to extend the proposed model to consider solid deformation (e.g., thermal expansion, hygroscopic swelling, and vapor pressure‐induced void growth). Coupling of conventional diffusion models with stress analysis has been studied in the literature . Similar approaches can be applied to the convection–diffusion model, except that vapor pressure must be included in the calculation of solid deformation.…”

“…Coupling of conventional diffusion models with stress analysis has been studied in the literature. 17,[76][77][78][79] Similar approaches can be applied to the convection-diffusion model, except that vapor pressure must be included in the calculation of solid deformation. Vapor pressure is crucial because it could result in large deformation and instability of soft thin films.…”

Nonlinear multiphysics finite element code architecture in object oriented Fortran environment

“…The mechanical and diffusive fields are two-way coupled in the sense that diffusivity is enhanced by hydrostatic strain, whereas strength and stiffness degrade due to moisture ingression [36]. The coupled constitutive model is outlined in Appendix A.…”

A coupled thermo‐chemo‐mechanical reduced‐order multiscale model for predicting process‐induced distortions, residual stresses, and strength

“…For more details, we refer to References for the case of a single physical process. ROH for two physical process, such as a mechanical problem coupled with an oxidation damage in ceramics and titanium or degradation due to moisture ingression in polymers, was studied in References , respectively.…”