Characterization and model-based mechanical analysis of moisture gradients in PA 6

In this contribution, a numerical calculation environment for the determination of the moisture absorption of polyamide 6 (PA 6) is developed. The focus in this context is on modeling and evaluating the influence of locally varying water concentrations and existing moisture gradients on the mechanical properties of the material. Defined moisture distributions are set by specific conditioning processes and compared to the results of an FE calculation environment. The developed numerical method combines a mass diffusion with a subsequent structural-mechanical simulation. The first includes a transient analysis of moisture absorption and the resulting swelling processes and residual stresses. The water concentration and residual stress distributions determined within this calculation are implemented as initial conditions in the structural mechanics FE analysis. The experimental setup of the three-point bending test is considered in this case. The evaluation of the moisture-induced influence on the mechanical behavior of the considered PA 6 is performed using a linear elastic modeling approach. The validation and evaluation of the calculation quality is carried out for the sorption and swelling calculation as well as for the FE model by means of experimental test data. The calculation methodology presented in this work provides a novel and even more accurate approach for the design of plastic components which are exposed to the influence of environmental humidity or direct water contact in their application.