Modeling of shrinkage-induced residual stresses during thecuring of reactive adhesives

The shrinkage induced residual stresses result in significat deformation, leading to warpingand distortion as well as impacting the strength of an component. Therefore, the main appli-cation of interest in this work is modelling of shrinkage-induced residual stresses in bi-materialbeams. Key mechanisms known to contribute to residual stress build-up are reviewed and theunderlying theories used to model these mechanisms are presented. These residual stresses aregenerated due to the chemical and thermal shrinkage during the curing process. The presentwork mainly focus on the modeling of shrinkage-induced residual stresses generated due tochemical reactions. The modelling approach chosen in the current study is finit element (FE) modeling of aluminum-polymer bi-material beam structures, enabling the prediction of deflection andresidual stresses during the curing process. For this, Ansys Parametric Design language (An-sys APDL) in FE program Ansys v2019 R1 is employed to perform numerical simulations.To characterise the material behavior, elastic and viscoelastic material models with degree ofcuring-dependent material properties are investigated. Two differet models are simulated andcompared, where possible, to experimental results which include relaxation test and bendingbeam test. The challenging task of incorporating the experimental characteristics such asYoung’s modulus, creep material constants and volumetric shrinkages that change with re-spect to time into the numerical model, is addressed during this work. The advantage ofusing curve fitting to implement these material characteristics is also pointed in this thesiswork. To model viscoelastic behaviour in Ansys APDL, strain hardening, and time hard-ening creep laws that correspond to the Maxwell rheological model are also incorporated inthe numerical transient FE analysis. The goal behind these creep model implementations isto validate the adhesive creep relaxation behaviour precisely. In the latter discussion, basedon the creep model results, a suitable Maxwell model for adhesive behaviour is finalize andresidual stresses developed during the curing process are presented. Additionally, the relax-ation behaviour of the partially cured 2C adhesive is also discussed and from the statisticalcomparison of the results a good correlation between experimental and numerical results areseen.