Abstract
In the industry the demands on environmentally friendly products and processes increase which in turn increases the focus on lightweight composite materials. Such materials often cannot be welded, and the use of adhesives is therefore an alternative. This requires new production processes for which a thorough understanding is needed in order to optimize the effectivity and ensure sufficient strength and quality of the joints.
A key part in understanding the processes is the ability to simulate the flow of adhesive materials, which have complex rheology and may be both viscoelastic and thixotropic. It is thus not sufficient to describe its rheology with a purely shear thinning model. This is due to that such models does not account for storage of energy and transient stress relaxation.
In this work the flow solver IPS IBOFlow is used for simulating the extrusion of adhesive. In IBOFlow internal objects are treated using implicit immersed boundary conditions. The flow equations are solved on a Cartesian octree grid which is automatically generated and adapted.
The two-phase flow of adhesive and air is modelled with the Volume of Fluid method.
The adhesive is modelled by a novel approach in which the constitutive equation for the viscoelastic stresses is solved on a Lagrangian grid represented by massless particles being convected by the fluid. The full stress tensor is interpolated to the fluid grid and explicitly added to the momentum equations. The method is computationally effective for multiphase flows compared to solving the constitutive equation on the Eulerian grid. The non-linear viscoelastic PPT model, which has been widely used in the literature to simulate viscoelastic polymeric fluids, is used as constitutive equation for the stresses. The method is validated with experimental data of the viscoelastic flow past a confined cylinder and by comparison between simulated adhesive beads and scanned experimental beads in the cross section. In both cases the simulations agree very well with the experiments.