Polycarbonate is an amorphous polymer which exhibits a pronounced strength-differential effect between compression and tension. Also strain rate and temperature influence the mechanical response of the polycarbonate. The concept of stress mode dependent weighting functions is used in the proposed model to simulate the asymmetric effects for different loading speeds. In this concept, an additive decomposition of the flow rule is assumed into a sum of weighted stress mode related quantities. The characterization of the stress modes is obtained in the octahedral plane of the deviatoric stress space in terms of the mode angle, such that stress mode dependent scalar weighting functions can be constructed. The resulting evolution equations are updated using a backward Euler scheme and the algorithmic tangent operator is derived for the finite element equilibrium iteration. The numerical implementation of the resulting set of constitutive equations is used in a finite element program for parameter identification. The proposed model is verified by showing a good agreement with the experimental data. After that the model is used to simulate the laser transmission welding process.

When it comes to the design of extrusion line components such as single‐screw extruders or extrusion dies, no one has yet succeeded in developing a well‐functioning concept for wall‐slipping materials. This article examines the fundamental influences of the wall slippage effect on flow behavior in the extrusion die and plastification unit. New and extended methods of calculation for describing this flow phenomenon are presented for both these extrusion line components, and the general possibilities for linking the two approaches are discussed. Diagram of the flow curve (τ = shear stress, $\dot \gamma$ = shear rate) of wall‐slipping plastics for constant pressure.magnified imageDiagram of the flow curve (τ = shear stress, $\dot \gamma$ = shear rate) of wall‐slipping plastics for constant pressure.

The mathematical models so far available for describing the throughput behavior of plasticising extruders were developed with the assumption of a wall-adhering melt. There are, however, a series of plastic melts, and also elastomers, polymer suspensions, ceramic materials and food products that display wall slippage during processing. A mathematical model has been developed for this material behavior, which describes the flow behavior for the unidimensional, Newtonian, isothermal case.Apart from the development of the analytical model, the flow behavior of wall-slipping polymer melts was also analysed with the aid of finite element calculations (FEM). A comparison of the results for the pressure/throughput behavior shows that the calculation results tally very well for the two methods. It is thus possible to develop a procedure which makes it possible to describe the phenomenon of wall-slippage for the non-Newtonian, multi-dimensional, non-isothermal case.

So far it has been assumed that when describing the flow process in single-screw extruder, the melt will be wall-adhering. Using certain process conditions, however, some materials such as PVCs, high-molecular PEs, elastomers, polymer suspensions, ceramic materials and food products become wall-slipping [1 to 4].During simulation of the flow process using the Finite Element Method (FEM), the boundary condition of “wall-adhering” was substituted for “wall-slipping”. The numeric results refer to one-dimensional, non-Newtonian, isothermal flow processes and have been evaluated accordingly.Since the wall-slipping properties are dependent on critical shear stress, the influence of non-Newtonian behaviour on wall shear stress is illustrated by investigating the barrel and screw root surface. Conclusions with regard to wall-slipping properties may be drawn from the resulting upper and lower limits.The effect of wall slippage on pressure/throughput behaviour is examined along with the various velocity profiles, resulting from different compression ratios, dimensionless critical shear stress, material-related constants and screw configuration.

This article presents the influence of the process parameters in laser transmission welding for plastics on the residual stress in the welded part. The contour welding process is modeled by means of finite element (FE) simulation. In this process, the weld seam is only partially heated, i.e., only part of it melts. The calculations are performed using a material model that describes the time-dependent temperature and stress development in a plate geometry, making allowance for the material's asymmetric compressive-tensile behavior. Experimental data were measured under different load cases to present the time-dependent material behavior, and then implemented in numerical terms by formulating the necessary constitutive equations. The calculations to simulate the influence of process parameters on the residual stress behavior were performed using a finite element model that was developed. The simulation covers the entire welding process, including the heating and cooling stages.